TCR origin and specificity to environmental or self-antigens on distinct antigen-presenting cells determine peripheral Treg cell differentiation.

Peripheral differentiation of regulatory T (pTreg) cells promotes immunological tolerance to obligate non-self, such as food or symbiotic microbes. We examined the relative importance of TCR recognition vs. environmental cues, leveraging CRISPR-based TCR editing of primary T cells with a large TCR panel, assessing pTreg cell differentiation induced by self-, microbial, or dietary antigens. All antigen classes drove stable pTreg cell differentiation, which varied with TCR origin: TCRs derived from Treg cells enabled pTreg cell differentiation more effectively than those from conventional T cells. TCRs recognizing self-, microbial, or dietary antigens elicited distinct pTreg cell phenotypes: Helios⁺, RORγ⁺, or both. Different TCR-antigen pairs established distinct transcriptional programs. These differences traced to the types of antigen-presenting cells (APCs) involved-food-reactive TCRs depended predominantly on RORγ⁺ APCs and self-reactive TCRs depended on conventional dendritic cells. Thus, TCR specificity is a primary determinant of CD4+ T cell fate and phenotype, integrating antigen specificity and presentation context, providing a framework to design TCR-based tolerogenic immunotherapies.