Increased transgene expression in NOD/SCID repopulating CD34⁺ PBSCs during prolonged ex vivo culture at the cost of human cell engraftment. CD34⁺ PBSCs were cultured ex vivo and transduced with RD114-MFGS-CFP for 4 (mice III-A, III-B, Table 1) 5 (mice III-C, III-D), or 6 (mice III-E, III-F) days before transplantation into NOD/SCID mice. Although transgene expression (solid line) increases with each extra day of transduction on days 5 and 6, human cell engraftment (dashed line) is lost substantially with ex vivo culture longer than 4 days.