Inhibitory effect of SDF-1α in the upper well on the migration of CD34⁺ cells, or CFU-Meg in response to SDF-1α in the lower well. CD34⁺ cells were loaded into the upper well with 0 to 300 ng/mL of SDF-1α and then applied to the lower well containing medium with or without 300 ng/mL of SDF-1α for migration assays. The migrated CD34⁺ cells were collected and counted. The number of CFU-Meg in the migrated CD34⁺cell population was assessed by culturing the migrated cells in the plasma clot culture system as described in Materials and Methods. The migration of the CD34⁺ cells or CFU-Meg was shown as the percentage of cell input. Results represent the mean ± SD of three separate experiments. * and ** show statistical significance compared with control (with 300 ng/mL of SDF-1α in the lower well and no SDF-1α in the upper well) and are assessed as P < .05 andP < .01, respectively.