Increased 67LR expression in BM CD34⁺ cells is involved in G-CSF–induced mobilization of murine HSCs. (A) G-CSF–mobilized CD34⁺ cells after treatment with anti-67LR antibodies. Balb/c mice were treated daily for 4 days with 300 μg/kg G-CSF (□) or saline (▪), as a control. Nonimmune (▦) or the MLuC5 neutralizing anti-67LR mAbs (▤) were injected into G-CSF–treated mice on days 3 and 4 of mobilization, immediately after each G-CSF stimulation. Four hours after the last injection, PB CD34⁺ cells were evaluated by flow cytometry, with a mouse-specific anti-CD34–PE antibody. Data are mean ± SEM of 3 separate experiments, each group being composed of 4 mice; **P < .001. (B) G-CSF–mobilized progenitors after treatment with anti-67LR antibodies. Balb/c mice were treated daily for 4 days with 300 μg/kg G-CSF (□) or saline (▪), as a control. G-CSF-treated mice were injected with nonimmune (▦) or MLuC5 neutralizing anti-67LR antibodies (▤) on days 3 and 4 of mobilization, immediately after each G-CSF stimulation. Four hours after the last injection, the number of progenitors mobilized into the circulation was evaluated by colony assays and reported as the number of CFC × 10³/mL. Data are mean ± SEM of 3 separate experiments, each group being composed of 4 mice; ***P < .001. Mobilization of murine progenitor cells, evaluated both as circulating CD34⁺ cells and as CFCs, is significantly inhibited by anti-67LR antibodies. (C) 67LR expression BM CD34⁺ cells in a representative mouse treated with nonimmune (left column) and MLuC5 (right column) antibodies. Total BM cellularity (top row) as well as the percentage of 67LR⁺ BM CD34⁺ cells (middle and bottom rows) in nonimmune antibody and MLuC5-treated mice were similar, thus demonstrating that the inhibition of mobilization occurred without affecting BM CD34⁺ cells.