Immunochemical characterization of the antigen recognized by the murine monoclonal antibody A7 against human colorectal cancer.

The nature of the antigen recognized by the murine monoclonal antibody A7 (Mab A7) against human colorectal carcinoma was investigated using immunochemical and biochemical techniques. Binding activity of 125I-labeled Mab A7 was examined using various human cancer cell lines. Mab A7 gave the highly specific binding to colon cancer cell lines, SW1116 and WiDr, and gave only a very weak or no reactivity to gastric cancer cell lines, pancreas cell lines or lung cancer cell lines. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting of the extractable antigen from SW1116 showed a single band at approximately 45,000 dalton formed by 125I-labeled Mab A7. Treatment of SW1116 with sodium periodate, pronase and ficin resulted in the loss of antigenic activity. These data strongly suggest that the antigen recognized by Mab A7 is composed of glycoprotein. Competitive binding analysis to the surface of the colon cancer cell line using polyclonal anti-CEA and Mab A7 as well as immunoblotting analysis using monoclonal anti-CEA and Mab A7 suggested that the antigen recognized by Mab A7 was different from CEA. Moreover, this antigen was also found in surgical specimens of colorectal cancer patients and its molecular property was identical to the antigen extracted from SW1116.