CTLA4 and colitis: While untreated mice revealed no secondary organ infiltration, mice treated with a combination of anti-PD-1 and anti-CTLA-4 antibodies showed hepatitis characterized with heavy infiltration of mononuclear cells to the periportal and pericentral hepatic veins, pancreatitis with perivascular infiltration, colitis with inframammary response in the base of the intestinal villus, and pneumonitis with multifocal peri-bronchial and perivascular inflammation in the lungs (Fig 1B).