The tyrosine residue at position 97 in the VH CDR3 region of a mouse/human chimeric anti-colorectal carcinoma antibody contributes hydrogen bonding to the TAG72 antigen

High-affinity chimeric anti-(colorectal carcinoma) antibody correlated to enhanced tumor targeting in biodistribution and imaging

The genetically engineered chimeric cB72.3m4 and cB72.3m12 antibodies recognize the same tumor-associated TAG72 antigen. The high-affinity cB72.3m4 antibody had an approximately 18-fold higher affinity constant for the TAG72 antigen than the low-affinity cB72.3m12 antibody. The relationship between antibody affinity and tumor targeting was studied by using these two antibodies. In biodistribution and imaging studies in athymic mice bearing LS174T human colon cancer xenografts, the radiolabelled high-affinity cB72.3m4 antibody was rapidly cleared from the blood, whereas the low-affinity cB72.3m12 antibody had slower blood clearance. The data showed that the high-affinity cB72.3m4 antibody appeared to localize more in tumors (based on tumor:normal-tissue ratios) than did the low-affinity cB72.3m12 antibody, and enhanced the target-to-nontarget image contrast. This study provides evidence that the high-affinity chimeric antibody cB72.3m4 may be useful in both immunodetection and immunotherapy of cancer.