Targeting the FOXP3–T-bet interaction to restore Treg stability in IFN-?–driven autoimmunity

Regulatory T cell (Treg) stability is maintained by dynamic remodeling of the FOXP3 transcriptional complex, and its disruption leads to Treg dysfunction and immune dysregulation. However, how specific FOXP3 mutations alter the dynamic remodeling of the FOXP3-complex and thereby contribute to pathogenic Treg reprogramming in IPEX syndrome remains unclear. Here, by uncovering the distinctive pathogenesis of FOXP3V408M mutation in IPEX syndrome, we demonstrate that the FOXP3–T-bet interaction fine-tunes Treg function by repressing IFN-? production, thereby preventing Th1-driven inflammation. Using an AI-driven virtual screening approach, we identified a first-in-class small molecule, 430C10, that directly binds FOXP3 and reinforces its interaction with T-bet. 430C10 robustly suppressed Treg-derived IFN-? production and alleviated IFN-?-driven tissue inflammation in FOXP3V408M knock-in mice as well as in models of acute colitis. Collectively, these findings establish the FOXP3–T-bet interaction as a central checkpoint governing Treg stability and IFN-?-driven Th1 pathology, providing proof-of-concept that pharmacologic stabilization of FOXP3–T-bet interaction can mitigate IFN-?–driven immune disorders. Overall design: For single-cell RNA-seq of the human samples, we used Ficoll-purified PBMCs from the son (PT) and mother (MOM).