Pro-tumor immunosuppressive mechanisms include T cell–centered mechanisms, such as programmed cell death 1/programmed cell death ligand 1 (PD1/PDL1) and regulatory T cells (TRegs), cellular factors, cytokines, growth factors, and small molecules derived from metabolites, such as kynurenines and polyamines (8–11). The gene discussed is PDCD1; the disease is neoplasm.