PROM1 and glioblastoma: To test whether ectopic expression of CD133 in a primary GBM line that contains only a small subset of CD133+ cells can increase the transduction efficiency of CD133-LV, we infected primary GBML27 cells, in which CD133+ cells represent only 1.4±0.4% (n = 5 measurements) of all cells, with a lentivirus that expresses PROM1 cDNA under the constitutive EF1α promoter (CD133-OE construct) (Fig. 2E).