Microbiota Transplantation Effectively Treats Immune Checkpoint Inhibitor‐Associated Colitis: A Multi‐Center, Retrospective Case Series

ABSTRACT Background Immune‐mediated colitis is an adverse effect of therapy with immune checkpoint inhibitors (ICIs). This study aims to evaluate the efficacy and safety of washed microbiota transplantation (WMT) in patients with ICI‐associated colitis. Methods This multi‐center, retrospective case series included six patients with ICI‐associated colitis who received WMT between September 2023 and December 2025. Cases were voluntarily contributed by each center where data were available and complete and thus do not represent a complete consecutive case series. Results In total, 6 patients with ICI‐associated colitis were included for analysis. Among all patients, 5 were male and 1 was female, with an age range of 46–71 years (mean 59.5 years). ICI‐associated colitis occurred between cycle 1 and cycle 6 of ICI treatments. According to Common Terminology Criteria for Adverse Events (CTCAE) grading, 3 patients had grade 2, 2 had grade 3, and 1 had grade 4 colitis. Endoscopic findings included mucosal hyperemia, edema, erosion, or shallow ulcers; pathology predominantly showed chronic active inflammation. All 6 patients (100%) achieved clinical remission, with time to remission ranging from 3 to 7 days (4 patients within 5 days). At the last follow‐up, all patients had recovered to 1–2 bowel movements per day with formed stools, and no clinical recurrence of colitis was observed during follow‐up. No tumor progression occurred during or after WMT. Five patients subsequently resumed or continued anti‐tumor therapy. No WMT‐related adverse events were observed. Conclusion WMT is associated with rapid clinical remission of ICI‐associated colitis with a favorable safety profile, and may create conditions for the resumption of anti‐tumor therapy. It also shows salvage therapy potential for severe, steroid‐refractory cases, although further prospective studies are needed.