Effect of ABC transporter substrate inhibitors on transduction using lentivirus vectors pseudotyped with RD114. CD34⁺ hematopoietic progenitor cells were transduced at 25 TU/cell in the presence or absence of 50 μg/mL verapamil with VSV-G- or RD114-pseudotyped lentivirus vectors. Transduction efficiency was measured on days 4, 11, and 17 after transduction.