AUTHOR=van Baren Nicolas , Van den Eynde Benoît J. TITLE=Tryptophan-Degrading Enzymes in Tumoral Immune Resistance JOURNAL=Frontiers in Immunology VOLUME=6 YEAR=2016 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2015.00034 DOI=10.3389/fimmu.2015.00034 ISSN=1664-3224 ABSTRACT=

Tryptophan is required for T lymphocyte effector functions. Its degradation is one of the mechanisms selected by tumors to resist immune destruction. Two enzymes, tryptophan-2,3-dioxygenase and indoleamine 2,3-dioxygenase 1, control tryptophan degradation through the kynurenine pathway. A third protein, indoleamine 2,3-dioxygenase 2, was identified more recently. All three enzymes were reported to be expressed in tumors, and are candidate targets for pharmacological inhibition aimed at restoring effective anti-tumoral immunity. In this review, we compare these three enzymes in terms of structure, activity, regulation, and expression in healthy and cancerous tissues, in order to appreciate their relevance to tumoral immune resistance.