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 non-antigen (Ag)–specific as well as Ag-specific 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 interferon-γ receptor (Ifnγr) and Il-5 mRNA and IL-4 induced a reciprocal profile with de novo IL-5Rα and increased IFN-γ mRNA 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 Ifnγr mRNA. Those from hosts given IL-4–cultured cells had enhanced IL-5Rα 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 T-helper 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.