Groβ administration decreases the number of circulating HSPCs in CXCR4^−/− chimeras. Circulating CFU-Cs were measured in CXCR4^+/+ (A, n = 3-6) and CXCR4^−/− (B, n = 5-11) chimeras at the indicated time points after administration of Groβ (2.5 mg/kg). (C) CXCR4^+/+ (WT) or CXCR4^−/− (KO) chimeras (n = 3-4 each group) were treated with Groβ or left untreated (ctrl). Serum was collected 15 minutes after treatment and assayed for metalloproteinase activity. (D) Wild-type mice (n = 4 each group) were given a single injection of AMD3100 (5 mg/kg) and 3 hours later Groβ was administered. Shown is number of circulating CFU-Cs before and 15 minutes after Groβ administration. Data represent mean ± SEM; *P < .05 compared with pretreatment; **P < .01 vs control.