Reduction of plasma fibrinolytic activity following high-dose cyclophosphamide is neutralized in vivo by GM-CSF administration.

Background: GM-CSF has broad clinical applicability as a potent myelopoietic stimulator. However, its function is not restricted to the myelopoietic system and several observations suggest that GM-CSF may interfere with the hemostatic balance. In order to assess whether GM-CSF has any influence on hemostasis, we evaluated some coagulative and fibrinolytic parameters in patients treated with GM-CSF following chemotherapy.

Methods: Fibrinolytic activity (FA), fibrinogen and D-dimer were evaluated before and after high-dose cyclophosphamide in 6 patients additionally treated with GM-CSF and in 5 control patients; moreover, tissue plasminogen activator (tPA) was assayed in those treated with GM-CSF. Comparative in vitro analysis was performed on cultured endothelial cells before and after exposure to GM-CSF.

Results: Control patients showed a significant decrease in plasma FA after chemotherapy compared to basal values (FA/mm2: 15.6 +/- 2.1 at day + 2 and 20.8 +/- 19 at day + 4 vs. 103.8 +/- 64.2 at day 0; p < 0.005); conversely, no FA reduction was observed in GM-CSF-treated subjects. In this latter group a marked increase in tPA antigen was seen, consistent with enhanced FA. No significant changes in plasma D-dimer and fibrinogen values were detected in the two groups. tPA, urokinase-type plasminogen activator, PAI-1 and procoagulant activity were evaluated in vitro on cultured human endothelial cells and found to be unchanged following GM-CSF addition.

Conclusions: The results demonstrate that high-dose chemotherapy may negatively influence plasma FA. This adverse side effect is neutralized by GM-CSF administration. The discrepancy found between in vitro and in vivo GM-CSF activity on hemostatic may be explained by in vivo GM-CSF stimulation of cell types other than endothelial cells.