Mesenchymal stem cells induce division arrest anergy of activated T cells

It has been demonstrated that bone marrow mesenchymal stem cells (MSC) inhibit T cell responses both to polyclonal stimuli and their cognate antigen. We analyzed the effect of MSC on T cell activation, effector function and proliferation using an in vitro murine model in which T cells were generated against the male HY minor histocompatibility antigen. T cell proliferation and intracellular IFN-γ staining were used to measure T cell responses. In the presence of MSC, early activation markers CD25 and CD69 were found to be up regulated on stimulated T cells, whereas IFN-γ production was inhibited. To determine the effect of MSC on T cell proliferation, CFSE-labeled HY-specific T cells were stimulated with class I-restricted HY peptides. In the presence of MSC the intensity of CFSE-stained T cells remained unchanged demonstrating that T cell proliferation was completely abrogated. Analysis of the cell cycle showed that T cells, stimulated in the presence of MSC, were arrested at the G1 phase. At the molecular level cyclinD2 expression was profoundly inhibited, whereas p27kip1 was upregulated. When MSC were removed from the cultures and restimulated with the cognate peptide, T cells produced IFN-γ but failed to proliferate. The addition of exogenous interleukin-2 did not restore proliferation. MSC did not preferentially target any T cell subset, and the inhibition was also extended to B cells. MSC mediated inhibition induces an unresponsive T cell profile that is fully consistent with that observed in division arrest anergy. Our data have important implications on the clinical use of MSC for tolerance induction.