The role of polymorphonuclear neutrophils (PMNs) in clearance of granulocyte colony-stimulating factor (G-CSF) in vivo and in vitro.

Previous studies have suggested that in vivo granulocyte colony-stimulating factor (G-CSF) pharmacokinetics may change over time. We studied three patients treated with high-dose chemotherapy followed by autologous bone marrow transplantation (ABMT) for metastatic breast cancer after intravenous administration of recombinant human (rh) G-CSF (5 or 16 microg/kg/day). We investigated plasma G-CSF concentrations and absolute neutrophil counts (ANCs/pL) in these patients on three separate days. G-CSF plasma clearance increased with time post-ABMT with no change in the apparent volume of distribution (Vd) of G-CSF. Regression analysis of G-CSF plasma clearance and ANCs revealed a linear relationship, with r2 = 0.85 (p = 0.00025). We further investigated this phenomenon in vitro by estimating pharmacokinetic parameters for rhG-CSF using a model in which polymorphonuclear neutrophils (PMNs) were incubated with rhG-CSF. We found that, at low G-CSF concentrations in vitro, there was an increase in G-CSF clearance with increasing ANCs, but at higher G-CSF concentrations this relationship did not hold. We suggest that this finding resulted from aggregation and polymerization of G-CSF at high concentrations when kept at 37 degrees C for 24-48 hours in vitro. Using fluorescence staining techniques, our data suggest there are changes over time in the amount of G-CSF bound to PMNs. These changes may reflect reexpression or recycling of the G-CSF receptor, and could explain the continuing clearance of G-CSF by PMNs in vitro. The strong positive correlation between G-CSF plasma clearance and ANCs in vivo is compatible with the hypothesis that neutrophils mediate one of the major pathways for rhG-CSF clearance.

Mature polymorphonuclear leukocytes express high-affinity receptors for IgG (Fc gamma RI) after stimulation with granulocyte colony-stimulating factor (G-CSF).

The high-affinity receptor for the constant region of immunoglobulin G IgG (Fc gamma RI; CD64) is virtually undetectable on mature polymorphonuclear neutrophils (PMNs) in healthy individuals but is expressed on PMNs in patients with certain infections and in patients treated with recombinant human granulocyte colony-stimulating factor (rhG-CSF). The induction of Fc gamma RI by rhG-CSF has previously been reported to result from effects on immature granulocyte progenitors. To evaluate the G-CSF effect on mature PMNs, we studied the correlation between G-CSF plasma concentration and expression of Fc gamma RI on PMNs in vivo as well as the effect of G-CSF on Fc gamma RI expression on mature PMNs in vitro. Fc gamma RI expression on PMNs correlated (R = 0.79; p < .001) with plasma concentrations of endogenous or recombinant G-CSF in healthy volunteers and in patients undergoing high-dose chemotherapy and autologous bone marrow transplantation. PMNs exhibited a unimodal distribution for elevated Fc gamma RI expression, suggesting that G-CSF induced increased expression of Fc gamma RI on mature as well as on immature PMNs. In vitro, incubation of mature PMNs with G-CSF induced mRNA for Fc gamma RI. Significant Fc gamma RI surface expression was induced in a time- and dose-dependent manner. Thus, G-CSF can act on mature PMNs to increase Fc gamma RI expression and may be useful for stimulating antibody mediated immune functions of PMNs in vivo.