TGF-β and NFAT control T cell receptor restimulation-induced cell death of CD4+CD25+Foxp3+ regulatory cells

Abstract

Abstract One of the key questions in the area of immunomodulation is how CD4+CD25+Foxp3+ regulatory cells (Tregs) are controlled. Here we studied how their survival is regulated in the context of T cell Receptor re-stimulation apoptosis. We show that both mouse and human Tregs and iTregs exhibit increased resistance to T cell Receptor restimulation-induced cell death (RICD) compared to conventional CD4+ cells. The enhanced survival was dependent on TGF-β signaling that results in reduced nuclear translocation of nuclear factor of activated T-cells (NFAT), as well as up-regulation of cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein (cFLIP) in Tregs. Tregs also showed significantly decreased susceptibility to α-CD3 antibody mediated apoptosis compared to the effector cells in vivo. While ionomycin increased Treg apoptosis, NFAT activation inhibitors reduced the apoptosis levels of effector cells almost to Treg levels, demonstrating that reduced NFAT activity contributes to decreased RICD in Tregs. Finally, RICD resistance in Tregs manifests itself as increased protection of these cells from cell death during mouse oropharyngeal candidiasis (OPC) infection and inflammatory bowel disease (IBD). Protection from cell death was abrogated in the absence of TGF-β signaling in Tregs. Taken together, our data unravel the previously unrecognized role of TGF-β in promoting Treg survival during TCR restimulation, through regulation of multiple pathways involving NFAT and cFLIP in Tregs. This novel mechanism that offers a selective survival advantage to Tregs may have broader ramifications in immune homeostasis during inflammation.