IDO1 and melanoma: Compared with the B16-F10 melanoma parental cell line (B16WT) mouse model, Tregs isolated from the B16-F10 melanoma overexpressing IDO (B16IDO) mouse model exhibited a higher level of immunosuppressive factors, including vascular endothelial growth factor (VEGF), CTLA-4, IL-10 and more remarkable ability to suppress immune activation of autologous CD8 + T cells [19].