Bmi1 marks intermediate precursors during differentiation of human brain tumor initiating cells

► We characterize the expression and role of Bmi1 in CD133-sorted human GBM. ► Bmi1 level is highest during intermediate stages of differentiation in BTICs. ► Bmi1 controls self-renewal in CD133+ and differentiation in CD133- cells. ► Stem cell assays are predictive of clinical outcome for GBM patients. ► Bmi1 in BTIC patient isolates may contribute to current molecular categories of GBM.