Mobilization of HSPCs by bortezomib alone or in combination with G-CSF and AMD3100 in mice. Mice were analyzed for PB CFU-Cs at various time points. (A) B6 mice were treated with bortezomib (0.8 mg/kg, intravenously) or phosphate-buffered saline (PBS). Mice were analyzed for PB CFU-Cs at baseline, 8 hours, 12 hours, 15 hours, 18 hours, 21 hours, and 24 hours (combination of 3 experiments; 3 mice in first experiment, 5 mice each in subsequent experiments). (B) Bortezomib (0.8 mg/kg IV) in B6 (Bor-B6), bortezomib (0.8 mg/kg IV) in BALB/c (Bor-BALB/c), and PBS in B6 and BALB/c (PBS). Mice were analyzed for PB CFU-Cs 15 hours after administration of PBS or bortezomib. Bor-BALB/c resulted in higher CFU-C mobilization compared with Bor-B6. (C) Splenectomized and nonsplenectomized (wild-type) B6 mice receiving bortezomib (0.8 mg/kg IV) at baseline. Splenectomized B6 mice that received PBS at baseline were used as a control. (D) Carfilzomib (5 mg/kg IV) was given to B6 mice at baseline and PB CFU-Cs were analyzed at various time points (combination of 2 experiments; 4 mice per arm in first experiment, 5 mice per arm in the second experiment). (E-F) Bortezomib (0.8 mg/kg IV) was given to VLA-4KO and wild-type B6 mice. VLA-4KO mice receiving PBS at baseline were used as control (combination of 2 experiments; 5 mice in each arm per experiment). (G) Competitive repopulation assay. Lethally irradiated CD45.1⁺ mice received transplants of 2 × 10⁵ congenic CD45.1⁺/CD45.2⁺ bone marrow competitor cells plus PBMCs (1.5-3 mL PB) from CD45.2⁺ mice mobilized with bortezomib, PBS, or AMD3100. PB was harvested 15 hours after injection for bortezomib and PBS, and 3 hours after injection for AMD3100. The contribution of mobilized cell populations to hematopoiesis was determined by flow cytometry for CD45.2+ donor cells 2 months after transplant (combination of 2 experiments; 4 mice in each arm per experiment). (H) Bortezomib (0.8 mg/kg IV) in combination with G-CSF (250 µg/kg, subcutaneously). The G-CSF + bortezomib group received G-CSF on days 1 (baseline), 2, 3, and 4, and bortezomib on day 4. The G-CSF control group received G-CSF on days 1 (baseline), 2, 3, and 4. The bortezomib and PBS control groups received bortezomib (0.8 mg/kg IV) and PBS, respectively, on day 4. Mean PB CFU-C in G-CSF + bortezomib vs G-CSF alone: 5600/mL vs 2300/mL, respectively (P = .005). (I-J) The bortezomib + AMD3100 group received bortezomib (0.8 mg/kg IV) at baseline and AMD3100 (5 mg/kg subcutaneously) 15 hours later. The PBS + AMD3100 group received PBS at baseline followed by AMD3100 15 hours later. The bortezomib control group received bortezomib at baseline. Mice were analyzed for PB CFU-Cs at baseline, 15 hours, 18 hours, and 24 hours. Mean PB CFU-C in bortezomib + AMD3100 vs PBS + AMD3100 at 18 hours: 2600/mL vs 1100/mL, respectively (P = .01). Fold increase in CFU-C over baseline in bortezomib + AMD3100 group vs PBS + AMD3100 group: 105 ± 16 vs 17 ± 3, respectively (P = .01). Data are mean ± standard error.