In vitro selection of transduced cells before transplantation results in increased engraftment of γ-globin–expressing cells and improved Hb levels. (A) The percentage of HbF-positive cells at 10 and 18 weeks after transplantation, as assessed by FACS, is shown for mice receiving transplantations of either untreated (n = 18) or drug-treated (n = 17) lineage-negative BM cells. P values of Student t test are shown. (B) The mean Hb levels of mice receiving transplantations of untreated or drug-treated BM cells are shown. As a control, the mean Hb level of all mice from both groups that had no γ-globin–expressing cells is shown. One-way analysis of variance with Bonferroni multiple comparison showed that Hb levels of treated and untreated groups significantly differed from the Hb level of mice that lacked γ-globin expression (P < .001 and P < .05, respectively). The difference between treated and untreated groups did not reach statistical significance. Data are expressed as mean ± SEM. (C) Vector copy number determination in animals receiving in vitro selected cells. Left panel: Southern blot analysis using BglII-digested BM DNA from the indicated animals. Left lanes indicate the copy number standards, as described in Figure 5 legend. Numbers indicate the VCN, as determined by densitometry, relative to the copy number standards. In addition to the hybridizing band of correct size, animal 50 also shows a second band that is smaller and probably represents vector containing a small deletion. Right panel: Southern blot analysis of BM DNA from the indicated animals, digested with the enzymes as labeled.