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. Author manuscript; available in PMC: 2016 Jul 1.
Published in final edited form as: J Thorac Oncol. 2015 Jul;10(7):974–984. doi: 10.1097/JTO.0000000000000551

FIGURE 3.

FIGURE 3

Immune checkpoints. A, Cytotoxic CTLA-4 is expressed on T cells after activation and competes with the co-stimulatory T-cell CD28 receptor for CD80/86 expressed by APCs, providing an inhibitory signal to the T cell. B, PD-1 receptor is up-regulated on activated T cells and subsequently binds to one of its ligands, PD-L1 or PD-L2, which are commonly expressed on tumor cells, providing an inhibitory signal to the T cell. APC, antigen-presenting cell; MHC, major histocompatibility; TCR, T-cell receptor; CTLA-4, cytotoxic T-lymphocyte antigen-4; PD-L1/L2, programmed death ligand-1/ligand-2; PD-1, programmed death-1. Adapted with permission from: Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 2012;12:252–264.