The TNFRSF members CD27 and OX40 coordinately limit TH17 differentiation in regulatory T cells.

Regulatory T cells (Tregs) are closely related to TH17 cells and use aspects of the TH17-differentiation program for optimal immune regulation. In several chronic inflammatory human diseases, Tregs express IL-17A, suggesting that dysregulation of TH17-associated pathways in Tregs may result in either loss of suppressive function and/or conversion into pathogenic cells. The pathways that regulate the TH17 program in Tregs are poorly understood. We have identified two TNF receptor superfamily (TNFRSF) members, CD27 and OX40, that are preferentially expressed by skin-resident Tregs Both CD27 and OX40 signaling suppressed the expression of TH17-associated genes from Tregs in a cell-intrinsic manner in vitro and in vivo. However, only OX40 played a nonredundant role in promoting Treg accumulation. Tregs that lacked both CD27 and OX40 were defective in controlling skin inflammation and expressed high levels of IL-17A, as well as the master TH17 transcription factor, RORγt. Last, we found that CD27 expression was inversely correlated with Treg IL-17 production in skin of patients with psoriasis and hidradenitis suppurativa. Together, our results suggest that TNFRSF members play both redundant and distinct roles in regulating Treg plasticity in tissues.