A versatile in vitro ELISA test for quantification and quality testing of infectious, inactivated and formulated rabies virus used in veterinary monovalent or combination vaccine

Development of a multiplex-based immunoassay for the characterization of diphtheria, tetanus and acellular pertussis antigens in human combined DTaP vaccines

Routine batch quality testing before vaccine release, notably for potency evaluation, still relies on animal use for several animal and human vaccines. In this context, the VAC2VAC project is a public-private consortium of 22 partners funded by EU whose the main objective is to reduce the number of animal used for batch testing by developing immunoassays that could be implemented for routine potency assessment of vaccines. This paper focused on the development of a Luminex-based multiplex assay to monitor the consistency of antigen quantity and quality throughout the production process of DTaP vaccines from two human vaccine manufacturers. Indepth characterized monoclonal antibody pairs were used for development and optimization of the Luminex assay with non-adsorbed and adsorbed antigens and with complete vaccine formulations from both manufacturers. The multiplex assay demonstrated good specificity, reproducibility and absence of cross-reactivity. Analysis of over and underdosed formulations, heat and H2O2-degraded products as well as batch to batch consistency of vaccines from both manufacturers brought the proof of concept for a future application of the multiplex immunoassay as a useful tool in the frame of DTaP vaccine quality control.

Quantification methods for viruses and virus-like particles applied in biopharmaceutical production processes

INTRODUCTION

Effective cell-based production processes of virus particles are the foundation for the global availability of classical vaccines, gene therapeutic vectors, and viral oncolytic treatments. Their production is subject to regulatory standards ensuring the safety and efficacy of the pharmaceutical product. Process analytics must be fast and reliable to provide an efficient process development and a robust process control during production. Additionally, for the product release, the drug compound and the contaminants must be quantified by assays specified by regulatory authorities.

AREAS COVERED

This review summarizes analytical methods suitable for the quantification of viruses or virus-like particles. The different techniques are grouped by the analytical question that may be addressed. Accordingly, methods focus on the infectivity of the drug component on the one hand, and on particle counting and the quantification of viral elements on the other hand. The different techniques are compared regarding their advantages, drawbacks, required assay time, and sample throughput.

EXPERT OPINION

Among the technologies summarized, a tendency toward fast methods, allowing a high throughput and a wide applicability, can be foreseen. Driving forces for this progress are miniaturization and automation, and the continuous enhancement of process-relevant databases for a successful future process control.

Characterisation of tetanus monoclonal antibodies as a first step towards the development of an in vitro vaccine potency immunoassay

Batch release testing for human and veterinary tetanus vaccines still relies heavily on methods that involve animals, particularly for potency testing. The quantity and quality of tetanus antigen present in these products is of utmost importance for product safety and clinical effect. Immunochemical methods that measure consistency of antigen content and quality, potentially as an indicator of potency, could be a better choice and negate the need for an in vivo potency test. These immunochemical methods require at least one well characterised monoclonal antibody (mAb) that is specific for the target antigen. In this paper we report the results of the comprehensive characterisation of a panel of mAbs against tetanus with a view to select antibodies that can be used for development of an in vitro potency immunoassay. We have assessed binding of the antibodies to native antigen (toxin), detoxified antigen (toxoid), adsorbed antigen and heat-altered antigen. Antibody function was determined using an in-house cell-based neutralisation assay to support prior in vivo potency data that was available for some, but not all, of the antibodies. In addition, antibody affinity was measured, and epitope competition analysis was performed to identify pairs of antibodies that could be deployed in a sandwich immunoassay format. Not all characterisation tests provided evidence of "superiority" of one mAb over another, but together the results from all characterisation studies allowed for selection of an antibody pair to be taken forward to assay development.

Characterisation of diphtheria monoclonal antibodies as a first step towards the development of an in vitro vaccine potency immunoassay

Immunoassays are used for routine potency assessment of several vaccines, in some cases having been specifically developed as alternatives to in vivo potency tests. These methods require at least one well characterised monoclonal antibody (mAb) that is specific for the target antigen. In this paper we report the results of the comprehensive characterisation of a panel of mAbs against diphtheria with a view to select antibodies that can be used for development of an in vitro potency immunoassay for diphtheria vaccines. We have assessed binding of the antibodies to native antigen (toxin), detoxified antigen (toxoid), adsorbed antigen and heat-altered antigen. Antibody function was determined by a cell-based toxin neutralisation test and diphtheria toxin-domain recognition was determined by Western blotting. In addition, antibody affinity was measured, and epitope competition analysis was performed to identify pairs of antibodies that could be deployed in a sandwich immunoassay format. Not all characterisation tests provided evidence of "superiority" of one mAb over another, but together the results from all characterisation studies allowed for selection of an antibody pair to be taken forward to assay development.

A novel electrophoretic immunoblot as antigen desorption and quantification method for alum-adjuvanted veterinary rabies vaccines

Rabies vaccines for domestic animals are adjuvanted with aluminum salts. A particular challenge for in-vitro batch potency tests with these products is the fact that the antigens are firmly adsorbed to the aluminum salt matrix and thus are not easily available for antigen quantification. In the current manuscript we describe a versatile technique to quantify antigens in aluminum adsorbed vaccine formulations. A combined electrophoretic desorption and blotting method is presented that transfers the antigens to a nitrocellulose membrane followed by an immunoblot quantification of the transferred rabies antigens. For the immunoblot a rabies G-protein specific, monoclonal antibody is used that by itself has neutralizing activity. This ensures that only relevant antigens are quantified. By comparing end products with non-adjuvanted in-process material it can be demonstrated that the antigens are quantitatively desorbed from the adjuvant matrix. Resuts of the new antigen quantification method were compared with the outcome of the serological batch potency test as described in the European Pharmacopoeia. It is demonstrated that the new antigen quantification method reveals relevant differences between experimental vaccine batches formulated with increasing antigen loads. This proves the broad detection range of the method. In general, the results show that this highly versatile technique can serve as an important component of a comprehensive consistency test strategy and may be applied in a modified form to any alum-adjuvanted vaccine.

Development of a Pertactin-Coated Beads Approach for Screening of Functional Monoclonal Antibodies

Vaccine manufacturers have recently focused on the development of in vitro potency assays to promote 3R's strategy to replace animal testing. To be able to develop an in vitro potency assay, the immunological characteristics of the monoclonal antibodies used in the assay should be well understood as these antibodies likely reflect the biological activity of a vaccine product. The PRN antigen is one of the immunogenic antigens included in many commercialized acellular pertussis vaccines. Development of an in vitro potency assay for PRN is challenging as the biological properties of PRN are not well understood. In addition, binding of Bordetella pertussis to human cells occurs through multiple bacterial molecules, which makes it very challenging to assess if antibodies contribute to prevention of bacterial adhesion. To overcome these challenges, the functionality of several in-house anti-PRN mAbs has been investigated through a novel approach using PRN-coated beads. We were able to consistently quantify the inhibition of PRN-mediated adhesion for each anti-PRN mAb. Application of the protein-coated beads model has not only enabled screening of functional anti-PRN mAbs but can also be expanded for screening of antibodies against other bacterial or viral antigens.

Evaluation of a capture antigen ELISA for the characterisation of tetanus vaccines for veterinary use

We previously developed an ELISA assay for detection of tetanus toxoid antigen in tetanus vaccines for human use. Tetanus vaccines for veterinary use are qualitatively different to those used in humans, often containing a larger number and variety of non-tetanus antigens in the multi-valent products, and adjuvants that are not found in human vaccines. We assessed performance of the capture ELISA with a range of veterinary tetanus vaccines as a first step towards development of an immunoassay as a potential in vivo potency substitute. Nine tetanus vaccines were tested and all produced a good dose response in the ELISA. The shape of the dose response curve for the whole vaccine compared to a matched non-adjuvanted tetanus toxoid antigen was more comparable for vaccines containing a non-aluminium adjuvant than products containing aluminium adjuvants. Elution of the antigen from aluminium adjuvant did not improve the comparability of the dose response curve but did increase the total amount of tetanus antigen available for detection. The ELISA was highly specific for tetanus with no signal obtained for a large number of non-tetanus antigens. These results suggest that a capture ELISA assay can be applied to a control strategy for veterinary tetanus vaccines.

Achieving scientific and regulatory success in implementing non-animal approaches to human and veterinary rabies vaccine testing: A NICEATM and IABS workshop report

This two-day workshop, co-sponsored by NICEATM and IABS-NA, brought together over 60 international scientists from government, academia, and industry to advance alternative methods for human and veterinary Rabies Virus Vaccine (RVV) potency testing. On day one, workshop presentations focused on regulatory perspectives related to in vitro potency testing, including recent additions to the European Pharmacopoeia (5.2.14) that provide a scientific rationale for why in vivo methods may be less suitable for vaccine quality control than appropriately designed in vitro methods. Further presentations reviewed the role of the consistency approach to manufacturing and vaccine batch comparison to provide supportive data for the substitution of existing animal-based methods with in vitro assays. In addition, updates from research programs evaluating and validating RVV glycoprotein (G) quantitation by ELISA as an in vitro potency test were presented. On the second day, RVV stakeholders participated in separate human and veterinary vaccine discussion groups focused on identifying potential obstacles or additional requirements for successful implementation of non-animal alternatives to the in vivo potency test. Workshop outcomes and proposed follow up activities are discussed herein.

Multifaceted characterization of recombinant protein-based vaccines: An immunochemical toolbox for epitope-specific analyses of the hepatitis E vaccine

The integrity of functional epitopes is a critical quality attribute for recombinant protein based vaccines since the presence of these native-like epitopes is the structural basis for vaccines to elicit functional antibodies. To demonstrate the quality and quantity of functional epitopes on vaccine antigens, a toolbox of assessing antigen characteristics is essential. Among the physicochemical, biophysical, immunochemical and in vivo potency analyses, the epitope-specific assays are most critical assessment of the antigen functionality. In this study, we used hepatitis E virus vaccine as an example to illustrated how the monoclonal antibody (mAb) based immunochemical assays were established for in-depth and multifaceted antigen characterization. A large panel of mAbs were developed and characterized using epitope clustering analysis. A subset of these mAbs recognizing non-overlapping epitopes were chosen to be used for assay development. Orthogonal methods, including surface plasma resonance-based BIAcore, solution competitive ELISA and sandwich ELISA, were developed for the antigenicity assessment. The sandwich ELISA with a pair of mAbs, recognizing two different epitopes, was used to assess the accelerated antigen stability, showing enhanced stability with adjuvant adsorption. Such a sandwich ELISA with robust performance has the potentials to be used for in vitro potency analysis to replace animal-based potency assay as product release test. In summary, using hepatitis E vaccine as an example, we demonstrated the importance and establishment of a mAb-based immunochemical toolbox for multifaceted antigen characterization. This is particularly important to demonstrate the successful reconstruction of the native-like and functional epitopes on a recombinant antigen post expression and purification. These epitope-specific and multifaceted assays serve as critical tools for process monitoring or lot consistency tests in support of vaccine development and manufacturing.

Development and pre-validation of a quantitative multi-dose serological assay for potency testing of inactivated rabies vaccines for human use

It is mandatory to ensure the quality of biological products used in the prevention of rabies, a zoonosis with nearly 100% lethality. Fifteen million people receive post-exposure prophylaxis yearly. The vaccine batches are assessed by the National Institutes of Health (NIH) test which has several disadvantages such as significant variability and animal welfare issues. The estimation of immunogenicity based on titration of neutralizing antibodies (NA) is not applied to the human vaccine yet. Despite this, a satisfactory concentration of NA (0.5 IU/ml) can be used as a predictor of the clinical efficacy and for estimating rabies vaccine potency. The objective of this study was to develop and pre-validate a Serological Potency Test (SPT) using the modified Rapid Fluorescent Focus Inhibition Test (mRFFIT) to determine the potency of rabies vaccines for human use, demonstrating its relevance and reliability. The results show good agreement between the potencies determined by the SPT and the NIH test. The assay was able to distinguish between potent and sub-potent lots of vaccines. The results demonstrated that SPT is a viable candidate for validation and inclusion in pharmacopeias as a reduction and refinement for the NIH test.

A novel in vitro ELISA for estimation of glycoprotein content in human rabies vaccines

In vitro methods for quantification of immunodominant glycoprotein in the rabies vaccine formulations serve as good alternative to the cumbersome and variable mice potency assay as a batch release test for the vaccine. The present study presents the development of a sandwich ELISA with optimal concentrations of a high affinity recombinant diabody (D06) and a specific monoclonal antibody (M5B4) against rabies glycoprotein for its quantification in the vaccine formulations. The glycoprotein estimate correlated linearly (r² = 0.8) to the in vivo potency estimate for the vaccine formulations. This ELISA promises a good forecast of the mice potency values and thereby can serve as a simple, yet effective batch release test for the rabies vaccines replacing the in vivo assay.