Isolation and Characterization of Neisseria meningitidis Groups A, C, X, and Y Polysaccharide Antigens

An efficient cell free enzyme-based total synthesis of a meningococcal vaccine candidate

Invasive meningococcal disease (IMD) is a global health problem and vaccination has proven the most effective way of disease control. Neisseria meningitidis serogroup X (NmX) is an emerging threat in the African sub-Saharan meningitis belt, but no vaccine is available today. Leading vaccines against Nm are glycoconjugates, in which capsular polysaccharides isolated from large-scale pathogen cultures are conjugated to adjuvant proteins. Though safe and efficacious even in infants, high costs and biohazard associated with the production limit abundant application of glycoconjugate vaccines particularly in the most afflicted nations. An existing NmX vaccine candidate (CPSXn-CRM₁₉₇) produced by established protocols from NmX capsule polysaccharide (CPSX) has been shown to elicit high bactericidal immunoglobulin G titres in mice. Here we describe the scalable in vitro synthesis of CPSXiv from chemically pure precursors by the use of recombinant NmX capsule polymerase. Application of the described coupling chemistry gives CPSXiv-CRM₁₉₇, which in mouse vaccination experiments behaves identical to the benchmark CPSXn-CRM₁₉₇. Excluding any biohazards, this novel process represents a paradigm shift in vaccine production and a premise towards vaccine manufacturing in emerging economies.

Development of a glycoconjugate vaccine to prevent meningitis in Africa caused by meningococcal serogroup X

Neisseria meningitidis is a major cause of bacterial meningitis worldwide, especially in the African meningitis belt, and has a high associated mortality. The meningococcal serogroups A, W, and X have been responsible for epidemics and almost all cases of meningococcal meningitis in the meningitis belt over the past 12 y. Currently no vaccine is available against meningococcal X (MenX). Because the development of a new vaccine through to licensure takes many years, this leaves Africa vulnerable to new epidemics of MenX meningitis at a time when the epidemiology of meningococcal meningitis on the continent is changing rapidly, following the recent introduction of a glycoconjugate vaccine against serogroup A. Here, we report the development of candidate glycoconjugate vaccines against MenX and preclinical data from their use in animal studies. Following optimization of growth conditions of our seed MenX strain for polysaccharide (PS) production, a scalable purification process was developed yielding high amounts of pure MenX PS. Different glycoconjugates were synthesized by coupling MenX oligosaccharides of varying chain length to CRM197 as carrier protein. Analytical methods were developed for in-process control and determination of purity and consistency of the vaccines. All conjugates induced high anti-MenX PS IgG titers in mice. Antibodies were strongly bactericidal against African MenX isolates. These findings support the further development of glycoconjugate vaccines against MenX and their assessment in clinical trials to produce a vaccine against the one cause of epidemic meningococcal meningitis that currently cannot be prevented by available vaccines.

Characterization of size, structure and purity of serogroup X Neisseria meningitidis polysaccharide, and development of an assay for quantification of human antibodies

Serogroup X Neisseria meningitidis (MenX) has recently emerged as a cause of localized disease outbreaks in sub-Saharan Africa. In order to prepare for vaccine development, MenX polysaccharide (MenX PS) was purified by standard methods and analyzed for identity and structure by NMR spectroscopy. This study presents the first full assignment of the structure of the MenX PS using (13)C, (1)H and (31)P NMR spectroscopy and total correlation spectroscopy (TOCSY) and (1)H-(13)C heteronuclear single quantum coherence (HSQC). Molecular size distribution analysis using HPLC-SEC with multi-angle laser light scattering (MALLS) found the single peak of MenX PS to have a weight-average molar mass of 247,000g/mol, slightly higher than a reference preparation of purified serogroup C meningococcal polysaccharide. MenX PS tended to be more thermostable than serogroup A PS. A method for the quantification of MenX PS was developed by use of high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). A novel and specific ELISA assay for quantification of human anti-MenX PS IgG based on covalent linkage of the MenX PS to functionally modified microtitre plates was developed and found valid for the assessment of the specific antibody concentrations produced in response to MenX vaccination or natural infection. The current work thus provides the necessary background for the development of a MenX PS-based vaccine to prevent meningococcal infection caused by bacteria bearing this capsule.

The meningococcus and mechanisms of pathogenicity

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Microbial carbohydrate specific antibodies distinguish between different stages of differentiating mouse cerebellum

High titered anticarbohydrate antibodies were used to identify cell surface carbohydrates during different stages in histogenesis of mouse cerebellum in a micro tissue-culture system which mimics selected features of in vivo cerebellum development. Blockage of fiber formation within the first few days in vitro and inhibition of cell migrations by carbohydrate-specific antibodies served as an assay system for possible contributions of surface carbohydrates to the behavior of developing cerebellar cells. Microbial strains were selected on the basis of carbohydrate structures of their cell wall antigens, and anticarbohydrate antibodies were raised against treated whole bacteria and yeast in rabbits. We found that antibodies to mannan were active at all stages of development tested (embryonic day 13, E13; the day of birth, PO; and postnatal day 7, P7). Antibodies to sialic acids prepared against strains B and C of Neisseria meningitidis distinguish different subterminal structures: anti-B reacted with E13 and PO cerebellar cells, and anti-C mostly with cells older than P7. Antifetuin antibody recognized E13 and PO but not P7 cell populations. Pneumococcus C strain R36A-specific antibodies were effective only after coating cells to C type carbohydrate before application of the antibody. The results demonstrate that antimicrobiol carbohydrate antibodies cross-react with mammalian cell surface carbohydrate structures and therefore can be used as a powerful tool in tissue culture to analyse those structures which might control cell behaviors pertinent to cerebellar development.

Immunological and biochemical studies of meningococcal C polysaccharides isolated by diethylaminoethyl chromatography

Meningococcal C polysaccharides isolated from the broth supernatant of C1+ and C1- strains by a combination of Sepharose 4B and diethylaminoethyl-52 chromatography are antigenically identical to the group C antigen isolated by the Cetavlon procedure. Immunizations result in the induction of precipitating, hemagglutinating, and bactericidal antibodies in rabbits and sheep and hemagglutinating and bactericidal antibodies in rabbits and sheep and hemagglutinating and bactericidal antibodies in gerbils. Selective destruction of C1- polysaccharides with neuraminidase has demonstrated that these antibodies are directed against the C polysaccharide. Neuraminidase digestions of the C1- polysaccharides resulted in release of up to 84% of the antigen as N-acetylneuraminic acid. C1+ polysaccharides proved to be more resistant to neuraminidase, requiring greater concentrations of enzyme and longer intervals of exposure for digestion. Chemical analysis of the C1+ and C1- polysaccharides indicated that they contain less than 0.5% protein and less than 0.5% nucleic acid.

Effect of pneumococci on blood clotting, platelets, and polymorphonuclear leukocytes

Infections due to Streptococcus pneumoniae and products from the organism have been associated with alterations in blood clotting and function of platelets. Pneumococci and pneumococcal polysaccharide shortened the clotting times of whole blood, platelet-rich plasma (PRP), and platelet-poor plasma (PPP) in vitro. Clotting times of PPP and PRP from C6-deficient animals were likewise decreased. The bacteria had no effect on the one-stage prothrombin time or the partial thromboplastin time when the organisms were used as activating agents. Platelets aggregated in the presence of pneumococci, but aggregation was prevented by the addition of cyclic adenosine 3', 5'-monophosphate (cAMP). Furthermore, cAMP corrected the shortened clotting time of PRP in the presence of pneumococci. The clumping and release of polymorphonuclear coagulant that was induced by pneumococci was not prevented by cAMP. Thus, pneumococci exert several dose-dependent thromboplastic effects: (i) release of platelet thromboplastic substances; (ii) a direct thromboplastic effect; and (iii) release of polymorphonuclear coagulant.

Latex agglutination in the diagnosis of meningococcal meningitis

Group-specific polysaccharides of Neisseria meningitidis groups A and C have been demonstrated by means of a rapid, sensitive slide agglutination test with latex particles coated with antibodies. In this manner, the diagnosis can be made from the cerebrospinal fluid of patients with meningococcal meningitis caused by serogroups A or C even when the culture is negative. The method appears to be more sensitive than countercurrent immunoelectrophoresis and less elaborate.

Physicochemical properties of Neisseria meningitidis group X polysaccharide antigen

Neisseria meningitidis group X occurs in human carrier populations and is rarely implicated in serious disease. This organism possesses a capsular group antigen which is an acidic polysaccharide. It is composed of the amino sugars, glucosamine, glucosamine-6-phosphate, galactosamine, and the simple hexose, glucose. The group X capsular antigen has an S(20,w) (0) of 3.6, and the acidic nature of the polysaccharide is reflected in an isoelectric point of 3.65. The meningococcal A, B, C, and Y polysaccharide group antigens are also composed primarily of amino sugars. The chemical composition of the group X antigen most closely resembles the capsular antigen of N. meningitidis group Y, which is also predominately a carrier organism.

Cross-protective antigens of Neisseria meningitidis obtained from Slaterus group Y

An extraction of the cells of Neisseria meningitidis serogroup Y with an aqueous solution of calcium choride (0.9 m) has been shown to solubilize a number of antigens. By immunodiffusion, this mixture of antigens has been shown to react with its group-specific antiserum and also to cross-react with a number of other group-specific antisera. The cross-reacting antigen appears to be an antigen common to a number of other serogroups of meningococci, and there is some evidence that it is protein in nature. It has been demonstrated further that the calcium chloride extract contains a strong cross-protective antigen, as shown by its ability to provide good, active immunity in mice to both the homologous and heterologous serogroups of meningococci.