Transgene expression and vector marking in canine repopulating cells. The percentage of EGFP-expressing leukocytes detected by flow cytometry are shown for dogs G272 (A) and G306 (B) at different times after transplantation with FV vector–transduced peripheral blood stem cells. The FV vector average provirus copy number per cell was determined from peripheral blood leukocyte DNA samples by quantitative real-time PCR for dogs G272 and G306 (C) or by Southern blot analysis with an FV-specific probe for dog G306 (D). In panel D, standards were dilutions of DNA containing a different single copy FV vector provirus, the expected size of the vector fragment is 4028 bp (base pair), and the calculated vector copy numbers are shown below the 2 experimental lanes.