Transduction of umbilical cord blood CD34⁺ cells with pseudotyped retroviral vector particles.

Cells were prestimulated for 24 hours in serum-free medium containing high-dose cytokines before a single exposure to viral supernatant on retronectin-coated plates. Cells were then expanded for a total of 96 hours in vitro and analyzed for EGFP expression. Cells transduced with retroviral particles pseudotyped with the amphotropic (A), GALV (B), or VSV-G (C) envelope proteins failed to significantly transduce the bulk CD34⁺ population at the low MOI of 5 used. However, retroviral particles pseudotyped with the RD114 envelope protein (D) transduced the target cell population at a high efficiency. Pseudotransduction was also ruled out by pretreating CD34⁺cells with 50 nmol/L AZT 1 hour before transduction with each vector. EGFP expression in all cases was less than 1% (data not shown). These results demonstrate that in this cell population, the major barrier to gene transfer is at the receptor level and is not due to the quiescence of the target cell.