Recognition of ovarian cancer antigen CA125 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 CA125, an antigen recognized by monoclonal antibody OC125 produced by immunization of mice with ovarian carcinoma cells. Although CA125 antigen was adsorbed by 130-22 antibody, 125I-labeled 130-22 did not compete with OC125, indicating that although these two antibodies recognized CA125 antigen, they reacted with separate antigenic determinants. The antigen defined by both antibodies was thought to be heat-labile glycoprotein with a molecular weight of over 1,000,000. A series of immunoradiometric assays was developed using combinations of two monoclonal antibodies in a simultaneous forward sandwich mode. Mixed monoclonal antibodies may provide a more sensitive assay for the detection of CA125 than the homologous assay, in which OC125 was used both as a tracer and as a catcher. These results indicate that CA125 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.