IDO1 and neoplasm: However, IFN-γ induces many pro-tumor reactions, including up-regulation of programmed death-ligand 1 (PD-L1), and Indoleamine 2,3-dioxygenase (IDO) affects T-cell immune response and, ultimately, has both pro- and antitumor properties depending on the concentration in the TME (reviewed in [25]).