(A–B) DBA2/J mice were treated with the VLA4 inhibitor firategrast (100 mg/kg, i.v.), the CXCR2 ligand tGro-β (2.5 mg/kg, s.c.) or both agents immediately after each other. Blood was analyzed for WBCs (A) and CFU-Cs (B). Data are mean ± SEM, n = 5. ***P < 0.001, **P < 0.01, compared with firategrast alone/compared with tGro-β alone. (C) Molecular structures. (D) G2-ALL cells were treated in duplicate with the VLA4 inhibitors shown in C. Percent inhibition of VCAM1 binding as compared with untreated samples. Data are mean ± SEM of a single experiment representative of 3 experiments. (E) DBA2/J mice were injected with tGro-β (2.5 mg/kg, s.c.), a VLA4 antagonist (3 mg/kg, i.v., for BIO5192, CWHM-823, and -842; 100 mg/kg, i.v., for firategrast), or their combination. Controls received vehicle only. Numbers of circulating CFU-Cs and LSK cells were analyzed 0.5 hours after the injection(s). Data are mean ± SEM, n = 8–10. ***P < 0.001, **P < 0.01, *P < 0.01, compared with tGro-β alone/VLA4 antagonist alone. (F) HSPC mobilization in CXCR2-KO mice using the CXCR2 ligands CXCL1, CXCL2 (tGro-β), and CXCL8 and the VLA4 antagonist CWHM-823 as well as their combinations was compared with that in WT BALB/cJ. Blood CFU-C numbers were analyzed at baseline, 15 minutes after injection of CXCR2 ligands (s.c., 1 mg/kg CXCL1 and CXCL8, 2 mg/kg tGro-β), 1 hour after injection of CWHM-823 (s.c., 3 mg/kg), and 30 minutes after the combined treatment (s.c. injection of each ligand together with CWHM-823 at same doses as single treatments). Data are mean ± SEM, n = 4–26 in mobilized groups, n = 51–78 in baseline groups. ***P < 0.001, compared with CXCR2 agonist alone/compared with CWHM-823 alone. Statistical comparisons were made using linear mixed models in A and B and ANOVA in all others, followed by step-down Bonferroni’s adjustment for multiple comparisons.