IDO1 and neoplasm: In contrast, induced production of IL-6 in the tumor microenvironment, as a result of either indoleamine 2,3-dioxygenase (IDO) inhibition or the transduction of tumor cells with the IL-6 gene, led to the conversion of Treg to Th17 cells and regression of mouse B16 melanoma [123] or Pan02 pancreatic tumors [122], respectively.