Essential role of a ThPOK autoregulatory loop in the maintenance of mature CD4

The transcription factor ThPOK is critical for homeostasis and differentiation of mature T helper cells. Recent studies have shown that the ThPOK transcriptional silencer element (Sil(ThPOK)) can be reactivated in mature CD4 T cell populations to repress ThPOK and thereby promote differentiation to CD4+ IELs in the intestinal mucosa. However, the molecular basis for this dynamic regulation of Sil(ThPOK) activity remains unknown. Here, using a combination of reverse genetic and reporter approaches, along with global RNA-, ATAC- and ChIP-seq analyses, we demonstrate an important mechanism of ThPOK regulation by which ThPOK binds to the Sil(ThPOK) to drive an auto-feedback loop that maintains its own long-term expression. Disruption of this loop in vivo prevents persistent ThPOK expression in mature peripheral CD4 T cells, leading to genome-wide changes in chromatin accessibility, widespread transcriptional deregulation, and creation of an unusual metastable state, characterized by gain of colonic Treg, cytotoxic T-cell and early DN thymic progenitor specific gene signatures in naïve CD4 T cells. Functionally, abrogation of the ThPOK autoregulatory loop promotes selective differentiation of naive CD4 T cells into GITR(lo) PD-1(lo) CD25(lo) (Triple(lo))Tregs in vitro and in vivo, as well as their conversion to CD4+ IELs in the gut, which provide dominant protection from colitis. Thus, the ThPOK autoregulatory loop represents a key mechanism to physiologically control ThPOK expression and T cell differentiation in the gut, with potential therapeutic relevance.