IDO1 and neoplasm: Camouflage is another immune system evasion mechanism, aiming to create an immunosuppressive environment through the recruitment of peripheral T reg cells, production of immunosuppressive enzymes and cytokines (such as IDO1, arginase, IL-10, and TGF-β), and expression of negative checkpoints (such as PDL-1/2) by the tumor (18, 22).