Comparison of a conventional γ-retroviral vector to a SIN lentiviral vector with insulator elements in the LTRs and an internal cellular promoter. The organization of the 2 vectors is shown. Each of the 6 clones having the conventional γ-retroviral vector inserted into the LMO2 gene gave a strong signal on Western blot analysis, whereas only 2 of the 7 clones having the insulated lentiviral vector gave a weak signal on Western blot analysis.