Diverging Concepts and Novel Perspectives in Regenerative Medicine

Understanding exosomes: Part 2-Emerging leaders in regenerative medicine

Exosomes are the smallest subset of extracellular signaling vesicles secreted by most cells with the ability to communicate with other tissues and cell types over long distances. Their use in regenerative medicine has gained tremendous momentum recently due to their ability to be utilized as therapeutic options for a wide array of diseases/conditions. Over 5000 publications are currently being published yearly on this topic, and this number is only expected to dramatically increase as novel therapeutic strategies continue to be developed. Today exosomes have been applied in numerous contexts including neurodegenerative disorders (Alzheimer's disease, central nervous system, depression, multiple sclerosis, Parkinson's disease, post-traumatic stress disorders, traumatic brain injury, peripheral nerve injury), damaged organs (heart, kidney, liver, stroke, myocardial infarctions, myocardial infarctions, ovaries), degenerative processes (atherosclerosis, diabetes, hematology disorders, musculoskeletal degeneration, osteoradionecrosis, respiratory disease), infectious diseases (COVID-19, hepatitis), regenerative procedures (antiaging, bone regeneration, cartilage/joint regeneration, osteoarthritis, cutaneous wounds, dental regeneration, dermatology/skin regeneration, erectile dysfunction, hair regrowth, intervertebral disc repair, spinal cord injury, vascular regeneration), and cancer therapy (breast, colorectal, gastric cancer and osteosarcomas), immune function (allergy, autoimmune disorders, immune regulation, inflammatory diseases, lupus, rheumatoid arthritis). This scoping review is a first of its kind aimed at summarizing the extensive regenerative potential of exosomes over a broad range of diseases and disorders.

Stem cells or their exosomes: which is preferred in COVID-19 treatment?

It only took 8 months for the pneumonia caused by a previously unknown coronavirus to turn into a global pandemic of unprecedentedly far-reaching implications. Failure of the already discovered treatment measures opened up a new opportunity to evaluate the potentials of mesenchymal stem cells and their extracellular vesicles (EVs), exosomes in particular. Eventually, the initial success experienced after the use of MSCs in treating the new pneumonia by Lnge and his team backed up the idea of MSC-based therapies and pushed them closer to becoming a reality. However, MSC-related concerns regarding safety such as abnormal differentiation, spontaneous malignant and the formation of ectopic tissues have triggered the replacement of MSCs by their secreted exosomes. The issue has been further strengthened by the fact that the exosomes leave similar treatment impacts when compared to their parental cells. In recent years, much attention has been paid to the use of MSC-derived exosomes in the treatment of a variety of diseases. With a primary focus on COVID-19 and its current treatment methods, the present review looks into the potentials of MSCs and MSC-derived exosomes in battling the ongoing pandemic. Finally, the research will draw an analogy between exosomes and their parental cells, when it comes to the progresses and challenges in using exosomes as a large-scale treatment method.

The Potential Role of Extracellular Vesicles in COVID-19 Treatment: Opportunity and Challenge

SARS-CoV-2 infection has become an urgent public health concern worldwide, severely affecting our society and economy due to the long incubation time and high prevalence. People spare no effort on the rapid development of vaccine and treatment all over the world. Amongst the numerous ways of tackling this pandemic, some approaches using extracellular vesicles (EVs) are emerging. In this review, we summarize current prevalence and pathogenesis of COVID-19, involving the combination of SARS-CoV-2 and virus receptor ACE2, endothelial dysfunction and micro thrombosis, together with cytokine storm. We also discuss the ongoing EVs-based strategies for the treatment of COVID-19, including mesenchymal stem cell (MSC)-EVs, drug-EVs, vaccine-EVs, platelet-EVs, and others. This manuscript provides the foundation for the development of targeted drugs and vaccines for SARS-CoV-2 infections.

Mesenchymal Stem Cells and COVID-19: Cure, Prevention, and Vaccination

COVID-19 disease has been a global health problem since late 2019. There are many concerns about the rapid spread of this disease, and yet, there is no approved treatment for COVID-19. Several biological interventions have been under study recently to investigate efficient treatment for this viral disease. Besides, many efforts have been made to find a safe way to prevent and vaccinate people against COVID-19 disease. In severe cases, patients suffer from acute respiratory distress syndrome usually associated with an increased level of inflammatory cytokines, called a cytokine storm. It seems that reequilibrating the hyperinflammatory response of the host immune system and regeneration of damaged cells could be the main way to manage the disease. Mesenchymal stem cells (MSCs) have been recently under investigation in this regard, and the achieved clinical outcomes show promising evidence for stem cell-based therapy of COVID-19. MSCs are known for their potential for immunomodulation, defense against virus infection, and tissue regeneration. MSCs are a newly emerged platform for designing vaccines and show promising evidence in this area. In the present study, we provided a thorough research study on the most recent clinical studies based on stem cells in the treatment of COVID-19 while introducing stem cell exclusivities for use as an immune disorder or lung cell therapy and its potential application for protection and vaccination against COVID-19.

Intratracheal administration of mesenchymal stem cell-derived extracellular vesicles reduces lung injuries in a chronic rat model of bronchopulmonary dysplasia

Early therapeutic effect of intratracheally (IT)-administered extracellular vesicles secreted by mesenchymal stem cells (MSC-EVs) has been demonstrated in a rat model of bronchopulmonary dysplasia (BPD) involving hyperoxia exposure in the first 2 postnatal weeks. The aim of this study was to evaluate the protective effects of IT-administered MSC-EVs in the long term. EVs were produced from MSCs following GMP standards. At birth, rats were distributed in three groups: (a) animals raised in ambient air for 6 weeks (n = 10); and animals exposed to 60% hyperoxia for 2 weeks and to room air for additional 4 weeks and treated with (b) IT-administered saline solution (n = 10), or (c) MSC-EVs (n = 10) on postnatal days 3, 7, 10, and 21. Hyperoxia exposure produced significant decreases in total number of alveoli, total surface area of alveolar air spaces, and proliferation index, together with increases in mean alveolar volume, mean linear intercept and fibrosis percentage; all these morphometric changes were prevented by MSC-EVs treatment. The medial thickness index for <100 µm vessels was higher for hyperoxia-exposed/sham-treated than for normoxia-exposed rats; MSC-EV treatment significantly reduced this index. There were no significant differences in interstitial/alveolar and perivascular F4/8-positive and CD86-positive macrophages. Conversely, hyperoxia exposure reduced CD163-positive macrophages both in interstitial/alveolar and perivascular populations and MSC-EV prevented these hyperoxia-induced reductions. These findings further support that IT-administered EVs could be an effective approach to prevent/treat BPD, ameliorating the impaired alveolarization and pulmonary artery remodeling also in a long-term model. M2 macrophage polarization could play a role through anti-inflammatory and proliferative mechanisms.

Holistic Approach of Swiss Fetal Progenitor Cell Banking: Optimizing Safe and Sustainable Substrates for Regenerative Medicine and Biotechnology

Safety, quality, and regulatory-driven iterative optimization of therapeutic cell source selection has constituted the core developmental bedrock for primary fetal progenitor cell (FPC) therapy in Switzerland throughout three decades. Customized Fetal Transplantation Programs were pragmatically devised as straightforward workflows for tissue procurement, traceability maximization, safety, consistency, and robustness of cultured progeny cellular materials. Whole-cell bioprocessing standardization has provided plethoric insights into the adequate conjugation of modern biotechnological advances with current restraining legislative, ethical, and regulatory frameworks. Pioneer translational advances in cutaneous and musculoskeletal regenerative medicine continuously demonstrate the therapeutic potential of FPCs. Extensive technical and clinical hindsight was gathered by managing pediatric burns and geriatric ulcers in Switzerland. Concomitant industrial transposition of dermal FPC banking, following good manufacturing practices, demonstrated the extensive potential of their therapeutic value. Furthermore, in extenso, exponential revalorization of Swiss FPC technology may be achieved via the renewal of integrative model frameworks. Consideration of both longitudinal and transversal aspects of simultaneous fetal tissue differential processing allows for a better understanding of the quasi-infinite expansion potential within multi-tiered primary FPC banking. Multiple fetal tissues (e.g., skin, cartilage, tendon, muscle, bone, lung) may be simultaneously harvested and processed for adherent cell cultures, establishing a unique model for sustainable therapeutic cellular material supply chains. Here, we integrated fundamental, preclinical, clinical, and industrial developments embodying the scientific advances supported by Swiss FPC banking and we focused on advances made to date for FPCs that may be derived from a single organ donation. A renewed model of single organ donation bioprocessing is proposed, achieving sustained standards and potential production of billions of affordable and efficient therapeutic doses. Thereby, the aim is to validate the core therapeutic value proposition, to increase awareness and use of standardized protocols for translational regenerative medicine, potentially impacting millions of patients suffering from cutaneous and musculoskeletal diseases. Alternative applications of FPC banking include biopharmaceutical therapeutic product manufacturing, thereby indirectly and synergistically enhancing the power of modern therapeutic armamentariums. It is hypothesized that a single qualifying fetal organ donation is sufficient to sustain decades of scientific, medical, and industrial developments, as technological optimization and standardization enable high efficiency.

Mesenchymal stromal cells and their secreted extracellular vesicles as therapeutic tools for COVID-19 pneumonia?

The COVID-19 epidemic represents an unprecedented global health emergency, further aggravated by the lack of effective therapies. For this reason, several clinical trials are testing different off-label drugs, already approved for other pathologies. Mesenchymal stem/stromal cells (MSCs) have been tested during the last two decades for the treatment of various pathologic conditions, including acute and chronic lung diseases, both in animal models and in patients. In particular, promising results have been obtained in the experimental therapy of acute respiratory distress syndrome, which represents the most threatening complication of COVID-19 infection. Furthermore, more recently, great interest has been devoted to the possible clinical applications of extracellular vesicles secreted by MSCs, nanoparticles that convey much of the biological effects and of the therapeutic efficacy of their cells of origin. This review summarizes the experimental evidence underlying the possible use of MSCs and of MSC-EVs in severe COVID-19 infection and underlines the need to evaluate the possible efficacy of these therapeutic approaches through controlled studies under the supervision of the Regulatory Authorities.

Present and Future of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is the most common respiratory disorder among infants born extremely preterm. The pathogenesis of BPD involves multiple prenatal and postnatal mechanisms affecting the development of a very immature lung. Their combined effects alter the lung's morphogenesis, disrupt capillary gas exchange in the alveoli, and lead to the pathological and clinical features of BPD. The disorder is ultimately the result of an aberrant repair response to antenatal and postnatal injuries to the developing lungs. Neonatology has made huge advances in dealing with conditions related to prematurity, but efforts to prevent and treat BPD have so far been only partially effective. Seeing that BPD appears to have a role in the early origin of chronic obstructive pulmonary disease, its prevention is pivotal also in long-term respiratory outcome of these patients. There is currently some evidence to support the use of antenatal glucocorticoids, surfactant therapy, protective noninvasive ventilation, targeted saturations, early caffeine treatment, vitamin A, and fluid restriction, but none of the existing strategies have had any significant impact in reducing the burden of BPD. New areas of research are raising novel therapeutic prospects, however. For instance, early topical (intratracheal or nebulized) steroids seem promising: they might help to limit BPD development without the side effects of systemic steroids. Evidence in favor of stem cell therapy has emerged from several preclinical trials, and from a couple of studies in humans. Mesenchymal stromal/stem cells (MSCs) have revealed a reparatory capability, preventing the progression of BPD in animal models. Administering MSC-conditioned media containing extracellular vesicles (EVs) have also demonstrated a preventive action, without the potential risks associated with unwanted engraftment or the adverse effects of administering cells. In this paper, we explore these emerging treatments and take a look at the revolutionary changes in BPD and neonatology on the horizon.

The role of preservation in the variability of regenerative medicine products

Regenerative medicine (RM) has the potential to restore or establish normal function of cells, tissues and organs that have been lost due to age, disease or injury. It is common for the site of raw material collection, site of manufacture and site of clinical use to be different for RM products, and at the same time cells must remain viable and functional during transportation among different sites. Freezing products down to cryogenic temperatures along with cold chain transportation has become an effective method of preserving RM products. The quality of RM products along this supply chain represents the cumulative effects of all of the processing steps and all of the reagents used in the process. A variety of sources of variability in the preservation of RM products can result in both cell losses and greater variability in the quality of RM products. The purpose of this article is to review the sources of variability in the preservation process as well as the methods by which variability can be controlled or avoided.

Raman spectroscopy as a quick tool to assess purity of extracellular vesicle preparations and predict their functionality

Extracellular vesicles (EVs) from a variety of stem cell sources are believed to harbour regenerative capacity, which may be exploited for therapeutic purposes. Because of EV interaction with other soluble secreted factors, EV activity may depend on the employed purification method, which limits cross-study comparisons and therapeutic development. Raman spectroscopy (RS) is a quick and easy method to assess EV purity and composition, giving in-depth biochemical overview on EV preparation. Hereby, we show how this method can be used to characterise EVs isolated from human liver stem cells and bone marrow mesenchymal stem/stromal cells by means of conventional ultracentrifugation (UC) and size exclusion chromatography (SEC) protocols. The obtained EV preparations were demonstrated to be characterised by different degrees of purity and a specific Raman fingerprint that represents both the cell source and the isolation procedure used. Moreover, RS provided useful hints to explore the factors underlying the functional diversity of EV preparations from the same cell source, thus representing a valuable tool to assess EV quality prior to functional assays or therapeutic application.

Intratracheal administration of clinical-grade mesenchymal stem cell-derived extracellular vesicles reduces lung injury in a rat model of bronchopulmonary dysplasia

Mesenchymal stem cells (MSCs) prevent the onset of bronchopulmonary dysplasia (BPD) in animal models, an effect that seems to be mediated by their secreted extracellular vesicles (EVs). The aim of this study was to compare the protective effects of intratracheally (IT) administered MSCs versus MSC-EVs in a hyperoxia-induced rat model of BPD. At birth, rats were distributed as follows: animals raised in ambient air for 2 wk ( n = 10), and animals exposed to 60% oxygen for 2 wk and treated with IT-administered physiological solution ( n = 10), MSCs ( n = 10), or MSC-EVs ( n = 10) on postnatal days 3, 7, and 10. The sham-treated hyperoxia-exposed animals showed reductions in total surface area of alveolar air spaces, and total number of alveoli ( Nalv), and an increased mean alveolar volume (Valv). EVs prompted a significant increase in Nalv ( P < 0.01) and a significant decrease in Valv ( P < 0.05) compared with sham-treated animals, whereas MSCs only significantly improved Nalv ( P < 0.05). Small pulmonary vessels of the sham-treated hyperoxia-exposed rats also showed an increase in medial thickness, which only EVs succeeded in preventing significantly ( P < 0.05). In conclusion, both EVs and MSCs reduce hyperoxia-induced damage, with EVs obtaining better results in terms of alveolarization and lung vascularization parameters. This suggests that IT-administered EVs could be an effective approach to BPD treatment.

Growth arrest-specific gene 6 transfer promotes mesenchymal stem cell survival and cardiac repair under hypoxia and ischemia via enhanced autocrine signaling and paracrine action

Poor cell viability after transplantation has restricted the therapeutic capacity of mesenchymal stem cells (MSCs) for cardiac dysfunction after myocardial infarction (MI). Growth arrest-specific gene 6 (Gas6) encodes a secreted γ-carboxyglutamic acid (Gla)-containing protein that functions in cell growth, adhesion, chemotaxis, mitogenesis and cell survival. In this study, we genetically modified MSCs with Gas6 and evaluated cell survival, cardiac function, and infarct size in a rat model of MI via intramyocardial delivery. Functional studies demonstrated that Gas6 transfer significantly reduced MSC apoptosis, increased survival of MSCs in vitro and in vivo, and that Gas6-engineered MSCs (MSC^Gas6)-treated animals had smaller infarct size and showed remarkably functional recovery as compared with control MSCs (MSC^Null)-treated animals. Mechanistically, Gas6 could enhance phosphatidylinositol 3-kinase (PI3K)/Akt signaling and improve hypoxia-inducible factor-1 alpha (HIF-1α)-driven secretion of four major growth factors (VEGF, bFGF, SDF and IGF-1) in MSCs under hypoxia in an Axl-dependent autocrine manner. The paracrine action of MSC^Gas6 was further validated by coculture neonatal rat cardiomyocytes with conditioned medium from hypoxia-treated MSC^Gas6, as well as by pretreatment cardiomyocytes with the specific receptor inhibitors of VEGF, bFGF, SDF and IGF-1. Collectively, our data suggest that Gas6 may advance the efficacy of MSC therapy for post-infarcted heart failure via enhanced Gas6/Axl autocrine prosurvival signaling and paracrine cytoprotective action.

Residual γH2AX foci induced by low dose x-ray radiation in bone marrow mesenchymal stem cells do not cause accelerated senescence in the progeny of irradiated cells

Mechanisms underlying the effects of low-dose ionizing radiation (IR) exposure (10-100 mGy) remain unknown. Here we present a comparative study of early (less than 24h) and delayed (up to 11 post-irradiation passages) radiation effects caused by low (80 mGy) vs intermediate (1000 mGy) dose X-ray exposure in cultured human bone marrow mesenchymal stem cells (MSCs). We show that γН2АХ foci induced by an intermediate dose returned back to the control value by 24 h post-irradiation. In contrast, low-dose irradiation resulted in residual γН2АХ foci still present at 24 h. Notably, these low dose induced residual γН2АХ foci were not co-localized with рАТМ foci and were observed predominantly in the proliferating Кi67 positive (Кi67+) cells. The number of γН2АХ foci and the fraction of nonproliferating (Кi67-) and senescent (SA-β-gal+) cells measured at passage 11 were increased in cultures exposed to an intermediate dose compared to unirradiated controls. These delayed effects were not seen in the progeny of cells that were irradiated with low-dose X-rays, although such exposure resulted in residual γН2АХ foci in directly irradiated cells. Taken together, our results support the hypothesis that the low-dose IR induced residual γH2AХ foci do not play a role in delayed irradiation consequences, associated with cellular senescence in cultured MSCs.

Challenges and Strategies for Improving the Regenerative Effects of Mesenchymal Stromal Cell-Based Therapies

Cell-based therapies have the potential to revolutionize current treatments for diseases with high prevalence and related economic and social burden. Unfortunately, clinical trials have made only modest improvements in restoring normal function to degenerating tissues. This limitation is due, at least in part, to the death of transplanted cells within a few hours after transplant due to a combination of mechanical, cellular, and host factors. In particular, mechanical stress during implantation, extracellular matrix loss upon delivery, nutrient and oxygen deprivation at the recipient site, and host inflammatory response are detrimental factors limiting long-term transplanted cell survival. The beneficial effect of cell therapy for regenerative medicine ultimately depends on the number of administered cells reaching the target tissue, their viability, and their promotion of tissue regeneration. Therefore, strategies aiming at improving viable cell engraftment are crucial for regenerative medicine. Here we review the major factors that hamper successful cell engraftment and the strategies that have been studied to enhance the beneficial effects of cell therapy. Moreover, we provide a perspective on whether mesenchymal stromal cell-derived extracellular vesicle delivery, as a cell-free regenerative approach, may circumvent current cell therapy limitations.