When PD-1 binds to its ligand, PD-L1, expressed on cancer cells within the TME, it transmits regulatory signals to effector T cells, leading to T cell exhaustion, sending anti-apoptotic signals to tumor cells, and promoting tumor survival, thereby exacerbating immune suppression.565 Indoleamine 2,3-dioxygenase 1 (IDO-1) is a cytosolic enzyme overexpressed in tumor cells and DCs, enhancing immune suppression by increasing the kynurenine to tryptophan ratio, inhibiting the antitumor capacity of NK cells, and promoting Treg infiltration.566. Here, CD274 is linked to neoplasm.