Monoclonal antibodies against CEA. Comparison of the immunoprecipitates by fingerprint analysis

By fusion of C3H mouse spleen cells, immunized with a PCA extract from liver metastases of a colon tumor, and Sp2/O-Ag14 myeloma cells, we produced several clones secreting monoclonal antibodies (MAb) with reactivity against carcinoembryonic antigen (CEA). For the screening of the different MAb, an ELISA technique with PCA extract and highly purified CEA coupled with alkaline phosphatase was employed. The specificities of the MAb prescreened with the ELISA technique were analyzed further by immunoprecipitation and separation on SDS-PAGE, followed by enzyme digestion and thin-layer chromatography for fingerprint analysis. The MAb recognized (a) an antigenic determinant present only on CEA, (b) common determinants present on CEA and at least six other molecules separated by SDS-PAGE and (c) antigenic determinants not present on CEA. The fingerprint analysis showed the relationship of the molecules on the basis of protein chemistry.