Increased IDO and TDO expression in human melanoma is associated with an elevated abundance of TAMs with increased CD206 expression and decreased expression of Nos2 (the gene encoding iNOS), Il12, Tnf, Cd86 and Cd40. These TAMs also upregulate the kynurenine receptor aryl hydrocarbon receptor (AHR), inhibit CD8+ cytotoxic functions and engage in a pro-tumoral cooperation with Tregs [78]. This evidence concerns the gene MRC1 and melanoma.