VLA-4 antagonism increases number of circulating HSPCs in CXCR4^+/+ and CXCR4^−/− chimeras. CXCR4^+/+ and CXCR4^−/− chimeras (n = 6-9 each group) were treated with BIO5192, a specific VLA-4 antagonist, and peripheral blood CFU-Cs were measured in (A) CXCR4^+/+ and (B) CXCR4^−/− chimeras. (C) Recipient mice (n = 3 each group) were administered VLA-4 inhibitor or vehicle 3 hours before adoptive transfer of 6 × 10⁶ wild-type bone marrow mononuclear cells. The number of circulating CFU-Cs was measured before adoptive transfer (t = 0) and 2 and 30 minutes after adoptive transfer. Data represent mean ± SEM; *P < .01.