Anti-Lea monoclonal antibody SPM 522 recognizes an extended Lea epitope

Abstract

Insights into the differential binding characteristics of anti-Lea and anti-LeaLex monoclonal antibodies (mAbs) provide information to develop LeaLex-based cancer immunotherapeutics while avoiding anti-Lea autoimmune reactions. We characterized the epitope recognized by anti-Lea mAb SPM 522. We synthesized the Lea 6-aminohexyl glycoside and report experimental evidence of a minor conformation in solution. The Lea and three other 6-aminohexyl glycosides were conjugated to BSA and titration experiments with SPM 522 show that: 1. SPM 522 binds to LeaLex better than to Lea; 2. the non-reducing Lea galactosyl residue is essential to binding. Competitive ELISA experiments using a panel of tri- to pentasaccharide fragments of LeaLex as well as Lea analogues indicate that: 1. the Lea β-d-galactosyl α hydrophobic patch is crucial to binding; 2. the Lea fucosyl residue contributes to binding; 3. the Lexd-galactosyl residue also contributes to binding. These results indicate that anti-Lea mAb SPM 522 recognizes the Lea[1,3]-β-d-Gal tetrasaccharide. We propose that a major recognition element is the extended hydrophobic surface defined by the Lea-β-d-Gal residue extending to the α faces of the β-d-GlcNAc and β-d-Gal residues.