Long-term migration of CD34⁺ cells to FL and/or CXCL12. (A) Freshly isolated UCB CD34⁺ cells were subjected to in vitro migration to a positive gradient of 10 ng/mL FL (▪), 100 ng/mL CXCL12 (⋄), or the combination of FL plus CXCL12 (•). Cell migration was quantitated at 4, 24, 48, and 72 hours. Replicate cultures were incubated with 10 ng/mL rhFL, 100 ng/mL CXCL12, or a combination of FL plus CXCL12 in the chemotaxis medium for 72 hours, and viable cell counts were determined by the forward and side scatter analysis. Percentage of migration was calculated based upon migration of CD34⁺ cells divided by fold change in viable cells. Data represent the mean ± SEM from 2 experiments. *P < .05 compared with background migration (0/0; ▵). (B) Migration of CD34⁺ cells in response to positive (0/FL+CXCL12; □) and zero (FL+CXCL12/FL+CXCL12; ▦) gradients of FL plus CXCL12 were determined for 48 hours. Data are the average ± SEM of 3 experiments. *P < .05 compared with background migration (0/0; ▪).