A Boston Children’s Hospital Phase I study reported that oral encapsulated fecal microbiome transplantation (FMT) was feasible and may increase peanut tolerance in adults with severe peanut allergy. In the trial (NCT02960074), 6 of 15 participants met a secondary endpoint, with responders showing immunologic shifts consistent with restored oral tolerance, including increased RORγt+ regulatory T cells. The study also included mechanistic mouse work pointing to bile-acid metabolites as potential mediators of tolerance. Importantly for adoption, the trial reported no FMT-related allergic reactions and no grade 3 or higher adverse events through the four-month clinical endpoint. The results add a new, microbiome-mediated path into the allergy pipeline and set up follow-on studies to validate efficacy and define which responders benefit.