Glycan Array Evaluation of Synthetic Epitopes between the Capsular Polysaccharides from Streptococcus pneumoniae 19F and 19A

Abstract

Vaccination represents the most effective way to prevent invasive pneumococcal diseases. The glycoconjugate vaccines licensed so far are obtained from capsular polysaccharides (CPSs) of the most virulent serotypes. Protection is largely limited to the specific vaccine serotypes, and the continuous need for broader coverage to control the outbreak of emerging serotypes is pushing the development of new vaccine candidates. Indeed, the development of efficacious vaccine formulation is complicated by the high number of bacterial serotypes with different CPSs. In this context, to simplify vaccine composition, we propose the design of new saccharide fragments containing chemical structures shared by different serotypes as cross-reactive and potentially cross-protective common antigens. In particular, we focused on Streptococcus pneumoniae (Sp) 19A and 19F. The CPS repeating units of Sp 19F and 19A are very similar and share a common structure, the disaccharide ManNAc-β-(1→4)-Glc (A-B). Herein, we describe the synthesis of a small library of compounds containing different combinations of the common 19F/19A disaccharide. The six new compounds were tested with a glycan array to evaluate their recognition by antibodies in reference group 19 antisera and factor reference antisera (reacting against 19F or 19A). The disaccharide A-B, phosphorylated at the upstream end, emerged as a hit from the glycan array screening because it is strongly recognized by the group 19 antisera and by the 19F and 19A factor antisera, with similar intensity compared with the CPSs used as controls. Our data give a strong indication that the phosphorylated disaccharide A-B can be considered a common epitope among different Sp 19 serotypes.

Synthetic Library of Oligosaccharides Derived from the Capsular Polysaccharide of Streptococcus pneumoniae Serotypes 6A and 6B and Their Immunological Studies

“…The antisera were collected 10 days after the third shots. Then, specific IgG from the antisera were analyzed under a glycan microarray − against all the synthetic glycan antigens we prepared in this study (Figure B,C; Figure S1–3). Briefly, the synthetic oligosaccharides were immobilized onto glass slides, and all the glycans were included in one single chamber, enabling high throughput identification of glycan-binding antibodies.…”

Serum antibody screening using glycan arrays

“…151 This indicates that the GroP moiety is the main recognition element for this anti-WTA mAb. 151 Glycan microarrays have also been used to assess antibody recognition of the capsular polysaccharides (CPSs) of the Grampositive bacteria S. pneumoniae [152][153][154][155] Clostridium difficile, and Bacillus anthracis. 148,156,157 The CPSs of S. pneumoniae, which serve as a critical virulence factor, vary between serotypes.…”

Strengths and weaknesses of pneumococcal conjugate vaccines

“…Furthermore, the antibodies were able to kill both strains of pneumococci [ 63 ]. Other researchers have synthesized a small library of compounds containing different combinations of the common disaccharide ManNAc-β-(1→4)-Glc present in the repeating unit of Spn-19F and 19A, demonstrating with a microarray format that the disaccharide phosphorylated at the upstream end is strongly recognized by antibodies in reference sera of rabbits immunized against either Spn-19F or Spn-19A [ 64 ].…”