CD8+ T cells play an important role in immune regulation and effective immune responses against tumor cells, viral infection, and intracellular pathogens. In this report, using tiger or 10BiT mice, we defined a population of IL-10-producing CD8+ T cells that were induced by IL-4. These IL-10+ CD8+ T cells possessed a strong inhibitory effect on the CD4+ T cell proliferation in an IL10-dependent and cell contact-dependent fashion. In comparison with IL-10-CD8+ T cells, IL-10+CD8+ T cells expressed an array of Th2-like cytokines (IL-4, IL-5), perforin, and granzymes, as well as the cell cycle regulatory protein Cdkn2a. Interestingly, knockdown of cdkn2a using siRNA reduced IL-4-induced IL-10 production significantly. Furthermore, CD8+ T cells from Cdkn2a-/- mice produced a significantly lower amount of IL-10, and the effect was limited to CD8+ T cells but not observed in CD4+ T cells and APCs. Finally, IL-10+CD8+ T cells played a protective role in the TNBSinduced murine colitis model, indicating a critical role of this population of CD8+ T cells in regulatory immune responses. Taken together, we have defined a population of IL-10-producing CD8+ Tregs induced by IL-4 and mediated by Cdkn2a. © Society for Leukocyte Biology.