A semisynthetic Streptococcus pneumoniae serotype 8 glycoconjugate vaccine

Abstract

Glycoconjugate vaccines based on capsular polysaccharides (CPSs) of pathogenic bacteria such as Streptococcus pneumoniae successfully protect from disease, but suffer from incomplete coverage, are troublesome to manufacture from isolated CPSs and lack efficacy against certain serotypes. Defined, synthetic oligosaccharides are an attractive alternative to isolated CPSs but require the identification of immunogenic and protective oligosaccharide antigens. Here, we describe a medicinal chemistry strategy based on a combination of automated glycan assembly (AGA), glycan microarray-based monoclonal antibody (mAb) reverse engineering and immunological evaluation in vivo to uncover a protective glycan epitope (glycotope) for S. pneumoniae serotype 8 (ST8). All four tetrasaccharide frameshifts of ST8 CPS were prepared by AGA and used in glycan microarray experiments to identify the glycotopes recognized by antibodies against ST8. One tetrasaccharide frameshift that was preferentially recognized by a protective, CPS-directed mAb was conjugated to the carrier protein CRM197. Immunization of mice with this semisynthetic glycoconjugate followed by generation and characterization of a protective mAb identified protective and non-protective glycotopes. Immunization of rabbits with semisynthetic ST8 glycoconjugates containing protective glycotopes induced an antibacterial immune response. Co-formulation of ST8 glycoconjugates with the marketed 13-valent glycoconjugate vaccine Prevnar 13 yielded a potent 14-valent S. pneumoniae vaccine. Our strategy presents a facile approach to develop efficient semisynthetic glycoconjugate vaccines.

Improving vaccines against Streptococcus pneumoniae using synthetic glycans

“…in the chemical synthesis of complex glycans including automated glycan assembly (AGA) have made the synthesis of a variety of diverse oligosaccharides resembling the CPS of different serotypes possible. Active immunization of mice and rabbits with CRM197 conjugates with ST2 (17), ST3 (18), ST5 (9), ST8 (19), and ST14 (20, 21) elicits opsonic antibodies that were shown in some cases to be protective in challenge models of disease.…”

“…The medicinal chemistry approach has identified di-to tetrasaccharides as potential vaccine candidates (11). The immunogenicity of the CPS depends among other factors on rare sugars and labile functional groups (9,17,19). Stable oligosaccharide analogs can fix production problems such as those encountered for ST5 CPS due to the labile ketone present in the repeating unit (9).…”

“…Stable oligosaccharide analogs can fix production problems such as those encountered for ST5 CPS due to the labile ketone present in the repeating unit (9). Defined oligosaccharide antigens have been identified as vaccine candidates to protect against bacterial infections caused by S. pneumoniae, C. difficile, K. pneumoniae, and N. meningitides via the medicinal chemistry approach (3,16,19,22).…”

Engineering a new generation of carbohydrate-based vaccines

“…This method eases the creation of glycan microarrays, which are used to uncover immunodominant glycan epitopes (glycotopes) that can subsequently be incorporated into glycoconjugate vaccines. This strategy was first demonstrated by Schumann et al to design a vaccine that protects against S. pneumoniae serotype 8 [21]. Although prohibitive cost has generally limited AGA technology to microarray applications and prevented it from being used to synthesize sufficient quantities of carbohydrates for vaccination, further developments that streamline the process may increase its scalability [22].…”

A Semi‐Synthetic Glycoconjugate Vaccine Candidate for Carbapenem‐Resistant Klebsiella pneumoniae

“…Synthetic glycan antigens elicit a significantly stronger antibody response in rabbits when compared to mice. [34] Rabbits were immunized with CRM197- 1 conjugate formulated with alum, an adjuvant approved for use in humans. [35] The serological analysis using glycan microarrays and ELISA revealed that CRM197- 1 conjugate elicits a robust immune responses against native CR- Kp CPS (Supporting Information, Figure S3).…”