Myeloid progenitor cells in the circulation of patients with myelofibrosis and other myeloproliferative disorders.

We have measured the numbers of myeloid progenitor cells in the circulation of patients with myelofibrosis (MF) and other myeloproliferative disorders. In general, progenitor cell numbers were increased in the circulation of patients with MF compared with controls. The mean increases were 9-fold for the multilineage progenitor cells (CFU-GEMM), 13-fold for the erythroid progenitor cells (BFU-E), 37-fold for the granulocyte-macrophage progenitor cells (CFU-GM) and 167-fold for the megakaryocyte progenitors (CFU-MK). Splenectomized patients generally had reduced numbers of circulating progenitor cells. In the CFU-MK assay, mature megakaryocytes cultured from patients with MF regularly showed large vacuoles in the nucleus and cytoplasm, unlike control cells. The increased colony formation in patients with MK, involving especially CFU-MK colonies, is consistent with the hypothesis that MF is a primary myeloproliferative disorder in which a megakaryocyte-derived factor predisposes to the formation of marrow fibrosis.