Summary donor cell engraftment in PeP3^b mice conditioned with AMD3100. (A) PeP3^b mice were treated with one cycle of AMD3100 (5 mg/kg) and 4 × 10⁷ donor marrow cells (from ROSA26 mice) were transplanted 2 hours (n = 6 mice), 6 hours (n = 3 mice), or both 2 and 6 hours later (n = 3 mice). Control animals (n = 3 mice/condition) also received 4 × 10⁷ donor marrow cells but no AMD3100. Donor cell engraftment was assayed at 3 months. ^*P values for donor cell engraftment of AMD3100-treated mice compared with control mice at 2 hours, 6 hours, and 2 and 6 hours were < .001, .02, and .02, respectively. (B) PeP3^b mice (n = 3 mice) received one weekly injection of AMD3100 (5 mg/kg) on 3 consecutive weeks and 4 × 10⁷ donor marrow cells (from ROSA26 mice) were transplanted 2 hours after each mobilization. Control animals (n = 3 mice) also received 3 weekly infusions of 4 × 10⁷ donor marrow cells but no AMD3100. Donor cell engraftment was assayed at 3 months. ^*P values for donor cell engraftment of mice treated with 3 cycles of AMD3100 compared with control mice and mice treated with only one cycle of AMD3100 were .006 and .001, respectively.