Radioimmunolocalization of monoclonal antibodies to human chorionic gonadotropin in choriocarcinoma transplanted into athymic mice.

Radioimmunodetection of monoclonal antibodies to human Chorionic Gonadotropin (hCG) or its beta-subunit in choriocarcinoma tissue was investigated in athymic mouse model system. Antibody to hCG exhibited a higher localization index (L.I.) in tumor tissue than those in other organs, but the tissue/blood ratio of this antibody in tumor tissue was not so high as expected (0.38 and 0.5 on Day 2 and 5 respectively). On the other hand, antibody to beta-subunit showed the same L.I. in tumor tissue as those in other organs. Gel filtration of serum of mouse given an antibody to hCG showed that the antibody was forming immune complexes in the blood stream. Autoradiography showed many grains in the capillary vessels and intercellular spaces in the tumor tissue. We concluded that a monoclonal antibody to hCG localized in choriocarcinoma tissue via a mechanism of retention of immune complexes in the tissue, and that there may be a limitation to the clinical application of localization of antibodies to secretory products such as hCG of tumor cells from their low specific localization.