The main immune checkpoints are cytotoxic T lymphocyte antigen 4 (CTLA-4, expressed on the activated CD8+ and CD4+ T cells), programmed cell death protein 1 (PD-1, expressed in myeloid, B- and activated T cells), and programmed cell death ligand 1 (PD-L1, myeloid and cancer cells). The gene discussed is PDCD1; the disease is cancer.