Several types of immunotherapy for cancer are known including monoclonal antibodies (e.g., anti-cytotoxic T-lymphocyte-associated protein 4), checkpoint inhibitors (e.g., anti-programmed cell death protein 1 (anti-PD-1) and its ligand programmed death-ligand 1 (anti-PD-L1)), cytokines, T-cell therapy, and vaccines. The gene discussed is PDCD1; the disease is cancer.