The Antitumor Monoclonal Antibody MOv2 Recognizes the Lewis A Hapten

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Abstract
Monoclonal antibody M0v2, produced against ovarian carcinoma, was previously found to bind a carbohydrate epitope (CAM0v2) present on mucins, glycoproteins and a neutral glycolipid. In this paper, the structure of the carbohydrate epitope is determined by immunological reactivity with purified glycolipids and oligosaccharides. Using solid-phase radioimmunoassay and immunostaining of thin layer chromatograms, M0v2 binds strongly to Lea-active pentasaccharide ceramide. A smaller neutral glycolipid also weakly binds M0v2. Fifty percent inhibition of binding to Lea-active pentasaccharide ceramide is achieved with approximately 8uM concentration of lacto-N-fucopentaose II (LNF II). Lacto-N-tetraose (LNT) also partially inhibits at about 103 times higher concentration suggesting that the faster migrating glycolipid antigen contains this carbohydrate sequence. Binding to Lea-active hapten is further confirmed by the specific inhibition of binding by authentic anti-Lea monoclonal antibodies but not by anti-Leb monoclonal antibodies. The correlation between Lea phenotype and reactivity of M0v2 antibody in a serum assay among healthy blood donors also supports these results. In conclusion, we have obtained direct evidence from several independent experiments that antibody M0v2 recognizes the Lea-active hapten.