Rapamycin and IL-2 reduce lethal acute graft-versus-host disease associated with increased expansion of donor type CD4+CD25+Foxp3+ regulatory T cells

Previous work has demonstrated that both rapamycin (RAPA) and IL-2 enhance CD4(+)CD25(+)Foxp3(+) regulatory T-cell (Treg) proliferation and function in vitro. We investigated whether the combination of RAPA plus IL-2 could impact acute GVHD induction after bone marrow transplantation (BMT). RAPA plus IL-2 resulted in improved survival and a reduction in acute GVHD lethality associated with an increased expansion of donor type CD4(+)Foxp3(+) Tregs and reduced CD4(+)CD25(-) conventional T cells (Tcons). RAPA plus IL-2, but not either drug alone, increased both expansion of donor natural Tregs and conversion of induced Tregs from donor CD25(-) Tcons while IL-2 alone increased conversion of Tregs from CD25(-) Tcon. RAPA plus IL-2 treatment resulted in less production of IFN-gamma and TNF, cytokines known to be important in the initiation of acute GVHD. These studies indicate that the pharmacologic stimulation of T cells with IL-2 and the suppression of Tcon proliferation with RAPA result in a selective expansion of functional Tregs and suppression of acute GVHD. (Blood. 2011; 118(8): 2342-2350)