Karen English

Cell contact, prostaglandin E2 and transforming growth factor beta 1 play non-redundant roles in human mesenchymal stem cell induction of CD4+CD25Highforkhead box P3+ regulatory T cells

Adult human mesenchymal stromal or stem cells (MSC) can differentiate into a variety of cell types and are candidate cellular therapeutics in regenerative medicine. Surprisingly, these cells also display multiple potent immunomodulatory capabilities, including allosuppression, making allogeneic cell therapy a possibility. The exact mechanisms involved in regulatory T cell induction by allogeneic human MSC was examined, using purified CD4+ populations and well‐characterized bone marrow‐derived adult human MSC. Allogeneic MSC were shown to induce forkhead box P3 (FoxP3)+ and CD25+ mRNA and protein expression in CD4+ T cells. This phenomenon required direct contact between MSC and purified T cells, although cell contact was not required for MSC induction of FoxP3 expression in an unseparated mononuclear cell population. In addition, through use of antagonists and neutralizing antibodies, MSC‐derived prostaglandins and transforming growth factor (TGF)‐β1 were shown to have a non‐redundant role in the induction of CD4+CD25+FoxP3+ T cells. Purified CD4+CD25+ T cells induced by MSC co‐culture expressed TGF‐β1 and were able to suppress alloantigen‐driven proliferative responses in mixed lymphocyte reaction. These data clarify the mechanisms of human MSC‐mediated allosuppression, supporting a sequential process of regulatory T cell induction involving direct MSC contact with CD4+ cells followed by both prostaglandin E2 and TGF‐β1 expression. Overall, this study provides a rational basis for ongoing clinical studies involving allogeneic MSC.

Mesenchymal stromal cells: facilitators of successful transplantation?

Mesenchymal stromal/stem cells (MSCs) possess immunomodulatory and reparative properties. Through specific interactions with immune cells that participate in both innate and adaptive responses, MSCs exposed to an inflammatory microenvironment can downregulate many immune effector functions. Clinical trials focusing on MSCs to treat graft-versus-host disease (GvHD) and autoimmune diseases are underway. Current analyses suggest that MSCs will improve cell and solid organ transplantation by ameliorating rejection and possibly eliminating the requirement for prolonged regimens of conventional immunosuppressive drugs. This review examines the in vitro and in vivo evidence for the clinical use of bone marrow derived MSCs.

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.

Mesenchymal stem cell inhibition of T-helper 17 cell- differentiation is triggered by cell–cell contact and mediated by prostaglandin E2 via the EP4 receptor

Mesenchymal stem cells (MSCs) inhibit T‐cell activation and proliferation but their effects on individual T‐cell‐effector pathways and on memory versus naïve T cells remain unclear. MSC influence on the differentiation of naïve and memory CD4+ T cells toward the Th17 phenotype was examined. CD4+ T cells exposed to Th17‐skewing conditions exhibited reduced CD25 and IL‐17A expression following MSC co‐culture. Inhibition of IL‐17A production persisted upon re‐stimulation in the absence of MSCs. These effects were attenuated when cell–cell contact was prevented. Th17 cultures from highly purified naïve‐ and memory‐phenotype responders were similarly inhibited. Th17 inhibition by MSCs was reversed by indomethacin and a selective COX‐2 inhibitor. Media from MSC/Th17 co‐cultures contained increased prostaglandin E2 (PGE2) levels and potently suppressed Th17 differentiation in fresh cultures. MSC‐mediated Th17 inhibition was reversed by a selective EP4 antagonist and was mimicked by synthetic PGE2 and a selective EP4 agonist. Activation‐induced IL‐17A secretion by naturally occurring, effector‐memory Th17 cells from a urinary obstruction model was also inhibited by MSC co‐culture in a COX‐dependent manner. Overall, MSCs potently inhibit Th17 differentiation from naïve and memory T‐cell precursors and inhibit naturally‐occurring Th17 cells derived from a site of inflammation. Suppression entails cell‐contact‐dependent COX‐2 induction resulting in direct Th17 inhibition by PGE2 via EP4.

Allogeneic Mesenchymal Stem Cells: Agents of Immune Modulation

Adult mesenchymal stem cells possess a remarkably diverse array of immunosuppressive characteristics. The capacity to suppress the regular processes of allogeneic rejection, have allowed the use of tissue mismatched cells as therapeutic approaches in regenerative medicine and as agents of immune deviation. This review describes recent advances in understanding the mechanistic basis of mesenchymal stromal or stem cells (MSC) interaction with innate immunity. Particular emphasis is placed on the effect of Toll‐like receptor signalling on MSC and a hypothesis that innate immune signals induce a ‘licensing switch’ in MSC is put forward. The mechanisms underlying MSC suppression of T cell responses and induction of regulatory populations are surveyed. Conflicting data regarding the influence of MSC on B cell function are outlined and discussed. Finally the limits to MSC mediated immune modulation are discussed with reference to the future clinical application of novel cell therapies. J. Cell. Biochem. 112: 1963–1968, 2011.

Concise review: Adult mesenchymal stromal cell therapy for inflammatory diseases: How well are we joining the dots?

Mesenchymal stromal (stem) cells (MSCs) continue to be a strong area of focus for academic‐ and industry‐based researchers who share the goal of expanding their therapeutic use for diverse inflammatory and immune‐mediated diseases. Recently, there has been an accelerated rate of scientific publication, clinical trial activity, and commercialisation in the field. This has included the reporting of exciting new developments in four areas that will be of key importance to future successful use of MSC‐based therapies in large numbers of patients: (a) fundamental biology of the primary cells in bone marrow and other tissues that give rise to MSCs in culture. (b) Mechanisms by which MSCs modulate immune and inflammatory responses in vivo. (c) Insights into MSC kinetics, safety, and efficacy in relevant animal disease models. (d) Isolation, definition, and clinical trial‐based testing of human MSCs by biomedical companies and academic medical centers. Despite this progress, it remains unclear whether MSCs will enter mainstream therapeutic practice as a frequently used alternative to pharmacotherapy or surgical/radiological procedures in the foreseeable future. In this review, we summarize some of the most significant new developments for each of the four areas that contribute to the process of translating MSC research to the clinical arena. In the context of this recent progress, we discuss key challenges and specific knowledge gaps which, if not addressed in a coordinated fashion, may hinder the creation of robust “translational pipelines” for consolidating the status of MSC‐based therapies. Stem Cells 2013;31:2033–2041

Human mesenchymal stem cells suppress donor CD4+ T cell proliferation and reduce pathology in a humanized mouse model of acute graft-versus-host disease

Acute graft‐versus‐host disease (aGVHD) is a life‐threatening complication following allogeneic haematopoietic stem cell transplantation (HSCT), occurring in up to 30–50% of patients who receive human leucocyte antigen (HLA)‐matched sibling transplants. Current therapies for steroid refractory aGVHD are limited, with the prognosis of patients suboptimal. Mesenchymal stem or stromal cells (MSC), a heterogeneous cell population present in many tissues, display potent immunomodulatory abilities. Autologous and allogeneic ex‐vivo expanded human MSC have been utilized to treat aGVHD with promising results, but the mechanisms of therapeutic action remain unclear. Here a robust humanized mouse model of aGVHD based on delivery of human peripheral blood mononuclear cells (PBMC) to non‐obese diabetic (NOD)‐severe combined immunodeficient (SCID) interleukin (IL)‐2rγnull (NSG) mice was developed that allowed the exploration of the role of MSC in cell therapy. MSC therapy resulted in the reduction of liver and gut pathology and significantly increased survival. Protection was dependent upon the timing of MSC therapy, with conventional MSC proving effective only after delayed administration. In contrast, interferon (IFN)‐γ‐stimulated MSC were effective when delivered with PBMC. The beneficial effect of MSC therapy in this model was not due to the inhibition of donor PBMC chimerism, as CD45+ and T cells engrafted successfully in this model. MSC therapy did not induce donor T cell anergy, FoxP3+ T regulatory cells or cause PBMC apoptosis in this model; however, it was associated with the direct inhibition of donor CD4+ T cell proliferation and reduction of human tumour necrosis factor‐α in serum.

Mesenchymal Stromal Cells in Transplantation Rejection and Tolerance

Mesenchymal stromal cells (MSCs) have recently emerged as promising candidates for cell-based immunotherapy in solid organ transplantation (SOT). In addition to immune modulation, MSCs possess proreparative properties and preclinical studies indicate that MSCs have the capacity to prolong graft survival and in some cases induce tolerance. Currently, the application of MSCs in SOT is being evaluated in phase I/II clinical trials. Whereas the mechanisms of action used by MSC immunomodulation have been somewhat elucidated in vitro, the data from preclinical transplant models have been unclear. Furthermore, the optimal timing, dose, and route of administration remain to be elucidated. Importantly, MSCs have the ability to sense their environment, which may influence their function. In this article, we discuss the impact of the local microenvironment on MSCs and the mechanisms of MSC immunomodulation in the setting of SOT.

IFN-γ Stimulated Human Umbilical-Tissue-Derived Cells Potently Suppress NK Activation and Resist NK-Mediated Cytotoxicity In Vitro

Umbilical cord tissue represents a unique source of cells with potential for cell therapy applications for multiple diseases. Human umbilical tissue-derived cells (hUTC) are a developmentally early stage, homogenous population of cells that are HLA-ABC dim, HLA-DR negative, and lack expression of co-stimulatory molecules in the unactivated state. The lack of HLA-DR and co-stimulatory molecule expression on unactivated hUTC may account for their reduced immunogenicity, facilitating their use in allogeneic settings. However, such approaches could be confounded by host innate cells such as natural killer (NK) cells. Here, we evaluate in vitro NK cell interactions with hUTC and compare them with human mesenchymal stem cells (MSC). Our investigations show that hUTC suppress NK activation, through prostaglandin-E2 secretion in a contact-independent manner. Prestimulation of hUTC or human MSC with interferon gamma (IFN-γ) induced expression of the tryptophan degrading enzyme indoleamine 2, 3 dioxygenase, facilitating enhanced suppression. However, resting NK cells of different killer immunoglobulin-like receptor haplotypes did not kill hUTC or MSC; only activated NK cells had the ability to kill nonstimulated hUTC and, to a lesser extent, MSC. The cell killing process involved signaling through the NKG2D receptor and the perforin/granzyme pathway; this was supported by CD54 (ICAM-1) expression by hUTC. IFN-γ-stimulated hUTC or hMSC were less susceptible to NK killing; in this case, protection was associated with elevated HLA-ABC expression. These data delineate the different mechanisms in a two-way interaction between NK cells and two distinct cell therapies, hUTC or hMSC, and how these interactions may influence their clinical applications.

Jagged-1 is required for the expansion of CD4+ CD25+ FoxP3+ regulatory T cells and tolerogenic dendritic cells by murine mesenchymal stromal cells

IntroductionMesenchymal stromal cells (MSC) have well defined immunomodulatory properties including the suppression of lymphocyte proliferation and inhibition of dendritic cell (DC) maturation involving both cell contact and soluble factors. These properties have made MSC attractive candidates for cellular therapy. However, the mechanism underlying these characteristics remains unclear. This study sought to investigate the mechanisms by which MSC induce a regulatory environment.MethodAllogeneic bone marrow mesenchymal stromal cells were cultured with T cells or dendritic cells in the presence or absence of gamma secretase inhibitor to block Notch receptor signalling. T cells and dendritic cells were examined by flow cytometry for changes in phenotype marker expression. Stable knock down MSC were generated to examine the influence of Jagged 1 signalling by MSC. Both wildtype and knockdown MSC were subsequently used in vivo in an animal model of allergic airway inflammation.ResultsThe Notch ligand Jagged-1 was demonstrated to be involved in MSC expansion of regulatory T cells (Treg). Additionally, MSC-induced a functional semi-mature DC phenotype, which further required Notch signalling for the expansion of Treg. MSC, but not Jagged-1 knock down MSC, reduced pathology in a mouse model of allergic airway inflammation. Protection mediated by MSC was associated with enhanced Treg in the lung and significantly increased production of interleukin (IL)-10 in splenocytes re-stimulated with allergen. Significantly less Treg and IL-10 was observed in mice treated with Jagged-1 knock down MSC.ConclusionsThe current study suggests that MSC-mediated immune modulation involves the education and expansion of regulatory immune cells in a Jagged-1 dependent manner and provides the first report of the importance of Jagged-1 signalling in MSC protection against inflammation in vivo.