Figure 2.

Mechanisms of T-cell activation and inhibition. T-cell activation is mediated by the interaction of the T-cell receptor with the major histocompatibility complex (MHC) and the CD28 receptor with the B7 costimulatory molecule on the antigen-presenting cell (APC). Activating interactions are noted with a plus sign (+). T-cell inhibition is mediated by the interaction of PD-L1 and PD-1, as well as CTLA-4 and B7. Inhibitory interactions are noted with a minus sign (−). Inhibitors of PD-1, PD-L1, and CTLA-4 prevent the inactivation of T-cells, thus allowing the T-cells to destroy the tumor cell more effectively. This figure is from an open-access journal and does not require copyright permission. It was reprinted from reference [10].