Epigenetic landscape, key transcriptional regulators, and in vivo identification of human Tr1 cells.

Type 1 regulatory T (Tr1) cells are CD4+ T cells with suppressive function that are induced from conventional T cells exposed to persistent or strong antigens. Human Tr1 cells are understudied; the regulators of their antigen-driven differentiation are unknown, and identifying them in tissues, where antigen interactions occur, is challenging. Here, we conducted a multiomic profiling of human antigen-induced Tr1 cells. Using CRISPR-based functional genomics, we uncovered essential roles of transcription factors IRF4, BATF, and MAF in human Tr1 differentiation, phenotype, and function. We also derived a Tr1 transcriptional signature that detects cells with a Tr1 phenotype in single-cell datasets from patients treated with Tr1 therapy and those with solid tumors. Cross-species analysis confirmed this signature identifies bona fide Tr1 cells induced in vivo in a murine solid tumor model. These findings provide a framework for development of Tr1-based and Tr1-targeting therapies and studies of Tr1 cell biology.