IDO1 and neoplasm: For example, the blood vascular system supplies nutrients and oxygen to the tumor hypoxic environment, while inflamed lymphatics induce an immunosuppressive microenvironment via reducing dendritic cell (DC)-mediated cytotoxic lymphocyte function by producing T cell inhibitory programmed-death ligand 1 (PD-L1), transforming growth factor-β (TGF-β), iNOS), and indoleamine 2,3-dioxygenase (IDO), thereby stimulating tumor progression [104].