Murine monoclonal IgG3 antibodies to human colorectal tumor-associated antigens: production and characterization of antibodies active in both antibody-dependent cellular cytotoxicity and complement-mediated cytolysis

Murine monoclonal antibodies have been developed against human colorectal tumors using immunogens consisting of extracts from xenografted human colon carcinoma bound to lectin-conjugated agarose beads. Antibodies of the IgG3 isotype were selected from the resulting fusions, since we and other investigators have reported that this class of antibody can mediate antibody-dependent cellular cytotoxicity (ADCC). They were characterized with respect to specificity, ADCC activity, and complement-mediated cytolytic activity. One antibody, NR-Co-01, was produced using wheat germ agglutinin-agarose, whereas NR-Co-03, NR-Co-04, and NR-Co-05 were independently derived after immunization with a Dolichos biflorus lectin-agarose carrier. All four antibodies reacted intensely with the cytoplasm and cell surface of colonic adenocarcinomas and showed a restricted normal tissue reactivity. Recognition of epithelial cells in some normal adult tissues was revealed by immunoperoxidase staining of frozen tissues. No binding was found to normal lymphocytes, monocytes, granulocytes, and erythrocytes by immunofluorescence flow cytometry. All four of the antibodies were reactive with neutral glycolipids partitioned by Folch extraction of human colon carcinoma cell lines and also with a glycoprotein extracted from ovarian cyst mucin, suggesting that they may recognize one or more carbohydrate structures. The NR-Co-01, NR-Co-03, NR-Co-04, and NR-Co-05 are potent inducers of ADCC with human peripheral blood mononuclear effector cells and of complement-mediated cytolysis with human complement. However, they exhibited no ADCC activity with nude or normal mouse peripheral blood mononuclear cells at target:effector ratios ranging from 40:1 to 160:1. Their tumor reactivity, restricted normal tissue distribution, and ability to direct ADCC and complement-mediated cytolysis make these antibodies promising candidates for cancer therapy.