Mesenchymal stromal cells infusions improve refractory chronic graft versus host disease through an increase of CD5+ regulatory B cells producing interleukin 10

Extracellular vesicles derived from human umbilical cord mesenchymal stem cells alleviate rat hepatic ischemia-reperfusion injury by suppressing oxidative stress and neutrophil inflammatory response

Mesenchymal stem cells (MSCs) have been reported to exert therapeutic effects on immunoregulation, tissue repair, and regeneration from the bench to the bedside. Increasing evidence demonstrates that extracellular vesicles (EVs) derived from MSCs could contribute to these effects and are considered as a potential replacement for stem cell-based therapies. However, the efficacy and underlying mechanisms of EV-based treatment in hepatic ischemia-reperfusion injury (IRI) remain unclear. Here, we demonstrated that human umbilical cord MSC-EVs (huc-MSC-EVs) could protect against IRI-induced hepatic apoptosis by reducing the infiltration of neutrophils and alleviating oxidative stress in hepatic tissue in vivo. Meanwhile, huc-MSC-EVs reduced the respiratory burst of neutrophils and prevented hepatocytes from oxidative stress-induced cell death in vitro. Interestingly, we found that the mitochondria-located antioxidant enzyme, manganese superoxide dismutase (MnSOD), was encapsulated in huc-MSC-EVs and reduced oxidative stress in the hepatic IRI model. Knockdown of MnSOD in huc-MSCs decreased the level of MnSOD in huc-MSC-EVs and attenuated the antiapoptotic and antioxidant capacities of huc-MSC-EVs, which could be partially rescued by MnSOD mimetic manganese (III) 5,10,15,20-tetrakis (4-benzoic acid) porphyrin (MnTBAP). In summary, these findings provide new clues to reveal the therapeutic effects of huc-MSC-EVs on hepatic IRI and evaluate their preclinical application.-Yao, J., Zheng, J., Cai, J., Zeng, K., Zhou, C., Zhang, J., Li, S., Li, H., Chen, L., He, L., Chen, H., Fu, H., Zhang, Q., Chen, G., Yang, Y., Zhang, Y. Extracellular vesicles derived from human umbilical cord mesenchymal stem cells alleviate rat hepatic ischemia-reperfusion injury by suppressing oxidative stress and neutrophil inflammatory response.

Stanniocalcin-2 contributes to mesenchymal stromal cells attenuating murine contact hypersensitivity mainly via reducing CD8+ Tc1 cells

Mesenchymal stromal cells (MSCs) have been demonstrated to ameliorate allergic contact dermatitis (ACD), a typical T-cell-mediated disorder. However, the underlying mechanisms behind the MSC-based treatment for ACD have not yet been fully elucidated. The stanniocalcins (STCs) comprise a family of secreted glycoprotein hormones that act as important anti-inflammatory proteins. Here, we investigated the roles of STCs in MSC-mediated T-cell suppression and their potential role in the MSC-based treatment for ACD. Gene expression profiling revealed that STC2, but not STC1, was highly expressed in MSCs. STC2 knockdown in MSCs significantly impaired their effects in reducing TNF-α- and IFN-γ-producing CD8+ T cells. Importantly, silencing the STC2 expression in MSCs abated their therapeutic effect on contact hypersensitivity (CHS) in mice, mainly restoring the generation and infiltration of IFN-γ-producing CD8+ T cells (Tc1 cells). Mechanistically, STC2 co-localized with heme oxygenase 1 (HO-1) in MSCs, and contributed to MSC-mediated reduction of CD8+ Tc1 cells via regulating HO-1 activity. Together, these findings newly identify STC2 as the first stanniocalcin responsible for mediating the immunomodulatory effects of MSCs on allogeneic T cells and STC2 contribute to MSC-based treatment for ACD mainly via reducing the CD8+ Tc1 cells.

How to Hit Mesenchymal Stromal Cells and Make the Tumor Microenvironment Immunostimulant Rather Than Immunosuppressive

Experimental evidence indicates that mesenchymal stromal cells (MSCs) may regulate tumor microenvironment (TME). It is conceivable that the interaction with MSC can influence neoplastic cell functional behavior, remodeling TME and generating a tumor cell niche that supports tissue neovascularization, tumor invasion and metastasization. In addition, MSC can release transforming growth factor-beta that is involved in the epithelial-mesenchymal transition of carcinoma cells; this transition is essential to give rise to aggressive tumor cells and favor cancer progression. Also, MSC can both affect the anti-tumor immune response and limit drug availability surrounding tumor cells, thus creating a sort of barrier. This mechanism, in principle, should limit tumor expansion but, on the contrary, often leads to the impairment of the immune system-mediated recognition of tumor cells. Furthermore, the cross-talk between MSC and anti-tumor lymphocytes of the innate and adaptive arms of the immune system strongly drives TME to become immunosuppressive. Indeed, MSC can trigger the generation of several types of regulatory cells which block immune response and eventually impair the elimination of tumor cells. Based on these considerations, it should be possible to favor the anti-tumor immune response acting on TME. First, we will review the molecular mechanisms involved in MSC-mediated regulation of immune response. Second, we will focus on the experimental data supporting that it is possible to convert TME from immunosuppressive to immunostimulant, specifically targeting MSC.

Tyrosine kinase inhibitors and mesenchymal stromal cells: effects on self-renewal, commitment and functions

The hope of selectively targeting cancer cells by therapy and eradicating definitively malignancies is based on the identification of pathways or metabolisms that clearly distinguish “normal” from “transformed” phenotypes. Some tyrosine kinase activities, specifically unregulated and potently activated in malignant cells, might represent important targets of therapy. Consequently, tyrosine kinase inhibitors (TKIs) might be thought as the “vanguard” of molecularly targeted therapy for human neoplasias. Imatinib and the successive generations of inhibitors of Bcr-Abl1 kinase, represent the major successful examples of TKI use in cancer treatment. Other tyrosine kinases have been selected as targets of therapy, but the efficacy of their inhibition, although evident, is less definite. Two major negative effects exist in this therapeutic strategy and are linked to the specificity of the drugs and to the role of the targeted kinase in non-malignant cells. In this review, we will discuss the data available on the TKIs effects on the metabolism and functions of mesenchymal stromal cells (MSCs). MSCs are widely distributed in human tissues and play key physiological roles; nevertheless, they might be responsible for important pathologies. At present, bone marrow (BM) MSCs have been studied in greater detail, for both embryological origins and functions. The available data are evocative of an unexpected degree of complexity and heterogeneity of BM-MSCs. It is conceivable that this grade of intricacy occurs also in MSCs of other organs. Therefore, in perspective, the negative effects of TKIs on MSCs might represent a critical problem in long-term cancer therapies based on such inhibitors.

Advances in mesenchymal stromal cell therapy in the management of Crohn's disease

The aim of therapy in Crohn's disease (CD) is induction and maintenance of remission, promotion of mucosal healing and restoration of quality of life. Even the best treatment regimes, including combinations of biologics and immunomodulators lack durable efficacy and have well documented side effects. Accordingly, there is an unmet need for novel therapies. Mesenchymal stromal cells (MSCs) are a subset of non-hematopoietic stem cells that home to sites of inflammation where they exert potent immunomodulatory effects and contribute to tissue repair. Their utility is being explored in several inflammatory and immune mediated disorders including CD, where they have demonstrated favourable safety, feasibility and efficacy profiles. Areas covered: This review highlights current knowledge on MSC therapy and critically evaluates their safety, efficacy and potential mechanisms of action in CD. Expert commentary: Building on positive early phase clinical trials and a recent phase 3 trial in perianal CD, there is considerable optimism for the possibility of MSCs changing the treatment landscape in complicated CD. Although important questions remain unanswered, including the safety and durability of MSC therapy, optimal adjunctive therapies and their sourcing and manufacturing, it is anticipated that MSCs are likely to enter mainstream treatment algorithms in the near future.

Sequential intensified conditioning followed by prophylactic DLI could reduce relapse of refractory acute leukemia after allo-HSCT

The major obstacle is leukemia relapse for refractory leukemia undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). We previously introduced a strategy of sequential intensified conditioning and early rapid immunosupressant withdrawal for refractory leukemia undergoing allo-HSCT, with 5-year overall survival (OS) and 3-year relapse rate of 44.6% and 33.3%. To reduce leukemia relapse, prophylactic donor lymphocyte infusion (DLI) was administered based on our historical strategy. A total of 153 refractory advanced acute leukemia patients were enrolled in this prospective study. According to the availability of donor lymphocytes and the criteria for DLI, 144 patients surviving day +60 were divided into two groups (80 DLI versus 64 non-DLI). The relapse rate was less and OS was better in patients receiving DLI than in those not receiving DLI (22.7% vs 33.9%, P=0.048; 58.1% vs 54.9%, P=0.043). The non-relapse mortality (NRM) was similar between DLI and non-DLI groups (P=0.104). Overall, the 5-year overall and disease-free survival post-transplantation were 51.1%±5.7% and 49.2%±5.3%. The 5-year relapse rate and NRM were 27.3%±4.4% and 29.7%±5.3%. Multivariate analysis revealed that lower bone marrow blasts on day 0, DLI and chronic graft-versus-host disease were associated with less relapse and better OS. The strategy of sequential intensified conditioning followed by early immunosupressant withdrawal and DLI could reduce relapse of refractory acute leukemia after allo-HSCT and improve survival.

Bone marrow mesenchymal stem cells suppress IL-9 in adjuvant-induced arthritis

Interleukin-9 (IL-9) has been shown to be upregulated in rheumatoid arthritis (RA). The exact role of IL-9 has not yet been effectively studied. Mesenchymal stem cells (MSCs) have shown a promising immunomodulatory role towards repairing cartilage and restoring joint function. One of the key problems influencing the therapeutic efficacy of stem cell therapy is the poor cell survival following transplantation. This is attributed to oxidative and inflammatory stresses at the injured sites. Hesperidin (Hsd), a flavanone present in citrus fruits, has been studied as potential therapeutic agents that have anti-oxidant and anti-inflammatory activities. The objective of this study is to evaluate the therapeutic paracrine action of bone marrow MSCs on the IL-9 level in adjuvant-induced arthritis (AIA) and the enhancement effect of Hsd on transplanted MSCs. Articular tissue inflammation and cartilage damage were assessed by histological scoring. Antinuclear autoantibodies, tumour necrosis factor-alpha (TNF-α), IL-9, IL-4, interferon gamma (IFN-δ), and transforming growth factor-beta1 (TGF-β1), as well as malondialdehyde (MDA), glutathione (GSH), and superoxide dismutase (SOD) levels, were assessed in spleen tissue homogenates after treatment with MSCs either alone or combined with Hsd for 4 weeks in an AIA rat model. Results of this study confirmed that MSCs decreased IL-9 levels in AIA and provide novel insights into the application of Hsd on MSC-based treatments. Highlights Adjuvant-induced arthritis (AIA) is one of the most widely used models that has a great similarity to rheumatoid arthritis (RA). Few studies in recent years have estimated IL-9 in rheumatic diseases and it remains an understudied cytokine. For the first time, bone marrow mesenchymal stem cells (MSCs) therapy has a vital role in splenocytes IL-9 level and further studies are required. Combined therapy of MSCs with antioxidants as hesperidin (Hsd) can alleviate oxidative stress and enhance stem cells immunomodulatory action.

Cell adhesion-mediated mitochondria transfer contributes to mesenchymal stem cell-induced chemoresistance on T cell acute lymphoblastic leukemia cells

BACKGROUND

Despite the high cure rate of T cell acute lymphoblastic leukemia (T-ALL), drug resistance to chemotherapy remains a significant clinical problem. Bone marrow mesenchymal stem cells (MSCs) protect leukemic cells from chemotherapy, but the underlying mechanisms are poorly understood. In this study, we aimed to uncover the mechanism of MSC-induced chemoresistance in T-ALL cells, thus providing a promising clinical therapy target.

METHODS

Cell viability was determined using the viability assay kit CCK-8. The mitochondrial ROS levels were detected using the fluorescent probe MitoSOX™ Red, and fluorescence intensity was measured by flow cytometry. In vitro, MSCs and Jurkat cells were cocultured. MSCs were labeled with green fluorescent protein (GFP), and Jurkat cells were labeled with the mitochondria-specific dye MitoTracker Red. Bidirectional mitochondrial transfer was detected by flow cytometry and confocal microscopy. The mechanism of mitochondria transfer was analyzed by inhibitor assays. Transcripts related to Jurkat cell/MSC adhesion in the coculture system were assessed by qRT-PCR. After treatment with a neutralizing antibody against a key adhesion molecule, mitochondria transfer from Jurkat cells to MSCs was again detected by flow cytometry and confocal microscopy. Finally, we verified our findings using human primary T-ALL cells cocultured with MSCs.

RESULTS

Chemotherapeutic drugs caused intracellular oxidative stress in Jurkat cells. Jurkat cells transfer mitochondria to MSCs but receive few mitochondria from MSCs, resulting in chemoresistance. This process of mitochondria transfer is mediated by tunneling nanotubes, which are protrusions that extend from the cell membrane . Moreover, we found that most Jurkat cells adhered to MSCs in the coculture system, which was mediated by the adhesion molecule ICAM-1. Treatment with a neutralizing antibody against ICAM-1 led to a decreased number of adhering Jurkat cells, decreased mitochondria transfer, and increased chemotherapy-induced cell death.

CONCLUSIONS

We show evidence that mitochondria transfer from Jurkat cells to MSCs, which is mediated by cell adhesion, may be a potential therapeutic target for T-ALL treatment.

Historical Perspectives and Advances in Mesenchymal Stem Cell Research for the Treatment of Liver Diseases

Liver transplantation is the only effective therapy for patients with decompensated cirrhosis and fulminant liver failure. However, due to a shortage of donor livers and complications associated with immune suppression, there is an urgent need for new therapeutic strategies for patients with end-stage liver diseases. Given their unique function in self-renewal and differentiation potential, stem cells might be used to regenerate damaged liver tissue. Recent studies have shown that stem cell-based therapies can improve liver function in a mouse model of hepatic failure. Moreover, acellular liver scaffolds seeded with hepatocytes produced functional bioengineered livers for organ transplantation in preclinical studies. The therapeutic potential of stem cells or their differentiated progenies will depend on their capacity to differentiate into mature and functional cell types after transplantation. It will also be important to devise methods to overcome their genomic instability, immune reactivity, and tumorigenic potential. We review directions and advances in the use of mesenchymal stem cells and their derived hepatocytes for liver regeneration. We also discuss the potential applications of hepatocytes derived from human pluripotent stem cells and challenges to using these cells in treating end-stage liver disease.

The Effect of Mesenchymal Stem Cell-Derived Extracellular Vesicles on Hematopoietic Stem Cells Fate

Hematopoietic stem cells (HSCs) are multipotent stem cells, with self-renewal ability as well as ability to generate all blood cells. Mesenchymal stem cells (MSCs) are multipotent stem cells, with self-renewal ability, and capable of differentiating into a variety of cell types. MSCs have supporting effects on hematopoiesis; through direct intercellular communications as well as secreting cytokines, chemokines, and extracellular vesicles (EVs). Recent investigations demonstrated that some biological functions and effects of MSCs are mediated by their EVs. MSC-EVs are the cell membrane and endosomal membrane compartments, which are important mediators in the intercellular communications. MSC-EVs contain some of the molecules such as proteins, mRNA, siRNA, and miRNA from their parental cells. MSC-EVs are able to inhibit tumor, repair damaged tissue, and modulate immune system responses. MSC-EVs compared to their parental cells, may have the specific safety advantages such as the lower potential to trigger immune system responses and limited side effects. Recently some studies demonstrated the effect of MSC-EVs on the expansion, differentiation, and clinical applications of HSCs such as improvement of hematopoietic stem cell transplantation (HSCT) and inhibition of graft versus host disease (GVHD). HSCT may be the only therapeutic choice for patients who suffer from malignant and non-malignant hematological disorders. However, there are several severe side effects such GVHD that restricts the successfulness of HSCT. In this review, we will discuss the most important effects of MSCs and MSC-EVs on the improvement of HSCT, inhibition and treatment of GVHD, as well as, on the expansion of HSCs.

Mesenchymal Stromal Cells in Hematopoietic Stem Cell Transplantation

Mesenchymal stromal cells (MSCs) comprise a heterogeneous population of multipotent cells that can be isolated from various human tissues and cultured ex vivo for clinical use. Thanks to their secretion of growth factors, immunomodulatory properties and cell-to-cell interactions, MSCs play a key role in the regulation of hematopoiesis and in the modulation of immune responses against allo- and autoantigens. In light of these properties, MSCs have been employed in clinical trials in the context of hematopoietic stem cell transplantation (HSCT) to prevent/treat graft rejection and to treat steroid-resistant acute graft-versus-host disease (GvHD). The available clinical evidence derived from these studies indicates that MSC administration is safe; moreover, promising preliminary results in terms of efficacy have been reported in some clinical trials. This chapter focuses on recent advances in MSC therapy by reporting on the most important relevant studies in the field of HSCT.

Immunomodulatory mechanisms of mesenchymal stem cells and their therapeutic applications

In the recent years, many studies have shown that MSCs must be stimulated by pro-inflammatory cytokines or other immune mediators before they can modulate immune cells in inflamed and damaged tissues. MSCs appear to be involved in inducing several regulatory immune cells, such as Tregs, Bregs, and regulatory NK cells. This new immune milieu created by MSCs may establish a tolerogenic environment that leads to an optimal condition for the treatment of immune diseases. The mechanisms of MSC action to treat immune disorders need to be further investigated in more detail. Since there have been some contradictory outcomes of clinical trials, it is necessary to perform large-scale and randomized clinical studies, such as a phase 3 placebo-controlled double-blind study of a third party MSCs to optimize MSC administration and to prove safety and efficacy of MSC treatment. MSCs offer great therapeutic promise, especially for the treatment of difficult-to-treat immune diseases.

Inflammatory Conditions Dictate the Effect of Mesenchymal Stem or Stromal Cells on B Cell Function

The immunomodulatory capacity of mesenchymal stem or stromal cells (MSC) makes them a promising tool for treatment of immune disease and organ transplantation. The effects of MSC on B cells are characterized by an abrogation of plasmablast formation and induction of regulatory B cells (Bregs). It is, however, unknown how MSC interact with B cells under inflammatory conditions. In this study, adipose tissue-derived MSC were pretreated with 50 ng/ml IFN-γ for 96 h (MSC–IFN-γ) to simulate inflammatory conditions. Mature B cells were obtained from spleens by CD43⁻ selection. B cells were co-cultured with MSC and stimulated with anti-IgM, anti-CD40, and IL-2; and after 7 days, B cell proliferation, phenotype, Immunoglobulin-G (IgG), and IL-10 production were analyzed. MSC did not inhibit B cell proliferation but increased the percentage of CD38^high CD24^high B cells (Bregs) and IL-10 production, while MSC–IFN-γ significantly reduced B cell proliferation and inhibited IgG production by B cells in a more potent fashion but did not induce Bregs or IL-10 production. Both MSC and MSC–IFN-γ required proximity to target cells and being metabolically active to exert their effects. Indoleamine 2,3 dioxygenase expression was highly induced in MSC–IFN-γ and was responsible of the anti-proliferative and Breg reduction since addition of tryptophan (TRP) restored MSC properties. Immunological conditions dictate the effect of MSC on B cell function. Under immunological quiescent conditions, MSC stimulate Breg induction; whereas, under inflammatory conditions, MSC inhibit B cell proliferation and maturation through depletion of TRP. This knowledge is useful for customizing MSC therapy for specific purposes by appropriate pretreatment of MSC.

Mesenchymal Stem Cells May Ameliorate Nephrotic Syndrome Post-Allogeneic Hematopoietic Stem Cell Transplantation-Case Report

INTRODUCTION

Because of their immunomodulatory and anti-inflammatory effects, mesenchymal stem cells (MSCs) have been considered as potential therapeutic agents for treating immune-related or autoimmune diseases, such as graft-versus-host disease (GVHD). Nephrotic syndrome (NS) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an uncommon complication with unclear etiology and pathogenesis. It may be an immune disorder involving immune complex deposition, B cells, regulatory T cells (Tregs), and Th1 cytokines and be a manifestation of chronic GVHD. Corticosteroids and calcium antagonists, alone or in combination, are the most common therapeutic agents in this setting. Rituximab is commonly administered as salvage treatment. However, treatment failure and progressive renal function deterioration has been reported to occur in approximately 20% of patients in a particular cohort.

CASE PRESENTATION

We present a patient who developed NS 10 months after allo-HSCT. After treatment failure with cyclosporine A, prednisone, and rituximab, she achieved a complete response with MSC treatment. The clinical improvement of this patient was accompanied by a decreased B cell population together with an increased frequency of regulatory B cells (Bregs) and Tregs after MSC treatment.

CONCLUSION

MSCs could modulate NS after allo-HSCT by suppressing B cell proliferation, inducing Tregs and Bregs, and inhibiting inflammatory cytokine production by monocytes and NK cells. Among all these, Bregs might play an important role in ameliorating the NS of this patient.

Mesenchymal stem cells and their immunosuppressive role in transplantation tolerance

Since they were first described, mesenchymal stem cells (MSCs) have been shown to have important effector mechanisms and the potential for use in cell therapy. A great deal of research has been focused on unveiling how MSCs contribute to anti-inflammatory responses, including describing several cell populations involved and identifying soluble and other effector molecules. In this review, we discuss some of the contemporary evidence for use of MSCs in the field of immune tolerance, with a special emphasis on transplantation. Although considerable effort has been devoted to understanding the biological function of MSCs, additional resources are required to clarify the mechanisms of their induction of immune tolerance, which will undoubtedly lead to improved clinical outcomes for MSC-based therapies.

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.

Effects of Mesenchymal Stem Cell Derivatives on Hematopoiesis and Hematopoietic Stem Cells

Hematopoiesis is a balance among quiescence, self-renewal, proliferation, and differentiation, which is believed to be firmly adjusted through interactions between hematopoietic stem and progenitor cells (HSPCs) with the microenvironment. This microenvironment is derived from a common progenitor of mesenchymal origin and its signals should be capable of regulating the cellular memory of transcriptional situation and lead to an exchange of stem cell genes expression. Mesenchymal stem cells (MSCs) have self-renewal and differentiation capacity into tissues of mesodermal origin, and these cells can support hematopoiesis through release various molecules that play a crucial role in migration, homing, self-renewal, proliferation, and differentiation of HSPCs. Studies on the effects of MSCs on HSPC differentiation can develop modern solutions in the treatment of patients with hematologic disorders for more effective Bone Marrow (BM) transplantation in the near future. However, considerable challenges remain on realization of how paracrine mechanisms of MSCs act on the target tissues, and how to design a therapeutic regimen with various paracrine factors in order to achieve optimal results for tissue conservation and regeneration. The aim of this review is to characterize and consider the related aspects of the ability of MSCs secretome in protection of hematopoiesis.

Mesenchymal Stem Cell Derived Extracellular Vesicles: A Role in Hematopoietic Transplantation?

Mesenchymal stem cells (MSCs) are a heterogeneous cellular population containing different progenitors able to repair tissues, support hematopoiesis, and modulate immune and inflammatory responses. Several clinical trials have used MSCs in allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent hematopoietic stem cell (HSC) engraftment failure, reduce aplasia post chemotherapy, and to control graft versus host disease (GvHD). The efficacy of MSCs is linked to their immune suppressive and anti-inflammatory properties primarily due to the release of soluble factors. Recent studies indicate that most of these effects are mediated by extracellular vesicles (EVs). MSC-EVs have therefore therapeutic effects in regenerative medicine, tumor inhibition, and immune-regulation. MSC-EVs may offer specific advantages for patient safety, such as lower propensity to trigger innate and adaptive immune responses. It has been also shown that MSC-EVs can prevent or treat acute-GvHD by modulating the immune-response and, combined with HSCs, may contribute to the hematopoietic microenvironment reconstitution. Finally, MSC-EVs may provide a new potential therapeutic option (e.g., transplantation, gene therapy) for different diseases, particularly hematological malignancies. In this review, we will describe MSC and MSC-EVs role in improving allo-HSCT procedures and in treating GvHD.

CXCR5-Overexpressing Mesenchymal Stromal Cells Exhibit Enhanced Homing and Can Decrease Contact Hypersensitivity

Mesenchymal stromal cells (MSCs) can modulate inflammation and contribute to tissue regeneration and, thus, have emerged as a promising option for cell-based therapy. However, the ability of MSCs to migrate to injured tissues still needs to be improved. In this study, we investigated whether genetically engineered MSCs could exhibit increased migratory properties and improved therapeutic efficacy. Using a mouse model of contact hypersensitivity (CHS), chemokine gene expression screening revealed that CXCL13 changed most significantly in injured tissue. Unfortunately, MSCs hardly express the corresponding receptor, CXCR5. Thus, CXCR5-overexpressing MSCs (MSC^CXCR5) were generated that retained their abilities of proliferation, differentiation, and immunomodulation. Furthermore, MSC^CXCR5 showed significantly increased migrating ability toward CXCL13. Importantly, systemic infusion of MSC^CXCR5 dramatically suppressed CHS in mice, as evidenced by decreased levels of inflammatory cell infiltration and pro-inflammatory cytokine production. Numerous MSC^CXCR5 migrated into inflamed ears, localized with T cells, inhibited T cell proliferation, promoted T cell apoptosis, and suppressed the production of T cell-derived pro-inflammatory factors. Collectively, these findings demonstrate that CXCR5 overexpression increases the ability of MSCs to respond to migratory stimuli and highly intensifies their immunomodulatory effects in vivo. This strategy for enhancing targeted stem/progenitor cell homing may improve the efficacy of MSC-based therapies.

Preconditioned mesenchymal stem cells treat myasthenia gravis in a humanized preclinical model

Myasthenia gravis (MG) with anti-acetylcholine receptor (AChR) Abs is an autoimmune disease characterized by severe defects in immune regulation and thymic inflammation. Because mesenchymal stem cells (MSCs) display immunomodulatory features, we investigated whether and how in vitro-preconditioned human MSCs (cMSCs) could treat MG disease. We developed a new humanized preclinical model by subcutaneously grafting thymic MG fragments into immunodeficient NSG mice (NSG-MG model). Ninety percent of the animals displayed human anti-AChR Abs in the serum, and 50% of the animals displayed MG-like symptoms that correlated with the loss of AChR at the muscle endplates. Interestingly, each mouse experiment recapitulated the MG features of each patient. We next demonstrated that cMSCs markedly improved MG, reducing the level of anti-AChR Abs in the serum and restoring AChR expression at the muscle endplate. Resting MSCs had a smaller effect. Finally, we showed that the underlying mechanisms involved (a) the inhibition of cell proliferation, (b) the inhibition of B cell-related and costimulatory molecules, and (c) the activation of the complement regulator DAF/CD55. In conclusion, this study shows that a preconditioning step promotes the therapeutic effects of MSCs via combined mechanisms, making cMSCs a promising strategy for treating MG and potentially other autoimmune diseases.

Immunomodulatory oligonucleotide IMT504: Effects on mesenchymal stem cells as a first-in-class immunoprotective/immunoregenerative therapy

The immune responses of humans and animals to insults (i.e., infections, traumas, tumoral transformation and radiation) are based on an intricate network of cells and chemical messengers. Abnormally high inflammation immediately after insult or abnormally prolonged pro-inflammatory stimuli bringing about chronic inflammation can lead to life-threatening or severely debilitating diseases. Mesenchymal stem cell (MSC) transplant has proved to be an effective therapy in preclinical studies which evaluated a vast diversity of inflammatory conditions. MSCs lead to resolution of inflammation, preparation for regeneration and actual regeneration, and then ultimate return to normal baseline or homeostasis. However, in clinical trials of transplanted MSCs, the expectations of great medical benefit have not yet been fulfilled. As a practical alternative to MSC transplant, a synthetic drug with the capacity to boost endogenous MSC expansion and/or activation may also be effective. Regarding this, IMT504, the prototype of a major class of immunomodulatory oligonucleotides, induces in vivo expansion of MSCs, resulting in a marked improvement in preclinical models of neuropathic pain, osteoporosis, diabetes and sepsis. IMT504 is easily manufactured and has an excellent preclinical safety record. In the small number of patients studied thus far, IMT504 has been well-tolerated, even at very high dosage. Further clinical investigation is necessary to demonstrate the utility of IMT504 for resolution of inflammation and regeneration in a broad array of human diseases that would likely benefit from an immunoprotective/immunoregenerative therapy.

Mesenchymal Stem Cell Therapy for Inflammatory Skin Diseases: Clinical Potential and Mode of Action

Inflammatory skin disorders that cause serious deterioration of the quality of life have become one of the major public concerns. Despite their significance, there is no fundamental cure to date. Mesenchymal stem cells (MSCs) possess unique immunomodulatory properties which make them a promising tool for the treatment of various inflammatory diseases. Our recent preclinical and clinical studies have shown that MSCs can be successfully used for the treatment of atopic dermatitis (AD), one of the major inflammatory skin diseases. This observation along with similar reports from other groups revealed the efficacy and underlying mechanisms of MSCs in inflammatory dermatosis. In addition, it has been proposed that cell priming or gene transduction can be novel strategies for the development of next-generation high-efficacy MSCs for treating inflammatory skin diseases. We discuss here existing evidence that demonstrates the regulatory properties of MSCs on immune responses under inflammatory conditions.

Guanylate-binding protein 1 (GBP1) contributes to the immunity of human mesenchymal stromal cells against Toxoplasma gondii

Mesenchymal stromal cells (MSCs) have recently been shown to play important roles in mammalian host defenses against intracellular pathogens, but the molecular mechanism still needs to be clarified. We confirmed that human MSCs (hMSCs) prestimulated with IFN-γ showed a significant and dose-dependent ability to inhibit the growth of two types of Toxoplasma gondii [type I RH strain with green fluorescent proteins (RH/GFP) or type II PLK strain with red fluorescent proteins (PLK/RED)]. However, in contrast to previous reports, the anti-T. gondii activity of hMSCs was not mediated by indoleamine 2,3-dioxygenase (IDO). Genome-wide RNA sequencing (RNA-seq) analysis revealed that IFN-γ increased the expression of the p65 family of human guanylate-binding proteins (hGBPs) in hMSCs, especially hGBP1. To analyze the functional role of hGBPs, stable knockdowns of hGBP1, -2, and -5 in hMSCs were established using a lentiviral transfection system. hGBP1 knockdown in hMSCs resulted in a significant loss of the anti-T. gondii host defense property, compared with hMSCs infected with nontargeted control sequences. hGBP2 and -5 knockdowns had no effect. Moreover, the hGBP1 accumulation on the parasitophorous vacuole (PV) membranes of IFN-γ-stimulated hMSCs might protect against T. gondii infection. Taken together, our results suggest that hGBP1 plays a pivotal role in anti-T. gondii protection of hMSCs and may shed new light on clarifying the mechanism of host defense properties of hMSCs.

Review article: mesenchymal stromal cell therapy for inflammatory bowel diseases

BACKGROUND

Inflammatory bowel diseases (IBD) are chronic relapsing diseases in which pro-inflammatory immune cells and cytokines induce intestinal tissue damage and disability. Mesenchymal stromal cells (MSCs) exert powerful immunomodulatory effects and stimulate tissue repair.

AIM

To review the current data on mesenchymal stromal cell therapy in IBD.

METHOD

We searched PubMed and 'ClinicalTrials.gov' databases using the terms 'mesenchymal stromal cells', 'mesenchymal stem cell transplantation', 'inflammatory bowel diseases', 'Crohn disease' and 'colitis, ulcerative'. Additional publications were identified from individual article reference lists.

RESULTS

MSCs include inhibition of Th1/Th17 lymphocytes and recruitment of regulatory T lymphocytes, induction of antigen-presenting cells into a regulatory-like profile, and stimulation of epithelial cell differentiation and proliferation. More than 200 patients with refractory fistulas have been treated with local injections of MSCs, resulting in complete response in more than half, and in overall response in approximately two thirds of patients. In refractory luminal Crohn's disease, 49 cases of systemic MSC infusions have been reported, while trials with autologous MSCs resulted in mitigated responses, studies using allogeneic MSCs were promising, with around 60% of patients experiencing a response and around 40% achieving clinical remission.

CONCLUSIONS

Mesenchymal stromal cells might represent a promising therapy for IBD, especially for Crohn's disease. There remain many unsolved questions concerning the optimal origin and source of mesenchymal stromal cells, dosage and modalities of administration. Moreover, mesenchymal stromal cells still need to prove their effectiveness compared with conventional treatments in randomised controlled trials.

Immune reconstitution 20 years after treatment with alemtuzumab in a rheumatoid arthritis cohort: implications for lymphocyte depleting therapies

Background

Alemtuzumab, an anti-CD52 monoclonal antibody, was administered to patients with RA between 1991 and 1994. We have followed a cohort of recipients since that time and previously reported significant delays in immune reconstitution. Here we report >20 years of follow-up data from this unique cohort.

Method

Surviving alemtuzumab recipients were age, sex and disease duration matched with RA controls. Updated mortality and morbidity data were collected for alemtuzumab recipients. For both groups antigenic responses were assessed following influenza, Pneumovax II and combined diphtheria/tetanus/poliovirus vaccines. Circulating cytokines and lymphocyte subsets were also quantified.

Results

Of 16 surviving alemtuzumab recipients, 13 were recruited: 9 recipients underwent a full clinical assessment and 4 had case notes review only. Since our last review 10 patients had died from causes of death consistent with long-standing RA, and no suggestion of compromised immune function. Compared with controls the alemtuzumab cohort had significantly reduced CD4⁺ and CD8⁺ central memory T-cells, CD5⁺ B cells, naïve B cells and CD19⁺CD24^hiCD38^hi transitional (putative regulatory) B cells. Nonetheless vaccine responses were comparable between groups. There were significantly higher serum IL-15 and IFN-γ levels in the alemtuzumab cohort. IL-15 levels were inversely associated with CD4⁺ total memory and central memory T cells.

Conclusion

After 20 years the immune system of alemtuzumab recipients continues to show differences from disease controls. Nonetheless mortality and morbidity data, alongside vaccination responses, do not suggest clinical immune compromise. As lymphodepleting therapies, including alemtuzumab, continue to be administered this work is important with regard to long-term immune monitoring and stages of immune recovery.

Tolerance in Kidney Transplantation: What Is on the B Side?

Regulatory B cells (Breg) are in the spotlight for their role in immune homeostasis maintenance and tolerance achievement as in the last years the correlation with functional and increased Breg numbers in autoimmune diseases and transplantation has been extensively proven. Their study is, however, in its infancy with still little knowledge and consensus on their origin, phenotype, and mechanism of action. All this hampers the pursuit of an effective Breg induction method for therapeutic purposes. In this review we aim to summarize the studies on human Breg and their implication in kidney transplantation and to further discuss the issues surrounding therapeutic applications of this cell subset.

ERK/Drp1-dependent mitochondrial fission is involved in the MSC-induced drug resistance of T-cell acute lymphoblastic leukemia cells

The bone marrow microenvironment facilitates the proliferation and survival of leukemia cells, contributing to disease relapse. Bone marrow-derived mesenchymal stem cells (MSCs) are well known to promote cancer chemoresistance via soluble factors and cell adhesion. However, little is known about the effects of MSCs on the mitochondrial dynamics of T-cell acute lymphoblastic leukemia (T-ALL) cells, or how this may influence the chemoresistance of these cells. Here, we tested both indirect (Transwell) and direct coculture strategies, and found that MSCs protected T-ALL cells from chemotherapeutic cell death and cytotoxicity under both culture conditions. In addition, cell viability was higher in the direct contact system compared with the Transwell system. We further showed that exposure of T-ALL cells to MSCs decreased mitochondrial reactive oxygen species (ROS) levels and promoted a pro-glycolytic shift that was characterized by increased glucose uptake and lactate production with concomitant reductions in adenosine triphosphate production and mitochondrial membrane potential. In T-ALL cells cocultured with MSCs, the mitochondrial morphology of T-ALL cells were altered from elongation to fragmentation because of the extracellular signal-regulated kinase activation-mediated phosphorylation of the pro-fission factor, dynamin-related protein 1 (Drp1), at residue S616. Consistent with this, the expression of S616-phosphorylated Drp1 recapitulated the mitochondrial dynamics, mitochondrial ROS levels, metabolic switching and chemoresistance seen in T-ALL cells cocultured with MSCs. These findings suggest that the ability of MSCs to trigger Drp1 activation-induced changes in mitochondrial dynamics is crucial to their ability to protect cells against chemotherapeutic agents.

Cellular Therapies in Systemic Sclerosis: Recent Progress

Systemic sclerosis (SSc) is a rare autoimmune connective tissue disease with a high mortality and morbidity. While progress has been made in terms of identifying high-risk patients and implementing new treatment strategies, therapeutic options remain limited. In the past few decades, various cellular therapies have emerged, which have been studied in SSc and other conditions. Here, we provide a comprehensive review of currently available cellular therapies and critically assess their merit as disease-modifying treatment for SSc. Currently, hematopoietic stem cell transplantation is the only cellular therapy that has demonstrated clinical effects on the immune system, neoangiogenesis, and fibrosis. Robust mechanistic studies as well as clinical trials are essential to move the field forward.

Immunomodulation by mesenchymal stem cells: Interplay between mesenchymal stem cells and regulatory lymphocytes

Mesenchymal stem cells (MSCs) possess immunomodulatory properties, which confer enormous potential for clinical application. Considerable evidence revealed their efficacy on various animal models of autoimmune diseases, such as multiple sclerosis, systemic lupus erythematosus and uveitis. MSCs elicit their immunomodulatory effects by inhibiting lymphocyte activation and proliferation, forbidding the secretion of proinflammatory cytokines, limiting the function of antigen presenting cells, and inducing regulatory T (Treg) and B (Breg) cells. The induction of Treg and Breg cells is of particular interest since Treg and Breg cells have significant roles in maintaining immune tolerance. Several mechanisms have been proposed regarding to the MSCs-mediated induction of Treg and Breg cells. Accordingly, MSCs induce regulatory lymphocytes through secretion of multiple pleiotropic cytokines, cell-to-cell contact with target cells and modulation of antigen-presenting cells. Here, we summarized how MSCs induce Treg and Breg cells to provoke immunosuppression.

Mesenchymal stromal cells and immunomodulation: A gathering of regulatory immune cells

Because of their well-recognized immunomodulatory properties, mesenchymal stromal cells (MSCs) represent an attractive cell population for therapeutic purposes. In particular, there is growing interest in the use of MSCs as cellular immunotherapeutics for tolerance induction in allogeneic transplantations and the treatment of autoimmune diseases. However, multiple mechanisms have been identified to mediate the immunomodulatory effects of MSCs, sometimes with several ambiguities and inconsistencies. Although published studies have mainly reported the role of soluble factors, we believe that a sizeable cellular component plays a critical role in MSC immunomodulation. We refer to these cells as regulatory immune cells, which are generated from both the innate and adaptive responses after co-culture with MSCs. In this review, we discuss the nature and role of these immune regulatory cells as well as the role of different mediators, and, in particular, regulatory immune cell induction by MSCs through interleukin-10. Once induced, immune regulatory cells accumulate and converge their regulatory pathways to create a tolerogenic environment conducive for immunomodulation. Thus, a better understanding of these regulatory immune cells, in terms of how they can be optimally manipulated and induced, would be suitable for improving MSC-based immunomodulatory therapeutic strategies.

CD19+CD24hiCD38hiBregs involved in downregulate helper T cells and upregulate regulatory T cells in gastric cancer

Regulatory B cells (Bregs) play a critical role in inflammation and autoimmune disease. We characterized the role of Bregs in the progression of gastric cancer. We detected an increase in Bregs producing IL-10 both in peripheral blood mononuclear cells (PBMCs) and in gastric tumors. Multicolor flow cytometry analysis revealed that a subset of CD19⁺CD24^hiCD38^hi B cells produces IL-10. Functional studies indicated that increased Bregs do not inhibit the proliferation of CD3⁺T cells or CD4⁺ helper T cells (Th cells). However, Bregs do suppress the secretion of IFN-γ and TNF-α by CD4⁺Th cells. CD19⁺CD24^hiCD38^hiBregs were also found to correlate positively with CD4⁺FoxP3⁺ regulatory T cells (Tregs). Neutralization experiments showed that Bregs convert CD4⁺CD25⁻ effector T cells to CD4⁺FoxP3⁺Tregs via TGF-β1. Collectively, these findings demonstrate that increased Bregs play a immunosuppressive role in gastric cancer by inhibiting T cells cytokines as well as conversion to Tregs. These results may provide new clues about the underlying mechanisms of immune escape in gastric cancer.

Human umbilical cord-derived mesenchymal stem cells protect against experimental colitis via CD5(+) B regulatory cells

Background

To clarify the effect of human umbilical cord-derived mesenchymal stem cell (hUC-MSCs) treatment on colitis and to explore the role of CD5⁺ B cells in MSC therapy.

Methods

The trinitrobenzenesulfonic acid (TNBS)-induced colitis mouse model was used. HUC-MSCs were transferred peritoneally. Survival rates, colitis symptoms, and macroscopic and histologic scores were evaluated. CD4⁺ T helper (Th) cell subgroups and CD5⁺ regulatory B cell (Bregs) in lymphocytes were quantitated by flow cytometry. Cytokine levels were detected by ELISA and Bio-plex. CD5⁺ B cells were isolated for in vitro co-culture and adaptive transfer.

Results

HUC-MSC treatment alleviated TNBS-induced colitis by increasing survival rates, relieving symptoms, and improving macroscopic and histologic scores. Labeled hUC-MSCs were located in the inflamed areas of colitis mice. Increases in regulatory T cells (Tregs) and CD5⁺ B cells and decreases in Th1 cells, Th17 cells, and several pro-inflammatory cytokines were observed with hUC-MSC treatment. After adaptive transfer, CD5⁺ B cells, which were located mainly in the peritoneal lavage fluid, improved TNBS-induced colitis by correcting Treg/Th1/Th17 imbalances. CD5⁺ B cells also inhibited T-cell proliferation and produced interleukin (IL)-10.

Conclusions

HUC-MSCs protected against experimental colitis by boosting the numbers of CD5⁺ B cells and IL-10-producing CD5⁺ Bregs, and correcting Treg/Th17/Th1 imbalances.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0376-2) contains supplementary material, which is available to authorized users.

Heterogeneity in Studies of Mesenchymal Stromal Cells to Treat or Prevent Graft-versus-Host Disease: A Scoping Review of the Evidence

Effective treatments are lacking for the treatment of steroid-refractory graft-versus-host disease (GVHD), a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. Mesenchymal stromal cells (MSCs) have demonstrated promise but there is uncertainty regarding their clinical effectiveness. A systematic scoping review of the literature was performed to characterize the heterogeneity of published studies and identify opportunities for standardization. Thirty studies were identified, including 19 studies (507 patients) addressing the treatment of acute or chronic GVHD and 11 prevention studies (277 patients). Significant heterogeneity was observed in the age and diagnoses of study subjects, intensity and specifics of the conditioning regimens, degree of HLA matching, and source of hematopoietic cells. MSCs were derived from bone marrow (83% of studies), cord blood (13%), or adipose tissue (3%) and were cryopreserved from third-party allogeneic donors in the majority of studies (91% of prevention studies and 63% of treatment studies). Culture conditions and media supplements were highly variable and characterization of MSCs did not conform to all International Society for Cellular Therapy criteria in any study. MSCs were harvested from cell culture at passage 1 to 7 and the dosage of MSCs ranged from 0.3 to 10 × 10(6)/kg, using varying schedules of administration. Treatment response criteria were not standardized and effectiveness in controlled treatment studies (5 studies) was unconvincing. Details of actively recruiting trials suggest heterogeneity still persists with only 53% of registered trials describing the use of standard GVHD response criteria and few detailing methods of MSC manufacturing. Future studies will need to make substantial coordinated efforts to reduce study heterogeneity and clarify the role of MSCs in GVHD.

Mesenchymal Stem Cells and Myeloid Derived Suppressor Cells: Common Traits in Immune Regulation

To protect host against immune-mediated damage, immune responses are tightly regulated. The regulation of immune responses is mediated by various populations of mature immune cells, such as T regulatory cells and B regulatory cells, but also by immature cells of different origins. In this review, we discuss regulatory properties and mechanisms whereby two distinct populations of immature cells, mesenchymal stem cells, and myeloid derived suppressor cells mediate immune regulation, focusing on their similarities, discrepancies, and potential clinical applications.

Phase II Multicenter, Randomized, Double-Blind Controlled Study of Efficacy and Safety of Umbilical Cord-Derived Mesenchymal Stromal Cells in the Prophylaxis of Chronic Graft-Versus-Host Disease After HLA-Haploidentical Stem-Cell Transplantation

PURPOSE

Although mesenchymal stromal cells (MSCs) possess immunomodulatory properties and exhibit promising efficacy against chronic graft-versus-host disease (cGVHD), little is known about the efficacy of MSCs in the prophylaxis of cGVHD after HLA-haploidentical hematopoietic stem-cell transplantation (HLA-haplo HSCT).

PATIENTS AND METHODS

In this multicenter, double-blind, randomized controlled trial, we investigated the incidence and severity of cGVHD among patients, and the changes in T, B, and natural killer (NK) cells after the repeated infusion of MSCs.

RESULTS

The 2-year cumulative incidence of cGVHD in the MSCs group was 27.4% (95% CI, 16.2% to 38.6%), compared with 49.0% (95% CI, 36.5% to 61.5%) in the non-MSCs control group (P = .021). Seven patients in the non-MSCs control group had severe lung cGVHD, but no patients in the MSCs group developed typical lung cGVHD (P = .047). After the MSC infusions, increasing memory B lymphocytes and regulatory T cells, as well as the ratio of type 1 T helper to type 2 T helper cells, were observed, whereas the number of NK cells decreased.

CONCLUSION

Our findings suggest that the repeated infusion of MSCs might inhibit cGVHD symptoms in patients after HLA-haplo HSCT, accompanied by changes in the numbers and subtypes of T, B, and NK cells, leading to the acquisition of immune tolerance.

The clinical application of mesenchymal stromal cells in hematopoietic stem cell transplantation

Mesenchymal stromal cells (MSCs) are multipotent stem cells well known for repairing tissue, supporting hematopoiesis, and modulating immune and inflammation response. These outstanding properties make MSCs as an attractive candidate for cellular therapy in immune-based disorders, especially hematopoietic stem cell transplantation (HSCT). In this review, we outline the progress of MSCs in preventing and treating engraftment failure (EF), graft-versus-host disease (GVHD) following HSCT and critically discuss unsolved issues in clinical applications.

Interaction between Mesenchymal Stem Cells and B-Cells

Mesenchymal stem cells (MSCs) are multipotent; non-hematopoietic stem cells. Because of their immunoregulatory abilities; MSCs are widely used for different clinical applications. Compared with that of other immune cells; the investigation of how MSCs specifically regulate B-cells has been superficial and insufficient. In addition; the few experimental studies on this regulation are often contradictory. In this review; we summarize the various interactions between different types or states of MSCs and B-cells; address how different types of MSCs and B-cells affect this interaction and examine how other immune cells influence the regulation of B-cells by MSCs. Finally; we hypothesize why there are conflicting results on the interaction between MSCs and B-cells in the literature.

Role of B cells in the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is an orphan disease characterized by progressive fibrosis of the skin and internal organs. Aside from vasculopathy and fibrotic processes, its pathogenesis involves an aberrant activation of immune cells, among which B cells seem to play a significant role. Indeed, B cell homeostasis is disturbed during SSc: the memory subset is activated and displays an increased susceptibility to apoptosis, which is responsible for their decreased number. This chronic loss of B cells enhances bone marrow production of the naïve subset that accounts for their increased number in peripheral blood. This permanent activation state can be explained mainly by two mechanisms: a dysregulation of B cell receptor (BCR) signaling, and an overproduction of B cell survival signals, B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL). These disturbances of B cell homeostasis induce several functional anomalies that participate in the inflammatory and fibrotic events observed during SSc: autoantibody production (some being directly pathogenic); secretion of pro-inflammatory and pro-fibrotic cytokines (interleukin-6); direct cooperation with other SSc-involved cells [fibroblasts, through transforming growth factor-β (TGF-β) signaling, and T cells]. These data justify the evaluation of anti-B cell strategies as therapeutic options for SSc, such as B cell depletion or blockage of B cell survival signaling.

Mesenchymal Stem Cell Treatment for Steroid Refractory Graft-versus-Host Disease in Children: A Pilot and First Study from Turkey

This study evaluated the efficacy of mesenchymal stem cells (MSCs) from bone marrow of a third-party donor for refractory aGVHD. We report the first experience using MSCs to treat refractory aGVHD in 33 pediatric patients undergoing allogeneic HSCT from Turkey. Totally, 68 doses of bone marrow derived MSCs were infused. The median dose of MSC was 1.18 × 10⁶ cells per kg body weight. Overall, complete response (CR) was documented in 18 patients, partial response (PR) was documented in 7 patients, and no response (NR) was documented in 8 patients. The 2-year estimated probability of overall survival (OS) for patients achieving CR and PR/NR was 63.8% and 29.4%, respectively (p = 0.0002). While the cumulative incidence of transplant related mortality (TRM) at day 100 after first MSC infusion was 46.6% in PR/NR patients, there was no any TRM at day 100 after first MSC infusion in CR patients (p = 0.001). Twelve patients developed chronic GVHD (cGVHD); eight of them were alive, with five having extensive disease and three having limited disease. In conclusion, MSCs appear to be safe and effective treatment option for pediatric patients with steroid refractory aGVHD. But the efficacy of MSCs on cGVHD in aGVHD patients treated with MSCs seems to be limited.

Mesenchymal Stem Cell-Derived Interleukin 1 Receptor Antagonist Promotes Macrophage Polarization and Inhibits B Cell Differentiation

The role of interleukin 1 receptor antagonist (IL1RA) in mediating the immunosuppressive effect of mesenchymal stem/stromal cells (MSCs) has been reported in several studies. However, how MSC-derived IL1RA influences the host response has not been clearly investigated. We therefore derived MSCs from the bone marrow of IL1RA knockout mice and evaluated their immunosuppressive effect on different immune cell subsets. IL1RA deficient (IL1RA(-/-) ) or wild type (wt) MSCs inhibited to the same extend the proliferation of T lymphocytes. On the contrary, IL1RA(-/-) MSCs were less effective than wt MSCs to induce in vitro the macrophage polarization from M1 to M2 phenotype secreting IL10 and exerting a suppressive effect on CD4(+) T cells. Moreover compared with wt MSCs, IL1RA(-/-) MSCs did not efficiently support the survival of quiescent B lymphocytes and block their differentiation toward CD19(+) CD138(+) plasmablasts secreting IgG antibodies. The effectiveness of IL1RA secreted by MSCs in controlling inflammation was further shown in vivo using the collagen-induced arthritis murine model. MSCs lacking IL1RA expression were unable to protect mice from arthritic progression and even worsened clinical signs, as shown by higher arthritic score and incidence than control arthritic mice. IL1RA(-/-) MSCs were not able to decrease the percentage of Th17 lymphocytes and increase the percentage of Treg cells as well as decreasing the differentiation of B cells toward plasmablasts. Altogether, our results provide evidence of the key role of IL1RA secreted by MSCs to both control the polarization of macrophages toward a M2 phenotype and inhibit B cell differentiation in vivo.

Strategies to improve the immunosuppressive properties of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are of particular interest for the treatment of immune-related diseases because of their immunosuppressive capacities. However, few clinical trials of MSCs have yielded satisfactory results. A number of clinical trials using MSCs are currently in progress worldwide. Unfortunately, protocols and methods, including optimized culture conditions for the harvest of MSCs, have not been standardized. In this regard, complications in the ex vivo expansion of MSCs and MSC heterogeneity have been implicated in the failure of clinical trials. In this review, potential strategies to obtain MSCs with improved immunosuppressive properties and the potential roles of specific immunomodulatory genes, which are differentially upregulated in certain culture conditions, will be discussed.

Safety and Efficacy Endpoints for Mesenchymal Stromal Cell Therapy in Renal Transplant Recipients

Despite excellent short-term graft survival after renal transplantation, the long-term graft outcome remains compromised. It has become evident that a combination of sustained alloreactivity and calcineurin-inhibitor- (CNI-) related nephrotoxicity results in fibrosis and consequently dysfunction of the graft. New immunosuppressive regimens that can minimize or eliminate side effects, while maintaining efficacy, are required to improve long-term graft survival. In this perspective mesenchymal stromal cells (MSCs) are an interesting candidate, since MSCs have immunosuppressive and regenerative properties. The first clinical trials with MSCs in renal transplantation showed safety and feasibility and displayed promising results. Recently, the first phase II studies have been started. One of the most difficult and challenging aspects in those early phase trials is to define accurate endpoints that can measure safety and efficacy of MSC treatment. Since both graft losses and acute rejection rates declined, alternative surrogate markers such as renal function, histological findings, and immunological markers are used to measure efficacy and to provide mechanistic insight. In this review, we will discuss the current status of MSCs in renal transplantation with a focus on the endpoints used in the different experimental and clinical studies.

Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model

B cells have been reported to promote graft rejection through alloantibody production. However, there is growing evidence that B cells can contribute to the maintenance of tolerance. Here, we used a mouse model of MHC-class I mismatched skin transplantation to investigate the contribution of B cells to graft survival. We demonstrate that adoptive transfer of B cells prolongs skin graft survival but only when the B cells were isolated from mice housed in low sterility "conventional" (CV) facilities and not from mice housed in pathogen free facilities (SPF). However, prolongation of skin graft survival was lost when B cells were isolated from IL-10 deficient mice housed in CV facilities. The suppressive function of B cells isolated from mice housed in CV facilities correlated with an anti-inflammatory environment and with the presence of a different gut microflora compared to mice maintained in SPF facilities. Treatment of mice in the CV facility with antibiotics abrogated the regulatory capacity of B cells. Finally, we identified transitional B cells isolated from CV facilities as possessing the regulatory function. These findings demonstrate that B cells, and in particular transitional B cells, can promote prolongation of graft survival, a function dependent on licensing by gut microflora.

Mesenchymal stromal cells and hematopoietic stem cell transplantation

Mesenchymal stromal cells (MSCs) comprise a heterogeneous population of multipotent cells that can be isolated from various human tissues and culture-expanded ex vivo for clinical use. Due to their immunoregulatory properties and their ability to secrete growth factors, MSCs play a key role in the regulation of hematopoiesis and in the modulation of immune responses against allo- and autoantigens. In light of these properties, MSCs have been employed in clinical trials in the context of hematopoietic stem cell transplantation (HSCT) to facilitate engraftment of hematopoietic stem cells (HSCs) and to prevent graft failure, as well as to treat steroid-resistant acute graft-versus-host disease (GvHD). The available clinical evidence derived from these studies indicates that MSC administration is safe. Moreover, promising preliminary results in terms of efficacy have been reported in some clinical trials, especially in the treatment of acute GvHD. In this review we critically discuss recent advances in MSC therapy by reporting on the most relevant studies in the field of HSCT.