Localization of human GW-39 tumors in hamsters by radiolabeled heterospecific antibody to carcinoembryonic antigen.

The in vivo localization of radiolabeled heterospecific antibody to carcinoembryonic antigen (CEA) was inves tigated in a human colonie tumor-hamster host model. With the paired-labeled antibody technique, a significant and specific accumulation of goat anti-CEA immunoglobulin G (IgG) was observed in small tumors (<5.0 g) l day after injection. The level of anti-CEA IgG in the tumor sub sequently decreased but at a slower rate than that of normal IgG in the tumor and both normal and anti-CEA IgG in the reference tissues. The tumor/blood ratio for anti-CEA IgG was approximately four times greater than that for normal IgG 8 days after injection. Absorption of labeled anti-CEA IgG with CEA reduced markedly its preferen tial accumulation in tumors. Since larger tumors (>5.0 g) failed to show preferential uptake of anti-CEA IgG, it is suggested that circulating antigen and/or hamster anti body against CEA interfere with the accumulation of localizing antibody in larger tumors.