title: Combined signaling through interleukin-7 receptors and flt3 but not c-kit potently and selectively promotes B-cell commitment and differentiation from uncommitted murine bone marrow progenitor cells.
abstract: Multiple cytokines can synergize to stimulate the in vitro proliferation and exclusive myeloid differentiation of multipotent bone marrow progenitor cells. The ligand for c-kit (stem cell factor [SCF]) plays a key role in stimulating myeloid and erythroid cell production of primitive hematopoietic progenitors. SCF in combination with interleukin-7 (IL-7) can also stimulate the combined myeloid and B-cell differentiation of uncommitted hematopoietic progenitor cells as well as the growth of early B-cell progenitor cells, although the involvement of c-kit in early B lymphopoiesis remains controversial. In the present study, the flt3-ligand (FL), which, in combination with other cytokines, has overlapping activities with SCF on myeloid cell production from uncommitted progenitors, was investigated for its ability to induce selective stroma-independent B-cell commitment from uncommitted Lin-Sca-1+ bone marrow progenitor cells. IL-7 alone did not induce any clonal growth and FL alone gave rise to a few clusters (< 50 cells) but no colonies (> 50 cells), whereas the combined stimulation with FL and IL-7 resulted in clonal growth of 10% of Lin-Sca-1+ bone marrow cells. After 12 days of incubation of Lin-Sca-1+ cells in FL + IL-7, an almost 400-fold increase in cell production was observed. Phenotyping showed that greater than 99% of the cells produced were of the B-cell lineage, in that they expressed B220, but not cell surface markers specific for myeloid, erythroid, or T-cell lineages. Furthermore, the cells did not express cytoplasmic mu-heavy chain (cmu) or surface IgM, but were positive for CD24 (heat stable antigen [HSA]) and CD43 (leukosialin), suggesting that the cells produced were blocked at a late pro-B-cell stage. Interestingly, although all FL + IL-7-responsive Lin-Sca-1+ progenitor cells and the resulting pro-B cells expressed c-kit, FL + IL-7 was much more potent (62-fold) than SCF + IL-7 in stimulating production of cells of the B-cell lineage. In addition, whereas FL + IL-7 selectively stimulated the production of pro-B cells, SCF + IL-7 predominantly stimulated the production of mature granulocytes. Replating studies showed that FL + IL-7-responsive Lin-Sca-1+ progenitors were not committed to the B-cell lineage, because after 2 days of incubation in FL + IL-7, 80% of the progenitors retained a myeloid potential. As much as 27% of the FL + IL-7-responsive progenitors remained uncommitted after 7 days of incubation, but all had committed to the B-cell lineage after 10 days of incubation in FL + IL-7. These results show that FL much more potently and selectively than SCF synergizes with IL-7 to enhance B-cell commitment and development from uncommitted progenitor cells.
authors.affiliation: Blood Cell Growth Factors Laboratory, Hipple Cancer Research Center, Dayton, OH 45439, USA.
authors.forename: O P
authors.initials: OP
authors.lastname: Veiby
authors.forename: S D
authors.initials: SD
authors.lastname: Lyman
authors.forename: S E
authors.initials: SE
authors.lastname: Jacobsen
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000502:physiology*; D000950:Antigens, Ly / Q000032:analysis; D001402:B-Lymphocytes / Q000166:cytology*; D001854:Bone Marrow Cells; D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004357:Drug Synergism; D006133:Growth Substances / Q000008:administration & dosage*; D006410:Hematopoiesis; D015851:Interleukin-7 / Q000008:administration & dosage*; D008565:Membrane Proteins / Q000008:administration & dosage* / Q000032:analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019009:Proto-Oncogene Proteins c-kit / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D018123:Receptors, Interleukin / Q000502:physiology*; D020395:Receptors, Interleukin-7; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000502:physiology; D051941:fms-Like Tyrosine Kinase 3
chemical_list: D015703:Antigens, CD; D000950:Antigens, Ly; D006133:Growth Substances; D015851:Interleukin-7; C074650:Ly6a protein, mouse; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D018123:Receptors, Interleukin; D020395:Receptors, Interleukin-7; D019089:Stem Cell Factor; C084881:flt3 ligand protein; C497971:Flt3 protein, mouse; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3