A Phase I open-label trial at Boston Children’s Hospital reported that oral encapsulated fecal microbiome transplantation (FMT) capsules can increase peanut tolerance in adults with peanut allergy, alongside mechanistic shifts consistent with restored oral immune regulation. The study used one-time frozen FMT capsules, with and without antibiotic pretreatment, and tracked changes in reaction thresholds over time. Across 15 enrolled adults, six met a secondary efficacy endpoint, with responses persisting through a four-month clinical endpoint and no grade 3 or higher adverse events attributed to the FMT. Responders showed immune changes including increased tolerogenic RORγt-positive regulatory T cells and decreased type 2 helper T cells. The trial adds to a growing evidence base that gut microbial metabolites and immune programming may be actionable in allergic disease, although larger controlled studies will be needed to establish durability and predict who will respond.