TRANSPLANTATION CD4 CD25 T cells alloactivated ex vivo by IL-2 or IL-4 become potent alloantigen-specific inhibitors of rejection with different phenotypes, suggesting separate pathways of activation by Th1 and Th2 responses

CD4 CD25 Foxp3 T cells are regulatory/ suppressor cells (Tregs) that include nonantigen (Ag)–specific as well as Agspecific Tregs. How non–Ag-specific naive CD4 CD25 Treg develop into specific Tregs is unknown. Here, we generated adaptive Tregs by culture of naive CD4 CD25 Foxp3 T cells with allo-Ag and either interleukin-2 (IL-2) or IL-4. Within days, IL-2 enhanced interferonreceptor (Ifn r) and Il-5 mRNA and IL-4 induced a reciprocal profile with de novo IL-5R and increased IFNmRNA expression. Both IL-2– and IL-4–alloactivated CD4 CD25 Tregs within 3 to 4 days of culture had enhanced capacity to induce tolerance to specific donor but not to third-party cardiac allografts. These hosts became tolerant as allografts functioned more than 250 days, with a physiologic ratio of less than 10% CD4 CD25 Foxp3 T cells in the CD4 population. CD4 CD25 T cells from tolerant hosts given IL-2–cultured cells had increased Il-5 and Ifn r mRNA. Those from hosts given IL-4–cultured cells had enhanced IL-5R mRNA expression and IL-5 enhanced their proliferation to donor but not third-party allo-Ag. Thus, IL-2 and IL-4 activated allo-Ag–specific Tregs with distinct phenotypes that were retained in vivo. These findings suggested that Thelper 1 (Th1) and Th2 responses activate 2 pathways of adaptive Ag-specific Tregs that mediate tolerance. We propose they be known as T-suppressor 1 (Ts1) and Ts2 cells. (Blood. 2009;113:479-487)