IDO1 and neoplasm: The indirect inhibitory effect is related to the interaction of various immunosuppressive cell components in the tumor microenvironment of PDAC, PDAC cells can promote the proliferation and activation of MDSC by secreting GM-CSF, and MDSC can continue to secrete cytokines such as IDO, IL-10, TGF-β, Arg-1, iNOS to inhibit the cell activity and immune effect of T cells.