ICIs are monoclonal antibodies that enhance anti-tumor, T-cell-mediated activity by blocking either the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4)/B7 or the programmed cell death protein-1 (PD-1)/programmed death ligand-1 (PD-L1) immune checkpoint pathways, thereby activating the immune system [17]. The gene discussed is PDCD1; the disease is neoplasm.