Unstimulated Mesenchymal Stem Cells Research Articles

The immunomodulatory function of equine MSCs is enhanced by priming through an inflammatory microenvironment or TLR3 ligand

Mesenchymal stem cells (MSCs) have the therapeutic potential to treat a variety of inflammatory and degenerative disease processes, however the effects of the tissue environment on MSCs have been overlooked. Our hypothesis was that the immunomodulatory function of MSCs would be impaired by TLR4 stimulation or exposure to inflammatory macrophages, whereas their immunosuppressive properties would be enhanced by TLR3 stimulation.MSCs were exposed to polyinosinic:polycytidylic acid (poly I:C) to stimulate TLR3 receptors or lipopolysaccharide (LPS) to stimulate TLR4 receptors. MSC1 proinflammatory phenotype in human MSCs was associated with increased IL-6 and IL-8 and MSC2 regenerative phenotype was associated with increased CCL2 and CXCL10. MSC immunomodulatory function was assessed by measuring the ability of primed MSCs to suppress mitogen-stimulated T cell proliferation. Peripheral blood monocytes were isolated using CD14 MACs positive selection, differentiated into macrophages, and polarized using interferon-gamma (IFN-γ). Polarization was confirmed by increased gene expression of TNFα, CCL2, and CXCL10. Inflammatory macrophages were co-cultured with MSCs for 6h, and the resultant MSC phenotype was analyzed as described above.Both TLR3 and TLR4 priming and co-culture of MSCs with inflammatory macrophages resulted in increased expression of IL-6, CCL2, and CXCL10 in MSCs. Both TLR3 and TLR4 priming or exposure of MSCs to inflammatory macrophages significantly (p<0.05) enhanced their immunomodulatory function, demonstrated by a decrease in T cell proliferation in the presence of poly I:C primed MSCs (11%), LPS primed MSCs (7%), or MSCs exposed to inflammatory macrophages (12%), compared to unstimulated MSCs. Additionally, MHC class II positive MSCs tended to have a greater magnitude of response to priming compared to MHC class II negative MSCs. These results suggest that MSCs can be activated by a variety of inflammatory stimuli, but the recipient injured tissue bed in chronic injuries may not contain sufficient inflammatory signals to activate MSC immunomodulatory function. Enhancement of MSCs immunomodulatory function through inflammatory priming prior to clinical application might improve the therapeutic effect of MSC treatments.

Co-encapsulation and co-transplantation of mesenchymal stem cells reduces pericapsular fibrosis and improves encapsulated islet survival and function when allografted

Pericapsular fibrotic overgrowth (PFO) is associated with poor survival of encapsulated islets. A strategy to combat PFO is the use of mesenchymal stem cells (MSC). MSC have anti-inflammatory properties and their potential can be enhanced by stimulation with proinflammatory cytokines. This study investigated whether co-encapsulation or co-transplantation of MSC with encapsulated islets would reduce PFO and improve graft survival. Stimulating MSC with a cytokine cocktail of IFN-γ and TNF-α enhanced their immunosuppressive potential by increasing nitric oxide production and secreting higher levels of immunomodulatory cytokines. In vitro, co-encapsulation with MSC did not affect islet viability but significantly enhanced glucose-induced insulin secretion. In vivo, normoglycemia was achieved in 100% mice receiving islets co-encapsulated with stimulated MSC as opposed to 71.4% receiving unstimulated MSC and only 9.1% receiving encapsulated islets alone. Microcapsules retrieved from both unstimulated and stimulated MSC groups had significantly less PFO with improved islet viability and function compared to encapsulated islets alone. Levels of peritoneal immunomodulatory cytokines IL-4, IL-6, IL-10 and G-CSF were significantly higher in MSC co-encapsulated groups. Similar results were obtained when encapsulated islets and MSC were co-transplanted. In summary, co-encapsulation or co-transplantation of MSC with encapsulated islets reduced PFO and improved the functional outcome of allotransplants.

Evaluation of Immunomodulatory Properties of Feline Mesenchymal Stem Cells.

Mesenchymal stem cells (MSC) offer a novel approach to treatment of inflammatory disorders in humans and companion animals. Cats spontaneously develop a wide variety of inflammatory disorders and may potentially benefit from MSC-based therapies. Multiple genes are involved in immunomodulation by MSC and interspecies differences between expressions of these genes exist. The goals of the study were to characterize the expression of genes known to be involved in MSC-based immunomodulation and determine the effect of MSC on proliferation of T cells in coculture experiments with peripheral blood mononuclear cells (PBMC). Unstimulated MSC expressed all immunomodulatory genes studied except for IL-10. Levels of iNOS and FASL were low or undetectable at the RNA level. INFγ stimulation resulted in significant dose-dependent upregulation of IDO1, PD-L1, IL-6, COX2, and HGF. Levels of kynurenine were increased after 3-day incubation with INFγ. TNFα stimulation increased expression of IL-6 at both RNA and protein level as well as upregulated COX2 gene expression and PTGES1.Stimulation with both INFγ and TNFα resulted in significant increase in PGE2 levels in cell culture medium. MSC significantly decreased proliferation of ConA-stimulated PBMC in coculture experiments at 1:5 ratio. Our results suggest that feline MSC have similar immunomodulatory gene expression and react to inflammatory cytokines in a manner similar to human MSC. Thus, MSC may play an important role in treatment of feline disease as well as serve as an important translational species to evaluate MSC-based therapies of diseases common to both humans and cats.

Mesenchymal stem cells: a new strategy for immunosuppression and tissue repair

Mesenchymal stem cells (MSCs) have great potential for treating various diseases, especially those related to tissue damage involving immune reactions. Various studies have demonstrated that MSCs are strongly immunosuppressive in vitro and in vivo. Our recent studies have shown that un-stimulated MSCs are indeed incapable of immunosuppression; they become potently immunosuppressive upon stimulation with the supernatant of activated lymphocytes, or with combinations of IFN-gamma with TNF-alpha, IL-1alpha or IL-1beta. This observation revealed that under certain circumstances, inflammatory cytokines can actually become immunosuppressive. We showed that there is a species variation in the mechanisms of MSC-mediated immunosuppression: immunosuppression by cytokine-primed mouse MSCs is mediated by nitric oxide (NO), whereas immunosuppression by cytokine-primed human MSCs is executed through indoleamine 2, 3-dioxygenase (IDO). Additionally, upon stimulation with the inflammatory cytokines, both mouse and human MSCs secrete several leukocyte chemokines that apparently serve to attract immune cells into the proximity with MSCs, where NO or IDO is predicted to be most active. Therefore, immunosuppression by inflammatory cytokine-stimulated MSCs occurs via the concerted action of chemokines and immune-inhibitory NO or IDO produced by MSCs. Thus, our results provide novel information about the mechanisms of MSC-mediated immunosuppression and for better application of MSCs in treating tissue injuries induced by immune responses.

Autocrine production of TGF-beta1 promotes myofibroblastic differentiation of neonatal lung mesenchymal stem cells.

We have isolated mesenchymal stem cells (MSCs) from tracheal aspirates of premature infants with respiratory distress. We examined the capacity of MSCs to differentiate into myofibroblasts, cells that participate in lung development, injury, and repair. Gene expression was measured by array, qPCR, immunoblot, and immunocytochemistry. Unstimulated MSCs expressed mRNAs encoding contractile (e.g., ACTA2, TAGLN), extracellular matrix (COL1A1 and ELN), and actin-binding (DBN1, PXN) proteins, consistent with a myofibroblast phenotype, although there was little translation into immunoreactive protein. Incubation in serum-free medium increased contractile protein (ACTA2, MYH11) gene expression. MSC-conditioned medium showed substantial levels of TGF-beta1, and treatment of serum-deprived cells with a type I activin receptor-like kinase inhibitor, SB-431542, attenuated the expression of genes encoding contractile and extracellular matrix proteins. Treatment of MSCs with TGF-beta1 further induced the expression of mRNAs encoding contractile (ACTA2, MYH11, TAGLN, DES) and extracellular matrix proteins (FN1, ELN, COL1A1, COL1A2), and increased the protein expression of alpha-smooth muscle actin, myosin heavy chain, and SM22. In contrast, human bone marrow-derived MSCs failed to undergo TGF-beta1-induced myofibroblastic differentiation. Finally, primary cells from tracheal aspirates behaved in an identical manner as later passage cells. We conclude that human neonatal lung MSCs demonstrate an mRNA expression pattern characteristic of myofibroblast progenitor cells. Autocrine production of TGF-beta1 further drives myofibroblastic differentiation, suggesting that, in the absence of other signals, fibrosis represents the "default program" for neonatal lung MSC gene expression. These data are consistent with the notion that MSCs play a key role in neonatal lung injury and repair.

Mesenchymal Stems Cells and Regulatory T Cells Inhibit Alloantigen Mediated Graft-Versus-Host Reaction but Also Impair Graft-Versus-Tumor Reactions Targeting Tumor Associated Antigens

Graft-versus-host disease (GvHD) is a common and potentially life-threatening complication after allogeneic hematopoietic stem cell transplantation (HSCT). It is mediated by donor immune cells reacting against alloantigens presented by host or donor derived professional antigen presenting cells or expressed on host tissue. In addition, donor derived T-cells contribute to the beneficial graft-versus-tumor (GvT) reaction targeting minor histocompatibility antigens and, as previously demonstrated (Stelljes et al., Blood 2004; 104:1210-6), tumor associated antigens (TAAs). Several publications have shown that regulatory T-cells (Tregs) and mesenchymal stem cells (MSCs) can be used to prevent or treat GvHD. Since both cell populations react in a largely unspecific manner on alloantigen mediated immune responses, it remains a matter of debate whether intervention with these cell populations might interfere with GvT reactions directed against TAAs. In order to investigate the effects of MSCs and Tregs on GvHD and tumor specific GvT reactions, we used a murine parent-into-F1 transplant model. After total body irradiation with 9 Gy F1[BALB/c × C57BL/6] (CB6F1) mice were transplanted with parental bone marrow and splenocytes from C57BL/6 (B6) or BALB/c donors, respectively. Following transplantation, CB6F1 recipients received either three doses of 1×106 MSCs of B6 or BALB/c origin s.c. within the first two weeks or 1×106 Tregs together with the transplant. To evaluate TAA specific GvT effects, transplanted recipients were inoculated with tumor cells sharing the MHC background of the donor strain. GvHD score and tumor size were monitored every other day. Treatment with unstimulated MSCs of B6 origin had only marginal effects on GvHD intensity. In contrast, mice treated with unstimulated MSCs of BALB/c origin or BL/6 MSCs stimulated in vitro with supernatant of allogeneic mixed lymphocyte cultures, showed no signs of GvHD like weight loss or skin damage. TAA specific GvT reactions were significantly impaired by MSCs of either origin resulting in markedly increased tumor growth. Analysis of in vivo primed T cells 25 days after transplantation by IFN-γ ELIspot assay revealed significantly reduced TAA specific T-cells in recipients treated with MSCs as compared to transplanted tumor bearing control animals. In our experimental setting, Tregs also reduced GvHD compared with transplanted controls. Again, specific immune responses targeting TAAs were also abolished. In conclusion, cellular immune modulation using MSCs or Tregs might be effective to modulate GvHD. However, both strategies clearly impair tumor specific GvT reactions in our experimental setting suggesting that these interventions might bear the risk of higher relapse rates after allogeneic HSCT. The different effects on GvHD by stimulated and unstimulated MSCs of B6 or BALB/c origin are being explored.

Although Pig Allogeneic Mesenchymal Stem Cells Are Not Immunogenic In Vitro, Intracardiac Injection Elicits an Immune Response In Vivo

In vitro, mesenchymal stem cells (MSCs) have demonstrated a low immunogenic profile. In this study, we tested the immune response to allogeneic MSCs in immunocompetent swines both in vitro and in vivo. Major histocompatibility complex-controlled swine leukocyte antigen (SLA) and SLA were used as donor and recipient, respectively. In vitro, proliferative responses were tested by mixed lymphocyte reaction (MLR) or cocultures and cytokine profiling by enzyme-linked immunosorbent assay. In vivo, allogeneic MSCs were injected in cardiac infarcted area (n=3) and compared with subcutaneous injections of either MSCs (n=2) or peripheral blood mononuclear cells (PBMCs; n=2). Two additional animals received a skin graft as controls. No immunosuppression was used. Specific antidonor humoral responses were tested by flow cytometry and complement-dependent cytotoxicity assay. In vitro, either unstimulated MSCs or interferon (IFN)-gamma stimulated MSC failed to elicit a proliferative response (stimulation index: 1.23 vs. 1.12 vs. 36.9 for controls, P<.001). Concomitantly to the absence of proliferation to MSCs, low production of IFN-gamma and interleukin-2 was evidenced in supernatants while the production of Th2 cytokines was comparable to controls. In vivo, all animals receiving skin grafts, subcutaneous PBMCs and intracardiac MSCs injections developed donor-specific cellular and humoral responses (immunoglobulins M and G) with antibody-complement-mediated cytotoxicity. Subcutaneous MSCs injection needed a rechallenge to similarly develop a cytotoxic humoral response. Intracardiac allogeneic porcine mesenchymal stem cells elicit an immune response despite their low immunogenic profile in vitro. This result suggests that in vivo characteristics of allogeneic MSCs might differ and emphasizes the importance of pursuing research both in vitro and in vivo.

IFNg-Mediated MHC-II Expression in Mesenchymal Stem Cells (MSC) Is Concentration-Dependent.

A significant concern in tissue repair is allo-rejection in a host with MHC-II mismatch. Since MSC appear to have veto properties to offset its own rejection, these stem cells may serve as ideal candidates in repair medicine. Interferon-g (IFN-g), which exacerbates immune responses, is known to enhance the expression of MHC-II in antigen presenting cells (e.g., macrophages). This led to the question on the mechanism by which MSC act as immune suppressor cells. We hypothesize that endogenous IFN-γ maintains basal MHC-II expression, while increased levels lead to its down regulation. Indeed, we observed a biphasic response of IFN-γ on the expression of MHC-II. While unstimulated MSC produced 19±5 pg/ml IFN-γ, exogenous IFN-γ (>100 U/ml) led to decreased expression of MHC-II. Suppression of IFN-g by siRNA resulted in undetectable MHC-II. The response of exogenous IFN-γ could not be explained by altered expression of IFN-g receptor type I (IFN-γRI) or changes in STAT-1 activation. However, western blots showed multiple isotypes of the MHC-II master regulator transcription factor, CIITA, in IFN-γ-stimulated MSC, with predominance of CIITA exhibiting low efficiency binding to DNA. This observation might explain why MHC-II is undetectable in the presence of high levels of IFN-γ. These findings support a potential for MSC as an adult stem cell in tissue repair.