Background：Pembrolizumab is an antibody drug that targets the cell surface receptor programmed cell death protein 1 PD-1 found on T cells. By preventing the binding of its ligands PD-L1 and PD-L2, pembrolizumab induces an antitumor immune response. Upregulation of PD-1 ligands is a mechanism for tumors to evade antitumor immune response; when PD-1 binds its ligand, the T cell receives an inhibitory signal leading to T cell anergy and blockade of anti-tumour immune response. Instead of directly targeting tumor tissue to induce tumor cell death, pembrolizumab acts as a checkpoint inhibitor to stimulate immune responses to eliminate cancer cells.
