**11.1 PD-1 inhibitors**

PD-1, also known as CD279, is a CD28 family member expressed on lymphoid cells such as T cells, B cells, and natural killer (NK) cells, as well as on myeloid cells [60]. The binding of PD-1 on T cells with the ligands PD-L1 or PD-L2 suppresses signals downstream of T-cell receptor activation in the context of antitumor immunity [61, 62]. The monoclonal antibody that target the programmed death-1 receptor is Pembrolizumab, which is a humanized monoclonal antibody directed against PD-1.
