Phagocytosis of tumor cells by human monocytes cultured in recombinant macrophage colony-stimulating factor.

Abstract

SummaryMacrophages 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 .

Differential Effect of Cytokine Treatment on Fcα Receptor I- and Fcγ Receptor I-Mediated Tumor Cytotoxicity by Monocyte-Derived Macrophages

“…The development of stable dyes and new methods has been essential to study this phenomenon in vitro. We have adapted a flow cytometry method, initially described by Munn and Cheung (27), to study tumor cell phagocytosis by MDM Fc␣RI and Fc␥RI. This twocolor method employs a red lypophilic dye to stain SKBR-3 carcinoma cells, and FITC-conjugated mAbs to label MDM.…”

“…BsAb-mediated phagocytosis of SKBR-3 cells by (MDM) was examined by a modification of the method described by Munn and Cheung (27). Briefly, monocytes, purified from normal adult source Leukopacs (Advanced Biotechnologies, Columbia, MD), were differentiated in 24-well plates in macrophage serum-free medium (Life Technologies, Grand Island, NY) supplemented with 10% FBS and either M-CSF (2 ng/ml; R&D Systems, Minneapolis, MN), GM-CSF (10 ng/ml; R&D Systems), or IFN-␥ (1000 U/ml; Genzyme, Cambridge, MA) for 5-10 days.…”

Bypassing tumor-specific and bispecific antibodies: triggering of antitumor immunity by expression of anti-FcγR scFv on cancer cell surface

“…FITC-CD14 + /CD64 + macrophages also exhibiting red fluorescence were considered as phagocytic cells or tumor cell/macrophage doublets. Percentage of phagocytosis was calculated using the following formula: 38,39 (FITC + PKH26 + cells (37°C) Ϫ FITC + PKH26 + cells (4°C)) × 100/FITC + PKH26 -cells (37°C) + FITC + PKH26 + cells (37°C) Ϫ FITC + PKH26 + cells (4°C).…”

Differentiation of Human Monocytes In Vitro: A Model of Macrophage Ontogeny

“…Addition of M-CSF and GM-CSF to serum results in a better survival rate and stimulates the capacity for antibody-dependent and antibody-independent cytotoxicity (Suzu et al 1989;Young et al 1990;Munn and Cheung 1990;Eischen et al 1991). In addition, both…”

“…In vitro it has been shown that different types of macrophages are generated from monocytes depending on the culture conditions (Munn and Cheung 1990;Ruppert and Peters 1991;Kreutz et al 1992). Most likely both mechanisms are responsible for macrophage heterogeneity (Rutherford etal.…”