In vivo generation of gut-homing regulatory T cells for the suppression of colitis

Current therapies for gut inflammation have not reached the desired specificity and are attended by unintended immune suppression. This study aimed to provide evidence for supporting a hypothesis that direct in vivo augmentation of the induction of gut-homing regulatory T (Treg) cells is a strategy of expected specificity for the treatment of chronic intestinal inflammation (e.g., inflammatory bowel disease). We showed that dendritic cells (DCs), engineered to de novo produce high concentrations of both 1,25-dihydroxyvitamin D, the active vitamin D metabolite, and retinoic acid, an active vitamin A metabolite, augmented the induction of T cells that express both the regulatory molecule Foxp3 and the gut-homing receptor CCR9 in vitro and in vivo. In vivo, the newly generated Ag-specific Foxp3⁺ T cells homed to intestines. Additionally, transfer of such engineered DCs robustly suppressed ongoing experimental colitis. Moreover, CD4⁺ T cells from spleens of the mice transferred with the engineered DCs suppressed experimental colitis in syngeneic hosts. The data suggest that the engineered DCs enhance regulatory function in CD4⁺ T cell population in peripheral lymphoid tissues. Finally, we showed that colitis suppression following in vivo transfer of the engineered DCs was significantly reduced when Foxp3⁺ Treg cells were depleted. The data indicate that maximal colitis suppression mediated by the engineered DCs requires Treg cells. Collectively, our data support that DCs de novo overproducing both 1,25-dihydroxyvitamin D and retinoic acid are a promising novel therapy for chronic intestinal inflammation.