SOX2 and glioblastoma: The RR GBM cells were enriched with glioblastoma stem cells (GSCs) confirmed by specific marks of CD133, OCT4, SOX2, NANOG, and HER2 by Western blot (Supplementary Fig. 2b) with elevated CD133/HER2 population identified by flow cytometry analysis (Supplementary Fig. 2c, d).