PDCD1 and neoplasm: Blocking of inhibitory checkpoints such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), programmed cell death ligand 1 (PD-L1) or lymphocyte activation gene 3 (LAG-3) can enhance the function of tumor-reactive T cells and induce anti-tumor immunity.