STAT6 controls the stability and suppressive function of regulatory T cells.

STAT6 promotes tumorigenesis by decreasing the Foxp3+ cell frequency allowing for the infiltration of inflammatory cells during the early stages of colitis-associated cancer (CAC). In this study, we dissected the role of STAT6 in the generation of inducible in vitro regulatory T cells (iTregs) and peripheral in vivo Tregs (pTregs) under inflammatory conditions. In in vitro assays, when STAT6 was lacking, iTregs preserved a stable phenotype and expressed high levels of Foxp3 and CD25 during long expansion periods, even in the presence of IL-6. This effect was associated with increased in vitro suppressive ability, over-expression of PD-1, CTLA-4, and Foxp3, and decreased IFN-γ expression. Furthermore, iTregs developed during STAT6 deficiency showed a higher demethylation status for the FOXP3 TSDR, coupled with lower DNA methyltransferase (DNMT1) mRNA expression, suggesting that STAT6 may lead to Foxp3 silencing. Using a mouse model of CAC, the STAT6-/- pTregs expressed a more activated phenotype at the intestine, had higher suppressive capacity, and expressed more significant levels of PD1 and LAP associated with their ability to attenuate tumor development. These data suggest that STAT6 signaling impairs the induction, stability, and suppressive capacity of Tregs developed in vitro or in vivo during gut inflammation. This article is protected by copyright. All rights reserved.