title: Modulation of haematopoietic progenitor development by FLT-3 ligand.
abstract: The Flt-3 receptor is expressed in primitive haematopoietic cells and its ligand exerts proliferative effects on these cells in vitro in synergy with other cytokines. To increase our knowledge of the functional properties of the human Flt-3 ligand (FL) as relating to in vitro expansion of haematopoietic stem cells, the effects on murine haematopoiesis of FL alone or in combination with other growth factors were studied. Analysis of Flk-2/Flt-3 mRNA expression indicated that Flk-2/Flt-3 was preferentially expressed in primitive haematopoietic cell populations. To examine the expression of the Flk-2/Flt-3 receptor on megakaryocyte progenitors (CFU-Meg), Flk-2/Flt-3 positive and negative CD34(+)populations were separated from human bone marrow and cultured in a plasma clot culture system. CFU-Meg colonies were found in the Flk-2/Flt-3 negative fraction. Myeloid (CFU-GM) derived colonies appeared in the presence of FL alone. Neither FL+IL-3 nor FL+IL-3+IL-6 had any effect on the generation of megakaryocyte colonies (CFU-MK), due to the lack of FL receptor expression on megakaryocyte progenitors. Bone marrow cells remaining after 5-fluorouracil (5-FU) treatment of mice represent a very primitive population of progenitors enriched for reconstituting stem cells. This cell population expressed FL receptors, as revealed by RT-PCR analysis. Addition of FL alone did not enhance the replication of such cells in liquid cultures as compared to controls. However, a significantly greater generation of myeloid progenitors (CFU-GM) in clonogenic assays was observed in the presence of FL+IL-3, FL+GM-CSF or FL+CSF-1. In addition, the effects of FL on in vitro expansion of murine haematopoietic stem cells were studied using lineage-negative (lin(-)) Sca-1 positive (Sca-1(+)) c-kit positive (c-kit(+)) marrow cells from 5-FU treated mice. FL enhanced the survival of primitive murine lin(-)Sca-1(+)c-kit(+)cells. FL and IL-6 were able to significantly expand murine progenitor stem cells in vitro and promote their survival. These studies strongly suggest that FL significantly and selectively enhanced the generation of myeloid progenitors in vitro and increased myeloid progenitor responsiveness to later acting growth factors. In addition, FL synergized with IL-6 to support in vitro expansion of haematopoietic progenitors and promoted the survival of lin(-)Sca-1(+)c-kit(+)cells.
authors.affiliation: Division of Experimental Medicine, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA.
authors.forename: N
authors.initials: N
authors.lastname: Banu
authors.forename: B
authors.initials: B
authors.lastname: Deng
authors.forename: S D
authors.initials: SD
authors.lastname: Lyman
authors.forename: H
authors.initials: H
authors.lastname: Avraham
mesh_terms: D000818:Animals; D001855:Bone Marrow Diseases / Q000139:chemically induced / Q000473:pathology; D019070:Cell Lineage; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D004790:Enzyme Induction / Q000187:drug effects; D005472:Fluorouracil / Q000633:toxicity; D016298:Hematopoietic Cell Growth Factors / Q000494:pharmacology; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects*; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D008533:Megakaryocytes / Q000166:cytology; D008565:Membrane Proteins / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D011518:Proto-Oncogene Proteins / Q000187:drug effects*; D012333:RNA, Messenger / Q000096:biosynthesis; D020794:Receptor Protein-Tyrosine Kinases / Q000187:drug effects*; D011994:Recombinant Proteins / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051941:fms-Like Tyrosine Kinase 3
chemical_list: D016298:Hematopoietic Cell Growth Factors; D007377:Interleukin-3; D015850:Interleukin-6; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; C084881:flt3 ligand protein; C497970:FLT3 protein, human; C497971:Flt3 protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3; D005472:Fluorouracil