One of the major checkpoints probed for therapy is programmed cell death protein 1 (PD-1), most prominently expressed on the surface of T cells, B cells, and natural killer cells, and its inducible ligand programmed death ligand 1 (PD-L1) naturally expressed on a variety of cell types including some tumour cells, hepatocytes, muscle cells, epithelium and antigen-presenting cells [1]. The gene discussed is PDCD1; the disease is neoplasm.