Severe colitis resulting from immunotherapy has been treated in two cancer patients by transplanting gut bacteria from healthy donors, reports a study published online this week in Nature Medicine.

Immunotherapy has revolutionized cancer treatment. Yet, despite its success, it is frequently accompanied by severe immune-related toxicities that are detrimental for patients and often lead to treatment discontinuation. One such side effect is severe colitis, the inflammation of the inner lining of the colon, which has been associated with alterations to the gut microbiome in immunotherapy patients.

Yinghong Wang and colleagues transplanted fecal microbiota from healthy donors into two cancer patients who had developed colitis following immunotherapy. Following the transplant, the patients’ colitis symptoms abated. The authors collected stool samples from the patients before and after the procedure and found that the transplant restored protective bacteria to the gut microbiome and resolved the inflammation associated with colitis.

Although these findings need to be confirmed in larger patient populations and a clinical trial setting, the authors demonstrate the potential of fecal transplants in treating a major adverse side effect of cancer immunotherapy.