Quantification of polysaccharide in Haemophilus influenzae type b conjugate and polysaccharide vaccines by high-performance anion-exchange chromatography with pulsed amperometric detection

Acid hydrolysis conditions for quantification of meningococcal X polysaccharide in a pentavalent vaccine using HPAEC-PAD/ESI-MS

A selective and sensitive method was evaluated for quantitation of meningococcal X (Men X) polysaccharide in pentavalent meningococcal A, C, W, Y and X conjugate vaccine using different acid hydrolysis conditions like HCl, TFA, HF, HF-TFA, and HF-HCl. High-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) using CarboPac PA10 column was used to identify the hydrolyzed products based on retention time and its comparison with monosaccharide standards. Complete release of glucosamine (GlcN) from Men X in monovalent bulk and pentavalent vaccine samples was achieved using HF hydrolysis at 80 °C for 2 h. The Men X HF-hydrolyzed polysaccharide to glucosamine along with the reference standard was identified using collision-induced dissociation (CID) electrospray mass spectroscopy and the MS/MS fragments of m/z 162, m/z 144 and m/z 84. Meningococcal polysaccharide concentration was determined with a correlation coefficient r2 >0.99 using polysaccharide reference standard. The serogroups A, W, and Y were converted to their monosaccharides units and quantified using this method however, milder acid hydrolysis 0.1 M HCl 80 °C 2 h for release of sialic acid for Men C polysaccharide was found to be more suitable. These methods will provide necessary tools and prove to be beneficial to laboratories developing new saccharide-based vaccine combinations.

High performance anion exchange chromatographic and colorimetric methods for quality assessment of total and free polysaccharide content in Haemophilus influenzae type b conjugate vaccine containing lactose

The presence of lactose as a stabilizer in Haemophilus influenzae type b (Hib) conjugate vaccine is a challenge for chromatographic resolution of its total and free poly ribosyl ribitol phosphate (PRP) content. Sample pretreatment using ultrafiltration was performed and had removed ≥95% of lactose in shorter time compared to the conventional dialysis process. Separation of free unconjugated PRP was performed using solid-phase extraction C₄ cartridges. Hib conjugate vaccine was then analyzed for determination of total and free PRP, using two validated techniques: high performance anion exchange chromatography with pulsed amperometry (HPAEC-PAD) for ribitol determination and a colorimetric assay for phosphorus determination. Lactose removal had enabled a rapid chromatographic assay via fast depolymerization of PRP using high temperature treatment. Modifying the burning process in the colorimetric assay reduced the analysis time significantly compared to the pharmacopoeial method. Linearity was obtained over the range of 0.10-10.0 μg mL^-1 for the HPAEC method and in the range of 1.0-8.0 μg mL^-1 for the colorimetric one. Stability of Hib conjugate vaccine was investigated. The HPAEC results revealed about a 35% increase in free PRP content after storage under stressed conditions (moisture and temperature). The proposed methods offered a reliable and economic platform for assessing the immunogenicity, efficacy and stability of Hib conjugate vaccine containing lactose for the biopharmaceutical industry.

Molecular size distribution assessment of Haemophilus influenzae vaccine containing lactose by HPAEC-PAD and colorimetric assays

Molecular size distribution of Haemophilus influenzae type b (Hib) conjugate vaccine is an important indicator for its immunogenicity and stability. Molecular size distribution was evaluated by High-Performance Protein Chromatography on Sepharose CL-4B column, and fractions were pooled. The use of high flow rate, incorporation of a calibration standard with the injected buffer and pooling method yielded a superior assay compared to conventional pharmacopeial method. The pools were analyzed for determination of distribution coefficient (K_D) of 0.2 and 0.5 using two validated techniques: High Performance Anion Exchange Chromatography with pulsed amperometric detection (HPAEC-PAD) for ribitol determination and an optimized colorimetric assay for phosphorus determination. Linearity was achieved over range of 0.10-10.0 μg/mL and 1.0-8.0 μg/mL with LOD of 0.03 and 0.28 μg/mL for HPAEC and colorimetric assays, respectively. The developed assays were successfully applied in quality control monitoring of Hib conjugate vaccine. The optimized colorimetric method had shortened the analysis time to 25 min compared to 3.5 h for the European pharmacopeial assay by modifying the burning process. HPAEC stability results revealed 40% decrease in MSD after stressed storage conditions. The proposed assays offer a reliable and economic platform for monitoring the quality attributes of Hib for biopharma industry.

Saccharide dosage content of meningococcal polysaccharide conjugate vaccines determined using WHO International Standards for serogroup A, C, W, Y and X polysaccharides

Potency of meningococcal polysaccharide-protein conjugate vaccines relies on the polysaccharide content to prevent meningitis. NIBSC, as the official national control laboratory in UK, analysed ten different mono- and multi-meningococcal conjugate vaccines, using established International Standards for meningococcal serogroups A, C, W, Y and X, by resorcinol or HPAEC-PAD assay. Most saccharide contents were within ±20% of their claimed content for licensure with taking different O-acetylation levels into consideration, with only MenC content in two vaccines below (by 60% and 54%) the labelled value, however, previous study showed different dosage was not necessarily correlated to the immunogenicity of those vaccines. This study demonstrated the use of International Standards to quantify saccharide content in polysaccharide-based vaccines with different percentage of O-acetylation. These International Standards are suitable to serve as either quantitative standard or calibrator of in-house standards, with supplied stability data.

Development of a Specific and Sensitive HPAEC-PAD Method for Quantification of Vi Polysaccharide Applicable to other Polysaccharides Containing Amino Uronic Acids

Typhoid fever is a major cause of morbidity and mortality in developing countries. Vaccines based on the Vi capsular polysaccharide are licensed or in development against typhoid fever. Vi content is a critical quality attribute for vaccines release, to monitor their stability and to ensure appropriate immune response. Vi polysaccharide is a homopolymer of α-1,4-N-acetylgalactosaminouronic acid, O-acetylated at the C-3 position, resistant to the commonly used acid hydrolysis for sugar chain depolymerization before monomer quantification. We previously developed a quantification method based on strong alkaline hydrolysis followed by High Performance Anion Exchange Chromatography-Pulsed Amperometric Detection analysis, but with low sensitivity and use for quantification of an unknown product coming from polysaccharide depolymerization. Here we describe the development of a method for Vi polysaccharide quantification based on acid hydrolysis with concomitant use of trifluoroacetic and hydrochloric acids. A Design of Experiment approach was used for the identification of the optimal hydrolysis conditions. The method is 100-fold more sensitive than the previous one, and specifically, resulting in the formation of a known product, confirmed to be the Vi monomer both de-O- and de-N-acetylated by mono- and bidimensional Nuclear Magnetic Resonance spectroscopy and mass spectrometry. Accuracy and precision were determined, and chromatographic conditions were improved to result in reduced time of analysis. This method will facilitate characterization of Vi-based vaccines. Furthermore, a similar approach has the potential to be extended to other polysaccharides containing 2-amino uronic acids, as already verified here for Shigella sonnei O-antigen, Streptococcus pneumoniae serotype 12F, and Staphylococcus aureus types 5 and 8 capsular polysaccharides.

Vaccine Quality Ensured by High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection

Many important vaccines use bacterial capsular polysaccharides, or shorter polysaccharides or oligosaccharides, derived from the capsular polysaccharides, conjugated to protein. It is imperative that manufacturers understand the carbohydrate composition of these vaccines and deliver a product with a consistent polysaccharide or polysaccharide conjugate composition and content. High-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) is a major technique used to understand the carbohydrate composition of these vaccines and ensure product quality. HPAE-PAD separates and detects carbohydrates without analyte derivatization. This paper describes the basics of the HPAE-PAD technique and then reviews how it has been applied to Haemophilus influenzae type b, pneumococcal, meningococcal, group B streptococcal, and Salmonella polysaccharide and corresponding conjugate vaccines.

Principles of vaccine potency assays

Compared with biologics, vaccine potency assays represent a special challenge due to their unique compositions, multivalency, long life cycles and global distribution. Historically, vaccines were released using in vivo potency assays requiring immunization of dozens of animals. Modern vaccines use a variety of newer analytical tools including biochemical, cell-based and immunochemical methods to measure potency. The choice of analytics largely depends on the mechanism of action and ability to ensure lot-to-lot consistency. Live vaccines often require cell-based assays to ensure infectivity, whereas recombinant vaccine potency can be reliably monitored with immunoassays. Several case studies are presented to demonstrate the relationship between mechanism of action and potency assay. A high-level decision tree is presented to assist with assay selection.

International collaborative study for establishment of the 2nd WHO International Standard for Haemophilus influenzae type b polysaccharide

In this report we present the results of a collaborative study for the preparation and calibration of a replacement International Standard (IS) for Haemophilus influenzae type b polysaccharide (polyribosyl ribitol phosphate; 5-d-ribitol-(1 → 1)-β-d-ribose-3-phosphate; PRP). Two candidate preparations were evaluated. Thirteen laboratories from 9 different countries participated in the collaborative study to assess the suitability and determine the PRP content of two candidate standards. On the basis of the results from this study, Candidate 2 (NIBSC code 12/306) has been established as the 2nd WHO IS for PRP by the Expert Committee of Biological Standards of the World Health Organisation with a content of 4.904 ± 0.185mg/ampoule, as determined by the ribose assays carried out by 11 of the participating laboratories.

Glycoconjugate Vaccines: The Regulatory Framework

Most vaccines, including the currently available glycoconjugate vaccines, are administered to healthy infants, to prevent future disease. The safety of a prospective vaccine is a key prerequisite for approval. Undesired side effects would not only have the potential to damage the individual infant but also lead to a loss of confidence in the respective vaccine-or vaccines in general-on a population level. Thus, regulatory requirements, particularly with regard to safety, are extremely rigorous. This chapter highlights regulatory aspects on carbohydrate-based vaccines with an emphasis on analytical approaches to ensure the consistent quality of successive manufacturing lots.

Control and lot release of meningococcal group C conjugate vaccines

Meningococcal group C conjugate vaccines were first introduced to the UK in 1999. To date, the vaccines have been demonstrated to have an efficacy of approximately 90% and have since been adopted by other countries worldwide. The development of control tests used for lot release of meningococcal group C vaccines has been based on those used for Haemophilus influenzae type b conjugates, the key criteria being measurement of free saccharide and conjugate integrity by physicochemical means. In future, meningococcal group C vaccines are likely to be replaced by multivalent formulations containing different components in combination. This will present a new challenge for regulatory authorities and more extensive testing will be required to ensure vaccine safety and efficacy.

A novel enzyme-linked immuno-sorbent assay (ELISA) for the quantification of total and free polysaccharide in Haemophilus influenzae b-Tetanus toxoid conjugate vaccines in monovalent and combined vaccine formulations

Current Haemophilus influenzae b conjugate vaccines (Hib), which are made of purified capsular polysaccharide (poly-ribosyl-ribitol-phosphate; PRP) conjugated to a carrier protein, are almost completely evaluated by physico-chemical methods to ensure the integrity and stability of the vaccine and consistency of manufacture of batches. The absence of a potency assay makes the quantification of total PRP content (in SI units) and of % free polysaccharide in final fills or bulk components of Hib vaccines critical release tests for both manufacturers and national control authorities. Here we describe a simple and sensitive Enzyme-Linked Immuno-sorbent Assay (ELISA) which has been developed to quantify total and free PRP content in Hib-TT vaccine alone or when in combination with other vaccines. The assay is robust, specific and highly sensitive.

HPAEC-PAD method for the analysis of alkaline hydrolyzates of Haemophilus influenzae type b capsular polysaccharide

A gradient method has been devised for the rapid analysis of alkaline hydrolyzates of Haemophilus influenzae type b (Hib) capsular polysaccharide-based vaccines by high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). As compared with published procedures, peak shape and sensitivity were significantly improved with this approach, analysis time was short and there was little interference from impurities. The limits of detection and quantification were established with a purified reference polysaccharide. We propose this method as a practical alternative for the analysis of minute amounts of Hib polysaccharide, which can be lower than with the conventional approaches.

Vi-CRM 197 as a new conjugate vaccine against Salmonella Typhi

An efficacious, low cost vaccine against typhoid fever, especially for young children, would make a major impact on disease burden in developing countries. The virulence capsular polysaccharide of Salmonella Typhi (Vi) coupled to recombinant mutant Pseudomonas aeruginosa exoprotein A (Vi-rEPA) has been shown to be highly efficacious. We investigated the use of carrier proteins included in infant vaccines, standardized the conjugation process and developed key assays required for routine lot release at production scale. Vi from a BSL1 organism, Citrobacter freundii, strain WR7011, was used as an alternative to Vi from S. Typhi. We showed that Vi conjugated to CRM(197), a non-toxic mutant of diphtheria toxin, widely used in commercial vaccines, was produced at high yield. Vi-CRM(197) proved immunogenic in animal studies, even without adjuvant. Thus, Vi-CRM(197) appears to be a suitable candidate for the development of a commercially viable, effective typhoid vaccine for developing countries.

Evaluation of the saccharide content and stability of the first WHO International Standard for Haemophilus influenzae b capsular polysaccharide

Haemophilus influenzae b conjugate vaccines (Hib) are almost entirely evaluated by physico-chemical methods to ensure the consistency of manufacture of batches. As different assays are employed for the quantification of Hib capsular polysaccharide PRP (polyribosyl ribitol phosphate; 5-D-ribitol-(1-->1)-beta-D-ribose-3-phosphate) in final formulations and bulk components, there was deemed a need for an International Standard of Hib PRP polysaccharide to be made available. Ten laboratories from 8 different countries participated in a collaborative study to determine the PRP content and assess the suitability of a candidate International Standard PRP preparation (02/208). The results illustrate that a reduction in between-laboratory variability could be achieved by use of a common reference preparation and data analysis showed no significant differences in the values obtained by the different assays: ribose, phosphorus, and high performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD), suggesting the suitability of the proposed reference for use across these assays for quantification of PRP content in Hib vaccines. On the basis of the results of this study, the First International Standard for PRP, NIBSC Code 02/208, has been established by the Expert Committee of Biological Standards of the World Health Organisation, with a content of 4.933+/-0.267mg/ampoule, as determined by the ribose assays carried out by 7 of the participating laboratories.

An integrity assay for a meningococcal type B conjugate vaccine

The development of an analytical procedure for the evaluation of a conjugate vaccine's structural wholeness or integrity is described. The principle component of the vaccine was the N-propionylated group B meningococcal polysaccharide (NPr-GBMP) covalently attached to a carrier protein. The goal of the procedure was to determine whether any whole polysaccharide, oligosaccharide, or monosaccharide, from minute to moderate levels, became detached off the conjugate. Free saccharide was isolated from the formulation, which included an aluminum hydroxide adjuvant for analysis. Due to its linkage, the NPr-GBMP did not release sialic acid efficiently with acid hydrolysis to the extent necessary for accurate quantitation. To accomplish depolymerization, the NPr-GBMP was subjected to methanolysis, 3N hydrochloric acid in methanol for 16h at 80 degrees C. The main product of the methanolysis reaction was a de-N-acylated methyl glycoside of sialic acid. N-acetylneuraminic acid oligomers and colominic acid were used to confirm the methanolysis depolymerization efficiency of the alpha(2 --> 8) saccharides; with the treatment all oligomers produced a common methyl glycoside. For this determination anion exchange chromatography and size exclusion chromatography were both interfaced to an integrated pulsed amperometric detector. Sensitivity and linearity were demonstrated to be sufficient for the application with vaccine dose formulations with low total saccharide concentrations.

Quantification of O-acetyl, N-acetyl and phosphate groups and determination of the extent of O-acetylation in bacterial vaccine polysaccharides by high-performance anion-exchange chromatography with conductivity detection (HPAEC-CD)

The O-acetyl groups in meningococcal A and typhoid Vi polysaccharides (PSs) are functional immunogenic epitopes in humans. To quantify and determine the extent of O-acetylation in these and other bacterial vaccine PSs, anion-exchange HPLC methods have been developed for quantification of O-acetyl, N-acetyl, and phosphate groups in the PSs after these groups were hydrolyzed into anions. The O-acetylation in meningococcal A, C, Y and W-135, pneumococcal 9 V and 18C and typhoid Vi PSs were analyzed. The O-acetyl group was selectively released from a PS as acetate by mild alkaline hydrolysis in 10 or 20 mM NaOH at 37 degrees C until maximum release. The acetate in the hydrolysate was then quantified by high-performance anion-exchange chromatography with conductivity detection (HPAEC-CD) after removal of the PS by filtration with a 10,000 molecular-weight-cut-off membrane. Since the extent of O-acetylation on the PSs depends on bacterial species, strains and growth conditions, the N-acetyl group of amino-sugars, phosphate or monosaccharide components of the PSs were also quantified using HPAEC with conductivity or amperometry detection to determine the molar ratios of the O-acetyl group to these components. The average numbers of O-acetyl molecules in one PS repeating unit of the PSs were obtained from the molar ratios. Besides the O-acetyl determination, the pyruvate component in non-O-acetylated pneumococcal type 4 PS was analyzed by the HPAEC method. The HPAEC method can quantify the O-acetyl content in 0.2 microg of the meningococcal C PS and has a sensitivity at least 10 times higher than that of the colorimetric Hestrin assay. The method can be used for routine analysis of O-acetylation of PSs for quality control of vaccine PSs.

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.

Development of a high-performance anion-exchange chromatography with pulsed-amperometric detection based quantification assay for pneumococcal polysaccharides and conjugates

A method, using high-performance anion-exchange chromatography with pulsed-amperometric detection (HPAEC-PAD), has been developed to determine the concentrations of Streptococcus pneumoniae capsular polysaccharides and polysaccharide conjugates used in formulating a conjugate vaccine for the prevention of pneumococcal infections. In an effort to determine optimum hydrolysis conditions for the analysis, pneumococcal polysaccharides were subjected to three different hydrolysis methods: trifluoroacetic acid (TFA) hydrolysis, methanolysis followed by TFA hydrolysis, or hydrofluoric acid (HF) hydrolysis followed by TFA hydrolysis. For quantification purposes, best results were obtained by methanolysis followed by TFA hydrolysis for uronic acid-containing polysaccharides, and by TFA hydrolysis for all the others. For the quantification of all the polysaccharides (from native to conjugated forms), a monosaccharide reference mixture (Rha, Gal and GlcA) hydrolyzed along with the samples can be used as standards for routine analysis. This is much more convenient than to hydrolyze a well-characterized reference polysaccharide (necessary standard only for type 1 capsular polysaccharide). This method is rapid, very sensitive (less than 10 microg of polysaccharide is required), and may replace advantageously the currently used colorimetric assays used to determine polysaccharides content. Moreover, it can be readily adapted for use with other bacterial polysaccharide preparations as well.

Quality control of polyvalent pneumococcal polysaccharide-protein conjugate vaccine by nephelometry

A nephelometric method was used for quantitative analysis of individual polysaccharides (PSs) in a polyvalent pneumococcal conjugate vaccine using CRM(197) as carrier protein. Using this method, the individual types 4, 6B, 9V, 14, 18C, 19F and 23F PSs were found to range between 82.3 to 119% of the manufacturer's indicated values. During conjugation using reductive amination, pneumococcal PS was first oxidized to introduce aldehyde groups. Higher or lower levels of antigen-antibody reaction were observed in periodate activated and then reduced PS of some serotypes compared to non-treated PS. Use of oxidized and reduced PS may provide an early indication of change in conjugation process. Furthermore, since the final monovalent and polyvalent conjugate vaccines gradually change during the storage period, the nephelometry provides an useful analytical method for stability study of these vaccines.

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

We describe the use of Nuclear Magnetic Resonance (NMR) spectroscopy to control the identity of purified bulk capsular polysaccharide [called poly(ribosylribitolphosphate) or PRP] from Haemophilus influenzae type b (Hib), and derivatised forms, used in the production of Hib polysaccharide-protein conjugate vaccines. We describe the approaches we have developed to validate this test.

Quantitative determination of saccharide in Haemophilus influenzae type b glycoconjugate vaccines, alone and in combination with DPT, by use of high-performance anion-exchange chromatography with pulsed amperometric detection

The stability and integrity of glycoconjugate vaccines requires determination of the total saccharide and quantification of the unbound or free saccharide present. The traditional assay for Hib conjugates, based on colorimetric determination of ribose, has been much improved by the use of base hydrolysis and analysis of the Hib subunit generated using high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The production of this subunit was confirmed by NMR analysis. However, quantification of free Hib saccharide using this method was not possible in the combination vaccines evaluated due to interferences emanating from DPT. Thus a method based on TFA hydrolysis followed by the chromatographic separation and quantification of ribitol on a CarboPac MA1 column was developed. The method is selective, and with the use of ED40 electrode, requires only nanomole amounts for the chromatographic step, thereby ensuring that free saccharide can be monitored accurately in the formulated Hib-CRM vaccine alone and when in combination with other vaccines.

Quantitation of low level unconjugated polysaccharide in tetanus toxoid-conjugate vaccine by HPAEC/PAD following rapid separation by deoxycholate/HCl

A simple and rapid acid precipitation method has been applied successfully for separating free capsular polysaccharide of Haemophilus influenzae type b (polyribosyl ribitol phosphate, PRP) from PRP tetanus toxoid conjugate (PRP-T) in a final dosage amount of low-level materials. The unconjugated PRP was found to stay in the supernatant without precipitation, while conjugated PRP-T was fully precipitated. High performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) has been applied for analysis of the PRP content in the supernatant after the separation. This method requires minimum sample handling and is specific, sensitive and reproducible making it suitable for release and stability testing of PRP-T in final containers.

Haemophilus influenzae type b conjugate vaccine stability: catalytic depolymerization of PRP in the presence of aluminum hydroxide

The structural stability of the Haemophilus influenzae type b (Hib) capsular polysaccharide, polyribosylribitolphosphate (PRP) in an aluminum hydroxide adsorbed, polysaccharide-protein conjugate vaccine was monitored using modifications of an HPLC assay developed by Tsai et al. [Tsai C-M, Gu X-X, Byrd RA. Quantification of polysaccharide in Haemophilus influenzae type b conjugate and polysaccharide vaccines by high-performance anion-exchange chromatography with pulsed amperometric detection. Vaccine 1993;12:700-706.]. As applied to products containing PRP conjugated to the outer membrane protein complex (OMPC) from Neisseria meningitidis, this assay allows direct measurement of the total PRP content in very complex samples including commercial vaccine products. In addition, with the use of a high-speed centrifugation step, the assay can be used to directly quantify any PRP that is not conjugated to the OMPC carrier protein. These results provide evidence of what appears to be a catalytic reaction taking place between the phosphodiester bond of PRP and the aluminum hydroxide adjuvant that results in hydrolysis of the PRP polymer into smaller chain lengths and liberation of PRP oligomers from the conjugate particle. The reaction approaches an asymptotic limit after approximately two years at 2-8 degrees C. Clinical studies which span this time period confirm that the modest decrease in conjugated PRP content over time does not impact the overall clinical effectiveness of PRP-OMPC-containing vaccines.