Semisynthetic glycoconjugate vaccine candidate againstStreptococcus pneumoniaeserotype 5

Abstract

Glycoconjugate vaccines based on isolated capsular polysaccharide (CPS) save millions of lives annually by preventing invasive pneumococcal disease caused byStreptococcus pneumoniae. Some components of theS. pneumoniaeglycoconjugate vaccine Prevnar13 that contains CPS antigens from 13 serotypes undergo modifications or degradation during isolation and conjugation, resulting in production problems and lower efficacy. We illustrate how stable, synthetic oligosaccharide analogs of labile CPS induce a specific protective immune response against native CPS usingS. pneumoniaeserotype 5 (ST-5), a problematic CPS component of Prevnar13. The rare aminosugarl-PneuNAc and a branchedl-FucNAc present in the natural repeating unit (RU) are essential for antibody recognition and avidity. The epitope responsible for specificity differs from the part of the antigen that is stabilized by chemical modification. Glycoconjugates containing stable, monovalent synthetic oligosaccharide analogs of ST-5 CPS RU induced long-term memory and protective immune responses in rabbits superior to those elicited by the ST-5 CPS component in multivalent Prevnar13.