New meningococcal C polysaccharide-tetanus toxoid conjugate

Higher mass meningococcal group C-tetanus toxoid vaccines conjugated with carbodiimide correlate with greater immunogenicity

To examine the link between meningococcal C (MenC) vaccine size and immunogenic response, a panel of MenC glycoconjugate vaccines were prepared differing in chain length, molar mass and hydrodynamic volume. The preparations consisted of different lengths of MenC polysaccharide (PS) covalently linked to monomeric purified tetanus toxoid (TT) carrier protein using the coupling reagent ethylcarbodiimide hydrochloride (EDC). Size exclusion chromatography with multi-angle light scattering (SEC-MALS) and viscometry analysis confirmed that the panel of MenC-TT conjugates spanned masses of 191,500 to 2,348,000 g/mol, and hydrodynamic radii ranging from 12.1 to 47.9 nm. The two largest conjugates were elliptical in shape, whereas the two smallest conjugates were more spherical. The larger conjugates appeared to fit a model described by multiple TTs with cross-linked PS, typical of lattice-like networks described previously for TT conjugates, while the smaller conjugates were found to fit a monomeric or dimeric TT configuration. The effect of vaccine conjugate size on immune responses was determined using a two-dose murine immunization. The two larger panel vaccine conjugates produced higher anti-MenC IgG1 and IgG2b titres after the second dose. Larger vaccine conjugate size also stimulated greater T-cell proliferative responses in an in vitro recall assay, although cytokines indicative of a T-helper response were not measurable. In conclusion, larger MenC-TT conjugates up to 2,348,000 g/mol produced by EDC chemistry correlate with greater humoral and cellular murine immune responses. These observations suggest that conjugate size can be an important modulator of immune response.

Mechanisms of depolymerization and activation of a polysialic acid and its tetramer by hydrogen peroxide

Naturally occurring polysialic acid (PSA), appropriately functionalized, has been widely used in different biological products. The present paper describes an original approach which enables to both activate and depolymerize the PSA, by reacting with hydrogen peroxide. In order to understand the mechanisms, we investigate the course of H2O2 reactions with the native PSA and with a simpler model, the tetrasialic acid (4SA). Three recurrent reactions were observed. First, we detected a very fast and irreversible decarbonylation at the reducing end of the polysaccharide. Then, the hydroxyl radicals (generated via the Fenton reaction) were responsible for the depolymerization of glycosidic linkages by substitution reactions. Finally, the oxidation of hydroxyl groups led to the formation of carbonyl groups and the carbohydrate's activation.

Glycosyltransferases in chemo-enzymatic synthesis of oligosaccharides

Many oligosaccharides are not commercially available, which limits studies focused on elucidation of glycan functions; therefore chemo-enzymatic methods to synthesize them can be very useful. Here, we describe the procedure to synthesize the Galα1-3GalNAcβ1-4GlcNAcβ-R (Gal-LDN) moiety, containing the Galα1-3GalNAc epitope found on the parasitic helminth Haemonchus contortus. An acceptor substrate providing a terminal N-acetylglucosamine was prepared by coupling the fluorescent hydrophobic aglycon, 2,6-diaminopyridine (DAP), to N,N'-diacetylchitobiose. By the subsequent action of recombinant Caenorhabditis elegans β1,4-N-acetylgalactosaminyltransferase the substrate was efficiently converted to GalNAcβ1-4GlcNAcβ-R (LDN-R). Since no recombinant α1,3-galactosyltransferase has been described that acts on terminal βGalNAc, we used bovine α1,3-galactosyltransferase to obtain a partial conversion of LDN-R to the Gal-LDN antigen. This method can be applied to synthesize any oligosaccharide, provided that specific glycosyltransferases are available, or related enzymes that can be pushed to elongate the selected acceptor.

Stability of seasonal influenza vaccines investigated by spectroscopy and microscopy methods

The stability of different seasonal influenza vaccines was investigated by spectroscopy and microscopy methods before and after the following stress-conditions: (i) 2 and 4 weeks storage at 25°C, (ii) 1 day storage at 37°C and (iii) one freeze-thaw cycle. The subunit vaccine Influvac (Solvay Pharma) and the split vaccine Mutagrip (Sanofi Pasteur) were affected by all stresses. The split vaccine Fluarix (GlaxoSmithKline) was affected only by storage at 25°C. The virosomal vaccine Inflexal V (Berna Biotech) was stable after the temperature stresses but aggregated after one freeze-thaw cycle. This study provides new insights into commercial vaccines of low antigen concentration and highlights the importance of using multiple techniques to assess vaccine stability.

Antibody- and cell-mediated immune responses to a synthetic oligosaccharide conjugate vaccine after booster immunization

Memory formation to CRM-neoglycoconjugate, a synthetic branched tetrasaccharide of Streptococcus pneumoniae type 14 polysaccharide (Pn14PS) that is conjugated to a CRM197 protein, was investigated using mice models. Mice were first immunized with the CRM-neoglycoconjugate and then boosted with either the same neoglycoconjugate or a native Pn14PS in order to investigate the effect of booster immunization. Boosting with the CRM-neoglycoconjugate resulted in increased levels of interleukin 5 (IL-5) in the serum on Day 1, followed by the appearance of high levels of specific anti-Pn14PS IgG antibodies on Day 7. Boosting with native Pn14PS resulted in neither IL-5 induction nor the generation of anti-Pn14PS IgG antibodies. In vitro (re)stimulation of spleen cells after booster injection with the neoglycoconjugate revealed the presence of IL-4 and IL-5. This was not seen in spleen cells obtained from mice boosted with the polysaccharide. When stimulated with heat-inactivated bacteria, however, the polysaccharide-boosted mice did have higher levels of IFN-γ and lower levels of IL-17 than both the CRM-neoglycoconjugate-boosted mice and the mock-immunized mice. In conclusion, neoglycoconjugate boosting is responsible for the activation of memory cells and the establishment of sustained immunity. Not only is a booster with native polysaccharide ineffective in inducing opsonic antibodies, but it also interferes with several immunoregulatory mechanisms.

AFCo1 as nasal adjuvant of capsular polysaccharide from Neisseria meningitidis serogroup C induces systemic and mucosal immune responses

Increasing emphasis is being placed on the mucosal administration of vaccines in order to stimulate mucosal as well as systemic responses. Findings from our group suggest that proteoliposome-derived cochleate (AFCo1) acts as a potent mucosal adjuvant. As an alternative to chemical conjugation, the current study aimed to determine the benefit of using AFCo1 to improve the mucosal and systemic immune responses to capsular polysaccharide of Neisseria meningitidis serogroup C (PsC), a model of a thymus-independent (TI) antigen. Therefore, intranasal (i.n.) immunization of 3 doses 1 week apart with AFCo1 plus PsC in mice was conducted. Highly specific anti-PsC IgA responses and an anti-PsC IgG response were obtained. The subclass pattern induced against PsC was similar to that induced with the meningococcal vaccine. In summary, AFCo1 as nasal adjuvant was demonstrated to be capable of eliciting mucosal and systemic specific responses against a TI antigen.

Chemoenzymatic synthesis of multivalent neoglycoconjugates carrying the helminth glycan antigen LDNF

Several parasitic helminthes, such as the human parasite Schistosoma mansoni, express glycoconjugates that contain terminal GalNAc beta1-4(Fuc alpha1-3)GlcNAc beta-R (LDNF) moieties. These LDNF glycans are dominant antigens of the parasite and are recognized by human dendritic cells via the C-type lectin DC-SIGN. To study the functional role of the LDNF antigen in interaction with the immune system, we have developed an easy chemoenzymatic method to synthesize multivalent neoglycoconjugates carrying defined amounts of LDNF antigens. An acceptor substrate providing a terminal N-acetylglucosamine was prepared by coupling a fluorescent hydrophobic aglycon, 2,6-diaminopyridine (DAP), to N,N'-diacetylchitobiose. By the subsequent action of recombinant Caenorhabditis elegans beta1,4-N-acetylgalactosaminyltransferase and human alpha1,3-fucosyltransferase VI (FucT-VI), this substrate was converted to the LDNF antigen. We showed that human FucT-VI has a relatively high affinity for the unusual substrate GalNAc beta1-4GlcNAc (LDN), and this enzyme was used to produce micromolar amounts of LDNF-DAP. The synthesized LDNF-DAP was coupled to carrier protein via activation of the DAP moiety by diethyl squarate. By varying the molar glycan:protein ratio, neoglycoconjugates were constructed with defined amounts of LDNF, as was determined by MALDI-TOF analysis and ELISA using an anti-LDNF antibody.

Characterization and immunogenicity of meningococcal group C conjugate vaccine prepared using hydrazide-activated tetanus toxoid

The steps to produce, purify and control an immunogenic Brazilian conjugate vaccine against group C meningococcus (MenCPS-TT) using hydrazide-activated tetanus toxoid were developed. The conjugation methodology reduced the reaction time easily allowing scale-up. One freeze-dried pilot vaccine lot purified by tangential filtration, showed satisfactory quality control results including safety and stability. The pilot vaccine was immunogenic in mice in a dose-dependent fashion generating a 10-20-fold rise in IgG response in mice. The vaccine also induced high bactericidal titers. Vaccine concentrations of 1 and 0.1 microg showed higher avidity indices, suggesting induction of immunologic memory. These results support initiation of Phase I clinical studies with the MenCPS-TT conjugate vaccine.