Indoleamine 2,3‑dioxygenase/IDO Immune Checkpoint Pathway

Indoleamine 2,3-dioxygenase 1 (IDO1) was specifically induced in corneal endothelial cells and is among the 10 most highly expressed enzymes in the whole genome. Indoleamine 2,3-dioxygenase/IDO is interferon (IFN) inducible as is the intracellular haem enzyme which is the rate-limiting enzyme for the degradation of tryptophan.
Indoleamine 2,3-dioxygenase/IDO Immune Checkpoint Pathway functions as an antimicrobial agent that acts against a wide range of intracellular pathogens including viruses and protozoans. However, the antiviral role of Indoleamine 2,3-dioxygenase/IDO has been challenged by the results of a study on an infectious disease model. On the other hand, Indoleamine 2,3-dioxygenase/IDO immune Checkpoint Pathway can induce regulatory T cells or T-cell anergy as has been observed in HIV. Because of its strong regulatory property, an Indoleamine 2,3-dioxygenase/IDO inhibitor has been developed as a promising anticancer drug. Clinical trials are being conducted to determine whether it can reduce tumour tolerance in conjunction with the anti-programmed death-ligand 1 (PD-L1) antibody for melanomas. Thus, Indoleamine 2,3-dioxygenase/IDO might have distinctive activities of limiting inflammatory responses, which are used by tumour cells to promote their own survival or to prevent the activation of antitumour responses.