DIFFERENTIAL EXPRESSION OF RECEPTORS FOR INTERLEUKIN-3 ON SUBSETS OF CD34-EXPRESSING HEMATOPOIETIC-CELLS OF RHESUS-MONKEYS

The target cell specificity of interleukin-3 (IL-3) was examined by flow cytometric analysis of IL-3 receptor (IL-3R) expression on rhesus monkey bone marrow (BM) cells using biotinylated IL-3. Only 2% to 5% of unfractionated cells stained specifically with the biotinylated IL-3 and most of these cells were present within the CD34(+) subset. IL-3Rs were detected on small CD34(dull)/RhLA-DR(bright)/CD10(+)/CD27(+)/CD2(-)/CD20(-) cells, which probably represent B-cell precursors. IL-3R(+) CD34(-) BM cells, which were detected at low frequencies, consisted of small CD20(dull)/surface-IgM(+)/RhLA-DR(+) cells. These cells represented immature B lymphocytes, whereas CD20(bright) mature B cells were IL-3R(-). The highest IL-3R levels were detected on CD34(dull)/RhLA-DR(bright) blast-like cells. These cells differentiated into monocytes, neutrophils, and basophils after IL-3 and/or granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulation in vitro. The CD34(bright)/IL3R(-) subset contained all clonogenic erythroid and myeloid progenitors (burst-forming unit-erythroid and colony-forming unit-culture), whereas CD34(bright)/IL-3R(dull) cells differentiated into monocytes, neutrophils, and erythroid cells after shorter culture periods. This finding showed that IL-3R expression increases during monocyte and granulocyte differentiation. Results of three-color experiments indicated that IL-3Rs are expressed on CD34(bright)/RhLA-DR(bright) cells as well as on CD34(bright)/RhLA-DR(dull) cells, with the latter population expression approximately twofold to threefold lower IL-3R levels. A large fraction (>30%) of single-cell/well-sorted CD34(bright)/RhLA-DR(dull) cells formed multilineage colonies after 2 to 4 weeks of stimulation with IL-3, GM-CSF, Kit ligand, and IL-6. Individual colonies contained cells that still expressed CD34 as well as differentiated monocytes, granulocytes, and erythroid cells, These results confirmed that the CD34(bright)/RhLA-DR(dull) subset was enriched for immature, multipotent progenitor cells, whereas the CD34(bright)/RhLA-DR(bright) population mainly contained lineage-committed precursors. The results are consistent with the concept that IL-3Rs are induced at very early stages of hematopoiesis, as identified by high expression of CD34 and low expression of RhLA-DR. IL-3R expression continues to be low during differentiation into lineage-committed progenitors; gradually increases on differentiating progenitor cells for B cells, granulocytes, monocytes, and, possibly also, erythrocytes; but finally declines to undetectable levels during terminal differentiation into mature cells of all lineages in peripheral blood, with the exception of basophils. These data show that differential IL-3R expression is a useful parameter to isolate specific progenitor cells subsets or to deplete IL-3R(+) cells from the CD34(bright) population to isolate the most immature stem cell candidates. (C) 1995 by The American Society of Hematology.