The S1P₁ agonist SEW2871 increases the mobilization of HPCs in response to AMD3100 and the combination of G-CSF and AMD3100. Mice received an IV injection of SEW2871 followed by AMD3100 1 hour later. Mice were killed after an additional hour. WBC counts (A, C, E, and G) and the number of CFUs present in cardiac blood (B, D, F, and H) of mice mobilized with AMD3100 (A-B), G-CSF (C-D), or G-CSF + AMD3100 (E-H) with or without the addition of SEW2871 as indicated were determined as described in “Methods.” #P < .05 compared with AMD3100 alone or G-CSF and AMD3100. Representative data from 1 of 2 experiments are shown.