Human Fetal Liver MSCs are More Effective Than Adult Bone Marrow MSCs for Their Immunosuppressive, Immunomodulatory and Foxp3+ T regs Induction Capacity

Abstract Background: Mesenchymal stem cells (MSCs) display active capacities of suppressing or modulating harmful immune responses through diverse molecular mechanisms. These cells are under extensive translational efforts as cell therapies for immune-mediated diseases and transplantations. A wide range of preclinical studies and limited number of clinical trials using MSCs have not only shown promising safety and efficacy profiles but have also revealed changes in regulatory T cell (T reg) frequency and function. However, the mechanisms underlying this important observation are not well understood. Cell-to-cell contact, production of soluble factors, reprogramming of antigen presenting cells to tolerogenic phenotypes have emerged as possible mechanisms by which MSCs produce an immunomodulatory environment for T reg expansion. We and others demonstrated that adult bone-marrow (BM)-MSCs suppress adaptive immune responses directly by inhibiting the proliferation of CD4+ (“helper”) and CD8+ (“cytotoxic”) T cells but also indirectly through induction of Tregs. In parallel we demonstrated that fetal liver (FL)-MSCs displays much longer-lasting immunomodulatory properties compared to BM-MSCs, by inhibiting directly the proliferation and activation of CD4+ and CD8+ T cells. Therefore, we investigated if FL-MSCs exert their strong immunosuppressive effect also indirectly through induction of T regs.Methods: MSCs were obtained from FL and adult BM and characterized according to their surface antigen expression, their multilineage differentiation and their proliferation potential. Using different in-vitro combinations, we performed co-cultures of FL or BM-MSCs and murine CD3+CD25-T cells to investigate immunosuppressive effects of MSCs on T cells and to quantify their capacity to induce functional T regs. Results: We demonstrated that although both types of MSC exhibit similar phenotype profile and differentiation capacity, FL-MSCs have significantly higher proliferative capacity and ability to suppress both CD4+ and CD8+ murine T cell proliferation and to modulate them towards less active phenotypes than adult BM-MSCs. Moreover, their substantial suppressive effect was associated with an outstanding increase of functional CD4+CD25+Foxp3+ T regs compared to BM-MSCs.Conclusions: These results highlight the immunosuppressive activity of FL-MSCs on T cells and show for the first time that one of the main immunoregulatory mechanisms of FL-MSCs passes through active and functional T reg induction.