2D0T, 2D0U, 4PK5, 4PK6, 4U72, 4U74, 5EK2, 5EK3, 5EK4, 5ETW362015930ENSG00000131203ENSMUSG00000031551P14902P28776NM_002164NM_008324NM_001293690NP_002155NP_001280619NP_032350Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO EC 1.13.11.52) is a heme-containing enzyme physiologically expressed in a number of tissues and cells, such as the small intestine, lungs, female genital tract or placenta.

[11] Emerging evidence suggests that IDO becomes activated during tumor development, helping malignant cells escape eradication by the immune system.

IDO is part of the malignant transformation process and plays a key role in suppressing the anti-tumor immune response in the body, so inhibiting it could increase the effect of chemotherapy as well as other immunotherapeutic protocols.

IDO is an important molecule in the mechanisms of tolerance and its physiological functions include the suppression of potentially dangerous inflammatory processes in the body.

Thus, mammalian placenta, due to intensive tryptophan catabolism has the ability to suppress T cell activity, thereby contributing to its position of immunologically privileged tissue.

[21] IDO is an immune checkpoint molecule in the sense that it is an immunomodulatory enzyme produced by alternatively activated macrophages and other immunoregulatory cells.

[29] Emerging clinical studies suggest that combination of IDO inhibitors with classical chemotherapy and radiotherapy could restore immune control and provide a therapeutic response to generally resistant tumors.