Indoleamine2,3-dioxygenase and tolerance to tumors

Indoleamine 2,3-dioxygenase(IDO)is the crucial rate-limiting enzyme of tryptophan outside the liver in the body and is considered as an immune defense mechanism in tumor microenvironment.IDO is expressed in a number of cells including cancer cell,dendretic cell and so on.In tumor microenvironment,the overexpression of IDO can lead to the exhaustion of tryptophan and induce the proliferation of regulatory cells,which can prevent the proliferation,diffenentiation and activity of T cells and result in the immune tolerance to tumors.