Engineering Affinity-Matured Variants of an Anti-Polysialic Acid Monoclonal Antibody with Superior Cytotoxicity-Mediating Potency

Abstract

Monoclonal antibodies (mAbs) that specifically recognize cell surface glycans associated with cancer and infectious disease hold tremendous value for basic research and clinical applications. However, high-quality anti-glycan mAbs with sufficiently high affinity and specificity remain scarce, highlighting the need for strategiesthat enable optimization of antigen-binding properties. To this end, we engineered the affinity of a polysialic acid (polySia)-specific antibody called mAb735, which possesses only modest affinity. Using a combination of rational design and directed evolution, we isolated several affinity-matured IgG variants with ~5-7-fold stronger affinity for polySia relative to mAb735. The higher affinity IgG variants opsonized polySia-positive cancer cells more avidly and triggered greater antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). Collectively, these results demonstrate the effective application of molecular evolution techniques to an important anti-glycan antibody, providing insights into its carbohydrate recognition and uncovering variants with greater therapeutic promise due to their enhanced affinity and potency.

Keywords: affinity maturation, cancer, capsular polysaccharides, carbohydrate, directed evolution, glycoprotein, glycosylation, monoclonal antibodies, tumor-associated carbohydrate antigen (TACA), yeast surface display