The DEL-1–β3 integrin axis promotes regulatory T cell responses during inflammation resolution [Li X. and Colamatteo A. Co-First]

FOXP3+CD4+ regulatory T cells (Tregs) are critical for immune homeostasis and respond to local tissue cues, which control their stability and function. We explored here whether DEL-1, which, like Tregs, increases during resolution of inflammation, promotes Treg responses. DEL-1 enhanced Treg numbers and function at barrier sites (oral and lung mucosa). The underlying mechanism was dissected using mice lacking DEL-1 or expressing a point mutant thereof, or mice with T cell-specific deletion of the transcription factor RUNX1, identified by RNA-seq analysis of the DEL-1-induced Treg transcriptome. Specifically, through interaction with αvβ3-integrin, DEL-1 promoted induction of RUNX1-dependent FOXP3 expression and conferred stability of FOXP3 expression upon Treg restimulation in the absence of exogenous TGFβ1. Consistently, DEL-1 enhanced the demethylation of the Treg-specific demethylated region (TSDR) in the mouse Foxp3 gene and the suppressive function of sorted induced Tregs. Similarly, DEL-1 increased RUNX1 and FOXP3 expression in human conventional T cells promoting their conversion into induced Tregs with increased TSDR demethylation, enhanced stability and suppressive activity. We thus uncovered a DEL-1-αvβ3-RUNX1 axis that promotes Treg responses at barrier sites and offers novel therapeutic options for modulating inflammatory/autoimmune disorders.