Fig. 2.

A model of T-cell activation, inhibition, and reactivation by blocking CTLA-4 with anti-CTLA-4 antibodies (ipilimumab, tremelimumab). T-cell activation requires 2 signals: the first, binding MCH with TCR; the second, interaction of CD28 on the T-cell with B7 (CD 80, CD 86) on APC. After T-cell activation, CTLA-4 is displaced to the plasma membrane and functions as a T-cell activation inhibitor. Anti-CTLA-4 antibody binds with CTLA-4 which results in T-cell reactivation. APC, antigen-presenting cell; TCR, T-cell receptor; CTLA-4, cytotoxic T lymphocyte-associated antigen 4; MHC, major histocompatibility complex