Figure 3. The immune system activation and checkpoint inhibitors. APC: antigen presenting cell; CTLA-4: cytotoxic T-lymphocyte-associated antigen 4; PD-1: programmed cell death protein 1; PD-L1: programmed death ligand 1; TCR: T cell receptors. Modified from Pardoll. Nat Rev Cancer 2012;12:252-64, with permission of Springer Nature27.
