Immunosuppressive Effects of Embryonic Stem Cells and Mesenchymal Stem Cells on Allogeneic Skin Graft.

Abstract

Purpose: Both embryonic stem cells (ESCs) and mesenchymal stem cells (MSCs) have immunosuppressive effects. However, there have been confl icting reports about their impact on transplantation tolerance. Therefore, we tried to elucidate the immuosuppressive effects of both stem cells on alloimmune response and their mechanisms. Methods: MSCs were isolated from both C57BL/6 and Balb/C mice and a ESC cell line originated from C57BL/6 mice were used. Naïve CD4+ T cells and CD11c+ splenic dendritic cells were isolated using MACS system for mixed lymphocyte reaction. In vitro suppressive activities of both stem cells were tested using CFSE /7-AAD staining and ELISA technique. To investigate in vivo immunosuppressive effects of stem cells, either ESCs or MSCs were adoptively transferred via tail vein, one week before allogeneic skin transplantation. Results: Both ESCs and MSCs suppressed not only proliferation, but also survival of CD4+ T cells in mixed lymphocyte reaction. They also suppressed cytokine production (IL-1b, IL-2, IL-4, IL-10, IL-12, IFN-g and TNF-a). MSCs increased IL-6 expression, whereas ESCs decreased it. However, there was no change in the levels of IDO and TGF-b by stem cells. Activation markers such as CD25 and CD44 were downregulated on CD4+ T cells by both stem cells. Transwell experiments demonstrated that immunosuppression by both stem cells was mainly mediated by cell to cell contact. Neither ESCs nor MSCs increased foxp3+ regulatory T cell population. In contrast to their in vitro data, both stem cells failed to prolong skin graft survival across a major mismatch barrier (Balb/C or DBA/2 to C57BL/6). They prolonged skin graft survival slightly across minor mismatch barrier(male to female). Combination therapy of ESCs and anti-CD40L didnot induce skin graft tolerance. Conclusion: murine ESCs and MSCs suppressed proliferation, survival and cytokine production of naïve CD4+ T cells in response to in vitro alloimmune stimuli mainly by cell to cell contact. However, neither ESCs nor MSCs can induce tolerance in stringent allogeneic skin transplantation models.