Response of CXCR4-overexpressing CB CD34⁺ cells to different SDF-1 concentrations. (A) Lentiviral-transduced CB CD34⁺ cells were incubated for 7 days in serum-free conditions with SDF-1 (50 ng/mL) in combination with SCF (50 ng/mL), FLT-3L (50 ng/mL), and IL-6 (50 ng/mL). Results are shown as fold increase in number of viable cells compared to cells incubated in the absence of SDF-1. Results represent mean ± SE of 3 independent experiments performed in duplicate. (B) Lentiviral-transduced CB CD34⁺ cells were incubated overnight with 1 μg/mL SDF-1 and examined for (i) CXCR4 expression by immunostaining and (ii) SDF-1 (125 ng/mL) induced in vitro migration using a transwell migration system. Bars represent mean ± SE of 2 independent experiments performed in duplicate. ^*P <.05 compared to untreated cells (▪).