These mechanisms include inefficient processing and presentation of tumor antigens, up-regulation of negative co-stimulatory ligands which mediate T cell anergy,12 expansion of regulatory cells, and production of “immunosuppressive molecules,” such as transforming growth factor β (TGF-β),13 Fas ligand,14 and the immunosuppressive enzyme indolamine-2,3-dioxygenase (IDO).15 Tumor cells can also directly escape T cell recognition through down-regulating major histocompatibility complex (MHC) class I or disabling other components of antigen process.16 Here, IDO1 is linked to neoplasm.