The invention provides, inter alia, methods of reducing gastrointestinal immune related adverse events, such as colitis and diarrhea, in subjects undergoing an immune treatment, such as an immune oncology treatment, such as anti-CTLA4 antibody and anti-PD-1 antibody combination treatment for melanoma. In certain aspects, the methods encompass administering a therapeutically effective amount of a polypeptide that inhibits MAdCAM-integrin binding, such as an anti-α4β7 integrin antibody, such vedolizumab or a related antibody.