PPARg marks splenic precursors of multiple nonlymphoid-tissue Treg compartments [scRNA-seq multiple tissues]

Foxp3+CD4+ regulatory T cells (Tregs) regulate most types of immune response as well as several processes important for tissue homeostasis – for example, metabolism and repair. Dedicated Treg compartments – with distinct transcriptomes, T-cell-receptor repertoires, and growth/survival factor dependencies – have been identified in several nonlymphoid tissues. These Tregs are specifically adapted to function and operate in their home tissue – when, where and how do they take on their specialized characteristics? We recently reported that a splenic Treg population expressing low levels of the transcription factor, PPARg, contains precursors of Tregs residing in visceral adipose tissue. This finding made sense given that PPARg, the “master-regulator” of adipocyte differentiation, is required for the accumulation and function of Tregs in visceral adipose tissue but not in lymphoid tissues. Here we use single-cell RNA sequencing, single-cell Tcra and Tcrb sequencing, and adoptive-transfer experiments to show that, unexpectedly, the splenic PPARglo Treg population is transcriptionally heterogeneous and engenders Tregs in multiple nonlymphoid tissues beyond visceral adipose tissue, e.g. skin and liver. The existence of a general pool of splenic precursors for nonlymphoid-tissue Tregs opens new possibilities for regulating their emergence experimentally or therapeutically.