An NMR spectroscopic identity test for the control of the capsular polysaccharide from Haemophilus influenzae type b

Monitoring bromide loss in bromoacetyl-derivatized polyribosylribitol polysaccharide in Haemophilus influenzae type b for PedvaxHIB® by capillary electrophoresis and NMR spectroscopy

PedvaxHIB® is an effective pediatric vaccine for protecting infants from invasive gram-negative bacterium Haemophilus influenzae type b. It is a highly purified capsular polysaccharide, polyribosylribitol phosphate that is covalently linked to an outer membrane protein complex of Neisseria meningitidis. PRP is first derivatized with an organic linker, followed by the coupling of a butadiamine group, and then at the end terminal, a bromoacetyl group is attached for conjugation with thiolated OMPC. The stability of the bromide group in derivatized PRP is monitored by two different methods, capillary electrophoresis and NMR spectroscopy. The loss of the bromide group is detected by measuring the amount of free bromide ion liberated using capillary electrophoresis and by observing a change in amide proton peaks near the bromide group using NMR. The two methods give similar rate hydrolysis results, therefore both can be employed as quick stability tools for bromoacetylation PRP content during manufacturing.

Reactivity characterization of bromoacetyl derivatized polyribosylribitol polysaccharide in Haemophilus influenzae type b for PedvaxHIB® by NMR spectroscopy

PedvaxHIB® is a highly purified capsular polysaccharide (polyribosylribitol phosphate or PRP) of Haemophilus influenzae type b (Hib) that is covalently linked to an outer membrane protein complex (OMPC) of Neisseria meningitidis pediatric vaccine. This Hib protein conjugate vaccine is very effective in protecting infants from invasive gram-negative bacterium Hib. Before conjugation of PRP to OMPC, PRP is first derivatized with butadiamine and bromoacetyl group which reacts with thiolated OMPC. This report describes an NMR method to analyze the reactivity of bromoacetyl group in derivatized PRP (BrAc-derivatized PRP) toward small molecule thiol group, 2-mercapto imidazole (MI) which is used as a surrogate for thiolated OMPC. Reaction with MI helped identify observable amide protons in BrAc-derivatized PRP according to presence or absence of bromine. Furthermore, the new method can be used to monitor the percent of bromoacetylation during manufacturing and potentially a stability indicating assay for loss of bromine in BrAc-derivatized PRP.

Cross-reactivity of Haemophilus influenzae type a and b polysaccharides: molecular modeling and conjugate immunogenicity studies

Haemophilus influenzae is a leading cause of meningitis disease and mortality, particularly in young children. Since the introduction of a licensed conjugate vaccine (targeting the outer capsular polysaccharide) against the most prevalent serotype, Haemophilus influenzae serotype b, the epidemiology of the disease has changed and Haemophilus influenzae serotype a is on the rise, especially in Indigenous North American populations. Here we apply molecular modeling to explore the preferred conformations of the serotype a and b capsular polysaccharides as well as a modified hydrolysis resistant serotype b polysaccharide. Although both serotype b and the modified serotype b have similar random coil behavior, our simulations reveal some differences in the polysaccharide conformations and surfaces which may impact antibody cross-reactivity between these two antigens. Importantly, we find significant conformational differences between the serotype a and b polysaccharides, indicating a potential lack of cross-reactivity that is corroborated by immunological data showing little recognition or killing between heterologous serotypes. These findings support the current development of a serotype a conjugate vaccine.

NMR characterization of a multi-valent conjugate vaccine against Neisseria meningitidis A, C, W, Y and Haemophilus influenzae b infections

Physicochemical technologies are a powerful tool for the structural characterization of vaccine antigens both at bulk level as well as on the final formulation. High-field Nuclear Magnetic Resonance (NMR) spectroscopy has been found to be an extremely and robust tool for tracking the industrial process manufacturing of carbohydrate-based vaccines. I have applied NMR spectroscopy to the characterization of a penta-valent conjugate vaccine against Neisseria meninigitidis group A, C, W, Y (MenACWY) and Haemophilus influenzae type b (Hib) infections, constituted of capsule derived polysaccharide fragments independently conjugated to CRM₁₉₇ protein carrier (CRM-MenA, CRM-MenC, CRM-MenW, CRM-MenY, CRM-Hib). ¹H NMR has been used for the identity testing of the carbohydrate antigens and of the vaccine formulation. The application of NMR-based assays on multivalent conjugate vaccines looks to be a promising approach for identity and stability analyses useful for future vaccines development.

Quantification of residual cetyltrimethylammonium bromide (CTAB) and sodium deoxycholate (DOC) in Haemophilus influenzae type b (Hib) polysaccharide using NMR

CTAB and DOC are used as reagents in the purification of Hib polysaccharide. Polysaccharide is purified by precipitation with CTAB from fermented broth followed by solvent extraction and DOC is used to remove the protein impurities. The reagents used in the purification process should be removed from the product as per regulatory requirements. These two residual reagents can be easily identified and quantified in purified Haemophilus influenzae type b polysaccharide by NMR. The LOD of these residual reagents is 0.1% (10 μg/mL) and LOQ is 0.5% (50 μg/mL) with respect to polysaccharide determined from the spectrum. The absence of the peaks corresponding to CTAB and DOC in the NMR spectrum of purified polysaccharide confirms either they are absent or present at less than 0.1%. The present study provides supporting data from the regulatory viewpoint, which can help in circumventing the time-consuming studies for the vaccine manufacturers to develop different analytical methods for identification and quantification of CTAB and DOC as per regulatory requirements.

Comparability studies of hemin from two different origins porcine and bovine in the production of Haemophilus influenzae type b (Hib) polysaccharide

Hemin is one of the critical components of medium required for growth of Haemophilus influenzae type b (Hib) organisms. It is important to have different sources of critical components to ensure continuous supply for commercial production. Regulatory bodies also recommend having multiple sources for critical components. Hemin is produced from animal blood and the main sources are porcine and bovine origin. The approved Hib vaccine of SIIPL used for immunization is produced using hemin obtained from porcine origin. The present work focuses on the comparison of the growth of organisms on a large scale using hemin from bovine or porcine origin. Purified polysaccharide obtained using bovine source is tested with respect to the set WHO specifications as recommended by regulatory bodies and compared with commercial lots of PRP obtained from using hemin of porcine source. Identical product profile and quality attributes were obtained for PRP produced using bovine hemin and the regular commercial product suggests that there is no change in the product. Hemin from bovine source can be used as a replacement for hemin from porcine source in the fermentation medium for country specific requirement of Hib conjugate vaccine as long as it meets the guidelines on TSE/BSE risk.

Nuclear Magnetic Resonance (NMR) Study for the Detection and Quantitation of Cholesterol in HSV529 Therapeutic Vaccine Candidate

This study describes the NMR-based method to determine the limit of quantitation (LOQ) and limit of detection (LOD) of cholesterol, a process-related impurity in the replication-deficient Herpes Simplex Virus (HSV) type 2 candidate vaccine HSV529. Three signature peaks from the 1D ¹H NMR of a cholesterol reference spectrum were selected for the identification of cholesterol. The LOQ for a cholesterol working standard was found to be 1 μg/mL, and the LOD was found to be 0.1 μg/mL. The identity of cholesterol, separated from the formulation of growth supplement by thin layer chromatography (TLC), was confirmed by 1D ¹H NMR and 2D ¹H-¹³C HSQC NMR. The three signature peaks of cholesterol were detected only in a six-times concentrated sample of HSV529 candidate vaccine sample and not in the single dose HSV529 vaccine sample under similar experimental conditions. Taken together, the results demonstrated that NMR is a direct method that can successfully identify and quantify cholesterol in viral vaccine samples, such as HSV529, and as well as in the growth supplement used during the upstream stages of HSV529 manufacturing.

A Synthetic Disaccharide Analogue from Neisseria meningitidis A Capsular Polysaccharide Stimulates Immune Cell Responses and Induces Immunoglobulin G (IgG) Production in Mice When Protein-Conjugated

Some new phosphonoester-linked oligomers, stabilized analogues of the corresponding phosphate-bridged oligomers of Neisseria meningitidis A (MenA) capsular polysaccharide (CPS), were conjugated to human serum albumin (HSA), as a protein carrier model, and studied for immunological activities. We determined (i) in vitro, their biocompatibility (CAM test) and activity in inducing both T cell proliferation (CFSE method) and IL-2 release (ELISA), and (ii) in vivo, their ability to stimulate specific IgG antibody production (ELISA). All HSA-conjugated compounds induce T cell proliferation (40% of proliferation at 10(2) μM), whereas only the phosphonodisaccharide was effective (28% of proliferation at 10(2) μM) among the unconjugated forms. IL-2 release confirmed these results. In addition, the HSA-conjugated showed in vivo the capacity of eliciting the production of specific IgG antibodies. In conclusion, we obtained novel biocompatible, water-stable, and immunoactive MenA CPS analogues. A short disaccharide fragment showed the unusual behavior of triggering T cell proliferation in vitro.

Characterization of Carbohydrate Vaccines by NMR Spectroscopy

Physicochemical techniques are a powerful tool for the structural characterization of carbohydrate-based vaccines. High-field Nuclear Magnetic Resonance (NMR) spectroscopy has been established as an extremely useful and robust method for tracking the industrial manufacturing process of these vaccines from polysaccharide bulk antigen through to the final formulation. Here, we describe the use of proton NMR for structural identity and conformity testing of carbohydrate-based vaccines.

Ensuring the quality, potency and safety of vaccines during preclinical development

There is an abundance of vaccines currently in development, with most of them exploring novel mechanisms, adjuvants and/or delivery systems not only for traditional prophylactic use, but also for therapeutic uses. As vaccines are generally administered to healthy individuals, ensuring their quality, potency and safety becomes crucial, especially prior to evaluation in humans. To ensure these key attributes, vaccine developers need to incorporate them as early in the development program as possible, starting in basic research and continuing through preclinical, clinical and postmarketing development. Fortunately for vaccine developers, ample guidance is available from various regulatory agencies to enlighten the long and arduous path of vaccine development. This review will highlight these regulatory expectations, and provide some clarity as to why they are in place.

Immunoactivity of protein conjugates of carba analogues from Neisseria meningitidis a capsular polysaccharide

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that is a major cause of epidemic meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of a liquid glycoconjugate vaccine against MenA are hampered by the poor hydrolytic stability of its capsular polysaccharide (CPS), consisting of (1→6)-linked 2-acetamido-2-deoxy-α-d-mannopyranosyl phosphate repeating units. The replacement of the ring oxygen with a methylene group to generate a carbocyclic analogue leads to enhancement of its chemical stability. Herein, we report conjugation of carbocyclic analogue monomer, dimer, and trimer to the protein carrier CRM197. After immunization in mice, only the conjugated trimer was able to induce specific anti-MenA polysaccharide IgG antibodies with in vitro bactericidal activity, although to a lesser extent than pentadecamer and hexamer oligomers obtained from mild acid hydrolysis of the native polysaccharide conjugated to the same protein carrier. This study represents the first proof-of-concept that hydrolytically stable structural analogues of saccharide antigens can be used for the development of efficacious antimicrobial preventative therapies. Conjugates with longer carbocyclic oligomers and/or precise acetylation patterns could further increase the induced immune response to a level comparable with those of commercially available anti-meningococcal glycoconjugate 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.

Two variants among Haemophilus influenzae serotype b strains with distinct bcs4, hcsA and hcsB genes display differences in expression of the polysaccharide capsule

Background

Despite nearly complete vaccine coverage, a small number of fully vaccinated children in the Netherlands have experienced invasive disease caused by Haemophilus influenzae serotype b (Hib). This increase started in 2002, nine years after the introduction of nationwide vaccination in the Netherlands. The capsular polysaccharide of Hib is used as a conjugate vaccine to protect against Hib disease. To evaluate the possible rise of escape variants, explaining the increased number of vaccine failures we analyzed the composition of the capsular genes and the expressed polysaccharide of Dutch Hib strains collected before and after the introduction of Hib vaccination.

Results

The DNA sequences of the complete capsular gene clusters of 9 Dutch Hib strains were assessed and two variants, designated type I and type II were found. The two variants displayed considerable sequence divergence in the hcsA and hcsB genes, involved in transport of capsular polysaccharide to the cell surface. Application of hcsA type specific PCRs on 670 Hib strains collected from Dutch patients with invasive Hib disease showed that 5% of the strains collected before 1996 were type II. No endogenous type II Hib strains were isolated after 1995 and all type II strains were isolated from 0–4 year old, non-vaccinated children only. Analysis of a worldwide collection of Hib strains from the pre-vaccination era revealed considerable geographic differences in the distribution of the type I and type II strains with up to 73% of type II strains in the USA. NMR analysis of type I and type II capsule polysaccharides did not reveal structural differences. However, type I strains were shown to produce twice as much surface bound capsular polysaccharide.

Conclusion

Type II strains were only isolated during the pre-vaccination era from young, non-vaccinated individuals and displayed a lower expression of capsular polysaccharide than type I strains. The higher polysaccharide expression may have provided a selective advantage for type I strains resulting in the rapid elimination of type II from the Dutch Hib population after introduction of nationwide Hib vaccination. However, this phenomenon does not explain the increase in the number of Hib vaccine failures in the Netherlands.

Synthesis and biological evaluation of phosphono analogues of capsular polysaccharide fragments from Neisseria meningitidis A

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that may cause explosive epidemics of meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of an efficient glycoconjugate vaccine against Neisseria meningitidis A is greatly hampered by the poor hydrolytic stability of its capsular polysaccharide, which is made up of (1-->6)-linked 2-acetamido-2-deoxy-alpha-D-mannopyranosyl phosphate repeating units. Since this chemical lability is a product of the inherent instability of the phosphodiester bridges, here we report the synthesis of phosphonoester-linked oligomers of N-acetyl mannosamine as candidates for stabilised analogues of the corresponding phosphate-bridged saccharides. The installation of each interglycosidic phosphonoester linkage was achieved by Mitsunobu coupling of a glycosyl C-phosphonate building block with the 6-OH moiety of a mannosaminyl residue. Each of the synthesised compounds contains an O-linked aminopropyl spacer at its reducing end (alpha- or beta-oriented) to allow for protein conjugation. The relative affinities of the synthetic molecules were investigated by a competitive ELISA assay and showed that a human polyclonal anti-MenA serum can recognise both the phosphonoester-bridged fragments 1-3 and their monomeric subunits, glycosides 20 and 21. Moreover, the biological results suggest that the abilities of these compounds to inhibit the binding of a specific antibody to MenA polysaccharide are dependent on the chain lengths of the molecules, but independent on the orientations of the anomeric linkers.

Full assignment of the 1H and 13C spectra and revision of the O-acetylation site of the capsular polysaccharide of Streptococcus pneumoniae Type 33F, a component of the current pneumococcal polysaccharide vaccine

The structure of the capsular polysaccharide from Streptococcus pneumoniae Type 33F was originally determined by a combination of chemical methods and limited use of NMR spectroscopy [Can. J. Biochem. Cell Biol.1984, 62, 666-677]. We report full 1H and 13C assignments and confirm the structure of the saccharide repeat unit, but find that the site of O-acetylation is O-2 of the -->5)-beta-D-Galf, rather than the -->3)-beta-D-Galf residue. We find that a slightly higher percentage of the repeat units are O-acetylated: [carbohydrate: see text].

Quantitative NMR spectroscopy--applications in drug analysis

NMR spectroscopy being a primary ratio method of measurement is highly suitable to evaluate the quality of drugs. NMR spectroscopy can be used for the identification of a drug substance, the identification and quantification of impurities arising from the synthesis pathway and degradation, or residual solvents as well as the determination of the content in the assay. This review gives an overview of the application of quantitative NMR spectroscopy in International Pharmacopoeias and for licensing purposes.

Development of a high-resolution magic-angle spinning nuclear magnetic resonance identity assay of the capsular polysaccharide from Haemophilus influenzae type b present in cetavlon precipitate

We describe the use of high-resolution magic-angle spinning nuclear magnetic resonance to control the identity of the capsular polysaccharide from Haemophilus influenzae type b (Hib) present in the cetavlon precipitate. This step is one of the earliest in the purification of this polysaccharide, which is further used in the production of Hib polysaccharide-protein conjugate vaccine. The effects of sample procedure and magnetic field strength have been investigated. Since this assay is rapid and simple, it may represent a useful technique for characterization of polysaccharides present in complex and insoluble matrices. Moreover, it allows a rapid evaluation of the structure of the produced polysaccharides very early on during the production process and is as such an essential analytical tool before starting the purification process.

Quantitative nuclear magnetic resonance analysis and characterization of the derivatized Haemophilus influenzae type b polysaccharide intermediate for PedvaxHIB

PedvaxHIB is a pediatric vaccine that protects children from severe disease caused by the gram-negative bacterium Haemophilus influenzae type b (Hib). The vaccine is made by chemically conjugating Hib capsular polysaccharide to the outer membrane protein complex of Neisseria meningitidis. The protein-conjugated vaccine has proven to be extremely effective in preventing invasive Hib disease in infants and young children. This paper presents the nuclear magnetic resonance (NMR) methodology for the quantitative characterization of derivatized polysaccharide and its validation closely following ICH guidelines. The assay has been shown to be precise and accurate (relative standard deviation [RSD]<or=1%), specific (no observable matrix interference), rugged (RSD <3% for day-to-day and operator-to-operator variations), and robust (to changes in temperature and polysaccharide concentration). Therefore, the quantitative NMR assay can be used as a reliable product release or process monitoring method and can replace several labor-intensive chromatographic and colorimetric methods.

Chemical structure, conjugation, and cross-reactivity of Bacillus pumilus Sh18 cell wall polysaccharide

Bacillus pumilus strain Sh18 cell wall polysaccharide (CWP), cross-reactive with the capsular polysaccharide of Haemophilus influenzae type b, was purified and its chemical structure was elucidated using fast atom bombardment mass spectrometry, nuclear magnetic resonance techniques, and sugar-specific degradation procedures. Two major structures, 1,5-poly(ribitol phosphate) and 1,3-poly(glycerol phosphate), with the latter partially substituted by 2-acetamido-2-deoxy-alpha-galactopyranose (13%) and 2-acetamido-2-deoxy-alpha-glucopyranose (6%) on position O-2, were found. A minor component was established to be a polymer of -->3-O-(2-acetamido-2-deoxy-beta-glucopyranosyl)-1-->4-ribitol-1-OPO3-->. The ratios of the three components were 56, 34, and 10 mol%, respectively. The Sh18 CWP was covalently bound to carrier proteins, and the immunogenicity of the resulting conjugates was evaluated in mice. Two methods of conjugation were compared: (i) binding of 1-cyano-4-dimethylaminopyridinium tetrafluoroborate-activated hydroxyl groups of the CWP to adipic acid dihydrazide (ADH)-derivatized protein, and (ii) binding of the carbodiimide-activated terminal phosphate group of the CWP to ADH-derivatized protein. The conjugate-induced antibodies reacted in an enzyme-linked immunosorbent assay with the homologous polysaccharide and with a number of other bacterial polysaccharides containing ribitol and glycerol phosphates, including H. influenzae types a and b and strains of Staphylococcus aureus and Staphylococcus epidermidis.

Reduction of animal use in human vaccine quality control: opportunities and problems

In vivo assays play a crucial role in the assessment of the potency and safety of human vaccines. Robust vaccine production procedures, improved characterisation methods and development of well-characterised vaccines create possibilities to reduce animal use. In this paper the current status in this field is reviewed. Achievements with regard to in vivo and in vitro potency and safety testing are discussed as well as new developments and possibilities in the field of in vitro characterisation of vaccine components. Finally, validation and implementation issues will be dealt with. Although replacement of in vivo tests for batch release of existing vaccines is difficult, emerging technologies allow well-considered reduction of in vivo experiments during product and process development and improvement. Inextricably bound up with this approach is good manufacturing practice (GMP), resulting in robust, validated production processes.