Streamlining Peptide Mapping LC-MS Approach for Studying Fusion Peptide-Conjugated Vaccine Immunogens.

A newly introduced HIV-1 vaccination utilizes a fusion peptide (FP)-based immunogen-carrier conjugate system, where the FP is coupled to a protein carrier via a bifunctional linker. Such heterogeneous materials present a challenge for the routine product quality assessment. Peptide mapping LC-MS analysis has become an indispensable tool for assessing the site-specific conjugation ratio, estimating site occupancy, monitoring conjugation profiles, and analyzing post-translational modifications (PTMs) and disulfide bonds as well as high-order protein structures. To streamline the peptide mapping approach to match the needs of a fast-paced conjugate vaccine product characterization, a selection of signature fragment ions generated by MSE fragmentation was successfully applied to assess the product quality at the different stages of a conjugates' manufacturing process with an emphasis on monitoring the amount of a reactive linker. This technique was employed in different conjugation studies of the protein carriers, linkers, and FP compositions as well as the cross-linked species formed during stress-degradation studies. Multiple derivatives of the intermediate and final conjugated products formed during a multistaged synthesis were monitored by means of the sensitive extracted-ion chromatogram (XIC) profiling and were included in the estimation of the site-specific conjugation loads. Differentiation of the conjugates with various FP compositions was demonstrated. The conjugation site occupancy was evaluated with respect to the solvent exposure of Lys residues. The findings of these LC-MS studies greatly aided in choosing the best conjugation strategy to ensure that the final recombinant tetanus toxoid heavy chain (rTTHc) product is chemically inert and represents a safe vaccine candidate for clinical evaluation.

Prefiltration enhances performance of sterile filtration for glycoconjugate vaccines.

Recent studies have reported very low capacity during sterile filtration of glycoconjugate vaccines due to rapid fouling of the sterile filter. The objective of this study was to explore the potential for significantly increasing the capacity of the sterile filter through the use of an appropriate prefilter. Data were obtained using prefilters with different pore size and chemistry, with the sterile filtration performed at constant filtrate flux using 0.22 µm nominal pore size Durapore® polyvinylidene difluoride membranes. Prefiltration through 5 µm pore size Durapore® or Nylon prefilters nearly eliminated the fouling of the sterile filter, leading to more than a 100-fold reduction in the rate of pressure increase for the sterile filter. This dramatic improvement in sterile filter performance was due to the removal of large components (greater than 1 µm in size) as confirmed by dynamic light scattering. These results demonstrate the potential of using large pore size prefilters to significantly enhance the performance of the sterile filtration process for the production of important glycoconjugate vaccines.

Use of NMR as an analytical tool in the process development of conjugate vaccines against Haemophilus influenzae type b (Hib) and meningococcal serogroup A (MenA).

The native structure of the bacterial polysaccharide is the key immunogenic component of conjugate vaccines and antibodies raised against the polysaccharide structure are responsible for providing protection against the corresponding pathogen. The manufacturing process of conjugate vaccines is very complex and has various biological and chemical steps. It is important to monitor the process to ensure that the structural identity of the polysaccharide is maintained throughout the process. NMR spectroscopy can be used as a versatile analytical tool to monitor the structural integrity of the polysaccharide component from isolated polysaccharide to conjugate vaccine and for identifying different impurities generated during the process.

Improving Analytical Characterization of Glycoconjugate Vaccines through Combined High-Resolution MS and NMR: Application to Neisseria meningitidis Serogroup B Oligosaccharide-Peptide Glycoconjugates.

Conjugate vaccines are highly heterogeneous in terms of glycosylation sites and linked oligosaccharide length. Therefore, the characterization of conjugate vaccines' glycosylation state is challenging. However, improved product characterization can lead to enhancements in product control and product quality. Here, we present a synergistic combination of high-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR) for the analysis of glycoconjugates. We use the power of this strategy to characterize model polysaccharide conjugates and to demonstrate a detailed level of glycoproteomic analysis. These are first steps on model compounds that will help untangle the details of complex product characterization in conjugate vaccines. Ultimately, this strategy can be applied to enhance the characterization of polysaccharide conjugate vaccines. In this study, we lay the groundwork for the analysis of conjugate vaccines. To begin this effort, oligosaccharide-peptide conjugates were synthesized by periodate oxidation of an oligosaccharide of a defined length, α,2-8 sialic acid trimer, followed by a reductive amination, and linking the trimer to an immunogenic peptide from tetanus toxoid. Combined mass spectrometry and nuclear magnetic resonance were used to monitor each reaction and conjugation products. Complete NMR peak assignment and detailed MS information on oxidized oligosialic acid and conjugates are reported. These studies provide a deeper understanding of the conjugation chemistry process and products, which can lead to a better controlled production process.

An ELISA method to estimate the mono ADP-ribosyltransferase activities: e.g in pertussis toxin and vaccines.

ADP-ribosyltransferase activities have been observed in many prokaryotic and eukaryotic species and viruses and are involved in many cellular processes, including cell signalling, DNA repair, gene regulation and apoptosis. In a number of bacterial toxins, mono ADP-ribosyltransferase is the main cause of host cell cytotoxicity. Several approaches have been used to analyse this biological system from measuring its enzyme products to its functions. By using a mono ADP-ribose binding protein we have now developed an ELISA method to estimate native pertussis toxin mono ADP-ribosyltransferase activity and its residual activities in pertussis vaccines as an example. This new approach is easy to perform and adaptable in most laboratories. In theory, this assay system is also very versatile and could measure the enzyme activity in other bacteria such as Cholera, Clostridium, E. coli, Diphtheria, Pertussis, Pseudomonas, Salmonella and Staphylococcus by just switching to their respective peptide substrates. Furthermore, this mono ADP-ribose binding protein could also be used for staining mono ADP-ribosyl products resolved on gels or membranes.

Determination of free polysaccharide in Vi glycoconjugate vaccine against typhoid fever.

Glycoconjugate vaccines based on the Vi capsular polysaccharide directed against Salmonella enterica serovar Typhi are licensed or in development against typhoid fever, an important cause of morbidity and mortality in developing countries. Quantification of free polysaccharide in conjugate vaccines is an important quality control for release, to monitor vaccine stability and to ensure appropriate immune response. However, we found that existing separation methods based on size are not appropriate as free Vi non-specifically binds to unconjugated and conjugated protein. We developed a method based on free Vi separation by Capto Adhere resin and quantification by HPAEC-PAD. The method has been tested for conjugates of Vi derived from Citrobacter freundii with different carrier proteins such as CRM197, Tetanus Toxoid and Diphtheria Toxoid.

Pharmacokinetic correlates of the effects of a heroin vaccine on heroin self-administration in rats.

The purpose of this study was to evaluate the effects of a morphine-conjugate vaccine (M-KLH) on the acquisition, maintenance, and reinstatement of heroin self-administration (HSA) in rats, and on heroin and metabolite distribution during heroin administration that approximated the self-administered dosing rate. Vaccination with M-KLH blocked heroin-primed reinstatement of heroin responding. Vaccination also decreased HSA at low heroin unit doses but produced a compensatory increase in heroin self-administration at high unit doses. Vaccination shifted the heroin dose-response curve to the right, indicating reduced heroin potency, and behavioral economic demand curve analysis further confirmed this effect. In a separate experiment heroin was administered at rates simulating heroin exposure during HSA. Heroin and its active metabolites, 6-acetylmorphine (6-AM) and morphine, were retained in plasma and metabolite concentrations were reduced in brain in vaccinated rats compared to controls. Reductions in 6-AM concentrations in brain after vaccination were consistent with the changes in HSA rates accompanying vaccination. These data provide evidence that 6-AM is the principal mediator of heroin reinforcement, and the principal target of the M-KLH vaccine, in this model. While heroin vaccines may have potential as therapies for heroin addiction, high antibody to drug ratios appear to be important for obtaining maximal efficacy.

Quantification of each serogroup polysaccharide of Neisseria meningitidis in A/C/Y/W-135-DT conjugate vaccine by high-performance anion-exchange chromatography-pulsed amperometric detection analysis.

Invasive bacterial meningitis caused by Neisseria meningitidis can be prevented by active immunization with meningococcal polysaccharide or polysaccharide-protein conjugate vaccines. In a tetravalent A/C/Y/W-135-DT meningococcal conjugate vaccine vial, or in a final formulated bulk, accurate identification and quantification of each polysaccharide are critical in product release. Determination of sialic acid serogroups (C, W-135, and Y) unambiguously is complex since all these serogroups contribute to the sialic acid monosaccharide peaks that overlap in the high-performance anion-exchange chromatography-pulsed amperometric detection (HPAEC-PAD). We report a quantification method that involves generation of monosaccharide standard plots for respective sugars mannosamine-6-phosphate, sialic acid, galactose- and glucose-derived from hydrolysis of mixtures of the four serogroups A, C, W, and Y reference polysaccharides. These plots were then used to obtain the unknown polysaccharide concentrations of A/C/Y/W-135 in vialed vaccine or from formulated final bulks. We also present our results of the HPAEC-PAD profiles on groups C, W-135, and Y polysaccharides when hydrolyzed individually and/or in mixtures to discuss the individual sialic acid peak contributions.

Bioanalysis of meningococcal vaccines.

Meningococcal meningitis is feared because of the rapid onset of severe disease from mild symptoms and, therefore, is an important target for vaccine research. Five serogroups, defined by the structures of their capsular polysaccharides, are responsible for the vast majority of disease. Protection against four of these five serogroups can be obtained with polysaccharide or glycoconjugate vaccines, in which fragments of the capsular polysaccharides attached to a carrier protein generate anticarbohydrate immune responses, whilst protection against group B disease requires protein immunogens, often presented in vesicles containing outer membrane proteins. Glycoconjugate vaccines are now an established technology, but outer-membrane protein vaccines are still under development and present significant challenges. This review discusses physicochemical approaches to the characterization and quality control of these vaccines, as well as highlighting the problems and differences in vaccine design required for protection against different serogroups of the same species of pathogen.

Advantages of a synthetic peptide immunogen over a protein immunogen in the development of an anti-pilus vaccine for Pseudomonas aeruginosa.

The type IV pilus is an important adhesin in the establishment of infection by Pseudomonas aeruginosa. We have previously reported on a synthetic peptide vaccine targeting the receptor-binding domain of the main structural subunit of the pilus, PilA. The receptor-binding domain is a 14-residue disulfide loop at the C-terminal end of the pilin protein. The objective of this study was to compare the immunogenicity of a peptide-conjugate to a protein subunit immunogen to determine which was superior for use in an anti-pilus vaccine. BALB/c mice were immunized with the native PAK strain pilin protein and a synthetic peptide of the receptor-binding domain conjugated to keyhole limpet haemocyanin. A novel pilin protein with a scrambled receptor-binding domain was used to characterize receptor-binding domain-specific antibodies. The titres against the native pilin of the animals immunized with the synthetic peptide-conjugate were higher than the titres of animals immunized with the pilin protein. In addition, the affinities of anti-peptide sera for the intact pilin receptor-binding domain were significantly higher than affinities of anti-pilin protein sera. These results have significant implications for vaccine design and show that there are significant advantages in using a synthetic peptide-conjugate over a subunit pilin protein for an anti-pilus vaccine.

NMR assays for carbohydrate-based vaccines.

Antibodies against the cell surface carbohydrates of many microbial pathogens protect against infection. This was initially exploited by the development of purified polysaccharide vaccines, but glycoconjugate vaccines, in which the cell surface carbohydrate of a microbial pathogen is covalently attached to an appropriate carrier protein, are proving the most effective means to generate this protective immunity. Carbohydrate-based vaccines against Haemophilus influenzae Type b, Neisseria meningitidis, Streptococcus pneumoniae and Salmonella enterica serotype Typhi (S. Typhi) are already licensed, and many similar products are in various stages of development. For many of these vaccines, biological assays are not available or are inappropriate and NMR spectroscopy is proving a valuable tool for the characterisation and quality control of existing and novel products. This review highlights some of the areas in which NMR spectroscopy is currently used, and where further developments may be expected.

Antibodies against Haemophilus influenzae type b capsular polysaccharide and tetanus toxoid before and after a booster dose of the carrier protein nine years after primary vaccination with a protein conjugate vaccine.

IgG antibodies against Haemophilus influenzae type b (Hib) capsular polysaccharide (CPS) and tetanus toxoid (TT) were measured for 53 children, 10 years of age, before and 1 month after a booster dose of diphtheria-tetanus vaccine (DT). All children had been vaccinated at 3, 5 and 12 months of age with DT and a Hib-TT conjugate. Geometric mean concentrations of Hib CPS serum IgG antibody were 4.16 and 4.30 microg/mL before and after the DT booster, respectively. The geometric mean concentration of TT IgG antibody increased from 0.09 IU/mL to 4.58 IU/mL (P < 0.001). Hib CPS IgG levels remained well above protective titers for 9 years after 3 doses of Hib-TT appropriately spaced in infancy. A booster dose of TT did not affect Hib CPS antibody concentrations but induced a pronounced IgG response against TT.

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.

Improved methods for the quantification of free and linked spacer in conjugate vaccine process.

In polysaccharide (PS)-protein conjugate vaccine process, indirect coupling via derivatization of the antigenic PS by diamino spacer molecules is widely used. Such a conjugation technology requires the accurate determination of both the degree of PS-amino substitution (linked spacer) and the removal of residual unlinked (free) diamino spacer. We report two methods for the microdetermination of the spacer primary amino groups, based on their fluorescent labelling. In the first developed assay, activated PS is derivatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) and the free spacer is separated and detected as its AQC derivative by RP-HPLC with fluorescence detection (lambda(Ex,Em) 246/396 nm). In the second assay, activated PS is derivatized with 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ) and its FQ derivative is separated by capillary zone electrophoresis (CZE) with laser-induced-fluorescence (LIF) detection (lambda(Ex/Em) 488/590 nm). Compared to the traditional gel filtration and colorimetric assays, these two methods show major advances in terms of sensitivity, reduced analysis time and small sample requirements.

Quantification of free polysaccharide in meningococcal polysaccharide-diphtheria toxoid conjugate vaccines.

A precipitation method using deoxycholate/HCI has been applied successfully to separate unconjugated free polysaccharide from carrier protein-bound material in meningococcal polysaccharide-diphtheria toxoid conjugate vaccines. The method effectively separated free and bound polysaccharide in conjugate vaccines prepared from Neisseria meningitidis serotypes A, C, W135 and Y. Free polysaccharide remained in the supernatant after deoxycholate treatment while protein-bound polysaccharide was fully precipitated. Testing by both colorimetric assay and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) has confirmed the selective loss of protein-bound polysaccharide in samples of conjugate vaccine or conjugate vaccine mixed with known amounts of free polysaccharide. This rapid separation method requires minimum sample handling and is specific, reproducible, and allows assessment of free polysaccharide levels in vaccines at final container concentration.

Size determination of bacterial capsular oligosaccharides used to prepare conjugate vaccines.

We recently described the use of ion exchange chromatography for analysis and the industrial scale preparation of pools of oligosaccharides of intermediate chain length from polysaccharides of Haemophilus influenzae type b (Hib) and Neisseria meningitidis groups A and C. These negatively charged "sized" oligosaccharides are activated and conjugated to the carrier protein (CRM197) to prepare the corresponding glycoconjugate vaccines. Characterization and accurate determination of the degree of polymerization (DP) of the pool of oligosaccharides is essential for the consistent production of these conjugate vaccines. This paper describes the colorimetric assays used for determination of the average DP of the Hib and meningococcal oligosaccharides, and the qualification of these assays achieved by size characterization of the respective oligosaccharides by use of physicochemical methods, including liquid chromatography, mass spectrometry (ionspray) and NMR spectroscopy.