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

Characterization of pneumococcal conjugates in vaccine process development by multi-detection hydrodynamic chromatography

Pneumococcal conjugate vaccines (PCVs) are developed by conjugating pneumococcal polysaccharides to a carrier protein, such as CRM197. Size and molecular weight are important attributes of each monovalent conjugate in a PCV, making accurate monitoring of molecular weights crucial during the conjugation process. While size-exclusion chromatography (SEC) coupled with multi-angle light scattering (MALS), refractive index (RI), and ultraviolet (UV) detectors (SEC-MALS) is the gold standard used for absolute molecular weight characterization, this study presents the development of a multi-detection (MALS, UV and RI) hydrodynamic chromatography (HDC-MALS) method and its utility for comprehensive PCV characterization. The optimized HDC-MALS method is employed for in-depth understanding of vaccine conjugation process and effective characterization of heterogeneous, large conjugates through granular molar mass distribution analysis. Compared to other mild separation techniques such as field flow fractionation (FFF), HDC allows for high mobile phase flow rates without compromising separation efficiency, enabling faster run times that meet the demands of in-process control with rapid turn-around times.

Immunization of BALB/c mice with detoxified lipopolysaccharide and hydrolytic O-polysaccharide from Brucella melitensis either in combination with or conjugated to tetanus toxoid, enhances protective immune responses against the pathogen

Lipopolysaccharide (LPS) is the major surface antigen of Brucella, an intracellular pathogen that causes brucellosis in both animals and humans. A deeper understanding of the immune responses elicited by this key antigen may offer valuable insights for the development of effective vaccines for use in both humans and animals. In this study, detoxified LPS (d-LPS) and hydrolytic O-polysaccharide (OPS) from B. melitensis were prepared and separately conjugated to tetanus toxoid (TT) as a carrier protein. The resulting conjugates, d-LPS-TT and OPS-TT, as well as mixture of d-LPS+TT and OPS+TT, were used to immunize separate groups of BALB/c mice. The conjugated antigens induced significant IgG2a-specific serum responses targeting the polysaccharide components. Furthermore, mice immunized with d-LPS-TT and OPS-TT demonstrated elevated levels of IL-12 and IFN-γ following intraperitoneal challenge with B. melitensis 16 M. Notably, the strongest protective immune responses were observed in mice receiving the d-LPS-TT. Most previous studies have attributed protective responses primarily to specific serum antibodies. Although antibodies against Brucella polysaccharides typically associated with T-helper 2 (Th2) type responses, develop during infection, they are insufficient to eliminate the intracellular pathogen from the host. While the precise mechanism remain to be fully elucidated, our findings suggest that immunization with covalently conjugated polysaccharide antigens may promote T-helper 1(Th1) type cellular immunity, which appear to play a more pivotal role in protection against B. melitensis.

Further Insights into the Measurement of Free Polysaccharide in Meningococcal Conjugate Vaccines

Objectives: The purpose of this study was to further characterize the ultrafiltration (UF) method for determining free saccharide levels in glycoconjugate vaccines and compare it with other methods used for the determination of free saccharide levels in meningococcal glycoconjugate vaccines. Methods: We performed experiments on both meningococcal glycoconjugates and capsular polysaccharides, and compared UF, deoxycholate (DOC) precipitation, and solid-phase extraction (SPE) methods. Meningococcal capsular polysaccharides from groups A (MenA), C (MenC), and W (MenW) were depolymerized and characterized using SEC-MALS (size-exclusion chromatography with multi-angle laser light scattering) to determine the molecular weight and hydrodynamic size and then subjected to UF. The free saccharide content was quantified using HPAEC-PAD (high-performance anion-exchange chromatography with pulsed amperometric detection). Results: The characterization of size-reduced group C polysaccharide revealed weight-average molecular mass (Mw) ranging from 22,200 g/mol to 287,300 g/mol and hydrodynamic radii of 3.7 to 19.5 nm. Pore size studies confirmed that polysaccharides with diameters up to 15 nm filtered through the 100 kDa cellulose membrane. The smallest PS fragment tested (22,200 g/mol, 7.4 nm diameter) was partially recovered from the 30 kDa membrane. For MenC-CRM197, DOC yielded the lowest free saccharide content (<1%), UF gave moderate results (7-8%), and SPE showed the highest and most variable values (up to 15%). For MenA- and MenW-CRM197, UF and DOC consistently provided low free saccharide levels (<2% and 3-11%, respectively). Conclusions: The upper limits on the size of free group C meningococcal polysaccharides that can be ultrafiltered were assessed. Differences in the relative amount of free saccharide were observed between various methods used to control meningococcal conjugate vaccines.

Decoration of Burkholderia Hcp1 protein to virus-like particles as a vaccine delivery platform

Virus-like particles (VLPs) are protein-based nanoparticles frequently used as carriers in conjugate vaccine platforms. VLPs have been used to display foreign antigens for vaccination and to deliver immunotherapy against diseases. Hemolysin-coregulated proteins 1 (Hcp1) is a protein component of the Burkholderia type 6 secretion system, which participates in intracellular invasion and dissemination. This protein has been reported as a protective antigen and is used in multiple vaccine candidates with various platforms against melioidosis, a severe infectious disease caused by the intracellular pathogen Burkholderia pseudomallei. In this study, we used P22 VLPs as a surface platform for decoration with Hcp1 using chemical conjugation. C57BL/6 mice were intranasally immunized with three doses of either PBS, VLPs, or conjugated Hcp1-VLPs. Immunization with Hcp1-VLPs formulation induced Hcp1-specific IgG, IgG1, IgG2c, and IgA antibody responses. Furthermore, the serum from Hcp1-VLPs immunized mice enhanced the bacterial uptake and opsonophagocytosis by macrophages in the presence of complement. This study demonstrated an alternative strategy to develop a VLPs-based vaccine platform against Burkholderia species.

Optimization of the Process for Preparing Bivalent Polysaccharide Conjugates to Develop Multivalent Conjugate Vaccines against Streptococcus pneumoniae or Neisseria meningitidis and Comparison with the Corresponding Licensed Vaccines in Animal Models

OBJECTIVE

This study aimed to describe, optimize and evaluate a method for preparing multivalent conjugate vaccines by simultaneous conjugation of two different bacterial capsular polysaccharides (CPs) with tetanus toxoid (TT) as bivalent conjugates.

METHODS

Different molecular weights (MWs) of polysaccharides, activating agents and capsular polysaccharide/protein (CP/Pro) ratio that may influence conjugation and immunogenicity were investigated and optimized to prepare the bivalent conjugate bulk. Using the described method and optimized parameters, a 20-valent pneumococcal conjugate vaccine and a bivalent meningococcal vaccine were developed and their effectiveness was compared to that of corresponding licensed vaccines in rabbit or mouse models.

RESULTS

The immunogenicity test revealed that polysaccharides with lower MWs were better for Pn1-TT-Pn3 and MenA-TT-MenC, while higher MWs were superior for Pn4-TT-Pn14, Pn6A-TT-Pn6B, Pn7F-TT-Pn23F and Pn8-TT-Pn11A. For activating polysaccharides, 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) was superior to cyanogen bromide (CNBr), but for Pn1, Pn3 and MenC, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC) was the most suitable option. For Pn6A-TT-Pn6B and Pn8-TT-Pn11A, rabbits immunized with bivalent conjugates with lower CP/Pro ratios showed significantly stronger CP-specific antibody responses, while for Pn4-TT-Pn14, higher CP/Pro ratio was better. Instead of interfering with the respective immunological activity, our bivalent conjugates usually induced higher IgG titers than their monovalent counterparts.

CONCLUSION

The result indicated that the described conjugation technique was feasible and efficacious to prepare glycoconjugate vaccines, laying a solid foundation for developing extended-valent multivalent or combined conjugate vaccines without potentially decreased immune function.

Characterization of High Molecular Weight Pneumococcal Conjugate by SEC-MALS and AF4-MALS

Infections by Streptococcus pneumoniae can cause serious pneumococcal diseases and other medical complications among patients. Polysaccharide-based vaccines have been successfully developed as prophylactic agents against such deadly bacterial infections. In the 1980s, PNEUMOVAX® 23 were introduced as the first pneumococcal polysaccharide vaccines (PPSV). Later, pneumococcal polysaccharides were conjugated to a carrier protein to improve immune responses. Pneumococcal conjugate vaccines (PCV) such as PREVNAR® and VAXNEUVANCE™ have been developed. Of the more than 90 pneumococcal bacteria serotypes, serotype 1 (ST-1) and serotype 4 (ST-4) are the two main types that cause invasive pneumococcal diseases (IPD) that could lead to morbidity and mortality. Development of a novel multi-valent PCV against these serotypes requires extensive biophysical and biochemical characterizations of each monovalent conjugate (MVC) in the vaccine. To understand and characterize these high molecular weight (Mw) polysaccharide protein conjugates, we employed the multi-angle light scattering (MALS) technique coupled with size-exclusion chromatography (SEC) separation and asymmetrical flow field flow fractionation (AF4). MALS analysis of MVCs from the two orthogonal separation mechanisms helps shed light on the heterogeneity in conformation and aggregation states of each conjugate.

Glycoconjugate vaccines against Salmonella enterica serovars and Shigella species: existing and emerging methods for their analysis

The global spread of enteric disease, the increasingly limited options for antimicrobial treatment and the need for effective eradication programs have resulted in an increased demand for glycoconjugate enteric vaccines, made with carbohydrate-based membrane components of the pathogen, and their precise characterisation. A set of physico-chemical and immunological tests are employed for complete vaccine characterisation and to ensure their consistency, potency, safety and stability, following the relevant World Health Organization and Pharmacopoeia guidelines. Variable requirements for analytical methods are linked to conjugate structure, carrier protein nature and size and O-acetyl content of polysaccharide. We investigated a key stability-indicating method which measures the percent free saccharide of Salmonella enterica subspecies enterica serovar Typhi capsular polysaccharide, by detergent precipitation, depolymerisation and HPAEC-PAD quantitation. Together with modern computational approaches, a more precise design of glycoconjugates is possible, allowing for improvements in solubility, structural conformation and stability, and immunogenicity of antigens, which may be applicable to a broad spectrum of vaccines. More validation experiments are required to establish the most effective and suitable methods for glycoconjugate analysis to bring uniformity to the existing protocols, although the need for product-specific approaches will apply, especially for the more complex vaccines. An overview of current and emerging analytical approaches for the characterisation of vaccines against Salmonella Typhi and Shigella species is described in this paper. This study should aid the development and licensing of new glycoconjugate vaccines aimed at the prevention of enteric diseases.

Immunochemical characteristics of Streptococcus pneumoniae type 3 capsular polysaccharide glycoconjugate constructs correlate with its immunogenicity in mice model

A panel of derivatives were prepared from Streptococcus pneumoniae polysaccharide type 3 (Ps3) modified with adipic acid dihydrazide (ADH). The degree of coupling between Ps3-adh derivatives and diphtheria (DTd) or tetanus (TTd) toxoids was varied by ADH linker loading. A series of Ps3 derivatives and the resultant glycoconjugates (GC) were tested for their immunochemical activity in an ELISA. Antigenic properties of components in GCs were estimated by interaction with serotype-specific and toxin-neutralizing antibodies to confirm the preservation of native protective epitopes both of Ps3 and DTd. After immunization of mice, a correlation was established between immunochemical activity and immunogenicity of these GCs. A correlation model developed for Ps3-DTd conjugates allowed to predict the immunogenicity of similar design Ps3-TTd conjugates based on ELISA testing data. The plausibility of this prediction was confirmed by the test immunization of mice with Ps3-TTds. The proposed immunochemical approach to the assessment and control of native structural and functional antigenic elements in GCs is important for the optimization of vaccine design and is an adequate alternative to extensive physicochemical characterization for assessing immunogenicity.