Immunoprivileged no more: measuring the immunogenicity of allogeneic adult mesenchymal stem cells

Ex vivo-expanded highly pure ABCB5+ mesenchymal stromal cells as Good Manufacturing Practice-compliant autologous advanced therapy medicinal product for clinical use: process validation and first in-human data

Background aim:

Mesenchymal stromal cells (MSCs) hold promise for the treatment of tissue damage and injury. However, MSCs comprise multiple subpopulations with diverse properties, which could explain inconsistent therapeutic outcomes seen among therapeutic attempts. Recently, the adenosine triphosphate-binding cassette transporter ABCB5 has been shown to identify a novel dermal immunomodulatory MSC subpopulation.

Methods:

The authors have established a validated Good Manufacturing Practice (GMP)-compliant expansion and manufacturing process by which ABCB5⁺ MSCs can be isolated from skin tissue and processed to generate a highly functional homogeneous cell population manufactured as an advanced therapy medicinal product (ATMP). This product has been approved by the German competent regulatory authority to be tested in a clinical trial to treat therapy-resistant chronic venous ulcers.

Results:

As of now, 12 wounds in nine patients have been treated with 5 × 10⁵ autologous ABCB5⁺ MSCs per cm² wound area, eliciting a median wound size reduction of 63% (range, 32–100%) at 12 weeks and early relief of pain.

Conclusions:

The authors describe here their GMP- and European Pharmacopoeia-compliant production and quality control process, report on a pre-clinical dose selection study and present the first in-human results. Together, these data substantiate the idea that ABCB5⁺ MSCs manufactured as ATMPs could deliver a clinically relevant wound closure strategy for patients with chronic therapy-resistant wounds.

Hypoxia-induced downregulation of cyclooxygenase 2 leads to the loss of immunoprivilege of allogeneic mesenchymal stem cells

Allogeneic mesenchymal stem cells (MSCs) from young and healthy donors are reported to hold the potential to treat several immunological and degenerative disorders. However, recent data from animal studies and clinical trials demonstrate that immunogenicity and poor survival of transplanted MSCs impaired the efficacy of cells for regenerative applications. It is reported that initially immunoprivileged under in vitro conditions, MSCs are targeted by the host immune system after transplantation in the ischemic tissues in vivo. We performed in vitro (in MSCs) and in vivo (in the rat model of myocardial infarction [MI]) studies to elucidate the mechanisms responsible for the change in the immunophenotype of MSCs from immunoprivileged to immunogenic under ischemic conditions. We have recently reported that a soluble factor prostaglandin E2 (PGE2) preserves the immunoprivilege of allogeneic MSCs. In the current study, we found that PGE2 levels, which were elevated during normoxia, decreased in MSCs following exposure to hypoxia. Further, we found that proteasome-mediated degradation of cyclooxygenase-2 (COX2, rate-limiting enzyme in PGE2 biosynthesis) in hypoxic MSCs is responsible for PGE2 decrease and loss of immunoprivilege of MSCs. While investigating the mechanisms of COX2 degradation in hypoxic MSCs, we found that in normoxic MSCs, COP9 signalosome subunit 5 (CSN5) binds to COX2 and prevents its degradation by the proteasome. However, exposure to hypoxia leads to a decrease in CSN5 levels and its binding to COX2, rendering COX2 protein susceptible to proteasome-mediated degradation. This subsequently causes PGE2 downregulation and loss of immunoprivilege of MSCs. Maintaining COX2 levels in MSCs preserves immunoprivilege in vitro and improves the survival of transplanted MSCs in a rat model of MI. These data provide novel mechanistic evidence that PGE2 is downregulated in hypoxic MSCs which is responsible for the post-transplantation rejection of allogeneic MSCs. Therefore, our data suggest that the new strategies that target CSN5-COX2 signaling may improve survival and utility of transplanted allogeneic MSCs in the ischemic heart.

Mesenchymal Stem Cells in Cardiac Repair: Effects on Myocytes, Vasculature, and Fibroblasts

PURPOSE

Cardiac pathologies remain a dominant cause of morbidity and mortality within the community. The drive to develop therapies capable of repairing damaged heart tissue to achieve clinically significant restoration of function has motivated the pursuit of novel approaches such as cell therapy. To this end, evidence of therapeutic benefits achieved by using mesenchymal stem cells (MSCs) has captured considerable interest despite a relative lack of information regarding the mechanisms involved. This narrative review synthesizes and interprets the current literature describing mechanisms by which MSCs can elicit cardiac repair, thereby directing attention to avenues of further inquiry.

METHODS

OVID versions of MEDLINE and EMBASE were searched for studies describing the role of MSCs in mammalian cardiac repair. Additional studies were sourced from the reference lists of relevant articles and other personal files.

FINDINGS

MSCs elicit cardiac repair in a range of in vitro systems and animal models of diseases such as myocardial infarction and heart failure. Important mechanisms include the preservation of myocardial contractility, the promotion of angiogenesis, and the modulation of fibrosis. Exposing in vitro MSCs to a microenvironment reflective of that encountered in the injured heart seems to potentiate these therapeutic mechanisms.

IMPLICATIONS

Promising results in animal studies warrant continuation of clinical MSC cardiac therapy studies. Paracrine functions of MSCs seem to be the dominant mechanism of cardiac repair over direct cellular effects. Although integral, the MSC secretome remains poorly defined. In addition, most of the mechanistic data within the literature have been derived from animal MSC research, necessitating more human MSC-based work.

The influence of oxygen deprivation and donor age on the effect of statins on human mesenchymal stromal cells

To date, no study evaluated the effect of oxygen deprivation together with statins pretreatment on human mesenchymal stromal cells (MSCs). The aim of our study was to establish the influence of atorvastatin and rosuvastatin on MSC proliferation and cytotoxicity in different oxygenic conditions. Human MSCs isolated from the bone marrow (n = 12) were incubated with statins. The proliferation rate and cytotoxic effect were evaluated in normoxic (21 %O₂) and hypoxic (2%O₂) conditions, also in relation to donor age. The treatment with atorvastatin was associated with significantly higher proliferation rate compared to control, both in hypoxic (19 % median increase) and normoxic conditions (20 %), p = 0.02 and p = 0.04, respectively. Atorvastatin had no significant cytotoxic effect on MSCs. Treatment with rosuvastatin in hypoxia resulted in significantly higher proliferation rate (15 %, p = 0.02) comparing to control with no significant cytotoxicity. In atmospheric oxygen concentration, rosuvastatin was associated with no significant change in proliferation and higher cytotoxicity compared to untreated control (p = 0.042 and p = 0.015, for 0.04 μM and 1 μM solutions respectively). There were no differences in the effect of statins on MSC from young donors vs. aged donors. These results suggest that statins could support MSC-based therapy of acute myocardial infarction.

Hypoxia-induced increase in Sug1 leads to poor post-transplantation survival of allogeneic mesenchymal stem cells

Allogeneic mesenchymal stem cells (MSCs) from young and healthy donors are immunoprivileged and have the potential to treat numerous degenerative diseases. However, recent reviews of clinical trials report poor long-term survival of transplanted cells in the recipient that turned down the enthusiasm regarding MSC therapies. Increasing evidence now confirm that though initially immunoprivileged, MSCs eventually become immunogenic after transplantation in the ischemic or hypoxic environment of diseased tissues and are rejected by the host immune system. We performed in vitro (in rat and human cells) and in vivo (in a rat model) investigations to understand the mechanisms of the immune switch in the phenotype of MSCs. The immunoprivilege of MSCs is preserved by the absence of cell surface immune antigen, major histocompatibility complex II (MHC-II) molecule. We found that the ATPase subunit of 19S proteasome "Sug1" regulates MHC-II biosynthesis in MSCs. Exposure to hypoxia upregulates Sug1 in MSCs and its binding to class II transactivator (CIITA), a coactivator of MHC-II transcription. Sug1 binding to CIITA in hypoxic MSCs promotes the acetylation and K63 ubiquitination of CIITA leading to its activation and translocation to the nucleus, and ultimately MHC-II upregulation. In both rat and human MSCs, knocking down Sug1 inactivated MHC-II and preserved immunoprivilege even following hypoxia. In a rat model of myocardial infarction, transplantation of Sug1-knockdown MSCs in ischemic heart preserved immunoprivilege and improved the survival of transplanted cells. Therefore, the current study provides novel mechanisms of post-transplantation loss of immunoprivilege of MSCs. This study may help in facilitating better planning for future clinical trials.

Adipose-derived stem cell therapy shows promising results for secondary lymphedema

Lymphedema is mainly identified by progressive soft tissue swelling in impaired lymphatic system. Secondary lymphedema attributed to cancer therapy, parasite infection, and trauma remains a serious global disease. Patients with lymphedema suffer swelling, pain, and fatigue, with the dysfunction of the deformed extremities reducing the quality of life and increasing the risk of infection and lymphangiosarcoma. Adipose-derived stem cells (ADSCs) possess prominent regenerative potential to differentiate into multilineage cells, and produce various lymphangiogenic factors, making ADSC therapy a promising approach for lymphedema. The development of lymphedema consists of local inflammation, the fibrosis of lymphatic vessels, and the deposition of adipose fat. Existing animal models do not mimic the chronic inflammation environment, therefore suitable models are required in further studies. Some signal pathways and molecular mechanisms in physiological and pathological lymphagiogenesis remain unclear. In previous animal and human trials, ADSC therapy reduced edema in varying degrees. A larger number of trials with larger samples and longer follow-up periods are required to verify the efficiency and feasibility of ADSC therapy. ADSCs are of easy availability and immune exemption, making them a candidate for lymphedema treatment. Whether ADSCs enhance malignant characteristics or trigger the malignant change deserves further exploration and study before ADSC therapy can be made widely available.

Xenogeneic mesenchymal stem cell transplantation for mandibular defect regeneration

BACKGROUND

It is commonly accepted that xenogeneic stem cell transplantation for tissue engineering is faced with host immune rejection. Using a rat critical-size mandibular defect model, this study examined whether the immune rejection can be evaded by diminishing T-cell immunity.

METHODS

To examine donor cell survival and host immune reaction, pig bone marrow-derived mesenchymal stem cells (BM-MSCs) were labeled with CM-DiI, loaded onto gelatin sponge (5 × 10⁶ cells/scaffold), and transplanted into 5-mm mandibular defects of immunocompetent and T cell-deficient athymic rats. To examine the effects of xenogeneic BM-MSCs on bone regeneration, athymic rats undergone the same surgeries were terminated at post-operative weeks 1, 3, and 6. Control rats underwent the same jaw surgery without BM-MSC transplantation.

RESULTS

The density of CM-DiI-labeled BM-MSCs decreased with time in both strains of rats. Although it was substantially higher in athymic rats than in immunocompetent rats at post-operative day 1, by day 3-7 the density became comparable between the two strains of rats. Apoptosis reflected by cleaved Caspase-3 staining was low in both strains. Stronger infiltration of neutrophils, macrophages, B cells and CD8⁺ T cells was found in MSC-treated animals. In athymic rats, infiltration of neutrophils and macrophages was strong, but it occurred later than that in immunocompetent rats. While bone volume fraction significantly increased with time (P < .001), no difference was found between MSC-treated and control groups.

CONCLUSIONS

Even in hosts with deficient T-cell immunity, xenogeneic BM-MSC transplantation into mandibular critical-sized defects still faces challenges from host innate immunity, which compromises their regenerative efficacy.

Mesenchymal Stromal Cells for Graft Versus Host Disease: Mechanism-Based Biomarkers

The immunosuppressive activity of mesenchymal stromal cells (MSCs) in graft versus host disease (GvHD) is well-documented, but their therapeutic benefit is rather unpredictable. Prospective randomized clinical trials remain the only means to address MSC clinical efficacy. However, the imperfect understanding of MSC biological mechanisms has undermined patients' stratification and the successful design of clinical studies. Furthermore, although MSC efficacy seems to be dependent on patient-associated factors, the role of patients' signature to predict and/or monitor clinical outcomes remains poorly elucidated. The analysis of GvHD patient serum has identified a set of molecules that are associated with high mortality. However, despite their importance in defining GvHD severity, their role in predicting or monitoring response to MSCs has not been confirmed. A new perspective on the use of MSCs for GvHD has been prompted by the recent findings that MSCs are actively induced to undergo apoptosis by recipient cytotoxic cells and that this process is essential to initiate MSC-induced immunosuppression. This discovery has not only reconciled the conundrum between MSC efficacy and their lack of engraftment, but also highlighted the determinant role of the patient in promoting and delivering MSC immunosuppression. In this review we will revisit the extensive use of MSCs for the treatment of GvHD and will elaborate on the need that future clinical trials must depend on mechanistic approaches that facilitate the development of robust and consistent assays to stratify patients and monitor clinical outcomes.

Modifying MSC Phenotype to Facilitate Bone Healing: Biological Approaches

Healing of fractures and bone defects normally follows an orderly series of events including formation of a hematoma and an initial stage of inflammation, development of soft callus, formation of hard callus, and finally the stage of bone remodeling. In cases of severe musculoskeletal injury due to trauma, infection, irradiation and other adverse stimuli, deficient healing may lead to delayed or non-union; this results in a residual bone defect with instability, pain and loss of function. Modern methods of mechanical stabilization and autologous bone grafting are often successful in achieving fracture union and healing of bone defects; however, in some cases, this treatment is unsuccessful because of inadequate biological factors. Specifically, the systemic and local microenvironment may not be conducive to bone healing because of a loss of the progenitor cell population for bone and vascular lineage cells. Autologous bone grafting can provide the necessary scaffold, progenitor and differentiated lineage cells, and biological cues for bone reconstruction, however, autologous bone graft may be limited in quantity or quality. These unfavorable circumstances are magnified in systemic conditions with chronic inflammation, including obesity, diabetes, chronic renal disease, aging and others. Recently, strategies have been devised to both mitigate the necessity for, and complications from, open procedures for harvesting of autologous bone by using minimally invasive aspiration techniques and concentration of iliac crest bone cells, followed by local injection into the defect site. More elaborate strategies (not yet approved by the U.S. Food and Drug Administration-FDA) include isolation and expansion of subpopulations of the harvested cells, preconditioning of these cells or inserting specific genes to modulate or facilitate bone healing. We review the literature pertinent to the subject of modifying autologous harvested cells including MSCs to facilitate bone healing. Although many of these techniques and technologies are still in the preclinical stage and not yet approved for use in humans by the FDA, novel approaches to accelerate bone healing by modifying cells has great potential to mitigate the physical, economic and social burden of non-healing fractures and bone defects.

Mesenchymal Stem Cells: A New Generation of Therapeutic Agents as Vehicles in Gene Therapy

In recent years, mesenchymal stem cells (MSCs) as a new tool for therapeutic gene delivery in clinics have attracted much attention. Their advantages cover longer lifespan, better isolation, and higher transfection efficiency and proliferation rate. MSCs are the preferred approach for cell-based therapies because of their in vitro self-renewal capacity, migrating especially to tumor tissues, as well as anti-inflammatory and immunomodulatory properties. Therefore, they have considerable efficiency in genetic engineering for future clinical applications in cancer gene therapy and other diseases. For improving therapeutic efficiency, targeted therapy of cancers can be achieved through the sustained release of therapeutic agents and functional gene expression induction to the intended tissues. The development of a new vector in gene therapy can improve the durability of a transgene expression. Also, the safety of the vector, if administered systemically, may resolve several problems, such as durability of expression and the host immune response. Currently, MSCs are prominent candidates as cell vehicles for both preclinical and clinical trials due to the secretion of therapeutic agents in several cancers. In the present study, we discuss the status of gene therapy in both viral and non-viral vectors along with their limitations. Throughout this study, the use of several nano-carriers for gene therapy is also investigated. Finally, we critically discuss the promising advantages of MSCs in targeted gene delivery, tumor inhibition and their utilization as the gene carriers in clinical situations.

TGF-β1-Licensed Murine MSCs Show Superior Therapeutic Efficacy in Modulating Corneal Allograft Immune Rejection In Vivo

Mesenchymal stromal cells (MSCs) are a promising therapeutic option for multiple immune diseases/disorders; however, efficacy of MSC treatments can vary significantly. We present a novel licensing strategy to improve the immunosuppressive capacity of MSCs. Licensing murine MSCs with transforming growth factor-β1 (TGF-β MSCs) significantly improved their ability to modulate both the phenotype and secretome of inflammatory bone marrow-derived macrophages and significantly increased the numbers of regulatory T lymphocytes following co-culture assays. These TGF-β MSC-expanded regulatory T lymphocytes also expressed significantly higher levels of PD-L1 and CD73, indicating enhanced suppressive potential. Detailed analysis of T lymphocyte co-cultures revealed modulation of secreted factors, most notably elevated prostaglandin E2 (PGE2). Furthermore, TGF-β MSCs could significantly prolong rejection-free survival (69.2% acceptance rate compared to 21.4% for unlicensed MSC-treated recipients) in a murine corneal allograft model. Mechanistic studies revealed that (1) therapeutic efficacy of TGF-β MSCs is Smad2/3-dependent, (2) the enhanced immunosuppressive capacity of TGF-β MSCs is contact-dependent, and (3) enhanced secretion of PGE2 (via prostaglandin EP4 [E-type prostanoid 4] receptor) by TGF-β MSCs is the predominant mediator of Treg expansion and T cell activation and is associated with corneal allograft survival. Collectively, we provide compelling evidence for the use of TGF-β1 licensing as an unconventional strategy for enhancing MSC immunosuppressive capacity.

Therapeutic Use of Mesenchymal Stem Cell-Derived Exosomes: From Basic Science to Clinics

Mesenchymal stem cells (MSC) are, due to their immunosuppressive and regenerative properties, used as new therapeutic agents in cell-based therapy of inflammatory and degenerative diseases. A large number of experimental and clinical studies revealed that most of MSC-mediated beneficial effects were attributed to the effects of MSC-sourced exosomes (MSC-Exos). MSC-Exos are nano-sized extracellular vesicles that contain MSC-derived bioactive molecules (messenger RNA (mRNA), microRNAs (miRNAs)), enzymes, cytokines, chemokines, and growth factors) that modulate phenotype, function and homing of immune cells, and regulate survival and proliferation of parenchymal cells. In this review article, we emphasized current knowledge about molecular and cellular mechanisms that were responsible for MSC-Exos-based beneficial effects in experimental models and clinical trials. Additionally, we elaborated on the challenges of conventional MSC-Exos administration and proposed the use of new bioengineering and cellular modification techniques which could enhance therapeutic effects of MSC-Exos in alleviation of inflammatory and degenerative diseases.

Allogeneic ADSCs Induce the Production of Alloreactive Memory-CD8 T Cells through HLA-ABC Antigens

We investigated the immunogenicity of allogeneic human adipose-derived mesenchymal stem cells (ADSCs) through the production of alloreactive-CD8 T and -memory CD8 T cells, based on their human leukocyte antigen (HLA) expression. In surface antigen analysis, ADSCs do not express co-stimulatory molecules, but expresses HLA-ABC, which is further increased by exposure to the pro-inflammatory cytokines as well as IFN-γ alone. For immunogenicity analysis, allogeneic ADSCs cultured in xenofree medium (XF-ADSCs) were incubated with the recipient immune cells for allogeneic-antigen stimulation. As a result, XF-ADSCs induced IFN-γ and IL-17A release by alloreactive-CD8 T cells and the production of alloreactive-CD8 T cell through a direct pathway, although they have immunomodulatory activity. In the analysis of alloreactive memory CD8 T cells, XF-ADSCs also significantly induced the production of CFSE-low-CD8 TEM and -CD8 TCM cells. However, HLA-blocking antibodies significantly inhibited the production of CFSE-low memory-CD8 T cells, indicating that HLAs are the main antigens responsible for the development of allogeneic ADSCs' immunogenicity. These results suggested that HLA surface antigens expressed in allogeneic MSCs should be solved in order to address concerns related to the immunogenicity problem.

Human Mesenchymal Stem Cell Secretome Exhibits a Neuroprotective Effect over In Vitro Retinal Photoreceptor Degeneration

Retinal photoreceptor degeneration occurs frequently in several neurodegenerative retinal diseases such as age-related macular degeneration, retinitis pigmentosa, or genetic retinal diseases related to the photoreceptors. Despite the impact on daily life and the social and economic consequences, there is no cure for these diseases. Considering this, cell-based therapy may be an optimal therapeutic option. This study evaluated the neuroprotective in vitro potential of a secretome of human bone marrow mesenchymal stem cells (MSCs) for retinal photoreceptors in vitro. We analyzed the photoreceptor morphologic changes and the paracrine factors secreted by human bone marrow MSCs in a physically separated co-culture with degenerated neuroretinas, using organotypic neuroretinal cultures. The results showed that the secretome of human bone marrow MSCs had a neuroprotective effect over the neuroretinal general organization and neuropreserved the photoreceptors from degeneration probably by secretion of neuroprotective proteins. The study of the expression of 1,000 proteins showed increased paracrine factors secreted by MSCs that could be crucial in the neuroprotective effect of the stem cell secretome over in vitro retinal degeneration. The current results reinforce the hypothesis that the paracrine effect of the human bone marrow MSCs may slow photoreceptor neurodegeneration and be a therapeutic option in retinal photoreceptor degenerative diseases.

A Comparison of Immune Responses Exerted Following Syngeneic, Allogeneic, and Xenogeneic Transplantation of Mesenchymal Stem Cells into the Mouse Brain

Due to their multifactorial aspects, mesenchymal stem cells (MSCs) have been widely established as an attractive and potential candidate for the treatment of a multitude of diseases. A substantial number of studies advocate that MSCs are poorly immunogenic. In several studies, however, immune responses were observed following injections of xenogeneic donor MSCs. In this study, the aim was to examine differences in immune responses exerted based on transplantations of xenogeneic, syngeneic, and allogeneic MSCs in the wild-type mouse brain. Xenogeneic, allogeneic, and syngeneic MSCs were intracerebrally injected into C57BL/6 mice. Mice were sacrificed one week following transplantation. Based on immunohistochemical (IHC) analysis, leukocytes and neutrophils were expressed at the injection sites in the following order (highest to lowest) xenogeneic, allogeneic, and syngeneic. In contrast, microglia and macrophages were expressed in the following order (highest to lowest): syngeneic, allogeneic, and xenogeneic. Residual human MSCs in the mouse brain were barely detected after seven days. Although the discrepancy between leukocytes versus macrophages/microglia infiltration should be resolved, our results overall argue against the previous notions that MSCs are poorly immunogenic and that modulation of immune responses is a prerequisite for preclinical and clinical studies in MSC therapy of central nervous system diseases.

Accept or Reject: The Role of Immune Tolerance in the Development of Stem Cell Therapies and Possible Future Approaches

In 2011, Goldring and colleagues published a review article describing the potential safety issues of novel stem cell-derived treatments. Immunogenicity and immunotoxicity of the administered cell product were considered risks in the light of clinical experience of transplantation. The relative immunogenicity of mesenchymal stem cells, embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs) was being addressed through in vitro and in vivo models. But the question arose as to whether the implanted cells needed to be identical to the recipient in every respect, including epigenetically, to evade immune recognition? If so, this set a high bar which may preclude use of many cells derived from iPSCs which have vestiges of a fetal phenotype and epigenetic memory of their cell of origin. However, for autologous iPSCs, the immunogenicity reduces once the surface antigen expression profile becomes close to that of the parent somatic cells. Therefore, a cell product containing incompletely differentiated cells could be more immunogenic. The properties of the administered cells, the immune privilege of the administration site, and the host immune status influence graft success or failure. In addition, the various approaches available to characterize potential immunogenicity of a cell therapy will be discussed.

Molecular and Cellular Mechanisms Responsible for Beneficial Effects of Mesenchymal Stem Cell-Derived Product "Exo-d-MAPPS" in Attenuation of Chronic Airway Inflammation

Mesenchymal stem cells (MSCs), due to their potential for differentiation into alveolar epithelial cells and their immunosuppressive characteristics, are considered a new therapeutic agent in cell-based therapy of inflammatory lung disorders, including chronic obstructive pulmonary disease (COPD). Since most of the MSC-mediated beneficent effects were the consequence of their paracrine action, herewith, we investigated the effects of a newly designed MSC-derived product "Exosome-derived Multiple Allogeneic Protein Paracrine Signaling (Exo-d-MAPPS)" in the attenuation of chronic airway inflammation by using an animal model of COPD (induced by chronic exposure to cigarette smoke (CS)) and clinical data obtained from Exo-d-MAPPS-treated COPD patients. Exo-d-MAPPS contains a high concentration of immunomodulatory factors which are capable of attenuating chronic airway inflammation, including soluble TNF receptors I and II, IL-1 receptor antagonist, and soluble receptor for advanced glycation end products. Accordingly, Exo-d-MAPPS significantly improved respiratory function, downregulated serum levels of inflammatory cytokines (TNF-α, IL-1β, IL-12, and IFN-γ), increased serum concentration of immunosuppressive IL-10, and attenuated chronic airway inflammation in CS-exposed mice. The cellular makeup of the lungs revealed that Exo-d-MAPPS treatment attenuated the production of inflammatory cytokines in lung-infiltrated macrophages, neutrophils, and natural killer and natural killer T cells and alleviated the antigen-presenting properties of lung-infiltrated macrophages and dendritic cells (DCs). Additionally, Exo-d-MAPPS promoted the expansion of immunosuppressive IL-10-producing alternatively activated macrophages, regulatory DCs, and CD4+FoxP3+T regulatory cells in inflamed lungs which resulted in the attenuation of chronic airway inflammation. In a similar manner, as it was observed in an animal model, Exo-d-MAPPS treatment significantly improved the pulmonary status and quality of life of COPD patients. Importantly, Exo-d-MAPPS was well tolerated since none of the 30 COPD patients reported any adverse effects after Exo-d-MAPPS administration. In summing up, we believe that Exo-d-MAPPS could be considered a potentially new therapeutic agent in the treatment of chronic inflammatory lung diseases whose efficacy should be further explored in large clinical trials.

Alternative Cell Sources for Liver Parenchyma Repopulation: Where Do We Stand?

Acute and chronic liver failure is a highly prevalent medical condition with high morbidity and mortality. Currently, the therapy is orthotopic liver transplantation. However, in some instances, chiefly in the setting of metabolic diseases, transplantation of individual cells, specifically functional hepatocytes, can be an acceptable alternative. The gold standard for this therapy is the use of primary human hepatocytes, isolated from livers that are not suitable for whole organ transplantations. Unfortunately, primary human hepatocytes are scarcely available, which has led to the evaluation of alternative sources of functional hepatocytes. In this review, we will compare the ability of most of these candidate alternative cell sources to engraft and repopulate the liver of preclinical animal models with the repopulation ability found with primary human hepatocytes. We will discuss the current shortcomings of the different cell types, and some of the next steps that we believe need to be taken to create alternative hepatocyte progeny capable of regenerating the failing liver.

Arrhythmogenic risks of stem cell replacement therapy for cardiovascular diseases

Ischemic heart disease and congestive heart failure are major contributors to high morbidity and mortality. Approximately 1.5 million cases of myocardial infarction occur annually in the United States; the yearly incidence rate is approximately 600 cases per 100,000 people. Although significant progress to improve the survival rate has been made by medications and implantable medical devices, damaged cardiomyocytes are unable to be recovered by current treatment strategies. After almost two decades of research, stem cell therapy has become a very promising approach to generate new cardiomyocytes and enhance the function of the heart. Along with clinical trials with stem cells conducted in cardiac regeneration, concerns regarding safety and potential risks have emerged. One of the contentious issues is the electrical dysfunctions of cardiomyocytes and cardiac arrhythmia after stem cell therapy. In this review, we focus on the cell sources currently used for stem cell therapy and discuss related arrhythmogenic risk.

Therapeutic Mesenchymal Stromal Cells for Immunotherapy and for Gene and Drug Delivery

Mesenchymal stromal cells (MSCs) possess several fairly unique properties that, when combined, make them ideally suited for cellular-based immunotherapy and as vehicles for gene and drug delivery for a wide range of diseases and disorders. Key among these are: (1) their relative ease of isolation from a variety of tissues; (2) the ability to be expanded in culture without a loss of functionality, a property that varies to some degree with tissue source; (3) they are relatively immune-inert, perhaps obviating the need for precise donor/recipient matching; (4) they possess potent immunomodulatory functions that can be tailored by so-called licensing in vitro and in vivo; (5) the efficiency with which they can be modified with viral-based vectors; and (6) their almost uncanny ability to selectively home to damaged tissues, tumors, and metastases following systemic administration. In this review, we summarize the latest research in the immunological properties of MSCs, their use as immunomodulatory/anti-inflammatory agents, methods for licensing MSCs to customize their immunological profile, and their use as vehicles for transferring both therapeutic genes in genetic disease and drugs and genes designed to destroy tumor cells.

Intravitreal stem cell paracrine properties as a potential neuroprotective therapy for retinal photoreceptor neurodegenerative diseases

Retinal degenerations are the leading causes of irreversible visual loss worldwide. Many pathologies included under this umbrella involve progressive degeneration and ultimate loss of the photoreceptor cells, with age-related macular degeneration and inherited and ischemic retinal diseases the most relevant. These diseases greatly impact patients’ daily lives, with accompanying marked social and economic consequences. However, the currently available treatments only delay the onset or slow progression of visual impairment, and there are no cures for these photoreceptor diseases. Therefore, new therapeutic strategies are being investigated, such as gene therapy, optogenetics, cell replacement, or cell-based neuroprotection. Specifically, stem cells can secrete neurotrophic, immunomodulatory, and anti-angiogenic factors that potentially protect and preserve retinal cells from neurodegeneration. Further, neuroprotection can be used in different types of retinal degenerative diseases and at different disease stages, unlike other potential therapies. This review summarizes stem cell-based paracrine neuroprotective strategies for photoreceptor degeneration, which are under study in clinical trials, and the latest preclinical studies. Effective retinal neuroprotection could be the next frontier in photoreceptor diseases, and the development of novel neuroprotective strategies will address the unmet therapeutic needs.

The Phenotype and Secretory Activity of Adipose-Derived Mesenchymal Stem Cells (ASCs) of Patients with Rheumatic Diseases

Mesenchymal stem/stromal cells (MSCs) have immunosuppressive and regenerative properties. Adipose tissue is an alternative source of MSCs, named adipose-derived mesenchymal stem cells (ASCs). Because the biology of ASCs in rheumatic diseases (RD) is poorly understood, we performed a basic characterization of RD/ASCs. The phenotype and expression of adhesion molecules (intracellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1) on commercially available healthy donors (HD), ASC lines (n = 5) and on ASCs isolated from patients with systemic lupus erythematosus (SLE, n = 16), systemic sclerosis (SSc, n = 17) and ankylosing spondylitis (AS, n = 16) were analyzed by flow cytometry. The secretion of immunomodulatory factors by untreated and cytokine-treated ASCs was measured by ELISA. RD/ASCs have reduced basal levels of CD90 and ICAM-1 expression, correlated with interleukin (IL)-6 and transforming growth factor (TGF)-β1 release, respectively. Compared with HD/ASCs, untreated and tumour necrosis factor (TNF) + interferon (IFN)-γ (TI)-treated RD/ASCs produced similar amounts of prostaglandin E2 (PGE2), IL-6, leukemia inhibiting factor (LIF), and TGF-β1, more IL-1Ra, soluble human leukocyte antigen G (sHLA-G) and tumor necrosis factor-inducible gene (TSG)-6, but less kynurenines and galectin-3. Basal secretion of galectin-3 was inversely correlated with the patient's erythrocyte sedimentation rate (ESR) value. IFN-α and IL-23 slightly raised galectin-3 release from SLE/ASCs and AS/ASCs, respectively. TGF-β1 up-regulated PGE2 secretion by SSc/ASCs. In conclusion, RD/ASCs are characterized by low basal levels of CD90 and ICAM-1 expression, upregulated secretion of IL-1Ra, TSG-6 and sHLA-G, but impaired release of kynurenines and galectin-3. These abnormalities may modify biological activities of RD/ASCs.

Blood type and breed-associated differences in cell marker expression on equine bone marrow-derived mesenchymal stem cells including major histocompatibility complex class II antigen expression

BACKGROUND

As the search for an immune privileged allogeneic donor mesenchymal stem cell (MSC) line continues in equine medicine, the characterization of the cells between different sources becomes important. Our research seeks to more clearly define the MSC marker expression of different equine MSC donors.

METHODS

The bone marrow-derived MSCs from two equine breeds and different blood donor-types were compared over successive culture passages to determine the differential expression of important antigens. Eighteen Thoroughbreds and 18 Standardbreds, including 8 blood donor (erythrocyte Aa, Ca, and Qa antigen negative) horses, were evaluated. Bone marrow was taken from each horse for isolation and culture of MSCs. Samples from passages 2, 4, 6, and 8 were labelled and evaluated by flow cytometry. The cell surface expression of CD11a/18, CD44, CD90 and MHC class II antigens were assessed. Trilineage assays for differentiation into adipogenic, chondrogenic and osteogenic lines were performed to verify characterization of the cells as MSCs.

FINDINGS

There were significant differences in mesenchymal stem cell marker expression between breeds and blood antigen-type groups over time. Standardbred horses showed a significantly lower expression of MHC class II than did Thoroughbred horses at passages 2, 4 and 6. CD90 was significantly higher in universal blood donor Standardbreds as compared to non-blood donor Standardbreds over all time points. All MSC samples showed high expression of CD44 and low expression of CD11a/18.

CONCLUSIONS

Universal blood donor- type Standardbred MSCs from passages 2-4 show the most ideal antigen expression pattern of the horses and passages that we characterized for use as a single treatment of donor bone marrow-derived MSCs. Further work is needed to determine the significance of this differential expression along with the effect of the expression of MHC I on equine bone marrow-derived MSCs.

Substantial Overview on Mesenchymal Stem Cell Biological and Physical Properties as an Opportunity in Translational Medicine

Mesenchymal stem cells (MSC) have piqued worldwide interest for their extensive potential to treat a large array of clinical indications, their unique and controversial immunogenic and immune modulatory properties allowing ample discussions and debates for their possible applications. Emerging data demonstrating that the interaction of biomaterials and physical cues with MSC can guide their differentiation into specific cell lineages also provide new interesting insights for further MSC manipulation in different clinical applications. Moreover, recent discoveries of some regulatory molecules and signaling pathways in MSC niche that may regulate cell fate to distinct lineage herald breakthroughs in regenerative medicine. Although the advancement and success in the MSC field had led to an enormous increase in the amount of ongoing clinical trials, we still lack defined clinical therapeutic protocols. This review will explore the exciting opportunities offered by human and animal MSC, describing relevant biological properties of these cells in the light of the novel emerging evidence mentioned above while addressing the limitations and challenges MSC are still facing.

Mesenchymal stem cells therapy in companion animals: useful for immune-mediated diseases?

Mesenchymal stem cells are multipotent cells, with capacity for self-renewal and differentiation into tissues of mesodermal origin. These cells are possible therapeutic agents for autoimmune disorders, since they present remarkable immunomodulatory ability.The increase of immune-mediated diseases in veterinary medicine has led to a growing interest in the research of these disorders and their medical treatment. Conventional immunomodulatory drug therapy such as glucocorticoids or other novel therapies such as cyclosporine or monoclonal antibodies are associated with numerous side effects that limit its long-term use, leading to the need for developing new therapeutic strategies that can be more effective and safe.The aim of this review is to provide a critical overview about the therapeutic potential of these cells in the treatment of some autoimmune disorders (canine atopic dermatitis, feline chronic gingivostomatitis, inflammatory bowel disease and feline asthma) compared with their conventional treatment.Mesenchymal stem cell-based therapy in autoimmune diseases has been showing that this approach can ameliorate clinical signs or even cause remission in most animals, with the exception of canine atopic dermatitis in which little to no improvement was observed.Although mesenchymal stem cells present a promising future in the treatment of most of these disorders, the variability in the outcomes of some clinical trials has led to the current controversy among authors regarding their efficacy. Mesenchymal stem cell-based therapy is currently requiring a deeper and detailed analysis that allows its standardization and better adaptation to the intended therapeutic results, in order to overcome current limitations in future trials.

Tendon stem/progenitor cell ageing: Modulation and rejuvenation

Tendon ageing is a complicated process caused by multifaceted pathways and ageing plays a critical role in the occurrence and severity of tendon injury. The role of tendon stem/progenitor cells (TSPCs) in tendon maintenance and regeneration has received increasing attention in recent years. The decreased capacity of TSPCs in seniors contributes to impaired tendon functions and raises questions as to what extent these cells either affect, or cause ageing, and whether these age-related cellular alterations are caused by intrinsic factors or the cellular environment. In this review, recent discoveries concerning the biological characteristics of TSPCs and age-related changes in TSPCs, including the effects of cellular epigenetic alterations and the mechanisms involved in the ageing process, are analyzed. During the ageing process, TSPCs ageing might occur as a natural part of the tendon ageing, but could also result from decreased levels of growth factor, hormone deficits and changes in other related factors. Here, we discuss methods that might induce the rejuvenation of TSPC functions that are impaired during ageing, including moderate exercise, cell extracellular matrix condition, growth factors and hormones; these methods aim to rejuvenate the features of youthfulness with the ultimate goal of improving human health during ageing.

Differentiation of equine induced pluripotent stem cells into mesenchymal lineage for therapeutic use

In previous work, we established an equine induced pluripotent stem cell line (E-iPSCs) from equine adipose-derived stem cells (ASCs) using a lentiviral vector encoding four transcription factors: Oct4, Sox2, Klf4, and c-Myc. In the current study, we attempted to differentiate these established E-iPSCs into mesenchymal stem cells (MSCs) by serial passaging using MSC-defined media for stem cell expansion. Differentiation of the MSCs was confirmed by analyzing expression levels of the MSC surface markers CD44 and CD29, and the pluripotency markers Nanog and Oct4. Results indicated that the E-iPSC-derived MSCs (E-iPSC-MSCs) retained the characteristics of MSCs, including the ability to differentiate into chondrogenic, osteogenic, or myogenic lineages. E-iPSC-MSCs were rendered suitable for therapeutic use by inhibiting immune rejection through exposure to transforming growth factor beta 2 (TGF-β2) in culture, which down-regulated the expression of major histocompatibility complex class I (MHC class I) proteins that cause immune rejection if they are incompatible with the MHC antigen of the recipient. We reported 16 cases of E-iPSC-MSC transplantations into injured horses with generally positive effects, such as reduced lameness and fraction lines. Our findings indicate that E-iPSC-MSCs can demonstrate MSC characteristics and be safely and practically used in the treatment of musculoskeletal injuries in horses.

Umbilical cord blood versus mesenchymal stem cells for inflammation-induced preterm brain injury in fetal sheep

BACKGROUND

Chorioamnionitis and fetal inflammation are principal causes of neuropathology detected after birth, particularly in very preterm infants. Preclinical studies show that umbilical cord blood (UCB) cells are neuroprotective, but it is uncertain if allogeneic UCB cells are a feasible early intervention for preterm infants. In contrast, mesenchymal stem cells (MSCs) are more readily accessible and show strong anti-inflammatory benefits. We aimed to compare the neuroprotective benefits of UCB versus MSCs in a large animal model of inflammation-induced preterm brain injury. We hypothesized that MSCs would afford greater neuroprotection.

METHODS

Chronically instrumented fetal sheep at 0.65 gestation received intravenous lipopolysaccharide (150 ng; 055:B5, n = 8) over 3 consecutive days; or saline for controls (n = 8). Cell-treated animals received 10⁸ UCB mononuclear cells (n = 7) or 10⁷ umbilical cord MSCs (n = 8), intravenously, 6 h after the final lipopolysaccharide dose. Seven days later, cerebrospinal fluid and brain tissue was collected for analysis.

RESULTS

Lipopolysaccharide induced neuroinflammation and apoptosis, and reduced the number of mature oligodendrocytes. MSCs reduced astrogliosis, but UCB did not have the same effect. UCB significantly decreased cerebral apoptosis and protected mature myelinating oligodendrocytes, but MSCs did not.

CONCLUSION

UCB appears to better protect white matter development in the preterm brain in response to inflammation-induced brain injury in fetal sheep.

Understanding the Immunological Mechanisms of Mesenchymal Stem Cells in Allogeneic Transplantation: From the Aspect of Major Histocompatibility Complex Class I

Mesenchymal stem cell (MSC) transplantation therapy appears to be an ideal strategy for repairing structural defects and restoring the functions of diseased tissues and organs. Additionally, MSCs are also used as immunosuppressants in allogeneic organ transplantation. However, owing to their inherent immunogenicity, MSC transplantation can induce the activation of an immune response, which can lead to the death and clearance of the transplanted MSCs. Major histocompatibility complex (MHC) molecules are responsible for antigen presentation, help T lymphocytes to recognize endogenous/extrinsic antigens, and trigger immune activation. Many studies have shown that MHC molecules (particularly class I) play key roles in the immunogenicity of MSCs. This review, therefore, focuses on the relationship between MHC-I surface expression on MSCs and its immunogenicity, as well as potential strategies to overcome the hurdle of MHC incompatibility.

Mesenchymal Stromal Cell Therapeutic Delivery: Translational Challenges to Clinical Application

For several decades, multipotent mesenchymal stromal cells (MSCs) have been extensively studied for their therapeutic potential across a wide range of diseases. In the preclinical setting, MSCs demonstrate consistent ability to promote tissue healing, down-regulate excessive inflammation and improve outcomes in animal models. Several proposed mechanisms of action have been posited and demonstrated across an array of in vitro models. However, translation into clinical practice has proven considerably more difficult. A number of prominent well-funded late-phase clinical trials have failed, thus calling out for new efforts to optimize product delivery in the clinical setting. In this review, we discuss novel topics critical to the successful translation of MSCs from pre-clinical to clinical applications. In particular, we focus on the major routes of cell delivery, aspects related to hemocompatibility, and potential safety concerns associated with MSC therapy in the different settings.

Enhanced Immunomodulation in Inflammatory Environments Favors Human Cardiac Mesenchymal Stromal-Like Cells for Allogeneic Cell Therapies

Rising numbers of patients with cardiovascular diseases and limited availability of donor hearts require new and improved therapy strategies. Human atrial appendage-derived cells (hAACs) are promising candidates for an allogeneic cell-based treatment. In this study, we evaluated their inductive and modulatory capacity regarding immune responses and underlying key mechanisms in vitro. For this, cryopreserved hAACs were either cultured in the presence of interferon-gamma (IFNγ) or left unstimulated. The expression of characteristic mesenchymal stromal cell markers (CD29, CD44, CD73, CD105, CD166) was revealed by flow cytometry that also highlighted a predominant negativity for CD90. A low immunogeneic phenotype in an inflammatory milieu was shown by lacking expression of co-stimulatory molecules and upregulation of the inhibitory ligands PD-L1 and PD-L2, despite de novo expression of HLA-DR. Co-cultures of hAACs with allogeneic peripheral blood mononuclear cells, proved their low immunogeneic state by absence of induced T cell proliferation and activation. Additionally, elevated levels of IL-1β, IL-33, and IL-10 were detectable in those cell culture supernatants. Furthermore, the immunomodulatory potential of hAACs was assessed in co-cultures with αCD3/αCD28-activated peripheral blood mononuclear cells. Here, a strong inhibition of T cell proliferation and reduction of pro-inflammatory cytokines (IFNγ, TNFα, TNFβ, IL-17A, IL-2) were observable after pre-stimulation of hAACs with IFNγ. Transwell experiments confirmed that mostly soluble factors are responsible for these suppressive effects. We were able to identify indolamin-2,3-dioxygenase (IDO) as a potential key player through a genome-wide gene expression analysis and could demonstrate its involvement in the observed immunological responses. While the application of blocking antibodies against both PD-1 ligands did not affect the immunomodulation by hAACs, 1-methyl-L-tryptophan as specific inhibitor of IDO was able to restore proliferation and to lower apoptosis of T cells. In conclusion, hAACs represent a cardiac-derived mesenchymal stromal-like cell type with a high potential for the application in an allogeneic setting, since they do not trigger T cell responses and even increase their immunomodulatory potential in inflammatory environments.

Dual delivery of encapsulated BM-MSCs and BMP-2 improves osteogenic differentiation and new bone formation

Stem cell-based therapies provide a promising approach for bone repair. In the present work, we developed a novel 3D vehicle system for dual-delivery of encapsulated bone marrow mesenchymal stem cells (BM-MSCs) and bone morphogenetic protein-2 (BMP-2) for treatment of large bone defects. The vehicle system consists of sodium alginate microcapsules and polylactic acid (PLLA) microspheres. BM-MSCs are encapsulated in the microcapsules, and BMP-2 proteins are encapsulated in the PLLA microspheres. This vehicle system acted as a multicore structure for sustained release of BMP-2, which enabled pulsed dosing induction of osteogenic differentiation of the co-embedded BM-MSCs. in vitro experiments showed that the loaded BMP-2 was constitutively released up to 30 days. Bioactivity of the incorporated BMP-2 in the microspheres was preserved and osteogenic differentiation of the BM-MSCs in the microcapsules was improved. In vivo, osteogenesis studies demonstrated that satisfactory degree of repair of a rat calvarial defect was achieved with the delivery of either encapsulated BM-MSCs alone or encapsulated BMP-2 alone. Transplantation of encapsulated both BM-MSCs and BMP-2 exhibited the greatest repair potential following 4- or 8-weeks treatment. In conclusion, microencapsulation of BM-MSCs and BMP-2 promoted the maturity of newly generated bone and improved new bone formation. Transplantation of BM-MSCs and BMP-2 in our novel 3-D vehicle system is a promising strategy for regenerative therapies of large bone defects.

Cx601 (darvadstrocel) for the treatment of perianal fistulizing Crohn's disease

Introduction: Given the well-documented difficulty to treat perianal fistulizing Crohn's disease (pCD), with 40% of patients experiencing recurrence even after reiterative surgery and advanced medical therapy, research in this field has focused on the role of mesenchymal stem cells (MSC). Areas covered: The aim of this article is to furnish an overview of the pathogenetic mechanisms, clinical applications and evidences for the use of MSC for pCD with particular focus on adipose-derived allogenic MSC including darvadstrocel. Expert Opinion: The effect of MSC on fistula healing is probably mediated by their anti-inflammatory properties more than by their ability to engraft and trans-differentiate in the healthy tissue. A holistic treatment of pCD, addressing different pathophysiological factors, may represent the key for an improvement in the healing rate. In this setting, MSC might play a role as 'augmentation' therapy in combination with more conventional treatments. Whether MSC have benefit in non-complex fistula in biological naïve patients, in complex fistula with many tracts and/or in rectovaginal fistulas, are unexplored fields that need further investigation. A central registry of pCD patients undergoing treatment with MSC should be created in order to elucidate the efficacy, safety and costs of stem cells treatment on long term follow up.

Single-Cell Profiles and Clinically Useful Properties of Human Mesenchymal Stem Cells of Adipose and Bone Marrow Origin

BACKGROUND

Mesenchymal stem cells (MSCs) can be isolated from various tissues and can present themselves as a promising cell source for cell-based therapies. Although adipose- and bone marrow-derived mesenchymal stem cells have already been used in a considerable number of clinical trials for osteoarthritis treatment, systematic analyses from single- to bulk-cell resolution as well as clinical outcomes of these 2 MSCs are still insufficient.

PURPOSE

To explore the characteristics and differences of adipose-derived stem cells (ADSCs) and bone marrow MSCs (BMSCs) at single- and bulk-cell levels, to study the clinical outcomes of these 2 cells on the treatment of osteoarthritis, and to provide potential guidance on the more precise clinical application of these MSCs.

STUDY DESIGN

Controlled laboratory study and meta-analysis.

METHODS

Same donor-derived ADSCs and BMSCs were isolated and cultured. Single- and bulk-cell assays were used to identify the characteristics of these 2 cells. Meta-analysis of clinical trials was done to compare the clinical therapeutic effects in osteoarthritis treatment with ADSCs and BMSCs.

RESULTS

Single-cell RNA sequencing analysis showed that the population of ADSCs showed lower transcriptomic heterogeneity when compared with BMSCs. Additionally, as compared with BMSCs, ADSCs were less dependent on mitochondrial respiration for energy production. Furthermore, ADSCs had a lower expression level of human leukocyte antigen class I antigen and higher immunosuppression capacity when compared with the BMSC population. Meta-analysis of current clinical trials of osteoarthritis treatment with MSCs consistently showed that ADSCs are more stable than BMSCs in their therapeutic effect.

CONCLUSION

These results provide basic biological insights into human ADSCs and BMSCs at the single-cell resolution. Findings indicated that ADSCs may be a more controllable stem cell source, may be more adaptable to surviving in the hypoxic articular cavity niche, and may exhibit superiority in regulating inflammation. Based on the meta-analysis results of the different characteristics of ADSCs and BMSCs, ADSCs were implicated as being a better cell source for osteoarthritis treatment.

CLINICAL RELEVANCE

These results guide a more precise clinical application of adipose and bone marrow mesenchymal stem cells.

Molecular Mechanisms Responsible for Therapeutic Potential of Mesenchymal Stem Cell-Derived Secretome

Mesenchymal stem cell (MSC)-sourced secretome, defined as the set of MSC-derived bioactive factors (soluble proteins, nucleic acids, lipids and extracellular vesicles), showed therapeutic effects similar to those observed after transplantation of MSCs. MSC-derived secretome may bypass many side effects of MSC-based therapy, including unwanted differentiation of engrafted MSCs. In contrast to MSCs which had to be expanded in culture to reach optimal cell number for transplantation, MSC-sourced secretome is immediately available for treatment of acute conditions, including fulminant hepatitis, cerebral ischemia and myocardial infarction. Additionally, MSC-derived secretome could be massively produced from commercially available cell lines avoiding invasive cell collection procedure. In this review article we emphasized molecular and cellular mechanisms that were responsible for beneficial effects of MSC-derived secretomes in the treatment of degenerative and inflammatory diseases of hepatobiliary, respiratory, musculoskeletal, gastrointestinal, cardiovascular and nervous system. Results obtained in a large number of studies suggested that administration of MSC-derived secretomes represents a new, cell-free therapeutic approach for attenuation of inflammatory and degenerative diseases. Therapeutic effects of MSC-sourced secretomes relied on their capacity to deliver genetic material, growth and immunomodulatory factors to the target cells enabling activation of anti-apoptotic and pro-survival pathways that resulted in tissue repair and regeneration.

The Plasticity of Mesenchymal Stem Cells in Regulating Surface HLA-I

A low surface expression level of human leukocyte antigen class I (HLA-I) ensures that the mesenchymal stem cells (MSCs) escape from the allogeneic recipients' immunological surveillance. Here, we discovered that both transcriptional and synthesis levels of HLA-I in MSCs increased continuously after interferon (IFN)-γ treatment, whereas interestingly, their surface HLA-I expression was downregulated after reaching an HLA-I surface expression peak. Microarray data indicated that the post-transcriptional process plays an important role in the downregulation of surface HLA-I. Further studies identified that IFN-γ-treated MSCs accelerated HLA-I endocytosis through a clathrin-independent dynamin-dependent endocytosis pathway. Furthermore, cells that have self-downregulated surface HLA-I expression elicit a weaker immune response than they previously could. Thus uncovering the plasticity of MSCs in the regulation of HLA-I surface expression would reveal insights into the membrane transportation events leading to the maintenance of low surface HLA-I expression, providing more evidence for selecting and optimizing low-immunogenic MSCs to improve the therapeutic efficiency.

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hESC-MSCs have the plasticity of maintaining low HLA-I expression on cell surface

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hESC-MSCs downregulate the surface HLA-I expression through endocytosis of HLA-I

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hESC-MSCs with lower HLA-I surface expression induce weaker MLR and slighter DTH

Activated Mesenchymal Stromal Cells Process and Present Antigens Regulating Adaptive Immunity

Mesenchymal stromal cells (MSCs) are inherently immunomodulatory through production of inhibiting soluble factors and expression of immunosuppressive cell surface markers. We tested whether activated MSCs qualify for the induction of antigen-specific immune regulation. Bone marrow derived human MSCs were activated by interferon-γ and analyzed for antigen uptake and processing and immune regulatory features including phenotype, immunosuppressive capacity, and metabolic activity. To assess whether activated MSC can modulate adaptive immunity, MSCs were pulsed with islet auto-antigen (GAD65) peptide to stimulate GAD65-specific T-cells. We confirm that inflammatory activation of MSCs increased HLA class II, PD-L1, and intracellular IDO expression, whereas co-stimulatory molecules including CD86 remained absent. MSCs remained locked in their metabolic phenotype, as activation did not alter glycolytic function or mitochondrial respiration. MSCs were able to uptake and process protein. Activated HLA-DR3-expressing MSCs pulsed with GAD65 peptide inhibited proliferation of HLA-DR3-restricted GAD65-specific T-cells, while this HLA class II expression did not induce cellular alloreactivity. Conditioning of antigen-specific T-cells by activated and antigen-pulsed MSCs prevented T-cells to proliferate upon subsequent activation by dendritic cells, even after removal of the MSCs. In sum, activation of MSCs with inflammatory stimuli turns these cells into suppressive cells capable of mediating adaptive regulation of proinflammatory pathogenic T-cells.

Immunoregulatory potential of mesenchymal stem cells following activation by macrophage-derived soluble factors

BACKGROUND

Immunoregulatory capacity of mesenchymal stem cells (MSC) is triggered by the inflammatory environment, which changes during tissue repair. Macrophages are essential in mediating the inflammatory response after injury and can adopt a range of functional phenotypes, exhibiting pro-inflammatory and anti-inflammatory activities. An accurate characterization of MSC activation by the inflammatory milieu is needed for improving the efficacy of regenerative therapies. In this work, we investigated the immunomodulatory functions of MSC primed with factors secreted from macrophages polarized toward a pro-inflammatory or an anti-inflammatory phenotype. We focused on the role of TNF-α and IL-10, prototypic pro-inflammatory and anti-inflammatory cytokines, respectively, as priming factors for MSC.

METHODS

Secretion of immunoregulatory mediators from human MSC primed with media conditioned by human macrophages polarized toward a pro-inflammatory or an anti-inflammatory phenotype was determined. Immunomodulatory potential of primed MSC on polarized macrophages was studied using indirect co-cultures. Involvement of TNF-α and IL-10 in priming MSC and of PGE2 in MSC-mediated immunomodulation was investigated employing neutralizing antibodies. Collagen hydrogels were used to study MSC and macrophages interactions in a more physiological environment.

RESULTS

Priming MSC with media conditioned by pro-inflammatory or anti-inflammatory macrophages enhanced their immunomodulatory potential through increased PGE2 secretion. We identified the pro-inflammatory cytokine TNF-α as a priming factor for MSC. Notably, the anti-inflammatory IL-10, mainly produced by pro-resolving macrophages, potentiated the priming effect of TNF-α. Collagen hydrogels acted as instructive microenvironments for MSC and macrophages functions and their crosstalk. Culturing macrophages on hydrogels stimulated anti-inflammatory versus pro-inflammatory cytokine secretion. Encapsulation of MSC within hydrogels increased PGE2 secretion and potentiated immunomodulation on macrophages, attenuating macrophage pro-inflammatory state and sustaining anti-inflammatory activation. Priming with inflammatory factors conferred to MSC loaded in hydrogels greater immunomodulatory potential, promoting anti-inflammatory activity of macrophages.

CONCLUSIONS

Factors secreted by pro-inflammatory and anti-inflammatory macrophages activated the immunomodulatory potential of MSC. This was partially attributed to the priming effect of TNF-α and IL-10. Immunoregulatory functions of primed MSC were enhanced after encapsulation in hydrogels. These findings may provide insight into novel strategies to enhance MSC immunoregulatory potency.

Meshes in a mess: Mesenchymal stem cell-based therapies for soft tissue reinforcement

Surgical meshes are frequently used for the treatment of abdominal hernias, pelvic organ prolapse, and stress urinary incontinence. Though these meshes are designed for tissue reinforcement, many complications have been reported. Both differentiated cell- and mesenchymal stem cell-based therapies have become attractive tools to improve their biocompatibility and tissue integration, minimizing adverse inflammatory reactions. However, current studies are highly heterogeneous, making it difficult to establish comparisons between cell types or cell coating methodologies. Moreover, only a few studies have been performed in clinically relevant animal models, leading to contradictory results. Finally, a thorough understanding of the biological mechanisms of mesenchymal stem cells in the context of foreign body reaction is lacking. This review aims to summarize in vitro and in vivo studies involving the use of differentiated and mesenchymal stem cells in combination with surgical meshes. According to preclinical and clinical studies and considering the therapeutic potential of mesenchymal stem cells, it is expected that these cells will become valuable tools in the treatment of pathologies requiring tissue reinforcement. STATEMENT OF SIGNIFICANCE: The implantation of surgical meshes is the standard procedure to reinforce tissue defects such as hernias. However, an adverse inflammatory response secondary to this implantation is frequently observed, leading to a strong discomfort and chronic pain in the patients. In many cases, an additional surgical intervention is needed to remove the mesh. Both differentiated cell- and stem cell-based therapies have become attractive tools to improve biocompatibility and tissue integration, minimizing adverse inflammatory reactions. However, current studies are incredibly heterogeneous and it is difficult to establish a comparison between cell types or cell coating methodologies. This review aims to summarize in vitro and in vivo studies where differentiated and stem cells have been combined with surgical meshes.

Manufacturing of primed mesenchymal stromal cells for therapy

Mesenchymal stromal cells (MSCs) for basic research and clinical applications are manufactured and developed as unique cell products by many different manufacturers and laboratories, often under different conditions. The lack of standardization of MSC identity has limited consensus around which MSC properties are relevant for specific outcomes. In this Review, we examine how the choice of media, cell source, culture environment and storage affects the phenotype and clinical utility of MSC-based products, and discuss the techniques better suited to prime MSCs with specific phenotypes of interest and the need for the continued development of standardized assays that provide quality assurance for clinical-grade MSCs. Bioequivalence between cell products and batches must be investigated rather than assumed, so that the diversity of phenotypes between differing MSC products can be accounted for to identify products with the highest therapeutic potential and to preserve their safety in clinical treatments.

Canine Adipose-Derived Mesenchymal Stromal Cells Enhance Neuroregeneration in a Rat Model of Sciatic Nerve Crush Injury

Crush injuries in peripheral nerves are frequent and induce long-term disability with motor and sensory deficits. Due to axonal and myelin sheath disruptions, strategies for optimized axonal regeneration are needed. Multipotent mesenchymal stromal cells (MSC) are promising because of their anti-inflammatory properties and secretion of neurotrophins. The present study investigated the effect of canine adipose tissue MSC (Ad-MSC) transplantation in an experimental sciatic nerve crush injury. Wistar rats were divided into three groups: sham ( n = 8); Crush+PBS ( n = 8); Crush+MSC ( n = 8). Measurements of sciatic nerve functional index (SFI), muscle mass, and electromyography (EMG) were performed. Canine Ad-MSC showed mesodermal characteristics (CD34-, CD45-, CD44+, CD90+ and CD105+) and multipotentiality due to chondrogenic, adipogenic, and osteogenic differentiation. SFI during weeks 3 and 4 was significantly higher in the Crush+MSC group ( p < 0.001). During week 4, the EMG latency in the Crush+MSC groups had better near normality ( p < 0.05). The EMG amplitude showed results close to normality during week 4 in the Crush+MSC group ( p < 0.04). There were no statistical differences in muscle weight between the groups ( p > 0.05), but there was a tendency toward weight gain in the Crush+MSC groups. Better motor functional recovery after crush and perineural canine Ad-MSC transplantation was observed during week 2. This was maintained till week 4. In conclusion, the canine Ad-MSC transplantation showed early pro-regenerative effects between 2-4 weeks in the rat model of sciatic nerve crush injury.

Mesenchymal stromal cell therapy: progress in manufacturing and assessments of potency

Mesenchymal stromal cell (MSC) therapies have been pursued for a broad spectrum of indications but mixed reports on clinical efficacy have given rise to some degree of skepticism regarding the effectiveness of this approach. However, recent reports of successful clinical outcomes and regulatory approvals for graft-versus-host disease, Crohn's disease and critical limb ischemia have prompted a shift in this perspective. With hundreds of clinical trials involving MSCs currently underway and an increasing demand for large-scale manufacturing protocols, there is a critical need to develop standards that can be applied to processing methods and to establish consensus assays for both MSC processing control and MSC product release. Reference materials and validated, uniformly applied tests for quality control of MSC products are needed. Here, we review recent developments in MSC manufacturing technologies, release testing and potency assays. We conclude that, although MSCs hold considerable promise clinically, economies of scale have yet to be achieved although numerous bioreactor technologies for scalable production of MSCs exist. Additionally, rigorous disease-specific product testing and comprehensive understanding of mechanisms of action, which are linked to relevant process and product release potency assays, will be required to ensure that these therapies continue to be successful.

Mesenchymal Stem Cell Therapy for Aging Frailty

Chronic diseases and degenerative conditions are strongly linked with the geriatric syndrome of frailty and account for a disproportionate percentage of the health care budget. Frailty increases the risk of falls, hospitalization, institutionalization, disability, and death. By definition, frailty syndrome is characterized by declines in lean body mass, strength, endurance, balance, gait speed, activity and energy levels, and organ physiologic reserve. Collectively, these changes lead to the loss of homeostasis and capability to withstand stressors and resulting vulnerabilities. There is a strong link between frailty, inflammation, and the impaired ability to repair tissue injury due to decreases in endogenous stem cell production. Although exercise and nutritional supplementation provide benefit to frail patients, there are currently no specific therapies for frailty. Bone marrow-derived allogeneic mesenchymal stem cells (MSCs) provide therapeutic benefits in heart failure patients irrespective of age. MSCs contribute to cellular repair and tissue regeneration through their multilineage differentiation capacity, immunomodulatory, and anti-inflammatory effects, homing and migratory capacity to injury sites, and stimulatory effect on endogenous tissue progenitors. The advantages of using MSCs as a therapeutic strategy include standardization of isolation and culture expansion techniques and safety in allogeneic transplantation. Based on this evidence, we performed a randomized, double-blinded, dose-finding study in elderly, frail individuals and showed that intravenously delivered allogeneic MSCs are safe and produce significant improvements in physical performance measures and inflammatory biomarkers. We thus propose that frailty can be treated and the link between frailty and chronic inflammation offers a potential therapeutic target, addressable by cell therapy.

Human Wharton's jelly mesenchymal stem cells protect axotomized rat retinal ganglion cells via secretion of anti-inflammatory and neurotrophic factors

Mesenchymal stem cell (MSC) transplantation is emerging as an ideal tool to restore the wounded central nervous system (CNS). MSCs isolated from extra-embryonic tissues have some advantages compared to MSCs derived from adult ones, such as an improved proliferative capacity, life span, differentiation potential and immunomodulatory properties. In addition, they are more immunoprivileged, reducing the probability of being rejected by the recipient. Umbilical cords (UCs) are a good source of MSCs because they are abundant, safe, non-invasively harvested after birth and, importantly, they are not encumbered with ethical problems. Here we show that the intravitreal transplant of Wharton´s jelly mesenchymal stem cells isolated from three different human UCs (hWJMSCs) delays axotomy-induced retinal ganglion cell (RGC) loss. In vivo, hWJMSCs secrete anti-inflammatory molecules and trophic factors, the latter alone may account for the elicited neuroprotection. Interestingly, this expression profile differs between naive and injured retinas, suggesting that the environment in which the hWJMSCs are modulates their secretome. Finally, even though the transplant itself is not toxic for RGCs, it is not innocuous as it triggers a transient but massive infiltration of Iba1⁺cells from the choroid to the retina that alters the retinal structure.

A review of clinical trials: mesenchymal stem cell transplant therapy in type 1 and type 2 diabetes mellitus

Type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) are widely prevalent metabolic diseases with differing pathologies. T1DM manifests due to autoimmune destruction of the pancreatic beta cells, resulting in a diminished secretion of insulin. T2DM originates from a state of insulin resistance, resulting in hyperglycemia and reduction in beta cell mass. Both diseases can cause severe health consequences. Despite the globally increasing prevalence of both T1DM and T2DM there remains to be a medically defined cure for either of these diseases. Recently, mesenchymal stem cells (MSCs) have been proposed as a possible curative treatment method. In this review, we explain the molecular mechanisms underlying MSCs and their potential ability to treat T1DM and T2DM. We describe the capability of MSCs to differentiate into insulin-producing cells and regenerate pancreatic beta cells, as well as assess their role in modulating the immune system. Lastly, we evaluate the current literature focusing on the clinical application of MSC transplantation in T1DM and T2DM. Despite the favorable results, study designs and analyses cast doubt on the effectiveness of MSCs for the management of T1DM. Conversely, the positive metabolic effects consistently demonstrated in the literature offer hope for MSCs as a treatment for T2DM, at least in the short-term.

Mesenchymal Stromal Cell Preconditioning: The Next Step Toward a Customized Treatment For Severe Burn

Over the last century, the clinical management of severe skin burns significantly progressed with the development of burn care units, topical antimicrobials, resuscitation methods, early eschar excision surgeries, and skin grafts. Despite these considerable advances, the present treatment of severe burns remains burdensome, and patients are highly susceptible to skin engraftment failure, infections, organ dysfunction, and hypertrophic scarring. Recent researches have focused on mesenchymal stromal cell (MSC) therapy and hold great promises for tissue repair, as reported in several animal studies and clinical cases. In the present review, we will provide an up-to-date outlook of the pathophysiology of severe skin burns, clinical treatment modalities and current limitations. We will then focus on MSCs and their potential in the burn wound healing both in in vitro and in vivo studies. A specific attention will be paid to the cell preconditioning approach, as a means of improving the MSC efficacy in the treatment of major skin burns. In particular, we will debate how several preconditioning cues would modulate the MSC properties to better match up with the burn pathophysiology in the course of the cell therapy. Finally, we will discuss the clinical interest and feasibility of a MSC-based therapy in comparison to their paracrine derivatives, including microvesicles and conditioned media for the treatment of major skin burn injuries.

Microenvironmental support for cell delivery to the inner ear

Transplantation of mesenchymal stromal cells (MSC) presents a promising approach not only for the replacement of lost or degenerated cells in diseased organs but also for local drug delivery. It can potentially be used to enhance the safety and efficacy of inner ear surgeries such as cochlear implantation. Options for enhancing the effects of MSC therapy include modulating cell behaviour with customized bio-matrixes or modulating their behaviour by ex vivo transfection of the cells with a variety of genes. In this study, we demonstrate that MSC delivered to the inner ear of guinea pigs or to decellularized cochleae preferentially bind to areas of high heparin concentration. This presents an opportunity for modulating cell behaviour ex vivo. We evaluated the effect of carboxymethylglucose sulfate (Cacicol^®), a heparan sulfate analogue on spiral ganglion cells and MSC and demonstrated support of neuronal survival and support of stem cell proliferation.