Radiolocalization of human mammary tumors in athymic mice by a monoclonal antibody.

Monoclonal antibody B6.2 reacts with a protein found on the surface of primary and metastatic human mammary tumors. B6.2 immunoglobulin G (IgG) was purified, F(ab')2 and Fab' fragments were generated by pepsin digestion, and the IgG and its fragments were radiolabeled with 125I; all were successful in localizing human mammary tumors transplanted into athymic mice, with tumor:tissue ratios increasing over a 4-day period. The 125I-labeled IgG gave tumor:spleen, tumor:liver, and tumor:kidney ratios of greater than 10:1 and tumor:brain and tumor:muscle ratios of 50:1 to 110:1. The F(ab')2 fragment gave higher tumor:tissue ratios than did the IgG, with tumor:liver and tumor:spleen ratios of 15:1 to 20:1. No localization of the labeled B6.2 monoclonal antibody or its fragments was observed in athymic mice bearing a human melanoma or with isotype-identical control immunoglobulin or its fragments in athymic mice bearing the mammary tumors. Imaging experiments confirmed the ability of radiolabeled monoclonal antibody B6.2 and its fragments to detect the presence of transplanted human mammary tumor lesions of less than 0.4 cm without the aid of background subtraction manipulations.