Differential Binding to Human Mammary and Nonmammary Tumors of Monoclonal Antibodies Reactive with Carcinoembryonic Antigen

Abstract

Splenic lymphocytes of mice immunized with membrane enriched fractions of human mammary carcinomas were fused with the NS-1 nonsecretor myeloma cell line. The resulting hybridomas were screened for the synthesis of immunoglobulins reactive with human mammary tumor associated antigens, and 2 IgG monoclonal antibodies (B1.1 and F5.5) were identified as being reactive with purified carcinoembryonic antigen (CEA). These antibodies were shown to bind to different epitopes on CEA based on their differential reactivities to 5 purified CEA preparations, and their differential binding to the surface of tumor cells derived from various organ sites. Monoclonal B1.1 bound equally to the surface of human breast, colon, and melanoma cell lines, and showed a differential binding to breast carcinoma vs. colon carcinoma cells. Monoclonals F5.5 and B1.1 were both used in immunoperoxidase studies with fixed tissue sections of a variety of histologic types of human mammary carcinomas and were shown to be reactive with 55% and 66%, respectively, of tumor masses.