Human fetal liver MSCs are more effective than adult bone marrow MSCs for their immunosuppressive, immunomodulatory, and Foxp3+ T reg induction capacity

Background Mesenchymal stem cells (MSCs) exhibit active abilities to suppress or modulate deleterious immune responses by various molecular mechanisms. These cells are the subject of major translational efforts as cellular therapies for immune-related diseases and transplantations. Plenty of preclinical studies and clinical trials employing MSCs have shown promising safety and efficacy outcomes and also shed light on the modifications in the frequency and function of regulatory T cells (T regs). Nevertheless, the mechanisms underlying these observations are not well known. Direct cell contact, soluble factor production, and turning antigen-presenting cells into tolerogenic phenotypes, have been proposed to be among possible mechanisms by which MSCs produce an immunomodulatory environment for T reg expansion and activity. 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 the induction of T regs. In parallel, we demonstrated that fetal liver (FL)-MSCs demonstrates 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 display similar cell surface phenotypic 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.

Human fetal liver MSCs are more effective than adult bone marrow MSCs for their immunosuppressive, immunomodulatory and Foxp3+ T regs induction capacity

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 phenotypic 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.

Hematopoietic Jagged1 Is Required for the Transition of Hematopoietic Stem Cells from the Fetal Liver to the Adult Bone Marrow Niche

Notch signaling is known to play important roles in hematopoietic development and differentiation. Notch1 is required for emergence of the definitive hematopoietic stem cells (HSCs) from the hemogenic endothelium, and we have previously shown that Notch signaling is essential for survival and function of HSCs in the fetal liver. Activation of canonical Notch signaling requires direct cellular contact; thus, the identity of the ligand and the ligand-presenting cell during hematopoietic development would provide valuable information of the Notch signaling mechanism in HSCs as well as the identity of key niche cells that drive the expansion and cell fate decisions of embryonic HSCs. In the present study, we have taken a comprehensive approach to determine the ligands and cells that initiate Notch signaling in the mouse fetal liver. To this end, we have performed single-cell PCR analysis for all Notch signaling proteins in E14.5 fetal HSCs and compared the findings to the adult bone marrow HSCs. We also have analyzed fetal liver endothelial cells for surface expression of all Notch ligands. We determined that Jagged1 (Jag1) is highly expressed in both endothelial cells as well as in fetal HSCs but not adult HSCs. We have performed conditional loss-of-function analysis of Jag1 in fetal endothelial cells using inducible Ve-cadherinCreERT2 as well as in fetal hematopoietic lineages using constitutive VavCre. Our results indicate that while loss of endothelial Jag1 has severe effects in embryonic vascular development, loss of hematopoietic Jag1 allows for normal fetal morphology, yet severely impedes the functional ability of fetal liver HSCs to expand and differentiate both in vitro and in vivo. Fetal to adult transplantation of VavCre+Jag1f/f HSCs indicated a defect in reconstitution potential of fetal HSCs that lack Jag1 expression. Our findings indicate that hematopoietic Jag1 is essential for maturation of HSCs in the fetal liver and for homing and reconstitution potential of HSCs into the post-natal bone marrow microenvironment. Disclosures No relevant conflicts of interest to declare.