Added effects of dexamethasone and mesenchymal stem cells on early Natural Killer cell activation

The potential of mesenchymal stem cells to induce immune tolerance to allogeneic transplants

Organ allograft transplantation is an effective treatment plan for patients with organ failure. Although the application of continuous immunosuppressants makes successful allograft survival possible, the patients' long-term survival rate and quality of life are not ideal. Therefore, it is necessary to find a new strategy to alleviate transplant rejection by developing therapies for permanent allograft acceptance. One promising approach is the application of tolerogenic mesenchymal stem cells (MSCs). Extensive research on MSCs has revealed that MSCs have potent differentiation potential and immunomodulatory properties. This review describes the molecular markers and functional properties of MSCs as well as the immunomodulatory mechanisms of MSCs in transplantation, focuses on the research progress in clinical trials of MSCs, and expounds on the future development prospects and possible limitations.

Combination of Dexamethasone and Tofacitinib Reduces Xenogeneic MSC-Induced Immune Responses in a Mouse Model of Alzheimer’s Disease

We have recently reported on how transplantation of human mesenchymal stem cells (MSCs) into the mouse parenchyma generated immune responses. To facilitate the clinical translation of MSC-based AD therapy, the safety and efficacy of human derived MSCs (hMSCs) must be confirmed in the pre-clinical stage. Thus, it is imperative to investigate measures to reduce immune responses exerted via xenotransplantation. In this study, immunosuppressants were co-administered to mice that had received injections of hMSCs into the parenchyma. Prior to performing experiments using transgenic AD mice (5xFAD), varying immunosuppressant regimens were tested in wild-type (WT) mice and the combination of dexamethasone and tofacitinib (DexaTofa) revealed to be effective in enhancing the persistence of hMSCs. According to transcriptome sequencing and immunohistochemical analyses, administration of DexaTofa reduced immune responses generated via transplantation of hMSCs in the parenchyma of 5xFAD mice. Significant mitigation of amyloid burden, however, was not noted following transplantation of hMSCs alone or hMSCs with DexaTofa. The efficacy of the immunosuppressant regimen should be tested in multiple AD mouse models to promote its successful application and use in AD stem cell therapy.

Emerging Trends in Mesenchymal Stem Cells Applications for Cardiac Regenerative Therapy: Current Status and Advances

Irreversible myocardium infarction is one of the leading causes of cardiovascular disease (CVD) related death and its quantum is expected to grow in coming years. Pharmacological intervention has been at the forefront to ameliorate injury-related morbidity and mortality. However, its outcomes are highly skewed. As an alternative, stem cell-based tissue engineering/regenerative medicine has been explored quite extensively to regenerate the damaged myocardium. The therapeutic modality that has been most widely studied both preclinically and clinically is based on adult multipotent mesenchymal stem cells (MSC) delivered to the injured heart. However, there is debate over the mechanistic therapeutic role of MSC in generating functional beating cardiomyocytes. This review intends to emphasize the role and use of MSC in cardiac regenerative therapy (CRT). We have elucidated in detail, the various aspects related to the history and progress of MSC use in cardiac tissue engineering and its multiple strategies to drive cardiomyogenesis. We have further discussed with a focus on the various therapeutic mechanism uncovered in recent times that has a significant role in ameliorating heart-related problems. We reviewed recent and advanced technologies using MSC to develop/create tissue construct for use in cardiac regenerative therapy. Finally, we have provided the latest update on the usage of MSC in clinical trials and discussed the outcome of such studies in realizing the full potential of MSC use in clinical management of cardiac injury as a cellular therapy module.

Dexamethasone priming enhances stemness and immunomodulatory property of tissue-specific human mesenchymal stem cells

BACKGROUND

Human Mesenchymal Stem Cells (hMSCs) represent a promising cell source for cell-based therapy in autoimmune diseases and other degenerative disorders due to their immunosuppressive, anti-inflammatory and regenerative potentials. Belonging to a glucocorticoid family, Dexamethasone (Dex) is a powerful anti-inflammatory compound that is widely used as therapy in autoimmune disease conditions or allogeneic transplantation. However, minimal immunomodulatory effect of hMSCs may limit their therapeutic uses. Moreover, the effect of glucocorticoids on the immunomodulatory molecules or other regenerative properties of tissue-specific hMSCs remains unknown.

METHOD

Herein, we evaluated the in vitro effect of Dex at various dose concentrations and time intervals, 1000 ng/ml, 2000 ng/ml, 3000 ng/ml and 24 h, 48 h respectively, on the basic characteristics and immunomodulatory properties of Bone marrow derived MSC (BM-MSCs), Adipose tissue derived MSCs (AD-MSCs), Dental Pulp derived MSC (DP-MSCs) and Umbilical cord derived MSCs (UC-MSCs).

RESULTS

The present study indicated that the concentration of Dex did not ramify the cellular morphology nor showed cytotoxicity as well as conserved the basic characteristics of tissue specific hMSCs including cell proliferation and surface marker profiling. However, quite interestingly it was observed that the stemness markers (Oct-4, Sox-2, Nanog and Klf-4) showed a significant upregulation in DP-MSCs and AD-MSCs followed by UC-MSCs and BM-MSCs. Additionally, immunomodulatory molecules, Prostaglandin E-2 (PGE-2), Indoleamine- 2,3-dioxygenase (IDO) and Human Leukocyte Antigen-G (HLA-G) were seen to be upregulated in a dose-dependent manner. Moreover, there was a differential response of tissue specific hMSCs after pre-conditioning with Dex during mixed lymphocyte reaction, wherein UC-MSCs and DP-MSCs showed enhanced immunosuppression as compared to AD-MSCs and BM-MSCs, thereby proving to be a better candidate for therapeutic applications in immune-related diseases.

CONCLUSION

Dex preconditioning improved the hMSCs immunomodulatory property and may have reduced the challenge associated with minimal potency and strengthen their therapeutic efficacy. Preconditioning of tissue specific hMSCs with dexamethasone biomanufacturers the enhanced potential hMSCs with better stemness and immunomodulatory properties for future therapeutics.

Immunomodulation effect of mesenchymal stem cells in islet transplantation

Mesenchymal stem cells (MSCs) therapy has brought a great enthusiasm to the treatment of various immune disorders, tissue regeneration and transplantation therapy. MSCs are being extensively investigated for their immunomodulatory actions. MSCs can deliver immunomodulatory signals to inhibit allogeneic T cell immune responses by downregulating pro-inflammatory cytokines and increasing regulatory cytokines and growth factors. Islet transplantation is a therapeutic alternative to the insulin therapy for the treatment of type 1 diabetes mellitus (T1DM). However, the acute loss of islets due to the lack of vasculature and hypoxic milieu in the immediate post-transplantation period may lead to treatment failure. Moreover, despite the use of potent immunosuppressive drugs, graft failure persists because of immunological rejection. Many in vitro and in vivo researches have demonstrated the multipotency of MSCs as a mediator of immunomodulation and a great approach for enhancement of islet engraftment. MSCs can interact with immune cells of the innate and adaptive immune systems via direct cell-cell contact or through secretomes containing numerous soluble growth and immunomodulatory factors or mitochondrial transfer. This review highlights the interactions between MSCs and different immune cells to mediate immunomodulatory functions along with the importance of MSCs therapy for the successful islet transplantation.

Fostering mesenchymal stem cell therapy to halt cytokine storm in COVID-19

The coronavirus disease 2019 (COVID-19) has been threatening the globe since the end of November 2019. The disease revealed cracks in the health care system as health care providers across the world were left without guidelines on definitive usage of pharmaceutical agents or vaccines. The World Health Organization (WHO) declared COVID-19 as a pandemic on the 11th of March 2020. Individuals with underlying systemic disorders have reported complications, such as cytokine storms, when infected with the virus. As the number of positive cases and the death toll across the globe continue to rise, various researchers have turned to cell based therapy using stem cells to combat COVID-19. The field of stem cells and regenerative medicine has provided a paradigm shift in treating a disease with minimally invasive techniques that provides maximal clinical and functional outcome for patients. With the available evidence of immunomodulatory and immune-privilege actions, mesenchymal stem cells (MSCs) can repair, regenerate and remodulate the native homeostasis of pulmonary parenchyma with improved pulmonary compliance. This article revolves around the usage of novel MSCs therapy for combating COVID-19.

Mesenchymal Stem Cell-Mediated Immuno-Modulatory and Anti- Inflammatory Mechanisms in Immune and Allergic Disorders

Background: Mesenchymal Stem Cells (MSCs) are present in almost all the tissues of the body and act as the backbone of the internal tissue homeostasis. Among their various characteristic features, immuno-modulatory and/ anti-inflammatory properties play an important role in therapeutics.

Objective: The current topic focuses on the characterization and immuno-modulatory and/ anti-inflammatory properties of MSCs. To present and discuss the current status of MSCs immuno-modulatory properties.

Methods: Available literature on MSCs properties and patents have been detailed, critically interpreted, and discussed based upon available literature. The main focus has been on their characteristic immuno-modulatory and anti-inflammatory properties though some of the basic characterization markers have also been detailed. The databases searched for the literature include PubMed, Med Line, PubMed Central, Science Direct and a few other scientific databases.

Results: MSCs are present in a very limited concentration in the tissues, and as such their culture expansion becomes imperative. MSCs immuno-modulatory and anti-inflammatory roles are achieved through direct cell-cell contact and / by the release of certain factors. Such properties are controlled by micro-environment upon which currently very limited control can be exerted. Besides, further insights in the xeno-protein free culture media as against the fetal bovine serum is required.

Conclusion: MSCs have been well-isolated, cultured and characterized from numerous tissues of the body. The majority of the studies have shown MSCs as immuno-compromised with immunomodulatory and / or anti-inflammatory properties except some of the latest studies that have failed to achieve the desired results and thus, demand further research. Further research is required in the area to translate the results into clinical application.

The mechanisms of cellular crosstalk between mesenchymal stem cells and natural killer cells: Therapeutic implications

Mesenchymal stem cells (MSCs) are mesenchymal precursors of various origins, with well-known immunomodulatory effects. Natural killer (NK) cells, the major cells of the innate immune system, are critical for the antitumor and antiviral defenses; however, in certain cases, they may be the main culprits in the pathogenesis of some NK-related conditions such as autoimmunities and hematological malignancies. On the other hand, these cells seem to be the major responders in beneficial phenomena like graft versus leukemia. Substantial data suggest that MSCs can variably affect NK cells and can be affected by these cells. Accordingly, acquiring a profound understanding of the crosstalk between MSCs and NK cells and the involved mechanisms seems to be a necessity to develop therapeutic approaches based on such interactions. Therefore, in this study, we made a thorough review of the existing literature on the interactions between MSCs and NK cells with a focus on the underlying mechanisms. The current knowledge herein suggests that MSCs possess a great potential to be used as tools for therapeutic targeting of NK cells in disease context and that preconditioning of MSCs, as well as their genetic manipulation before administration, may provide a wider variety of options in terms of eliciting more specific and desirable therapeutic outcomes. Nevertheless, our knowledge regarding the effects of MSCs on NK cells is still in its infancy, and further studies with well-defined conditions are warranted herein.

Mechanisms of Key Innate Immune Cells in Early- and Late-Onset Preeclampsia

Preeclampsia is a complex cardiovascular disorder of pregnancy with underlying multifactorial pathogeneses; however, its etiology is not fully understood. It is characterized by the new onset of maternal hypertension after 20 weeks of gestation, accompanied by proteinuria, maternal organ damage, and/or uteroplacental dysfunction. Preeclampsia can be subdivided into early- and late-onset phenotypes (EOPE and LOPE), diagnosed before 34 weeks or from 34 weeks of gestation, respectively. Impaired placental development in early pregnancy and subsequent growth restriction is often associated with EOPE, while LOPE is associated with maternal endothelial dysfunction. The innate immune system plays an essential role in normal progression of physiological pregnancy and fetal development. However, inappropriate or excessive activation of this system can lead to placental dysfunction or poor maternal vascular adaptation and contribute to the development of preeclampsia. This review aims to comprehensively outline the mechanisms of key innate immune cells including macrophages, neutrophils, natural killer (NK) cells, and innate B1 cells, in normal physiological pregnancy, EOPE and LOPE. The roles of the complement system, syncytiotrophoblast extracellular vesicles and mesenchymal stem cells (MSCs) are also discussed in the context of innate immune system regulation and preeclampsia. The outlined molecular mechanisms, which represent potential therapeutic targets, and associated emerging treatments, are evaluated as treatments for preeclampsia. Therefore, by addressing the current understanding of innate immunity in the pathogenesis of EOPE and LOPE, this review will contribute to the body of research that could lead to the development of better diagnosis, prevention, and treatment strategies. Importantly, it will delineate the differences in the mechanisms of the innate immune system in two different types of preeclampsia, which is necessary for a more personalized approach to the monitoring and treatment of affected women.

Mesenchymal stromal cell therapies: immunomodulatory properties and clinical progress

Mesenchymal stromal cells (MSCs) are a subset of heterogeneous non-hematopoietic fibroblast-like cells that can differentiate into cells of multiple lineages, such as chondrocytes, osteoblasts, adipocytes, myoblasts, and others. These multipotent MSCs can be found in nearly all tissues but mostly located in perivascular niches, playing a significant role in tissue repair and regeneration. Additionally, MSCs interact with immune cells both in innate and adaptive immune systems, modulating immune responses and enabling immunosuppression and tolerance induction. Understanding the biology of MSCs and their roles in clinical treatment is crucial for developing MSC-based cellular therapy for a variety of pathological conditions. Here, we review the progress in the study on the mechanisms underlying the immunomodulatory and regenerative effects of MSCs; update the medical translation of MSCs, focusing on the registration trials leading to regulatory approvals; and discuss how to improve therapeutic efficacy and safety of MSC applications for future.

Mesenchymal Stromal Cells, a New Player in Reducing Complications From Liver Transplantation?

In response to the global burden of liver disease there has been a commensurate increase in the demand for liver transplantation. However, due to a paucity of donor organs many centers have moved toward the routine use of marginal allografts, which can be associated with a greater risk of complications and poorer clinical outcomes. Mesenchymal stromal cells (MSC) are a multi-potent progenitor cell population that have been utilized to modulate aberrant immune responses in acute and chronic inflammatory conditions. MSC exert an immunomodulatory effect on innate and adaptive immune systems through the release of both paracrine soluble factors and extracellular vesicles. Through these routes MSC can switch the regulatory function of the immune system through effects on macrophages and T regulatory cells enabling a switch of phenotype from injury to restoration. A key benefit seems to be their ability to tailor their response to the inflammatory environment without compromising the host ability to fight infection. With over 200 clinical trials registered to examine MSC therapy in liver disease and an increasing number of trials of MSC therapy in solid organ transplant recipients, there is increasing consideration for their use in liver transplantation. In this review we critically appraise the potential role of MSC therapy in the context of liver transplantation, including their ability to modulate reperfusion injury, their role in the reduction of medium term complications in the biliary tree and their potential to enhance tolerance in transplanted organs.

Modulation of the secretion of mesenchymal stem cell immunoregulatory factors by hydrolyzed fish collagen

The aim of the present study was to investigate the possible immunomodulatory effects of osteogenically differentiated bone marrow mesenchymal stem cells induced by hydrolyzed fish collagen. Marine biomaterials have attracted significant attention for their environmental friendliness and renewability. Hydrolyzed fish collagen (HFC) has been discovered to induce the osteoblastic differentiation of stem cells, which underlies the foundation for its application in tissue engineering. Stem cells and their biomaterial carriers face acute immune rejection mediated by host macrophages. A potential strategy for combatting rejection in stem cell therapy is to modify the polarization of macrophages. However, whether HFC-induced mesenchymal stem cells maintain their immunomodulatory ability remains to be determined. To understand this phenomenon, a co-culture model of direct contact was established between bone marrow mesenchymal stem cells (BMSCs) and RAW264.7 macrophages, where the secretion of nitrous oxide from macrophages was measured using Griess colorimetric assay. ELISAs were performed to measure the secretion of interleukin (IL)-1β, IL-6, transforming growth factor (TGF)-β and IL-10, whilst reverse transcription-quantitative PCR was used to assess the expression levels of IL-1β, IL-6, CD206, resistin-like molecule α (FIZZ1) and prostaglandin E2 receptor 4 (EP4). In addition, the expression levels of relevant proteins in the phosphorylated-cyclic AMP-responsive element-binding protein-CCAAT/enhancer-binding protein β (EBPβ) pathway were investigated using western blotting. HFC-induced BMSCs were found to suppress the expression levels of IL-1β and IL-6, whilst increasing the expression levels of CD206 and FIZZ1 in RAW264.7 macrophages. HFC-induced BMSCs also inhibited the secretion of IL-1β and IL-6, whilst promoting the secretion of TGF-β and IL-10 secretion from RAW264.7 macrophages. Mechanistic studies using western blotting discovered that HFC stimulated the secretion of prostaglandin E2 from BMSCs, which subsequently increased the expression of EP4 on the macrophages. EP4 then increased the expression levels of C/EBPβ and arginase 1 further. In conclusion, results from the present study suggested that following induction with HFC, BMSCs maintain their immunomodulatory activity.

Aggregation of Human Mesenchymal Stromal Cells Eliminates Their Ability to Suppress Human T Cells

Mesenchymal stromal cells (MSCs) are administered locally to treat sites of inflammation. Local delivery is known to cause MSCs to aggregate into “spheroids,” which alters gene expression and phenotype. While adherent MSCs are highly efficient in their inhibition of T cells, whether or not this property is altered upon MSC aggregation has not been thoroughly determined. In this study, we discovered that aggregation of MSCs into spheroids causes them to lose their T cell-suppressive abilities. Interestingly, adding budesonide, a topical glucocorticoid steroid, alongside spheroids partially restored MSC suppression of T cell proliferation. Through a series of inhibition and add-back studies, we determined budesonide acts synergistically with spheroid MSC-produced PGE2 to suppress T cell proliferation through the PGE2 receptors EP2 and EP4. These findings highlight critical differences between adherent and spheroid MSC interactions with human immune cells that have significant translational consequences. In addition, we uncovered a mechanism through which spheroid MSC suppression of T cells can be partly restored. By understanding the phenotypic changes that occur upon MSC aggregation and the impact of MSC drug interactions, improved immunosuppressive MSC therapies for localized delivery can be designed.

Unique natural killer cell subpopulations are associated with exacerbation risk in chronic obstructive pulmonary disease

Chronic Obstructive Pulmonary Disease (COPD) is the third leading cause of death worldwide. COPD is frequently punctuated by acute exacerbations that are precipitated primarily by infections, which increase both morbidity and mortality and inflates healthcare costs. Despite the significance of exacerbations, little understanding of immune function in COPD exacerbations exists. Natural killer (NK) cells are important effectors of innate and adaptive immune responses to pathogens and NK cell function is altered in smokers and COPD. Using high-dimensional flow cytometry, we phenotyped peripheral blood NK cells from never smokers, smokers, and COPD patients and employed a non-supervised clustering algorithm to define and detect changes in NK cell populations. We identified greater than 1,000 unique NK cell subpopulations across patient groups and describe 13 altered NK populations in patients who experienced prior exacerbations. Based upon cluster sizes and associated fluorescence data, we generated a logistic regression model to predict patients with a history of exacerbations with high sensitivity and specificity. Moreover, highly enriched NK cell subpopulations implicated in the regression model exhibited enhanced effector functions as defined by in vitro cytotoxicity assays. These novel data reflect the effects of smoking and disease on peripheral blood NK cell phenotypes, provide insight into the potential immune pathophysiology of COPD exacerbations, and indicate that NK cell phenotyping may be a useful and biologically relevant marker to predict COPD exacerbations.

Immune modulation by mesenchymal stem cells

Mesenchymal stem cells (MSCs) can be derived from various adult tissues with multipotent and self‐renewal abilities. The characteristics of presenting no major ethical concerns, having low immunogenicity and possessing immune modulation functions make MSCs promising candidates for stem cell therapies. MSCs could promote inflammation when the immune system is underactivated and restrain inflammation when the immune system is overactivated to avoid self‐overattack. These cells express many immune suppressors to switch them from a pro‐inflammatory phenotype to an anti‐inflammatory phenotype, resulting in immune effector cell suppression and immune suppressor cell activation. We would discuss the mechanisms governing the immune modulation function of these cells in this review, especially the immune‐suppressive effects of MSCs.

Human menstrual blood-derived stromal/stem cells modulate functional features of natural killer cells

Although natural killer (NK) cells play a crucial role in the maintenance of a successful pregnancy, their cytotoxic activity should be tightly controlled. We hypothesized that endometrial mesenchymal stromal/stem cells (eMSCs) could potentially attenuate the functional features of NK cells. Herein, we assessed immunomodulatory effects of menstrual blood-derived stromal/stem cells (MenSCs), as a surrogate for eMSCs, on NK cells function. Our results showed that MenSCs induced proliferation of NK cells. However, IFN-γ/IL-1β pretreated MenSCs significantly inhibited NK cell proliferation. Of 41 growth factors tested, MenSCs produced lower levels of insulin-like growth factor binding proteins (IGFBPs) 1-4, VEGF-A, β-NGF, and M-CSF compared to bone marrow-derived mesenchymal stem cells (BMSCs). MenSCs displayed high activity of IDO upon IFN-γ treatment. The antiproliferative potential of IFN-γ/IL-1β-pretreated MenSCs was mediated through IL-6 and TGF-β. MenSCs impaired the cytotoxic activity of NK cells on K562 cells, consistent with the lower expression of perforin, granzymes A, and B. We also observed that in vitro decidualization of MenSCs in the presence of IFN-γ reduced the inhibitory effect of MenSCs on NK cell cytotoxicity against K562 target cells. Additionally, MenSCs were found to be prone to NK cell-mediated lysis in an MHC-independent manner. Our findings imply that dysregulation of NK cells in such pregnancy-related disorders as miscarriage may stem from dysfunctioning of eMSCs.

Effect of Comedications and Endotoxins on Mesenchymal Stem Cell Secretomes, Migratory and Immunomodulatory Capacity

Mesenchymal stem cells (MSCs) are becoming an increasingly popular therapeutic option among patients with a broad range of ailments to modulate immunity and induce regeneration. The majority of patients receiving these MSC therapies are on concurrent medication or have ongoing infection. In the present study, we examined the effect of immunosuppressive drugs and lipopolysaccharides (LPS)/endotoxins on the secretory profile, migration towards site of injury, and suppression of lymphocyte proliferation of bone marrow-derived MSCs (BMSCs). Generally, LPS coculture augmented the secretory capacity of BMSCs while exposure to immunosuppressive drugs resulted primarily in no change or attenuated secretion, with some cases of increased secretion, dependent on the cytokine assayed. Among the immunosuppressants evaluated, Hydrocortisone had the most widespread inhibitory effect, while LPS from E. coli O111:B4 had the most potent stimulatory effect. In addition, we also showed that Hydrocortisone or LPS from E. coli O111:B4 affected the migratory and immunosuppressive capacity of BMSCs. Following simulation with Hydrocortisone, BMSC migration was attenuated, and immunosuppressive capacity against T cell proliferation was enhanced, however, the opposite effects were seen with LPS from E. coli O111:B4. Our data suggests that the clinical outcomes of MSC-based therapy are affected by the use of immunosuppressive medication or the presence of endotoxemia in patients.

Skin tissue engineering: wound healing based on stem-cell-based therapeutic strategies

Normal wound healing is a dynamic and complex multiple phase process involving coordinated interactions between growth factors, cytokines, chemokines, and various cells. Any failure in these phases may lead wounds to become chronic and have abnormal scar formation. Chronic wounds affect patients' quality of life, since they require repetitive treatments and incur considerable medical costs. Thus, much effort has been focused on developing novel therapeutic approaches for wound treatment. Stem-cell-based therapeutic strategies have been proposed to treat these wounds. They have shown considerable potential for improving the rate and quality of wound healing and regenerating the skin. However, there are many challenges for using stem cells in skin regeneration. In this review, we present some sets of the data published on using embryonic stem cells, induced pluripotent stem cells, and adult stem cells in healing wounds. Additionally, we will discuss the different angles whereby these cells can contribute to their unique features and show the current drawbacks.

Mesenchymal Stem Cell-Based Immunomodulation: Properties and Clinical Application

Mesenchymal stem cells (MSCs) are multipotent stem cells characterized by self-renewal, production of clonal cell populations, and multilineage differentiation. They exist in nearly all tissues and play a significant role in tissue repair and regeneration. Additionally, MSCs possess wide immunoregulatory properties via interaction with immune cells in both innate and adaptive immune systems, leading to immunosuppression of various effector functions. Numerous bioactive molecules secreted by MSCs, particularly cytokines, growth factors, and chemokines, exert autocrine/paracrine effects that modulate the physiological processes of MSCs. These invaluable virtues of MSCs provide new insight into potential treatments for tissue damage and inflammation. In particular, their extensive immunosuppressive properties are being explored for promising therapeutic application in immune disorders. Recently, clinical trials for MSC-mediated therapies have rapidly developed for immune-related diseases following reports from preclinical studies declaring their therapeutic safety and efficacy. Though immunotherapy of MSCs remains controversial, these clinical trials pave the way for their widespread therapeutic application in immune-based diseases. In this review, we will summarize and update the latest research findings and clinical trials on MSC-based immunomodulation.

The effect of clinically relevant doses of immunosuppressive drugs on human mesenchymal stem cells

Immunosuppressive drugs are used to suppress graft rejection after transplantation and for the treatment of various diseases. The main limitations of their use in clinical settings are severe side effects, therefore alternative approaches are desirable. In this respect, mesenchymal stem cells (MSCs) possess a regenerative and immunomodulatory capacity that has generated considerable interest for their use in cell-based therapy. Currently, MSCs are tested in many clinical trials, including the treatment of diseases which require simultaneous immunosuppressive treatment. Since the molecular targets of immunosuppressive drugs are also present in MSCs, we investigated whether immunosuppressive drugs interact with the activity of MSCs. Human MSCs isolated from the bone marrow (BM) or adipose tissue (AT) were cultured in the presence of clinical doses of five widely used immunosuppressive drugs (cyclosporine A, mycophenolate mofetil, rapamycin, prednisone and dexamethasone), and the influence of these drugs on several factors related to the immunosuppressive properties of MSCs, including the expression of immunomodulatory enzymes, various growth factors, cytokines, chemokines, adhesion molecules and proapoptotic ligands, was assessed. Glucocorticoids, especially dexamethasone, showed the most prominent effects on both types of MSCs and suppressed the expression of the majority of the factors that were tested. A significant increase of hepatocyte growth factor production in AT-MSCs and of indoleamine 2,3-dioxygenase expression in both types of MSCs were the only exceptions. In conclusion, clinically relevant doses of inhibitors of calcineurin, mTOR and IMPDH and glucocorticoids interfere with MSC functions, but do not restrain their immunosuppressive properties. These findings should be taken into account before preparing immunosuppressive strategies combining the use of immunosuppressive drugs and MSCs.

Interactions between mesenchymal stem cells and the immune system

In addition to being multi-potent, mesenchymal stem cells (MSCs) possess immunomodulatory functions that have been investigated as potential treatments in various immune disorders. MSCs can robustly interact with cells of the innate and adaptive immune systems, either through direct cell-cell contact or through their secretome. In this review, we discuss current findings regarding the interplay between MSCs and different immune cell subsets. We also draw attention to the mechanisms involved.

Mesenchymal stem cells increase skin graft survival time and up-regulate PD-L1 expression in splenocytes of mice

Recently, mesenchymal stem cells (MSCs) have gained considerable interests as hopeful therapeutic cells in transplantation due to their immunoregulatory functions. But exact mechanisms underlying MSCs immunoregulatory function is not fully understood. Herein, in addition to investigate the ability of MSCs to prolong graft survival time, the effects of them on the expression of PD-L1 and IDO immunomodulatory molecules in splenocytes of skin graft recipient mice was clarified. To achieve this goal, full-thickness skins were transplanted from C57BL/6 to BALB/c mice. MSCs were isolated from bone marrow of BALB/c mice and injected to the recipient mice. Skin graft survival was monitored daily to determine graft rejection time. On days 2, 5 and 10 post skin transplantation, serum cytokine levels and expression of PD-L1 and IDO mRNA and protein in the splenocytes of recipient mice were evaluated. The results showed that administration of MSCs prolonged skin graft survival time from 11 to 14 days. On days 2 and 5 post transplantation, splenocytes PD-L1 expression and IL-10 serum level in MSCs treated mice were higher than those in the controls, while IL-2 and IFN-γ levels were lower. Rejection in MSCs treated mice was accompanied by an increase in IL-2 and IFN-γ, and decrease in PD-L1 expression and IL-10 level. No difference in the expression of IDO between MSCs treated mice and controls was observed. In conclusion, we found that one of the mechanisms underlying MSCs immunomodulatory function could be up-regulating PD-L1 expression.