GFAP and central nervous system cancer: All GSCs used in this study were derived from human surgical resection specimens and have been previously functionally validated through their capacity to form tumors in serial transplantation assays and expressed high levels of the stem marker OLIG2 and low levels of the astrocyte differentiation marker GFAP compared with matched in vitro–differentiated glioma cells (DGCs) (Figure 2, A and B, Supplemental Figure 2A, and Tables 1 and 2).