Mesenchymal stem cells (MSCs) derived from bone marrow (BM), adipose tissue (AT), umbilical cord blood (CB), and umbilical cord tissue (CT) are increasingly being used to treat equine inflammatory and degenerative lesions. MSCs modulate the immune system in part through mediator secretion. Animal species and MSC tissue of origin are both important determinants of MSC function. In spite of widespread clinical use, how equine MSCs function to heal tissues is fully unknown. In this study, MSCs derived from BM, AT, CB, and CT were compared for their ability to inhibit lymphocyte proliferation and secrete mediators in response to activation. Five MSC lines from each tissue were isolated. Lymphocyte proliferation was assessed in a mixed leukocyte reaction, and mediator secretion was determined by ELISA. Regardless of tissue of origin, quiescent MSCs did not alter lymphocyte proliferation or secrete mediators, except for transforming growth factor-β (TGF-β1). When stimulated, MSCs of all tissue types decreased lymphocyte proliferation, increased prostaglandin (PGE2) and interleukin-6 (IL-6) secretion, and decreased production of tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). BM-MSCs and CB-MSCs also produced nitric oxide (NO), while AT-MSCs and CT-MSCs did not. Equine MSCs did not produce indoleamine 2,3-dioxygenase (IDO). These data suggest that activated equine MSCs derived from BM, AT, CT, and CB secrete high concentration of mediators and are similar to MSCs from rodents and humans in their immunomodulatory profiles. These findings have implication for the treatment of inflammatory lesions dominated by activated lymphocytes and TNF-α and IFN-γ in vivo.

Mesenchymal stem cells (MSCs) have potent immunomodulatory functions and are a promising therapy for immune‐mediated inflammatory disorders. We previously demonstrated the efficacy of fresh, autologous, adipose‐derived MSCs (ASCs) to treat feline chronic gingivostomatitis (FCGS), a chronic oral mucosal inflammatory disease similar to human oral lichen planus. Here, we investigate the use of fresh allogeneic ASCs for treatment of FCGS in seven cats. Radiolabeled ASCs were also tracked systemically. Each cat received two intravenous injections of 20 million ASCs, 1 month apart. Oral inflammation, blood lymphocyte subsets, anti‐fetal bovine serum antibody levels, ASC crossmatching and serum proteins and cytokine concentrations were determined. Four of the 7 cats (57%) responded to treatment [complete clinical remission (n = 2) or substantial clinical improvement (n = 2)]. Three cats were nonresponders. Prior to therapy, most cats had increased circulating CD8+ T cells, decreased CD8lo cells, and a decreased CD4/CD8 ratio, however clinical resolution was not associated with normalization of these parameters. Nonresponders showed more severe systemic inflammation (neutrophilia, hyperglobulinemia and increased interferon gamma and tumor necrosis factor alpha concentration) prior to ASC therapy. Clinical remission took up to 20 months and no clinical relapse has occurred. A higher fraction of radiolabeled ASCs were identified in the oral cavity of FCGS affected cats than the control cat. The administration of fresh, allogenic ASCs appeared to have lower clinical efficacy with a delayed response as compared to the fresh, autologous ASCs. In addition, the mechanism(s) of action for autologous and allogenic ASCs may differ in this model of oral inflammation. Stem Cells Translational Medicine 2017;6:1710–1722

Mesenchymal stem/stromal cells (MSCs) display potent immunomodulatory and regenerative capabilities through the secretion of bioactive factors, such as proteins, cytokines, chemokines as well as the release of extracellular vesicles (EVs). These functional properties of MSCs make them ideal candidates for the treatment of degenerative and inflammatory diseases, including multiple sclerosis (MS). MS is a heterogenous disease that is typically characterized by inflammation, demyelination, gliosis and axonal loss. In the current study, an induced experimental autoimmune encephalomyelitis (EAE) murine model of MS was utilized. At peak disease onset, animals were treated with saline, placenta-derived MSCs (PMSCs), as well as low and high doses of PMSC-EVs. Animals treated with PMSCs and high-dose PMSC-EVs displayed improved motor function outcomes as compared to animals treated with saline. Symptom improvement by PMSCs and PMSC-EVs led to reduced DNA damage in oligodendroglia populations and increased myelination within the spinal cord of treated mice. In vitro data demonstrate that PMSC-EVs promote myelin regeneration by inducing endogenous oligodendrocyte precursor cells to differentiate into mature myelinating oligodendrocytes. These findings support that PMSCs' mechanism of action is mediated by the secretion of EVs. Therefore, PMSC-derived EVs are a feasible alternative to cellular based therapies for MS, as demonstrated in an animal model of the disease.

Mesenchymal stem cells (MSCs) are used in both human clinical trials and veterinary medicine for the treatment of inflammatory and immune-mediated diseases. MSCs modulate inflammation by decreasing the cells and products of the inflammatory response. Stimulated equine MSCs from bone marrow (BM), adipose tissue (AT), cord blood (CB), and umbilical cord tissue (CT) inhibit lymphocyte proliferation and decrease inflammatory cytokine production. We hypothesized that equine MSCs inhibit T cell proliferation through secreted mediators and that MSCs from different tissue sources decrease T cell proliferation through different mechanisms. To test our hypotheses, we inhibited interleukin-6 (IL-6), nitric oxide (NO), and prostaglandin E2 (PGE2) to determine their impact on stimulated T cell proliferation. We also determined how equine MSCs modulate lymphocyte proliferation either via cell cycle arrest or apoptosis. Inhibition of IL-6 or NO did not reverse the immunomodulatory effect of MSCs on activated T cells. In contrast, inhibition of PGE2 restored T cell proliferation, restored the secretion of tumor necrosis factor-α and interferon-γ, and increased IL-10 levels. MSCs from solid-tissue-derived sources, AT and CT, inhibited T cell proliferation through induction of lymphocyte apoptosis while blood-derived MSCs, BM and CB, induced lymphocyte cell cycle arrest. Equine MSCs from different tissue sources modulated immune cell function by both overlapping and unique mechanisms. MSC tissue source may determine immunomodulatory properties of MSCs and may have very practical implications for MSC selection in the application of MSC therapy.