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

Abstract

Streptococcus pneumoniae serotypes 6A and 6B are two of the common causes of invasive pneumococcal diseases. Although capsular polysaccharide conjugates of these two serotypes are included in the leading 13-valent pneumococcal conjugate vaccine, its low immunogenicity and high threshold for manufacturing technology indicated the need for vaccine improvement. Structurally defined synthetic immunogens have potential in dealing with these problems. To this end, we built a library of capsular polysaccharide fragments through convergent chemical synthesis in [2 + 2], [4 + 4], [4 + 3], [4 + 2], and [4 + 1] coupling manners. The library is comprised of 18 glycan antigens from trisaccharides to pseudo-octasaccharides, derived from the capsular repeating phosphorylated pseudo-tetrasaccharide with or without phosphate. Eight of them were selected for mouse immunization and further immunological studies. Four pseudo-tetrasaccharides with terminal or bridging phosphate elicited opsonic antibodies, which exhibited bactericidal activities and moderate cross-reactivities.

Chemical Synthesis of Truncated Capsular Oligosaccharide of Serotypes 6C and 6D of Streptococcus pneumoniae with Their Immunological Studies

“…Therefore, oligosaccharides 8 and 12 are not considered to be candidate vaccine antigens in this study. Three synthetic oligosaccharide antigens each for ST6C ( 5 – 7 ) and ST6D ( 9 – 11 ) were incorporated onto the carrier protein CRM197 following the procedure described previously . The resulting glycoconjugates ( C1 – C3 and D1 – D3 ) were analyzed by MALDI-TOF mass spectrometry to determine the average glycan percentage (Table ).…”

“…B1 and B2 antisera were also observed but not strong either in SPn6A. 48 In this study, we measured the cross-opsonic antibodies from ST6A and ST6B antisera with the bacteria SPn6C and SPn6D. The cross-opsonic antibodies in A1 and A2 antisera were observed, however, not strong in SPn6C; however, the cross-opsonic antibodies in A2 antisera were significantly higher than that in A1 antisera in SPn6D (Figure 5A).…”

“…In previous studies, the antibodies from ST6A and ST6B did not recognize the glycans that are composed of Gal-Glc-Rha-Rbo-phosphate, similar to oligosaccharides 8 and 12 . Therefore, oligosaccharides 8 and 12 are not considered to be candidate vaccine antigens in this study.…”

“…Moreover, our previously synthesized ST6A and ST6B vaccines (1−4; Figure 2A,2B) were included in this study. 48 These oligosaccharide antigens were conjugated to carrier proteins for immunological evaluation in a mouse model, and the mouse antisera were analyzed for glycan binding intensity and bactericidal activity in cross-reactivity. constructed through sequential glycosylation from the nonreducing end.…”

“…Identifying the minimal epitope can help avoid redundant epitope preparation, resulting in significant cost savings during the manufacturing process. Moreover, the synthetic oligosaccharides offer a well-defined structure and stable purity, which supply significant advantages over CPS fragment mixtures obtained from natural sources in terms of vaccine development and the improvement of vaccine. , Although in studies, various lengths of oligosaccharides related to ST6A and ST6B have been synthesized and their immunological properties were tested, − none of them studied the role of the phosphate group and complete immunological studies for serogroup 6. Further, research on the synthesis of oligosaccharide and immemorial studies of ST6C and ST6D have been relatively limited to the best of our knowledge.…”