IDO1 and colorectal cancer: For instance, STING agonists can enhance IDO activity, leading to immune suppression.221 By combining with an IDO inhibitor, the anti-tumor effect of the STING agonist is substantially amplified in murine models of colorectal cancer.622 Furthermore, the type I IFN produced by the STING pathway induces the expression of CCL2, CCL7, and CCL12, promoting the recruitment of CCR2-expressing MDSCs to tumors and thus fostering immune suppression.