Phosphorylation of STAT3 is associated with increased PD-L1 expression on Treg cells (49, 54) and Indoleamine 2,3-dioxygenase 1(IDO1) on myeloid-derived suppressor cells (55), frequently observed in dedifferentiated cancer cells and infiltrating lymphocytes (45, 56). This evidence concerns the gene IDO1 and cancer.