The promising anti-tumor activity of mAbs targeting the immune-checkpoint proteins, such as cytotoxic T-lymphocyte antigen-4 (CTLA-4), programmed cell death protein 1 (PD-1), and the PD-1 ligand (PD-L1), led to regulatory approvals of these agents for the treatment of a variety of malignancies. Here, PDCD1 is linked to neoplasm.