Increase in circulating stem cells in patients with myelofibrosis.

An increased number of granulocytic and mononuclear cell colonies was grown in vitro from blood of patients with myelofibrosis and ranged between 162-4370 colonies/mi of blood. The number of colonies grown from normal individuals and ranged between 40120/mI blood. There was no correlation between the number of colonies and number of potentially proliferating granulocytic cells (myeloblasts, promyelocytes, myelocytes) plated. In six patients colony size was similar to that of colonies grown from normal individuals and larger than colonies grown from patients with leukemia. Morphologically, colonies consisted of either eosinophils, neutrophils, monocytes, or macrophages. These data indicate that an increased number of stem cells capable of giving rise to in vitro colonies of granulocytes and mononuclear cells circulate in patients with myelofibrosis. The growth pattern of these colonies differed from colonies grown from leukemia cells suggesting that these may not be closely related diseases.