Antibodies specific for immune checkpoint proteins, whether they be antagonist antibodies that block immunosuppressive pathways such as anti–PD-1 and anti–CTLA-4 or agonist antibodies that trigger T cell activation and proliferation such as anti–4-1BB, have demonstrated significant success in cancer immunotherapy either clinically or in preclinical settings, respectively. The gene discussed is TNFRSF9; the disease is cancer.