ENRICHMENT AND CHARACTERIZATION OF PERIPHERAL BLOOD-DERIVED MEGAKARYOCYTE PROGENITORS THAT MATURE IN SHORT-TERM LIQUID CULTURE

A population of peripheral blood-derived cells that mature into megaka ryocytes within four to eight days of liquid culture is described. Thi s population was enriched from normal leukapheresis units by counterfl ow centrifugal elutriation and CD34 selection. The cells were incubate d in suspension with known megakaryocyte growth or maturation factors. Megakaryocytes were identified within the cultures with antibodies to platelet-glycoproteins (Ib and IIb) and cytologically classified as s tage I-IV cells. Plasma from aplastic dogs (APK9) or human recombinant interleukin 3 (IL-3) were the only culture additives which reproducib ly resulted in megakaryocyte development. The activity present in APK9 was relatively megakaryocyte-specific while IL-3 was not. The phenoty pe of the short term megakaryocyte progenitor cell population was dete rmined by FACS and found to be CD34(bright) but not CD34(dull) or CD34 (-). The population was further characterized as CD34(+)/CD38(+) and C D34(+)/HLA-DR(+). Both CD34(+)/CD41(-) and CD34(+)/CD41(+) populations contained megakaryocyte progenitor cells, although megakaryocytes tha t developed from the latter population were fewer in number. In summar y, we have developed an enrichment protocol that, when coupled with a liquid culture assay system, enabled us to characterize short-term meg akaryocyte progenitors from peripheral blood. These cells may be impor tant for early platelet recovery in transplantation settings.