7.4　Indoleamine 2,3-dioxygenase

In the process of tumorigenesis and development, cancer cells can avoid the body’s immune system through various immune escape mechanisms.In normal humans, Indoleamine 2,3-dioxygenase(IDO) is an enzyme that exists in immune cells and can catalyze tryptophan metabolism through the kynurenine pathway.Inflammation caused by the occurrence and development of tumors can induce dendritic cells and tumor cells in the tumor microenvironment to continuously overexpress IDO.The continuous consumption of tryptophan in the tumor microenvironment can inhibit the functional activity of tryptophan-sensitive T cells, thereby suppressing the local immune activity of tumor tissues, and eventually cause cancer cells to escape the killing of immune cells.Inhibition of IDO activity and its expression can effectively activate the killing effect of the immune system on tumors, so IDO has become a new target for tumor immunotherapy [18].(https://www.daowen.com)