IDO1 and pancreatic neoplasm: Moreover, pancreatic cancer cells themselves actively contribute to immune suppression through production of immune suppressive cytokines (e.g., TGF-β, IL-10, and IL-6) and by expressing surface molecules that mediate immune suppression (e.g., vascular endothelial growth factor (VEGF), Fas ligand (Fas-L), programmed death-1 ligand (PD-L1) and indolamine-2, and 3-dioxygenase (IDO)) [44].