Phagocytosis of tumor cells by human monocytes cultured in recombinant macrophage colony-stimulating factor.
Macrophages and cultured human monocytes can mediate efficient antibody-dependent cytotoxicity (ADCC) against human tumor cells using monoclonal antibodies (mAbs). The mechanism of this killing is usually assumed to involve secreted factors (reactive oxygen intermediates, tumor necrosis factor, or other cytotoxic factors) leading to target cell lysis. In this study, we present evidence that phagocytosis of intact target cells is the principal mechanism of antitumor cytotoxicity in our in vitro model of ADCC by cultured monocytes. Human monocytes cultured in recombinant human macrophage colony-stimulating factor ingested up to 100% of fluorochrome-labeled melanoma and neuroblastoma target cells, in the presence of an appropriate antitumor mAb. Electron microscopy demonstrated phagocytosis of intact tumor cells by cultured monocytes during ADCC. All of the radionuclide in radiolabeled target cells was taken up by monocytes during phagocytosis. By preventing the release of radioisotope tracers, phagocytosis thus prevents the detection of this very efficient form of cytotoxicity by most conventional assays.
Department of Pediatrics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
D H
DH
Munn
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NK
Cheung
D000911:Antibodies, Monoclonal / Q000276:immunology; D000920:Antibody-Dependent Cell Cytotoxicity / Q000276:immunology*; D002478:Cells, Cultured; D003115:Colony-Stimulating Factors; D005456:Fluorescent Dyes; D006801:Humans; D016173:Macrophage Colony-Stimulating Factor; D009000:Monocytes / Q000276:immunology* / Q000648:ultrastructure; D009369:Neoplasms / Q000276:immunology*; D009895:Opsonin Proteins; D010587:Phagocytosis / Q000276:immunology*; D011994:Recombinant Proteins; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D003115:Colony-Stimulating Factors; D005456:Fluorescent Dyes; D009895:Opsonin Proteins; D011994:Recombinant Proteins; D016173:Macrophage Colony-Stimulating Factor