EXPRESSION OF TUMOR ASSOCIATED ANTIGENS ON HUMAN COLON CARCINOMA CELLS (HUMAN COLON CANCER, MONOCLONAL ANTIBODY)
Human colon cancer cells, LS180 and 174T, exhibit monoclonal antibody (mAb) 1083-17-1A and 5E113 defined tumor associated antigens. By radioimmunoassay, LS180 cells expressed the highest amount of mAb1083 defined antigens among the cell lines tested. Another mAb, 5E113, competed with mAb1083 for binding to LS180 cells, suggesting that both mAbs might bind onto identical (or adjacent) epitopes. By Scatchard analysis, about one million copies of the epitopes were present on LS180 colon cancer cells. The affinity of mAb1083 binding to the cells was 2.97 x 10('10) M('-1); the Sipsian heteroclonality value of mAb1083 was 0.9, thus approximating a single clone of reactive antibody. The qualitative studies showed that the epitopes were probably not carbohydrate because of their sensitivity to proteinases and not to mixed glucosidases and neuraminidase. The tunicamycin homologue B(,2) inhibited the incoporation of ('3)H-labeled galactose but not uptake of ('35)S-labeled methionine, nor expression of monoclonal antibody defined antigens providing further evidence to exclude the possibility of carbohydrate epitopes. There was evidence that the epitope might be partially masked in its "native" conformation, since short exposure or low dose treatment with proteases increased mAbs binding. The best detergent for antigen extraction, as detected by dot blotting and competitive inhibition assays, was octylglucoside at 30 mM concentration. Three methods, immunoprecipitation, Western blotting and photoaffinity labeling, were used to determine the molecular nature of the antigens. These results demonstrated that the antibody bound both 43 K daltons (KD) and 22 KD proteins. An in vitro cell-mediated immune approach was also used to attempt identifying function for the antigens. The strategy was to use mAbs to block cytotoxic effector cell killing. However, instead of blocking, the mAb1083 and 5E113 showed strong antibody-dependent cell-mediated cytotoxicities (ADCCs) in the in vitro xenoimmune assay system. In addition, cytotoxic T lymphocytes (CTLs), natural killer cells, and K cell activity were found. Since even the F(ab')2 fragment of mAbs did not inhibit the cytolytic effect, the mAbs defined antigens may not be major target molecules for CTLs. In summary, two molecular species of tumor antigen(s) were identified by mAbs to be present on colon tumor cell lines, LS180 and LS174T. (Abstract shortened with permission of author.)
PENG, CHENG, "EXPRESSION OF TUMOR ASSOCIATED ANTIGENS ON HUMAN COLON CARCINOMA CELLS (HUMAN COLON CANCER, MONOCLONAL ANTIBODY)" (1986). Texas Medical Center Dissertations (via ProQuest). AAI8700556.