Epigenetic Control of the foxp3 Locus in Regulatory T Cells

TLDR

Compelling evidence indicates that Foxp3 functions as a master regulator of CD4⁺ regulatory T cell development and function. The study aimed to determine whether transcriptional control of Foxp3 itself is required for establishing a stable Treg lineage. The authors identified an evolutionarily conserved upstream region of the foxp3 locus that possesses transcriptional activity. Natural Tregs display complete demethylation and active histone marks in this region, whereas TGF‑β–induced Tregs show only partial demethylation and lose Foxp3 expression and suppressive function upon restimulation, demonstrating that epigenetic stabilization of Foxp3 is essential for a permanent suppressor lineage.

Abstract

Compelling evidence suggests that the transcription factor Foxp3 acts as a master switch governing the development and function of CD4+ regulatory T cells (Tregs). However, whether transcriptional control of Foxp3 expression itself contributes to the development of a stable Treg lineage has thus far not been investigated. We here identified an evolutionarily conserved region within the foxp3 locus upstream of exon-1 possessing transcriptional activity. Bisulphite sequencing and chromatin immunoprecipitation revealed complete demethylation of CpG motifs as well as histone modifications within the conserved region in ex vivo isolated Foxp3+CD25+CD4+ Tregs, but not in naïve CD25−CD4+ T cells. Partial DNA demethylation is already found within developing Foxp3+ thymocytes; however, Tregs induced by TGF-β in vitro display only incomplete demethylation despite high Foxp3 expression. In contrast to natural Tregs, these TGF-β–induced Foxp3+ Tregs lose both Foxp3 expression and suppressive activity upon restimulation in the absence of TGF-β. Our data suggest that expression of Foxp3 must be stabilized by epigenetic modification to allow the development of a permanent suppressor cell lineage, a finding of significant importance for therapeutic applications involving induction or transfer of Tregs and for the understanding of long-term cell lineage decisions.