Indoleamine 2,3-Dioxygenase 1 (IDO1) Is Up-Regulated in Thyroid Carcinoma and Drives the Development of an Immunosuppressant Tumor Microenvironment

Context: Indoleamine 2,3-dioxygenase 1 (IDO1) is a single chain oxidoreductase that catalyzes tryptophan degradation to kynurenine. In cancer, it appears to exert an immunosuppressive function as part of an acquired mechanism of immune escape mediated by the inhibition of lymphocyte proliferation and survival and by the induction of FoxP3+ T regulatory cells. Objective: The objective of the study was to evaluate IDO1 expression in thyroid carcinoma and demonstrate its immunosuppressive function in the context of thyroid tumors. Setting: IDO1 expression was evaluated by quantitative PCR in 105 papillary thyroid carcinomas (PTCs), 11 medullary thyroid carcinomas, six anaplastic thyroid carcinomas, and five thyroid carcinoma cell lines (TCCLs), by immunohistochemistry in 55 PTCs and by Western blotting in five TCCLs. FoxP3+ Treg lymphocyte density was evaluated by immunohistochemistry in 29 PTCs. IDO1 inhibitory effect on lymphocyte proliferation was tested in coculture experiments of TCCLs and activated lym...