IDO1 and neoplasm: The immune effects of tumor‐directed vaccines, PD‐L1 blockade, TGF‐β sequestration, IL‐15 agonism, and IDO1 inhibition can be additive and/or synergistic. This includes TGF‐β’s putative role in T‐cell exclusion from the tumor microenvironment (TME) in metastatic urothelial carcinoma, which can be reversed with dual targeting of TGF‐β and PD‐L1.