Sequential administration of cyclophosphamide and granulocyte-colony stimulating factor relieves impaired myeloid maturation in Felty's syndrome.

A patient with Felty's syndrome (FS) and persistent profound neutropenia developed recurrent infections and sepsis syndrome. No impairment of granulocyte-macrophage colony development was observed in vitro. Marrow morphology revealed an absence of mature neutrophil forms despite administration of granulocyte-colony stimulating factor (G-CSF). However, pretreatment with bolus cyclophosphamide (CY) permitted the growth factor to relieve this impairment of late myeloid maturation and resulted in a brisk, albeit short, burst of neutrophilia. This suggests that immune interference in myelopoiesis can be overcome by growth factor administration if immune activity is adequately dampened by immunosuppressive therapy.