Molecular diversification of regulatory T cells in nonlymphoid tissues.

Foxp3(+)CD4(+) regulatory T cells (T-regs) accumulate in certain nonlymphoid tissues, where they control diverse aspects of organ homeostasis. Populations of tissue T-regs, as they have been termed, have transcriptomes distinct from those of their counterparts in lymphoid organs and other nonlymphoid tissues. We examined the diversification of T-regs in visceral adipose tissue, skeletal muscle, and the colon vis-a-vis lymphoid organs from the same individuals. The unique transcriptomes of the various tissue T-reg populations resulted from layering of tissue-restricted open chromatin regions over regions already open in the spleen, the latter tagged by super-enhancers and particular histone marks. The binding motifs for a small number of transcription factor (TF) families were repeatedly enriched within the accessible chromatin stretches of T-regs in the three nonlymphoid tissues. However, a bioinformatically and experimentally validated transcriptional network, constructed by integrating chromatin accessibility and single-cell transcriptomic data, predicted reliance on different TF families in the different tissues. The network analysis also revealed that tissue-restricted and broadly acting TFs were integrated into feed-forward loops to enforce tissue-specific gene expression in nonlymphoid-tissue T-regs. Overall, this study provides a framework for understanding the epigenetic dynamics of T cells operating in nonlymphoid tissues, which should inform strategies for specifically targeting them.