Abstract

Foxp3(+) regulatory T cells (Tregs) play essential roles in maintaining the immune balance. Although the majority of Tregs are formed in the thymus, increasing evidence suggests that induced Tregs (iTregs) may be generated in the periphery from naive cells. However, unlike in the murine system, significant controversy exists regarding the suppressive capacity of these iTregs in humans, especially those generated in vitro in the presence of TGF-β. Although it is well known that IL-10 is an important mediator of Treg suppression, the action of IL-10 on Tregs themselves is less well characterized. In this article, we show that the presence of IL-10, in addition to TGF-β, leads to increased expansion of Foxp3(+) iTregs with enhanced CTLA-4 expression and suppressive capability, comparable to that of natural Tregs. This process is dependent on IL-10R-mediated STAT3 signaling, as supported by the lack of an IL-10 effect in patients with IL-10R deficiency and dominant-negative STAT3 mutation. Additionally, IL-10-induced inhibition of Akt phosphorylation and subsequent preservation of Foxo1 function are critical. These results highlight a previously unrecognized function of IL-10 in human iTreg generation, with potential therapeutic implications for the treatment of immune diseases, such as autoimmunity and allergy.