IDO1 and melanoma: Alternatively, the immunosuppressive action of FTY720 can be reduced by a blockade of immune inhibitory pathways using anti-CTLA-4 mAb, anti-PD-L1 mAb, and/or the indoleamine-pyrrole 2,3-dioxygenase (IDO) inhibitor INCB23843 which restored IL-2 production, proliferation of intratumoural T cells, and tumour growth control in FTY720 treated murine B16.SIY melanoma model [245].