Moreover, various other tumor-derived factors, such as prostaglandin-E2 (PGE2) (36), IL-10 (37), VEGF (38), and TGF-β (39–41), have been suggested to contribute to the induction and expansion of MDSCs (36), and these factors are also derived from glioma cells. This evidence concerns the gene TGFB1 and central nervous system cancer.