Antibodies against the immune checkpoints CTLA-4 or PDCD1/CD274 (also known as PD-1/PD-L1) (Box 1) can reactivate the T-cell anti-tumor activity that is abrogated in many cancers (Leach et al., 1996; Melero et al., 2007). The gene discussed is PDCD1; the disease is neoplasm.