A repertoire of monoclonal antibodies reveals extensive epitope heterogeneity in CEA purified from neoplasms originating from different organs

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Abstract
The heterogeneity of carcinoembryonic antigen (CEA) from 5 individual hepatic metastases of tumours originating in different organs (I colon, I stomach and 3 breast adenocarcinomas) was analyzed with a repertoire of 56 αCEA murine MAbs. In each tumour preparation, the MAbs disclosed 2 distinct molecular species displaying remarkable variability in their apparent molecular weights (e.g. 130–170 kDa for the fast‐migrating CEA variant and 180–260 kDa for the slowly‐migrating one). After chemical deglycosylation this heterogeneity was abolished and 2 main proteins of 84 and 64 kDa were generated; the difference in their molecular weights could not be accounted for by differential glycosylation. Although 3 of the analyzed preparations were derived from individual adenocarcinomas of the breast, the glycosylated molecules differed considerably from one another, in their relative molecular mass. The MAbs used showed essentially 3 different recognition patterns according to their reactivity either with both CEA molecular weight variants, or just with the higher or the lower one. In a quantitative comparison of the immunoprecipitation yields of the MAbs with CEA, considerable immunological variability (ranging up to 26‐fold), as well as preferential expression of CEA epitopes, could be demonstrated among the 5 different preparations. Here again no uniform epitope presentation could be observed among the 3 breast tumours thus far tested. Comparison of the precipitation yields with the glycosylated and deglycosylated CEA species revealed that, whereas the CEA antigenic heterogeneity remained in some cases unchanged, most of the MAbs exhibited, in carbohydrate‐free CEA, the appearance of a new heterogeneity.