G-CSF-mobilized peripheral blood progenitor cells: in vitro growth pattern and hematopoietic growth factor receptor...

The kinetics of colony formation by granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood progenitor cells (PBPCs) were monitored using clone-mapping experiments. Compared with normal resting bone marrow (BM), where the ratio of Day 7:Day 14 granulocyte-macrophage colony-forming cells (GM-CFCs) was 1:0.76-1.9, PB was found to be relatively deficient in progenitor cells with the capacity to form colonies by Day 7 (median ratio Day 7:Day 14 1:21). The most mature Day 7 GM-CFCs, those dispersing or extinguishing before Day 14, were almost absent in PB (< 1% of all GM-CFCs) but comprised 77% of Day 7 GM-CFCs and 32% of all GM-CFCs in BM. The expression patterns of high affinity receptors for G-CSF, GM-CSF, stem cell factor (SCF), and the ligand for flk-2 on CD38hi and CD38-/dim PB CD34+ cells were determined by binding of 125I-labeled ligand and autoradiography. G-CSF receptor (G-CSFR) expression was detected on approximately 25% of CD38-/dim cells (estimated mean 105 receptors per positive cell) and was higher in CD38hi cells (approximately 50% positive, with a mean of 227 receptors per cell). GM-CSFR expression was low (approximately 25% of cells positive, mean of 120 receptor per cell) and did not vary with CD38 expression. c-kit (SCFR) and flk-2 were expressed by > or = 90% and > or = 80% of CD34+ cells, respectively. SCF binding per cell was greater in the CD38hi population, while flk-2 expression did not vary with CD38 expression. These results confirm the heterogeneity of receptor expression by progenitor cells and imply differential regulation of receptor expression during maturation.