Defects of Granulopoiesis in Patients with Severe Congenital Neutropenia

To confirm the abnormalities of primitive myeloid progenitor cells in patients withsevere congenital neutropenia (SCN), we studied their responsiveness to hematopoieticfactors including granulocyte colony-stimulating factor (G-CSF). In all SCN patientsstudied no abnormalities of granulocyte colony-stimulating factor receptor (G-CSFR) genewere detected by polymerase chain reaction-single-strand conformation polymorphism analysisand sequence analysis. A flow cytometric analysis of bone marrow cells based on theexpression of CD34, Kit receptor, and G-CSFR demonstrated a reduced frequency ofCD34+/Kit+/G-CSFR+ cells in patients with SCN. The granulocyte/macrophage (GM)-colonyformation of CD34+/Kit+/G-CSFR+ cells in patients was markedly decreased at allconcentrations of G-CSF in serum-deprived semisolid culture. The responsiveness ofCD34+/Kit+/G-CSFR+ cells in patients showed a reduced response to the combination of stemcell factor, the ligand for flk2/flt3, and interleukin-3 with or without G-CSF inserum-deprived semisolid and liquid suspension cultures. In contrast, no difference in theresponsiveness of CD34+/Kit+/G-CSFR- cells was noted between SCN patients and normalsubjects. The bone marrow cells from a patient who underwent bone marrow transplantationshowed a restoration of both the reduced frequency and the decreased level of GM-colonyformation of CD34+/Kit+/G-CSFR+ cells. These results demonstrate that the presence ofqualitative and quantitative abnormalities of primitive myeloid progenitor cells expressingG-CSFR may play an important role in the impairment of granulopoiesis in patients with SCN.