Cancer cells upregulate not only PD1 (PDCD1) but also other immune check points (ICPs) such as PD-L1 (CD274), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), lymphocyte-activation gene (LAG)-3, hepatitis A virus cellular receptor 2 (HAVCR2), and indoleamine 2,3-dioxygenase 1 (IDO1), which, upon ligand triggering, reduce (some of) CD8+ T cell effector functions. The gene discussed is IDO1; the disease is cancer.