The AFT024 stromal cell line improves MDR1 gene transfer to CD34+ cells derived from human umbilical cord blood

Human hematopoietic stem cells (HSCs) are difficult to transfect with retroviral vectors because of their quiescent nature. Based on the theory that the murine fetal stromal cell line AFT024 can recruit significant numbers of HSC into cell cycle without loss of their primitive function, we transduced human umbilical cord blood cells (UCB) derived CD34+ cells with a retroviral vector pHaMDR1/A containing the human multidrug resistant 1 gene (MDR1) during co-culture with the AFT024 feeders. We found that the presence of the AFT024 cells increased the proportion of Rh-123dull cells up to 35.5%+/-11.4% and transduced colony-forming cells (CFCs) up to 15.2%. Six weeks after transplantation of 5x10(4) day 0 uncultured CD34+ HSCs or their equivalents expanded in the presence or absence of the AFT024 cells for 21 days into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice, we found that CD34+ cells expanded in the presence of the AFT024 cells engrafted in each receptor mouse and the percentage of CD45+ cells reached 18.8%+/-9.5%, of which 18.1%+/-6.0% were Rh-123dull cells. These results suggest that the AFT024 stromal cells can significantly improve MDR1 gene transfer efficiency and maintain the engrafting ability of the CD34+ HSCs derived from UCB.