Neisseria meningitidis serogroup A capsular polysaccharide (MenA CPS) consists of (1 → 6)-2-acetamido-2-deoxy-α-D-mannopyranosyl phosphate repeating units, O-acetylated at position C3 or C4. Glycomimetics appear attractive to overcome the CPS intrinsic lability in physiological media, due to cleavage of the phosphodiester bridge, and to develop a stable vaccine with longer shelf life in liquid formulation. Here, we generate a series of non-acetylated carbaMenA oligomers which are proven more stable than the CPS. An octamer (DP8) inhibits the binding of a MenA specific bactericidal mAb and polyclonal serum to the CPS, and is selected for further in vivo testing. However, its CRM197 conjugate raises murine antibodies towards the non-acetylated CPS backbone, but not the natural acetylated form. Accordingly, random O-acetylation of the DP8 is performed, resulting in a structure (Ac-carbaMenA) showing improved inhibition of anti-MenA CPS antibody binding and, after conjugation to CRM197, eliciting anti-MenA protective murine antibodies, comparably to the vaccine benchmark.
Group B
Streptococcus
(GBS) is a Gram-positive
bacterium and the most common cause of neonatal blood and brain infections.
At least 10 different serotypes exist, that are characterized by their
different capsular polysaccharides. The Group B carbohydrate (GBC)
is shared by all serotypes and therefore attractive be used in a glycoconjugate
vaccine. The GBC is a highly complex multiantennary structure, composed
of rhamnose rich oligosaccharides interspaced with glucitol phosphates.
We here report the development of a convergent approach to assemble
a pentamer, octamer, and tridecamer fragment of the termini of the
antennae. Phosphoramidite chemistry was used to fuse the pentamer
and octamer fragments to deliver the 13-mer GBC oligosaccharide. Nuclear
magnetic resonance spectroscopy of the generated fragments confirmed
the structures of the naturally occurring polysaccharide. The fragments
were used to generate model glycoconjugate vaccine by coupling with
CRM197. Immunization of mice delivered sera that was shown to be capable
of recognizing different GBS strains. The antibodies raised using
the 13-mer conjugate were shown to recognize the bacteria best and
the serum raised against this GBC fragment-mediated opsonophagocytic
killing best, but in a capsule dependent manner. Overall, the GBC
13-mer was identified to be a highly promising antigen for incorporation
into future (multicomponent) anti-GBS vaccines.
Infections caused by Enterococcus spp. are a major concern in the clinical setting. In Enterococcus faecalis, the capsular polysaccharide diheteroglycan (DHG), composed of ß-D-galactofuranose-(1 → 3)-ß-D-glucopyranose repeats, has been described as an important virulence factor and as a potential vaccine candidate against encapsulated strains. Synthetic structures emulating immunogenic polysaccharides present many advantages over native polysaccharides for vaccine development. In this work, we described the synthesis of a library of DHG oligomers, differing in length and order of the monosaccharide constituents. Using suitably protected thioglycoside building blocks, oligosaccharides up to 8-mer in length built up from either Galf-Glcp or Glcp-Galf dimers were generated, and we evaluated their immunoreactivity with antibodies raised against DHG. After the screening, we selected two octasaccharides, having either a galactofuranose or glucopyranose terminus, which were conjugated to a carrier protein for the production of polyclonal antibodies. The resulting antibodies were specific toward the synthetic structures and mediated in vitro opsonophagocytic killing of different encapsulated E. feacalis strains. The evaluated oligosaccharides are the first synthetic structures described to elicit antibodies that target encapsulated E. faecalis strains and are, therefore, promising candidates for the development of a well-defined enterococcal glycoconjugate vaccine.
Additive controlled glycosylation reactions are used for the construction of α-(1,2)-glucosidic linkages, such as those featuring in E. faecalis lipoteichoic acid.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.