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

白细胞介素-2受体（Interleukin-2 receptor, IL-2R）下游的信号转导与转录激活因子5（STAT5）激活可促进Foxp3的表达，而Foxp3是调节性T（regulatory T, Treg）细胞分化与功能所必需的。然而，由于IL-2R信号通路具有多效性，目前尚不清楚STAT5如何作用于Foxp3基因座以推动Treg细胞的谱系定型。本研究发现，在Foxp3早期诱导过程中，IL-2-STAT5信号通路会聚于一个增强子（CNS4）。该增强子可促进并维持胸腺内IL-2依赖的CD25+Foxp3-前体细胞向Treg细胞的转化。CNS4的缺失会导致新生小鼠的Treg细胞生成显著受损，且该缺陷会随年龄增长得到部分缓解。尽管CNS4缺失导致的胸腺Treg细胞匮乏本身并不会引发自身免疫，但会加重Aire基因破坏所导致的自身免疫表型。因此，CNS4增强子活性可确保出生后早期阶段Treg细胞的高效分化，并与其他耐受机制协同作用，以最大限度降低自身免疫风险。实验设计：从Foxp3增强子CNS4 flox型及缺失型小鼠中分选调节性T细胞，提取总RNA以扩增T细胞受体（T cell receptor, TCR）α及β链，采用高通量测序解析T细胞受体库的多样性。