Activation of Soluble Polysaccharides with 1-Cyano-4-Dimethylaminopyridine Tetrafluoroborate (CDAP) for Use in Protein-Polysaccharide Conjugate Vaccines and Immunological Reagents. III Optimization of CDAP Activation

Quantitation and characterization of serotype 6A activation for pneumococcal conjugate vaccine by cryo-EM and SEC methods

Pneumococcal conjugate vaccines (PCV) typically consist of capsular polysaccharides from different S. pneumoniae serotypes which are covalently attached to carrier protein. A well-established process to manufacture PCV is through activating polysaccharide by oxidation of vicinal diols to aldehydes, followed by protein conjugation via reductive amination. Polysaccharide activation is a crucial step that affects vaccine product critical attributes including conjugate size and structure. Therefore, it is highly desired to have robust analytical methods to well characterize this activation process. In this study, using pneumococcal serotype 6A as the model, we present two complimentary analytical methods for characterization of activated polysaccharide. First, a size exclusion chromatography (SEC) method was developed for quantitative measurement of polysaccharide activation levels. This SEC method demonstrated good assay characteristics on accuracy, precision and linearity. Second, a gold nanoparticle labeled cryo-electron microscopy (Cryo-EM) technique was developed to visualize activation site distribution along polysaccharide chain and provide information on activation heterogeneity. These two complimentary methods can be utilized to control polysaccharide activation process and ensure consistent delivery of conjugate vaccine products.

Effect of trifluoroacetic acid on the antigenicity of capsular polysaccharides obtained from various Streptococcus pneumoniae serotypes

Determining the safety, antigenicity, and immunogenicity by in vitro and in vivo studies is a prerequisite for the development of new vaccines. And this study investigated it for a vaccine made from Streptococcus pneumoniae serotypes 2, 5, 12F, 18C, and 22F. The crude CPS was purified and partially depolymerized by conventional and trifluoroacetic acid methods. 1H NMR analysis confirmed the identity of the depolymerized CPS which gave similar profiles to reference polysaccharides, except for serotype 18C which was de-O-acetylated during TFA treatment. The antigenicity of the depolymerized CPS prepared by either method was comparable to that of the native CPS for serotypes 2, 5, 18C, and 22F based on multiplex bead based competitive inhibition assay. This study demonstrated a relationship between antigenicity and immunogenicity, which offers more suitable candidates for conjugation. It was found that after partial depolymerization process, the CPS with optimal molecular size resulted in higher antigenicity. The immunogenicity of S. pneumoniae serotype 2 conjugates in mice was evaluated by opsonophagocytic assay and a multiplex bead-based assay, wherein on day 42 after immunization, the total and functional IgG titer was found to be increased by 32-fold.

Structural verification and new reactivity for Stang's reagent, [PhI(CN)][OTf]

The structure of Stang's reagent [PhI(CN)][OTf] is confirmed by X-ray crystallography and is determined to be best described as an ion-pair in organic solution. It is found to be a strong Lewis acid, but reaction with pyridine ligands gives [Pyr-CN][OTf] salts via oxidation of pyridine giving a new derivative of the CDAP reagent widely used as an activation agent for polysaccharides.

Transferrin binding protein-B from Neisseria meningitidis C as a novel carrier protein in glycoconjugate preparation: an in silico approach

The linking of polysaccharide in glycoconjugate vaccine with carrier protein is an imperative step to develop a strong memory response. The excessive use of similar carrier protein known to result in bystander immunity warrants an urgent need for new carrier protein. The preparation of the glycoconjugate vaccine using cyanylation chemistry is to link the active cyanate ester site of polysaccharide with the carrier protein. In the present study, transferrin binding protein-B (Tbp-B) has been explored as a new carrier protein to develop in silico pneumococcal polysaccharide serotype-5 (PnPs-5) conjugate vaccine. The homology model of Tbp-B was constructed using the Prime module and stereochemically validated using ProSA, PDBsum and ProQ. The selected model revealed a Z-score of -5.6 within the X-ray region in ProSA analysis, LGscore: 9.776, and MaxSub: 0.8 in protein quality predictor suggesting its preferred use. Loop modeling and active site analysis followed by in silico PnPs-5 activation with cyanalyting agent CDAP was docked with Tbp-B using Glide module. The complex stability of cyanate esters with Tbp-B, analyzed by molecular dynamics (MD) simulation, revealed an average RMSD of 2.49 Å for its binding to the receptor. The RMSF values of cyanate ester-1, -2, and -3 were observed to be 1.06, 1.39 and 0.79 Å, respectively. The higher RMSF of 1.39 Å of cyanate ester-2 was further found unstable which corroborates its non-binding to the protein and also incurring conformational changes to a carrier protein. Molecular simulations revealed that cyanate ester-1 and cyanate ester-3 formed stable conjugates with carrier protein Tbp-B. Communicated by Ramaswamy H. Sarma.

Conjugation Mechanism for Pneumococcal Glycoconjugate Vaccines: Classic and Emerging Methods

Licensed glycoconjugate vaccines are generally prepared using native or sized polysaccharides coupled to a carrier protein through random linkages along the polysaccharide chain. These polysaccharides must be chemically modified before covalent linking to a carrier protein in order to obtain a more defined polysaccharide structure that leads to a more rational design and safer vaccines. There are classic and new methods for site-selective glycopolysaccharide conjugation, either chemical or enzymatic modification of the polysaccharide length or of specific amino acid residues of the protein carrier. Here, we discuss the state of the art and the advancement of conjugation of S. pneumoniae glycoconjugate vaccines based on pneumococcal capsular polysaccharides to improve existing vaccines.

A novel pneumococcal protein-polysaccharide conjugate vaccine based on biotin-streptavidin

Pneumococcal disease is a serious public health problem worldwide and an important cause of morbidity and mortality among children and adults in developing countries. Although vaccination is among the most effective approaches to prevent and control pneumococcal diseases, approved vaccines have limited protective effects. We developed a pneumococcal protein-polysaccharide conjugate vaccine that is mediated by the non-covalent interaction between biotin and streptavidin. Biotinylated type IV capsular polysaccharide was incubated with a fusion protein containing core streptavidin and Streptococcus pneumoniae virulence protein and relying on the non-covalent interaction between biotin and streptavidin to prepare the protein-polysaccharide conjugate vaccine. Analysis of vaccine efficacy revealed that mice immunized with the protein-polysaccharide conjugate vaccine produced antibodies with high potency against virulence proteins and polysaccharide antigens and were able to induce Th1 and Th17 responses. The antibodies identified using an opsonophagocytic assay were capable of activating the complement system and promoting pathogen elimination by phagocytes. Additionally, mice immunized with the protein-polysaccharide conjugate vaccine and then infected with a lethal dose of Streptococcus pneumoniae demonstrated induced protective immunity. The data indicated that the pneumococcal protein-polysaccharide (biotin-streptavidin) conjugate vaccine demonstrated broad-spectrum activity applicable to a wide range of people and ease of direct coupling between protein and polysaccharide. These findings provide further evidence for the application of biotin-streptavidin in S. pneumoniae vaccines.