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The administration of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) is being evaluated in various clinical circumstances, including iatrogenic neutropenia (e.g., chemotherapy-induced), bone marrow transplantation, aplastic anemia, myelodysplastic syndrome, and acquired immunodeficiency syndrome. In addition to its proliferative and differentiating activities, GM-CSF also stimulates various functional activities of mature granulocytes and macrophages. For instance, it inhibits neutrophil migration, augments neutrophil superoxide production in response to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP), increases phagocytosis, and induces changes in granulocyte surface marker expression [1, 4]. This activation of polymorphonuclear leukocytes (PMN) might contribute to undesired side effects. Several adverse effects [8] of GM-CSF therapy have been noted. Mild transient pyrexia, bone pain, and pruritus occur in some patients. Thrombophlebitis is common under GM-CSF administration in a peripheral vein. At very high doses serious side effects have occurred, such as fluid retention, pericarditis, capillary endothelial leakage syndrome, and central venous thrombosis. Some patients developed hypoalbuminemia [5] after prolonged treatment. A transient neutropenia [3] due to sequestration of PMN within the lungs is induced by GM-CSF infusion. Another complication, leukocytoclastic vasculitis [6], has been described only once during GM-CSF therapy.

Severe congenital neutropenia (SCN) is a disorder of myelopoiesis characterized by severe neutropenia, secondary to a maturation arrest at the promyelocyte stage and an absolute neutrophil count below 200/μl in the blood of affected patients, and the onset of severe bacterial infections during the first 12 months of life [1]. Therapy with recombinant human granulocyte colony-stimulating factor (rhG-CSF) at daily doses between 1 and 60 μg/kg subcutaneously led to an increase in absolute neutrophil counts, associated with significant clinical improvement [2].