Radioimmunolocation of a heterotransplanted human choriocarcinoma (BeWo) using monoclonal anti-SSEA-1: pharmacokinetics.

Stage-Specific Embryonic Antigen-1 (SSEA-1), originally discovered on mouse teratocarcinomas, has since been found on some human non-seminomatous germ-cell tumors and adenocarcinomas, as well as on some adult mouse and human tissues. A monoclonal antibody to this antigen (anti-SSEA-1; IgM, kappa) was used for radioimmunolocation. Nude mice bearing the human choriocarcinoma BeWo, which is SSEA-1 positive, were injected using a mixture of [131I]anti-SSEA-1 and [125I]MOPC 104E, an unselected myeloma protein of the same heavy-chain isotype. Animals were sacrificed at 24 hour intervals; the radioactive deposition due to both antibodies was determined for both tumors and normal organs. Accumulation of anti-SSEA-1 in the tumor was consistantly rapid and specific, while little accumulation of the unselected myeloma protein occurred. At five days after injection, an average of 3% of the initial dose of specific antibody was retained per gram of tumor; the tumor/blood ratio was 11, tumor/muscle was 80. Gamma-camera imaging allowed ready location of the tumors. Tumors could also be imaged using F(ab')2 antibody fragments.