Radioimmunodetection of human tumor xenografts by monoclonal antibodies.

Mouse IgG2a monoclonal antibodies with specific binding reactivity in vitro to human tumors of the gastrointestinal tract were radioiodinated and injected into immunosuppressed mice xenografted with human colon carcinoma tumors. The antibodies preferentially localized in tumor tissue compared to normal mouse tissue, as determined by differential tissue counting of radioactivity. Preferential antibody localization in tumor tissue was greatly enhanced when F(ab')2 fragments of the antibodies were used, and the fragments localized specifically only in those tumors that bind the antibodies in vitro and not in unrelated tumors. Radiolabeled fragments of an anti-hepatitis virus monoclonal antibody of the same isotype as the specific antibody did not localize in tumors. Tumors could be located by whole-body gamma-scintigraphy with radiolabeled specific antibody F(ab')2 fragments without background subtraction.