CTLA4 and Autoimmunity: Both fully CTLA-4-deficient (Ctla4−/−) and CTLA-4 Treg knockout mice develop fatal autoimmunity at earlier age, i.e., Ctla4−/− mice die by 3–4 weeks of age26,27, whereas the CTLA-4 Treg knockout mice become inactive ~7 weeks22.