Figure 1.
Dual roles of IDO in cancer. IDO is overexpressed in many types of tumor cells where its presence has been associated with poor prognosis.6 In tumor cells, IDO dysregulation has been linked to inactivation of tumor suppressor gene Bin1, an amphiphysin-like gene that is widely attenuated or misspliced in cancer.13,14 In tumor-draining lymph nodes, IDO is upregulated in a regulatory subset of plasmacytoid dendritic cells that has been suggested to inform a positive feedback loop in the activation of T regulatory cells (Tregs), while also blunting their interconversion to Th17 inflammatory cells.15,16 IDO activity consumes tryptophan, depriving it from local tissue microenvironments, also generating kynurenine as a product. Both of these processes have been implicated in T cell suppression, including by blunting T effector cell function as well as recruitment of Tregs.12