Methods to reduce adverse gastrointestinal events related to the immune system, such as E.coli and diarrhea, in subjects receiving immunotherapy, such as treatment； immunooncology, such as combination therapy with anti-CTLA4 antibody and anti-PD-1 antibody of melanoma. In some ways, these methods include effective treatment of peptides that inhibit the MADCAM Integra alliance, such as anti a4b7 antibodies.Like vedolizumab or related antibodies Council decision 1242； Item 1 requires: a method for the treatment of adverse gastrointestinal events related to the immune system in mammals with antibodies positive for PD-1, anti-CTLA4 or PD-1, and anti-CTLA4. This includes the treatment of peptides that inhibit the binding of madcam-a4b7. Claim 2: the method of claim 1, that is, the polypeptide inhibiting the binding of madcam-a4b7 is a proantibody against a4b7,As an anti-a4b7 proantibody, it competes with vedolizumab to merge the a4b7 proantibody, especially where the antibody has the epilepsy characteristics of vedolizumab, especially where the antibody contains the complementary determining region of vedolizumab, Especially where the antibody is vedoolizumabMétodos para reducir eventos adversos gastrointestinales relacionados con el sistema inmunitario, tales como colitis y diarrea, en sujetos que se someten a un tratamiento inmunológico, tal como un tratamiento de； oncología inmunológica, tal como un tratamiento de combinación de anticuerpo anti-CTLA4 y un anticuerpo anti-PD-1 para melanomas. En determinados aspectos, los métodos comprenden administrar una cantidad terapéuticamente eficaz de un polipéptido que inhibe la unión de MAdCAM-integrina, tal como un anticuerpo anti-a4b7 integrina, tal como vedolizumab o un anticuerpo relacionado. Reivindicación 1: Un método para tratar un evento adverso gastrointestinal relacionado con el sistema inmunitario (gi-irAE) en un sujeto mamífero que se somete a un tratamiento con un antagonista de PD-1, un anticuerpo anti-CTLA4, o
