Because BMI1 is a stem cell gene involved in regulation of glioma cell stemness [23, 24], we investigated whether U251-TgCOX4-1 cells are enriched in glioma stem cells (GSCs) when cultured in defined serum-free culture medium supplemented with epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) (Figure 7A). Here, EGF is linked to glioma.