Fecal Microbiota Transplantation in Refractory Immune-Mediated Colitis: Case Series and Review of the Literature.

Background/Objectives: Immune checkpoint inhibitors (ICI) represent a significant breakthrough in cancer management, but they can cause adverse effects such as immune-mediated colitis (IMC). The standard first-line treatment is corticosteroids, and second-line treatment is infliximab or vedolizumab. However, a proportion of immune-mediated colitis (IMC) cases are refractory to immunosuppressive treatment, which has led to the exploration of novel approaches such as fecal microbiota transplantation. Methods: We present two patients who both developed grade III IMC following application of durvalumab and pembrolizumab, respectively. Both patients were refractory to corticosteroid therapy, while the first one also showed no improvement to infliximab. We performed two separate applications of FMT on both patients, from different donors, as a rescue treatment. Results: After unsuccessful immunosuppressive treatment and following rescue FMT, both patients demonstrated a rapid and sustained improvement in inflammatory markers, clinical symptoms, quality-of-life scores, and colonoscopy findings, without additional immunosuppressive treatment. Conclusions: FMT appears to be safe and a potentially effective treatment option for patients with refractory IMC both as second- and third-line therapy options. Continued efforts toward rigorous donor screening, use of standardized biobanks, and standardizing FMT protocols will further enhance safety and reproducibility.