CHARACTERIZATION OF A NOVEL BISPECIFIC ANTIBODY THAT MEDIATES FC-GAMMA RECEPTOR-TYPE I-DEPENDENT KILLING OF TUMOR-ASSOCIATED GLYCOPROTEIN-72-EXPRESSING TUMOR-CELLS

A bispecific antibody was made by chemical conjugation of Fab' fragmen ts from humanized antibodies specific for tumor-associated glycoprotei n-72 (TAG-72) and high-affinity immunoglobulin receptor, Fc gamma rece ptor type I(Fc gamma RI). The purified anti-TAG-72 x anti-Fc gamma RI (HCC49xH22) bispecific antibody had an approximate M-r of 111,000, con sistent with a F(ab')(2), and bound specifically to KLEB and LS174T tu mor cell lines, which express the TAG-72 tumor antigen. Furthermore, K CC49xH22 was shown to simultaneously bind to KLEB cells and a soluble Fc gamma RI fusion protein, demonstrating the bifunctional nature of t he molecule. Using IFN-gamma-treated monocytes as effector cells, conc entrations of the bispecific antibody in the range of 1-10,000 ng/ml m ediated specific lysis of TAG-72-positive tumor cells. In contrast, th e bispecific antibody did not promote antibody-dependent cellular cyto toxicity of a cell line that was negative for TAG-72 antigen, Importan tly, the antibody-dependent cellular cytotoxicity activity of the bisp ecific antibody was significantly greater than that of the monoclonal antibody HCC49. These in vitro data indicate that the humanized bispec ific antibody HCC49xH22 has the appropriate specificity and functional activity for Further evaluation as potential immunotherapy for TAG-72 -positive malignancies.