title: Flt3 ligand induces proliferation of quiescent human bone marrow CD34+CD38- cells and maintains progenitor cells in vitro.
abstract: Flt3 is a class III tyrosine kinase receptor expressed on primitive human and murine hematopoietic progenitor cells (HPC). In previous studies using stroma-free short term assays, Flt3 ligand (FL) has been shown to induce proliferation of HPC at proportions similar to or less than c-kit ligand (steel factor, SF). Using long term stromal cocultivation assays, we studied the effects of FL on proliferation and differentiation of a highly primitive and cytokine nonresponsive subpopulation of human HPC, CD34+cd38- cells. Cell Proliferation was significantly greater with FL than with SF, when used individually or in combinations with interleukin-3 (IL-3) and/or IL-6. The effect of FL was greater on bone marrow (BM) CD34+CD38- cells than the more cytokine responsive cord blood CD34+CD38- cells. Little or no effect was seen with FL on more mature CD34+CD38+ cells from either BM or cord blood. The frequency of colony-forming units (CFU) and high proliferative potential-colony forming cells (HPP-CFC) during early culture ( < or = 30 days) was increased by both SF and FL to similar levels. However, in the LTC-IC period (35 to 60 days) and extended long-term culture initiating cell (ELTC-IC) period ( > 60 days), the frequency of CFU and HPP-CFC was significantly greater in cultures containing FL than those without FL (P < .0025). Fluorescence-activated cell sorter analysis of cultures after 21 days showed a significantly higher percentage of cells remained CD34+ in the combination of FL, IL-3, IL-6, and SF (F/3/6/S) than in 3/6/S (0.78% +/- 0.52% v 0.21% +/- 0.29% respectively, mean +/- SD). Cloning efficiency of BM CD34+CD38- cells was significantly increased by the addition of FL to the combination of 3/6/S (mean 11.7% v 0.5%, P < .0001). These data show that FL is able to induce proliferation of CD34+CD38-cells that are nonresponsive to other early acting cytokines and to improve the maintenance of progenitors in vitro.
authors.affiliation: Division of Hematology-Oncology, Childrens Hospital Los Angeles, CA 90027, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Shah
authors.forename: E M
authors.initials: EM
authors.lastname: Smogorzewska
authors.forename: C
authors.initials: C
authors.lastname: Hannum
authors.forename: G M
authors.initials: GM
authors.lastname: Crooks
mesh_terms: D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D015703:Antigens, CD; D018952:Antigens, CD34; D000943:Antigens, Differentiation; D001853:Bone Marrow / Q000276:immunology; D001854:Bone Marrow Cells; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000276:immunology; D006801:Humans; D016130:Immunophenotyping; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000494:pharmacology*; D009699:N-Glycosyl Hydrolases
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D000943:Antigens, Differentiation; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C084881:flt3 ligand protein; D009699:N-Glycosyl Hydrolases; D036541:ADP-ribosyl Cyclase; C498154:CD38 protein, human; D051997:ADP-ribosyl Cyclase 1