To analyze the potential of both lentiviral vectors to infect cancer stem-like cells, transduced tumors were enzymatically dissociated and CD133 expression was measured by flow cytometry. Both vectors transduced CD133-positive and CD133-negative cells ( Figure 5A ). Although there were high interindividual differences in the fraction of total CD133-positive tumor cells in the different xenografts, both vectors showed similar efficiency in transducing CD133-positive cells, which was slightly higher than the overall fraction of CD133-positive cells (table 1) .