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 fl ow cytometric analysis of IL-3 receptor (IL-3R) expression on rhesus m onkey 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 ll)/RhLA-DR(bright)/CD10(+)/CD27(+)/CD2(-)/CD2 0(-) cells, which probably represent B-cell precursors. IL-3R(+) CD34( -) BM cells, which were detected at low frequencies, consisted of smal l 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(brig ht) blast-like cells. These cells differentiated into monocytes, neutr ophils, and basophils after IL-3 and/or granulocyte-macrophage colony- stimulating factor (GM-CSF) stimulation in vitro. The CD34(bright)/IL3 R(-) subset contained all clonogenic erythroid and myeloid progenitors (burst-forming unit-erythroid and colony-forming unit-culture), where as CD34(bright)/IL-3R(dull) cells differentiated into monocytes, neutr ophils, and erythroid cells after shorter culture periods. This findin g showed that IL-3R expression increases during monocyte and granulocy te 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 expres sion approximately twofold to threefold lower IL-3R levels. A large fr action (>30%) of single-cell/well-sorted CD34(bright)/RhLA-DR(dull) ce lls formed multilineage colonies after 2 to 4 weeks of stimulation wit h IL-3, GM-CSF, Kit ligand, and IL-6. Individual colonies contained ce lls that still expressed CD34 as well as differentiated monocytes, gra nulocytes, and erythroid cells, These results confirmed that the CD34( bright)/RhLA-DR(dull) subset was enriched for immature, multipotent pr ogenitor cells, whereas the CD34(bright)/RhLA-DR(bright) population ma inly contained lineage-committed precursors. The results are consisten t with the concept that IL-3Rs are induced at very early stages of hem atopoiesis, as identified by high expression of CD34 and low expressio n of RhLA-DR. IL-3R expression continues to be low during differentiat ion into lineage-committed progenitors; gradually increases on differe ntiating progenitor cells for B cells, granulocytes, monocytes, and, p ossibly also, erythrocytes; but finally declines to undetectable level s during terminal differentiation into mature cells of all lineages in peripheral blood, with the exception of basophils. These data show th at differential IL-3R expression is a useful parameter to isolate spec ific progenitor cells subsets or to deplete IL-3R(+) cells from the CD 34(bright) population to isolate the most immature stem cell candidate s. (C) 1995 by The American Society of Hematology.