Role for thymic and splenic regulatory CD4+ T cells induced by donor dendritic cell sin allograft tolerance by LF15-0195 treatment

A 20-day treatment with LF15-0195, a deoxyspergualine analogue, induced allograft tolerance in a fully; MHC-mismatched heart allograft model in the rat. Long-term allografts displayed minimal cell infiltration with no signs of chronic rejection. CD4+ spleen T cells; from tolerant LF15-0195-treated recipients were able to suppress in vitro proliferation of allogeneic CD4(+) T cells and to transfer tolerance to second syngeneic recipients, demonstrating dominant suppression by regulatory cells. A significant increase in the percentage of CD4(+)CD25(+) T cells was observed in the thymus and spleen from tolerant LF15-0195-treated recipient. In vitro direct stimulation with donor APCs demonstrated that CD4(+) regulatory T cells proliferated weakly and expressed low levels of ITN-gamma, IL-10, and IL-2. CD4(+)CD25(+) cell depletion increased IL-2 production by CD4(+)CD25(-) thymic cells, but not splenic cells. Moreover, tolerance was transferable with splenic and thymic CD4(+)CD25(+) cells, but also in 50% of cases with splenic CD4+CD25- cells, demonstrating that CD25 can be a marker for regulatory cells in the thymus, but not in the periphery. In addition, we presented evidences that donor APCs were required to induce tolerance and to expand regulatory CD4(+) T cells. This study demonstrates that LF15-0195 treatment induces donor APCs to expand powerful regulatory CD4(+) CD25(+/-) T cells present in both the central and peripheral compartments.