High tumor expression of IDO is an independent risk factor for poor outcome in a variety of human cancers, including glioblastoma, and orthotopic syngeneic GL261 tumors grown in C57BL/6 mice were shown in 2012 to exhibit an IDO-rich tumor microenvironment that protects tumors from T cell attack [7]. This evidence concerns the gene IDO1 and glioblastoma.