Summary of PCR analysis of single colonies isolated from LTCs at weeks 2, 3, 4, and 5. Each bar represents the transduction efficiency calculated for a particular group of cells at a given time point calculated as the mean of 3 to 6 values detected in 6 separate experiments initiated with BM cells from 6 different normal donors. Whichever vector was used on d1 is designated vector 1, and that used on d5 and d6 is designated vector 2. Each bar is divided into 3 sections reflecting the percentage of colonies at each time point containing vector 1 sequences, vector 2 sequences, or both as defined in the legend. For every data point, between 26 and 59 colonies were analyzed. *P < .05, percentage of progenitor cells expressing vector 1–derived v vector 2–derived neo^Rsequences within the same group. The percentage of progenitors expressing both sequences was not considered for this analysis.^#Not significant.