Phenotypic analysis of transmigrating cells compared with the untreated starting cell population before migration. Flow cytometric analysis of Lin^- progenitors (CD34⁺ cells, gated = R2) migrating in response to SDF-1 (MS-5 conditioned medium) after preincubation with 100 nM FTY720 showed a similar percentage of CD34⁺/CD38^- cells (gate R3, middle panels), only the proportion of CD34⁺/CXCR4^- cells (gate R3, lower panels) was lower compared with the starting population, demonstrating the migratory capabilities of more immature progenitors in the employed in vitro assay and additionally underlining the CXCR4 dependency of the transmigration process, as already observed in the blocking experiments shown in Figure 2B. Transmigrating cells, right panels; untreated cell population before migration, left panels.