A colitogenic memory CD4^sup +^ T cell population mediates gastrointestinal graft-versus-host disease

Damage to the gastrointestinal tract is a major cause of morbidity and mortality in graft-versus-host disease (GVHD) and is attributable to T cell-mediated inflammation. In this work, we identified a unique CD4* T cell population that constitutively expresses the ß2 integrin CD11c and displays a biased central memory phenotype and memory T cell transcriptional profile, innate-like properties, and increased expression of the gut-homing molecules a4ß7 and CCR9. Using several complementary murine GVHD models, we determined that adoptive transfer and early accumulation of ß2 integrin-expressing CD4* T cells in the gastrointestinal tract initiated Th1-mediated proinflammatory cytokine production, augmented pathological damage in the colon, and increased mortality. The pathogenic effect of this CD4* T cell population critically depended on coexpression of the IL-23 receptor, which was required for maximal inflammatory effects. Non-Foxp3-expressing CD4* T cells produced IL-10, which regulated colonic inflammation and attenuated lethality in the absence of functional CD4*Foxp3* T cells. Thus, the coordinate expression of CD11c and the IL-23 receptor defines an IL-10-regulated, colitogenic memory CD4* T cell subset that is poised to initiate inflammation when there is loss of tolerance and breakdown of mucosal barriers.