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

• Published in: Blood Vol. 88; no. 4; pp. 1256 - 1265
• Main Authors: Veiby, O P, Lyman, S D, Jacobsen, S E
• Format: Journal Article
• Language: English
• Published: United States 15.08.1996
• Subjects: Animals; Antigens, CD - physiology; Antigens, Ly - analysis; B-Lymphocytes - cytology; Bone Marrow Cells; Cell Differentiation; Cell Division - drug effects; Cells, Cultured; Drug Synergism; fms-Like Tyrosine Kinase 3; Growth Substances - administration & dosage; Hematopoiesis; Interleukin-7 - administration & dosage; Membrane Proteins - administration & dosage; Membrane Proteins - analysis; Mice; Mice, Inbred C57BL; Proto-Oncogene Proteins - physiology; Proto-Oncogene Proteins c-kit - physiology; Receptor Protein-Tyrosine Kinases - physiology; Receptors, Interleukin - physiology; Receptors, Interleukin-7; Signal Transduction; Stem Cell Factor - physiology
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.v88.4.1256.bloodjournal8841256

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.