Differential effects of a stem cell factor-immunoglobulin fusion protein on malignant and normal hematopoietic cells.
We genetically connected the extracellular domain of human stem cell factor to the Fc-portion of human IgG1. The chimeric recombinant stem cell factor IgG1 fusion protein (rSCF-IgG1) had an apparent approximately Mr 190,000 and consisted of three identical covalently linked subunits. It specifically bound to c-kit and the high affinity Fc gamma receptor, respectively. Liquid phase rSCF-IgG1 was, on a molar basis, about eight times more potent than native human rSCF in stimulating the proliferation of c-kit-positive leukemic cell lines and of nonmalignant CD34-positive hematopoietic progenitor cells. Although the effective dose conferring half maximum of [methyl-3H]thymidine uptake by liquid phase and solid phase-bound rSCF-IgG1 were comparable, the plateau level of [methyl-3H]thymidine uptake by malignant cells was decreased by the latter, whereas proliferation of nonmalignant progenitor cells was supported. Liquid phase rSCF-IgG1 had a 2-fold increased potential to maintain primitive nonmalignant progenitor cells in stroma-free long-term culture compared with rSCF. Liquid phase rSCF-IgG1 caused enhanced and prolonged receptor phosphorylation and a more rapid down modulation of c-kit. Our data support the concept that solid phase-attachment of rSCF-IgG1 is sufficient for alteration of biological function and that rSCF-IgG1 partially blocks SCF-stimulated malignant cell growth while supporting normal progenitor cells.
Erben
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U
Department of Hematology, Oncology and Transfusion Medicine, Universitaetsklinikum Benjamin Franklin, Berlin, Germany.
Thiel
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Notter
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M
D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D019337:Hematologic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D006412:Hematopoietic Stem Cells / Q000187:drug effects*; D006801:Humans; D018796:Immunoconjugates / Q000235:genetics / Q000494:pharmacology*; D007141:Immunoglobulin Fc Fragments / Q000235:genetics / Q000494:pharmacology; D007074:Immunoglobulin G / Q000235:genetics / Q000494:pharmacology; D051379:Mice; D010766:Phosphorylation; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000494:pharmacology; D019089:Stem Cell Factor / Q000235:genetics / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D018796:Immunoconjugates; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D011993:Recombinant Fusion Proteins; D019089:Stem Cell Factor; D019009:Proto-Oncogene Proteins c-kit