Mesenchymal stromal cells: facilitators of successful transplantation? Cell Stem Cell. 2010;7:431-442. [PMID: 20887949 DOI: 10.1016/j.stem.2010.09.009]

Mesenchymal stem cells secretome: a new paradigm for central nervous system regeneration?

The low regeneration potential of the central nervous system (CNS) represents a challenge for the development of new therapeutic strategies. Mesenchymal stem cells (MSCs) have been proposed as a possible therapeutic tool for CNS disorders. In addition to their differentiation potential, it is well accepted nowadays that their beneficial actions can also be mediated by their secretome. Indeed, it was already demonstrated, both in vitro and in vivo, that MSCs are able to secrete a broad range of neuroregulatory factors that promote an increase in neurogenesis, inhibition of apoptosis and glial scar formation, immunomodulation, angiogenesis, neuronal and glial cell survival, as well as relevant neuroprotective actions on different pathophysiological contexts. Considering their protective action in lesioned sites, MSCs' secretome might also improve the integration of local progenitor cells in neuroregeneration processes, opening a door for their future use as therapeutical strategies in human clinical trials. Thus, in this review we analyze the current understanding of MSCs secretome as a new paradigm for the treatment of CNS neurodegenerative diseases.

Human T cells upregulate CD69 after coculture with xenogeneic genetically-modified pig mesenchymal stromal cells

Mesenchymal stromal cells (MSC) obtained from α1,3-galactosyltransferase gene knock-out pigs transgenic for the human complement-regulatory protein CD46 (GTKO/CD46 pMSC) suppress in vitro human anti-pig cellular responses as efficiently as allogeneic human MSC. We investigated the immunoregulatory effects of GTKO/CD46 pMSC on human CD4(+) and CD8(+) T cell proliferation in response to pig aortic endothelial cells (pAEC). pMSC efficiently suppressed T cell proliferation, which was associated with downregulation of granzyme B expression. No induction of CD4(+)CD25(+)Foxp3(hi) regulatory T cells or T cell apoptosis was documented. In correlation with T cell proliferation, CD25 expression was upregulated on T cells in response to pAEC but not to pMSC. In contrast, CD69 expression was upregulated on T cells in response to both pMSC and pAEC, which was associated with a significant increase in the phosphorylation of STAT5. GTKO/CD46 pMSC possibly regulate human T cell responses through modulation of CD69 expression and STAT5 signaling.

Bone marrow-derived mesenchymal stem cells favor the immunosuppressive T cells skewing in a Helicobacter pylori model of gastric cancer

Bone marrow-derived mesenchymal stem cells (BM-MSCs) play an important role in Helicobacter pylori-induced gastric carcinogenesis. While the mechanism is not well understood, BM-MSCs have been shown to contribute to the immunosuppressive response found in a number of diseases. Here, BM-MSCs were transplanted into the stomach of mice with a 44-week mouse-adapted H. pylori infection. At day 28 post-transplantation, BM-MSCs migrated from the subserosal to the mucosal layer of the stomach. The grafted BM-MSCs significantly stimulated systemic and local interleukin-10 (IL-10)-secreting T cell and regulatory T cell (Treg) functions. This observation was correlated with an increased percentage of CD4⁺IL-10⁺ cells and CD4⁺CD25⁺FoxP3⁺ cells in splenic mononuclear cells compared with H. pylori-infected mice not receiving BM-MSCs. Moreover, inhibitory cytokines IL-10 and transforming growth factor-β1 increased in the gastric tissue, while there was a decrease in inflammatory interferon-γ (IFN-γ). BM-MSC-transplanted mice also developed elevated IL-10/IFN-γ secreting and Treg/Th17 ratios. A coculture system in the presence or absence of BM-MSCs was also established to evaluate the immune responses in vitro. An increase in IL-10-secreting T cells and Tregs, associated with increased expression of Gata-3 and FoxP3, generation of IL-10 in the supernatant, and proliferation of gastric epithelial cells (GECs) was observed. These findings demonstrate that transplantation of BM-MSCs into a chronic H. pylori-infected mouse model results in the generation of an immunosuppressive environment. The local and systemic immunosuppression mediated by BM-MSCs likely contributed to an environment that is compatible with the development of H. pylori-induced gastric cancer.

Human adipose-derived mesenchymal stromal cells injected systemically into GRMD dogs without immunosuppression are able to reach the host muscle and express human dystrophin

Duchenne muscular dystrophy (DMD), a lethal X-linked disorder, is the most common and severe form of muscular dystrophies, affecting 1 in 3,500 male births. Mutations in the DMD gene lead to the absence of muscle dystrophin and a progressive degeneration of skeletal muscle. The possibility to treat DMD through cell therapy has been widely investigated. We have previously shown that human adipose-derived stromal cells (hASCs) injected systemically in SJL mice are able to reach and engraft in the host muscle, express human muscle proteins, and ameliorate the functional performance of injected animals without any immunosuppression. However, before starting clinical trials in humans many questions still need to be addressed in preclinical studies, in particular in larger animal models, when available. The best animal model to address these questions is the golden retriever muscular dystrophy (GRMD) dog that reproduces the full spectrum of human DMD. Affected animals carry a mutation that predicts a premature termination codon in exon 8 and a peptide that is 5% the size of normal dystrophin. These dogs present clinical signs within the first weeks and most of them do not survive beyond age two. Here we show the results of local and intravenous injections of hASCs into GRMD dogs, without immunosuppression. We observed that hASCs injected systemically into the dog cephalic vein are able to reach, engraft, and express human dystrophin in the host GRMD dystrophic muscle up to 6 months after transplantation. Most importantly, we demonstrated that injecting a huge quantity of human mesenchymal cells in a large-animal model, without immunosuppression, is a safe procedure, which may have important applications for future therapy in patients with different forms of muscular dystrophies.

Synthetic surface for expansion of human mesenchymal stem cells in xeno-free, chemically defined culture conditions

Human mesenchymal stem cells (HMSCS) possess three properties of great interest for the development of cell therapies and tissue engineering: multilineage differentiation, immunomodulation, and production of trophic factors. Efficient ex vivo expansion of hMSCs is a challenging requirement for large scale production of clinical grade cells. Low-cost, robust, scalable culture methods using chemically defined materials need to be developed to address this need. This study describes the use of a xeno-free synthetic peptide acrylate surface, the Corning® Synthemax® Surface, for culture of hMSCs in serum-free, defined medium. Cell performance on the Corning Synthemax Surface was compared to cells cultured on biological extracellular matrix (ECM) coatings in xeno-free defined medium and in traditional conditions on tissue culture treated (TCT) plastic in fetal bovine serum (FBS) supplemented medium. Our results show successful maintenance of hMSCs on Corning Synthemax Surface for eight passages, with cell expansion rate comparable to cells cultured on ECM and significantly higher than for cells in TCT/FBS condition. Importantly, on the Corning Synthemax Surface, cells maintained elongated, spindle-like morphology, typical hMSC marker profile and in vitro multilineage differentiation potential. We believe the Corning Synthemax Surface, in combination with defined media, provides a complete synthetic, xeno-free, cell culture system for scalable production of hMSCs.

Proinflammatory stimuli induce galectin-9 in human mesenchymal stromal cells to suppress T-cell proliferation

Human multipotent mesenchymal stromal cells (MSCs) are clinically applied to treat autoimmune diseases and graft-versus-host disease due to their immunomodulatory properties. Several molecules have been identified to mediate these effects, including constitutively expressed galectin-1. However, there are indications in the literature that MSCs exert enhanced immunosuppressive functions after interaction with an inflammatory environment. Therefore, we analyzed how inflammatory stimuli influence the expression of the galectin network in MSCs and functionally tested the relevance for the immunomodulatory effects of MSCs. We found that galectin-9 was strongly induced in MSCs upon interaction with activated PBMCs. Proinflammatory cytokines, such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α), and also ligands of the Toll-like receptors (TLRs) TLR2, TLR3, and TLR4 elicited similar induction of galectin-9 in activated PBMCs. Galectin-9 was not only upregulated intracellularly, but also released by MSCs in significant amounts into the supernatant after exposure to proinflammatory stimuli. In proliferation assays, MSCs with a galectin-9 knockdown lost a significant portion of their antiproliferative effects on T cells. In conclusion, we found that unlike constitutively expressed galectin-1, galectin-9 is induced by several proinflammatory stimuli and released by MSCs. Thus, galectin-9 contributes to the inducible immunomodulatory functions of MSCs.

Systemic delivery of human mesenchymal stromal cells combined with IGF-1 enhances muscle functional recovery in LAMA2 dy/2j dystrophic mice

The combination of cell therapy with growth factors could be a useful approach to treat progressive muscular dystrophies. Here, we demonstrate, for the first time, that IGF-1 considerably enhances the myogenesis of human umbilical cord (UC) mesenchymal stromal cells (MSCs) in vitro and that IGF-1 enhances interaction and restoration of dystrophin expression in co-cultures of MSCs and muscle cells from Duchenne patients. In vivo studies showed that human MSCs were able to reach the skeletal muscle of LAMA2(dy/2j) dystrophic mice, through systemic delivery, without immunosuppression. Moreover, we showed, for the first time, that IGF-1 injected systemically together with MSCs markedly reduced muscle inflammation and fibrosis, and significantly improved muscle strength in dystrophic mice. Our results suggest that a combined treatment with IGF-1 and MSCs enhances efficiency of muscle repair and, therefore, should be further considered as a potential therapeutic approach in muscular dystrophies.

Combined intrathymic and intravenous injection of mesenchymal stem cells can prolong the survival of rat cardiac allograft associated with decrease in miR-155 expression

BACKGROUND

Mesenchymal stem cells (MSCs) have the potential to improve graft outcomes and promote allograft tolerance. In this study, we examined the effects and mechanism of combined intrathymic (i.t.) and intravenous (i.v.) injection of MSCs on the survival of transplanted hearts in a rat allograft model.

METHODS

Recipient Sprague-Dawley rats were transplanted with hearts from Wistar rats. Wistar rat MSCs were infused via i.t. or i.v. or combined i.t. and i.v. (i.t./i.v.) injection at designated intervals. In vitro mixed lymphocyte reaction assays were performed to assess the immunosuppressive capacity of MSCs. Mesenchymal stem cell surface markers and CD4+, CD25+, and Foxp3+ T-cells in the peripheral blood were detected using flow cytometry analysis. The expression of microRNAs and cytokines in graft infiltrating lymphocytes was analyzed by real-time polymerase chain reaction.

RESULTS

The MSCs cultured in vitro had multipotential differentiation capacity. Mixed lymphocyte reaction assays showed that donor-derived MSCs could not stimulate a proliferative response of recipient lymphocytes and could markedly suppress T-cell responses. Survival of the allografts was significantly prolonged by administration of i.t./i.v. injection of MSCs compared with controls, with a mean survival of 32.2 versus 6.5 d, respectively. Compared with the syngeneic groups posttransplant, miR-155 expression was significantly increased in the allogeneic group, and could be restored by injection of MSCs, especially i.t./i.v. injection of MSCs. Moreover, i.t./i.v. injection of MSCs decreased the level of interleukin (IL)-2 and interferon-gamma, but increased the levels of IL-4 and IL-10 in the allogeneic group. More important, i.t./i.v. injection of MSCs was the best way to increase the percentage of CD4+, CD25+, and Foxp3+ T-cell peripheral blood.

CONCLUSIONS

Our results indicated that i.t./i.v. injection of MSCs can prolong the survival of rat cardiac allograft, which may be associated with down-regulating miR-155 expression, a shift in the Th1/Th2 balance, and up-regulation of Treg cells expression.

Immunogenicity of embryonic stem cell-derived progenitors after transplantation

PURPOSE OF REVIEW

This review focuses on the immunogenicity of embryonic stem cell (ESC)-derived progenitors and the impact of the immune response on applications of cell replacement therapy (CRT). Possible strategies to induce immunological tolerance to ESC-derived progenitor cells will also be discussed.

RECENT FINDINGS

Evidence for the differential epigenetic control of major histocompatibility (MHC) and antigen processing molecules in ESCs and differentiated ESCs has recently been described. The presence of T cells recognizing the pluripotency-associated transcription factor octamer-binding transcription factor 4 (OCT4) in healthy patient-derived peripheral blood mononuclear cells adds further complexity to the immune response against ESCs and ESC-derived progenitors.

SUMMARY

Although ESCs and ESC-derived progenitors appear to exert some level of immune privilege in specific circumstances, these allogeneic cells are indeed recognized by the immune system and can be subject to mechanisms of rejection. Herein, we discuss the importance of the recent reports describing an immunosuppressive capacity of ESCs, and the epigenetic control of MHC in ESCs and how these characteristics may be harnessed in the development of strategies to induce immunological tolerance.

The Necessity of a Systematic Approach for the Use of MSCs in the Clinical Setting

Cell therapy has emerged as a potential therapeutic strategy in regenerative disease. Among different cell types, mesenchymal stem/stromal cells have been wildly studied in vitro, in vivo in animal models and even used in clinical trials. However, while clinical applications continue to increase markedly, the understanding of their physiological properties and interactions raises many questions and drives the necessity of more caution and supervised strategy in their use.

Cell fate conversion: direct induction of hepatocyte-like cells from fibroblasts

One of the essential features of stem cells is their cellular plasticity to differentiate into daughter cells with defined functions. Recently, induction of pluripotent stem cells from somatic cells by defined transcription factors led to the focus on cellular plasticity of terminally differentiated cells. This approach is adopted by other studies to demonstrate the cell fate conversion between different lineages of terminally differentiated cells. We and others showed that induced hepatocyte-like (iHep) cells are directly converted from mouse fibroblasts by overexpression of liver-enriched transcription factors. iHep cells as well as pluripotent stem cell- or mesenchymal stem cell-derived hepatocyte-like cells provide potential cell sources for disease modeling, transplantation, and tissue engineering independent of donor organs. Here, we review the latest advances in generating hepatocyte-like cells and summarize general criteria for evaluating these cells. In addition, we propose a possible role of the p19(Arf) /p53 pathway in cell fate maintenance, which apparently limits the formation of induced pluripotent stem (iPS) cells and iHep cells.

Cell biological effects of mechanical stimulations generated by focused extracorporeal shock wave applications on cultured human bone marrow stromal cells

Human bone marrow stromal cells (hBMSCs) bear tremendous clinical potential due to their immunomodulatory properties in transplantation settings and their contribution to tissue regeneration. In fact, they are among the most promising types of stem-like cells for therapeutic applications and are the subject of intense research. However, the clinical use of hBMSCs has been confounded by limitations in their availability; they are scarce cells cumbersome to isolate and purify. Additionally, they are difficult to target to the site of injury in regeneration experiments. In order to combat these limitations, focused extracorporeal shock waves (fESW, 0.2/0.3mJ∗mm(-2)) were applied to purified, cultured hBMSCs. fESW (0.2mJ∗mm(-2)) stimulations were found to increase hBMSCs' growth rate (p<0.05), proliferation (p<0.05), migration, cell tracking and wound healing (p<0.05, respectively), as well as to reduce the rate of apoptosis activation (p<0.05). The increase in hBMSC migration behavior was found to be mediated by active remodeling of the actin cytoskeleton as indicated by increased directed stress fiber formations (p<0.05). Furthermore, hBMSCs maintain their differentiation potentials after fESW treatment, whereas 0.2mJ∗mm(-2) is the most effective application. In conclusion, our results establish first-timely that hBMSCs' behavior can be modified and optimized in response to defined mechanical stimulation. These findings appear particularly promising as they suggest that mechanical stress preconditions hBMSCs for improved therapeutic performance without genetic manipulations and that mechanically preconditioned hBMSCs will be advantageous for hBMSC-based tissue regeneration. Therefore, this approach opens the door for exploiting the full potential of these cells in regenerative medicine.

Myocilin stimulates osteogenic differentiation of mesenchymal stem cells through mitogen-activated protein kinase signaling

Myocilin is a secreted glycoprotein that is expressed in ocular and non-ocular tissues. Mutations in the MYOCILIN gene may lead to juvenile- and adult-onset primary open-angle glaucoma. Here we report that myocilin is expressed in bone marrow-derived mesenchymal stem cells (MSCs) and plays a role in their differentiation into osteoblasts in vitro and in osteogenesis in vivo. Expression of myocilin was detected in MSCs derived from mouse, rat, and human bone marrow, with human MSCs exhibiting the highest level of myocilin expression. Expression of myocilin rose during the course of human MSC differentiation into osteoblasts but not into adipocytes, and treatment with exogenous myocilin further enhanced osteogenesis. MSCs derived from Myoc-null mice had a reduced ability to differentiate into the osteoblastic lineage, which was partially rescued by exogenous extracellular myocilin treatment. Myocilin also stimulated osteogenic differentiation of wild-type MSCs, which was associated with activation of the p38, Erk1/2, and JNK MAP kinase signaling pathways as well as up-regulated expression of the osteogenic transcription factors Runx2 and Dlx5. Finally, cortical bone thickness and trabecular volume, as well as the expression level of osteopontin, a known factor of bone remodeling and osteoblast differentiation, were reduced dramatically in the femurs of Myoc-null mice compared with wild-type mice. These data suggest that myocilin should be considered as a target for improving the bone regenerative potential of MSCs and may identify a new role for myocilin in bone formation and/or maintenance in vivo.

AF-MSCs fate can be regulated by culture conditions

Human mesenchymal stem cells (hMSCs) represent a population of multipotent adherent cells able to differentiate into many lineages. In our previous studies, we isolated and expanded fetal MSCs from second-trimester amniotic fluid (AF) and characterized them based on their phenotype, pluripotency and proteomic profile. In the present study, we investigated the plasticity of these cells based on their differentiation, dedifferentiation and transdifferentiation potential in vitro. To this end, adipocyte-like cells (AL cells) derived from AF-MSCs can regain, under certain culture conditions, a more primitive phenotype through the process of dedifferentiation. Dedifferentiated AL cells derived from AF-MSCs (DAF-MSCs), gradually lost the expression of adipogenic markers and obtained similar morphology and differentiation potential to AF-MSCs, together with regaining the pluripotency marker expression. Moreover, a comparative proteomic analysis of AF-MSCs, AL cells and DAF-MSCs revealed 31 differentially expressed proteins among the three cell populations. Proteins, such as vimentin, galectin-1 and prohibitin that have a significant role in stem cell regulatory mechanisms, were expressed in higher levels in AF-MSCs and DAF-MSCs compared with AL cells. We next investigated whether AL cells could transdifferentiate into hepatocyte-like cells (HL cells) directly or through a dedifferentiation step. AL cells were cultured in hepatogenic medium and 4 days later they obtained a phenotype similar to AF-MSCs, and were termed as transdifferentiated AF-MSCs (TRAF-MSCs). This finding, together with the increase in pluripotency marker expression, indicated the adaption of a more primitive phenotype before transdifferentiation. Additionally, we observed that AF-, DAF- and TRAF-MSCs displayed similar clonogenic potential, secretome and proteome profile. Considering the easy access to this fetal cell source, the plasticity of AF-MSCs and their potential to dedifferentiate and transdifferentiate, AF may provide a valuable tool for cell therapy and tissue engineering applications.

Achieving operational tolerance in transplantation: how can lessons from the clinic inform research directions?

Since the first solid organ transplant between the Herrick twins in 1954, transplantation immunology has sought to move away from harmful immunosuppressive regimens towards tolerogenic strategies that promote long-term graft survival. This has required a concerted multinational effort with scientists and clinicians working towards a common goal. Reports of immunosuppression-free kidney and liver allograft recipients have provided the proof-of-principle, but intentional generation of tolerance in clinical transplantation is still only achieved infrequently. Recently, there have been an increasing number of encouraging developments in the field in both experimental and clinical studies. In this article, we review the latest advances in tolerance research and consider possible future barriers and solutions in achieving reliable graft acceptance in the long term.

The future of glioma treatment: stem cells, nanotechnology and personalized medicine

The development of novel therapies, imaging techniques and insights into the processes that drive growth of CNS tumors have allowed growing enthusiasm for the treatment of CNS malignancies. Despite this energized effort to investigate and treat brain cancer, clinical outcomes for most patients continue to be dismal. Recognition of diverse tumor subtypes, behaviors and outcomes has led to an interest in personalized medicine for the treatment of brain tumors. This new paradigm requires evaluation of the tumor phenotype at the time of diagnosis so that therapy can be specifically tailored to each individual patient. Investigating novel therapies involving stem cells, nanotechnology and molecular medicine will allow diversity of therapeutic options for patients with brain cancer. These exciting new therapeutic strategies for brain tumors are reviewed in this article.

Spindle shaped human mesenchymal stem/stromal cells from amniotic fluid promote neovascularization

Human amniotic fluid obtained at amniocentesis, when cultured, generates at least two morphologically distinct mesenchymal stem/stromal cell (MSC) subsets. Of these, the spindle shaped amniotic fluid MSCs (SS-AF-MSCs) contain multipotent cells with enhanced adipogenic, osteogenic and chondrogenic capacity. Here, we demonstrate, for the first time, the capacity of these SS-AF-MSCs to support neovascularization by umbilical cord blood (UCB) endothelial colony forming cell (ECFC) derived cells in both in vitro and in vivo models. Interestingly, although the kinetics of vascular tubule formation in vitro were similar when the supporting SS-AF-MSCs were compared with the best vasculogenic supportive batches of bone marrow MSCs (BMSCs) or human dermal fibroblasts (hDFs), SS-AF-MSCs supported vascular tubule formation in vivo more effectively than BMSCs. In NOD/SCID mice, the human vessels inosculated with murine vessels demonstrating their functionality. Proteome profiler array analyses revealed both common and distinct secretion profiles of angiogenic factors by the SS-AF-MSCs as opposed to the hDFs and BMSCs. Thus, SS-AF-MSCs, which are considered to be less mature developmentally than adult BMSCs, and intermediate between adult and embryonic stem cells in their potentiality, have the additional and very interesting potential of supporting increased neovascularisation, further enhancing their promise as vehicles for tissue repair and regeneration.

Autologous bone marrow-derived mesenchymal stromal cells for the treatment of allograft rejection after renal transplantation: results of a phase I study

Despite excellent short-term results, long-term survival of transplanted kidneys has not improved accordingly. Although alloimmune responses and calcineurin inhibitor-related nephrotoxicity have been identified as main drivers of fibrosis, no effective treatment options have emerged. In this perspective, mesenchymal stromal cells (MSCs) are an interesting candidate because of their immunosuppressive and regenerative properties. Of importance, no other clinical studies have investigated their effects in allograft rejection and fibrosis. We performed a safety and feasibility study in kidney allograft recipients to whom two intravenous infusions (1 million cells per kilogram) of autologous bone marrow (BM) MSCs were given, when a protocol renal biopsy at 4 weeks or 6 months showed signs of rejection and/or an increase in interstitial fibrosis/tubular atrophy (IF/TA). Six patients received MSC infusions. Clinical and immune monitoring was performed up to 24 weeks after MSC infusions. MSCs fulfilled the release criteria, infusions were well-tolerated, and no treatment-related serious adverse events were reported. In two recipients with allograft rejection, we had a clinical indication to perform surveillance biopsies and are able to report on the potential effects of MSCs in rejection. Although maintenance immunosuppression remained unaltered, there was a resolution of tubulitis without IF/TA in both patients. Additionally, three patients developed an opportunistic viral infection, and five of the six patients displayed a donor-specific downregulation of the peripheral blood mononuclear cell proliferation assay, not reported in patients without MSC treatment. Autologous BM MSC treatment in transplant recipients with subclinical rejection and IF/TA is clinically feasible and safe, and the findings are suggestive of systemic immunosuppression.

Mesenchymal stem cell: keystone of the hematopoietic stem cell niche and a stepping-stone for regenerative medicine

Mesenchymal stem cells (MSCs) are self-renewing precursor cells that can differentiate into bone, fat, cartilage, and stromal cells of the bone marrow. Recent studies suggest that MSCs themselves are critical for forming a niche that maintains hematopoietic stem cells (HSCs). The ease by which human MSC-like and stromal progenitor cells can be isolated from the bone marrow and other tissues has led to the rapid development of clinical investigations exploring their anti-inflammatory properties, tissue preservation capabilities, and regenerative potential. However, the identity of genuine MSCs and their specific contributions to these various beneficial effects have remained enigmatic. In this article, we examine the definition of MSCs and discuss the importance of rigorously characterizing their stem cell activity. We review their role and that of other putative niche constituents in the regulation of bone marrow HSCs. Additionally, how MSCs and their stromal progeny alter immune function is discussed, as well as potential therapeutic implications.

Statins and stem cell modulation

Stem cell-based therapy is a promising option for the treatment of ischemic heart diseases. As to a successful stem cell-based therapy, one of the most important issues is that the stable engraftment and survival of implanted stem cells in cardiac microenvironment. There are evidences suggest that pharmacological treatment devoted to regulate stem cell function might represent a potential new therapeutic strategy and are drawing nearer to becoming a part of treatment in clinical settings. Statins could exert cholesterol-independent or pleiotropic effects to cardiovascular system. Recent studies have shown that statins could modulate the biological characteristics and function of various stem cells, thus could be an effective method to facilitate stem cell therapy. This review will focus on statins and their modulation effects on various stem cells.

The angiogenic properties of mesenchymal stem/stromal cells and their therapeutic potential

BACKGROUND

Blood vessel formation is fundamental to development, while its dysregulation can contribute to serious disease. Expectations are that hundreds of millions of individuals will benefit from therapeutic developments in vascular biology. MSCs are central to the three main vascular repair mechanisms.

SOURCES OF DATA

Key recent published literature and ClinicalTrials.gov.

AREAS OF AGREEMENT

MSCs are heterogeneous, containing multi-lineage stem and partly differentiated progenitor cells, and are easily expandable ex vivo. There is no single marker defining native MSCs in vivo. Their phenotype is strongly determined by their specific microenvironment. Bone marrow MSCs have skeletal stem cell properties. Having a perivascular/vascular location, they contribute to vascular formation and function and might be harnessed to regenerate a blood supply to injured tissues.

AREAS OF CONTROVERSY

These include MSC origin, phenotype and location in vivo and their ability to differentiate into functional cardiomyocytes and endothelial cells or act as vascular stem cells. In addition their efficacy, safety and potency in clinical trials in relation to cell source, dose, delivery route, passage and timing of administration, but probably even more on the local preconditioning and the mechanisms by which they exert their effects.

GROWING POINTS

Understanding the origin and the regenerative environment of MSCs, and manipulating their homing properties, proliferative ability and functionality through drug discovery and reprogramming strategies are important for their efficacy in vascular repair for regenerative medicine therapies and tissue engineering approaches.

AREAS TIMELY FOR DEVELOPING RESEARCH

Characterization of MSCs' in vivo origins and biological properties in relation to their localization within tissue niches, reprogramming strategies and newer imaging/bioengineering approaches.

Primary marrow-derived stromal cells: isolation and manipulation

Marrow stromal cells (MSCs) are relatively rare cells difficult to visualize in marrow biopsies or detect in aspirated marrow. Under specific conditions MSC can be expanded in vitro and the population can give rise to several mesenchymal lineages. "MSC" also refers to mesenchymal stem cells which implies that all cells in the population are multipotent. It is generally agreed that while there may be a few multipotent stem cells in an MSC population the majority are not stem cells. In either case MSCs do not produce hematopoietic cells. Although MSCs have been isolated and characterized from several tissues, bone marrow is their most common source for research and clinical use. Primary MSC populations can be derived from bone marrow mononuclear cells with relative ease, but it is important to recognize the cellular heterogeneity within a culture and how this may vary from donor to donor. In this chapter, we describe methodology to derive primary MSCs from bone marrow screens, an otherwise discarded by-product of bone marrow harvests used for clinical transplantation. We also describe some useful techniques to characterize and manipulate MSCs-both primary and immortalized cell lines.

Allogenicity of human cardiac stem/progenitor cells orchestrated by programmed death ligand 1

RATIONALE

Transplantation of allogeneic cardiac stem/progenitor cells (CPC) in experimental myocardial infarction promoted cardiac regeneration and improved heart function. Although this has enhanced prospects of using allogeneic CPC for cardiac repair, the mechanisms regulating the behavior of these allogeneic cells, which are central to clinical applications, remain poorly understood.

OBJECTIVE

T cells orchestrate the allogeneic adaptive immune response. Therefore, to provide insight into the mechanisms regulating the immunologic behavior of human CPC (hCPC), we investigated the allogeneic T-cell response elicited by cryopreserved c-kit-selected hCPC.

METHODS AND RESULTS

By using an experimental model of allogeneic stimulation, we demonstrate that, whether under inflammatory conditions or not, hCPC do not trigger conventional allogeneic Th1 or Th2 type responses but instead induce proliferation and selective expansion of suppressive CD25(high)CD127(low)human leukocyte antigen-DR(+)FoxP3(high) effector regulatory T cells. The regulatory T-cell proliferation and amplification were dependent on the interaction with the B7 family member programmed death ligand 1 (PD-L1), which is substantially expressed on hCPC and increased under inflammatory conditions. Thus, hCPC in allogeneic settings acquire the capacity to downregulate an ongoing immune response, which was dependent on PD-L1.

CONCLUSIONS

Collectively, these data reveal that hCPC in allogeneic settings have a tolerogenic immune behavior, promoting a contact PD-L1-dependent regulatory response and a PD-L1-dependent allogeneic-driven immunomodulation. Our study attributes an important role for PD-L1 in the immune behavior of allogeneic hCPC and raises the possibility of using PD-L1 expression as a marker to identify and select low-risk high-benefit allogeneic cardiac repair cells.

Anti-donor immune responses elicited by allogeneic mesenchymal stem cells: what have we learned so far?

Mesenchymal stem (stromal) cells (MSCs) have potent anti-inflammatory/immunosuppressive properties which underlie much of their therapeutic potential. This fact has led to the widely accepted belief that MSCs from genetically unrelated individuals (allogeneic (allo)-MSCs) can be used therapeutically with equal efficacy to autologous MSCs and without triggering the donor-specific immune responses that are typically associated with allo-transplants. In this article, we critically review available experimental data to determine whether good in vivo evidence exists in support of the 'immune privileged' status of allo-MSCs. We also examine published studies regarding the immunogenicity of allo-MSCs following activation ('licensing') by inflammatory stimuli or following differentiation. Among the identified studies which have addressed in vivo immunogenicity of allo-MSCs, there was substantial variability as regards experimental species, disease model, route of MSC administration, cell dose and stringency of the immunological assays employed. Nonetheless, the majority of these studies has documented specific cellular (T-cell) and humoral (B-cell/antibody) immune responses against donor antigens following administration of non-manipulated, interferon-γ-activated and differentiated allo-MSCs. The consequences of such anti-donor immune responses were also variable and ranged from reduced in vivo survival of allo-MSCs with accelerated rejection of subsequent allogeneic transplants to apparent promotion of donor-specific tolerance. On the basis of these findings and on existing knowledge of allo-antigen recognition from the field of transplant immunology, we propose that the concept of the immune privileged nature of allo-MSCs should be reconsidered and that the range and clinical implications of anti-donor immune responses elicited by allo-MSCs be more precisely studied in human and animal recipients.

Enhanced homing permeability and retention of bone marrow stromal cells by noninvasive pulsed focused ultrasound

Bone marrow stromal cells (BMSCs) have shown significant promise in the treatment of disease, but their therapeutic efficacy is often limited by inefficient homing of systemically administered cells, which results in low number of cells accumulating at sites of pathology. BMSC home to areas of inflammation where local expression of integrins and chemokine gradients is present. We demonstrated that nondestructive pulsed focused ultrasound (pFUS) exposures that emphasize the mechanical effects of ultrasound-tissue interactions induced local and transient elevations of chemoattractants (i.e., cytokines, integrins, and growth factors) in the murine kidney. pFUS-induced upregulation of cytokines occurred through approximately 1 day post-treatment and returned to contralateral kidney levels by day 3. This window of significant increases in cytokine expression was accompanied by local increases of other trophic factors and integrins that have been shown to promote BMSC homing. When BMSCs were intravenously administered following pFUS treatment to a single kidney, enhanced homing, permeability, and retention of BMSC was observed in the treated kidney versus the contralateral kidney. Histological analysis revealed up to eight times more BMSC in the peritubular regions of the treated kidneys on days 1 and 3 post-treatment. Furthermore, cytokine levels in pFUS-treated kidneys following BMSC administration were found to be similar to controls, suggesting modulation of cytokine levels by BMSC. pFUS could potentially improve cell-based therapies as a noninvasive modality to target homing by establishing local chemoattractant gradients and increasing expression of integrins to enhance tropism of cells toward treated tissues.

High levels of ephrinB2 over-expression increases the osteogenic differentiation of human mesenchymal stem cells and promotes enhanced cell mediated mineralisation in a polyethyleneimine-ephrinB2 gene-activated matrix

Gene therapy can be combined with tissue engineering constructs to produce gene-activated matrices (GAMs) with enhanced capacity for repair. Polyethyleneimine (PEI), a non-viral vector, has previously been optimised for high efficiency gene transfer in rat mesenchymal stem cells (rMSCs). The use of PEI to transfect human MSCs (hMSCs) with ephrinB2 is assessed here. Recently a role for the ephrinB2 ligand and EphB4 receptor duo has been proposed in bone remodelling. Herein, over-expression of the ephrinB2 ligand resulted in increased osteogenic differentiation in hMSCs. As ephrinB2 is a cell surface anchored ligand which only interacts with cells expressing the cognate EphB4 receptor through direct contact, we have shown that direct cell-cell contact between two neighbouring cells is responsible for enhanced osteogenesis. In an effort to begin to elucidate the molecular mechanisms at play downstream of ephrinB2 over-expression, RT-PCR was performed on the GAMs which revealed no significant changes in runx2 or BMP2 expression but an upregulation of osterix (Osx) and Dlx5 expression prompting the belief that the mode of osteogenesis is independent of the BMP2 pathway. This select interaction, coupled with the transient gene expression profile of PEI, makes the PEI-ephrinB2 GAM an ideal candidate matrix for a bone targeted GAM.

Mesenchymal stem cells as immunomodulators in a vascularized composite allotransplantation

Vascularized composite allotransplantations (VCAs) are not routinely performed for tissue reconstruction because of the potentially harmful adverse effects associated with lifelong administration of immunosuppressive agents. Researchers have been eagerly seeking alternative methods that circumvent the long-term use of immunosuppressants. Mesenchymal stem cells (MSCs) show promise as an immunomodulatory therapeutic agent and are currently being tested in preclinical and clinical settings as therapies for autoimmune disorders or transplant rejection. The mechanisms by which MSCs modulate the immune response are still under thorough investigation, but these most likely involve expression of local factors influencing T-cell regulation, modulation of cytokine expression (e.g., IL-10, TGF-β, TNF-α, INF-γ, etc.), and interactions with dendritic or antigen presenting cells. In this paper, we summarize the current understanding of immunomodulation achieved by MSC therapies and introduce a possible outline for future clinical applications in VCA.

CCR2-dependent recruitment of macrophages by tumor-educated mesenchymal stromal cells promotes tumor development and is mimicked by TNFα

Mesenchymal stromal cells (MSCs) tend to infiltrate into tumors and form a major component of the tumor microenvironment. These tumor-resident MSCs are known to affect tumor growth, but the mechanisms are largely unknown. We found that MSCs isolated from spontaneous lymphomas in mouse (L-MSCs) strikingly enhanced tumor growth in comparison to bone marrow MSCs (BM-MSCs). L-MSCs contributed to greater recruitment of CD11b(+)Ly6C(+) monocytes, F4/80(+) macrophages, and CD11b(+)Ly6G(+) neutrophils to the tumor. Depletion of monocytes/macrophages, but not neutrophils, completely abolished tumor promotion of L-MSCs. Furthermore, L-MSCs expressed high levels of CCR2 ligands, and monocyte/macrophage accumulation and L-MSC-mediated tumor promotion were largely abolished in CCR2(-/-) mice. Intriguingly, TNFα-pretreated BM-MSCs mimicked L-MSCs in their chemokine production profile and ability to promote tumorigenesis of lymphoma, melanoma, and breast carcinoma. Therefore, our findings demonstrate that, in an inflammatory environment, tumor-resident MSCs promote tumor growth by recruiting monocytes/macrophages.

Treatment-emergent adverse events after infusion of adherent stem cells: the MiSOT-I score for solid organ transplantation

BACKGROUND

Cellular therapy after organ transplantation is emerging as an intriguing strategy to achieve dose reduction of classical immunosuppressive pharmacotherapy. Here, we introduce a new scoring system to assess treatment-emergent adverse events (TEAEs) of adherent stem cell therapies in the clinical setting of allogeneic liver transplantation (for example, the MiSOT-I trial Eudract CT: 2009-017795-25).

METHODS

The score consists of three independent modalities (set of parameters) that focus on clinically relevant events early after intravenous or intraportal stem cell infusion: pulmonary toxicity, intraportal-infusional toxicity and systemic toxicity. For each modality, values between 0 (no TEAE) and 3 (severe TEAE) were defined. The score was validated retrospectively on a cohort of n=187 recipients of liver allografts not receiving investigational cell therapy between July 2004 and December 2010. These patients represent a control population for further trials. Score values were calculated for days 1, 4, and 10 after liver transplantation.

RESULTS

Grade 3 events were most commonly related to the pulmonary system (3.5% of study cohort on day 4). Almost no systemic-related TEAEs were observed during the study period. The relative frequency of grade 3 events never exceeded 5% over all modalities and time points. A subgroup analysis for grade 3 patients provided no descriptors associated with severe TEAEs.

CONCLUSION

The MiSOT-I score provides an assessment tool to score specific adverse events that may occur after adherent stem cell therapy in the clinical setting of organ transplantation and is thus a helpful tool to conduct a safety study.

Mesenchymal stem cells promote the sustained expression of CD69 on activated T lymphocytes: roles of canonical and non-canonical NF-κB signalling

Mesenchymal stem cells (MSCs) are known to induce the conversion of activated T cells into regulatory T cells in vitro. The marker CD69 is a target of canonical nuclear factor kappa-B (NF-κB) signalling and is transiently expressed upon activation; however, stable CD69 expression defines cells with immunoregulatory properties. Given its enormous therapeutic potential, we explored the molecular mechanisms underlying the induction of regulatory cells by MSCs. Peripheral blood CD3⁺ T cells were activated and cultured in the presence or absence of MSCs. CD4⁺ cell mRNA expression was then characterized by microarray analysis. The drug BAY11-7082 (BAY) and a siRNA against v-rel reticuloendotheliosis viral oncogene homolog B (RELB) were used to explore the differential roles of canonical and non-canonical NF-κB signalling, respectively. Flow cytometry and real-time PCR were used for analyses. Genes with immunoregulatory functions, CD69 and non-canonical NF-κB subunits (RELB and NFKB2) were all expressed at higher levels in lymphocytes co-cultured with MSCs. The frequency of CD69⁺ cells among lymphocytes cultured alone progressively decreased after activation. In contrast, the frequency of CD69⁺ cells increased significantly following activation in lymphocytes co-cultured with MSCs. Inhibition of canonical NF-κB signalling by BAY immediately following activation blocked the induction of CD69; however, inhibition of canonical NF-κB signalling on the third day further induced the expression of CD69. Furthermore, late expression of CD69 was inhibited by RELB siRNA. These results indicate that the canonical NF-κB pathway controls the early expression of CD69 after activation; however, in an immunoregulatory context, late and sustained CD69 expression is promoted by the non-canonical pathway and is inhibited by canonical NF-κB signalling.

The role of recipient T cells in mesenchymal stem cell-based tissue regeneration

Significant progress has been made in stem cell biology, regenerative medicine, and stem cell-based tissue engineering. Such scientific strides highlight the potential of replacing or repairing damaged tissues in congenital abnormalities, diseases, or injuries, as well as constructing functional tissue or organs in vivo. Since mesenchymal stem cells (MSCs) are capable of differentiating into bone-forming cells, they constitute an appropriate cell source to repair damaged bone tissues. In addition, the immunoregulatory property of MSCs provides a foundation for their use in treating a variety of autoimmune diseases. However, the interaction between MSCs and immune cells in cell-based tissue regeneration is largely unknown. In this review, we will discuss the current understanding of MSC-based tissue regeneration, emphasizing the role of the immune microenvironment in bone regeneration.

Hypoxia-preconditioned mesenchymal stromal cells improve cardiac function in a swine model of chronic myocardial ischaemia

OBJECTIVES

Cell loss during cardiac injection and hostility of the host-tissue microenvironment have the potential to diminish the overall effect of stem cell therapy. The purposes of this study were to evaluate the effect of a hypoxic preconditioning of mesenchymal stromal cells (MSC), to determine its safety and effectiveness, and to improve the efficacy of cell therapy using MSC in the setting of chronic myocardial ischaemia in swine.

METHODS

Myocardial ischaemia was induced by an ameroid constrictor. Human MSC were cultured under normoxic (20% O2) or hypoxic conditions (1.5% O2) before transplantation. One month after ischaemia, pigs were randomly assigned to saline injection (sham), and 1 × 10(6)/kg normoxic or hypoxic MSC transplantation into the ischaemic inferior-lateral zone.

RESULTS

Twenty-seven pigs were operated on and the mortality rate was 33.3%. The remaining 18 animals were randomly assigned to sham (n = 4), normoxic (n = 8) or hypoxic MSC (n = 6) treatment. Global systolic (left ventricle ejection fraction, P = 0.04) and diastolic (E/Ea, P = 0.008) functions were increased in the hypoxic group compared with other groups. The peak of 2-dimensional longitudinal strain was less altered in the hypoxic group compared with other groups (P < 0.001). Haemodynamic data showed that dP/dT max was improved in the hypoxic group compared with the other group (P < 0.01). Capillary density was increased in the hypoxic group (P = 0.001). MSC density was significantly higher in the ischaemic zone in the hypoxic group (P < 0.01).

CONCLUSION

MSC engraftment with hypoxic preconditioning significantly improves capillary density and cell survival, resulting in improvement in global, regional and diastolic left ventricular functions. This highlights the therapeutic potential of transplanting hypoxic-preconditioned MSC in the setting of chronic ischaemic heart failure.

Mechanisms of mesenchymal stromal cell immunomodulation

Multipotent mesenchymal stromal cells (MSCs) have generated considerable interest in the fields of regenerative medicine, cell therapy and immune modulation. Over the past 5 years, the initial observations that MSCs could enhance regeneration and modulate immune responses have been significantly advanced and we now have a clearer picture of the effects that MSCs have on the immune system particularly in the context of inflammatory-mediated disorders. A number of mechanisms of action have been reported in MSC immunomodulation, which encompass the secretion of soluble factors, induction of anergy, apoptosis, regulatory T cells and tolerogenic dendritic cells. It is clear that MSCs modulate both innate and adaptive responses and evidence is now emerging that the local microenvironment is key in the activation or licensing of MSCs to become immunosuppressive. More recently, studies have suggested that MSCs have the capacity to sense their environment and have a role in pathogen clearance in conjunction with the resolution of insult or injury. This review focuses on the mechanisms of MSC immunomodulation discussing the multistep process of MSC localisation at sites of inflammation, the cross talk between MSCs and the local microenvironment as well as the subsequent mechanisms of action used to resolve inflammation.

Development and characterization of a clinically compliant xeno-free culture medium in good manufacturing practice for human multipotent mesenchymal stem cells

Human multipotent mesenchymal stem cell (MSC) therapies are currently being tested in clinical trials for Crohn's disease, multiple sclerosis, graft-versus-host disease, type 1 diabetes, bone fractures, cartilage damage, and cardiac diseases. Despite remarkable progress in clinical trials, most applications still use traditional culture media containing fetal bovine serum or serum-free media that contain serum albumin, insulin, and transferrin. The ill-defined and variable nature of traditional culture media remains a challenge and has created a need for better defined xeno-free culture media to meet the regulatory and long-term safety requirements for cell-based therapies. We developed and tested a serum-free and xeno-free culture medium (SFM-XF) using human bone marrow- and adipose-derived MSCs by investigating primary cell isolation, multiple passage expansion, mesoderm differentiation, cellular phenotype, and gene expression analysis, which are critical for complying with translation to cell therapy. Human MSCs expanded in SFM-XF showed continual propagation, with an expected phenotype and differentiation potential to adipogenic, chondrogenic, and osteogenic lineages similar to that of MSCs expanded in traditional serum-containing culture medium (SCM). To monitor global gene expression, the transcriptomes of bone marrow-derived MSCs expanded in SFM-XF and SCM were compared, revealing relatively similar expression profiles. In addition, the SFM-XF supported the isolation and propagation of human MSCs from primary human marrow aspirates, ensuring that these methods and reagents are compatible for translation to therapy. The SFM-XF culture system allows better expansion and multipotentiality of MSCs and serves as a preferred alternative to serum-containing media for the production of large scale, functionally competent MSCs for future clinical applications.

Stem cell educator therapy and induction of immune balance

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that causes the deficit of pancreatic islet β cells. A true cure has proven elusive despite intensive research pressure by using conventional approaches over the past 25 years. The situation highlights the challenges we face in conquering this disease. Alternative approaches are needed. Increasing evidence demonstrates that stem cells possess the function of immune modulation. We established the Stem Cell Educator therapy by using cord blood-derived multipotent stem cells (CB-SCs). A closed-loop system that circulates a patient's blood through a blood cell separator, briefly co-cultures the patient's lymphocytes with adherent CB-SCs in vitro, and returns the educated lymphocytes (but not the CB-SCs) to the patient's circulation. Our clinical trial reveals that a single treatment with the Stem Cell Educator provides lasting reversal of autoimmunity that allows regeneration of islet β cells and improvement of metabolic control in subjects with long-standing T1D.

Mesoangioblasts suppress T cell proliferation through IDO and PGE-2-dependent pathways

Human mesoangioblasts are vessel-associated stem cells that are currently in phase I/II clinical trials for the treatment of patients with Duchenne muscular dystrophy. To date, little is known about the effect of mesoangioblasts on human immune cells and vice versa. We hypothesized that mesoangioblasts could modulate the function of immune cells in a similar manner to mesenchymal stromal cells. Human mesoangioblasts did not evoke, but rather potently suppressed human T-cell proliferation and effector function in vitro in a dose- and time-dependent manner. Furthermore, mesoangioblasts exert these inhibitory effects uniformly on human CD4+ and CD8+ T cells in a reversible manner without inducing a state of anergy. Interferon (IFN)-γ and tumor necrosis factor (TNF)-α play crucial roles in the initial activation of mesoangioblasts. Indoleamine 2,3-dioxygenase (IDO) and prostaglandin E-2 (PGE) were identified as key mechanisms of action involved in the mesoangioblast suppression of T-cell proliferation. Together, these data demonstrate a previously unrecognized capacity of mesoangioblasts to modulate immune responses.

Intravenous mesenchymal stem cells prevented rejection of allogeneic corneal transplants by aborting the early inflammatory response

Mesenchymal stem/progenitor cells (MSCs) were reported to enhance the survival of cellular and organ transplants. However, their mode of action was not established. We here used a mouse model of corneal allotransplantation and demonstrated that peri-transplant intravenous (i.v.) infusion of human MSCs (hMSCs) decreased the early surgically induced inflammation and reduced the activation of antigen-presenting cells (APCs) in the cornea and draining lymph nodes (DLNs). Subsequently, immune rejection was decreased, and allograft survival was prolonged. Quantitative assays for human GAPDH revealed that <10 hMSCs out of 1 × 10(6) injected cells were recovered in the cornea 10 hours to 28 days after i.v. infusion. Most of hMSCs were trapped in lungs where they were activated to increase expression of the gene for a multifunctional anti-inflammatory protein tumor necrosis factor-α stimulated gene/protein 6 (TSG-6). i.v. hMSCs with a knockdown of TSG-6 did not suppress the early inflammation and failed to prolong the allograft survival. Also, i.v. infusion of recombinant TSG-6 reproduced the effects of hMSCs. Results suggest that hMSCs improve the survival of corneal allografts without engraftment and primarily by secreting TSG-6 that acts by aborting early inflammatory responses. The same mechanism may explain previous reports that MSCs decrease rejection of other organ transplants.

Immune effects of mesenchymal stromal cells in experimental stroke

Preclinical trials confirmed the potential of mesenchymal stromal cells (MSCs) to improve functional recovery after experimental stroke. Beneficial effects of MSCs are often attributed to their immunosuppressive/immunomodulatory functions. Surprisingly, the influence of MSCs on the immune system after stroke is poorly understood, but requires special consideration because cerebral ischemia is associated with stroke-induced immunodepression that predisposes to bacterial infections with increased mortality. In this study, we intravenously transplanted syngeneic murine bone marrow-derived MSCs (mMSCs) into C57BL/6 mice at 6 hours after transient middle cerebral artery occlusion (MCAo; 60 minutes) to investigate the impact of MSCs on stroke-induced immunodepression. Transplantation of syngeneic splenocytes or phosphate-buffered saline (PBS) served as controls. An immune status was determined by flow cytometry on days 3 and 14 after MCAo, which did not reveal any negative effects of cell transplantation on stroke-induced immunodepression. Although our mMSCs were found to exert immunosuppressive effects in vitro, stroke-mediated immune cell dysfunction was not altered by mMSCs in ex-vivo stimulation assays with lipopolysaccharide or concanavalin A. Moreover, systemic inflammatory cytokine levels (interleukin-6, tumor necrosis factorα, interferonγ, monocyte chemoattractant protein-1) remained unchanged in the sera of mice after cerebral ischemia and cell transplantation. These results reduce safety concerns about MSC administration in ongoing clinical stroke trials.

Genetic mismatch affects the immunosuppressive properties of mesenchymal stem cells in vitro and their ability to influence the course of collagen-induced arthritis

Introduction

The immunological and homing properties of mesenchymal stem cells (MSCs) provide a potentially attractive treatment for arthritis. The objective of this study was to determine effects of genetic disparity on the immunosuppressive potential of MSCs in vitro and in vivo within collagen induced arthritis (CIA).

Methods

The ability of DBA/1, FVB and BALB/c MSC preparations to impact the cytokine release profile of CD3/CD28 stimulated DBA/1 T cells was assessed in vitro. The effect of systemically delivered MSCs on the progression of CIA and cytokine production was assessed in vivo.

Results

All MSC preparations suppressed the release of TNFα and augmented the secretion of IL-4 and IL-10 by stimulated DBA/1 T-cells. However, assessment of the ratio of IFNγ to IL-4 production indicated that the more genetically distant BALB/c MSCs had significantly less immunosuppressive capacity. Systemic delivery of BALB/c MSC resulted in an exacerbation of CIA disease score in vivo and a higher erosive disease burden. This was not seen after treatment with syngeneic or partially mismatched MSCs. An increase in serum levels of IL-1β was observed up to 20 days post treatment with allogeneic MSCs. An initial elevation of IL-17 in these treatment groups persisted in those treated with fully mismatched BALB/c MSCs. Over the course of the study, there was a significant suppression of serum IL-17 levels in groups treated with syngeneic MSCs.

Conclusions

These data demonstrate a significant difference in the immunosuppressive properties of syngeneic and allogeneic MSCs in vitro and in vivo, which needs to be appreciated when developing MSC based therapies for inflammatory arthritis.

Systemic transplantation of allogenic fetal membrane-derived mesenchymal stem cells suppresses Th1 and Th17 T cell responses in experimental autoimmune myocarditis

We have reported that systemic administration of autologous bone marrow or allogenic fetal membrane (FM)-derived mesenchymal stem cells (MSCs) similarly attenuated myocardial injury in rats with experimental autoimmune myocarditis (EAM). Since rat EAM is a T-helper (Th) cell-mediated autoimmune disease, and recent evidence has indicated that both autologous and allogenic MSCs exert an immunosuppressive effect on Th cell activity, we focused on Th cell differentiation in allogenic FM-MSC administered EAM rats. EAM was induced in Lewis rats by injecting porcine cardiac myosin (day 0). Allogenic FM-MSCs, obtained from major histocompatibility complex mismatched ACI rats, were intravenously injected (5 × 10(5)cells/rat) on days 7, 10, or 14 (MSCd7, MSCd10, or MSCd14 groups, respectively). At day 21, echocardiography confirmed that reduced ejection fraction in the untreated EAM group (63 ± 2%) was significantly improved in the MSCd10 and MSCd14 groups (74 ± 1 and 75 ± 2%, respectively, P<0.01). CD68 immunostaining revealed that prominent macrophage infiltration in the myocardium of the EAM group (1466 ± 93 cells/mm(2)) was significantly decreased in the MSCd10 group (958 ± 139 cells/mm(2), P<0.05). To evaluate Th cell differentiation, we used flow cytometry to determine the percentage of interferon (IFN)-γ positive Th1 and interleukin (IL)-17 positive Th17 cells in peripheral CD4-positive Th cells. The percentage of Th1 cells at day 16 was significantly lower in the MSCd10 (1.3 ± 0.2%) and MSCd14 (1.6 ± 0.3%) groups compared to the EAM group (2.4 ± 0.3%, P<0.05), as was the percentage of Th17 cells in the MSCd10 group (1.9 ± 0.5%) compared to the EAM group (2.2 ± 0.9%, P<0.05). At day 21, infiltrating Th17 cells in myocardium were significantly decreased in the MSCd10 group (501 ± 132 cells/mm(2), P<0.05) compared to EAM (921 ± 109 cells/mm(2)). In addition, human CD4+ Th cells co-cultured with human FM-MSCs exhibited reduced Th1 and Th17 cell-differentiation and proliferation, with increased expression of immunosuppressive molecules including indoleamine 2,3-dioxygenase 2 and IL-6 in co-cultured FM-MSCs. These results suggest that intravenous administration of allogenic FM-MSCs ameliorates EAM via the suppression of Th1/Th17 immunity.

Double allogenic mesenchymal stem cells transplantations could not enhance therapeutic effect compared with single transplantation in systemic lupus erythematosus

The clinical trial of allogenic mesenchymal stem cells (MSCs) transplantation for refractory SLE patients has shown significant safety and efficacy profiles. However, the optimum frequency of the MSCs transplantation (MSCT) is unknown. This study was undertaken to observe whether double transplantations of MSCs is superior to single transplantation. Fifty-eight refractory SLE patients were enrolled in this study, in which 30 were randomly given single MSCT, and the other 28 were given double MSCT. Patients were followed up for rates of survival, disease remission, and relapse, as well as transplantation-related adverse events. SLE disease activity index (SLEDAI) and serologic features were evaluated. Our results showed that no remarkable differences between single and double allogenic MSCT were found in terms of disease remission and relapse, amelioration of disease activity, and serum indexes in an SLE clinical trial with more than one year followup. This study demonstrated that single MSCs transplantation at the dose of one million MSCs per kilogram of body weight was sufficient to induce disease remission for refractory SLE patients.

Therapeutic potential of mesenchymal stem cells for oral and systemic diseases

Mesenchymal stem cells (MSCs) are adult stem cells whose self-renewal, multipotency, and immunosuppressive functions have been investigated for therapeutic applications. MSCs have used for various systemic organ regenerative therapies, allowing rescue of tissue function in damaged or failing organs. This article reviews the regenerative and immunomodulatory functions of MSCs and their applications in dental, orofacial, and systemic tissue regeneration and treatment of inflammatory disorders. It also addresses challenges to MSC-mediated therapeutics arising from tissue and MSC aging and host immune response against allogenic MSC transplantation, and discusses alternative sources of MSCs aimed at overcoming these limitations.

Human fallopian tube mesenchymal stromal cells enhance bone regeneration in a xenotransplanted model

We have recently reported that human fallopian tubes, which are discarded during surgical procedures of women submitted to sterilization or hysterectomies, are a rich source of human fallopian tube mesenchymal stromal cells (htMSCs). It has been previously shown that human mesenchymal stromal cells may be useful in enhancing the speed of bone regeneration. This prompted us to investigate whether htMSCs might be useful for the treatment of osteoporosis or other bone diseases, since they present a pronounced capacity for osteogenic differentiation in vitro. Based on this prior knowledge, our aim was to evaluate, in vivo, the osteogenic capacity of htMSCs to regenerate bone through an already described xenotransplantation model: nonimmunosuppressed (NIS) rats with cranial defects. htMSCs were obtained from five 30-50 years old healthy women and characterized by flow cytometry and for their multipotenciality in vitro capacity (osteogenic, chondrogenic and adipogenic differentiations). Two symmetric full-thickness cranial defects on each parietal region of seven NIS rats were performed. The left side (LS) of six animals was covered with CellCeram (Scaffdex)-a bioabsorbable ceramic composite scaffold that contains 60% hydroxyapatite and 40% β-tricalciumphosphate-only, and the right side (RS) with the CellCeram and htMSCs (10(6) cells/scaffold). The animals were euthanized at 30, 60 and 90 days postoperatively and cranial tissue samples were taken for histological analysis. After 90 days we observed neobone formation in both sides. However, in animals euthanized 30 and 60 days after the procedure, a mature bone was observed only on the side with htMSCs. PCR and immunofluorescence analysis confirmed the presence of human DNA and thus that human cells were not rejected, which further supports the imunomodulatory property of htMSCs. In conclusion, htMSCs can be used successfully to enhance bone regeneration in vivo, opening a new field for future treatments of osteoporosis and bone reconstruction.

Human gingiva-derived mesenchymal stromal cells attenuate contact hypersensitivity via prostaglandin E2-dependent mechanisms

The immunomodulatory and anti-inflammatory functions of mesenchymal stromal cells (MSCs) have been demonstrated in several autoimmune/inflammatory disease models, but their contribution to the mitigation of contact hypersensitivity (CHS) remains unclear. Here, we report a new immunological approach using human gingiva-derived MSCs (GMSCs) to desensitize and suppress CHS and the underlying mechanisms. Our results showed that systemic infusion of GMSCs before the sensitization and challenge phase dramatically suppress CHS, manifested as a decreased infiltration of dendritic cells (DCs), CD8(+) T cells, T(H)-17 and mast cells (MCs), a suppression of a variety of inflammatory cytokines, and a reciprocal increased infiltration of regulatory T cells and expression of IL-10 at the regional lymph nodes and the allergic contact areas. The GMSC-mediated immunosuppressive effects and mitigation of CHS were significantly abrogated on pretreatment with indomethacin, an inhibitor of cyclooxygenases. Under coculture condition of direct cell-cell contact or via transwell system, GMSCs were capable of direct suppression of differentiation of DCs and phorbol 12-myristate 13-acetate-stimulated activation of MCs, whereas the inhibitory effects were attenuated by indomethacin. Mechanistically, GMSC-induced blockage of de novo synthesis of proinflammatory cytokines by MCs is mediated partly by the tumor necrosis factor-alpha/prostaglandin E(2) (PGE(2)) feedback axis. These results demonstrate that GMSCs are capable of desensitizing allergic contact dermatitis via PGE(2)-dependent mechanisms.

Sarcomas as a mise en abyme of mesenchymal stem cells: exploiting interrelationships for cell mediated anticancer therapy

Mise en abyme meaning "placed into abyss or infinite recurrence" is an apt paradigm for the relentless growth of sarcoma cells. Its alternative meaning, "self-reflexive embedding" fits the central role attributed to cancer stem cells (CSCs). Diversely sourced and defined, mesenchymal stem cells (MSCs) may be the cells of sarcoma origin, evolve a CSC phenotype and/or contribute to tumor growth through inherent qualities for homing, neovascularization, paracrine cross-feeding, microvesicle secretion, cell fusion, entosis and immune modulation. Exploiting these qualities, MSC expressing modified forms of the TNF-related apoptosis-inducing ligand (Apo2L/TRAIL) are being developed to complement more conventional radiation and chemotherapy.