Immunohistochemical and biochemical characterization of the mucin-type tumor associated antigen TAG-12 by monoclonal antibody 7A9.

The reactivity of monoclonal antibody 7A9 with normal and neoplastic human tissues and some biochemical characteristics of the antigen (TAG-12) bound by 7A9 were evaluated. Antibody 7A9 showed broad reactivity with various carcinomas in paraffin sections. High percentages of positive tumor cells, displaying membrane and cytoplasmic staining, were noticed in adenocarcinomas of the breast (83/85), serous cystadenocarcinomas of the ovary (15/16), and lung adenocarcinomas (14/16). TAG-12 antigen was also detectable in normal adult and fetal tissues, but the reactivity of 7A9 was mainly restricted to the luminal surface of epithelial cells. For biochemical analyses, TAG-12 antigen purified from T47-D breast carcinoma cells by lectin affinity chromatography was treated with different glycosidases and proteases and analyzed by immunoblotting with 7A9. The data indicate that the antigen recognized by 7A9 is a heavily sialated mucin-type glycoprotein with a molecular weight of more than 200 KD. Similar to all other antibodies against tumor associated antigens, monoclonal antibody 7A9 is not tumor-specific but displays tissue staining patterns with a high carcinoma-to-normal ratio. The strong reactivity with the majority of tumor cells in several carcinoma types suggests that 7A9 is useful for in vitro and in vivo targeting of those tumors.