Activation of the aryl hydrocarbon receptor induces human type 1 regulatory T cell–like and Foxp3+ regulatory T cells

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Abstract
Type 1 regulatory T cells control autoinflammatory diseases. In two linked papers, groups led by Kuchroo and Quintana demonstrate the role of the aryl hydrocarbon receptor in the differentiation of these cells. The aryl hydrocarbon receptor (AhR) participates in the differentiation of mouse regulatory T cells (Treg cells) and interleukin 17 (IL-17)-producing helper T cells (TH17 cells), but its role in human T cell differentiation is unknown. We investigated the role of AhR in the differentiation of human induced Treg cells (iTreg cells). We found that AhR activation promoted the differentiation of CD4+Foxp3− T cells, which produce IL-10 and control responder T cells through granzyme B. However, activation of AhR in the presence of transforming growth factor-β1 induced Foxp3+ iTreg cells, which suppress responder T cells through the ectonucleoside triphosphate diphosphohydrolase CD39. The induction of functional Foxp3+ iTreg cells required coordinated action of the transcriptional regulators Smad1 and Aiolos. Thus, AhR is a potential target through which functional iTreg cells could be induced in human autoimmune disorders.