CTLA4 and autoimmune disease: PD-1/PD-L1 and CTLA-4 play important roles in regulating the immune system; hence, patients with autoimmune diseases requiring systemic immunosuppression and/or patients with hepatitis B/C (HBV/HCV) or human immunodeficiency virus (HIV) infection have been excluded from studies evaluating these agents over concerns about inadvertent augmentation of infectious and/or inflammatory activity.