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Production and Characterization of a Tumor-Specific Monoclonal Antibody Act19 Recognizing an Epitope Distinctive from Sialosyl-Tn on the TAG72 Antigen

Aims A murine monoclonal antibody ACT19 directed at the TAG72 tumor-associated antigen, which was originally defined by the B72.3 antibody, was established. Methods This was done by immunizing mice with the bovine mucin followed by the selection of hybridomas secreting antibodies with the desired specificity. In order to better characterize this antibody, its immunoreactivity was compared to that of the B72.3 antibody. Results The data showed that the ACT19 antibody bound specifically to the TAG72 antigen as the B72.3 antibody did. However, there were some differences between ACT19 and B72.3. Firstly, the immunoreactivity of ACT19 for the bovine mucin was lower than that of B72.3. Secondly, the immunoreactivity of ACT19 for the TAG72 antigen was not inhibited by N-acetylgalactosamine, nor was that of B72.3. Thirdly, ACT19 did not compete the binding reactivity of B72.3 for the TAG72 antigen. This suggests that the epitope defined by ACT19 is different from the sialosyl-Tn epitope recognized by B72.3. Immunoperoxidase staining of various tumors, normal and embryonic tissues for ACT19 was carried out. For the various tumors, only adenocarcinomas from the colon and stomach showed remarkable positivity. All the normal tissues were negative, except for weak positivity involving the zona reticularis of the adrenal cortex, and intestinal goblet cells. Embryonic tissues showed a wide spectrum of positivity with staining of the small and large intestine, stomach and renal tubules. Conclusions The ACT19 antibody appears to be a useful marker for colon and stomach cancers, and this additional anti-TAG72 antibody may be useful in conjunction with the B72.3 antibody in pathology and clinical application.