Figure 2. Shows the interactions of PD-1 and CTLA-4 expressed on the surface of the T cells with the respective ligands and the subsequent activation of immune checkpoint signalling pathways that inhibit lymphocytes survival and proliferation.

CTLA-4:Cytotoxic T-Lymphocyte Antigen 4; MHC: Major histocompatibility complex; MMR: Mismatch repair PD-1: Programmed cell death protein 1; PD-L1: Programmed death-ligand 1; TAA: Tumor associated antigen ;TCR: T-cell receptor.