Characterization of eosinophils generated in vitro from CD34+ peripheral blood progenitor cells

Methods for isolation and cultivation of CD34+ peripheral blood progenitor cells (PBPCs) have facilitated their use in autologous transplantation and as potential targets for gene therapy. In this work, we present the possibility of using these isolated cells to study lineage-specific hematopoietic differentiation. We have shown that differentiating PBPCs faithfully replicate transcriptional events that occur during maturation of the eosinophil lineage; messenger RNAs encoding the five eosinophil granule proteins were detected by reverse-transcriptase polymerase chain reaction (RT-PCR) after 2-3 days of cytokine-stimulated growth. Only three of the five proteins were detected by immunofluorescence staining after 14 days of cytokine-stimulated growth; the percentage of Charcot-Leyden crystal protein (CLC)-containing cells (16-18%) exceeded that of eosinophil peroxidase (EPO)-containing cells (7-8%), which in turn exceeded that of eosinophil-derived neurotoxin (EDN)-containing cells (2-4%). While the electrophoretic mobilities of both CLC and EPO synthesized by differentiating PBPCs were similar to those of their normal counterparts, immunoreactive EDN was found to be heterogeneous and of higher molecular weight that EDN found in mature eosinophils. It is not clear whether our results, which show progressive, but incomplete, differentiation of PBPCs into eosinophils, reflect a lack of knowledge as to what factors are essential for complete differentiation in vitro or relate to the inherent capacity of PBPCs to differentiate along this lineage.