[Analysis of tumor-associated antigen of the digestive tract by monoclonal antibody].

A sandwich enzyme immunoassay was established for measuring an adenocarcinoma-associated antigen (antigen YH206) detected by monoclonal antibody YH206. A level of antigen YH206 exceeding the cut-off value (25 U/ml) was found in the following proportions of 136 patients with digestive organ cancers: stomach cancer 37.2%, colon cancer 14.8%, pancreas cancer 43.3%, common bile duct cancer 28.6%. In contrast, only one out of 33 (3.0%) healthy donors and 7 of 104 (6.7%) patients with benign diseases had slightly elevated levels of the antigen. It was also found that perchloric acid treatment of serum might be useful for decreasing any false-positive reactions. The YH206 antigen was then purified by affinity chromatography using MoAb YH206-coupled CNBr-Sepharose. This antigen was not recognized by MoAb CA19-9. Studies on the chemical nature of the antigenic determinant of the YH206 antigen suggested that MoAb YH206 recognized a unique carbohydrate determinant of a novel adenocarcinoma-associated antigen in the sera of cancer patients. In addition, a new monoclonal antibody BM2 (IgM) was established using YH206 antigen as an immunogen. This antibody might be more useful than antibody YH206 in the detection of circulating antigen in the sera of patients with digestive tract cancer.