Transferable Immunoglobulin A–Coated Odoribacter splanchnicus in Responders to Fecal Microbiota Transplantation for Ulcerative Colitis Limits Colonic Inflammation

Background & Aims: Fecal microbiota transplantation (FMT) is an emerging treatment modality for ulcerative colitis (UC). Several randomized controlled trials have shown efficacy for FMT in the treatment of UC, but a better understanding of the transferable microbiota and their immune impact is needed to develop more efficient microbiome-based therapies for UC. Methods: Metagenomic analysis and strain tracking was performed on 60 donor and recipient samples receiving FMT for active UC. Sorting and sequencing of immunoglobulin (Ig) A–coated microbiota (called IgA-seq) was used to define immune-reactive microbiota. Colonization of germ-free or genetically engineered mice with patient-derived strains was performed to determine the mechanism of microbial impact on intestinal immunity. Results: Metagenomic analysis defined a core set of donor-derived transferable bacterial strains in UC subjects achieving clinical response, which predicted response in an independent trial of FMT for UC. IgA-seq of FMT recipient samples and gnotobiotic mice colonized with donor microbiota identified Odoribacter splanchnicus as a transferable strain shaping mucosal immunity, which correlated with clinical response and the induction of mucosal regulatory T cells. Colonization of mice with O splanchnicus led to an increase in Foxp3⁺/RORγt⁺ regulatory T cells, induction of interleukin (IL) 10, and production of short chain fatty acids, all of which were required for O splanchnicus to limit colitis in mouse models. Conclusions: This work provides the first evidence of transferable, donor-derived strains that correlate with clinical response to FMT in UC and reveals O splanchnicus as a key component promoting both metabolic and immune cell protection from colitis. These mechanistic features will help enable strategies to enhance the efficacy of microbial therapy for UC. Clinicaltrials.gov ID NCT02516384.