Abstract
CD8+ Cytotoxic T lymphocytes (CTL) and CD4+ T helper cells are key effectors in autoimmune, graft versus host diseases and graft rejection. Mesenchymal Stromal Cells (MSCs) are self-renewing multipotent cells with tissue repair and immunomodulatory properties. Due to their ability to repress pathogenic immune responses they show therapeutic potential for the treatment of immune mediated diseases. MSCs have the unique ability to export their own mitochondria to neighboring cells in response to injury and inflammation. However, whether mitochondrial transfer occurs and has any role in the repression of CD4+ Th1 and CD8+ T cell responses is unknown. We have addressed this issue utilizing a transgenic mouse model of disease and allogeneic bone marrow derived MSCs in vitro and in vivo. Our results showed:1) MSCs inhibited expansion, gain of effector phenotype and the production of the effector cytokine IFNγ in vitro and the diabetogenic potential in vivo of CD4+ Th1 cells after activation. Remarkably, CD4+ T cells took up mitochondria from MSCs during suppression. The transfer of MSC mitochondria to CD4+ Th1 cells resulted in decreased proliferation and production of IFNγ. Finally, we demonstrated that both MSCs and MSC mitochondria prevent the upregulation of the master Th1 transcription factor on activated CD4+ T cells.2) MSCs decreased the expansion, gain of effector phenotype and the production of the effector cytokine IFNγ in CD8+ T cells after activation in vitro. Notably, we found that during their interaction conducting to suppression, MSCs also transferred mitochondria to CTL. MSC mitochondrial transfer to CD8+ T cells resulted in decreased proliferation and production of IFNγ upon activation contributing to the global suppressive effect of MSCs. Finally, we demonstrated that both MSCs and MSC mitochondria differentially regulate the balance of two transcription factors key for CTL differentiation, T-bet and Eomes, on activated CD8+ T cells.