PDCD1 and neoplasm: In passive immunotherapies, the goal is to enhance the patient’s immune response by targeting existing anti-tumor mechanism such as antibodies against immune checkpoints, which are the most widely used (e.g., cytotoxic T-lymphocyte associated protein 4 – CTLA-4, programmed cell death protein-1 – PD–1, programmed death-ligand 1 – PDL1).