Close Association between Clearance of Recombinant Human Granulocyte Colony-Stimulating Factor (G-CSF) and G-CSF Receptor on Neutrophils in Cancer Patients

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is used to counter chemotherapy-induced neutropenia. Our previous study showed an inverse correlation between serum rhG-CSF levels and the number of circulating neutrophils in cancer patients (H. Takatani, H. Soda, M. Fukuda, M. Watanabe, A. Kinoshita, T. Nakamura, and M. Oka, Antimicrob. Agents Chemother. 40:988–991, 1996). The aim of this study was to clarify the relationship between rhG-CSF clearance and G-CSF receptors on circulating neutrophils. In five cancer patients receiving chemotherapy, a bolus dose of rhG-CSF (5 μg/kg) was injected intravenously during defined phases of posttreatment neutropenia and neutrophilia. Serum rhG-CSF levels were measured by a chemiluminescence enzyme immunoassay and analyzed by moment analysis. G-CSF receptors on neutrophils were detected by flow cytometry with biotinylated rhG-CSF. rhG-CSF clearance was significantly higher at neutrophilia than at neutropenia (1,497 ± 132 versus 995 ± 266 ml/h;P < 0.01). The percentage of G-CSF receptor-positive neutrophils, reflecting the number of G-CSF receptors per cell, was low at neutropenia without rhG-CSF therapy (44.5% ± 22.1%) and high at neutrophilia with rhG-CSF therapy (73.0% ± 11.4%;P < 0.01). rhG-CSF clearance closely correlated with the percentage of G-CSF receptor-positive neutrophils (r 2 = 0.91;P < 0.0001) and neutrophil count (r 2 = 0.72;P < 0.005). Our results indicate that, in cancer patients receiving chemotherapy, rhG-CSF increases the number of G-CSF receptors per cell as well as circulating neutrophil counts, resulting in modulation of its own clearance.