High CD34⁺ progenitor cell transduction efficiencies by using clinically relevant amounts of vector with verapamil. (A) Average vector transduction efficiencies in CB, BM, and mPB CD34⁺ progenitors in liquid culture 11 days after transduction, primary CFU, and secondary CFU (LTC-IC) cultures. CD34⁺ progenitors were transduced at 50 TU/cell for each of 2 consecutive days with column-purified vector. CFUs were pooled and analyzed by flow cytometry. Standard error bars are shown, and the population for each experiment is shown below the graph. (B) Stable eGFP expression in mPB CD34 (left) and LTC-IC (right) in the presence (▦) or absence (□) of 75 μg/mL verapamil after transduction with 25 TU/cell for each of 2 consecutive days with high-speed centrifuged (HC) or column-purified (CPC) vector. Pooled CFUs were analyzed by flow cytometry. (C) Stability of eGFP expression in 3 separate CB CD34⁺ stroma-free liquid cultures after transduction with (▴) or without (▪) verapamil using 25 TU/cell column-purified vector for 2 days. Average vector copy number per cell at day 11 after transduction is displayed to the right of the graph for each culture. (D) Verapamil dose-dependent increase in CD34⁺ cell transduction efficiency in mPB, CB, and BM cultures using column-purified vector. (E) Total cell number averaged between mPB, BM, and CB cultures (□) and relative cellular viability (•) 4 days after transduction at increasing doses of verapamil. Of note, verapamil-induced decrease in SRC viability is not observed. Error bars indicate SD.