CTLA4 and autoimmune disease: Nevertheless, the successful treatment of patients with partial defects [30, 31, 34, 35] in CTLA‐4 expression or autoimmune disease [36] with exogenous CTLA‐4‐Ig (Abatacept) is consistent with a model in which the combination of decreased levels of endogenous CTLA‐4 in combination with exogenous CTLA‐4 can restore immune homeostasis.