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Revolutionizing medicine: recent developments and future prospects in …

Saturday, December 28th, 2024

Abstract

Stem-cell therapy is a revolutionary frontier in modern medicine, offering enormous capacity to transform the treatment landscape of numerous debilitating illnesses and injuries. This review examines the revolutionary frontier of treatments utilizing stem cells, highlighting the distinctive abilities of stem cells to undergo regeneration and specialized cell differentiation into a wide variety of phenotypes. This paper aims to guide researchers, physicians, and stakeholders through the intricate terrain of stem-cell therapy, examining the processes, applications, and challenges inherent in utilizing stem cells across diverse medical disciplines. The historical journey from foundational contributions in the late 19th and early 20th centuries to recent breakthroughs, including ESC isolation and iPSC discovery, has set the stage for monumental leaps in medical science. Stem cells regenerative potential spans embryonic, adult, induced pluripotent, and perinatal stages, offering unprecedented therapeutic opportunities in cancer, neurodegenerative disorders, cardiovascular ailments, spinal cord injuries, diabetes, and tissue damage. However, difficulties, such as immunological rejection, tumorigenesis, and precise manipulation of stem-cell behavior, necessitate comprehensive exploration and innovative solutions. This manuscript summarizes recent biotechnological advancements, critical trial evaluations, and emerging technologies, providing a nuanced understanding of the triumphs, difficulties, and future trajectories in stem cell-based regenerative medicine. Future directions, including precision medicine integration, immune modulation strategies, advancements in gene-editing technologies, and bioengineering synergy, offer a roadmap in stem cell treatment. The focus on stem-cell therapys potential highlights its significant influence on contemporary medicine and points to a future in which individualized regenerative therapies will alleviate various medical disorders.

Keywords: biotechnology advancements, clinical trials, medical revolution, stem-cell therapy

Stem cell therapy represents a groundbreaking frontier in modern medicine, offering unprecedented potential to address a wide range of debilitating diseases and injuries.

Stem cells possess unique properties, including self-renewal and differentiation into specialized cell types, making them indispensable for regenerative medicine applications.

The historical journey of stem cell research, from foundational contributions in the late 19th and early 20th centuries to recent breakthroughs like the isolation of embryonic stem cells and induced pluripotent stem cells, highlights the monumental progress in medical science.

Stem cell therapy holds promise for treating various conditions, including cancer, neurodegenerative disorders, cardiovascular diseases, spinal cord injuries, diabetes, and tissue damage.

Despite the immense potential, stem cell therapy faces challenges such as immune rejection, tumorigenesis, and the precise manipulation of stem cell behaviors, necessitating innovative solutions for clinical translation.

Recent biotechnological advancements, such as exosome-based therapeutics, single-cell RNA sequencing, and CRISPR technology, have revolutionized stem cell research, offering new opportunities for precise genome editing and therapeutic interventions.

Regulatory considerations are paramount in the clinical translation of stem cell therapies, requiring adherence to strict guidelines and directives to ensure safety and efficacy.

The future of stem cell therapy lies in precision medicine integration, immune modulation strategies, advancements in gene editing technologies, and synergies with bioengineering, paving the way for continued evolution and personalized regenerative therapies.

Stem-cell therapy signifies a pioneering frontier in modern medicine that uses the extraordinary power of stem cells and their revolutionary potential to treat diverse illnesses. Stem cells play a crucial role in regenerative medicine and exhibit the extraordinary ability to differentiate into various cell types and to renew themselves. Their intrinsic capacity to repair and regenerate tissues holds immense promise for revolutionizing therapeutic interventions1,2. The historical journey of stem-cell investigation can be traced to pivotal contributions from visionaries such as Boveri, Hcker, Maximow, and Cohnheim during the late 19th and early 20th centuries3. Their foundational work placed the groundwork for comprehension of the fundamental principles of stem cells and for shedding light on their roles in developmental processes and tissue repair. These early insights have laid the foundation for contemporary stem-cell investigations, fueling a deeper exploration of their biological significance3,4. Important turning points in the history of this field include the identification of ESCs in 1981 by Kaufman and Evans57 and Thomsons discovery of iPSCs in 20078. Although stem-cell therapies have vast and promising potential, several challenges and complexities loom in their clinical translation9. Issues like immunological rejection, tumorigenesis, and precise manipulation of stem-cell behavior for optimal therapeutic outcomes are critical hurdles that necessitate comprehensive exploration and innovative solutions1,1012. Advances in biotechnology, especially the revolution in exosome-based therapeutics, single-cell RNA sequencing (scRNA-Seq), and CRISPR technology1315, one of the major developments in genetic engineering, has made precise and effective genome editing possible, which opens new avenues for modified genetic material, leading to advances in a variety of fields such as biotechnology and medicine16,17. Regenerative medicine represents a novel and promising therapeutic approach for individuals with exhausted or nonexistent options for managing their medical condition. Research studies, such as identification, clinical trials, and therapeutic applications on stem-cell have been extensive in recent years because of promising results from preclinical research (Fig. 1). The process of bringing these novel medicinal items from laboratories to the market is governed by strict guidelines and directives issued by qualified regulatory bodies18. Stem cells can be obtained for tissue engineering and cell treatments from four primary sources. The stem cells primary sources are embryonic and fetal tissues, comprising the placenta (including the chorion and amnion), umbilical cord (Wharton jelly), and particular tissues inside the adult, such as blood, skin, skeletal muscle, fat, and bone marrow, and somatic cells that have undergone genetic reprogramming to become distinct from their original state, such as iPSCs19.

A timeline depicting the introduction of mesenchymal stem cells (MSCs), their early research, and their substantial application in clinical trials, immunoregulation, and disease treatment.

Through an extensive synthesis of recent biotechnological advancements, critical evaluations, and emerging technologies, this review offers a nuanced comprehension of the advantages, difficulties, and future trajectories of stem cell-based regenerative therapy. By examining the historical foundations, current landscape, and prospects, this study endeavors to serve as a guide for researchers, clinicians, and stakeholders in navigating the intricate terrain of stem-cell therapy.

An extensive examination of existing literature was performed using the Embase, Web of Science, PubMed, and Scopus databases. The terms stem cell therapy, medical revolution, biotechnology advancements, and clinical trial were used in the search. Only articles published in English were included in the search. We assessed the abstracts of each article to determine the relevance of the retrieved papers to the topic. Subsequently, every relevant paper (in vivo, in vitro, and human-based research) was selected as part of the study.

ESCs exhibit characteristics that distinguish them from each other in stem cell biology. Notably, their pluripotency, which is defined by distinct features to differentiate into any human body cell, makes them highly adaptable and has great therapeutic promise20. Additionally, ESCs have a notably high self-renewal capacity, which contributes to their sustained presence and functionality over extended periods21. Potential ESC sources include mice, nonhuman primates, and humans. They are isolated from the blastocysts inner cell mass before implantation22,23. Because they are pluripotent cells, they can produce various kinds of cells from fetuses and adults in vivo and in vitro2426. Two methods were employed to separate ESCs from blastocysts inner cell masses. Microsurgery is the most commonly used surgical approach. Mechanical dissection in the microscopic direction is used to isolate cells of the trophoblastic lineage from the rest of the cell mass. The second approach entails employing an antibody to target trophoblast lineage cells27,28.

Regarding potential applications, the pluripotent nature of ESCs opens avenues for significant contributions to tissue regeneration and repair. Their capacity to undergo differentiation into many cell lineages holds promise for treating degenerative conditions and injuries, making them pivotal players in regenerative medicine. Furthermore, ESCs serve as invaluable tools in disease modeling for research purposes29. By replicating specific cellular environments, researchers can discover more about the workings of various disorders, providing a framework for cellular disease research and aiding in the creation of focused therapies. The unique properties of ESCs are relevant to drug testing and development30. Because of their pluripotency, a variety of cell populations can be created to provide a more complete picture of human cellular responses. This capability is particularly valuable for evaluating drug efficacy and safety and provides a sophisticated model for preclinical testing. Consequently, the multifaceted potential of ESCs dramatically enhances our comprehension of biology, fostering medical research and shaping the landscape of therapeutic innovation31,32.

ASCs stand out in the realm of regenerative biology because of their distinctive properties and vital roles in maintaining tissue homeostasis33. Multipotency is the ability of cells to possess various potential fates or abilities to develop into a restricted, diverse array of cellular phenotypes34. ASCs are endogenous stem cells that are crucial for preserving the tissues structural integrity, like bone, skin, and blood. They are located in specific niches or tissue sections35. ASCs have been discovered in several tissues, including blood, stomach, muscle, skin, brain, and heart36. They are less potent than ESCs; however, they have demonstrated efficacy in disease treatment. They can be extracted and harvested from individuals and used for tissue regeneration through autologous or allogeneic transplantation37. ASCs have a more specialized differentiation capability than pluripotent cells, such as ESCs, and can help generate particular cell lineages within their original tissue34.

Stem cells function in repairing damaged tissues and maintenance is essential throughout an individuals lifespan38. The unique ability of ASCs to maintain tissue and exhibit multipotency lends itself to a variety of possible uses within the regenerative medicine field39. Tissue-specific regeneration and repair are among the most promising approaches. ASCs can be utilized to regenerate damaged or deteriorated tissues due to their presence in diverse tissues, including the bone marrow, skin, and muscle40. Their capacity to undergo cell type-specific differentiation that is relevant to their native tissues places them at the forefront of tailored regeneration techniques, offering potential treatment options for ailments ranging from degenerative illnesses unique to certain organs to musculoskeletal injuries41.

ASCs are an appealing therapeutic choice for degenerative diseases. Because of their functions in tissue repair and regeneration, they are desirable targets for therapies aimed at slowing the advancement of illnesses marked by cellular degeneration42. Through the utilization of the regenerative capacity of these cells, scientists and medical professionals have investigated ways to create novel treatments that target the root causes of degenerative illnesses with the aim of enhancing patient outcomes and quality of life43. Within the class of ASCs, hematopoietic stem cells are a specific subset essential for bone marrow transplantation44. The immune system and blood regeneration rely on hematopoietic stem cells (HSCs), which are essential due to their versatility in cell differentiation into various blood cell types45. The utilization of these cells in bone marrow transplants represents a cornerstone in hematological therapies, offering a curative approach for conditions like leukemia and other disorders affecting the blood and immune systems46,47. Transplantation of hematopoietic stem cells is a life-saving intervention that reinstates functional blood and immune cell populations in individuals with hematopoietic disorders48.

Embryonic stem cells are derived from the amniotic fluid, placenta, and umbilical cord and represent a unique category within the spectrum of stem cell types49. Fetal cells possess multipotent capabilities and can differentiate into a restricted type of cells50. These cells are distinctively derived from tissues associated with the prenatal and perinatal stages of development, indicating their specialized origin49. Notably, perinatal stem cells exhibit a hybrid nature, sharing characteristics analogous to those of adults and ESCs. Their dual features make them adaptable and potentially useful for various regenerative medicine applications51. Perinatal stem cells offer a noncontroversial and ethically sound reservoir for therapeutic purposes49. Their properties, which are reminiscent of those of ESCs and ASCs, contribute to their unique regenerative potential. Since these cells undergo cell differentiation into a wide variety of cells, tailored approaches for tissue regeneration and repair are possible52. Perinatal stem cells show promise in furthering regenerative medicine across a range of tissues in terms of prospective uses. They are important components in targeted tissue renewal because of their capacity to specialize in particular cell lineages52.

Moreover, its therapeutic potential can be extended to other conditions, such as cerebral palsy and diabetes. Perinatal stem cells offer a novel and innovative approach to the development of medicines tailored to address the complexities of these disorders by exploiting their regenerative properties and versatile differentiation capabilities53. One notable advantage of perinatal stem cells is their potential for allogeneic transplantation without eliciting immune rejection. The immunomodulatory characteristics of these cells make them well-suited for transplantation across different individuals, eliminating the need for a perfect match between the donor and recipient54. This opens new possibilities for allogeneic stem-cell therapies, providing a feasible and practical approach to transplantation procedures without the intricate challenges associated with immune compatibility.

In summary, perinatal stem cells signify a distinct and highly promising category of stem cells with hybrid properties. Their application in regenerative medicine, therapeutic interventions for specific conditions, and allogeneic transplantation underscore their potential to reshape the landscape of stem cell-based therapies.

The iPSCs represent a revolutionary category in stem-cell studies and are characterized by properties that mirror those of ESCs55. Several human and mouse investigations have utilized fibroblasts and skin cells as the primary sources of adult cells. It has been discovered that adult brain stem cells have been identified as the primary cell type in investigations of reprograming cells56. Another study reported that murine bone marrow mononuclear cells can be reprogrammed more effectively than mouse embryonic fibroblasts57. Notably, iPSCs and their embryonic counterparts possess the capacity to undergo pluripotency to differentiate into distinct kinds of specialized cells58. One important way to iPSCs is to distinguish them from ESCs by their source, in which in order to create iPSCs, adult cells are reprogrammed. This methodology provides a novel means of addressing ethical concerns regarding the use of ESCs in scientific investigation59. Personalized medicine could undergo significant transformations if adult cells are reprogrammed to become iPSCs. The advancement of individualized cellular therapeutics involves the process of cellular reprogramming for individual patients is one of the main uses of iPSCs60. The iPSCs have the remarkable ability to transform into a wide variety of disease-specific cell types during cell reprogramming. This personalized approach improves the integrity and efficiency of cell-based treatments and offers a potential path in order to treat numerous illnesses and traumas.

Furthermore, iPSCs play a pivotal role in disease modeling in personalized medicine61. The capacity to generate iPSCs from individuals with particular genetic conditions has enabled researchers to create in vitro disease models. These models are extremely invaluable tools for understanding disease mechanisms at the cellular level and enable the exploration of targeted therapeutic interventions62. iPSC-based disease modeling advances the field of personalized medicine by enabling a more accurate and customized approach to medical research, thus opening the door for customized treatments. Beyond illness modeling and customized treatments, iPSCs have a major impact on toxicity assessments and drug development63. The pluripotent characteristics of iPSCs allow the generation of diverse cellular phenotypes, providing a flexible platform for evaluating the safety and effectiveness of pharmaceuticals. iPSC-based assays offer a more thorough understanding of how pharmaceuticals interact with various cell types, which helps identify possible side effects and directs advancements in the creation of remedies that are both safer and more effective64.

In conclusion, iPSCs offer a revolutionary approach to stem-cell investigation, owing to their pluripotent characteristics and the origin of adult cell reprogramming. Their applications in patient-specific cell therapies, disease modeling for personalized medicine, and drug discovery underscore their potential to revolutionize medical treatment and contribute to advancements in personalized healthcare.

Stem cells secrete numerous factors and exosomes that are responsible for immunomodulatory, antiapoptotic, antibacterial, and microbial properties. In addition to the ability for repair, communication, and regeneration (Fig. 2).

The schematic diagram represents the mesenchymal stem cells mechanism of action and their interaction with immune cells, including differentiation, immunomodulation, antiapoptotic effects, exosome and microvesicle release, migration and homing, and matrix remodeling.

Stem cells immunomodulatory actions have undergone extensive research when contrasted with other stem cell types65,66. Stem cells have a role in suppressing acute-phase responses by suppressing excessive activation of macrophages and T cells and initiating the secretion of inflammatory cytokines. This could decrease the likelihood of a cytokine storm67. Toll-like receptors (TLRs) present in MSCs detect injury signals and initiate immunomodulatory responses68. MSCs exhibit immunomodulatory properties via paracrine activity and direct intercellular communication facilitated by several bioactive compounds like cytokines, chemokines, and growth factors. These molecules affect both adaptive and innate immunity. MSCs can prevent the activation of T-cells via several immunomodulatory substances, such as TGF-1, PGE2, and HLA-G5. They also utilize molecules that are linked to a membrane, such as VCAM-1, PD-L1, and Gal-169,70. MSCs regulate NK cell cytotoxicity by reducing the expression of IFN-71. Cytokines are crucial for preserving the ability of ESCs to reproduce. This is achieved through the action of a specific cytokine called leukemia inhibitory factor (LIF), which belongs to the class of cytokines known as interleukin-672. The iPSCs can modulate the immune system, as demonstrated through their capacity to suppress the rapid increase of responder T cells in modified combined leukocyte reactions in vitro73.

In addition, apoptosis serves as a protective process within the immunological response of the host to combat pathogens and has a crucial function in interactions between the host and pathogens71. MSCs can inhibit apoptosis, which may occur due to pathogens, low oxygen levels, mechanical stress, or radiation. For instance, the ability of MSCs to avoid cell death (antiapoptotic effects) has been investigated in cardiac ischemia, neurological conditions, and respiratory ailments74. In addition, during apoptosis caused by hypoxia, MSCs stimulate the expression of certain proteins, including HGF, VEGF, and TGF-1, with the potential to prevent endothelial cell death75. Additional variables contribute to the antiapoptotic effect of MSCs, such as IL-6 and IGF-1, which results in enhanced secretion of SFRP2 protein76.

Stem cells exert their antimicrobial activity by secreting molecules and direct cell-to-cell interactions, namely by releasing antimicrobial peptides (AMPs). The antimicrobial activities are carried out by specific AMPs like the family of lipocalins (Lcn2), hepcidin, and b-defensins (hBD-1, hBD-2, and hBD-3)77,78. Stem cells boost their antimicrobial activity by upregulating LL-37, a peptide that is stimulated by bacteria and inhibits bacterial growth79.

Regeneration and restoration of damaged tissues rely heavily on stem cells because of their distinctive ability to suppress aberrant immune responses, their capacity to transform into specific tissues, and produce certain substances that stimulate the hosts reparative and regenerative systems80. Furthermore, the micro-vesicles and exosomes generated from stem cells are important for stem-cell communication and regeneration. Lipids, proteins, nucleic acids, including RNA and micro RNA, and signaling molecules are among the many bioactive compounds that are transported within the extracellular vesicles (EVs) emitted by stem cells of the body81. Compounds secreted by stem cells facilitate tissue regeneration by promoting the growth and specialization of stem/progenitor cells in the immediate vicinity. In addition, they control the placement of molecules in the extracellular matrix, activate pathways that prevent scarring, and promote the development of new blood vessels82,83. MSCs release soluble paracrine factors, including ANGPT1, HGF, EGF, VEGF, KGF, PGE2, and interleukin-10 (IL10). These factors can improve the restoration of epithelial and endothelial cells84,85.

Recent years have seen remarkable progress in stem-cell research that has greatly expanded our comprehension of stem-cell biology86. One notable milestone was the elucidation of novel mechanisms governing stem cell fate decisions. Researchers have uncovered key signaling pathways and transcription factors that play pivotal roles in directing stem-cell differentiation87,88. A cellular communication system known as the Notch signaling pathway is vital for various physiological and developmental functions89. Researchers have demonstrated the significance of the Notch pathway in determining the outcome of cells by either promoting the renewal of cells or their differentiation into various types of stem cells, including ESCs90, PSCs91, HSCs92, NSCs93, and ISCs94. Other instances of the signaling pathways are the PI3k/AKT signaling95 and TGF- signaling96. A transcription factor known as NF-B controls the diverse functions of NF-B in stem cells and developmental processes97. These findings enhance stem cell manipulation capabilities for specific therapeutic purposes, offering unprecedented opportunities for targeted cell-based interventions98. Recent studies have explored the nuances of lineage commitment and cellular specialization within the framework of stem-cell development. Scientists have identified regulatory networks that govern stem cell differentiation into distinct cell types, shedding light on the molecular events that dictate cell fate99,100.

Researchers have also unveiled insights into the epigenetic modifications associated with reprogramming, enhancing our comprehension of the molecular mechanisms by which somatic cells transform into pluripotent states101. For example, studies proved that gene expression and cellular identity are influenced by changes in DNA methylation patterns during the formation of iPSCs102. Modification of histones through acetylation and methylation, which affect chromatin structure and gene regulation, also play significant roles in reprogramming. This new understanding of epigenetic pathways helps clarify the complex processes involved in pluripotency induction and cellular reprogramming.

These advancements have contributed to improvements in iPSC-based methods for pharmaceutical innovation, disease modeling, and customized regenerative medicine62. Another significant stride in stem-cell research pertains to the tissue regeneration field103.

Transplantation of stem cells has great potential as a medicine applied to numerous illnesses. In neurology clinical trials, scientists are presently investigating stem cell therapys feasibility for the purpose of alleviating neurological disorders, such as Alzheimers and Parkinsons104. Additionally, investigations are being conducted on stem-cell therapy for cardiovascular illnesses, orthopedic conditions, hematological conditions, and diabetes. The adaptability of stem cells, coupled with advancements in delivery techniques, positions them as potential game-changers in regenerative medicine105. Emerging applications include the use of stem cells in immunotherapy, where they are engineered to target and treat certain cancers106. Furthermore, continuous investigations have investigated the possibility of using stem cells to regulate the immune system in disorders like autoimmune illnesses107. As these clinical applications progress from research to practice, the landscape of healthcare is poised to undergo significant transformation.

Neural stem-cell transplants have been administered to patients with PD in a clinical trial. In addition to improving motor system function, the data demonstrated a slowing of the diseases progression and suggested the prospects of stem cells for neurological regeneration108,109. Individuals with heart failure participated in a cardiac stem-cell clinical trial. The outcomes showed less scar tissue, increased angiogenesis, and improved heart function, indicating the effectiveness of stem-cell treatment in promoting the regrowth of cardiac tissue110,111. Additionally, bone marrow-derived MSCs (BM-MSCs) have been utilized in a clinical study of osteoarthritis. Patients experience decreased pain, improved joint function, and evidence of cartilage regeneration, demonstrating the therapeutic prospects of stem cells in orthopedic applications112114.

Treating leukemia with HSC transplantation (HSCT) has proven beneficial. Patients undergoing this procedure achieve complete remission and hematopoietic system reconstitution, leading to prolonged survival and improved quality of life46,115. Furthermore, clinical trials utilizing iPSCs to generate pancreatic progenitor cells have demonstrated promise for the treatment of diabetes. Patients exhibit restored insulin production and improved glycemic control, suggesting a regenerative approach to diabetes management116,117 (Table 1) (Fig. 3).

The advancement in stem-cell therapies in various diseases.

MSC sources, such as bone marrow, adipose tissue, and placenta, and their role in the therapy of different diseases. MSCs improve and combat diseases including pneumonia, leukemia, neuron diseases, osteoarthritis hear diseases, and the two types of diabetes. MSCs have immunoregulator and anti-inflammatory properties.

In combating the COVID-19 pandemic, universal vaccination remains the primary strategy; however, uncertainties persist regarding the duration of vaccine protection and the inability of any vaccine to provide absolute immunity137. Stem-cell therapy has arisen as a potential substitute, building on successes observed in severe H7N9 avian influenza138,139. Stem cells, particularly those derived from human umbilical cord stem cells (hUCMSCs), are effective and safe for treating severe COVID-19, demonstrating their potential in over 100 international clinical trials140. Allogeneic MSCs, notably hUCMSCs, contribute to anti-inflammatory responses, tissue repair, and the modulation of immune functions, showcasing their therapeutic promise141. Challenges include difficulties in recruitment due to the evolving clinical landscape, lack of preclinical data, and variations in stem-cell properties. Despite these hurdles, stem-cell therapy, especially considering advancements in organoid technology for better modeling of viral effects, has significant clinical potential142. Despite current limitations and technological challenges, the continuous advancement of stem-cell treatment offers optimism in the fight to preserve lives and improve treatment results for individuals with severe COVID-19 infection (Fig. 4).

Potential and mechanism of action of mesenchymal stem cell treatment for COVID-19 pneumonia using MSCs, which have immunoregulatory characteristics, can help control the cytokine storm and COVID-19 lung injury. Mesenchymal stromal cells (MSCs) play an important role in a number of processes, including preventing neutrophil infiltration and transforming hyperactivated T cells into regulatory T cells (Tregs). They also promote the production of anti-inflammatory cytokines, such as prostaglandin E2 (PGE2), transforming growth factor beta (TGF), indoleamine 2,3-dioxygenase (IDO), and interleukin 10 (IL-10). Nevertheless, MSCs play a crucial function by stimulating the synthesis of growth factors by endothelial and epithelial cells, which in turn inhibits fibrosis and boosts the infusion of alveolar fluid.

Regenerative medicine with stem cells has investigated significant capacity across diverse medical specialties, offering innovative solutions for previously challenging conditions143. Patients stem cells are harvested for autologous stem-cell treatment. Autologous stem cells that have been cultured are cultivated in the lab before transplantation. These cells have the potential to be categorized into modified and unmodified expanded autologous stem cells. Allogeneic stem cells are classified similarly to autologous stem cells, but they come from healthy donors18. Autologous stem cells can be readily acquired and do not cause immunological rejection after infusion. Allogeneic stem cells provide multiple benefits, including the ability to select a donor, availability from different sources, minimal likelihood of causing an immune response, and the convenience of being readily available. Allogeneic MSCs are also immunogenic, indicating that they can trigger an immunological response. These cells can generate a memory response in the immune system under specific circumstances144146.

Regenerative medicine can restore, repair, or regenerate impaired tissues or organs by harnessing the unique characteristics of stem cells147. This topic includes a range of approaches that seek to leverage the extraordinary capacity of stem cells for medical applications. Although stem cells possess the capacity to undergo self-renewal and differentiate into various distinct cell types, they hold great promise as therapeutic agents against various illnesses and wounds148. Regenerative medicine aims to create novel methods to repair damaged tissues caused by disease, injury, or aging using stem cells to restore normal function and structure to damaged organs or tissues149. These therapies have great potential to revolutionize medical treatments, particularly in areas where conventional medicine falls short of providing effective remedies or cures150.

This emerging field presents a promising avenue for personalized cancer treatments, as researchers have delved into harnessing the unique attributes of stem cells to create innovative strategies for cancer management and potential cures. These investigations signify a significant paradigm shift in oncology, offering a progressive outlook for tailored therapies and potential breakthroughs in cancer treatment151,152. Stem cell-based cancer treatments are becoming increasingly promising. Because stem cells can locate and target primary and metastatic tumors, and serve as innovative delivery approaches. In preclinical animal models, stem cells modified to express different cytotoxic chemicals consistently reduced tumor size and increased survival153,154. They have also been used to reduce side effects and improve primary medicinal efficacy by acting as carriers of viruses and nanoparticles. Additionally, stem cells have the potential for utilization in immunotherapy, anticancer drug screening, regenerative medicine, and cancer stem cell-targeted therapy for diverse forms of malignancies, including lung cancer, breast cancer, and osteosarcoma155.

Regenerative strategies in orthopedics include advanced osteonecrosis of the hip joint, intervertebral hernias, osteoporosis, targeted joint injuries, cartilage restoration, and bone healing through stem-cell and tissue-engineering methodologies156,157. Recent investigations have shown innovative approaches, like MSC therapy, platelet-rich plasma (PRP) injections, and biocompatible scaffolds infused with growth factors158. These methods aim to optimize cartilage repair and bone regeneration, offering promising outcomes under musculoskeletal conditions159,160. Research has focused on refining MSC isolation techniques, deciphering the crucial signaling pathways involved in tissue regeneration, and developing bioactive materials that enhance healing161.

In the cardiology field, innovative approaches, including stem-cell therapy and bioengineered cardiac patches, are being explored to mend and regenerate impaired heart tissues after cardiac events such as myocardial infarctions162. Current research has been focused on different stem-cell types, including iPSCs and cardiac progenitor cells, to regenerate impaired heart muscles and restore cardiac function. Furthermore, research has focused on creating bioengineered cardiac patches using cell-based structures and biomaterials that resemble genuine heart tissue163.

In the field of neurology, ongoing investigations have delved into the domain of medicines based on stem cells developed to fight diseases affecting the nervous system, including Parkinsons and Alzheimers164,165. Studies have focused on using stem cell-derived neurons to replace and regenerate impaired nerve cells166. Recent studies have shown that there are numerous varieties of stem cells, including neural stem cells and iPSCs, with the aim of producing functional neurons capable of integrating into damaged neural networks167,168.

Regenerative medicine in dermatology represents a dynamic frontier of research, particularly concerning stem-cell applications in the skin169. Stem cells residing in the skin tissues offer promising avenues for innovative therapeutic strategies that target various dermatological conditions and injuries170. Their remarkable regenerative potential holds immense promise for advancing wound healing, addressing burns, and managing skin disorders such as psoriasis and vitiligo171,172. Additionally, stem cell use in cosmetic dermatology for antiaging treatments and improving skin quality underscores their diverse clinical utility173. Researchers have actively explored methods to harness the inherent regenerative abilities of stem cells with the aim of developing tailored and effective therapies for combating skin-related diseases and facilitating cosmetic enhancements. This transformative approach involves tissue engineering techniques utilizing stem cells, biomaterials, and growth factors to create skin substitutes that promote tissue regeneration and repair174177.

Due to their potential function, an enormous amount of curiosity about stem cells has persisted in rejuvenating the retina and addressing corneal damage, particularly in diseases such as macular degeneration178. Noteworthy studies featured in journals such as Investigative Ophthalmology and Visual Science and British Journal of Ophthalmology delve into the strides made in utilizing stem cells for ocular regeneration179,180. Studies have employed stem-cell therapies to restore retinal cells and heal corneal injuries, presenting encouraging pathways for managing vision-related ailments181. These studies signify a burgeoning field of ophthalmology research, offering promising prospects for innovative treatments aimed at addressing ocular disorders and enhancing vision182.

Stem-cell utilization in oncology, regenerative medicine, and disease therapeutics is an expanding field of research and innovation151. Research has focused on leveraging stem cells for targeted cancer therapies and exploring their potential for cellular reprogramming and immune cell modulation to combat tumors183. The immunomodulatory potential of stem cells presents a compelling avenue in biomedical research, particularly in addressing autoimmune disorders and graft-versus-host disease (GVHD) and improving transplantation outcomes184. Stem cells show a remarkable ability to influence immune cell behavior and function, offering promising prospects for novel therapeutic interventions185. This intersection of immunology and stem-cell biology promises not only innovative treatments but also deeper insights into the complex mechanisms governing immune system regulation and dysregulation. This rapidly expanding field has an enormous potential to improve our knowledge of immune-related disorders and provide efficient treatment plans186.

Stem-cell utilization in hematology is a dynamic area of scientific inquiry and clinical application in the regenerative medicine field and therapeutic interventions for diseases187. Leveraging the potential of stem cells to regenerate is the main goal of research, particularly in HSCs, for transplanting bone marrow and exploring its role in immune cell therapies to combat various blood-related ailments188. This growing field represents a promising avenue for innovative treatments, emphasizing the pivotal role of stem cells in revolutionizing hematology by offering potential cures and personalized therapeutic solutions for blood disorders, thereby marking a transformative shift in disease management189,190.

Stem-cell research offers the potential for addressing illnesses such as inflammatory bowel disease (IBD)191,192 and managing various gastrointestinal disorders193. Researchers are investigating stem cell-based approaches to repair gastrointestinal tract injuries, manage ulcers, and alleviate the symptoms of chronic conditions like ulcerative colitis and Crohns disease194,195. Despite ongoing investigations, the clinical application of stem-cell therapies in gastroenterology remains the subject of clinical trials and extensive research, emphasizing the need for further exploration and understanding of their efficacy and safety in treating many immunopathological diseases (Fig. 5)196.

MSCs inhibit many immunopathological disease conditions, including skin infection, inflammatory bowel disease, and endocrine hormone disorders; they also suppress tumor cells, the aging process, and reproductive infertility.

Ongoing investigations explore the potential of stem cells in restoring lung tissue damaged by diseases like serious respiratory disease or chronic obstructive pulmonary disease (COPD)197. Researchers have investigated the capacity of stem cells to restore impaired lung tissue, alleviate COPD symptoms, and target conditions such as idiopathic pulmonary fibrosis198. Despite extensive research, the use of stem-cell therapies in pulmonology requires further examination to establish their safety, effectiveness, and long-term effects on respiratory illnesses199. Although this emerging field shows promise for future treatment, it requires thorough comprehension and robust clinical validation200.

Stem-cell research in reproductive medicine opens new avenues for treating infertility and addressing various reproductive system disorders201. Stem cells, whether derived from embryonic, adult, or induced pluripotent sources, hold promise for regenerating and repairing damaged reproductive tissues202. This area of study covers various aspects of reproductive health, including the restoration of ovarian function, addressing endometrial issues, and potentially aiding fertility preservation. Research endeavors detailed in publications such as the Journal of Assisted Reproduction and Genetics and Fertility and Sterility, explore the potential of interventions utilizing stem cells to revolutionize infertility treatments and offer new hope to individuals facing reproductive health challenges. These advancements represent a burgeoning field that may reshape the landscape of reproductive medicine and provide innovative solutions for the treatment of infertility and related disorders201,203.

Stem-cell research in endocrinology presents a promising avenue for managing endocrine disorders such as diabetes by focusing on the generation of insulin-producing cells and regenerating pancreatic tissues204. Through various studies documented in journals like Diabetes and Endocrine Reviews, researchers work to create functional beta cells or islet-like structures that can secrete insulin by utilizing the regeneration ability of stem cells205. This pioneering field aims to address deficiencies observed in traditional diabetes management by offering cell-based therapies that can potentially restore insulin production and regulate glucose levels206. The exploration of stem-cell therapies in endocrinology has heralded a new era of diabetes treatment, offering hope for more effective and sustainable management strategies for this chronic condition207.

In dentistry, cutting-edge research has focused on the innovative utilization of stem cells to regenerate crucial dental tissues, including tooth enamel, dentin, and dental pulp208. This revolutionary exploration seeks to redefine conventional approaches to dental care by offering transformative treatments for prevalent conditions such as cavities, gum diseases, and dental trauma209. Utilizing their unique regenerative stem-cell capacities, scientists aim to generate interventions that induce the natural regeneration and repair of diseased or impaired dental tissues, potentially revolutionizing the oral healthcare landscape210,211. This promising field of study in dentistry holds the potential to pave the way for novel therapeutic strategies that offer patients improved outcomes and enhanced oral health212.

In the domains of trauma and wound healing, intensive research efforts have focused on uncovering the regenerative processes of stem cells to address the complexities of chronic wounds, burns, and traumatic injuries213. Stem cells exhibit promising capabilities in fostering tissue regeneration and mitigating scarring by influencing cell differentiation and supporting repair mechanisms in damaged tissues214,215. This exploration of stem cell-based interventions aims to revolutionize conventional wound care approaches by fostering natural tissue regeneration, accelerating healing processes, and minimizing scarring, thereby offering renewed hope to patients with challenging wounds and traumatic injuries216. In the quest for more potent treatment approaches to enhance patient outcomes and accelerate recovery, the potential of stem cells in trauma and wound healing serves as a ray of hope217,218. Stem-cell regenerative medicine is a dynamic and expansive field, continuously expanding its applications across various medical disciplines to address a wide spectrum of health conditions and diseases219 (Table 2).

Stem-cell therapy is utilized in specific medical fields.

In addition, various types of stimulation have been utilized during stem-cell therapy to enhance differentiation proliferation and improve healing, such as shock wave stimulation242. MSCs are increasingly being acknowledged as valuable resources for various orthopedic applications, and radial shock waves have been shown to substantially enhance the development and regrowth of MSCs in a laboratory setting. Furthermore, this type of stimulation safely accelerates cartilage repair in living organisms, suggesting positive results for clinical applications243. IR is a type of high-energy radiation that has enough energy to dislodge firmly bound electrons from atoms, leading to the creation of ions. In addition to being a carcinogen, IR is also used as a therapeutic option for patients with cancer. However, there is increasing data showing that extranuclear components, such as mitochondria, play a significant role in the cellular response to IR, and the mitochondrial function of MSCs was observed to be considerably increased after 4h of exposure to ionizing radiation, as determined by measuring mitochondrial oxygen consumption244. Cell proliferation has been induced in many in vitro trials using a modest amount of laser therapy. Osteoblasts, lymphocytes, keratinocytes, and fibroblasts exhibit enhanced proliferation when exposed to laser irradiation245. Other types of stimulation include electrical stimulation to enhance stem-cell therapy in nerve regeneration242, electrical stimulation to promote cell differentiation and proliferation of fatal neuronal stem cells into neuronal stem cells246, and nonpeptide small molecules247, in addition to mechanical stimuli such as cyclic stretch, three forces, laminar shear stress, cyclic pressure248, and gamma radiation249.

Stem-cell studies have been significantly promoted by cutting-edge technologies that have revolutionized our understanding and utilization of these versatile cells. This discussion focuses on some of the most impactful biotechnological advancements in stem-cell studies, with a specific focus on exosome-based therapeutics, scRNA-Seq, and the revolutionary CRISPR-Cas9 gene-editing technology250252.

The new frontier of exosomes produced from stem cell-based therapeutics represents a promising avenue for the field of regenerative medicine253. RNAs, signaling molecules, and proteins are bioactive substances encapsulated in exosomes and small vessels secreted by stem cells. These nanovesicles are essential for intercellular interactions and can control a number of cellular functions254. Stem cell-derived exosomes exhibit unique properties that modulate immune responses, promote tissue regeneration, and foster repair mechanisms255. Harnessing the therapeutic potential of these exosomes holds considerable promise for developing innovative treatments for diverse medical conditions, including inflammatory disorders, neurodegenerative diseases, and tissue injuries253,256258. Stem cell-derived exosome-based therapies represent a burgeoning frontier in regenerative medicine, providing new opportunities for targeted, minimally invasive therapeutic interventions259.

Advances in scRNA-seq have allowed investigators to examine stem-cell transcriptomes individually, providing unprecedented insights into cellular heterogeneity and gene expression patterns13. This technology has played an essential role in comprehending the dynamics of stem-cell populations during differentiation and disease progression260,261.

With the advent of CRISPR-Cas9, a new era in gene editing has begun, which enables the precise modifications of stem-cell DNA14. Researchers can now edit or introduce specific genes with unprecedented accuracy, facilitating cancer and disease modeling, studying gene function, and developing potential therapeutic interventions262,263.

CRISPR-based technologies have enabled large-scale functional genomic studies and high-throughput screening of stem cells. That allows researchers to systematically interrogate gene function on a genome-wide scale, uncovering novel regulators of stem-cell fate, pluripotency, and differentiation264,265.

Beyond traditional CRISPR-Cas9, recent innovations, such as base editing and prime editing, offer enhanced precision in gene editing266. These techniques allow the modification of specific nucleotides without causing double-strand breaks, minimizing off-target effects and expanding the possibilities for therapeutic genome editing in stem cells267 (Fig. 6).

Immunotherapy chimeric antigen receptor (CAR) T-cell therapy can be filled with the help of recent developments in genome editing using CRISPR-Cas9. To enable robust, accurate, and controllable genetic alteration, genome editing techniques are used, such as base and prime editing. In both hematopoietic and non-hematopoietic cancers, T-cells can be circumvented through CRISPR-Cas9-induced multiplex deletion of inhibitory molecules, which enhances CAR T-cell growth and persistence. The use of targeted knock-in techniques during CAR T-cell engineering offers the possibility of producing highly effective and potent cell products. Lentivirus is viral particles modified to carry CRISPR components in T cells, CRISPR-Cas9 based on the precise insertion of CAR genes, more and strong CAR T-cells product engineered using CRISPR-Cas9 to overcome specific histocompatibility hurdles and with improved persistence/antitumor function could greatly improve the production of cellular immunotherapies and the therapeutic durability.

Overall, CRISPR-based gene editing shows great promise for therapeutic applications in stem cell-based regenerative medicine. This opens new avenues for correcting genetic mutations underlying various diseases, generating genetically modified cells for transplantation, and developing personalized cell therapies.

Stem cells are integral to the advancement of personalized medicine, aligned with the goal of tailoring healthcare to individual characteristics and encompassing genetic, environmental, and lifestyle factors16. From a patients cells, iPSCs provide a potent platform for building disease models that accurately reflect the persons genetic background268. This capability facilitates in-depth studies of disease mechanisms at the cellular and molecular levels, enabling more precise diagnosis and the establishment of targeted therapeutic strategies60. Moreover, modern gene-editing techniques, including CRISPR-Cas9, enable accurate alterations in stem-cell genomes269.

This breakthrough allowed the correction of genetic mutations associated with diseases, laying the groundwork for personalized therapies addressing specific genetic alterations in individual cells270. In pharmacogenomics, stem cells significantly contribute to the assessment of individual drug responses. Leveraging patient-derived stem cells in pharmacogenomic studies enables researchers to understand the impact of an individuals genetic composition on their reaction to various medications271. This knowledge serves as a guide for formulating personalized treatment plans, minimizing adverse reactions, and enhancing the overall therapeutic outcomes. Moreover, stem cells actively contribute to the identification of personalized biomarkers associated with specific diseases272. Differentiating patient-derived stem cells into cell types relevant to the disease makes it easier to identify molecular signatures that can be used as diagnostic indicators. These personalized biomarkers substantially improve the accuracy of disease detection and monitoring, marking a significant step toward more individualized and effective healthcare strategies273,274.

Stem-cell therapy is witnessing a surge in clinical trials, reflecting a growing interest in translating laboratory findings into viable treatments275. Clinical trials involving various stem-cell types are currently underway and include a wide range of health issues276. The goal of ongoing trials is to determine whether stem-cell therapies are effective in alleviating symptoms of neurological diseases such as Alzheimers, Parkinsons, and spinal cord injuries277 (Table 3). Researchers are investigating how stem cells might be able to repair damaged neurons, encourage brain regeneration, and lessen the symptoms of these crippling conditions288.

Examples of clinical trials with results involved in neurological diseases, cancer, cardiovascular, and Orthopedics, from http://clinicaltrials.gov/.

Clinical trials in cardiovascular medicine aim to evaluate the use of stem cells, such as progenitor cells and MSCs, for treating conditions like heart failure and ischemic heart disease. These trials explored the regenerative potential of stem cells in repairing impaired cardiac tissues and improving overall cardiac function289.

Research is now being conducted on stem cell-based therapeutics for cancer treatment, including studies focusing on HSC transplantation (SCT) to treat hematological malignancies290. In addition, researchers have explored potential applications for stem cells in conjunction with traditional cancer therapies in order to enhance therapeutic results and minimize negative consequences291. Additionally, clinical trials in orthopedics and musculoskeletal disorders involve the use of stem cells to treat conditions like osteoarthritis and bone defects. MSCs, which are known for their capacity to differentiate into bone and cartilage, are being studied for their regenerative potential in restoring joint and bone health292. Furthermore, stem-cell therapies are now under investigation for their potential applications to treat diabetes by replenishing pancreatic beta cells. Clinical trials have investigated the use of stem cell-derived insulin-producing cells as transplants to regulate blood glucose levels in patients with diabetes293.

Stem-cell therapy, although showing great promise, faces multiple obstacles and constraints that need to be carefully considered. One prominent challenge is the potential for tumorigenesis, wherein the number of transplanted stem cells may increase uncontrollably, leading to tumor formation294,295. The security of stem cells can only be ensured by thorough preclinical examinations before they can be used in clinical settings. Additionally, the immune response poses a challenge due to the recipients immune system perceiving the transplanted cells as alien, leading to rejection296,297. The development of strategies to mitigate immune rejection and improve engraftment remains an ongoing challenge.

Furthermore, precisely controlling stem cell development into the desired cell types is a significant challenge298. The variability in differentiation protocols and the possibility of off-target consequences raise concerns regarding the reliability and safety of the therapeutic outcomes. Additionally, scalability and cost-effectiveness in the production of sufficient quantities of quality-controlled stem cells for widespread clinical use remain logistic obstacles that must be overcome for the field to attain its full potential110,299,300.

Ethical considerations are central to the discourse surrounding stem-cell therapy, particularly the use of ESCs301. Discussions over the moral standing of the early human embryo arose because of the killing of embryos during the extraction of ESCs. Because of these concerns, scientists are looking at alternative sources of pluripotent stem cells, such as iPSCs, which are reprogrammed from adult cells and do not have the same ethical concerns as ESCs. Regulatory frameworks are essential for negotiating the moral challenges presented by different stem cell therapies302.

Countries have varying regulations governing the clinical utilization of stem cells, ranging from permissive to restrictive. Achieving a balance between promoting innovation and ensuring patient safety remains a challenge for regulatory bodies303. The evolving nature of stem-cell research and therapies necessitates dynamic regulatory frameworks that can be adapted for scientific advancement. Ongoing debates persist in this field, particularly regarding the commercialization of stem-cell therapies. Issues of accessibility, affordability, and equitable distribution of these therapies raise ethical questions.

Moreover, concerns regarding the premature marketing of unproven stem-cell therapies and the need for transparent communication regarding the state of scientific evidence contribute to the ethical complexity of this field304. In conclusion, addressing the difficulties and ethical considerations of stem-cell therapy requires a multidisciplinary approach that encompasses rigorous scientific research, transparent communication, and dynamic regulatory frameworks. Realizing the full promise of stem-cell therapies will require a careful balance between ethical responsibility and innovation as the field develops.

With the help of new technologies and the results of continuing research, stem-cell treatment might potentially transform many different areas of medicine. One key direction involves the integration of stem-cell therapy into precision medicine approaches, opening a new chapter in medical history, where customized care based on a persons genetic composition promises enhanced therapeutic outcomes and reduced side effects. Advances in genomics and the application of patient-specific stem cells are expected to drive this integration. Additionally, future research should focus on refining the immune modulation strategies associated with stem-cell therapies and addressing challenges such as immune rejection and graft-versus-host responses. Innovative approaches, including engineered stem cells and immunomodulatory molecules, aim to enhance compatibility with stem-cell treatment.

The continued evolution of gene-editing tools, including CRISPR-Cas9, will perform a key function in ensuring the precision and safety of stem-cell therapies. This technology enables the modification of specific genes in stem cells, offering avenues for targeted therapeutic interventions and correction of genetic disorders at the cellular level. The synergy between stem-cell therapy and bioengineering has emerged as a significant area of exploration. The integration of stem cells with advanced biomaterials can potentially create functional tissues and organs with improved structural and functional properties. Bioengineered constructs provide innovative solutions for tissue-specific regeneration and transplantation. These key directions underscore the multidimensional nature of future advancements in stem-cell therapy, bringing together precision medicine, immune modulation, gene editing, and bioengineering to propel the field toward transformative developments.

Recent developments in stem-cell therapy have illuminated a path of immense promise and transformative potential for revolutionizing modern medicine. The exploration of stem cells across diverse medical disciplines guided by advancements in science, biotechnology, and clinical trial applications has positioned this field at the forefront of biomedical research. The historical journey from foundational concepts laid by pioneering scientists in the late 19th and early 20th centuries to groundbreaking milestones such as the isolation of ESCs and the discovery of iPSCs underscores a monumental leap in medical science.

The regenerative processes of stem cells, categorized into embryonic, adult, induced pluripotent, and perinatal stem cells, offer unprecedented opportunities for therapeutic interventions. Development, tissue repair, and regeneration are all intricately linked to stem cells due to their remarkable capacity to differentiate into different cell types and self-renew. Their diverse applications include neurodegenerative disorders, cardiovascular ailments, spinal cord injuries, diabetes, and tissue damage, opening novel avenues for treating debilitating conditions. However, as the field advances, the critical challenges and complexities must be addressed. Problems like immunological rejection, tumorigenesis, and the precise manipulation of stem-cell behavior pose hurdles that demand comprehensive exploration and innovative solutions. The landscape of stem-cell therapy is intricate and requires a nuanced understanding of its historical foundations, current realities, and future trajectories.

In collating recent biotechnology advancements, critical trial evaluations, and emerging technologies, this review provides a comprehensive compass for clinicians, researchers, and stakeholders navigating the intricate terrain of stem-cell therapy. Future directions, marked by precision medicine integration, immune modulation strategies, advancements in gene-editing technologies, and synergy with bioengineering, offer a roadmap for the continued evolution of stem-cell therapies.

Resonating with the revolutionary promise of stem-cell therapy not only in the realms of science and medicine but also in the lives of individuals with debilitating diseases and injuries. The journey from conceptualization to practical utilization represents a testament to human ingenuity and the relentless pursuit of improving healthcare. As stem-cell research continues, it holds the promise of reshaping the landscape of medicine, bringing forth a new era in which personalized regenerative therapies can mitigate the impact of a spectrum of medical challenges.

Not applicable.

Not applicable.

No funding was received for this study.

B.M.H.: study design and data analysis; R.K.Y.: writing the paper; G.H.A.: data collection; S.R.A. and R.K.K.: data analysis and interpretation; S.A.M.: study design and writing the paper.

The authors declare no conflicts of interest.

Not applicable.

Bashdar Mahmud Hussen and Suhad A. Mustafa.

All the data are available in the manuscript.

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Revolutionizing medicine: recent developments and future prospects in ...

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Researchers find success with stem cell therapy in mice model of …

Thursday, December 19th, 2024

Scientists have observed that some genetic variations in microglia show a strong correlation with an increased risk of Alzheimers disease. One such correlation involves a gene called TREM2, which plays an essential role in in how microglia detect and address neurodegeneration. Certain genetic variants of TREM2 are among the strongest genetic risk factors for Alzheimers disease, Wernig said.

The data are convincing that microglial dysfunction can cause neurodegeneration in the brain, so it makes sense that restoring defective microglial function might be a way to fight neurodegeneration in Alzheimers disease, he added.

In the study, mice with a defective TREM2 gene received hematopoietic stem and progenitor cell transplants from mice with normal TREM2 function. The researchers found that the transplanted cells reconstituted the blood system and that some of them efficiently incorporated into the recipients brains and became cells that looked and behaved like microglia.

We showed that most of the brains original microglia were replaced by healthy cells, which led to a restoration of normal TREM2 activity, Wernig said.

Next, they investigated whether the restored TREM2 activity was enough to improve the brain health of the TREM2-deficient mice. Indeed, in the transplanted mice we saw a clear reduction in the deposits of amyloid plaques normally seen TREM2-deficient mice, Wernig said. They were also able to show a restoration of microglial function and reduction of other disease markers, indicating that functional restoration of this one gene had widespread positive effects.

Wernig and colleagues said they could transplant cells engineered to have supercharged TREM2 activity that may have an even greater effect.

They caution, however, that the microglia that formed from the transplanted cells were slightly different from the natural microglia in mouse brains. These differences might in some way have their own detrimental effect, Wernig said. We have to look at that very carefully.

In addition, the current procedure would be highly risky if it were developed for human therapy because transplantation of blood stem cells requires the recipient to undergo a highly toxic chemotherapy or radiation treatment to kill off native blood stem cells. However, many researchers, including some at the Institute for Stem Cell Biology and Regenerative Medicine, are developing less toxic methods of preconditioning patients for stem cell transplants. A brain cell therapy could then piggyback on such improved and safer transplantation methods.

The work was supported by the Kleberg Foundation, the Emerson Collective, a Howard Hughes Medical Institute faculty scholar award, a New York Stem Cell Foundation Druckenmiller award, a postdoctoral overseas training fellowship from the National Research Foundation of Korea and the German Research Foundation.

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Comparing Genetics and Molecular Genetics: What’s the Difference?

Thursday, December 19th, 2024

When it comes to the study of genes, there are two different approaches that scientists use to gain a deeper understanding of genetic makeup and its role in various biological processes. These approaches are genetics and molecular genetics. While both involve the analysis and research of genetic material, there are significant differences between the two.

Genetics, as a field of study, focuses on the inheritance and variation of genes in organisms. It involves the examination of traits, such as eye color or height, and the mapping of these traits to specific genes. This approach involves studying the DNA sequences and chromosomes to understand how genes are passed down from one generation to another.

On the other hand, molecular genetics takes a more detailed and intricate look at genes and their functions. It delves into the molecular mechanisms behind genetic processes, such as DNA replication, transcription, and translation. Molecular genetics employs advanced techniques and tools to analyze the structure and function of genes at the molecular level, including the study of specific gene mutations that may cause diseases.

Therefore, the main difference between genetics and molecular genetics lies in their scope and depth of analysis. While genetics looks at the broader picture of gene inheritance and variation, molecular genetics zooms in to elucidate the complex molecular processes and interactions that occur within genes. Both disciplines are valuable in their own right, complementing each other to provide a comprehensive understanding of how genes function and contribute to the diversity of life on Earth.

In the study of genetics, two main approaches are often compared: genetics and molecular genetics. Although these terms may sound similar, they represent different fields of analysis and study.

Genetics is the branch of biology that focuses on the study of genes, heredity, and variation in living organisms. It involves the analysis of inherited traits and the passing of genetic information from one generation to the next. Geneticists use various techniques, such as pedigree analysis and population genetics, to understand how genes are inherited and how they contribute to the diversity of organisms.

Molecular genetics, on the other hand, takes a more detailed and specific approach. It focuses on the study of the structure, function, and organization of genes at a molecular level. Molecular geneticists use advanced techniques, such as DNA sequencing and gene cloning, to analyze the DNA molecules and understand how specific genes function and interact. They study the mechanisms of gene expression, regulation, and mutations, and how they relate to genetic disorders and diseases.

While genetics provides a broad overview of inherited traits and genetic patterns in populations, molecular genetics delves deeper into the molecular mechanisms that underlie these patterns. It is a more specialized field that allows for a more detailed understanding of how genes function and how they contribute to the diversity of life forms.

In summary, genetics and molecular genetics are two distinct but related fields of study. Genetics provides a broader analysis of inherited traits and genetic patterns, while molecular genetics takes a more specific approach in understanding the molecular mechanisms of genes. Both fields are crucial for advancing our knowledge of genetics and its impact on living organisms.

In the field of genetics, the study of inheritance and variation in living organisms has been a subject of fascination since ancient times. However, it wasnt until the mid-20th century that the field took a major leap forward with the advent of molecular genetics.

Prior to the emergence of molecular genetics, the study of genetics primarily focused on observing and analyzing the hereditary traits of organisms through methods such as breeding experiments, statistical analysis, and observation of visible characteristics. This approach, known as classical genetics, provided valuable insights into the patterns of inheritance but had limitations in its ability to interrogate the underlying molecular mechanisms.

Molecular genetics, on the other hand, revolutionized the field by introducing a more detailed and comprehensive approach to the study of genetics. This approach involved the exploration of the structure and function of genes at the molecular level, analyzing the role of DNA and RNA in gene expression, and understanding the mechanisms of mutation and genetic variation.

The comparison between classical genetics and molecular genetics reveals significant differences in their research methodology and analysis. Classical genetics relied on observational data and statistical analysis to infer patterns of inheritance, while molecular genetics employs sophisticated laboratory techniques to manipulate and analyze DNA and RNA molecules.

Furthermore, the advent of molecular genetics has allowed researchers to delve deeper into the intricate mechanisms of genetic inheritance and variation. By studying molecular processes such as DNA replication, transcription, and translation, scientists have gained a more nuanced understanding of how genes interact and contribute to the development and functioning of organisms.

Overall, the emergence of molecular genetics as a distinct discipline has greatly expanded our knowledge of genetics and opened up new avenues of research. Its focus on the molecular level has provided invaluable insights into the complexities of genetic processes and has paved the way for advancements in fields such as biotechnology, genomics, and personalized medicine.

When it comes to the study of genetics and molecular genetics, there are several key concepts to understand. A comparison between genetics and molecular genetics provides insights into the differences in their approaches and analysis.

Genetics is the study of genes and heredity. It focuses on the inheritance of traits from one generation to another. Geneticists analyze the variations and similarities in genes to understand how certain traits are passed on and expressed through generations. They study the genes at a macroscopic level, observing the patterns of inheritance and the effects of genetic mutations on individuals.

Molecular genetics, on the other hand, takes a more microscopic approach. It zooms in on the molecular level to understand the structure and function of genes. By analyzing DNA and RNA sequences, molecular geneticists can unravel the intricacies of genetic information. They study the changes and interactions within genes and delve deeper into the mechanisms of gene expression and regulation.

The main difference between genetics and molecular genetics lies in their level of analysis. Genetics takes a broader approach, while molecular genetics focuses on a more detailed examination of genes and their molecular components. Both fields contribute to the understanding of how genetic information is inherited and expressed, but they employ different methodologies and perspectives.

In conclusion, genetics and molecular genetics are two related fields that study genes and heredity. Genetics focuses on the inheritance of traits at a macroscopic level, while molecular genetics delves into the molecular components and mechanisms of gene expression. By understanding the differences between these two approaches, scientists can gain a more comprehensive understanding of the complexities of genetic information.

In the research field of genetics, the methodology often involves the study of genetic variations and heredity patterns in living organisms. This can be achieved through various techniques such as pedigree analysis, gene mapping, and DNA sequencing. The primary focus of genetic research is to understand the differences and similarities between individuals and populations in terms of their genetic makeup.

On the other hand, molecular genetics is a more specific branch of genetics that focuses on the analysis of DNA and RNA molecules. It involves studying the structure, function, and regulation of genes at a molecular level. Molecular geneticists use techniques like PCR (polymerase chain reaction), gel electrophoresis, and DNA cloning to isolate and analyze specific genes or DNA sequences.

One key difference between genetic research and molecular genetics is the scale at which they operate. While traditional genetics looks at broader genetic traits and inheritance patterns, molecular genetics examines the specific molecular mechanisms behind these traits. This enables researchers to gain a more in-depth understanding of the biological processes involved.

Another difference is the level of detail in the analysis. Genetic research often involves observations at the organism level, such as comparing traits between individuals or populations. In contrast, molecular genetics focuses on the molecular level, analyzing DNA sequences and gene expression patterns.

In summary, the comparison between genetics and molecular genetics reveals the differences in the scope and approach of the two fields. While genetics provides a broader perspective on heredity and genetic variation, molecular genetics delves into the intricate molecular mechanisms underlying these phenomena. Both disciplines contribute valuable insights to our understanding of the genetic basis of life.

Both genetics and molecular genetics have important applications in the field of medicine. While there are some differences in their approaches and methodologies, they both contribute to our understanding of genetic diseases and provide valuable insights for diagnosis, treatment, and prevention.

Genetics is the study of heredity and the variation of inherited traits in organisms. It focuses on the examination of genes, their structures, functions, and how they are transmitted from one generation to another. Genetic analysis has long been used in the medical field to identify the genetic basis of diseases and to assess an individuals risk for developing certain conditions. It has played a crucial role in the identification of genetic disorders, such as Down syndrome and cystic fibrosis. Genetic counseling, which involves assessing an individuals risk for genetic conditions and providing information and support, is another important application of genetics in medicine.

Molecular genetics, on the other hand, takes a more focused approach by studying the structure and function of individual genes at a molecular level. It involves the analysis of DNA, RNA, and proteins to understand how genes are regulated and how they contribute to the development of diseases. The molecular analysis of genes has revolutionized the field of medicine by enabling researchers to identify specific molecular markers for diseases, develop targeted therapies, and predict therapeutic responses. This approach has led to personalized medicine, where treatments can be tailored to an individuals genetic profile.

Both genetics and molecular genetics have contributed significantly to the understanding and treatment of genetic diseases. While genetics provides a broader picture of genetic inheritance and variation, molecular genetics offers a more detailed analysis of genes and their functions. Together, they form a powerful combination for medical research and have paved the way for breakthroughs in the diagnosis, treatment, and prevention of genetic disorders.

When it comes to the field of agriculture, both genetics and molecular genetics play crucial roles in research and advancements. While they may have similarities in their approaches and analyses, there are also significant differences between the two.

Genetics, as a branch of biology, studies the inheritance and variation of traits in living organisms, including plants and animals. In agriculture, genetics is applied to breed selectively and improve the desirable traits of crops and livestock. Through traditional breeding methods, geneticists identify and cross-breed plants and animals with specific desirable traits to create new varieties with enhanced characteristics such as disease resistance, productivity, and quality.

The Role of Molecular Genetics in Agriculture

Molecular genetics takes a more advanced and precise approach compared to traditional genetics. It involves the study of genes and their functions at the molecular level, focusing on analyzing DNA and other genetic materials.

Advancements in molecular genetics have revolutionized the field of agriculture.

While traditional genetics relies on breeding experiments and observations, molecular genetics utilizes various laboratory techniques and technologies to directly manipulate and analyze genetic materials. This includes techniques such as polymerase chain reaction (PCR), gene cloning, and genome sequencing.

Analysis and Study of Genes

Molecular genetics allows for a more in-depth analysis and study of individual genes, their interactions, and their functions. This provides valuable insights into the underlying genetic mechanisms responsible for specific traits in plants and animals, leading to a better understanding of their biology and potential for improvement.

The study of molecular genetics also enables the identification and characterization of genes associated with valuable traits in crops, such as drought tolerance, nutrient efficiency, and pest resistance.

By identifying and manipulating these genes, scientists can develop genetically modified organisms (GMOs) with enhanced traits, such as genetically modified crops with increased yield or improved nutritional content.

In conclusion, both genetics and molecular genetics have significant applications in agriculture. While traditional genetics focuses on selective breeding, molecular genetics allows for a more advanced and precise understanding and manipulation of genes. Together, these fields contribute to the development of improved crops and livestock for a more sustainable and efficient agricultural industry.

In the field of forensics, the study of genetics and molecular genetics has been instrumental in solving crimes and identifying individuals involved in criminal activities. Through the analysis of genetic material found at crime scenes, forensic scientists are able to compare and identify differences in the genetic profiles of suspects. This approach allows for a more reliable and accurate comparison of DNA samples, which is crucial in criminal investigations.

Molecular genetics, with its focus on the study of molecular structure and function, offers a more detailed and precise approach to forensic analysis. By examining specific genes and their variations, forensic scientists can establish a genetic profile of an individual, providing important clues in identifying suspects or victims.

Genetics, on the other hand, takes a broader perspective in the study of inherited traits and the genetic makeup of individuals. It involves the comparison of DNA sequences, studying inherited variations, and determining the likelihood of individuals carrying certain traits or diseases. In forensics, genetic analysis is crucial in establishing familial relationships, such as paternity or kinship, which can be helpful in suspect identification or victim identification.

By comparing the genetic profiles of individuals found at crime scenes with those in a database, forensic scientists can identify potential suspects or rule out individuals who may be wrongly implicated. This process involves a comprehensive analysis of DNA samples, including the identification of specific genetic markers that are unique to each individual.

While both genetics and molecular genetics play vital roles in forensic analysis, there are differences in their approaches and focus. Genetics offers a broader perspective on inherited traits, while molecular genetics provides a more detailed and in-depth analysis of genetic material. The comparison of genetic profiles and the identification of unique markers are common goals in both fields.

Overall, the study of genetics and molecular genetics is essential in forensic research and analysis. By using these approaches, forensic scientists are able to provide valuable evidence and insights in solving crimes, identifying suspects, and bringing justice to victims and their families.

In the study of genetics and molecular genetics, researchers employ different approaches and techniques to gain insights into the complex world of genes and their functions. The analysis of genetic information requires a combination of both genetic and molecular research methods.

Genetics research typically focuses on the inheritance and variation of genes among different individuals or populations. It often involves studying the physical traits, hereditary patterns, and genetic disorders in order to understand the role of genes in biological processes. Geneticists use various techniques such as pedigree analysis, linkage analysis, and genetic mapping to uncover the inheritance patterns of specific traits.

Molecular genetics, on the other hand, delves deeper into the molecular mechanisms behind genetic processes. This field employs advanced techniques to analyze DNA, RNA, and protein molecules. Researchers in molecular genetics use tools like polymerase chain reaction (PCR), DNA sequencing, and gene expression analysis to study the structure, function, and regulation of genes at the molecular level.

While genetics research focuses on broader patterns of inheritance and genetic variation, molecular genetics provides a more detailed understanding of the molecular events governing gene expression and regulation. Both approaches are crucial for unraveling the complexities of genetic information and its implications for health and disease.

In summary, genetics research and molecular genetics employ distinct research techniques to study genes and their functions. Genetics research takes a broader approach, focusing on inheritance patterns and genetic variation, while molecular genetics provides a deeper analysis of the molecular mechanisms behind genetic processes. Combining these two approaches enables researchers to gain a comprehensive understanding of genetics and its role in various biological processes.

The study of genetics and molecular genetics has had a significant impact on the field of evolutionary biology. By comparing the differences between genetic information and its molecular analysis, scientists have been able to gain a deeper understanding of the processes and mechanisms that drive evolution.

In traditional genetic study, scientists focus on the study of genes and their inheritance patterns within populations. This approach allows researchers to track the transmission of specific traits and determine how they are passed down through generations. However, this method does not provide detailed information about the molecular mechanisms that underlie genetic changes.

In contrast, molecular analysis takes a more detailed and precise approach. It involves the study of DNA and other molecules that make up the genetic material. Molecular techniques such as DNA sequencing, PCR, and gene expression analysis allow scientists to analyze the structure and function of genes at the molecular level. By understanding the molecular differences between individuals and species, researchers can gain insights into the evolutionary processes that shape biodiversity.

By combining the study of genetics with molecular analysis, scientists can compare genetic information across different species and populations. This comparative approach provides valuable insights into the evolutionary relationships between organisms and helps researchers reconstruct the evolutionary history of species.

Molecular genetics also allows researchers to study the impact of genetic variation and genetic changes on evolution. By analyzing DNA sequences, scientists can identify mutations and other genetic changes that occur over time. These studies help researchers understand the mechanisms of adaptation, speciation, and genetic drift, all of which play crucial roles in shaping evolution.

In summary, the integration of genetics and molecular analysis has revolutionized the field of evolutionary biology. This interdisciplinary approach provides researchers with a powerful tool to decipher the genetic and molecular basis of evolutionary processes. By understanding the impact of genetic variation and molecular differences, scientists can gain a deeper understanding of how species evolve and adapt in response to their changing environments.

In the field of genetics, the role of molecular genetics plays a crucial part in the process of genetic counseling. Genetic counseling aims to provide individuals and families with accurate information about the risk of genetic conditions and to support them in making informed decisions about their health and reproduction.

Molecular genetics involves the analysis of DNA, genes, and chromosomes to understand the underlying causes of genetic disorders. This study uses a different approach compared to traditional genetics, which focuses on studying the observable differences and traits in individuals.

One of the key roles of molecular genetics in genetic counseling is to analyze genetic variations that may contribute to an individuals risk of developing a genetic condition. Through advanced research techniques and technologies, molecular geneticists can identify specific changes in an individuals DNA sequence that could be associated with inherited diseases.

This analysis helps genetic counselors provide accurate information about the chances of the condition being passed on to future generations, providing individuals with a better understanding of their genetic risks. With this information, individuals can make informed decisions about family planning, reproductive options, and potential medical interventions.

Another important aspect of molecular genetics in genetic counseling is the comparison of DNA sequences. By comparing DNA sequences of individuals with and without certain genetic conditions, researchers can identify genetic variations that may contribute to the development of these disorders.

Comparative analysis helps in the early detection, diagnosis, and treatment of various genetic conditions, allowing individuals and families to access appropriate medical care and support. This approach enables genetic counselors to provide personalized genetic counseling, tailoring their recommendations and support based on the specific genetic profile of each individual.

Conclusion

The role of molecular genetics in genetic counseling is essential for understanding the underlying genetic factors contributing to inherited diseases. By analyzing genetic variations and comparing DNA sequences, molecular genetics provides valuable information that can guide individuals and families in making informed decisions about their health and reproduction. Through this approach, genetic counseling becomes more accurate, personalized, and effective in supporting individuals and families.

The comparison between genetics and molecular genetics in the context of disease diagnosis is crucial for understanding the approach and differences in the analysis of genetic disorders.

Genetics, as a field of study, focuses on the inheritance and variation of genes in organisms. It examines the role of genes in transmitting traits, including disease susceptibility. Genetic analysis involves studying the genetic makeup of individuals to identify mutations or alterations in specific genes that may contribute to the development of diseases.

In disease diagnosis, the study of genetics plays a significant role. Genetic tests can determine the presence or absence of specific genes associated with certain diseases. These tests help identify individuals who may be at risk or carriers for genetic disorders. Genetic counseling based on these findings can aid in making informed decisions about treatment options or preventive measures.

Traditional genetics primarily focuses on the study of inherited diseases caused by mutations in specific genes. It involves analyzing the presence of these mutations within families or populations to understand the pattern of disease transmission. This information is valuable in identifying affected individuals, predicting disease outcomes, and providing appropriate interventions.

Molecular genetics takes a more detailed and advanced approach to disease diagnosis compared to traditional genetics. It involves analyzing the structure and function of genes at a molecular level, including DNA sequencing and gene expression studies. The study of molecular genetics allows for a deeper understanding of the underlying mechanisms behind the development and progression of genetic disorders.

Molecular genetic analysis can identify specific genetic mutations or alterations that may contribute to disease susceptibility. It provides insights into the molecular pathways involved in disease development, allowing for targeted therapies and personalized treatment approaches. This approach also enables the identification of potential therapeutic targets and the development of novel treatment strategies.

In conclusion, both genetics and molecular genetics play essential roles in disease diagnosis. While genetics focuses on the inheritance and variation of genes, molecular genetics provides a more detailed analysis at the molecular level. Understanding the differences between these approaches is crucial for advancing our knowledge of genetic disorders and improving disease diagnosis and treatment.

In drug development, both genetics and molecular genetics play an important role in understanding the mechanisms of action of drugs and their potential effects on individuals. However, there are some differences in their approach and focus on research and study.

Genetics: a field of study that focuses on the inheritance and variation of genes in individuals and populations. It explores how genes influence the development, functioning, and characteristics of organisms. In drug development, genetics research aims to identify genetic variations that may affect the response to drugs, such as the presence of specific genes associated with drug metabolism or drug targets.

Molecular Genetics: a subfield of genetics that involves the study of DNA, RNA, and other molecules involved in genetic information and gene expression. It focuses on understanding the molecular mechanisms underlying various genetic processes, such as DNA replication, gene transcription, and protein synthesis. In drug development, molecular genetics research aims to unravel the molecular pathways and targets that drugs interact with in order to develop more targeted and effective treatments.

While genetics provides a broader perspective on the influence of genes on drug response and potential side effects, molecular genetics delves deeper into the specific molecular mechanisms through which drugs exert their effects. By combining the knowledge gained from genetics and molecular genetics, researchers can better understand the genetic basis of diseases and tailor drug therapies to individual patients.

By comparing the genetic profiles of patients who respond well to a drug with those who do not, researchers can identify genetic markers that predict drug response. This information can then be used to develop diagnostic tests that help identify individuals who are more likely to benefit from a particular drug or who may experience adverse reactions. Additionally, the study of molecular genetics can uncover new drug targets and pathways that can be exploited for drug development.

When comparing genetics and molecular genetics, it is important to consider the ethical implications of both approaches. While genetics is the study of genes and heredity, molecular genetics takes a more focused and analytical approach by examining the structure and function of genes at a molecular level. This difference in approach can lead to different ethical considerations in research and analysis.

In genetics, ethical considerations often revolve around issues such as privacy and informed consent. Researchers may need to handle sensitive information related to an individuals genetic makeup, which raises concerns about data privacy and confidentiality. Additionally, when conducting genetic studies, informed consent from participants is crucial to ensure that they fully understand the risks and benefits of participating in the research.

There is also the issue of genetic discrimination, where individuals may face discrimination based on their genetic information. This can have significant social and psychological impacts, highlighting the need for policies and laws to protect individuals from such discrimination.

In molecular genetics, ethical considerations are more focused on the research and analysis techniques used. Molecular genetics often involves the manipulation and modification of genetic material in a laboratory setting. This raises concerns about the potential risks and consequences of such manipulations. It is important to ensure that these techniques are conducted safely and in accordance with ethical guidelines to minimize any harm to both humans and other organisms.

Furthermore, the use of genetically modified organisms (GMOs) in molecular genetics research also raises ethical concerns. GMOs can have ecological implications and may raise questions about the potential long-term effects on the environment and other organisms.

In conclusion, while both genetics and molecular genetics share similarities in their study of genes, they have different approaches that can lead to distinct ethical considerations. Understanding and addressing these ethical concerns is essential to ensure the responsible and ethical advancement of genetic and molecular genetics research.

The analysis of genetics and molecular genetics is a field of research and study that poses several challenges for scientists. Both approaches involve the study of genes and the hereditary material, but they differ in their methodologies and scope. Understanding these challenges is crucial for advancing our knowledge in genetics and molecular genetics.

One of the current challenges in the field of molecular genetics is understanding the complexity of the molecular mechanisms that govern gene expression and regulation. Molecular genetics focuses on studying the individual molecules, such as DNA, RNA, and proteins, that make up the genetic material. This approach requires advanced techniques and technologies to analyze and manipulate these molecules, as well as computational methods to interpret the vast amount of data generated. The complexity of these molecular interactions presents a challenge for researchers in understanding the underlying mechanisms that control gene expression.

Another challenge in genetics and molecular genetics is the comparative analysis of data obtained from different organisms. While genetics traditionally involves studying specific traits and genes within a particular species, molecular genetics allows for a broader comparison across species. However, comparing genetic information between organisms can be difficult due to variations in gene structure, gene function, and regulatory mechanisms. Researchers need to develop standardized approaches and tools to compare and analyze genetic data from diverse organisms, which can help identify common patterns and evolutionary relationships.

In conclusion, the study of genetics and molecular genetics faces various challenges. The molecular complexity of gene regulation and expression requires advanced techniques and computational methods. Additionally, the comparative analysis of genetic data across different organisms calls for standardized approaches and tools. Overcoming these challenges is essential for advancing our understanding of genetics and molecular genetics and their applications in various fields, including medicine and agriculture.

The study of genetics and molecular genetics has provided valuable insights into the complexities and mechanisms of inheritance and genetic variation. However, there is still much to be discovered and understood in these fields. As technology continues to advance, new approaches and techniques are being developed that will further enhance our understanding of genetics.

One future direction is the use of comparative analysis to deepen our understanding of genetics. By comparing the genomes of different organisms, scientists can identify similarities and differences in their genetic makeup. This comparative approach allows for a more comprehensive understanding of how genetics shape biological traits and functions.

Furthermore, comparative analysis can help us uncover the evolutionary relationships between species. By examining the similarities and differences in their genetic information, scientists can reconstruct the evolutionary history of different organisms, shedding light on how life has evolved over millions of years.

Another future direction is the integration of molecular and genetic approaches. While genetics focuses on the study of inheritance and variation at the organismal level, molecular genetics delves into the underlying molecular mechanisms that drive these processes.

By combining these two approaches, researchers can gain a more comprehensive understanding of the genetic basis of traits and diseases. Molecular genetics provides the tools and techniques to examine the specific genes and molecules involved, while genetics provides the broader context and understanding of how these genes and molecules interact within an organism.

This integration of molecular and genetic approaches will allow for a more nuanced and sophisticated analysis of genetic variation and inheritance, providing valuable insights into the differences and similarities between individuals and populations.

In conclusion, the future of genetics and molecular genetics lies in the continued exploration of comparative analysis and the integration of molecular and genetic approaches. These advancements will further enhance our understanding of the complexities of genetics and pave the way for breakthroughs in fields such as personalized medicine and genetic engineering.

In the field of genetics, data analysis plays a crucial role in understanding the complexities of genetic information. Both genetics and molecular genetics employ different approaches in the study of genes and genetic variations.

In traditional genetics, the analysis focuses on studying traits and heredity patterns within populations or families. It involves observing and quantifying physical characteristics, as well as tracking the inheritance of specific traits through generations. This approach relies on family trees, Punnett squares, and statistical methods to analyze the data.

On the other hand, molecular genetics takes a more detailed and precise approach in analyzing genetic data. It involves studying the structure and function of DNA, genes, and proteins at the molecular level. This field has revolutionized the study of genetics by introducing techniques such as DNA sequencing and polymerase chain reaction (PCR).

Molecular genetics uses advanced laboratory techniques to isolate, amplify, and analyze specific regions of DNA. This allows researchers to identify and study genetic variations, mutations, and gene expression patterns. Data analysis in molecular genetics often involves complex algorithms, bioinformatics tools, and statistical methods.

By comparing genetics and molecular genetics, it becomes evident that the main difference lies in the level of detail and precision in data analysis. Traditional genetics provides a broader perspective on genetic traits and inheritance patterns, while molecular genetics offers a deeper understanding of the molecular mechanisms underlying genetic variations and gene functions.

Overall, the comparison between genetics and molecular genetics highlights the evolving nature of genetic studies. While both approaches contribute to our understanding of genes and heredity, molecular genetics allows for a more in-depth analysis of genetic data, paving the way for new discoveries and advancements in the field.

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Comparing Genetics and Molecular Genetics: What's the Difference?

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Chapter 12: Techniques of Molecular Genetics – Biology LibreTexts

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Genetics is the study of the inheritance and variation of biological traits. We have previously noted that it is possible to conduct genetic research without directly studying DNA. Indeed some of the greatest geneticists had no special knowledge of DNA at all, but relied instead on analysis of phenotypes, inheritance patterns, and their ratios in carefully designed crosses.

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Chapter 12: Techniques of Molecular Genetics - Biology LibreTexts

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Molecular Genetics Testing – StatPearls – NCBI Bookshelf

Saturday, November 16th, 2024

Continuing Education Activity

Molecular diagnostics encompasses the analysis of human, viral, and microbial genomesand the products they encode. Molecular genetics utilizesmolecular biology's laboratory tools to relate genetic structureto protein function and, ultimately, health and disease.Variants identified during genetic testing are classified based on diverse evidence types, as the American College of Medical Genetics and Genomics recommends, emphasizing the need for board-certified geneticists to interpret the results.Integrating genetic testing methodologies with clinical expertise is crucial in translating molecular genetics advancements tobetter patient care.

The field of molecular genetic and genomic testing is undergoing rapid change due to improvements in our understanding of the molecular causes of uncommon and common illnesses and DNA analysis technologies.The advent of molecular genetics has revolutionized healthcare by offering unprecedented insights into the genetic basis of diseases, enabling personalized diagnostics, treatment strategies, and risk assessments. However, this progress brings with it the responsibility for healthcare providers to stay updated with the latest advancements and best practices in genetic testing.

This activity for healthcare professionals is designed to enhance learners' proficiency in identifying patients withindications for molecular genetics testing and interpreting genetic test results. Participants acquire a broader grasp of specimen collection, procedures, indications, potential diagnosis, normal and critical findings, interfering factors, and complications. Learners gain insights into thecomplexities of molecular genetics, preparing them to collaborate with an interprofessional team that aims to improve outcomes for patients who need molecular genetics testing.

Objectives:

Identify clinicalencounters appropriate for genetic molecular testing, distinguishing cases where such testing can contribute to diagnosis, prognosis, or treatment decisions.

Evaluate genetic test results accurately, discerning their clinical significance and relevance to patient management.

Differentiatebetween genetic testing methodologies, understanding their strengths, limitations, and optimal applications to diagnose patients.

Implement best interprofessional collaboration and communication practices to ensure that patientswho need molecular genetics testing receive comprehensive care that considers their medical, psychological, and social needs, thus improving outcomes.

Molecular genetics testing is fundamental in evaluating inherited disorders, somatic or acquired diseases with genetic associations, and pharmacogenetic responses. Genotyping can provide valuable disease diagnosis, prognosis, and progression indicators, guide treatment selection and response, and identify gene-specific therapeutic targets.[1]Human genetic material primarily consists of double-stranded, helical DNA. This molecule has a backbone composed of alternating sugar (deoxyribose) and phosphate groups, with hydrogen bonds linking nitrogenous base pairs. Specifically, adenine (purine) pairs with thymine (pyrimidine), while guanine (purine) pairs with cytosine (pyrimidine), forming the complementary base pairs within the DNA double helix.[2][3]

DNA in human cells is wrapped around histone proteins and packaged into nucleosome units, compacted further to form chromosomes.[4]Somatic cells normally have 23 chromosome pairs, with 1 pair comprised of the sex chromosomes X and Y. Each chromosome has DNA with a terminal stretch of short repeats called telomeres and additional repeats in the centromere region.[5]

Humans have 2 sets of 23 chromosomes, one derived from the mothers egg and the other from the father's sperm. Therefore, each egg and sperm is a single or haploid set of 23 chromosomes. Combining the 2 creates a diploid set of human DNA, allowing each individual to possess 2 different sequences, genes, and alleles on each chromosome.[6]Homologous recombination during meiosis generates unique allele combinations in gametes, leading to genetic diversity among offspring in the human population.[7]

The complete decoding of the human genome sequence and the development of powerful identification and cloning methods for genes linked to inherited diseases have transformed the practice of molecular genetics and molecular pathology. Advanced molecular analysis methods can now determine presymptomatic individuals' illness risk, detect asymptomatic recessive trait carriers, and prenatally diagnose conditions not yet evident in pregnancy.[8]Molecular genetics techniques are often the only approaches to these puzzles. Thus, genetic tests are powerful tools for diagnosis, genetic consultation, and prevention of heritable diseases.[9]

Many genetic testscan analyze gene, chromosome, and protein alterations. A clinician often considers several factors when selecting the appropriate test, including suspected conditions and their possible genetic variations. A broad genetic test is employed when a diagnosis is uncertain, while a targeted test is preferred for suspected specific conditions.[10]Molecular tests look for changes in 1 or more genes. These tests analyze the sequence of DNA building blocks (nucleotides) in an individual's genetic code, a process known as DNA sequencing, which can vary in scope.[11]

The targeted single variant test identifies a specific variant in a single gene known to cause a disorder, eg, the HBB gene variant causing-globin abnormalities that give rise to sickle cell disease. This test assesses the family members of an individual with the known variant to ascertain if they have the familial condition.[12]Single-gene tests examine genetic alterations in 1 gene to confirm or rule out a specific diagnosis, notably when many variants in the gene can cause the suspected condition. Gene panel tests look for variants in multiple genes to pinpoint a diagnosis when a person has symptoms that may fit various conditions or when many gene variants can cause the suspected condition.[13][14]

Whole-exome sequencing or whole-genome sequencing tests analyze the bulk of an individual's DNA to find genetic variations. This approach is useful when a single-gene or panel testing has not provided a diagnosis or when the suspected condition or genetic cause is unclear.[15]This sequencing method is often more cost- and time-effective than performing multiple single gene or panel tests.[16]

Chromosomal tests analyze whole chromosomes or long DNA lengths to identify significant alterations, including extra or missing chromosome copies (trisomy or monosomy), large chromosomal segment duplications or deletions, and segment rearrangements (translocations) (see Image. Trisomy 21on G-Banded Chromosomal Studies).[17]Chromosomal tests are employed when specific genetic conditions linked to chromosomal changes are suspected. For instance, Williams syndrome results from deleting a chromosome 7 segment.

Gene expression tests assess gene activation status in cells, indicating whether genes are active or inactive, with activated genes producing mRNA molecules that serve as templates for protein synthesis.[18]The mRNA produced helps determine which genes are highly active. Too much activity (overexpression) or too little activity (underexpression) of specific genes may suggest particular genetic disorders, including various cancer types.[19]Biochemical tests assess protein or enzyme levels and activity rather than directly analyzing DNA.[20]Abnormalities in these substances may indicate DNA changes underlying a genetic disorder.

Heritable mutations are detectable in all nucleated cells and are thus considered germline or constitutional genetic changes. Somatic genetic changes are characteristic of acquired or sporadic diseases like cancer.[21]Both scenarios are investigated using similar molecular biology methods to detect DNA and RNA variations, although the interpretation and utility of the laboratory results often differ significantly.[22]

Fluorescent in situ hybridization (FISH), chromosomal microarray analysis (CMA), and cytogenetic analysis (karyotyping) can be used to detect gross mutations like whole- and large-scale gene deletions, duplications, or rearrangements. Conventional karyotyping identifies rearrangements over 5 DNA megabases.[23]FISH has a resolution of 100 kilobases to 1 megabase. Minor alterations, such as single-base substitutions, insertions, and deletions, are detectable with single-strand conformation polymorphism (SSCP) and sequence analysis through next-generation sequencing (NGS). NGS uses genomic DNA (gDNA) or complementary DNA (cDNA) and has 3 modalities: whole genomic DNA, targeted, and exome sequencing.[24]

Denaturing high-performance liquid chromatography (DHPLC) can detect small deletions and duplications. Multiplex ligation-dependent probe amplification (MLPA) extends the range of deletions and duplications detected, bridging the gap between FISH or cytogenetic analysis and HPLC. MLPA is particularly useful in identifying complete or single and multiexon deletions or duplications.[25][26]

Peripheral blood is the specimen required for FISH, MLPA, DHPLC, and sequencing.Amniotic fluid cells and, more recently, cell-free fetal DNAmay be used for noninvasive prenatal testing.[27]Ethylenediaminetetraacetic acid is the most commonly used anticoagulant for molecular-based testing. However, acid citrate dextrose (ACD) is an acceptable alternative in cases where cellular form and function must be preserved.

ACD A and ACD B are the only ACD tube designations recognized, differing only by their additive concentrations.[28]Both enhancewhite blood cell viability and recovery for several days after specimen collection, making them suitable for molecular diagnostic and cytogenetic testing.

FISH utilizes fluorescent DNA probes to target specific gene sequences in interphase or metaphase cells, enabling their visualization and detection. Housekeeping gene probes always serve as positive internal controls. The probe must be large enough to hybridize specifically with the target without impeding the hybridization process. Conventional FISH involves pipetting the hybridization mix onto the cytological sample and incubating them together.

The technique can be applied to suspended cells, cultured cells, and frozen or formalin-fixed paraffin-embedded tissue sections, with subsequent cell sorting for fluorescence signal separation.[29]Preserving nucleic acid integrity and cell morphology is necessary during sample fixation. The experimental FISH procedure includes several preparatory steps, the hybridization reaction itself, and the removal of unbound probes.[30]The probe may be directly labeled with fluorophores or targeted for fluorescent detection using labeled antibodies or similar substrates. Different tags may be used, and different targets may be detected in the same sample simultaneously (multi-color FISH). Tagging is performed in various ways, including nick translation or polymerase chain reaction (PCR) using tagged nucleotides (see Image. Polymerase Chain Reaction). Probes can vary from 20 to 30 nucleotides to much longer sequences.

Locus-specific probes provide insight into gene amplification, deletion, or normal copy number status. Dual-fusion probes are adept at identifying frequently translocated gene regions associated with cancer development. These probes target regions spanning the breakpoints of translocation partners. Intact green and red signals are determined when they are closer than one signal's width. Conversely, a break in the gene sequence results in separate green and red signals.[31]

Break-apart probes target 2 areas of a specific gene sequence, using a green fluorescent label on one end and a red fluorescent label on the other. Intact gene sequences typically produce a yellow signal, known as a fusion signal. Whole-chromosome probes consist of smaller probes, each binding to different sequences along a chromosome.[32]Multiple probes, labeled with fluorescent dyes, enable unique color labeling of each chromosome, creating a spectral karyotypea full-color chromosome map identifyingall chromosome pairs.[33]Whole-chromosome probes are useful for examining chromosomal abnormalities, such as translocations.

Chromosomal microarray (CMA) consists of thousands of tiny probes, each representing small DNA fragments from known locations on the 46 chromosomes. CMA detects imbalances in chromosomal material between patient and control DNA samples, identifying copy number differenceswhether gains (duplications) or losses (deletions)in specific DNA segments.[34]These differences pinpoint the cause of the patient's health condition based on the location and type of change detected.[35]

Denaturing high-performance liquid chromatography (DHPLC) relies on differential chromatography retention of DNA heteroduplexes post-denaturation and renaturation. DNA heteroduplex migration is influenced by both molecule length and melting temperature, which is crucial for test sensitivity. DHPLC typically compares 2 PCR products amplified from 2 genes: 1 wild type and 1 mutated. These PCR products can originate from either RNA (cDNA) or genomic DNA. The PCR products are denatured at 95 C and gradually reannealed by cooling from 95 C to 65 C before chromatography. A major advantage of this technology is that multiple samples can be pooled together for variant detection.[36]Sequencing detects single-base substitutions and small deletions and insertions in DNA fragments ranging from 80 to 1500 base pairs, with close to 100% accuracy within minutes.

When a mismatch is present, both the original homoduplexes and 2 heteroduplexes are simultaneously produced. The original homoduplexes form from the reannealing of perfectly matching sense and antisense strands (25% each). The heteroduplexes form from the reannealing of the sense strand of one homoduplex with the antisense strand of the other (also 25% each). Heteroduplexes denature more extensively than homoduplexes, resulting in earlier elution from the chromatography column. The separation of all 4 species is based on their differences in stacking interactions with the chromatography column (solid phase). More detailed theoretical explanations of DHPLC are available in the literature.[37]

MLPA utilizes genomic DNA samples, with specific MLPA probes hybridizing with denatured genomic DNA. These probes are uniquely designed to hybridize adjacent to each other on the target DNA region and confer a distinct length to each amplified MLPA probe pair. Detection and quantification occur via capillary electrophoresis.[38]All MLPA probes are amplified using the same primer pair, with the abundance of each fragment proportional to its target's copy number in the sample.

NGS amplifies DNA with random priming, providing a genome-wide view of the patient's genetic background through millions of reads. Library generation begins with nucleic acid fragmentation, representing the individual's entire genome or transcriptome. Whole-exome sequencing uses cDNA fragments, whereas the whole-genome modality includes complete genomic DNA. Fragments join using enriched sequence adaptors. Only some genes (gene panel) are analyzed in targeted libraries. Fragments hybridize with cDNA fragments for the region or genes of interest and are specifically enriched.[39]During sequencing, nucleotide addition is detected by fluorescent dyes or pH changes from hydrogen ion release during DNA polymerization.[40]

Sanger sequencing begins with PCR-based target DNA amplification, followed by removing excess deoxynucleotide triphosphates (dNTPs) and PCR primers. The Sanger method has 99.99% base accuracy and is thus the "gold standard" for validating DNA sequences, including those from NGS. The test's stepsinclude denaturing the double-stranded DNA (dsDNA) into 2 single-stranded DNA (ssDNA), attaching a primer corresponding to one end of the sequence, and sequencing 4 polymerase solutions with 4 dNTPs. Only one type of ddNTP is incorporated, initiating DNA synthesis until termination. The resulting DNA fragments are denatured into ssDNA.

Denatured fragments undergo gel electrophoresis for sequence determination. DNA polymerase synthesizes DNA only in the 5 to 3 direction, initiating at a provided primer. Each terminal ddNTP corresponds to a specific nucleotide in the original sequence. For example, the shortest fragment must terminate at the first nucleotide from the 5 end, the second-shortest fragment must terminate at the second nucleotide from the 5 end, and so on. Reading gel bands from smallest to largest reveals the 5 to 3 sequence of the original DNA strand.[41]

In manual Sanger sequencing, the user reads all 4 gel lanes simultaneously, moving from bottom to top to identify the terminal ddNTP for each band. For instance, if the bottom band is found in the ddGTP column, then the smallest PCR fragment terminates with ddGTP, and the first nucleotide from the 5 end of the original sequence has a guanine (G) base.[42]Automated Sanger sequencing employs a computer to read each capillary gel band sequentially, using fluorescence to determine the terminal ddNTP identity. Laser activation of fluorescent tags emits light, detected by the computer, with each ddNTP tagged with a unique fluorescent label. The output is a chromatogram displaying fluorescent peaks corresponding to each nucleotide along the template DNA's length.[43]

Third-generation sequencing enables sequencing long DNA or RNA stretches without fragmentation. Single strands of DNA or RNA are directed through protein nanopores, with nucleotide bases distinguished by characteristic changes in electric current to determine the sequence.[44]Compared to 2nd-generation sequencing, 3rd-generation sequencing requires minimal sample preprocessing, enabling the design of smaller and more portable equipment.[45]

Molecular genetic testing has distinct indications, differing from traditional clinical and molecular biological testing used for diagnosing other diseases.[46]This modalitys applications encompass newborn screening, diagnostic testing for genetic or chromosomal conditions, carrier testing, prenatal testing, predictive and presymptomatic testing for adult-onset disorders, and forensic testing for legal identification purposes.[47]

FISH is employed for patients with a family history of known deletions and has been utilized to detect deletions in single blastomeres during preimplantation genetic diagnosis. FISH tests use gene-specific probe panels to investigate deletions, amplifications, and translocations in hematologic and solid tumors. FISH can also identify intracellular microorganisms and parasites.

CMA is recommended for individuals lacking specific clinical indicators to identify genetic or nongenetic causes of intellectual disability, developmental delay, autism spectrum disorder, or multiple congenital anomalies.[48]CMA can be helpful if prenatal structural anomalies are linked to particular microdeletions or microduplications. This modality can also evaluate copy number variants in cases of de novo balanced rearrangements or marker chromosomes.[49]

MLPA has diverse applications, such as mutation detection, single nucleotide polymorphisms (SNP) analysis, DNA methylation analysis, mRNA quantification, chromosomal characterization, gene copy number detection, and identification of duplications and deletions in cancer predisposition genes like BRCA1, BRCA2, hMLH1, and hMSH2. MLPA also holds promise for prenatal diagnosis, both invasive and noninvasive.[50]

DHPLC is well-suited for scanning genes for novel mutations and analyzing large sample sizes cost-effectively. This test is also useful for genotyping specific mutations or polymorphisms. DHPLC offers various applications beyond detecting genetic variants, including size-based double-strand DNA separation, single-strand DNA separation, and DNA purification analysis.[51]

NGS rapidly sequences whole genomes and target regions, employs RNA sequencing to identify novel RNA variants and splice sites, quantifies mRNAs for gene expression analysis, and analyzes epigenetic factors like DNA methylation and DNA-protein interactions. Sequence cancer samples study rare somatic variant tumor subclones and identify novel pathogens. Sanger sequencing, or the "chain termination method," determines DNA nucleotide sequences.

FISH swiftly diagnoses common fetal aneuploidies but with reduced sensitivity compared to cytogenetic analysis. FISH cannot identify cytogenetic abnormalities beyond the most common ones, such as translocations, inversions, and markers. DHPLC detects single nucleotide changes, small deletions, or insertions requiring subsequent confirmation by sequencing. This method identifies unknown mutations, making it advantageous for diseases with a high proportion of de novo mutations. Neurofibromatosis type 1 (NF1) is an example, as approximately 50% of cases arise from new mutations. CMAs are first-tier tests for developmental delays, intellectual disabilities, autism spectrum disorders, or multiple congenital disabilities, replacing karyotyping.

MLPA detects gene abnormalities, particularly small deletions in diseases like multiple endocrine neoplasia type 1 (MEN1partial or complete deletion). MLPA can also assess methylation alterations, such as in pseudohypoparathyroidism 1b (PHP1b), where deletion of 1 or 4 of four differentially methylated regions is common.

NGS generates millions of sequences, which are then processed, analyzed, and interpreted to identify variants. Bioinformatics analysis begins with raw data generated by nucleotide incorporation signal detection. Read quality is evaluated during primary data analysis. Sequences are aligned or mapped against a reference genome, with computational algorithms searching for the best match for each read while allowing for some mismatches to detect genetic variants.[52]

Sanger sequencing is reliable in detecting point mutations, small deletions, or duplications. This method has a long history of use across various settings, including tumor mutational spectrum analysis and diagnostic testing for constitutional variants. Primers can cover multiple regions (amplicons) or any desired region size.

The increasing demand for genetic testing has led to greater availability. Ensuring uniformity and standardization in communicating the complex results to referring clinicians is essential. Failure to include pertinent information is considered a deficiency in the molecular pathology laboratory accreditation inspection.[53]All molecular genetic laboratories offering clinical testing should be accredited according to the Clinical Laboratory Improvement Amendments and actively participate in proficiency testing.[54]

A comprehensive genetic report must include essential patient details such as name, medical record number or birth date, sex, and ethnicity. The report should also specify the type of specimen received, identification number, laboratory test requested, the performing laboratorys name and address, and referring healthcare professional or hospital. The date of the report, analytic result interpretation using standard nomenclature, detailed method description (including literature citations if applicable), and assay sensitivity and specificity should be provided. For example, sensitivity and specificity should be reported regarding the number of variants analyzed, the proportion of variants not detected, and the possibility of genetic heterogeneity and recombination.[55]Reports from clinical DNA laboratories should include a disclaimer due to the prevalence of laboratory-developed tests (LDTs) or procedures (LDPs) designed, developed, and validated internally by each laboratory but remain unapproved by the FDA.[56]

Fluorescent tags binding to chromosomes reveal chromosomal abnormalities in FISH. MLPA detects copy number variations by correlating peak intensity during capillary electrophoresis with sample copy numbers. An MLPA probe's amplification signals the presence of a mutation in the sample.

An MLPA test can yield two outcomes:

DHPLC detects mutations by identifying heteroduplexes compared to the reference genome in the same sample. NGS identifies various genetic variants, including single nucleotides, small insertions or deletions, and some structural variants, but their role in the disease is not implied. Clinical analysis and assessment of the pathological potential of detected variants require consideration in different contexts.[58]Sanger sequencing results interpretation depends on the target DNA strand and primer availability. If strand A is of interest but the primer suits strand B better, the output matches strand A. Conversely, if the primer suits strand A better, the output aligns with strand B, necessitating conversion back to strand A.

FISH probe specificity prevents unintended hybridization with nontarget genes. Some FISH preparations may exhibit autofluorescence, necessitating thorough cell washing to remove fluorescent residues and reduce background fluorescence.

MPLA has limitations, including its ability to detect only known mutations designed into probes, making gene rearrangements like inversions and translocations undetectable. Sample purity is essential as contaminants such as phenol can interfere with the ligation step. MLPA may yield false positive or negative results due to rare sequence variants in target regions detected by probes. Reduced probe binding efficiency from point mutations or polymorphisms candiminishthe relative peak areas height. Confirmation of single exon deletions detected by MLPA is thus recommended using other methods like multiplex PCR or sequencing.[59]

DHPLC sensitivity relies on melting temperature. Computational algorithms can predict the melting temperature, and the procedure typically involves at least 2 melting temperatures for increased sensitivity. CMA does not detect point mutations, small DNA segment changes (eg, in Fragile X syndrome), or balanced chromosomal rearrangements (eg, balanced translocations, inversions).

NGS technologies continue to evolve to address various challenges. Some large sequencers can detect large insertions, duplications, and deletions, while sequencing long homopolymer regions remains problematic. However, establishing the infrastructure and expertise for data analysis remains a significant challenge in clinical settings. The primary limitation of implementing NGS in clinical settings is the requirement for adequate infrastructure, including computational resources, storage capacity, and skilled personnel for comprehensive data analysis and interpretation.

Despite automation, Sanger sequencing remains labor-intensive, time-consuming, and expensive, relying on specialized equipment. Sanger sequencing exhibits reduced sensitivity in detecting point mutations when 20% of mutant DNA is of a wild-type background. Additionally, it lacks quantifiability, making it impossible to differentiate mutation prevalence accurately based solely on peak sizes, necessitating supplementary testing approaches.

Peripheral blood collection via venipuncture infrequently leads to serious complications. Some patients, especially children, may experience hematomas, pain, and fear, which are expected. In contrast, procedures like amniocentesis are more invasive, thus posing more serious risks such as infection, preterm delivery, respiratory distress, trauma, and alloimmunization, though these complications are also infrequent.[60]Genetic tests using NGS of free-cell DNA from maternal peripheral blood offer an alternative to diagnosis using amniocentesis fluid.[61]

Molecular testing may give rise to legal, medical, psychological, and ethical issues besides the sampling procedures potential complications.[62]While molecular testing primarily aims to demonstrate a genetic trait associated with a disease, the current recommendation is to integrate the results into genetic counseling.[63]

Genetic counseling, led by a team including genetic counselors and other professionals, begins with clinically identifying suspected diseases to guide molecular testing. Patients are informed about the testing procedure, potential results, and legal considerations like informed consent, particularly for children.[64]Patient education is integral to this process.

NGS technologies applied to genetic counseling yield complex results surpassing traditional tests, necessitating informed patient discussions due to the considerable information and ethical implications involved.[65]Laboratories conducting molecular genetic tests should address preexamination, examination, and postexamination considerations, tailoring methodology and interpretation to each test's indication, application, and ethical implications.

Any permanent alteration in a gene's nucleotide sequence compared to a reference genome is deemed a genetic change or mutation. Variants identified through a tiered protocol must undergo sequencing confirmation, and their role in disease pathology must be assessed. Genetic testing may reveal variants classified as benign, likely benign, pathogenic, likely pathogenic, or of uncertain significance.[66]Variants must be rigorously classified based on various types of evidencepopulation, computational, functional, or segregation datato determine clinical significance.[67]

The American College of Medical Genetics and Genomics recommends this nomenclature and classification for genetic test findings, covering genotyping, single genes, panels, exomes, and genomes. NGS applications have deepened our understanding of genetic diseases and led to the discovery of variants requiring further study of their disease implications.[68]Interprofessional collaboration is essential for leveraging genetic tests for patient benefit, withan expertpanel advocating for results interpretation by a board-certified geneticist.[69]

Molecular genetic testing advanced significantly with PCR and NGS, providing genome-wide data.[70]Multidisciplinary teams collaborate to integrate various testing methods with clinical, pathological, functional, computational, ethical, and social aspects of diseases for patient benefit.[71]

Polymerase Chain Reaction. This diagram shows the polymerase chain reaction steps. Enzoklop,Public Domain via Wikimedia Commons

Trisomy 21 on G-Banded Chromosome Studies. This karyogram depicts trisomy 21 resulting from an inherited Robertsonian translocation between chromosomes 14 and 21. The infant's father was a carrier of the translocation in a balanced form. Crotwell PL, (more...)

Disclosure: Cecilia Ishida declares no relevant financial relationships with ineligible companies.

Disclosure: Muhammad Zubair declares no relevant financial relationships with ineligible companies.

Disclosure: Vikas Gupta declares no relevant financial relationships with ineligible companies.

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Molecular Genetics Testing - StatPearls - NCBI Bookshelf

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New Study Links Ozempic to BlindnessBut They Can Actually Protect Your Eyes – First For Women

Tuesday, October 22nd, 2024

New Study Links Ozempic to BlindnessBut They Can Actually Protect Your Eyes  First For Women

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New Study Links Ozempic to BlindnessBut They Can Actually Protect Your Eyes - First For Women

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$1.8 Million Awarded to Study the Durability of Gene Therapy – University of Arkansas Newswire

Tuesday, October 22nd, 2024

$1.8 Million Awarded to Study the Durability of Gene Therapy  University of Arkansas Newswire

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$1.8 Million Awarded to Study the Durability of Gene Therapy - University of Arkansas Newswire

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Gene therapy: advances, challenges and perspectives – PMC

Sunday, October 6th, 2024

ABSTRACT

The ability to make site-specific modifications to the human genome has been an objective in medicine since the recognition of the gene as the basic unit of heredity. Thus, gene therapy is understood as the ability of genetic improvement through the correction of altered (mutated) genes or site-specific modifications that target therapeutic treatment. This therapy became possible through the advances of genetics and bioengineering that enabled manipulating vectors for delivery of extrachromosomal material to target cells. One of the main focuses of this technique is the optimization of delivery vehicles (vectors) that are mostly plasmids, nanostructured or viruses. The viruses are more often investigated due to their excellence of invading cells and inserting their genetic material. However, there is great concern regarding exacerbated immune responses and genome manipulation, especially in germ line cells. In vivo studies in in somatic cell showed satisfactory results with approved protocols in clinical trials. These trials have been conducted in the United States, Europe, Australia and China. Recent biotechnological advances, such as induced pluripotent stem cells in patients with liver diseases, chimeric antigen receptor T-cell immunotherapy, and genomic editing by CRISPR/Cas9, are addressed in this review.

Keywords: Gene therapy, Genetic Vectors, Gene transfer, horizontal, CRISPR-Cas9, CAR-T cell, Genetic therapy, Clustered regularly interspaced short palindromic repeats

A habilidade de fazer modificaes pontuais no genoma humano tem sido o objetivo da medicina desde o conhecimento do DNA como unidade bsica da hereditariedade. Entende-se terapia gnica como a capacidade do melhoramento gentico por meio da correo de genes alterados (mutados) ou modificaes stio-especficas, que tenham como alvo o tratamento teraputico. Este tipo de procedimento tornou-se possvel por conta dos avanos da gentica e da bioengenharia, que permitiram a manipulao de vetores para a entrega do material extracromossomal em clulas-alvo. Um dos principais focos desta tcnica a otimizao dos veculos de entrega (vetores) que, em sua maioria, so plasmdeos, nanoestruturados ou vrus sendo estes ltimos os mais estudados, devido sua excelncia em invadir as clulas e inserir seu material gentico. No entanto, existe grande preocupao referente s respostas imunes exacerbadas e manipulao do genoma, principalmente em linhagens germinativas. Estudos em clulas somticas in vivo apresentaram resultados satisfatrios, e j existem protocolos aprovados para uso clnico. Os principais trials tm sido conduzidos nos Estados Unidos, Europa, Austrlia e China. Recentes avanos biotecnolgicos empregados para o aprimoramento da terapia gnica, como clulas-tronco pluripotentes induzidas em pacientes portadores de doenas hepticas, imunoterapia com clulas T do receptor do antgeno quimera e edio genmica pelos sistema CRISPR/Cas9, so abordados nesta reviso.

Keywords: Terapia gnica, Vetores genticos, Transferncia gentica horizontal, CRISPR-Cas9, CAR-T cell, Terapia gentica, Repeties palindrmicas curtas agrupadas e regularmente espaadas

In 1991, James Watson declared that many people say they are worried about the changes in our genetic instructions. But these (genetic instructions) are merely a product of evolution, shaped so we can adapt to certain conditions which might no longer exist. We all know how imperfect we are. Why not become a little better apt to survive?.(1) Since the beginning, humans understand that the peculiar characteristics of the parents can be transmitted to their descendents. The first speculation originated from the ancient Greek students, and some of these theories continued for many centuries. Genetic-scientific studies initiated in the early 1850s, when the Austrian monk, Gregor Mendel, in a series of experiments with green peas, described the inheritance pattern by observing the traces that were inherited as separate units, which we know today as genes. Up until 1950, little was known as to the physical nature of genes, which was when the American biochemist, James Watson, and the British biophysicist, Francis Crick, developed the revolutionary model of the double strand DNA. In 1970, researchers discovered a series of enzymes that enabled the separation of the genes in predetermined sites along the DNA molecule and their reinsertion in a reproducible manner. These genetic advances prepared the scenario for the emergence of genetic engineering with the production of new drugs and antibodies, and as of 1980, gene therapy has been incorporated by scientists.(2,3)

In this review, we cover gene therapy, the different methodologies of genetic engineering used for this technique, its limitations, applications, and perspectives.

The ability to make local modificiations in the human genome has been the objective of Medicine since the knowledge of DNA as the basic unit of heredity. Gene therapy is understood as the capacity for gene improvement by means of the correction of altered (mutated) genes or site-specific modifications that have therapeutic treatment as target. Further on, diffrent strategies are described, which are often used for this purpose.(4)

Currently, gene therapy is an area that exists predominantly in research laboratories, and its application is still experimental.(5) Most trials are conducted in the United States, Europe, and Australia. The approach is broad, with potential treatment of diseases caused by recessive gene disorders (cystic fibrosis, hemophilia, muscular dystrophy, and sickle cell anemia), acquired genetic diseases such as cancer, and certain viral infections, such as AIDS.(3,6)

One of the most often used techniques consists of recombinant DNA technology, in which the gene of interest or healthy gene is inserted into a vector, which can be a plasmidial, nanoestrutured, or viral; the latter is the most often used due to its efficiency in invading cells and introducing its genetic material. On , a few gene therapy protocols are summarized, approved and published for clinical use, exemplifying the disease, the target, and the type of vector used.(3)

Gene therapy protocols

Although several protocols have been successful, the gene therapy process remains complex, and many techniques need new developments. The specific body cells that need treatment should be identified and accessible. A way to effectively distribute the gene copies to the cells must be available, and the diseases and their strict genetic bonds need to be completely understood.(3) There is also the important issue of the target cell type of gene therapy that currently is subdivided into two large groups: gene therapy of the germline(7) and gene therapy of somatic cells.(8) In germline gene therapy, the stem cells, e.g., with the sperm and egg, are modified by the introduction of functional genes, which are integrated into the genome. The modifications are hereditary and pass on to subsequent generations. In theory, this approach should be highly effective in the fight against genetic and hereditary diseases. Somatic cell gene therapy is when therapeutic genes are transferred to a patients somatic cells. Any modification and any effects are restricted only to that patient and are not inherited by future generations.

In gene therapy, a normal gene is inserted into the genome to replace an abnormal gene responsible for causing a certain disease. Of the various challenges involved in the process, one of the most significant is the difficulty in releasing the gene into the stem cell. Thus, a molecular carrier called a vector is used to release the gene, which needs to be very specific, display efficiency in the release of one or more genes of the sizes necessary for clinical applications, not be recognized by the immune system, and be purified in large quantities and high concentrations so that it can be produced and made available on a large scale. Once the vector is inserted into the patient, it cannot induce allergic reactions or inflammatory process; it should increase the normal functions, correct deficiencies, or inhibit deleterious activities. Furthermore, it should be safe not only for the patient, but also for the environment and for the professionals who manipulate it. Finally, the vector should be capable to express the gene, in general, for the patients entire life.(3,9)

Although the efficacy of viral vectors is confirmed, recently some studies demonstrated that the use of these carriers presented with several limitations. The presence of viral genetic material in the plasmid is a strong aggravating factor, since it can induce an acute immune response, besides a possible oncogenic transformation. Currently, there are two main approaches for genetic modifications of the cells, namely: virus-mediated () and via physical mechanisms, from preparations obtained by advanced nanotechnology techniques.(5) Within this context, included are polymers that form networks that capture a gene and release its load when they penetrate the cells, such as DNA microinjections,(10) cationic polymers,(11) cationic liposomes,(12,13) and particle bombardment.(14)

Viral vectors for gene therapy

Each exogenous material introduction technique differs from the other and depends on the type of application proposed. Some are more efficient, others more apt to carry large genes (>10kB) and integrate with the genome, allowing a permanent expression.(1)

Hematopoietic stem cells have become ideal targets for gene transfer due to the high potential for longevity and the capacity for self-renovation. One example of this combination of gene therapy and stem cells would be the production of gene transfer vectors for the creation of induced pluripotent stem cells (iPS), in order to generate the differentiation of the iPS and afford an additional phenotype from this differentiated derived cell. Patients with chronic liver disease and infection by the hepatitis virus (e.g., hepatitis B virus and hepatitis C virus), which require a liver transplant, may be likely to undergo the hepatic transplantation of mature hepatocytes or those derived from iPS.(15) Not only the transfer of genes might be needed to convert stem cells into hepatocytes; since the transplanted cells are susceptible to reinfection by the hepatitis virus, the transfer of a vector that encodes a short hairpin RNA directed against the virus would provide the transferred cells with resistance or immunity to reinfection. Resistant cells can repopulate the liver over time and restore normal hepatic function ().(15)

Combination of stem cells and gene therapy

shRA: short hairpin RNA; iPS: induced pluripotent stem cells.

Chimeric antigen recipient T (CAR-T) cell therapy is a type of immunotherapy that involves manipulation/reprogramming of immune cells (T lymphocytes) of the patients themselves, in order to recognize and attack the tumor T cells. Initial advancement in the design of the first CAR generation, by Eshhar et al.,(16) was marked by the fusion of a single chain fragment variable (scFv) to a transmembrane domain and an intracellular signaling unit: chain CD3 zeta.(17,18) This design combined the active element of a well-characterized monoclonal antibody with a signaling domain, increasing the recognition of the tumor-specific epitope and the activation of T cells, without depending on molecules from the histocompatibility complex.

An improvement in the first generation of CAR was made by means of integrating co-stimulating molecules necessary for signal transduction. The stimulatory recipient most commonly used in this CAR generation is CD28. This recipient acts as a second activating event of the route, enabling a marked proliferation of T cells along with an increased expression of cytokines.(19)

The most recent generation of CAR incorporated the addition of a co-stimulatory domain addition to increase the CAR function. Co-stimulatory molecules as recipients of the tumor necrosis factor (CD134 or CD137) are required for this methodology. In summary, the most recent forms of CAR include scFv, the initial chain of CD3-, along with the stimulatory chains of CD28 and CD134 or CD137.(20)

With the third CAR generation, Zhong et al., demonstrated an improvement in T cell activation of the Akt route (protein kinase B), which regulates the cell cycle. According to other studies, this last generation shows greater persistence of the T cells in comparison with the second generation of CAR.(21)

The most critical point of the adverse effects of CAR-T therapy is the identification of non-tumor cells that express the target epitope by CAR. Tumor antigens are molecules highly expressed in the tumor cells, but are not exclusive of these cells. For example, the CD19 antigen can be found in normal or malignant B cells, and the CAR design for the CD19 target in not capable of distinguishing them.(20,22) Other common toxicity for CAR-T therapy (and many other types of immunotherapy for cancer) is the cytokine release syndrome (CRS). Activation of the immune system after CAR-T infusion can induce a rapid increase in the levels of inflammatory cytokines.(20,23)

New developments in the design of vectors and trials with CAR-T provide balance and reinforcement in safety for amplification of the clinical application. The progressive improvement in the CAR trials has already advanced, as was observed from the first to the third generation. Knowledge and experience acquired in the assessment of CAR-T toxicity will increase the success of the progressive improvements for future trials.

During the 1980s, in the genome of Escherichia coli, a region was identified with an uncommon pattern, in which a highly variable sequence was intercalated by a repeated sequence with no known function. In 2005, it was assumed that the variable sequences were of extra-chromosomal origin, acting as an immune memory against phages and plasmids, starting the then unknown CRISPR system (Clustered Regularly Interspaced Short Palindromic Repeats) and Cas (Associated Proteins), that shines since 2012 as one of the primary biotechnological tools for gene edition.(24) Originating in the immune-adaptive system of procaryontes, this mechanism recognizes the invading genetic mateiral, cleaves it into small fragments, and integrates it into its own DNA. In a second infection by the same agent, the following sequence occurs: transcription of the CRISPR locus, RNAm processing, and creation of small fragments of RNA (crRNAs) that form complexes with the Cas proteins, and these recognize the alien nucleic acids and finally destroy them.(24)

Based on this natural mechanism, the CRIPSR technique was developed enabling editing of the target-specific DNA sequences of the genome of any organism by means of basically three molecules: nuclease (Cas9), responsible for cleavage of the double-strand DNA; an RNA guide, which guides the complex to the target; and the target DNA, as is shown in .(25,26)

CRISPR Cas-9 system. The technique involves basically three molecules: one nuclease (generally wild type Cas-9 of Streptococcus pyogenes), an RNA guide (known as single guide RNA), and the target (frequently the DNA)

Due to its simplicity and its precision when compared to other techniques (Zinc-Finger Nucleases, TALENs, and Gene Targeting), the CRISPR system arrives as a versitile tool that promotes the genetic editing by means of inactivation (knockout gene KO), integration of exogenous sequences (knock-in), and allele substitution, among others.(27,28)

The guide RNA hybridizes with the target DNA. Cas-9 recognizes this complex and should mediate cleavage of the DNA double strand and reparation in the presence of a (homologous) donor DNA. The result of this process is the integration of an exogenous sequence into the genome (knock-in) or allele substitution.

The rapid advancement of this new technology allowed the performance of translational trials in human somatic cells, using genetic editing by CRISPR. The first applications with a therapeutic focus already stood out in describing even the optimization steps of the delivery systems and specificity for the safety and efectiveness of the system.(28,29)

Researchers from the University of California and of Utah recently were successful in correcting the mutation of the hemoglobin gene, which originates sickle cell anemia. CD34+ cells from patients who are carriers of sickle cell anemia were isolated, edited by CRISPR-Cas9, and after 16 weeks, the results showed a reduction in the expression levels of the mutated gene and an increased gene expression of the wild type.(29)

The technology referred to is in use mainly in monogenic genetic pathologies, which, despite being rare, can reach about 10 thousand diseases already described.(4) Phase 1 clinical trials are foreseen for 2017, as well as the appearance of companies geared toward the clinical use of this system.

The possibility of genetically modifying germlines has been the object of heated discussion in the field of science for a long time. Bioethics is always present when new techniques are created, in order to assess the risks of the procedure and the moral implications involved.

A large part of the scientific community approves genetic therapy in somatic cells, especially in cases of severe disorders, such as cystic fibrosis and Duchenne muscular dystrophy.

In 2015, however, Chinese researchers went beyond the moral issues and announced, for the first time, the genetic modification of embryonic cells using the CRISPR-Cas9 technique. Next, another Chinese group also reported the conduction of the same process done with the intention of conferring resistance to HIV by insertion of the CCR5 gene mutation. The genetic analysis showed that 4 of the 26 embryos were successfully modified. The result clearly reveals the need for improving the technique, alerting that, possibly, such trials could be previously tested in animal models.(4,30)

These recent publications rekindled the debate regarding genetic editing. On one side, the Japanese Ethics Committee declared that the manner in which the experiment was conducted was correct, since there had been approval by the local Ethics Committee for the study conducted, as well as the consent of the egg donors. In the United Kingdom, the first project for healthy human embryo editing was approved. On the other hand, American research groups remained conservative, reiterating their position of not supporting this type of experiment and declaring that they await improvement in the techniques and of the definitions of ethical issues.(30)

Since the declaration of James Watson in 1991, in reference to the likely optimization of human genetics, gene therapy has advanced throughout the decades, whether by optimization of the types of vectors, by the introduction of new techniques, such as induced pluripotent stem cells in combination with current models of genetic editing (CRISPR-Cas9), and even by trials in germ cells, bringing with it the contradictory ethical and moral aspects that accompany the technique.

Local successes have already solidified the viability of treatments using gene therapy in clinical practice, as an alternative form for patients with congenital diseases or monogenic disorders and cancer, especially when the pharmacological or surgical interventions do not show good results.

The design of new experimental vectors, the increase in efficiency, the specificity of the delivery systems, and the greater understanding of the inflammatory response induction may balance the improvement of safety with the expansion of techniques in clinical applications. Yet the knowledge and experience acquired with the careful assessment of toxicity of these technologies also allow significant advances in the application of these methods.

Therefore, historically, gene therapy and the discovery of antibiotics and chemotherapy agents, or any new technology, need more clarifying preclinical studies. In the future, there is the promise of applying these techniques in several fields of Medicine and a greater percentage of clinical trials.

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Danish Study Reveals Connection Between Diabetic Neuropathy, Retinopathy, and Severe Periodontitis – Medical Dialogues

Saturday, September 21st, 2024

Danish Study Reveals Connection Between Diabetic Neuropathy, Retinopathy, and Severe Periodontitis  Medical Dialogues

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Stem cell therapies for chronic obstructive pulmonary disease …

Saturday, September 21st, 2024

Chronic obstructive pulmonary diseases (COPD) is a heterogeneous lung disease that has high morbidity and mortality worldwide, and is an increasing economic and social burden [1, 2]. The recent burden of obstructive lung disease study and other large-scale epidemiological studies estimated that the global prevalence of COPD is 10.3% [3]. Another recent study estimated that the increasing prevalence of smoking in low- and middle-income countries and aging populations in high-income countries will lead to more than 5.4million annual deaths from COPD and related conditions by 2060 [4]. Long-term exposure to cigarette smoke, harmful chemicals, smoke from burning fuels, and 1-antitrypsin deficiency are the main causes of COPD [5] (Fig.1). As COPD progresses, patients experience irreversible obstruction of airflow, hypersecretion of mucus, destruction of alveolar wall, and proliferation of airway smooth muscle cells due to the chronic bronchitis and/or emphysema [6].

Risk factors and pathogenesis of COPD. By figdraw (www.figdraw.com)

Chronic bronchitis is characterized by non-specific inflammation of the mucosa and surrounding tissues of the trachea and bronchi, and is triggered by an infection or non-infectious factors (allergy, oxidative stress) in which the major pathological change is damage of epithelia in the central airway [7]. Prolonged inflammatory stimulation causes proliferation of bronchial mucosal cells and mucosal hypertrophy, resulting in obstruction of the airways and decreased ventilation. The excessive secretion of mucus and infiltration of inflammatory cells leads to the accumulation of mucus in the bronchial lumen, further aggravating the narrowing and obstruction of airways [8]. Emphysema is characterised by dilatation and destruction of lung tissue beyond the terminal fine bronchioles. Its manifestations are thinning of the alveolar walls; enlargement, rupture, or formation of large blisters in the alveolar cavities; reduced blood supply; and destruction of the elastic fibrous network [9].

COPD is, therefore, a multifactorial disease with a complex pathogenesis, and many studies have focused on the accumulation of inflammatory cells, the imbalance of protease/antiprotease activity, and oxidative stress [5, 10, 11] (Fig.1). There is evidence that cigarette smoke and other inhaled particulates stimulate epithelial cells to produce reactive oxygen species, and that this induces inflammatory cells to infiltrate the periphery of the airways, leading to an imbalance of protease/antiprotease activity [12,13,14]. Elastin is a major protein in the connective tissue of the lung parenchyma, and an imbalance between proteases and antiproteases can decrease the level of elastin, leading to lung hyperinflation, lung dilatation, and loss of lung elasticity, culminating emphysema [15,16,17]. During disease progression, COPD patients experience a gradual decline in lung capacity which initially limits their ability to exercise, and eventually becomes disabling [18]. Although chronic bronchitis and emphysema are the predominant clinical phenotypes of COPD, these patients may also present with several other complications, such as airway hyperresponsiveness, hyperimmune response, asthma, and other lung diseases [19]. The many symptoms of COPD are responsible for its huge personal, social, and economic burden. COPD is incurable, but the clinical management of symptoms includes smoking cessation, vaccinations for respiratory pathogens, various medications (especially bronchodilators and steroids), oxygen therapy, and pulmonary rehabilitation [8]. These treatments aim to control the symptoms, decrease inflammation, and improve functional capacity. The use of anti-inflammatory drugs and bronchodilators reduces the severity of symptoms and improves patient quality-of-life, but these treatments only relieve symptoms and do not block or reverse lung damage [20]. Although smoking cessation and long-term oxygen therapy are relatively effective, they do not halt the underlying pathology of increased inflammation, apoptosis, and oxidative stress [21,22,23]. There are currently no treatments for the irreversible loss of lung function and incompletely reversible limitation of expiratory airflow, so there is an urgent need to develop new treatments that can repair the damaged lung tissues of patients with COPD.

Stem cells are undifferentiated cells with the capacity for self-renewal and multispectral differentiation, and cell-based tissue reconstruction using stem cells is an important part of regenerative medicine [24]. Cellular therapeutic approaches may provide new treatment options for COPD in the future. The unique properties of stem cells are that they can promote tissue repair and regeneration by replacing damaged cells, modulate immune responses, reduce inflammation, and promote tissue homeostasis [25]. Thus, a promising general approach for using stem cells to treat COPD is to harness their capacity for differentiation by stimulating them to regenerate lung parenchymal cells and airways, and/or to promote stem/progenitor cell differentiation of epithelial cells to restore the balance between proliferation and apoptosis.

The most important function of stem cells is their maintenance of cellular regeneration, in that they can differentiate into at least one type of highly mature cell. This means that stem cells have great potential for use in tissue repair if they can be promoted to replace diseased and damaged tissues [26]. There are three general types of stem cells: embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and adult stem cells (MSCs and several others) [27]. ESCs and iPSCs have the potential for unlimited proliferation and differentiation into all germ layers, and therefore have great potential for treatment of refractory diseases and injuries [28]. Adult stem cells are immature cells in adult tissues that are in a resting state, which function as a reservoir for self-renewal because of their ability to differentiate into highly specialised cells and repair tissue following injury [29]. There are two types of adult stem cells that affect airway function in COPD: mesenchymal stem cells (MSCs) and lung progenitor/stem cells.

ESCs are pluripotent stem cells isolated from blastomeres that can differentiate into all types of cells, making them highly valuable in regenerative medicine [30, 31]. Since 1998, when hESCs were first cultured and differentiated, many studies of drug-based therapies using ESCs have examined their use for treatment of spinal cord injury, macular degeneration, type 1 diabetes, heart failure, and other conditions [32]. ESCs also have potential for treatment of lung diseases, and studies have demonstrated that hESCs and mouse ESCs can differentiate into type II alveolar epithelial cells (ATIICs) using controlled culture conditions [33, 34]. Previous studies have used established transfection and culture procedures in a laboratory setting to develop genetically screened and highly purified hESC-ATIICs that have characteristics typical of ATIICs, including formation of lamellipodia, expression of surfactant protein, and the ability to proliferate and differentiate into type I alveolar epithelial cells (ATICs) [35]. Previous research demonstrated that ATIICs derived from hESCs can be engrafted into the lungs of mice with acute lung injury, and that this treatment inhibited or reversed fibrotic changes induced by bleomycin [36]. Although hESC-ATIICs have potential as a cellular source for treatments of distal lung diseases, there are many concerns regarding the safety of cell transplantation from differentiated ESCs. Methods such as the formation of embryoid bodies or coculture of these cells with lung mesenchyme have only produced small numbers of ATIICs [33, 34, 37, 38]. Another important concern is that the presence of pluripotent cells within a mixed population of ESC-derived cells may lead to formation of a teratoma, making this approach unsuitable for transplantation into the lungs. There are also serious ethical concerns, because the acquisition of hESCs necessitates the destruction of embryos.

A disadvantage of allogeneic transplantation of hESCs is that they can elicit a strong immune reaction; this necessitates intensive immunosuppressive treatment to prevent rejection, which increases the risk of an opportunistic infection and tumor development [39, 40].Many studies have therefore attempted to produce personalized hESCs to prevent immune rejection. For example, the implementation of alternative targeted methods, such as b2-microglobulin-deficient hESCs, greatly decreases the susceptibility of stem cells to recognition by CD8+T cells. This approach can potentially provide a sustainable reservoir of cells for tissue regeneration without the need for matching of human leukocyte antigens (HLAs) [41]. A clinical case report showed that treatment with hESCs decreased symptoms in a patient with emphysema [42]. Although preclinical studies showed that ESCs can regenerate lung structures, the potential for teratoma formation, immune rejection, and ethical issues have prevented the development of clinical trials that use hESCs for treatment of COPD [43]. To address these ethical concerns and technical limitations, researchers have instead taken alternative approaches that use adult stem cells or iPSCs.

iPSCs, which are generated by reprogramming adult somatic cells (e.g., skin cells) into a pluripotent state, have great potential for use in regenerative medicine. In 2006, the Yamanaka team reported the successful reprogramming of differentiated somatic cells into a cell type resembling embryonic stem cells by introduction of specific transcription factors. Since then, many researchers have utilized these cells as a source for regeneration in studies of disease-specific cells in different animal models, drug screening, and development of cell-based therapies [44]. hiPSCs are a promising source of therapeutic cells because they have totipotency similar to hESCs, they can differentiate into a variety of cell types, they do not induce strong immune responses, and there are no serious ethical concerns regarding their use [45, 46]. Extracting somatic cells from a patient and reprogramming them into iPSCs greatly reduces the risk of immune rejection after transplantation and improves the feasibility and safety of cell transplantation. Controlled differentiation programs allow iPSCs to develop into specific cell lineages, so they can replace the damaged cells that are in the tissues or organs affected by specific diseases [47]. There is also evidence that hiPSCs undergo targeted differentiation to produce alveolar epithelial cell type 2 (iAT2) cells, and that hiPSCs derived from distal lung cells can be implanted into the lungs, where they contribute to the formation of functional distal lung units and slow the progression of emphysema [48, 49].

Although iPSCs appear to have great potential, several limitations need to be addressed. One concern is reprogramming efficiency, because the process is slow and inefficient, even though it is reproducible [50]. Although recent advances showed that iPSCs can be amplified in scalable suspension cultures, and that large quantities of human iPSCs can be produced in a fully controlled bioreactor [51], further technological improvements are needed for producing clinical-grade iPSCs. Another important consideration is the risk of genetic and epigenetic abnormalities during reprogramming, because reprogrammed iPSCs may have different genomic instabilities that lead to development of a malignancy. In particular, the random integration of multiple copies of a transgene into the host genome during the overexpression of reprogramming factors can lead to significant phenotypic variability, and to potential disruptions in the function of critical genes in the generated iPSCs [44]. An even greater concern is that genomic alterations caused by the integration of transcription factor genes into the genome could lead to tumorigenicity [31]. There are also immunological concerns associated with cell therapies that utilize iPSCs [52]. Given the continuing improvements in the protocols used for differentiation and the availability of better techniques for enrichment, purification, and analysis, it may soon be possible to eliminate undifferentiated cells from the differentiated cell products. The risk of teratoma formation appears to be very low when using highly enriched cell products [53].

iPSCs have several potential uses in regenerative medicine studies: directly for cell transplantation, as a source of differentiated cells, and in model systems to explore the role of epigenetic reprogramming in abnormally functioning cells. Most research has focused on the last two methods [54]. Although clinical trials are increasingly using hESC or hiPSC derivatives to repair organs and treat diseases, our search of ClinicalTrials.gov identified 96 clinical trials using iPSCs, but only 5 that were related to lung and respiratory diseases, and none that examined iPSCs as a treatment for lung diseases in [53]. The challenges associated with vector integration, suboptimal efficiency in generation of hiPSCs, and the demand for different types of transplantable cells led to the development of a novel vector incorporating a Tet-On inducible gene expression system, an ATII C-specific NEOR transgene, and loxP target sequences. This innovative approach enabled the successful generation of hiPSC-ATIICs whose ultrastructural characteristics and functional properties were similar to those of ATIICs [55]. Similar hESCs-ATIICs and hiPSCs-ATIICs have significant promise for in vivo transplantation, differentiation into ATICs for alveolar regeneration following bleomycin-induced injury, and improving the function of damaged lungs [44]. However, the process of obtaining tissue-specific cells from iPSCs requires labor-intensive reprogramming and directed differentiation. It is imperative to develop expedited approaches, such as direct reprogramming of one somatic cell type into another cell type, as a more effective strategy for generation of iPSCs [56].

The adult lung is a complex organ consisting of many types of cells that are distributed throughout the respiratory tract, and each region is characterized by its own distinct population of epithelial cells. Stem/progenitor cells from various epithelial lineages within the lung function in lung development, tissue maintenance, and repair following injury [57]. The maintenance of a precise equilibrium between each region-specific type of stem cell and its specific microenvironments is essential for the preservation of normal lung function and airway integrity during normal conditions and during the repair of lung damage. The region-specific epithelial stem/progenitor cells in the lungs of human adults and mice consist of basal cells, secretory cells, and mucous cells in the proximal airway submucosal glands; variant secretory cells in the small bronchi; bronchoalveolar duct junction stem cells; and a subset of ATIICs in the alveolar sac [58, 59]. Lung progenitor/stem cells have the capacity to undergo proliferation and differentiation following lung injury in order to restore damaged cell populations and uphold the typical physiological functioning of the lung [25]. Among these, basal cells are a key type of epithelial stem cell, because they play a crucial role in maintaining environmental homeostasis and promoting the repair of epithelial in the proximal airways. Bronchioalveolar stem cells are essential for repairing damage to the small bronchi and alveolar cells, and they play a crucial role in maintaining stability of the lung environment. Bronchoalveolar stem cells exhibit a diverse differentiation response to various forms of injury, giving rise to cell types including club cells and ciliated cells. Within the gas exchange region of the adult lung, a subset of ATIICs are stem/progenitor cells for ATICs, and ATIICs function as stem cells by maintaining epithelial homeostasis during normal conditions and in response to injury [57]. Through lineage tracing experiments, it has been demonstrated that AT2 cells, serving as stem/progenitor cells, possess the ability to self-renew and undergo transdifferentiation into AT1 cells [25]. The ability of the lung to self-repair following injury requires activation of stem cells and progenitor cells within each respiratory alveolus.

Individuals with COPD experience oxidative stress and disruption of the equilibrium between self-renewal and differentiation of stem/progenitor cells, and this prevents the regeneration of lung tissue [9]. Thus, there is an urgent need for more basic studies and clinical studies that examine the use of lung stem/progenitor cells for the management of COPD and other pulmonary ailments. We searched for clinical trials using bronchial basal cells for the treatment of COPD, of which only one had relevant results published. In this study, autologous P63+lung progenitor cells were transplanted into COPD subjects, and the results suggest that transplantation of cultured P63 lung progenitor cells is safe and may represent a potential therapeutic strategy for COPD (NCT03188627) [60]. There has been great interest in the potential use of exogenous stem/progenitor cells to regenerate or enhance lung repair in patients with COPD, but significant hurdles must be overcome. Firstly, it is difficult to obtain sufficient quantities of autologous stem cells. Secondly, there is insufficient information regarding the identification and characterization of defined lung stem/progenitor cell subpopulations. Lastly, most current cell implantation techniques are inefficient and lack long-term efficacy [61]. Although several clinical studies have examined the use of endothelial progenitor cells and basal epithelial cells from the bronchus for investigational interventions, direct implantation of cells required for airway function is a potential approach for regenerating damaged lung tissue, and further studies using animal models are needed.

MSCs are a subset of stem cells that exhibit morphological similarities to fibroblasts and are found within the connective tissues of nearly all organs. In 2006, the International Society for Cellular Therapy (ISCT) delineated specific criteria for the identification of MSCs [62]: (1) adherence to plastic surfaces under standard culture conditions, (2) expression of a defined set of surface antigens, and (3) the capacity to differentiate into osteoblasts, chondrocytes, and adipocytes. MSCs exhibit low immunogenicity due to their lack of MHC-II antigen expression. Additionally, MSCs possess immunosuppressive capabilities, forming the foundation for their application in cell therapy. Extensive research utilizing animal models has been undertaken to evaluate the efficacy of MSCs and to progressively elucidate the mechanisms underlying MSC-based tissue repair therapies. Consequently, MSCs are emerging as a potent therapeutic tool for a wide range of diseases. Further investigation into their biological properties is essential to establish the theoretical groundwork necessary for clinical applications. MSCs will be elaborated in more detail below.

Stem cells, with their unique characteristics of self-renewal and differentiation, are the focus of regenerative medicine. These different types of stem cells have distinct biological characteristics and differentiation potentials, and the best is still controversial. Advantages and disadvantages of different types of stem cells are briefly summarized in Fig.2. Embryonic stem cells are highly undifferentiated cells that can be induced to differentiate into almost all cell types of the organism, but cannot develop into complete individuals. ESCs have long been expected to be the most promising cell source in the regenerative medicine. Ethical controversies, tumour formation and immune rejection make the use of embryonic stem cells a huge obstacle. As a replacement for ESCs, iPSCs are not beset with any serious ethical issues, but oncogenicity and cellular deterioration due to incomplete reprogramming remain challenges. Lung progenitor/stem cells are adult stem cells with the advantages of having low tumourigenicity, being suitable for autologous transplantation, and being less ethically problematic. However, lung progenitor/stem cells are rare and difficult to isolate and characterize. All of these cells seem to have insurmountable difficulties to be used in therapy, but the discovery of mesenchymal stem cells offers new hope for the development of regenerative medicine. MSCs are not only readily available from a wide range of sources, with low immunogenicity to avoid rejection, but also perfectly avoid the major drawbacks of other stem cells through immune modulation and suppression of inflammatory responses, making them an ideal cell choice for use in regenerative medicine and therapeutic areas. Conversely, most small-scale clinical trials in regenerative medicine that used MSCs, which are considered non-pluripotent, have not reported significant safety concerns [63]. Despite these advantages, the heterogeneity of MSCs poses problems such as unstable differentiation efficiency and susceptibility to senescence. Extensive and ongoing research is underway to ensure that MSCs are safe and effective in the long term. The future strategies may include: pre-treating stem cells prior to transplantation, or combining stem cell therapies with other therapeutic modalities (e.g., pharmacological interventions or gene therapy) to enhance their therapeutic effects; and developing biomaterials and scaffolds that are structurally similar to tissues and provide structural support that promotes stem cell survival, differentiation, and integration into damaged lung tissues [47]. A number of other cellular approaches may lead to better treatments for chronic respiratory diseases, such as the use of stem/progenitor cells for lung repair, implantation of cells in small animal models, derivation of clinically relevant cell types from human iPSCs, and ex vivo lung generation using decellularized lung scaffolds [64].

Advantages and disadvantages of different types of stem cells. By figdraw (www.figdraw.com)

MSCs are multipotent stem cells that are widely used in regenerative medicine because they are easy to isolate and culture, and because they have immunomodulatory effects and immune privilege. Many preclinical and clinical trials have reported that MSCs have a favorable safety profile, making them suitable for therapeutic interventions that target chronic lung diseases because they can rapidly localize to the lungs after infusion. Compared to other types of stem cells, MSCs are easier to isolate and widely available, and their use is not prevented by ethical concerns.

MSCs are believed to reside within the connective tissue of numerous organs, such as adipose tissue, the placenta, umbilical cord blood, the umbilical cord, and dental pulp, and the most widely used types are bone marrow MSCs (BM-MSCs), adipose MSCs (AD-MSCs), and umbilical cord MSCs (UC-MSCs) [65,66,67,68,69]. A patient who receives MSCs that are obtained by isolating and culturing the patients own bone marrow or adipose tissue (autologous transplantation) have a greatly reduced the risk of immune rejection [47]. MSCs can also be manipulated in vitro and in vivo to differentiate into various cell types, including endodermal cells (pneumocytes, myoblasts, and intestinal epithelial cells) and ectodermal cells (epithelial cells and neurons), making them especially promising for treatment of lung diseases [70,71,72]. Moreover, MSCs have immunomodulatory properties, in that they can dampen inflammatory and autoimmune reactions, and they release growth factors and extracellular vesicles that can facilitate tissue regeneration and repair.

Studies of animal models of emphysema demonstrated that intravenous or intratracheal administration of lung-MSCs or BM-MSCs led to repair of lung injury; improved lung function; increased the levels of EGF, HGF, and VEGF; decreased airway inflammation; inhibited the release of proteases from inflammatory cells due to down-regulation of cyclooxygenase-2; and increased the proliferation of AT1 and AT2 cells [73,74,75]. Moreover, preclinical studies demonstrated that MSCs have significant therapeutic potential due to their anti-inflammatory, microbicidal, angiogenic, and antifibrotic properties, properties that lead to improved lung function and increased survival rates in individuals with chronic inflammatory lung diseases [76].

Despite the significant therapeutic potential of MSCs, their limitations must also be considered before they are used in patients. Firstly, because MSCs are adult stem cells they have a limited potential for differentiation, and therefore a limited ability to generate the specific types of lung cells required for complete tissue regeneration [47]. Secondly, MSCs are a heterogeneous group of cells whose therapeutic efficacy is highly variable, and there are differences in disease phenotypes and patient phenotypes. Different cell sources, therapeutic dosages, and routes of administration may all affect the function of MSCs; culture conditions, number of passages, and other factors can also affect their function. More notably, a growing number of studies showed that MSCs undergo rapid apoptosis, autophagy, or have cytotoxic effects after systemic and potentially after intratracheal administration [64]. Although a wealth of data from preclinical studies suggest that MSCs can decrease chronic inflammation, whether this also occurs in clinical settings and produces clinical benefits remains to be determined. Finally, aging and a decreased proliferative capacity can adversely affect the function and regenerative potential of MSCs. More specifically, multiple passaging of MSC cultures induces cellular senescence and decreases their potential therapeutic efficacy. Sorting and exclusion of CD26-positive MSCs from heterologous cell populations leads to enhanced cell attachment in vitro and reduces the secretion of senescence-associated cytokines, and CD26-negative MSCs had excellent efficacy in a mouse model of emphysema [77]. Therefore, strategies that rejuvenate or selectively remove senescent MSCs may increase the clinical efficacy of this approach.

To date, a relatively large number of clinical trials have demonstrated that MSCs are safe. However, despite the initial hope that implantation of MSCs would be an efficacious treatment for lung diseases, the therapeutic efficacy of MSCs in clinical settings has not yet been demonstrated. In 2011, a clinical trial of infusion of autologous bone marrow mononuclear cell for the treatment of patients with advanced emphysema was carried out in Brazil, and the follow-up results confirmed that bone marrow mononuclear cell infusion is safe (NCT01110252) [78]. Treatment of COPD with MSCs (Prochymal) showed a decrease in c-reactive protein levels, suggesting a possible improvement in the inflammatory process. However, no improvement in lung function or patient quality of life was found (NTC00683722) [79]. No adverse events were found in patients with severe emphysema who underwent lung volume reduction surgery followed by infusion of autologous MSC (NCT01306513) [80]. We found that individuals enrolled in clinical trials investigating MSC therapy for COPD primarily consisted of patients with moderate-to-severe COPD, potentially reflecting the progressive nature of the disease. While early-stage COPD symptoms can be managed with medication, individuals with end-stage respiratory failure from severe emphysema often require lung transplantation as the final treatment option. Numerous uncertainties and unresolved concerns persist regarding the effectiveness and safety of MSC therapies, underscoring the necessity for further clinical trials to address these gaps in knowledge.

MSCs of various origins, including bone marrow, adipose tissue, and the umbilical cord, are frequently used in clinical trials. Bone marrow is the primary and paramount reservoir of MSCs, and BM-MSCs have been extensively studied in preclinical studies and clinical stem cell therapy trials. Friedenstein and colleagues initially discovered MSCs in bone marrow stromal cells in the 1970s by using natural adhesion techniques. Since then, many preclinical studies have investigated the potential use of BM-MSCs for treating a range of diseases. Despite the perceived safety of bone marrow aspiration, the procedure is invasive, uncomfortable, and can lead to severe pain and infection [65]. Moreover, the restricted availability and high density of bone marrow lead to low yields of isolatable cells [81]. BM-MSCs from elderly patients have elevated expression of genes associated with aging, shorter telomeres, diminished proliferative capability, and decreased potential for differentiation [82].

There has been significant interest in AD-MSCs in recent years due to their high versatility and capability for differentiation. These cells are a distinct population of progenitor cells within adipose tissue stromal compartments that can differentiate into various types of cells, including neurons, skeletal muscle cells, and osteoblasts [65]. The pioneering work of Zuk et al. in 2001 described the isolation of AD-MSCs that had the potential for multilineage differentiation from liposuction-derived adipose tissue, demonstrating that AD-MSCs were a promising alternative to BM-MSCs [65]. Notably, adipose tissue has more MSCs than bone marrow, and the surge in clinical trials examining AD-MSCs may be because adipose tissue is more plentiful and easily obtained than bone marrow. AD-MSCs will likely play a prominent role in future research until superior alternatives are developed.

AD-MSCs are morphologically similar to BM-MSCs, they can differentiate into diverse mesodermal tissues, and they express analogous cell surface proteins. Adipose tissue contains significant number of primitive stromal stem cells, with up to 5000 AD-MSCs per gram of fat, in contrast, bone marrow contains 100 to 1000 stem cells per milliliter [65]. Collection of AD-MSCs is also more convenient than collection of BM-MSCs, because it can achieved by the minimally invasive procedure of liposuction under local anesthesia. Liposuction is a common cosmetic procedure in which the fat tissue is frequently discarded, but these tissues could be used as a valuable source of stem cells [83]. There is evidence that the proliferation of AD-MSCs is approximately two-fold greater than that of other types of stem cells. Thus, extracting a small quantity of fat allows the rapid collection of a large number of AD-MSCs, thereby mitigating the risks associated with cell differentiation and mutation during in vitro culture [84]. Although AD-MSCs and BM-MSCs have many biological similarities, they also have some differences in terms of immunophenotype, differentiation potential, transcriptome, proteome, and immunomodulatory activity. Despite these differences, AD-MSCs appear to be as effective as BM-MSCs in certain clinical applications and may be more suitable in some cases [85].

Perinatal mesenchymal stem cells can be obtained from various sources, such as the umbilical cord, umbilical cord blood, and Whartons jelly (muco-polysaccharides in the umbilical cord), and their collection is typically considered noninvasive and free from ethical concerns. Although UC-MSCs account for only 710% of all cells in the umbilical cord, their rapid proliferation allows for efficient expansion using in vitro culture [86].

Although MSCs from bone marrow, adipose tissue, and the umbilical cord have many characteristics in common, they differ in terms of immunophenotype, differentiation potential, and immunomodulatory properties. Clinical trials examining the efficacy of these different MSCs in treating neurodegenerative diseases, endocrine and reproductive disorders, skin regeneration, abnormalities in pulmonary development, and cardiovascular diseases have confirmed they have diverse functions and presumably different therapeutic potential. The process of selecting specific types of MSCs for treatment of different specific diseases is currently problematic. These cells may have similar effects on inhibiting disease progression in vitro, but the mechanisms differ, necessitating further preclinical research and clinical trials to indentify the mechanisms of MSCs that are from different sources [25].

MSCs, which are considered to be multipotent stem cells, can be obtained from diverse tissues. Previous studies have administered MSCs from different sources utilizing a range of techniques, dosages, and timing of administration. The therapeutic effects of MSC treatment on lung function were demonstrated by reductions in the mean linear intercept, decreased pulmonary epithelial cell apoptosis, and improvements in the structural integrity of injured lung tissue [87,88,89,90]. The cell-based approach to regenerative medicine posits that MSC transplantation promotes the repair of lung injury because it introduces healthy cells that function in the structural and functional regeneration of damaged or diseased lung tissue (i.e., cell replacement or implantation), or because the paracrine effects of MSCs promote endogenous regeneration and repair [64]. Studies of different types of lung injuries showed that systemic or direct injection of airways with MSCs successfully introduced these cells into rodent lungs, but most of these studies found that the population of cells implanted in the lungs was too low to be physiologically or functionally significant. Instead, the therapeutic effects of these cells were attributed to paracrine signaling. In fact, many studies found that MSCs can decrease systemic inflammation and stimulate the production of diverse anti-inflammatory molecules [75]. Additionally, MSCs can stimulate the proliferation of different cell types within the lungs, thereby facilitating endogenous repair of lung tissue [91, 92]. Some research showed that MSCs can attract native stem cells to the injury site and promote their differentiation, thereby initiating the regeneration of epithelial tissue [93]. Despite the many research findings supporting the potential efficacy of MSCs in the treatment of respiratory and degenerative disorders, there is still an incomplete understanding of the precise mechanisms by which they decrease lung inflammation and facilitate organ recovery. It seems likely that the type of stem cell and the nature of the injury or disease determines the mechanism, which may include direct differentiation into different cell types, immunomodulation, activation of paracrine pathways, and increasing antiapoptotic activity [74, 94,95,96,97] (Fig.3).

Mechanisms of MSCs-based therapies for COPD. VEGF: vascular endothelial growth factor; HGF: hepatocyte-derived growth factor; Bcl-2: B cell lymphoma-2; Bax: Bcl-2-associated X protein; ROS: reactive oxygen species; TGF-: transforming growth factor-; MMPs: matrix metalloproteinases; ECM: extracellular matrix; IL: interleukin. By figdraw (www.figdraw.com)

MSCs have unique properties that make them suitable candidates for treatment of COPD. MSCs can differentiate into lung-specific cells and replace damaged or dead cells, increase the activity and regenerative potential of endogenous tissue-resident stem cells, promote regeneration of lung structures, improve the structural integrity of airways, and decrease airflow limitation and restore lung function [47]. Some in vitro studies shown that ESCs and adult stem cells can induce the expression of phenotype markers for airway and/or alveolar epithelial cells [98]. When administered intravenously, MSCs primarily target the lungs [99, 100]. Some research suggests that transplanted MSCs have an initial preference for the lungs before migrating to other organs, such as the liver [101]. Multiple studies have demonstrated that MSCs can engraft into mature differentiated airway and alveolar epithelial cells. AD-MSCs can differentiate into alveolar epithelial cells, thereby ameliorating lung injury in a murine model of elastase-induced emphysema [102]. Additionally, the implantation of BM-MSCs into the lungs of an animal model led to their differentiation into ATIICs and the inhibition of alveolar cell apoptosis, thereby preventing lung emphysema induced by radiation and papain protease [103]. The mechanisms underlying the recruitment of circulating or systemically administered stem cells or progenitor cells into the lungs have not yet been fully elucidated, but are likely to be influenced the age of both the donor and recipient, cell type, and route of administration. However, the current understanding suggests that exogenous stem cells have limited potential for structural repair or replacement of damaged lung epithelial cells, indicating the need for additional research to verify the potential of functional epithelial transplantation [104]. Recently, the concept of cell replacement or implantation has been revived. Implantation of basal-like airway epithelial progenitor cells, iPSC-derived lung epithelial cells, or embryonic stem cell-derived AT2 cells using alternative cell sources appears to provide potential therapeutic effect in regenerating damaged lung tissues [64].

In recent years, there has been growing interest in the paracrine effects of MSCs, and the secretome of MSCs has emerged as a potential alternative to cell therapy for various lung diseases. Schweitzer et al. demonstrated that AD-MSCs had therapeutic effects on lung and systemic injuries induced by cigarette smoke, such as lung airway dilation, weight loss, and bone marrow suppression, and proposed that paracrine factors released by AD-MSCs were responsible for these effects [105]. Shigemura et al. validated that the reparative potential of AD-MSCs in treating emphysema was mediated by secretion of hepatocyte growth factor, and this intervention led to improved gas exchange and enhanced exercise tolerance [91]. Hence, there is great interest in the MSC-mediated mechanism of lung tissue repair and the role of paracrine activity in this process. The secretome of MSCs, which includes conditioned medium (CM) and extracellular vesicles (EVs), has immunomodulatory effects and decreases inflammation in pulmonary airways [106].

MSC-CM is readily accessible and regarded as minimally manipulated cell-free material derived from MSCs. There is evidence that administration of MSC-CM leads to a significant reduction in the severity of lung injury, and had efficacy comparable to MSCs in various in vitro and in vivo animal models. For example, Shologu et al. studied CM from BM-MSCs and AD-MSCs, and examined its effect on low-oxygen-induced lung epithelial injury in alveolar epithelial cells. Their findings indicated that MSC-CM improved alveolar epithelial cell viability, decreased the secretion of proinflammatory mediators, and increased the production of the anti-inflammatory cytokine IL-10 [107]. Other studies evaluated the therapeutic efficacy of MSC-CM in a rodent model of COPD induced by cigarette smoke exposure, and the results suggested that MSC and MSC-CM lead to a notable decrease in emphysema and an increase in the quantity of pulmonary capillaries [108]. In addition to emphysema, cigarette smoke can also trigger apoptosis in lung fibroblasts. Thus, Kim et al. reported that MSC-CM mitigated the apoptosis of lung fibroblasts and promoted their proliferation in vivo and in vitro [109]. The findings of these many studies of lung injury models indicate a significant potential for utilization of MSC-CM for decreasing cell death and inflammatory reactions and for increasing tissue repair and endogenous regeneration.

EVs, which include proteins, mRNAs, miRNAs, long noncoding RNAs, and lipids, can regulate gene expression and modulate diverse pathways [110]. EVs are categorized as exosomes, microvesicles, or apoptotic bodies based on their origin, mechanism of secretion, size, and surface markers. A study in mice demonstrated that MSC-EVs decreased pulmonary fibrosis, restored lung structure, improved alveolar formation, and enhanced lung function [111]. MSCs-EVs presumably had these effects by transferring bioactive mediators to injured cells, thereby regulating pathological and physiological responses and promoting cell survival, while decreasing immune and inflammatory responses [112]. Thus, these recent preclinical studies of lung injury indicate that the secretome of MSCs, including CM and EVs, has promising therapeutic effects.

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MAIA Biotechnology Announces Positive Survival Updates in Phase 2 Study of THIO in Non-Small Cell Lung Cancer – Business Wire

Friday, September 13th, 2024

MAIA Biotechnology Announces Positive Survival Updates in Phase 2 Study of THIO in Non-Small Cell Lung Cancer  Business Wire

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Regenerative medicine applications: An overview of clinical trials

Friday, September 13th, 2024

Abstract

Insights into the use of cellular therapeutics, extracellular vesicles (EVs), and tissue engineering strategies for regenerative medicine applications are continually emerging with a focus on personalized, patient-specific treatments. Multiple pre-clinical and clinical trials have demonstrated the strong potential of cellular therapies, such as stem cells, immune cells, and EVs, to modulate inflammatory immune responses and promote neoangiogenic regeneration in diseased organs, damaged grafts, and inflammatory diseases, including COVID-19. Over 5,000 registered clinical trials on ClinicalTrials.gov involve stem cell therapies across various organs such as lung, kidney, heart, and liver, among other applications. A vast majority of stem cell clinical trials have been focused on these therapies safety and effectiveness. Advances in our understanding of stem cell heterogeneity, dosage specificity, and ex vivo manipulation of stem cell activity have shed light on the potential benefits of cellular therapies and supported expansion into clinical indications such as optimizing organ preservation before transplantation. Standardization of manufacturing protocols of tissue-engineered grafts is a critical first step towards the ultimate goal of whole organ engineering. Although various challenges and uncertainties are present in applying cellular and tissue engineering therapies, these fields prospect remains promising for customized patient-specific treatments. Here we will review novel regenerative medicine applications involving cellular therapies, EVs, and tissue-engineered constructs currently investigated in the clinic to mitigate diseases and possible use of cellular therapeutics for solid organ transplantation. We will discuss how these strategies may help advance the therapeutic potential of regenerative and transplant medicine.

Keywords: regenerative medicine, stem cells, extracellular vesicles, COVID-19, tissue engineering, transplantation, bioengineering

Regenerative medicine focuses on replenishing and repairing tissue or organs impaired by disease, trauma, or congenital issues. Cellular therapies, conditioned media, extracellular vesicles (EVs), and seeded cellular patches are promising therapeutic tools to combat various inflammatory conditions and diseases. A large body of pre-clinical research has shown that stem cell therapies can delay disease onset within multiple organs such as the kidney (Sedrakyan et al., 2012; Urt-Filho et al., 2016; Frank and Petrosyan, 2020), lung (Mei et al., 2007; Zhen et al., 2008, 2010; Garcia et al., 2013; Xu et al., 2018), heart (Wang et al., 2015; Galipeau et al., 2016; Miteva et al., 2017), and liver (Gilsanz et al., 2017; Tsuchiya et al., 2019) through immunomodulatory and paracrine mechanisms. Conditioned media and EVs derived from stem cells also demonstrate similar characteristics (Lener et al., 2015; Nassar et al., 2016; Bruno et al., 2017; Riazifar et al., 2017; Sedrakyan et al., 2017; Grange et al., 2019). Mesenchymal stromal cells (mesenchymal stem cells; MSCs), which are used mainly in clinical trials, have a potent self-renewal and differentiation capacity into multi-lineages and may be isolated from various adult tissues such as bone marrow (BM), adipose tissue, and fetal specimens (amniotic fluid and umbilical cord). Cellular therapies are also investigated for transplant medicine with the hopes of repairing marginal organs, minimizing ischemia-reperfusion injury (IRI), and inducing immune tolerance in solid organ transplantation (Leventhal et al., 2016; Sawitzki et al., 2020). In addition to stem cell therapies, immune cell therapies that specifically isolate and enrich anti-inflammatory immune cells are also investigated as a promising regenerative medicine tool towards treating inflammation, promoting tissue regeneration, and enhancing transplant tolerance (Zwang and Leventhal, 2017). Currently, clinicians and scientists have begun providing novel insights into optimizing cellular therapy in the clinical setting to provide a more deliverable, sustained, and impactful clinical benefit to patients (Okano and Sipp, 2020). However, further studies with larger patient cohorts are needed to show the efficacy of cellular therapies, conditioned media, extracellular vesicles (EVs), and seeded cellular patches for regenerative medicine. Here we will review results obtained from current clinical trials and novel cellular therapeutic options investigated towards clinical use. We will discuss how these findings and current novel techniques may help advance the potential therapeutic effects of cellular transplantations, EVs, and tissue-engineered constructs for regenerative medicine and transplantation.

Promising pre-clinical research studies have shown the potential of multipotent mesenchymal stem cells (MSCs) transplantation as a regenerative medicine therapy option (Vu et al., 2014; Wang et al., 2021). Currently, the U.S. Food and Drug Administration (FDA) has approved a small set of therapies for clinical use (). Clinical trials have focused on using MSCs immunomodulatory, immunosuppressive, and regenerative potentials with hopes of treating chronic diseases and immune resetting of autoimmune disorders (). MSCs immunoregulatory properties are attributed to their secretion of numerous cytokines (anti-inflammatory factors: iNOS, IDO, PGE2, TSG6, HO1 and galectins, cytokines: TGF, IL-10, CCL2, IL-6 and IL-7, chemokines: IL-6, CXCR3, CCR5, CCL5, CXCL9-11) and putative angiogenic proteins (VEGF, PDGF, TGF) (Shi et al., 2018). The Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy (ISCT) has set standards to define multipotent mesenchymal stromal cells (MSC) for both laboratory-based scientific investigations and pre-clinical studies (Dominici et al., 2006). Three guidelines must be met for the designation of MSC. Firstly, MSC must be plastic-adherent (tissue culture flasks) in cultured under standard conditions. Secondly, MSC (measured by flow cytometry) must have specific surface antigen (Ag) expression (95% expression of CD105, CD73 and CD90, with absence (5/2%) in expression of CD45, CD34, CD14 or CD11b, CD79a or CD19 and HLA class II). Thirdly, MSC must exhibit differentiation capabilities towards osteoblasts, adipocytes, and chondroblasts under standard in vitro differentiating conditions. Not all published clinical trials have adhered to these guidelines, limiting our ability to compare and contrast study outcomes and hindering the fields progression ().

A list of cellular and tissue engineered products with the proposed treatments currently FDA approved. All of the approved cellular products are hematopoietic progenitor cell derived from Cord Blood approved for disorders affecting the hematopoietic system. The tissue engineered scaffolds are allowed for the treatment of mucogingival conditions, cartilage defects of the knee, and thermal burns.

A list of clinical trials using regenerative medicine applications. Each trial is identified by disease reference, patient gender, method of treatment, outcome, and International Society for Cellular Therapy Criteria Check (1, 2, 3). 1) MSC must be plastic-adherent when maintained in standard culture conditions. 2) MSC must express CD105, CD73 and CD90, and lack expression of CD45, CD34, CD14 or CD11b, CD79alpha or CD19 and HLA-DR surface molecules. 3) MSC must differentiate to osteoblasts, adipocytes and chondroblasts in vitro. Most clinical trials using MSC appeared to have the 1st and 2nd criteria mentioned, and a large difference was noted between the trials regarding cell number, type, from of transplantation, and culture conditions. Such variation allows for the identification of different forms of effect per experimental group but shows little consistency in the trials performed. Thus, it would be beneficial if clinical trials followed a clearer guideline with minor changes per experimental group to understand better the applicability and efficacy of cellular and tissue engineered therapies.

In current clinical trials, similar to pre-clinical data, clinical administration of cellular therapies has shown angiogenic properties (active secretion of proangiogenic factors) and anti-inflammatory effects (reduced expression of pro-inflammatory markers and T cell proliferation) (Saad et al., 2017; Ye et al., 2017; Zhang et al., 2017). The angiogenic properties of autologous adipose tissue-derived MSCs are attributed to significantly increasing renal tissue oxygenation, cortical blood flow, and stabilizing glomerular filtration rates (GFR) up to 3months in patients with the atherosclerotic renovascular disease (RVD) (Saad et al., 2017). The anti-inflammatory effects of autologous hematopoietic stem cells are predicted to be beneficial for patients with type 1 diabetes mellitus by lowering the proportion of white blood cells, lymphocytes, T-cell proliferation, and pro-inflammatory cytokine production (Ye et al., 2017). Similarly, anti-inflammatory properties of allogeneic umbilical cord-derived MSCs, show improvements in patients with systemic sclerosis-associated, with better skin thickness scores, lung function, significantly decrease in anti-Scl70 autoantibody titers, and reduction of pro-inflammatory cytokine levels (including transforming growth factor- (TGF-) and vascular endothelial growth factor (VEGF) levels in serum) (Zhang et al., 2017). Although clinical trials show promising results for MSC use in the clinic, there are limitations in MSCs scalability, interdonor variability, clinical trial outcomes inconsistency, low engraftment rates, variation in immunomodulatory response, and potential regenerative limitations (Tanavde et al., 2015). Recently, induced pluripotent stem cells (iPSCs) derived MSCs (CPY-001) are shown to be safe and well-tolerated in a limited number of patients with steroid-resistant acute graft versus host disease (Bloor et al., 2020). This trial demonstrates for the first time, the possible applicability of iPSC-derived MSCs for a range of other clinical targets that may overcome the fundamental limitations of conventional, donor-derived MSC production processes. Although current clinical trials exhibit similar and limited anti-inflammatory beneficial effects with MSC treatments like previous pre-clinical trials, there is a large variation between each trial. Variations such as cell culture conditions, cell number transplantation, from of transplantation, cell type, and characterization limited the interpretation of each trial. Additional studies with larger cohorts are also needed to address the efficacy of cellular therapeutics in regenerative medicine.

MSCs preconditioned with either recombinant proteins, drugs, or ex-vivo cell culture conditions and techniques are also investigated to enhance their therapeutic potential before transplantation (). One form of enhancement strategy applied for cardiac regenerative cell therapy is using a guided cardiopoiesis approach to deliver BM-MSCs expanded and processed for lineage specification to derive cardiopoietic cells. In a Phase III Congestive Heart Failure Cardiopoietic Regenerative Therapy (CHART-1) clinical trial, cardiopoietic stem cells were delivered via the endomyocardial route with a retention-enhanced catheter to patients with ischemic heart failure (Bartunek et al., 2017). However, after thirty-nine weeks, the primary outcome was neutral, except for a subset of patients with severe heart enlargement that appeared to have had a consistent beneficial effect. The results suggest that cardiopoietic cell treatment beneficial outcomes may vary depending on the type of cardiac damage present in patients. Another alternative method used to enhance MSC regenerative potential aside from preconditioning the cells with recombinant growth factors, cytokines, or drugs is the use of environmental stimuli, such as hypoxia. Preconditioned MSCs under chronic hypoxic conditions (itMSC) show enhanced immunomodulatory properties when transplanted in non-ischemic cardiomyopathy patients (Butler et al., 2017). After 90 days, the administration of itMSCs was associated with a reduced number of natural killer cells, and the magnitude of this reduction was correlated with improved left ventricular ejection fraction (Butler et al., 2017). However, a single injection of itMSC was not efficient in promoting significant cardiac structural or functional improvements, highlighting the need to investigate the efficacy of serial dosing of intravenously administered itMSCs to promote a sustained immunomodulatory effect along with structural and functional improvements in the clinic. Thus, clinicians have also carried out studies identifying how different dosages of stem cells and numbers of injections (transplants) may dictate their therapeutic potential. In the TRIDENT Study, Florea et al. have demonstrated in patients with ischemic cardiomyopathy that there are different beneficial outcomes when patients are administered either 20 million or 100 million allogeneic MSC via transendocardial injection (Florea et al., 2017). Both groups showed improvement in scar formation; however, improved ejection fraction was noted only in patients receiving 100 million cells. The authors stated that although the two doses of allogeneic MSC are safe for patients, it is crucial to design trials to evaluate optimal dosing for cell-based therapies. Clinical trials have also begun to understand how different cell types produce better results than single-cell transplantation. In pre-clinical studies (Park K.-S. et al., 2019), have recently demonstrated that delivering both cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) and human mesenchymal stem cell-loaded patch (hMSC-PA) to rats with myocardial infractions can amplify cardiac repair with enhanced vascular regeneration and improved cellular retention and engraftment (Park S.-J. et al., 2019). The combinatory cell delivery can also be applied to organ transplantations to enhance/preserve newly transplanted partial organ engraftment. Benomar et al. demonstrated that patients who were transplanted with pancreatic tissue comprising more than 50% of non-islet cells (likely enriched in ductal, acinar, and MSCs) had a statistically significant lower level of hemoglobin A1c and lower daily requirement of insulin even 5years after transplantation, compared to those who received islet transplant with more than 50% tissue purity (Benomar et al., 2018); thus, suggesting that non-endocrine cells have a beneficial effect on long-term islet graft metabolic function. The authors identified elevated expression of CA19-9 generally synthesized by pancreatic ductal cells and hypothesized that ductal cells must have been transplanted and continued to proliferate and contributed to the beneficial outcomes. These findings bring forth an important concept, the need to transplant multiple cell types for better long-term engraftment and function. These results suggest and warrant further investigation into the understanding and application of methods to enhance the therapeutic potential of MSC, either through improved cell culture techniques, the route of delivery, dosage specificity, or a combination of various cell types to further amplify their regenerative potential.

Current therapies are also designed to mobilize patients tissue-specific progenitor cells using various bioactive molecules such as growth factors, cytokines, and hormones to enhance endogenous regeneration. Activation of endogenous stem cells to promote regeneration or repair holds great promise for the future of translational medicine (Xia et al., 2018). Ansheles et al. demonstrated that using statins (Atorvastatin therapy) in patients with coronary heart disease could significantly increase the pool of endothelial progenitor cells by 72% in 3months (Ansheles et al., 2017). Patients also displayed a significant decrease in VEGF expression and various metabolic markers such as C-reactive protein, total cholesterol, LDL cholesterol, and triglycerides. Pantin et al. also investigated how to enhance endothelial cell mobilization from patients following allogeneic transplantation to sustain donor-derived hematopoiesis (Pantin et al., 2017). They identified that a high-dose (480mg/kg) Plerixafor is safe and effective in mobilizing CD31 expressing cells in healthy donors. These studies highlight the use of molecules to enhance tissue regeneration and restoration in disease by activating endogenous resident cells without the need for exogenous cellular infusions.

Cell-to-cell communication is vital to control wound healing and modulate chronic and acute diseases via paracrine signaling. Cells communicate via the secretion of numerous extracellular vesicles (EVs) which are a heterogeneous population and ranging from 40nm to a few mm in size under physiological and pathophysiological conditions. EV populations most widely studied and characterized are exosomes (derived from intracellular endosomal compartments and range from 30 to 120nm in diameter), microvesicles (also known as shedding vesicles are non-apoptotic EVs that originate from the plasma membrane and range from 50 to 1,000nm in diameter), and apoptotic bodies (originate from cells undergoing apoptosis and range from 50 to 2,000nm). Multiple pre-clinical studies have demonstrated that conditioned media of cultured stem cells and stem cell EVs show beneficial effects on various diseases (Lener et al., 2015; Bruno et al., 2017; Riazifar et al., 2017; Nguyen et al., 2020). The discovery of exosomes, microvesicles, and apoptotic bodies within the conditioned media has led to a new avenue of research exploring EVs for clinical use. Using EVs, most of the therapeutic effects of stem cells can be achieved with a reduced risk associated with live-cell injection late effects, such as neoplastic transformation and immune response activation (Nassar et al., 2016; Wang et al., 2017; Guo et al., 2020). A limited number of clinical trials have investigated EVs therapeutic potential in patients with cancer (Morse et al., 2005; Dai et al., 2008) and disease (Nassar et al., 2016). In chronic kidney disease patients (), EVs isolated from umbilical cord MSCs were shown to be safe and potentially effective in modulating the inflammatory immune reaction (Nassar et al., 2016). Patients who were given two doses of MSC-EVs showed improved eGFR, serum creatinine level, blood urea, and urinary albumin-creatinine ratio, possibly due to a significant plasma level increase in TGF-1 and IL-10 with a decrease in plasma levels of inflammatory cytokine, TNF-. Although patients saw a vast improvement after two dosages of therapy at 8weeks to 9months, the improvements were not sustained after 9months, and an additional administration of the EV might be needed (Nassar et al., 2016).

Further studies are also necessary to clarify fundamental questions regarding the generation, origin of isolation (body fluids: plasma, serum, blood, amniotic fluid, cell lines: MSCs, progenitor cells, IPSCs distribution, tissue derived) (Crescitelli et al., 2021) and uptake of EVs and how to scale up to cGMP manufacturing and improve associated quality control and batch tracking methods for the clinic (Riazifar et al., 2017). Another issue brought forth by the International Society for Extracellular Vesicles is the general lack of proper characterization of the different forms of EVs used in pre-clinical and clinical trials as each type contains different cargos and may promote different effects (Thry et al., 2018). There are currently multiple clinical trials initiated and recruiting patients to investigate EVs application in various diseased organs such as lung, liver, kidney, and heart. The potential use of EVs as a regenerative medicine therapeutic option is vast and promising. There are currently no FDA-approved EV products.

Cellular therapeutics have also been applied ex vivo to improve and recondition donor organ quality before transplantations. Thompson et al. show how ex vivo delivery of multipotent adult progenitor cells via normothermic machine perfusion in kidneys deemed un-transplantable prompted improved clinically relevant parameters (urine output, decreased expression of injury biomarker NGAL, improved microvascular perfusion) and decreased neutrophil recruitment and pro-inflammatory cytokines (downregulation of interleukin (IL)-1, upregulation of IL-10 and Indolamine-2, 3-dioxygenase) (Thompson et al., 2020). Brasile et al. also show how 24h ex vivo perfusion of MSC in an Exsanguinous Metabolic Support tissue-engineering can accelerate the repair of ischemic damage in human kidneys. Promoting regeneration identified by the increased synthesis of ATP (both in the renal cortex and medulla), a reduced inflammatory response (TNF-, RANTES, IL1-B, IL6), increased synthesis of growth factors (EGF, FGF-2, and TGF-), normalization of the cytoskeleton (ZO-1 expressed exclusively at the plasma membrane) and increased cellular proliferation (higher expression of PCNA and mitosis) (Brasile et al., 2019). The authors suggest a more prolonged warm reperfusion of a donors kidney may further improve and repair tubule damages attained from severe ischemic insult. The potential of MSCs to prevent or decrease injuries due to ischemia-reperfusion to further improve organ preservation has also been shown in various organs such as the lung (La Francesca et al., 2014; Lu et al., 2015), liver (Laing et al., 2020), and heart (Yano et al., 2018). Thus, these techniques involving reperfusion using various cell types provide a new avenue to significantly expanding donor criteria to offset current donor shortages. Future studies directed towards identifying the precise reperfusion media, the extent of reperfusion time, and the most suitable cell source can further enhance these techniques applicability in the clinic.

COVID-19, the disease attributed to the novel SARS-CoV-2 coronavirus, has given rise to a global pandemic. Although many patients do well, some present fever, dyspnea, hypoxia, and even exhibit moderate-to-severe acute respiratory distress syndrome (ARDS). This group of patients typically require intubation, which is associated with high mortality rates (up to 67%94%) (King et al., 2020). The detrimental effect of COVID-19 that causes multiple organ failure and even death is correlated with the presentation of a cytokine storm, which is identified as a maladaptive release of cytokines (Brodin, 2021). Elevated expression of inflammatory cytokines such as IL-1B, IFN-, IP-10, and monocyte chemoattractant protein 1 (MCP-1) detected in patients with COVID-19 is linked with Th1 cell response (Ye et al., 2020). Currently, MSC and their EVs are considered as a potential therapeutic option against COVID-19 (). MSC has the innate capacity to promote anti-inflammatory and immune regulatory functions by directly inhibiting abnormal activation of T lymphocytes and macrophages, pro-inflammatory cytokines, and secreting anti-inflammatory cytokines and growth factors such as IL-10 and VEGF to stimulate regeneration and repair. There are currently 16 clinical trials completed with over one thousand studies listed on ClinicalTrials.gov on the use of stem cells or stem cell exosomes to treat coronavirus-related injuries, such as acute kidney and lung injury and various inflammatory processes. Non-randomized case studies, phase 1 and phase 2 clinical trials have shown that human umbilical cord-derived mesenchymal stem cell (UC-MSCs) infusions in patients with moderate and severe COVID-19 pulmonary disease is safe and well-tolerated (Liang et al., 2020; Meng et al., 2020; Shu et al., 2020; Hashemian et al., 2021; Shi et al., 2021). A phase 1 and phase 2 clinical trial with limited patients shows that administration of UC-MSCs or clinical-grade MSCs may help reduce inflammatory cytokines (TNF-, IFN-, IL6, IL8, C-reactive protein) and promote lung recovery in surviving patients (Liang et al., 2020; Hashemian et al., 2021; Shi et al., 2021). Intravenous injection of clinical-grade MSCs (lacking ACE-2 receptor and TMPRSS2) led to increased levels of anti-inflammatory cytokine IL-10, and the normalized presence of immune cells. The patients presented an increase of peripheral lymphocytes, a decrease in C-reactive protein (CRP), a reduced activated cytokine-secreting immune cells (CXCR3+CD4+T-cells, CXCR3+CD8+Tcells, and CXCR3+NK-cells), and a restored levels of regulatory DC cell population (CD14+CD11c+CD11bmodregulatory DC cell) (Leng et al., 2020). The use of MSC with the absence of ACE-2 receptor and TMPRSS2 to prevent infection with SARS-Cov-2 may have enhanced the therapeutic effects of MSCs.

There are currently multiple studies listed on ClinicalTrials.gov on the use of EVs to treat COVID-19. Sengupta et al. show that a single dose of intravenous infusion of exosomes derived from BM-MSC (ExoFloTM) in patients presenting moderate-to-severe ARDS helps restore oxygenation, reduces the cytokine storm, to bring back a healthy immune system with no adverse effects (Sengupta et al., 2020). The authors state that exosomes may be used as a preventative measure against progression to invasive oxygen support and mechanical ventilation, which is associated with a high mortality rate. Further studies with randomized controlled trials (RCTs) are warranted to prove efficacy and address what type of EVs and what dosage of EVs are needed to treat COVID-19 patients. A short-term (84days) Phase 1 clinical trial of twenty-seven COVID-19 patients with pulmonary fibrosis treated with human embryonic stem cell-derived immunity and matrix-regulatory cells, which poses high expression of proliferative, immunomodulatory and anti-fibrotic genes, also show improvements in clinical symptoms (Wu et al., 2020). Additional multicenter randomized placebo-controlled Phase 2/3 trials are underway for further proof. Although these findings are promising, additional studies with larger cohorts are needed to assess the efficacy of MSCs and EVs therapeutic potential to treat and prevent the progression of COVID-19 related injuries in patients. While many clinical trials are listed, not all have begun, and only a few have been completed. Additionally, the completed trials consist of a small sample size, various cellular products, different culture methodology, and need more time for result interpretation. Leading to a discouraging notion that COVID-19 treatment with cellular therapies may not be available soon to treat a significant number of patients. COVID-19 clinical trial moving forward should focus on clear identification of cellular products used and improve quality of study design to further the future of cellular therapies in treatment of COVID-19.

Aside from using stem cells, the field of regenerative medicine also investigates the potential isolation and enrichment of specific anti-inflammatory immune cells to treat inflammation, promote tissue regeneration and transplant tolerance (). In non-acute stroke patients, administration of autologous M2 macrophages is shown to be safe and can modulate inflammatory responses, contributing to angiogenesis and tissue repair (Chernykh et al., 2016). However, the treatment appeared to be more effective in patients with lower endogenous immunosuppressive mechanisms (IL-10, FGF-, PDGF, VEGF) and increased pro-inflammatory activity (IL-1, TNF-, IFN-, IL-6). Infusion of autologous Treg cells has also been investigated for kidney transplantation patients to promote transplant tolerance in hopes of avoiding long-term use of toxic immunosuppressive agents that cause increased morbidity/mortality (Mathew et al., 2018). The administration of transplanted polyclonal Tregs (CD4+CD25+ T cells) derived from the thymus or peripheral tissues of the recipients and expanded in vitro into living donor kidney transplant recipients showed a reduction of total CD4+T and CD8+ T cells and a 520 fold increased circulating Tregs levels after 90 days. The authors aim to move into a phase II clinical trial to test Treg infusions efficacy for tolerance induction or drug minimization (Mathew et al., 2018). Chimeric antigen receptor transduced natural killer (CAR-NK) therapy (Liu et al., 2020), and pluripotent stem cell-derived immunosuppressive cells (macrophages) (Tsuji et al., 2020) are also investigated for use in solid organ transplantation as an alternative method of posttransplant management to improve allograft survival and minimize secondary complications. Recently, Tsuji et al. showed the successful generation of immunosuppressive cells from non-human primate ESCs that expressed several immunosuppressive molecules and significantly inhibited allogeneic mixed lymphocyte reaction (Tsuji et al., 2020). The future goal is to move into pre-clinical trials and demonstrate their potential to suppress allogeneic immune reactions against grafts derived from the same donor in transplantation models. Although advancements in surgical technique and immunosuppression regimens have progressed in transplant medicine, many limitations still exist. The chronic use of immunosuppression in transplant medicine promotes several side effects and increases the relative risk of infections, malignancy, cardiovascular morbidity, and organ damage (e.g., liver toxicity, nephrotoxicity, neurotoxicity, and diabetes mellitus). Thus, to further improve solid organ transplantation outcomes, discovering a novel immunoregulating strategy in regenerative medicine using pluripotent stem cells and engineered immune cells to enhance organ survival and tolerance is vital for the growth of transplant medicine.

In tissue engineering, a combination of cells, a scaffold, and biologically active molecules are used to reconstruct or regenerate damaged tissues or whole organs. The success of tissue engineering relies on the interplay between multiple scientific disciplines such as cell biology, biomedical engineering, and material science. The identification of proper scaffolds, bioreactors, cell sources, and biomolecules such as growth factors and chemokines are needed to reconstruct or regenerate organs correctly. Currently, contrary to 2D planar tissues, bioengineering solid organs for transplantation is still challenging. Advances have been made towards identifying novel scaffolds, biomolecules, and cells, but protocols towards combining the mixture for solid organs de novo reconstruction are still a limiting factor. Although scientific thinking and approaches towards fully realizing the exciting potential of whole organ engineering are still in their early phases, there have been advances in using novel technology with cell therapy to enhance tissue regeneration and function in the clinic ().

Tissue engineering is currently applied to creating alternative materials for the reconstruction of multiple organs. Ram-Liebig et al. show that manufactured tissue-engineered oral mucosa graft is safe and efficient in urethroplasty in male patients with surgically unsuccessful pretreated urethral stricture (Ram-Liebig et al., 2017). The procedure involves harvesting a small oral biopsy from the patients and sending it out to a Good Manufacturing Practice (GMP) laboratory manufacturing company, MukoCell, where the sample is used to create a tissue-engineered oral mucosa graft for the urethroplasty. The transplant success rate was 67.3% at 12 and 58.2% at 24 months and the authors hypothesize that the success rate may be higher if the patients are initially treated with the graft from the beginning. Nonetheless, the authors show that the bulbar and penile urethra reconstruction is feasible, safe, and efficacious in a heavily pretreated population using a tissue-engineered oral mucosa graft. This study demonstrates how current tissue engineering therapies could be successfully standardized and manufactured in a company to provide a constant viable product tailored to everyone.

Clinical studies are also exploring the mechanisms of how tissue-engineered constructs cross-communicate with the diseased milieu to promote healing of a chronic wound. Stone et al. used transcriptomics to understand mechanistically how an FDA-approved bilayer living cell construct (BLCC) promotes the healing of chronic non-healing venous leg ulcers (Stone et al., 2017). BLCC consists of a layer of the human foreskinderived neonatal fibroblasts in a bovine type I collagen matrix under a layer of the human foreskinderived neonatal epidermal keratinocytes. The authors identified that BLCC provides bioactive signals after transplant to the damaged tissue site to promote wound healing via modulation of inflammatory and growth factor signaling, keratinocyte activation, and attenuation Wnt/-catenin signaling. This study identifies mechanistically how tissue-engineered constructs can communicate at the site of injury to promote healing (Stone et al., 2017). The use of a cardiac patch has also garnered much attention, which provides cells a proper microenvironment for tissue development and maturation (Menasch et al., 2018). Bayes-Genis et al. have shown that autologous pericardial adipose graft transplanted within patients treated with coronary artery bypass graft surgery promotes a noticeable improvement in reducing the necrotic mass-sized ventricular volumes after 1year (Bayes-Genis et al., 2016). The authors used an autologous pericardial adipose graft directly obtained from the patients and surgical glued it in place over the necrotic zone after the coronary artery bypass. The surgeons harnessed the biological regenerative capacity of adipose tissue for patients with a chronic myocardial scar. However, no statistically significant difference was noted in necrosis size, possibly due to the limited patient numbers and the need to refine the surgical procedure (Bayes-Genis et al., 2016). Cardiac patches are also used to address the limitation in the retention and need of large cell numbers for cardiac regenerative therapy. In a phase I clinical trial, Menasche et al. assessed the safety and efficacy of transplanting human embryonic stem cell (hESC)-derived cardiovascular progenitors embedded in a fibrin patch in severe ischemic left ventricular dysfunction patients receiving a coronary artery bypass procedure (Menasch et al., 2018). The cardiac fibrin patch showed no evidence of tumor formation or arrhythmias during the 18 months follow-up. Although the feasibility of producing clinical-grade hESC-CM for transplantation was demonstrated, clinical trials assessing efficacy were not yet conducted due to the small sample size, lack of blinded assessment, and confounding effect of the associated coronary artery bypass grafting. Based on these results, there is still a need to identify the best source of stem or progenitor cells and extracellular matrix or biomaterial to promote tissue regeneration and repair in efficacy and safe manner.

Researchers have identified how stem cell heterogeneity, due to differences in source and donor to donor variations, may limit their clinical effectiveness. Autologous (isolated from and transplanted back into the same patient) and allogeneic (isolated from a different patient) stem cells have a different beneficial therapeutic potential based on disease and organ model. Hare et al. demonstrate that although transplantation of both autologous and allogeneic BM-MSCs is safe, feasible, and beneficial when applied in chronic non-ischemic dilated cardiomyopathy (NIDCM), there are slight differences in their beneficial outcomes (Hare et al., 2017). Allogeneic BM-MSCs transplants promote a more significant improvement in functional tests like Ejection Fraction (EF), Minnesota Living with Heart Failure Questionnaire (MLHFQ), Six Minute Walk Test (6MWT), along with the better functional restoration of endothelium and reduction of pro-inflammatory cytokines (TNF-) 6 months after transplantation compared to autologous BM-MSCs. Similarly, Bhansali et al. also show that autologous bone-marrow or mononuclear cells (MNCs) transplanted in patients with type 2 diabetes mellitus effectively reduce the need for insulin after a year (Bhansali et al., 2017). However, patients with MNC transplants showed a significant increase in second-phase C-peptide response during the hyperglycemic clamp indicating insulin production, while MSC transplanted patients had a significant improvement in insulin sensitivity index and an increase in insulin receptor substrate-1 gene expression. Thus, demonstrating the need for more informative studies to distinguish the differential beneficial effects of different cell cellular therapies. Xiao et al. also compared the efficacy of intracoronary administration of BM-MNCs or BM-MSCs for patients with dilated cardiomyopathy (DCM) (Xiao et al., 2017). After 3months, both injections showed an improvement in New York Heart Association (NYHA) functional class and left ventricular ejection fraction (LVEF) in patients. However, after 12 months, BM-MSCs transplanted patients continued to significantly improve LVEF and NYHA, unlike BM-MNCs transplanted patients who showed a decrease in LVEF compared to their 3months follow-up. These results suggest that BM-MNCs provided a temporary improvement in LVEF and NYHA class and only accelerate cardiac function recovery while the improvement observed following BM-MSC therapy is sustained (Xiao et al., 2017). These studies provide novel insights and a comprehensive understanding of how various cell sources and cell types may deliver different therapeutic effects based on disease. Additionally, they highlight the need to tailor stem cell therapies specific to each patients need to enhance their regenerative potential. Further conformational studies with large, randomized, placebo-controlled clinical trials are needed to clarify the complexity of MSCs (based on origin and application) and their interaction with host tissue.

Although advancements are being made daily in cellular therapy, there are still many challenges in translating pre-clinical results regarding cellular therapy efficacy to promote tissue healing, reduce excessive inflammation, and improve the clinics survival (Galipeau et al., 2016; Chinnadurai et al., 2018). It has been shown that not all stem cell therapies are initially beneficial. Makhlough et al. show the safety and tolerability of autologous BM-MSC transplanted into six autosomal dominant polycystic kidney disease patients but with no physiological improvement detected after 1year (Makhlough et al., 2017). Patients exhibited a continuous decrease of GFR with a significant increase in serum creatinine levels. The study was limited to only six patients, and only a single cell transplant was administered, which may partially explain the limited beneficial effects detected (Makhlough et al., 2017). Stem cell therapys effectiveness may also be limited by the extent of chronic inflammation and fibrosis already present within the patients damaged tissue. In patients with decompensated (severe) alcoholic liver disease, transplantation of BM-MSCs showed no modification of the diseases progression after 4weeks (Lanthier et al., 2017) to 8weeks (Rajaram et al., 2017). Although patients showed an elevation of liver macrophages and upregulation of regenerative liver markers (SPINK1 and HGF), no difference was detected regarding proliferative hepatocyte numbers (Lanthier et al., 2017). There are also potential safety concerns with cellular therapy, such as the potential for malignant transformation of MSCs (Steinemann et al., 2013). A long-term follow-up study of patients with decompensated (severe) alcoholic liver disease transplanted with autologous BM-derived mononuclear cells showed improved liver function and decreased collagen levels in patients liver transiently 6months post-transplantation (Kim et al., 2017). Patients also displayed improved biochemical parameters, CP class, and increased liver volume, indicating liver regeneration. Although improved liver function was still evident at the five-year follow-up, patients who had received cell transplantation had an alarming increased risk of developing hepatocellular carcinoma (HCC). This relatively high incidence of HCC within 2years after autologous bone marrow cell infusion warrants further investigation (Kim et al., 2017). Other studies have also shown that a small group of hematopoietic cell transplant survivors may suffer from not only solid tumors but also from other significant late effects such as diseases of the cardiovascular, pulmonary, and endocrine systems, dysfunction of the thyroid gland, gonads, liver and kidneys, infertility, iron overload, bone diseases, infection, and neuropsychological effects (Inamoto and Lee, 2017). The leading cause of mortality in adult patients who had received hematopoietic cell transplants includes recurrent malignancy, lung diseases, infection, secondary cancers, and chronic graft-versus-host disease. Thus, long-term risk assessment studies of patients receiving stem cell transplantation are needed to understand the risk of developing cancer and other harmful late effects versus the long-term benefits of stem cell therapy. Another limitation preventing comparison of current clinical trials and their outcomes, is that not all clinical trials adhered to ISCT criteria in defining the cellular treatments. Moving forward, improved methodological quality, increased sample size, and extended trial duration are needed for a better comparison of clinical trial data and results amongst each study. Cossu et al. and others also emphasized the need for better science, funding models, governance, public and patient engagement to enhance cellular therapys efficacy and safety in the clinic (Cossu et al., 2018). Regulatory limitations are another hurdle for the application of cell therapies or new technologies. With growing innovations made in regenerative medicine, outdated regulations may not adequately address new challenges posed as technology advances. Thus, new regulations must be designed to protect the patients from unnecessary risk while encouraging investigators, funding bodies, and investors to support research and development and market commercialization of novel products.

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Regenerative medicine applications: An overview of clinical trials

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The Progression of Regenerative Medicine and its Impact on Therapy …

Friday, September 13th, 2024

Clin Transl Sci. 2020 May; 13(3): 440450.

1Division of Cardiac Surgery, University of Ottawa Heart Institute, OttawaOntario, Canada

2School of Human Kinetics, University of Ottawa, OttawaCanada

1Division of Cardiac Surgery, University of Ottawa Heart Institute, OttawaOntario, Canada

3Department of Cellular & Molecular Medicine, University of Ottawa, OttawaCanada

1Division of Cardiac Surgery, University of Ottawa Heart Institute, OttawaOntario, Canada

2School of Human Kinetics, University of Ottawa, OttawaCanada

3Department of Cellular & Molecular Medicine, University of Ottawa, OttawaCanada

Received 2019 Nov 6; Accepted 2019 Nov 7.

Despite regenerative medicine (RM) being one of the hottest topics in biotechnology for the past 3decades, it is generally acknowledged that the fields performance at the bedside has been somewhat disappointing. This may be linked to the novelty of these technologies and their disruptive nature, which has brought an increasing level of complexity to translation. Therefore, we look at how the historical development of the RM field has changed the translational strategy. Specifically, we explore how the pursuit of such novel regenerative therapies has changed the way experts aim to translate their ideas into clinical applications, and then identify areas that need to be corrected or reinforced in order for these therapies to eventually be incorporated into the standardofcare. This is then linked to a discussion of the preclinical and postclinical challenges remaining today, which offer insights that can contribute to the future progression of RM.

In 1954, Dr. Joseph Murray performed the first transplant in a human when he transferred a kidney from one identical twin to another.1 This successful procedure, which would go on to have a profound impact on medical history, was the culmination of >50years of transplantation and grafting research. In the following years, organ replacement became more widespread but also led to a plateau in terms of landmark successes.1 The technology was working, but limitations were already being encountered; the most prominent of them being the lack of organ availability and the increasing need from the aging population.2 During the same time period, chronic diseases were on the rise and the associated process of tissue degeneration was becoming evident. Additionally, the available clinical interventions were merely capable of treating symptoms, rather than curing the disease, and, therefore, once a loss of tissue function occurred, it was nearly impossible to regain.3 Overall, the coupling of all these factors that took place in the 1960s and 1970s created urgency for disruptive technologies and led to the creation of tissue engineering (TE).

TE can be described as a field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ.4 TE is considered to be under the umbrella of regenerative medicine (RM) and, according to Dr. Heather Greenwood et al., regenerative medicine is an emerging interdisciplinary field of research and clinical applications focused on the repair, replacement or regeneration of cells, tissues or organs to restore impaired function resulting from any cause, including congenital defects, diseases, trauma and aging.5 It uses a combination of technological approaches that moves it beyond traditional transplantation and replacement therapies. These approaches may include, but are not limited to, the use of soluble molecules, gene therapy, stem cell transplantation, tissue engineering, and the reprogramming of cell and tissue types.3, 6, 7 A summary of the recent history of RM is presented in Figure.

A summary timeline of the recent history of regenerative medicine (RM). Selected milestones in the development of RM are presented starting from the 1950s all the way up to the present day.

Although RM may have seemed novel, the principles of regeneration are as old as humanity and are found in its many cultures.8 A common example used is the tale of Prometheus that appeared in 8th century BCE. Prometheus, an immortal Titan in Greek mythology, stole fire and gave it to humanity for them to use, defying the gods in consequence. As punishment, Zeus decreed that he was to be bound to a rock where an eagle would feast on his liver every day and said liver would regenerate itself every night, leading to a continuous loop of torture.9 RM came about at the time it did, not only because of the combining factors mentioned above, but also because researchers had been successfully keeping tissue alive in vitro and understanding the biological processes involved in regeneration and degeneration. Consequently, possible therapeutic outcomes came into fruition. Since the arrival of TE and RM, strides made on the benchside have been ever increasing with now >280,000 search results on PubMed relating to regeneration. Discoveries and advances made by cell/molecular biologists, engineers, clinicians, and many more led to a paradigm shift from treatmentbased to curebased therapies.10 In addition to Greenwoods definition, RMs arsenal now contains controlled release matrices, scaffolds, and bioreactors.5, 8 Despite this impressive profile on the benchside, RM has so far underperformed in terms of clinical applications (i.e., poor therapy translation).8 Simply put, a disappointing number of discoveries are making it through clinical trials and onto the market.11 Although some experts say that the field is reaching a critical mass in terms of potential therapies and that we will soon see results, others, like Dr. Harper Jr. from the Mayo Clinic in Minnesota, say that the transformative power of RM is well recognized, but the complexity of translating isnt.7, 8, 12

This brings us to the subject matter of the present paper: RM and translation. The goals of this historical review are twofold. The first is to understand how RM, over the past 50years or so, has changed the way discoveries/new technologies are transferred to the clinic. How has the translational strategy changed in response to these new therapies? The second is to identify challenges that have led to RMs modest performance on the bedside. Some articles have already documented these but have focused on the clinical and postclinical factors, and whereas they will be briefly discussed here, the focus will be on preclinical factors.13 To accomplish these objectives, we will begin by summarizing the historical development of RM (which has been extensively documented by other works2, 3, 14, 15), followed by a detailed look at the definition of translational medicine (TM). With this background information established, we then look at the various preclinical and clinical impacts of RM on TM, as well as some of its effects on the private sector. Limiting factors of the field are then described, again focusing on those that are preclinical. This endeavor was initiated via a librarianassisted literature search for original research and historical documentation of the field of RM and other related subjects. The documents were then screened for relevance and the analyzed information was categorized into the themes discussed below. Conclusions were then drawn based on the interplay among these themes.

As mentioned, the idea of regeneration first started in myths and legends. This is logical because, as Drs. Himanshu Kaul and Yiannis Ventikos put it, myths shape ideas, and ideas then shape technologies.8 In addition to the tale of Prometheus, there are many others. For example, there is the Hindu myth of Raktabeej whose blood drops could each form a clone of himself, or the Indian story of the birth of the Kaurava brothers where pieces of flesh were grown in pots and treated with herbs to grow fullsized humans.8 The idea of regeneration has persisted throughout history and started to become a possibility in the early 1900s when scientists like Alexis Carrel (who invented the technique of cell culture) were finally able to keep cells and tissues alive outside of the body. This allowed them to study the mechanisms of cell renewal, regulation, and repair.8 In addition, studying regeneration goes handinhand with developmental biology. Seminal work in experimental embryology began in the 1820s with the detailed description of the differentiation of embryonic germ layers.16 An increased understanding of basic embryological mechanisms led to Hans Spemanns Nobel Prize for his theory of embryonic induction; a field that was further elaborated by his students and others, advancing it toward the possibility of cloning and demonstrating how development and regeneration are intimately linked.16 Before this era, the study of regeneration was done through the study of animals, with scientists studying the phenomena in serpents, snails, and crustaceans, for example.17, 18 However, the modern study of regeneration is said to have started with Abraham Trembleys study of the hydra, which showed that it was possible for an entire organism to regenerate from its cut appendage.19 The 18th century on through to the 19th century is also when scientists became intrigued by the amphibian newts and axolotls for their astonishing regenerative capabilities, which are still used today as the gold standard models for studying regeneration along with certain fish, such as the zebrafish.20

Now, although the term RM as we know it today would only be coined in 1999 by William Haseltine, the field itself started in the late 1970s in the form of TE (pioneered by Drs. Joseph Vacanti and Robert Langer) in the city of Boston.2, 14, 21 To address the need for novel therapies, biomedical engineers, material scientists, and biologists at Harvard and MIT started working on regenerating parts of the largest and simplest organ of the human body: the skin. In 1979, the first cellbased TE product appeared and was named Epicel.15 Developed by Dr. Howard Green et al., this technology consisted of isolating keratinocytes from a skin biopsy and having them proliferate outside of the body to make cell sheets that were then used as an autologous treatment for burn patients.15 Another famous product (this time allogeneic), developed in 1981, was Apligraf, a composite skin invention capable of rebuilding both the dermis and epidermis of skin wounds.15 With these two therapies and many more being created, TE in the 1980s was booming. At the time, researchers were also developing therapies for cartilage regeneration.

Once the 1990s came around, TE strategies were combined with stem cells (which had just been discovered) to create RM.3, 8 At that time, RM was a hot topic. After the first products for skin were commercialized, scientists became more enthused and started trying other tissues.15 Startup companies were popping up left and right, private funding was abnormally high, and public hype was gaining lots of traction. However, governments were not so quick to fund this research and took their time before making decisions, whereas private investors saw this field as very promising and thought it was their ticket to the top.14 Given that 90% of the funding of RM came from the private sector, this greatly influenced the direction of the research and its timeframe.14 People were simply trying to copy tissue formation rather than understanding it, so as to make the development process quicker.3 As a result, many of the technologies that initially looked promising failed in clinical trials or on the market.

These disappointing results coupled with the dot.com crash meant that by the end of 2002, the capital value of the industry was reduced by 90%, the workforce by 80%, and out of the 20 US Food and Drug Administration (FDA) products with clinical trials, only 4 were approved and none had any success.22 This phenomenon has been extensively studied and, according to Lysaght and Hazlehurst, five factors contributed to the industry crash22:

The products were not much better than the existing treatment options and so making the switch was not worth it for clinicians.

Even if the science was good, lowcost manufacturing procedures did not exist.

The approval process for these novel therapies was unrealistically challenging and the regulatory cost was too high.

Companies lacked the skill to market their new products.

The reimbursement strategies were unclear.

Despite these events, the industry had 89 firms survive the crash and stem cell research was not affected. In fact, from 2000 to 2004, the number of companies increased but the number of jobs decreased, which means investors were supporting research in basic and applied science with smaller firms that were lower risk, and by 2004, the field was dominated by startup companies.22 Before the crash, RM was primarily happening in the United States, but in 2004, other countries like the United Kingdom and Japan started catching up.22 The industry slowly started growing again. In 2006, the first engineered tissue (bladder) was implanted, and by 2008, commercial successes were being achieved.3, 10 As an example, hematopoietic stem cell transplants were approved and are now a curative treatment for blood disorders and other immunodeficiencies.7 Now, the RM field had ironically regenerated itself.3 It has gained increased governmental attention (federal funding has increased) and has been recognized as being at the forefront of health care.7, 22 There is once again intense media coverage that is raising public expectations.23 The number and variety of clinical trials is also increasing everywhere.23 According to allied market research, RM is predicted to be worth US $67.5 billion by 2020.10

Unfortunately, regardless of these seemingly cheerful notes, the fact remains that cell therapies remain experimental, except for the aforementioned hematopoietic stem cell treatments.13 The market for RM is still small and will remain so until RM proves that its therapies are better and cheaper than the existing ones.15 Yet, the pressure for clinical translation is increasing through the needs of the population, investors that are eager to make a return on their investments, and scientists who believe that these technologies are the future.23 Moreover, there has been a growing appreciation of the magnitude and complexity of the obstacles the field is facing, but it remains to be seen how they will be solved; although initial steps have already been taken, which will be discussed further below.

Now that we have established the background for RM, there needs to be a proper understanding of TM before conclusions on how the two are related can be drawn, which is the purpose of the following section.

The European Society for Translational Medicine (EUSTM) has defined TM as an interdisciplinary branch of the biomedical field supported by three main pillars: benchside, bedside, and community. The goals of TM are to combine disciplines, resources, expertise, and techniques within these pillars to promote enhancements in prevention, diagnosis, and therapies.24 TMs goals can be split into two categories: T1 and T2. T1 is to apply research from bench to bedside and back, whereas T2 is to help move successful new therapies from a research context to an everyday clinical context.25 In other words, TM is a medical practice explicitly devoted to helping basic research attain clinical application. Conceptual medical research, preclinical studies, clinical trials, and implementation of research findings are all included within TM.26

Between basic science and the clinic is an area that is popularly referred to as the valley of death.25 This gap is fraught with not only scientific obstacles (like an unknown molecular mechanism), but social and economic ones as well. This is where many novel ideas die and, consequently, companies are weary of going through this valley for fear of wasted financial resources.25 For these reasons, many of the approved drugs we get now are derivatives of others that have been previously approved.25 This is the area that TM seeks to impact, to be the bridge between idea and cure, and to act as a catalyst to increase the efficiency between laboratory and clinic.25, 26 The term bench to bedside and back is commonly used. The cost of development for a therapy is very high (estimated at US $800 million to $2.6 billion for a drug) because of increasing regulatory demands and the complexity of clinical trials, among others. TM aims to streamline the early development stages to reduce the time and cost of development.24

What will be important to note for the discussion below is that TM focuses more on the pathophysiological mechanisms of a disease and/or treatment and favors a more trialanderror method rather than an evidencebased method. Dr. Miriam Solomon argues in his book chapter entitled What is Translational Medicine? that most medical innovations proceed unpredictably with interdisciplinary teams and with shifts from laboratory to patient and back again, and that freedom of trialanderror is what will lead to more therapeutic translation.25 Furthermore, for years, TM did not have any technical suggestions for improving translation, only two broad categories that were claimed to be essential for translatability: improving research infrastructure and broadening the goals of inquiry. This discrepancy has since been identified and efforts have been made to address it. For example, the EUSTM provided a textbook called Translational Medicine: Tools and Techniques as an initiative to provide concise knowledge to the fields stakeholders.24

Presently, TM has attracted considerable attention with substantial funding and numerous institutions and journals committed to its cause.25, 27 But before this, its arrival had to be incited. TM emerged in the late 1990s to offer hope in response to the shortcomings of evidencebased medicine and basic science research, such as the unsatisfactory results from the Human Genome Project, for instance.25 There were growing concerns that the explosion of biomedical research was not being translated in a meaningful manner proportionate with the expenditures and growing needs of the patients.27 The research had ignored what it took to properly disseminate new ideas.25 The difficulties of translation from bench to bedside have always been known, but what is different with TM is the amount of emphasis that is now put on translation and the recognition on how difficult and multifaceted it is to translate technologies.25 Over the past 20years, the role, power, and research volume of the field has increased, and TM is now a top priority for the scientific community.26 TM is also often used as common justification for research funding and conveys the message to politicians and taxpayers that research activities ultimately serve the public, which is also why it appeals to todays generation of students who want to work on big, realworld problems and make a meaningful difference.28, 29

As already mentioned, RM therapies are proving difficult to translate to the clinic.11 Although the basic research discoveries are never ceasing (books such as NewPerspectives in Regeneration by Drs. HeberKatz and Stocum30, and articles such as "Tissue Engineering and Regenerative Medicine: Past, Present, and Future" by Dr. Antnio Salgado et al.,31 provide comprehensive summaries of these advancements), therapy approval is practically nonexistent.30, 31, 32 This may be due, in part, to a tendency for people to blame the lack of translation of their technologies on extrinsic factors, thus removing responsibility.11 Additionally, the failures are not being studied. For example, stem cell research looks good in small animals but often fails in larger ones and then does not progress beyond phase II or III clinical trials because no benefits are found, and historically we have not been exploring why.11, 32 Consequently, the next therapies that are developed are improved by guesses rather than through a better understanding of the disease in mind (Figure).11

The negative feedback cycle currently present in most discovery and development processes of regenerative medicine. This cycle obstructs progression of the field.

RM has the potential to impact not only the quality of healthcare but also the economy, because the costs that could be avoided with curative therapies are immense.33 For this reason, analyzing the impact of RM on the translational strategy over time can help identify aspects that should be encouraged or discouraged to drastically improve translation. Reflecting on this history cannot only help us to avoid past mistakes but can also aid in redirecting the field to a onceproductive path.34 In the following section, the preclinical impact of RM on TM will be discussed, focusing on the shift from evidencebased medicine to trialanderror, the role of the basic scientist, and the emergence of the multidisciplinary approach. Clinical impact is also covered, concentrating on regulatory modifications. Last, changes in the private sector are considered as the shift in business models is detailed.

Because the RM field is essentially comprised of new ideas on cell renewal and tissue healing, it is logical that most of its impact would be on the preclinical side, as this is where ideas are tested, finetuned, and developed. Coincidentally, it is also where the translational strategy begins. Considering certain aspects early in the developmental process, such as realistic applications and ease of use, can help facilitate translation. RMs influence on TM can thus be separated into the three themes below.

Before the late 20th century, the majority of medical research was done using evidencebased medicine. This is a systematic approach to solving a clinical problem that integrates the best available research evidence together with clinical signs, patient values, and individual clinical experience all to support scientific decision making and research progression.35 As such, evidencebased medicine favors clinical trials and does not allow for much tinkering and only that which possesses highquality clinical evidence is to be pursued. This has its limitations, as it devalues mechanistic reasoning, and both in vitro and animal studies. Therefore, evidencebased medicine may have played a role in RMs downfall in the early 2000s. TE in the 1990s was using evidencebased medicine and was simply trying to copy tissue formation rather than trying to understand it.3 That most of the funding was coming from the private sector probably did not help either. Investors saw TE as an opportunity for quick returns on their investments, so therapies were rushed to clinical trials, which led to inconsistent results.14, 25, 32

As well, evidencebased medicine obscured the need for different methods of discovery. After RMs decline and the idea of TM came about, a trialanderror method was adopted. This technique favors a team effort, mechanistic reasoning, and seeks to change the social structure of research.25 Although clinical trials are still deemed important, the trialanderror method identifies that an idea needs to first be explored and should not necessarily require the confirmation of a hypothesis.11, 25 This new method is based more so on facts and has stimulated a more informed dialogue among stakeholders (whereas the confirmation or refusal of a hypothesis cannot always be made relevant to people outside the field). This, in turn, can help the regulatory agencies reduce the burden on their review boards in the evaluation and acceptance of novel strategies.11 Therefore, the failures of RM had helped to highlight the boundaries of evidencebased medicine and, combined with the rising intensity put on TM in the 1990s, assisted in defining the trialanderror based method.

Another thing that is changed with the historical development of RM has been the role of the basic scientist. Please see Figure for a summary of the differences between the traditional and modern scientist discussed in this review. Traditionally, basic scientists have worked with a discovery mindset, but without a noticeable regard for potential therapeutic applications. It has been noted that RM has made us realize how important it is to take the practical and industrializing aspects (like cost, for example) into account even at the basic research level.7, 14 The needs of the end users need to be considered during the developmental phase if RM is to establish a proper foothold within the market.15 In view of this, over the past 2decades, medical philosophy has changed in that it encourages basic scientists to communicate more with clinicians and vice versa. Experts like Barry Coller, MD, Vice President for Medical Affairs and PhysicianinChief at the Rockefeller University Medical Center, have identified various skills that a basic scientist must possess if translational research is to be improved.26, 28 Additionally, other researchers have commented that more and more basic scientists are motivated to have an impact on global health and this passion can be a source of inspiration that can help fuel interdisciplinary cooperation.28 Efforts have also been made to familiarize basic scientists with regulatory requirements. For example, the FDA publishes guide documents with recommendations on how to address these requirements.36 Despite this, much remains to be done, as there is still a lack of TM professionals and the current research environment hampers cooperation between experts (e.g., specialization is still encouraged, and achievement awards are individualized).26, 28

A comparison between the traditional and modern scientist. Although traditional scientists are more hypothesisdriven and rigid in terms of research methodology, if the concepts shown above are used, it can generate the modern scientist who is better suited for the translation of regenerative therapies. RM, regenerative medicine.

An additional point that can be argued is that because RM got basic scientists more involved in the translational process, this has consequently made them more realistic.37 As already mentioned, early RM therapies were comprised of complex cell therapies that were not fully understood. From 2004 onward, the field diversified to include research into simpler acellular products.38 Other avenues, such as induced pluripotent stem cells, endogenous repair, nanotechnology, and regenerative pharmacology, are also being explored.37, 39, 40, 41 Increasingly, experts are trying to spread this message; for instance, in the field of cardiology, Dr. Mark Sussman, a world renowned cardiac researcher, and his colleague Dr. Kathleen Broughton at the San Diego State University Heart Institute and the Integrated Regenerative Research Institute, recently stated that After over a decade of myocardial regenerative research studies, the initial optimism and enthusiasm that fueled rapid and widespread adoption of cellular therapies for heart failure has given way to more pragmatic, realistic, and achievable goals.9

The last preclinical impact of RM to be discussed is the arrival of the multidisciplinary approach. This now widespread notion identifies that to improve translation and accelerate technology development, it is better to have a team composed of experts from multiple disciplines, because the various backgrounds and schools of thought can be combined with each contributing to a project in a different way.25, 39 What has surely incited its evolution is that RM inherently requires contributions from biologists, chemists, engineers, and medical professionals. This need has led to the formation of institutions that house all the required expertise under the same roof (such centers have increased in number since 2003), which promotes more teamwork between laboratories and clinics.28 Dr. Jennifer Hobin et al.28 states that bringing dissimilar research expertise together in close proximity is the key to creating an environment that facilitates collaboration. In addition, it could be said that these collaborative environments help minimize the flaws of medical specialization, which occurred in the second half of the 19th century; where the ideological basis that the human body can be categorized combined with the rapid arrival of new medical technologies led to the specialization of medical practice, which, in turn, led to the segregation of medical professionals from each other and the patient.42 Coincidentally, if one recalls the definition of TM, it, along with the trialanderror based method, suggests that improved research infrastructures and team efforts can facilitate the translation of therapies.

We now look at the influence that RM has had on the clinical side of therapy development. Before the subject is discussed, it is important to note that the reason clinical research has been affected is because of the uniqueness of RM therapies. Their novelty does not fit within the current regulatory process or use in clinical trials, and although the latter has yet to adapt, the regulatory sector has attempted over the years to facilitate the journey from bench to bedside.7, 43, 44

Initially, when RM was in its infancy, its therapies were regulated by the criteria originally developed for drugs; and as we have seen, this was identified as a factor that led to its downfall. Now, in 2019, several regulatory changes have been implemented to rectify this. What has helped has been the input from other countries. As mentioned above, RM started in the United States, but after the crash, other countries like the United Kingdom and Japan caught up, and their less stringent regulatory procedures have allowed them to better adapt the framework for these new therapies.22 In 2007, the European Union passed the Advanced Therapy Products Regulation law, which defined regenerative therapies, categorized them, and provided them with separate regulatory criteria for advanced approval.13, 43 In 2014, public pressure and researcher demands led Japan to enact three new laws: the Regenerative Medicine Promotion Act, the Pharmaceuticals, Medical Devices, and Other Therapeutic Products Act, and the Act on the Safety of Regenerative Medicine. These unprecedented national policies now help therapies gain accelerated and conditional approval to better conduct clinical trials and to better meet the demands of the patients.7, 13, 44, 45 During this time, the United States has not stood idle. In 2012, the US Congress passed the FDA Safety and Innovation Act (FDASIA), which expanded its existing Accelerated Approval Pathway to include breakthrough therapies, a category created for new emerging technologies, including regenerative strategies.13, 46 Drs. Celia Witten, Richard McFarland, and Stephanie Simek provide a wellwritten overview on the efforts of the FDA to accommodate RM.36 By and large, it is safe to say that RM has spurred a drastic change in traditional regulatory pathways to not only better manage these novel therapies but also put more weight on efficient translation.

It is also important to discuss changes in the private sector because manufacturing and marketing is and will remain one of the greatest obstacles facing RM, and, once again, the novelty of the field is responsible. Although the bulk of the problems remain, there has nonetheless been a change in business strategies that is worth appreciating.

Throughout its history, RM research has been carried out by academic research institutions or small and mediumsized enterprises.23, 47 With this in mind, the business model used in the health industry varies depending on the type of company. The royalty model is the one primarily used by biotech companies.8, 14 Here, businesses will develop a therapy up to the clinical stage and then hand it off to a company with more resources (usually a pharmaceutical one) who can carry out the larger scale studies. With this model, biotech companies make money simply through royalties and this carries both pros and cons (Figure).

A comparison of both the royalty and integrated business models used by private companies in the biomedical industry. The pros and cons are listed with the assumption that they are for a startup company in regenerative medicine.

Because the market for regenerative therapies currently is not big enough for the royalty model, startups have had to shift to an integrated model where the discovery, development, approval, and manufacturing of a new therapy are all done internally (which is unusual for small startups).8 Using this strategy, the companies can reap all the rewards but obviously also assume all the risk.

The market for regenerative therapies has so far been small enough that smaller firms do not have to manufacture large quantities of their products (like they do in the pharmaceutical industry) and they can start making money in a quicker fashion.8 Whether the business model will change again as the market grows or if the original startups will grow in proportion remains to be seen.14 What is to be highlighted here is that those who seek to commercialize regenerative therapies have had to shift to an integrated business model (that was not previously the norm for smaller ventures), which has affected translation by letting them have more influence in determining how their therapy is being developed, marketed, and manufactured.

Having detailed RMs relationship with the translation strategy and the aspects that changed in conjunction with the fields development, the remainder of the review will summarize the challenges that are contributing to RMs modest performance in the clinic.

With increased funding and a growing number of committed institutions, many countries have become increasingly invested in RMs success. For example, the US Department of Health and Human Services recognizes RM as being at the forefront of healthcare.7 As well, the UK government has identified RM as a field in which they can become global leaders and that will generate significant economic returns.44 The literature indicates that RM is reaching a critical mass and is on the verge of a significant clinical transition. The optimism is as high as it has ever been and the rush to succeed with clinical trials is equally felt.23 However, the bottom line is that the clinical and market performance is still very poor. Being that a gold standard for treatment in RM remains elusive, clinicians are often illinformed about current applications, and studies on safety and efficacy are lacking.23, 44, 48, 49 The National Institute of Health estimates that 8090% of potential therapies run into problems during the preclinical phase.28 Naturally, scientists have offered various explanations for these results, such as deficiencies in translational science and poor research practices in the clinical sciences.50 Shockingly, in a 2004 analysis, 101 articles by basic scientists were found that clearly promised a product with major clinical application, and yet 20years later, only 5 were licensed and only 1 had a major impact.50 Therefore, it is easily deducible that many challenges still lie ahead. The perceived riskbenefit ratio remains high and, as a consequence, clinical trials have been proceeding with caution.13, 23, 33 Numerous reviews have been published on these challenges but with an emphasis on those relating to the clinical phase.11, 13, 22, 51 Although these will be summarized below, the present study highlights the identification and analysis of the preclinical challenges. Please see Figure for a summary of the preclinical and clinical obstacles discussed herein.

Summary of the preclinical and postclinical challenges discussed. Even though preclinical obstacles to the translation of regenerative medicine therapies are more elusive, they are just as significant as their counterparts.

To begin, a possible explanation for the preclinical obstacles being underrepresented in the literature is because of the pliability of the phase itself. Although the clinical phase is composed of numerous subphases and strict protocols, the preclinical research is much less structured with less oversight. Whereas rigorous scientific method is applied to the experiments themselves, which usually consist of in vitro followed by in vivo experiments, the basic scientist has more flexibility regarding experimental organization, structure, and backtracking; thus, making explicit challenges possibly harder to recognize.

Some researchers have nevertheless attempted to do so. For example, Dr. Jennifer Hobin et al. have identified three major risks associated with RM technologies as being tumorigenicity, immunogenicity, and risks involved with the implantation procedure.13 The first two relate to arguably the largest preclinical challenge, which have been identified as needing a better understanding of the mechanism of action.12 Although the difficulties of identifying a mechanism are appreciated in the scientific community, it is imperative that improvements in this area are made as it will affect application and manufacturing decisions. Hence, greater emphasis on identifying the mechanism of action(s) will need to be adopted by basic scientists who are looking to develop a technology.

Another significant preclinical challenge is the lack of translation streamlining for basic scientists. Although basic scientists have become more involved in the translational process and more pragmatic over the years, there is, in general, still a lack of incentive and available resources to help a scientist translate their research. Academic faculty members are given tenure and promotion based on funding success (grants) and intellectual contributions (publications).28 Thus, researchers who have received money to conduct research and publish their work on a promising new therapy might stop short of translation as there may be no additional recognizable accomplishment or motivation for such an endeavor. For example, Jennifer Hobin et al. described the case of Dr. Daria MochlyRosen at Stanford Universitys Translational Research Program, who sought help for an interesting idea for a heart rate regulation therapy.13 She was turned down by numerous companies that found the clinical challenges too daunting and her colleagues offered no support but rather discouraged her from pursuing the idea saying that it would not be worthwhile for her career.

Last, a very important preclinical challenge that has gained recognition over the past few years is the lack of appropriate preclinical testing models. It is often reported that novel therapies that do well in the laboratory but then fail in larger animal studies or clinical trials. This is partly due to a lack of mechanistic insight, but also because of a shortage of appropriate in vitro, in vivo, and ex vivo models.9, 36 With properly validated preclinical models, we would be better able to gauge the performance of novel therapies and predict their future clinical success, but instead we are misidentifying the potential of therapies. Notably, the lack of appropriate models also contributes to the difficulty in obtaining reliable data on the underlying mechanism(s) of action of RM therapies, as differences may exist between the preclinical and clinical settings.

As far as clinical challenges go, they are numerous. Stem cell trials in particular have received criticism from a perceived lack of rigor and controlled trials.23 Related to this, a potent point that has arisen over the past few years is the absence of longterm followup studies for clinical trials, which is clearly necessary to establish the safety and efficacy of these interventions.13, 33 Unfortunately, they are costly and they are timeconsuming. Efforts are nonetheless being made to overcome these obstacles. For example, in 2015, the Mayo Clinic released an RM buildout perspective offering a blueprint for the discovery, translation and application of regenerative medicine therapies for accelerated adoption into standard of care.7 Institutions, such as Canadas Center for Commercialization of Regenerative Medicine, have been launched to help researchers mitigate the risks of cell therapy development by offering technical as well as business services.12, 51 Experts are also stepping up; for example, Drs. Arnold Caplan and Michael West proposed a new regulatory pathway that incorporates large postmarket studies into clinical trials.33

In terms of manufacturing, it is difficult to engage industry because the necessary technology to produce RM therapies at an industrial level does not exist yet. Scaleout and automated production methods for the manufacturing of regenerative therapies are needed.7, 10, 12, 23, 52, 53 This challenge stems from the complexity and natural intrinsic variation of the biological components, which makes longterm stability difficult to achieve and increases manufacturing costs.13, 44 Now, if RM therapies could establish their superiority over conventional treatments, then this would potentially alleviate costs and increase the likelihood of being reimbursed, but it remains to be seen.13 A hot topic at the moment is the choice between autologous or allogeneicbased products, which would entail either a centralized or decentralized manufacturing model, respectively (although hybrid models have been proposed).7, 23, 54 Autologous products, being patientspecific, have the advantage of having smaller startup costs, simpler regulations, and point of care processing.47 As for allogeneic products, they are more suitable for an off the shelf product, for a scaleout model and quality controls can be applied in bulk.47, 54 Dr. Yves Bayon et al.51 provided a thorough description of this topic while simultaneously indicating areas that have been identified for improvement.

As mentioned above, regulatory challenges are what have been most addressed thus far through scientific and public pressure. Moving forward, the goal identified by expert thinktank sessions is to harmonize RMspecific regulations across agencies and countries.7, 36 Reimbursement is the last of the regulatory challenges to be considered. In order for RM treatments to become broadly available, reimbursement is a necessity and both public and private healthcare need to determine how the regulations will be modified for disruptive therapies coming down the pipeline.13, 23, 44

RM has had an undeniable influence on the process of bench to bedside research. Preclinically, it has helped identify the limitations of evidencebased medicine and contributed to the paradigm shift to the trialanderror method. Likewise, the field has changed its mindset and the basic scientist is adopting new responsibilities becoming more motivated, pragmatic, and involved in TM, rivaling researchers in the applied sciences. The multidisciplinary approach has also been promoted by RM over the years and institutions dedicated to fostering collaborative research in RM have increased in numbers. Clinically, regulatory pathways that were developed for drugs and biomedical devices, and which have been in place for decades, have been adapted to aid RMs disruptive technologies, leading to new guidelines that favor translation. In the private sector, the novel nature of RM therapies has led to startup companies using an alternative business model that provides them toptobottom authority over the development of their products and it is yet to be seen if the business strategy in place will be sufficient as the industry grows.

If the translation of RM therapies is to be improved, many of the challenges to be overcome lie in the early stages of therapy development, such as identifying the mechanism(s) of action, validating preclinical experimental models, and incentivizing translational research for basic scientists. In later stages, regulatory changes have been made, but much still needs to be addressed. This includes the adoption of clinical trials that are more rigorous and include longterm followup studies, the development of appropriate manufacturing technology, the synchronization of regulatory agencies, and a clear plan for reimbursement strategies. Once again, these challenges have been discussed in greater detail in previous works.2, 3, 7, 12, 13, 15, 22, 23, 26, 31, 38, 44, 48, 51, 52 While it seems that the field may be at a tipping point with many challenges remaining, the fact that translation has been influenced in a positive way gives promise to the future progression of RM therapies.

This work was supported by a Collaborative Research Grant from the Canadian Institutes of Health Research (CIHR) and the Natural Sciences and Engineering Research Council (NSERC; CPG158280 to E.J.S.), and the Hetenyi Memorial Studentship from the University of Ottawa (to E.J.).

All authors declared no competing interest for this work.

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BridgeBio Receives FDAs Regenerative Medicine Advanced Therapy (RMAT …

Friday, September 13th, 2024

- Receipt of RMAT Designation is based on preliminary clinical evidence from the CANaspire Phase 1/2 clinical trial, which showed functional improvements in all dosed patients indicating that BBP-812 has potential to address the unmet needs of individuals with Canavan disease

- BridgeBio will leverage the benefits of RMAT designation, including early and more frequent interactions with the FDA, to establish an Accelerated Approval pathway for BBP-812

- If approved, BridgeBios gene therapy for Canavan disease could be the first therapeutic option for children born with this devastating and fatal neurodevelopmental disorder

PALO ALTO, Calif., Sept. 10, 2024 (GLOBE NEWSWIRE) -- BridgeBio Pharma, Inc. (Nasdaq: BBIO) (BridgeBio), a commercial-stage biopharmaceutical company focused on genetic diseases, today announced that the United States Food and Drug Administration (FDA) has granted Regenerative Medicine Advanced Therapy (RMAT) designation to BBP-812, an investigational intravenous (IV) adeno-associated virus serotype 9 (AAV9) gene therapy for the treatment of Canavan disease. RMAT designation was granted following the FDAs review of clinical data from the CANaspire Phase 1/2 clinical trial investigating BBP-812 as a potential therapy to address the unmet medical needs of individuals with Canavan disease.

RMAT is an expedited FDA program available to sponsors of regenerative medicine therapies intended to treat, modify, reverse, or cure serious conditions. Benefits of the RMAT designation include all the advantages of the Fast Track and Breakthrough Therapy Designation programs, including faster and more frequent interactions with the FDA to achieve early alignment on critical aspects of the program. FDA granted RMAT designation based on its review of 12 months of safety and efficacy data from the first eight patients with Canavan disease dosed with BBP-812 in the CANaspire Phase 1/2 clinical trial.

We are honored to be granted RMAT designation for BBP-812 and are eager to work closely with the FDA and the Canavan community with the goal of bringing our therapy to families living with Canavan disease as fast as possible, said Eric David, M.D., J.D., CEO at BridgeBio Gene Therapy. We are beyond grateful to the children and their families who are participating in CANaspire, as well as to the study investigators. RMAT will allow us to work more closely with FDA to ensure we are responding to the urgency that families feel.

To date, results from CANaspire show that all patients dosedwith at least one follow-up assessment havedemonstrated improvements in functional outcomes in key areas important to caregivers such as head control, sitting upright, reaching for and grasping objects, and visual tracking. All patients dosed with BBP-812 with at least one follow-up assessment have shownreductions in N-acetylaspartate (NAA), both in urine and in the central nervous system, to levels associated with mild disease. BBP-812 has been well-tolerated, with a safety profile generally consistent with that of other AAV9 gene therapy programs.

Canavan disease is an extremely rare and rapidly progressive neurodegenerative disease that prevents most children from meeting basic developmental milestones, such as crawling, walking, speaking, and even holding their heads up. It is a terminal diagnosis with no approved treatment to date. The news of the RMAT designation, coupled with the preliminary results seen in the clinical trial, provides hope to children worldwide living with Canavan disease and their families, said Kathleen Flynn,CEO of National Tay-Sachs & Allied Diseases Association, an advocacy organization dedicated to driving research, forging collaboration, and supporting families within the Tay-Sachs, Canavan, GM1, and Sandhoff disease communities.

In addition to RMAT designation, BBP-812 has been granted Orphan Drug, Rare Pediatric Disease (RPDD), and Fast Track Designations from the FDA, as well as Orphan Drug Designation from the European Medicines Agency. With RPDD, if approved, BridgeBio may qualify for a Priority Review Voucher.

About CANaspireCANaspire is a Phase 1/2 open-label study designed to evaluate the safety, tolerability, and pharmacodynamic activity of BridgeBios AAV9 gene therapy candidate, BBP-812, in pediatric patients with Canavan disease. Each eligible patient will receive a single IV infusion of BBP-812. The primary outcomes of the study are safety, as well as change from baseline of urine and central nervous system NAA levels. Motor function and development will also be assessed.

For more information about the CANaspire trial, visit TreatCanavan.com or ClinicalTrials.gov (NCT04998396).

About Canavan DiseaseAffecting approximately 1,000 children in the U.S. and European Union, Canavan disease is an ultra-rare, disabling and fatal disease with no approved therapy. Most children are not able to meet developmental milestones, are unable to crawl, walk, sit or talk, and die at a young age. The disease is caused by an inherited mutation of the ASPA gene that codes for aspartoacylase, a protein that breaks down a compound called NAA. Deficiency of aspartoacylase activity results in accumulation of NAA, and ultimately results in toxicity to myelin in ways that are not currently well understood. Myelin insulates neuronal axons, and without it, neurons are unable to send and receive messages as they should. The current standard of care for Canavan disease is limited to supportive therapy.

About BridgeBio Pharma, Inc.BridgeBio Pharma, Inc. (BridgeBio) is a commercial-stage biopharmaceutical company founded to discover, create, test and deliver transformative medicines to treat patients who suffer from genetic diseases. BridgeBios pipeline of development programs ranges from early science to advanced clinical trials. BridgeBio was founded in 2015 and its team of experienced drug discoverers, developers and innovators are committed to applying advances in genetic medicine to help patients as quickly as possible. For more information visitbridgebio.comand follow us onLinkedIn,Twitter and Facebook.

BridgeBio Pharma, Inc. Forward-Looking StatementsThis press release contains forward-looking statements. Statements BridgeBio makes in this press release may include statements that are not historical facts and are considered forward-looking within the meaning of Section 27A of the Securities Act of 1933, as amended (the Securities Act), and Section 21E of the Securities Exchange Act of 1934, as amended (the Exchange Act), which are usually identified by the use of words such as anticipates, believes, continues, estimates, expects, hopes, intends, may, plans, projects, remains, seeks, should, will, and variations of such words or similar expressions. BridgeBio intends these forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 27A of the Securities Act and Section 21E of the Exchange Act. These forward-looking statements, including statements relating to the timing and success of BridgeBios Phase 1/2 clinical trial of BBP-812 for the treatment of Canavan disease, expectations, plans and prospects regarding BridgeBios regulatory approval process for BBP-812, the ability of BBP-812 to be the first therapeutic treatment option for children born with Canavan disease, reflect BridgeBios current views about its plans, intentions, expectations, strategies and prospects, which are based on the information currently available to BridgeBio and on assumptions BridgeBio has made. Although BridgeBio believes that its plans, intentions, expectations, strategies and prospects as reflected in or suggested by those forward-looking statements are reasonable, BridgeBio can give no assurance that the plans, intentions, expectations or strategies will be attained or achieved. Furthermore, actual results may differ materially from those described in the forward-looking statements and will be affected by a number of risks, uncertainties and assumptions, including, but not limited to, BridgeBios ability to continue and complete its Phase 1/2 clinical trial of BBP-812 for the treatment of Canavan disease, BridgeBios ability to advance BBP-812 in clinical development according to its plans, the ability of BBP-812 to treat Canavan disease, the ability of BBP-812 to retain Fast Track Designation, Rare Pediatric Drug Designation, Regenerative Medicine Advanced Therapy Designation and Orphan Drug Designation from the U.S. Food and Drug Administration and Orphan Drug Designation from the European Medicines Agency, and potential adverse impacts due to global health emergencies, including delays in regulatory review, manufacturing and supply chain interruptions, adverse effects on healthcare systems and disruption of the global economy, the impacts of current macroeconomic and geopolitical events, including changing conditions from hostilities in Ukraine and in Israel and the Gaza Strip, increasing rates of inflation and rising interest rates, on our business operations and expectations as well as those risks set forth in the Risk Factors section of BridgeBios most recent Annual Report on Form 10-K, and BridgeBios other filings with the U.S. Securities and Exchange Commission. Moreover, BridgeBio operates in a very competitive and rapidly changing environment in which new risks emerge from time to time. These forward-looking statements are based upon the current expectations and beliefs of BridgeBios management as of the date of this press release and are subject to certain risks and uncertainties that could cause actual results to differ materially from those described in the forward-looking statements. Except as required by applicable law, we assume no obligation to update publicly any forward-looking statements, whether as a result of new information, future events or otherwise.

BridgeBio Contact:Vikram Balicontact@bridgebio.com(650)-789-8220

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Molecular genetics made simple – PMC – National Center for …

Wednesday, September 4th, 2024

Abstract

Genetics have undoubtedly become an integral part of biomedical science and clinical practice, with important implications in deciphering disease pathogenesis and progression, identifying diagnostic and prognostic markers, as well as designing better targeted treatments. The exponential growth of our understanding of different genetic concepts is paralleled by a growing list of genetic terminology that can easily intimidate the unfamiliar reader. Rendering genetics incomprehensible to the clinician however, defeats the very essence of genetic research: its utilization for combating disease and improving quality of life. Herein we attempt to correct this notion by presenting the basic genetic concepts along with their usefulness in the cardiology clinic. Bringing genetics closer to the clinician will enable its harmonious incorporation into clinical care, thus not only restoring our perception of its simple and elegant nature, but importantly ensuring the maximal benefit for our patients.

All inheritable traits of living organisms are determined by their genetic material, the genome, a long nucleic acid called deoxyribonucleic acid (DNA). The DNA consists of 3109 nucleotides. Each nucleotide is made up of a sugar (deoxyribose), a nitrogenous base (adenine (A), guanine (G), cytosine (C) or thymine (T)) and a phosphate group () [1,2]. The four nitrogenous bases are divided into two groups: purines (including A and G) have two joined heterocyclinc rings and pyrimides (including C and T) have a single heterocyclic ring. Successive sugar and phosphate residues are linked by covalent phosphodiester bonds, forming the backbone of the DNA molecule and a nitrogenous base is attached to each sugar. The stability of DNA is primarily dependent on the strong covalent bonds that connect the constituent atoms of its linear backbone, and also on a number of weak non-covalent bonds that exist. Meanwhile, because of the phosphate group charges present in each nucleotide, DNA is negatively charged and therefore highly soluble in water.

The chemical structure of a nucleotide including the phosphate (yellow), the sugar (deoxyribose in green) and adenine as the nitrogenous base (pink).

The DNA structure is a double helix, in which two DNA molecules are held together by weak hydrogen bonds [37]. Hydrogen bonding occurs between laterally opposed bases, of the two strands according to Watson-Crick rules: A specifically binds to T, and G to C. The two strands are therefore complementary [8]. As the phosphodiester bonds link carbon atoms number 3 and number 5 of successive sugar residues, the end of each DNA strand will have a terminal sugar residue where carbon atom number 5 is not linked to a neighboring sugar residue, and is therefore called 5 end. The other end of the molecule is similarly called 3 end. The two DNA strands are antiparallel because they always associate (anneal) in such a way that the 53 direction of one DNA strand is the opposite to that of its partner. To describe a DNA sequence, the sequence of bases of one strand only, are usually provided, and are provided in the 53 direction. This is the direction of DNA replication as well as transcription.

The human DNA is estimated to be approximately 2 m long. In order for it to fit in the 10 m nucleus of human cells it is imperative that it is tightly folded. The DNA double helix is therefore subjected to at least two levels of coiling: the first involving coiling around a central core of eight histone proteins, resulting in units called nucleosomes, which are connected by spacer DNA; and the second involving coiling of this string of nucleosomes into a chromatin fiber [3]. During the different phases of the cell cycle, the DNA varies in the extent of its condensation. For example, during interphase the chromatin fibers are organized into long loops, whereas in metaphase chromosomes, the DNA is compacted to about 1/10,000 of its stretched out length. In humans there are 24 different chromosomes, namely 122 autosomes, and sex chromosomes X and Y [9]. Since humans are diploid organisms, our DNA is found in two copies, one inherited from each parent, and is folded into 46 chromosomes. Among the major DNA sequence elements of each chromosome are: the centromeres (constriction site where sister chromatics are joined and chromosomes link to the mitotic spindle), the telomeres (structures capping the ends of chromosomes) and the origins of replication (where DNA replication begins). Chromatin is encountered in extended (euchromatin) or highly condensed (heterochromatin) states, which in turn affect the transcriptional status of the corresponding DNA regions (being active or inactive, respectively) [10]. Under the light microscope, these regions appear as light and dark bands of metaphase chromosomes ().

Diagrammatical representation of the human karyotype of haploid chromosome set with X and Y as the sex chromosome complement. The alternating light and dark bands are characteristic of each chromosome in standard G-banding karyotype, and they represent euchromatic and heterochromatic regions, respectively.

Genomic DNA contains coding as well as non-coding regions. The non-coding regions are involved in DNA folding, chromosome formation, chromatin organization within the nucleus, regulation of transcription and more [1114]. The coding regions are responsible for the transcription of RNA molecules and ultimately protein synthesis.

The genes are stretches of DNA that code for polypeptides. Specifically, genes contain regulatory and coding regions, which regulate their transcription or code for the polypeptide product, respectively. A key regulatory region is the promoter, where the transcription machinery binds for transcription to be initiated. Other possible regulatory regions include enhancers, which regulate gene expression in different tissues or cells, and can be found upstream or downstream of the coding region, as far as several thousand bases. The coding regions are represented by exons, whose size and number varies among different genes. Interspersed between gene exons, there are non-coding sequences named introns, which tend to make up the largest percentage of a gene. The human genome is estimated to contain approximately 20,000 different genes [15]. Interestingly, it is estimated that 80% of the human genome is expressed, yet only 2% is coding for proteins [16].

The central dogma of molecular biology was first stated in 1958 and re-stated in 1970 by Francis Crick [17,18]. According to this dogma there are three major classes of biopolymers: DNA, RNA and protein, and three classes of direct transfer of information that can occur between these biopolymers: general transfers, special transfers and unknown transfers. Of these, only the general transfers are believed to occur normally in most cells and they involve DNA replication to DNA, DNA transcription to mRNA and mRNA translation to proteins ().

The central dogma of molecular biology, as it currently applies in most cells (general transfers = black),or under specific conditions (in some viruses and in vitro: special transfers = grey).

The transfer of information from the DNA to the protein level is achieved step-wise and starts with the transcription of a gene to mRNA. Specifically, the transcription machinery (including RNA polymerase and a variety of transcription factors) binds to the gene promoter, the double helix opens in that location and a single strand primary mRNA molecule (hn-RNA), complementary to that gene sequence, is synthesized base by base () [19]. RNA as opposed to DNA, is a single strand nucleic acid containing ribose instead of deoxyribose and uracil instead of thymine. The heterogenous (hn)-RNA molecules go through a series of processing steps including a 5 cap, a poly-A (50250 adenine molecules and a 70kDa protein) tail at the 3 end and splicing, to remove the intronic sequences () [2023]. Alternative splicing can also occur, which removes certain exons and contributes to the diversity of proteins any single gene can produce [24].

During transcription the transcription machinery (including RNA polymerase and a variety of transcription factors) binds to the gene promoter, the double helix opens in that location and a single strand primary mRNA molecule (hn-RNA),complementary to that gene sequence, is synthesized base by base.

The promoter and enhancer elements of each gene are involved in gene transcription to precursor mRNA (hn-RNA) molecules which are then appropriately processed to give mature mRNA.

The mature mRNA molecules can be translated to proteins [25]. This process takes place in the cytoplasm with the aid of ribosomes, which are complexes of RNAs and proteins called ribonucleoproteins. The ribosomes are divided into two subunits: the smaller subunit binds to the mRNA, while the larger subunit binds to the tRNA which carries the amino acids. When a ribosome finishes reading a mRNA, these two subunits split apart. In particular, ribosomes bind mRNA and read through it as triplet codons, usually starting with an AUG triplet (initiation codon) downstream of the ribosome binding site. For each codon, the ribosome, with the aid of initiation and elongation factors, recruits a complementary tRNA molecule, which in turn carries a specific amino acid. Each codon codes for a specific amino acid as shown in . As the amino acids are linked into the growing peptide chain, they begin folding into the correct conformation. The translation process ends with the stop codons UAA, UGA or UAG. The nascent polypeptide chain is then released from the ribosome as a mature protein [25]. In some cases the new polypeptide chain requires additional processing to make a mature protein. Mature proteins in turn can be subjected to a range of post-translational modifications. Their ultimate roles in cell physiology can be highly variable including cytoarchitecture, enzymatic activity, intracellular signalling, transportation, communication etc.

Genetic variation refers to genetic difference between individuals within or between different populations. This variation is what renders each individual unique in its phenotypic characteristics. Genetic variation occurs on many different scales, ranging from gross alterations in the human karyotype to single nucleotide changes. These variations can be divided in polymorphisms and mutations.

Polymorphisms are defined as variants found in >1% of the general population [26]. Due to their high frequency they are considered unlikely to be causative of genetic disease. They can however, together with other genetic and environmental factors, affect disease predisposition, disease progression or response to treatments (e.g. [27]). Three common types of polymorphisms are the single nucleotide polymorphisms (SNPs), small insertions/deletions (indels) and the large-scale copy number polymorphisms (CNPs or CNVs). SNPs are single base changes that occur on average about every 1000 bases in the genome. Their distribution is not homogenous and they occur more frequently in non-coding regions where there is less selective pressure () [28,29]. Most SNPs are neutral; yet 35% are thought to have a functional role, i.e. affect the phenotype of the individual carrying them. Depending on their effect at the protein level, SNPs can be characterized as synonymous (coding for the same amino acid as the wild type DNA sequence) or non-synonymous (coding for a different amino acid than the wild type DNA sequence) [29]. Indels are small insertions or deletions ranging from 1 to 10,000 bp in length, although the majority involves only a few nucleotides [30,31]. They are considered the second most common form of variation in the human genome following SNPs, with over 3 million short indels listed in public databases. CNVs are variations in the number of copies of DNA regions. They can involve loss of one or both copies of a region of DNA, or the presence of more than two copies of this region. They can arise from DNA deletions, amplifications, inversions or insertions and their size can range from 1 kb (1,000 bases) to several megabases [32]. SNPs, indels and CNVs can either be inherited or arise de novo.

A Single-Nucleotide DNA Polymorphism (SNP) is defined as a single DNA variation detected when a single nucleotide in the genome (or other common sequence) is different between species or paired chromosomes in an individual. In this case there is a substitution of a C (Cytosine) in a T (Tymine) which causes the change of a G (Guanine) in a A (Adenine) in the complementary DNA strand.

Mutations on the other hand, are rare (by some defined as variations with <1% frequency in the general population, although there are many exceptions to this rule) changes in the DNA sequence that can change the resulting protein, impair or inhibit the expression of the gene, or leave both the gene function and protein levels/structure unaffected. Although a variety of definitions have been considered over the years, for most scientists mutation has become synonymous with disease. They can arise during DNA replication or as a result of DNA damage through environmental agents including sunlight, cigarette smoke and radiation. A variety of different types of mutations exist and the terminology used to describe them is based on their effect either on DNA structure, on protein product function, or on the fitness of the individual carrying them.

In terms of DNA structure modification, mutations can be categorized as:

A) point mutations in which a single nucleotide is changed for a different one (). These are divided into missense mutations (meaning that when translated this DNA sequence leads to the incorporation of a different amino acid into the produced protein, with possible implications in the protein function), nonsense mutations (where the new nucleotide changes the sequence so that a stop codon is formed earlier than in the normal sequence and therefore the produced protein is truncated), silent mutations (where the nucleotide change does not affect the amino acid in the corresponding position of the produced protein, and therefore the final protein product remains unaltered), and splice-site mutations (which affects the splice site invariant donor or acceptor dinucleotides (5GT or 3AG).

Different types of mutation and possible conseuquence on protein function:A) missense mutation; B) nonsense mutation; C) deletion; D) inversion.

B) insertions in which one or more nucleotides are inserted in the normal DNA sequence, therefore disrupting it. This can have a moderate or severe effect on the corresponding mutant protein product. For example it can affect the splicing or the reading frame ( frame-shift mutations), therefore leading an incorrect reading of all the downstream nucleotide triplets and consequently their translation to a significantly different and/or truncated amino acid sequence.

C) deletions in which one or more nucleotides are deleted from the normal DNA sequence (). As in the case of insertions this can lead to minor (e.g. single amino acid changes) or major protein defects (e.g. reading frame modifications with implications for the entire downstream amino acid sequence of the mutant protein). When larger chromosomal regions are deleted, multiple genes can be lost and/or previously distant DNA sequences can now be juxtaposed (such juxtapositions can lead, for example, to the production of abnormal proteins containing sequences from different genes that have now been merged or abnormal expression of otherwise normal proteins by deletions affecting their upstream regulatory regions).

D) amplifications leading to multiple copies of chromosomal regions and consequently to an increased number of copies of the genes located within them and increased levels of the corresponding proteins.

E) inversions involving the reversal of the orientation of a DNA segment, with variable implications for the protein product, similar to the ones described above ().

F) translocations where regions from non-homologous chromosomes are interchanged.

Mutations can affect the expression of a transcript and its corresponding protein, or modify the structure of the resulting protein therefore impairing its function [33]. Depending on their functional effect, mutations can be classified as dominant negative (the mutant gene product acts antagonistically to the wild-type allele), gain-of-function (the mutant gene product gains a new and abnormal function), and loss-of-function (the mutant gene product has less or no function). Loss-of-function mutations can be associated with haploinsufficiency, a common occurrence in the molecular cardiomyopathy setting.

Haploinsufficiency occurs when the gene product of one of the two alleles in an individual is lost due to a DNA deletion or to instability/degradation of the mutant protein. Other terms used to describe the effect of a mutation on the fitness of the carrier are: harmful or deleterious mutations (decreases the fitness of the carrier), beneficial or advantageous mutations (increases the fitness of the carrier), and lethal mutations (leading to the death of the individual carrying them).

In the field of cardiovascular genetics, when a new genetic variant is identified a common occurrence given the large number of genes and different variants thereof being screened it is crucial to first determine whether it represents a benign polymorphism or a pathogenic mutation. Identifying pathogenic mutations enables the characterization of the molecular mechanisms of pathogenesis, and more importantly for the clinical setting, it allows the development of genetic tests for mutation detection in other family members (including pre-symptomatically) as well as unrelated patients with similar phenotypes (see section on Cardiovascular genetics in clinical practice).

The Clinical Molecular Genetics Society1 and the American College of Medical Genetics2 have issued guidelines to facilitate the determination of the potential pathogenic role of a novel/unclassified variant (). The Human Gene Mutation Database,3 along with locus-specific or disease-specific mutation databases, are valuable resources for first deciphering whether a detected genetic variant represents a known mutation. The databases Online Mendelian Inheritance in Man,4 dbSNP5 and Ensembl,6 along with thorough searches of the literature via PubMED, Google Scholar, Scopus or the Web of Science, can also provide valuable information. From thereon carefully matched controls need to be included in the study populations, co-occurrence with known (in trans) deleterious mutations in the same gene needs to be ruled out, co-segregation with the disease in the family represents useful information, and occurrence of the novel variant concurrent with the incidence of a sporadic disease can be a strong indicator. Bioinformatically, it is important to determine if the unclassified variant leads to an animo acid change and how different the biophysical properties of the new amino acid are: the greater the difference, the higher the likelihood to possess a pathogenic role. Similarly, the more conserved a DNA region is across species, the greater an impact any variations therein are likely to have. A range of in silico analysis tools can also be used for the predication of a pathogenic effect (e.g. Align GVGD, Sorting Intolerant From Tolerant [SIFT], Polyphen, and Alamut) or the prediction of splice sites. One of the best means of determining pathogenicity, however, is the use of suitable functional assays and transgenic animal models [34,35].

From mutation to disease. A DNA mutation can cause qualitative or quantitative changes at the protein level, leading to either a dysfunctional/non-functional protein product and/or aberrant protein expression levels. Both mechanisms can in turn lead to CVD.

Once a mutation has been directly associated with a pathological phenotype a number of additional parameters need to be evaluated in order to maximize its value in the clinical setting. These parameters relate to the mode of inheritance of a mutation, which impacts directly the chances of detecting it in other family members of the patient, or his/her offspring. The categorization gonosomal or autosomal depends on whether the mutations are located on either of the sex chromosomes or not. For example a mutation on the Y chromosome will only affect males. The dominant or recessive nature relates to the need of one or both alleles, respectively, to carry the mutation for the pathogenic phenotype to develop. In hypertrophic cardiomyopathy (HCM) a number of cases have been reported with homozygosity for the pathogenic mutation. Nishi et al. first reported homozygosity for a MYH7 mutation in two brothers with HCM [36]. Homozygous mutations were also detected in MyBPC in HCM patients [37]. The patients who harbour homozygous mutations present with a more severe clinical phenotype than their heterozygous family members. These observations support the notion of a mutation dosage effect, in which a larger amount of the defective protein leads to a greater disruption of the sarcomere function and results in a more severe clinical outcome. For example, in our Egyptian HCM cohort, none of the mutation-positive patients were homozygous for the mutation detected (data not published) which might be explained either by the rarity of its occurrence in the specific cohort or due to technical limitations in the mutation screening method ().

Mutation screening by denaturing high performance liquid chromatography (dHPLC) using WAVE, Transgenomics. dHPLC can be used as an initial mutation screening method, being dependent on heteroduplex (wild type-mutant) formation, and variant profiles from the wild pattern are subsequently sequenced. Note however, that dHPLC is not capable of detecting homozygosity.

Importantly, a number of exceptions apply to the aforementioned inheritance mode rules, such as in the case of incomplete penetrance (a percentage of the individuals carrying the mutation fail to present the corresponding trait) where mutation carriers may not present with any symptoms even in the presence of a dominant mutation. Furthermore, the phenomena of variable expressivity (variations in a phenotype among individuals carrying a particular genotype) and epistasis (one gene is modified by one or several other genes, e.g. modifier genes) can lead to a range of pathological characteristics despite the presence of the same mutation. These parameters, potentially in combination with environmental factors, can often lead to significant clinical heterogeneity in most inherited CVDs, between unrelated individuals as well as family members carrying the same mutation () [38].

Role of genetic and environmental factors in determining the spectrum of the disease phenotype.(Strachan T, Read AP. Genes in pedigrees and populations in Human molecular genetics 3. 3rd ed. London; New York: Garland Press; 2004).

Another exception is this of compound heterozygotes (carriers of two different mutations on the two alleles of the same gene) or double heterozygotes (carriers of mutations in two different genes), which carry one copy of each mutation, yet they can develop the disease. Notably, the concomitant presence of multiple genetic defects contributing to the same disease is usually associated with a more severe clinical phenotype. For example, in HCM the presence of multiple pathogenic mutations could be included amongst the risk stratification criteria [39]. Multiple mutations have been observed in about 5% of HCM patients and they are usually associated with higher septal thickness and worse clinical outcomes, such as heart failure and sudden death [4043]. Double heterozygosity is commonly detected in the Myosin heavy chain (MYH7) and Myosin binding protein C (MyBPC) genes, probably because they represent the most commonly involved genes in the pathogenesis of HCM. Compound heterozygosity in MyBPC however, leading to the absence of a normal protein, has been reported to results in neonatal death in two independent cases, where the parents were each heterozygous for one of the mutations [44]. Similarly to HCM, double heterozygosity has been reported in other CVDs such as long QT, with a similar frequency of 5% [45].

Hereditary CVDs include a variety of different aspects and structures of the cardiovascular system such as inherited cardiomyopathies, arrhythmias, metabolic disorders affecting the heart, congenital heart diseases, as well as vascular disorders such as Marfan syndrome [4648]. Over the past two decades significant progress has been made towards the identification of the genetic basis of CVD, with tens of genes now known to be implicated in almost all of the different disorders. The magnitude of the role of genetics however, remains elusive. Although in some cases the pathogenesis appears to involve complex mechanisms and multifactorial (genetic and environmental) aetiology, multigenic inheritance (e.g. familial hypercholesterolemia: LDLR, APOB, ABCG5, ABCG8, ARH, PCSK9; hypertrophic cardiomyopathy: MYH7, TNNT2, TPM1, TNNI3, MYL2, MYBPC3, ACTC, MYL3) or even monogenic, also known as Mendelian, inheritance (e.g. Marfan syndrome: FNB1) has been described. Pinpointing the gene(s) and their specific mutations that lead to each pathological phenotype can give rise to valuable, complementary genetic diagnostic/prognostic tools for significantly improved clinical management of CVD patients and their families.

For example, the recently published consensus statement on the state of genetic testing for cardiomyopathies and channelopathies has elegantly presented the list of different genes which contribute by >5% to these inherited disorders. [49,50]. There are more than 50 distinct channelopathy/cardiomyopathy-associated genes with hundreds of mutations discovered to date. Each of these mutations/genes usually accounts for a small percentage of the reported cases, while in many cases the causative mutation/gene is never identified. For example, in channelopathies a mutation is found in <20% of short QT syndrome cases and up to 75% in long QT syndrome cases. An exceptional scenario is this of mutations in the cardiac ryanodine receptor (RYR2) gene in catecholaminergic polymorphic ventricular tachychardia, which account for up to 65% of affected patients [51]. In cardiomyopathies, positive genetic testing results range in frequency from <20% in restrictive cardiomyopathy to 60% in familial HCM. Despite the fact that two decades ago, HCM was termed a disease of the sarcomere involving at least 8 causative genes, the rate of mutation detection ranged in frequency from 2530% in MyBPC and MYH7 to 5% in TNNT2 and TNNTI3, and 1% in other sarcomeric genes [42,52]. Additionally, there are HCM phenocopies (same phenotype) associated with non-sarcomeric gene mutations and different modes of inheritance, which may on occasion be difficult to exclude from sarcomeric HCM based on clinical evaluation alone. Therefore, multiple genes need to be screened for a multigenic disease such as HCM.

Overall, our understanding of the genetic basis of CVD has been rapidly expanding over the years with important lessons learned both on monogenic as well as complex disease forms [53]. However, the true value of these findings lies in their translation to the clinical setting and their utilisation towards improved CVD diagnosis, prognosis and treatment. Along these lines, genetic testing is currently available for a number of CVDs in the form of clinical service in most Western countries, and increasingly in the developing world.

Genetic testing can serve three main goals in the clinical practice: first to determine the mode of inheritance of the specific disease in the specific family and identify if there is risk for other family members; second to organize the clinical assessment of unaffected family members through predictive genetic testing so as to distinguish those who are at risk for the disease and should have regular cardiac follow-up (mutation carriers) and those who are not (mutation non-carriers); third, following the establishment of distinct genotypephenotype correlations, the application of genetic testing in disease diagnosis, prognosis and personalized treatment (i.e. identification of the drugs to which each patient will respond best) [54].

The clinical value of genetic screening of a cardiovascular disease patient is therefore valuable initially at the diagnostic/prognostic/therapeutic level, provided the genotypephenotype associations have been established first. These associations vary considerably among different cardiovascular diseases, different genes and different mutations thereof. The relevance of genetic testing towards these three levels of clinical management is possibly best shown in the setting of the long QT syndrome [49,50]. It is critical to note however, that genetic testing in the cardiovascular disease setting cannot be the basis for clinical management of patients, but can serve a complementary role to the comprehensive clinical evaluation to better address the patient's and his/her family's needs.

Identifying the causative mutation of a proband further allows the genetic screening of its family members, a process of marked predictive power and therefore high importance in the cardiovascular clinic [55]. The significance of such pre-symptomatic genetic testing for the probands family members ranges from ensuring that unaffected mutation carriers receive regular clinical follow-up and prophylactic treatment (where available) to reassurance that clinically suspicious findings are unlikely to be indicative of the specific form of the disease in the absence of the specific family mutation (e.g. ) [56,57]. Importantly however, a negative genetic test result in the proband's family members cannot by itself exclude the presence of disease in general, since a large number of different genes and a variety of mutations thereof can contribute to the same or a different pathological cardiovascular phenotype and by chance, a family member could be a carrier of a different gene mutation.

Pedigree of an HCM positive family from the BA HCM Study. A pathogenic mutation in MYH7 exon 23 (Glu927Lys) was detected in the proband II-4. Echo screening of all siblings was undertaken, and sister II-10 was found to have an interventricular septal measurement of 14 mm. Genetic screening of all family members excluded HCM diagnosis for the sister (II-10).However, the symptom free and echo clear son of the proband, was positive for the mutation and therefore given a pre-symptomatic diagnosis of HCM at the age of12 years. Symbols in white represent unaffected individuals, in black are individuals with HCM based on clinical or genetic findings, and in blue are individuals who have not been screened by echo or genetic testing (unpublished data).

Genetic testing of children in the family has always posed an ethical concern, particularly for adult-onset diseases. Therefore pre-symptomatic testing of children should be extensively discussed with the family after a mutation has been identified in the proband, and in the context of the specific cardiovascular disease [58]. In cases where pre-symptomatic genetic screening and mutation identification has direct implications on the child's clinical follow-up, lifestyle adaptations and preventive treatments, it would be valuable to proceed with genetic testing, upon the parents approval. For example, for long QT syndrome and catecholaminergic polymorphic ventricular tachychardia, and occasionally in high risk HCM families, in which preventive measures or prophylactic therapy is advisable for asymptomatic mutation positive family members, genetic testing should be undertaken in early childhood, i.e. regardless of age. On the other hand, for late-onset and/or reduced penetrance diseases, it is reasonable to proceed with clinical monitoring as needed during childhood, leaving the genetic testing option open for when the individual reaches adulthood [49,50]. When a child has already presented with a CVD, the use of genetic testing is complementary to all other clinical tests, and especially valuable for identifying other family members at risk, since childhood-onset cases, even when presumed as sporadic, can often have a genetic aetiology. For example, approximately half of the presumed sporadic cases of childhood-onset hypertrophy have genetic causes [59].

Although the translation of molecular genetics to routine clinical practice is slow, a series of certified genetic testing centers (www.genetests.org) have been established, and guidelines have already been issued for a number of cardiovascular diseases such as HCM, dilated cardiomyopathy (DCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC) [60,61]. The consensus is that a minimum of three to four generation family history needs to be obtained, the relatives at risk need to be identified and directed for clinical screening, the potential genetic nature of the disease needs to be explained, and the possibility of genetic testing should be discussed where appropriate.

In order to follow these guidelines, cardiology clinics around the world need to ensure that cardiologists are provided with appropriate training in key genetic concepts, along with information on the latest developments in cardiovascular genetics and the best means to apply them in the clinic. Importantly, the close interaction between cardiologists, geneticists and genetic counsellors, especially in complex cases, will significantly expedite the benchside-to-bedside translation of the latest genetic discoveries and optimize the clinical care provided to the patient [62,63]. For example, when routine cardiovascular genetic screening fails to detect the causative mutations, screening can be extended to include broad gene panels and/or application of high throughput technologies. Similarly, in cases where new mutations are identified, targeted genetic tests can be designed, if needed, for screening family members at risk. Currently, different modes of cardiologist-geneticist interactions are being adopted in clinical settings around the world, a process that requires time, continuing education and to some extent, reorganization of health systems [64]. An example of such an evolving system of interdisciplinary interactions is that of the Egyptian National Genetic study of HCM ().

Combined clinical and genetic evaluation of CVD patients will allow for improved disease management and patient care.

In conclusion, cardiovascular genetic testing is valuable for improving the standards of care for CVD patients and their families at the diagnostic, prognostic and therapeutic level. Importantly, for healthcare systems worldwide, it further represents a cost-effective approach by enabling the timely identification of individuals at risk, ensuring regular follow-up only for the individuals at risk and early disease detection, as well as enabling, where possible, the use of disease preventative measures in order to minimize the environmental contributing factors [65]. To this end, clinical cardiovascular genetics is increasingly emphasized in undergraduate and postgraduate medical education and incorporated in cardiological clinics worldwide [54].

The tremendous technological advancements over the past decade have empowered the discovery of new biological concepts and the emergence of entirely new scientific fields. Among them, cardiac systems genetics a systems-based analysis of genetic variants considering all different levels spanning from their effect on the cardiac transcriptome, proteome, metabolome to organ physiology/pathophysiology (phenome) (). The global analysis of the downstream functional molecular and cellular implications of different genetic variants, will allow the meaningful integration of molecular and clinical data in a powerful way.

To fully unravel the intricate pathways regulating cardiac physiology and pathophysiology the global studies of the human genome will need to be extended to similar studies at the epigenome (chemical changes to the DNA and histone affecting the chromatin structure and function of the genome),transcriptome (the full set of transcripts produced from the human DNA), miRNome (the full set of microRNAs produced from the human DNA), proteome (the full set of proteins) and metabolome (full set of metabolites) levels.

Systems genetics will in turn, serve as an integral part of network medicine, an advanced form of molecular medicine, where perturbations, rather than individual molecules, are investigated as the underlying causes of complex diseases [66]. In cardiology, examples of important first steps in this direction are the identification of cardiac gene expression signatures related with response to left ventricular assist device implantation [67,68] and peripheral leukocyte expression signatures indicative of post-cardiac transplantation tissue rejection [69]. Parameters such as epigenetics and microRNAs are increasingly integrated in network medicine, adding new dimensions to the intricate mechanisms of cardiovascular disease (e.g. [70,71]). A likely next addition to network medicine, based on emerging new data [72,73], could be this of metagenomics the genomic investigation of micro-organisms inside the human body, and their effect on the global networks orchestrating human cardiac physiology/pathophysiology.

Cardiology is rapidly transformed with powerful new technologies expediting the acquisition of new knowledge and exciting new discoveries enriching our understanding of the intricate genotypephenotype correlations. The close interaction of cardiologists and geneticists is facilitating the transition of novel findings to clinical practice and vice versa. It is also enabling the rapid establishment of appropriate research strategies to address emerging clinical questions. Ultimately the convergence of the two disciplines promises to transform the way we perceive, manage and treat CVD.

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