Memory CD4 T Cells Are Suppressed by CD8 Regulatory T Cells in Vitro and in Vivo

Background: Acute graft rejection mediated by alloreactive memory CD4 T cells is a major obstacle to transplantation tolerance. It has been reported that CD8 T regulatory cells (Tregs) have the ability to induce graft tolerance by restraining the function of activated CD4 T cells, but not including memory T cells. The aim of this study is to elucidate the effect of CD8 Tregs on alloreactive memory CD4 T cells.

Methods: We detected Qa-1 expression and performed proliferative assay on memory CD4 T cells. All memory CD4 T cells were purified from mice receiving skin allografts. We performed inhibitory and cytotoxic assays on CD8 Tregs, which were isolated from a T cell vaccination mouse model, and IL-2, IL-4, IL-10 and IFN-γ levels were measured in co-culture supernatants by ELISA. To confirm CD8 Tregs inhibition of memory CD4 T cells in-vivo, we utilized a murine model of cardiac allograft transplantation.

Results: Memory CD4 T cells mediated acute allograft rejection, and CD8 Tregs suppressed the proliferation of memory CD4 T cells. In vitro, memory CD4 T cells were inhibited and lysed by CD8 Tregs. There was a positive correlation between IFN-γ levels, and cell lysis rate induced by CD8 Tregs. In-vivo studies demonstrated CD8 Tregs prolonged graft survival times, by inhibiting CD4 memory T cells, through a Qa-1-peptide-TCR pathway.

Conclusions: CD8 Tregs inhibit CD4 memory T cell-mediated acute murine cardiac allograft rejection, and further prolong graft survival times. These results provide new insights into immune regulation of organ rejection.