IDO1 and cancer: When we believe that immunotherapy could be a panacea in cancer care, we combine anti-PD1/L1 with another CPI (such as anti-CTLA-4, anti-IDO1, anti-TIGIT) and with agents that target immune factors (e.g., IL-2) and effectors (e.g., dendritic cells, T cells, macrophages, NK cells), etc.