The antitumor monoclonal antibody MOv2 recognizes the Lewis A hapten

Monoclonal antibody MOv2, produced against ovarian carcinoma, was previously found to bind a carbohydrate epitope (CAMOv2) 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, MOv2 binds strongly to Le(a)-active pentasaccharide ceramide. A smaller neutral glycolipid also weakly binds MOv2. Fifty percent inhibition of binding to Le(a)-active pentasaccharide ceramide is achieved with approximately 8 μM 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 Le(a)-active hapten is further confirmed by the specific inhibition of binding by authentic anti-Le(a) monoclonal antibodies but not by anti-Le(b) monoclonal antibodies. The correlation between Le(a) phenotype and reactivity of MOv2 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 MOv2 recognizes the Le(a)-active hapten.