CD4+ Foxp3+ T-regulatory cells support fecal microbiota transplantation engraftment and resolution of Clostridioides difficile infection

Clostridioides difficile is an opportunistic pathogen that infects the large intestine following perturbation of the intestinal microbiota causing epithelial damage and debilitating, potentially fatal, colitis. Fecal microbiota transplantation (FMT) is a successful therapeutic strategy for treating recurrent C. difficile infection. Despite remarkable efficacy, implementation of FMT therapy is limited and the mechanism of action remains poorly understood. Here, we demonstrate a critical role for Foxp3+ CD4+T-regulatory cells in supporting FMT therapy using a murine C. difficile infection system. Following FMT, chronically infected wild-type mice resolve C. difficile. In contrast, cohoused Rag1−/− or CD4+ T cell deficient mice fail to clear the infection. Genetic deletion of TH1 or TH17 effector cytokines does not impact efficacy of FMT, however, C. difficile infected Il10−/− mice are non-responsive to FMT therapy. Further, targeted ablation of CD4+ Foxp3+T-regulatory cells in C. difficile infected Foxp3-DTR mice prior to FMT reveal a necessary role for this CD4+T cell subset in FMT-mediated resolution of C. difficile infection. FMT non-responsive mice exhibit impaired engraftment of the FMT bacterial consortia and failed restoration of commensal bacteria-derived secondary bile acids in the large intestine, metabolites associated with limiting C. difficile disease in FMT recipient patients. These data demonstrate that the host’s inflammatory immune status can limit the efficacy of microbiota-based therapeutics to treat C. difficile infection.