Modulation of cancer-specific immune responses by amino acid degrading enzymes

To evade immune destruction, tumours exploit a wide range of immune escape mechanisms, including the induction of an immunosuppressive tumour microenvironment. This is mediated, in part, by amino acid-degrading enzymes indoleamine 2,3-dioxygenase, tryptophan 2,3-dioxygenase, arginase 1 and arginase 2, which have emerged as key players in the regulation of tumour-induced immune tolerance. Here we describe how the expression of tryptophan- and arginine-degrading enzymes by tumour and tumour-infiltrating cells can hamper cancer-specific immune responses, and discuss how this knowledge is being exploited to develop new strategies for cancer immunotherapy