Oral antigen exposure under costimulation blockade induces Treg cells to establish immune tolerance

Antigen-specific oral tolerance prevents harmful immune responses in naïve animals but is difficult to induce in antigen-primed hosts. Here, we showed that feeding of antigen-containing diet generated peripherally derived regulatory T (pTreg) cells with tissue-adapted effector properties. They acquired Treg-specific epigenomic changes at Treg signature genes, including Foxp3, exhibiting stable suppressive function. Cessation of antigen feeding diminished pTreg cells, hampering tolerance induction. Notably, pTreg cells induced by antigen feeding predominantly expressed CD101. CD101+ Treg cells with similar phenotypic and epigenetic features could also be generated in vitro from antigen-primed naïve CD4+ T cells by blocking CD28-mediated costimulation during TGF-β-dependent Treg induction. Furthermore, in mice already antigen-sensitized by nonoral routes, in vivo blockade of CD28 signaling with CTLA4-Ig prior to antigen feeding promoted differentiation of antigen-specific T cells into CD101+ pTreg cells, facilitating oral tolerance. Thus, continuous oral antigen exposure combined with CD28 blockade generates functionally stable CD101+ pTreg cells, thereby establishing systemic antigen-specific tolerance even in antigen-presensitized hosts.