Definition

A humanized immunoglobulin (Ig) G4 monoclonal antibody directed against the negative immunoregulatory human cell surface receptor programmed cell death 1 (programmed death-1; PD-1), with potential immune checkpoint inhibitory and antineoplastic activities. Upon administration, toripalimab binds to PD-1 and inhibits the binding of PD-1 to its ligands, programmed cell death-1 ligand 1 (PD-L1) and PD-1 ligand 2 (PD-L2). This prevents the activation of PD-1 and its downstream signaling pathways. This may restore immune function through the activation of both T cells and T-cell-mediated immune responses against tumor cells. PD-1, a transmembrane protein in the Ig superfamily that is expressed on activated T cells, negatively regulates T-cell activation and effector function when activated by its ligands; it plays an important role in tumor evasion from host immunity.