A distal Foxp3 enhancer enables interleukin-2 dependent thymic Treg cell lineage commitment for robust immune tolerance[TCR-seq]

STAT5 activation downstream of the Interleukin-2 receptor (IL-2R) facilitates Foxp3 expression, which is required for the differentiation and function of regulatory T (Treg) cells. However, due to the pleiotropic roles of IL-2R signaling, it is unclear how STAT5 acts on the Foxp3 locus to promote Treg cell lineage commitment. Here, we report that IL-2–STAT5 signaling converges on an enhancer (CNS4) during early Foxp3 induction. CNS4 facilitates and sustains the IL-2–dependent CD25+Foxp3– precursor to Treg cell transition in the thymus. Its deficiency results in markedly impaired Treg cell generation in neonates, which is partially mitigated with age. While the thymic Treg cell paucity caused by CNS4 deficiency did not result in autoimmunity on its own, it exacerbated autoimmune manifestations caused by disruption of the Aire gene. Thus, CNS4 enhancer activity ensures robust Treg cell differentiation early in postnatal life and, cooperatively with other tolerance mechanisms, minimizes autoimmunity. Overall design: Regulatory T cells were sorted from Foxp3 enhancer CNS4-floxed and deficient mice. Total RNA was extracted to amplify T cell receptor (TCR) alpha and beta chains to uncover TCR repertoire diversities with high throughput sequencing.