Generation of a Monoclonal Antibody (G9) Reactive with an Organ-specific, Tumor-associated Epitope of Human Colon Carcinoma

Abstract

A monoclonal antibody (G9), having an organ-specific and tumor-associated reactivity with colon carcinoma, has been generated. Monoclonal antibody G9 is an IgG1 immunoglobulin produced by immunization of mice with mucin which had been purified from a liver metastasis of a moderately differentiated human colon carcinoma. Examination of normal adult tissues, by enzyme immunoassay and immunohistochemical procedures, showed the G9-reactive epitope to be restricted to the gastrointestinal tract. Within the gastrointestinal tract the colon produced the highest amount of the epitope. A sharp, decreasing gradient of reactivity was observed, ending in the small intestine. Although the normal colonic epithelium did produce the G9-reactive determinant, there was a significant quantitative increase of the epitope in neoplastic colonic tissue; mucins derived from normal colon contained less than 10% of the specific epitope as compared with mucins derived from colon cancer tissues (P < 0.01). In addition, a tumor xenograft contained 100 times the amount of epitope as did normal colonic tissue. By immunohistochemical procedures 70% of all colon carcinomas were positive. A relationship with differentiation was noted, with 80% of well differentiated and 83% of moderately differentiated tumors being positive, whereas only 1 of 6 poorly differentiated tumors were stained. The organ specificity was noted in neoplastic as well as normal tissues. Monoclonal antibody G9 was nonreactive with breast, lung, and ovarian tumors. The data suggest that at the level of sensitivity obtained by the immunoassays used, and within the range of tissues examined, monoclonal antibody G9 is organ specific and highly tumor associated in its reactivity.