Recognition of Ovarian Cancer Antigen CAI 25 by Murine Monoclonal Antibody Produced by Immunization of Lung Cancer Cells

In studies aimed at developing monoclonal antibodies against lung adenocarcinomas, we produced a murine monoclonal antibody designated 130-22 by immunizing mice with lung cancer cells. Since in immunoperoxidase staining experiments this antibody was reactive not only with lung adenocarcinomas but also with ovarian carcinomas, we examined its relationship to the ovarian cancer marker CAI25, an antigen recognized by monoclonal antibody OC12S produced by immunization of mice with ovarian carcinoma cells. Although CAI25 antigen was adsorbed by 13022 antibody, I2sl-labeled 130-22 did not compete with (HI 25, indicating that although these two antibodies recognized CAI25 antigen, they reacted with separate antigenic determinants. The antigen defined by both antibodies was thought to be heat-labile glycoprotein with a molec ular weight of over 1,000,000. A series of immunoradiometric assays was developed using combinations of two monoclonal antibodies in a simul taneous forward sandwich mode. Mixed monoclonal antibodies may provide a more sensitive assay for the detection of CAI25 than the homologous assay, in which OC 125 was used both as a tracer and as a catcher. These results indicate that CAI 25 is an antigen with two separate epitopes present in both ovarian and lung adenocarcinomas and that combination use of monoclonal antibodies reactive with different antigenic determinants will give certain advantages to the immunoradiometric assay of cancer markers.