Abnormal erythropoiesis in the myeloproliferative disorders: an analysis of underlying cellular and humoral mechanisms.

Peripheral blood and bone marrow specimens from patients with polycythemia vera (PV) and chronic myelogenous leukemia (CML) were assayed for erythroid and granulopoietic progenitor cells. All compartments were increased in CML patients in relapse although the ratio of BFU-E to CFU-C numbers remained constant in all CML patients where values ranged over several orders of magnitude. By comparison with normal ratios there was only a slight shift towards increased CFU-C numbers. No quantitative changes in any progenitor compartment was found in PV except for a marginal increase in marrow CFU-E. Erythropoietin (epo)-independent colony formation has been documented in all 61 cases of PV studied to date, and the proportion of progenitors classified as abnormal on this basis increases on average 3- to 5-fold as they differentiate in vivo from primitive BFU-E to CFU-E. Preliminary replating studies suggest that when this occurs in vitro individual BFU-E produce both normal and abnormal phenotypes. Epo-independent erythropoiesis has also been commonly observed in assays of CML cells, although its expression is more variable and in the absence of epo progenitors in CML usually make fewer erythroblasts containing even less hemoglobin than do their counterparts in PV. Expression of a common regulatory defect in erythroid cells in PV and CML suggests a possible relationship to the initial transformation event(s).