In vitro and in vivo activity of human recombinant granulocyte-macrophage colony-stimulating factor in dogs.

ABSTRACT

Although it is well documented that human granulocyte-macrophage colony-stimulating factor (GM-CSF) controls the production and functional activity of human and nonhuman primate granulocytes and macrophages, relatively little is known about its effects on cells obtained from other species. The molecular cloning of the complementary DNA for human GM-CSF has made it possible to determine the cross-reactivity of the purified recombinant human material (rhGM-CSF) on cells of other species. The results presented herein show that specific receptors for human GM-CSF exist on dog bone marrow cells and mature circulating dog granulocytes. The number of the receptors and the apparent binding affinity of the rhGM-CSF to its receptors on granulocytes were similar to those observed either on human or monkey cells. In cultures of dog bone marrow cells, rhGM-CSF was capable of promoting colony formation in a dose-dependent manner. Human GM-CSF also primed dog granulocytes for increased production of reactive oxygen metabolites in response to either phorbolmyristic acetate-or zymosan-activated dog serum. In vivo, s.c. administration to healthy dogs of rhGM-CSF in daily doses of 15, 50, or 150 micrograms/kg body weight over a period of 7-20 days induced a dose-dependent rise of up to a maximum of a fourfold increase in peripheral WBC counts. The rise in WBC counts was mainly due to elevated neutrophil levels, but an increase in the numbers of monocytes and eosinophils was also observed. However, the rhGM-CSF-induced leukocytosis in dogs was not as dramatic as that observed in nonhuman primates. In all rhGM-CSF-treated dogs, circulating platelet counts dropped to nadir levels of about 20%-30% of normal numbers. Dogs that were treated with 150 micrograms/kg rhGM-CSF developed specific antibodies after about 10-12 days of treatment. These antibodies were able to neutralize the effect of rhGM-CSF in in vitro assays. In vivo WBC counts began to decline when specific antibodies developed, but they never dropped below normal levels. Taken together, the results suggest that human GM-CSF does not appear to exhibit absolute species specificity.