In vivo selection results in significant increases in HbF in mice transplanted with γ-globin/MGMT lentiviral vector transduced β-thalassemic BM cells. (A) Cellulose acetate gel electrophoresis of RBC lysates from individual mice transplanted with V5-Mp-MGMT vector-transduced β-thalassemic cells (top panel) or V5-EF1-MGMT vector-transduced β-thalassemic cells (bottom panel) and either not treated or administered drug treatment as indicated in the Figure 1 legend. Vertical lines have been inserted to indicate a repositioned gel lane. (B) HbF levels as determined by quantitative HPLC are shown for individual mice transplanted with V5-EF1-MGMT–transduced β-thalassemic cells and left untreated or after drug selection, as indicated. Data represent the mean ± SEM. Statistically significant differences are indicated by the P value, as determined by the Student t test.