To counteract the activity of the immunosuppressive TME, ICIs which block the inhibitory receptor programmed cell death protein-1 (PD-1) and its ligand (PD-L1) or the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), have shown promising results and can restore the anti-tumor effects of T-cell effectors [92]. The gene discussed is PDCD1; the disease is neoplasm.