PDCD1 and neoplasm: Immune checkpoint inhibitors (ICIs) target coinhibitory receptors, such as cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1), on T cells and other immune cell subsets or their ligands, such as programmed cell death ligand 1 (PD-L1), on tumor cells and various immune cells [38].