IDO1 and breast cancer: In the tumor microenvironment of primary breast cancer and lymph node metastasis, the increased proportion of Tregs is associated with the high expression of indoleamine 2 and 3-dioxygenase (IDO) [13], but is the very tumor site tissue of Th17 cells related to IL-17A, RORC, and CCR6 upregulation [14], and breast cancer patients with mononuclear dendritic cells mediate allogeneic CD3+CD2−Foxp3-T cells into CD25+T cells [15].