The consistency approach for quality control of vaccines – A strategy to improve quality control and implement 3Rs

Integrating 3Rs approaches in WHO guidelines for the batch release testing of biologicals: Responses from a survey of National Control Laboratories and National Regulatory Authorities

The UK National Centre for the Replacement, Refinement, and Reduction of Animals in Research (NC3Rs) is reviewing World Health Organization (WHO) manuals, guidelines and recommendations for vaccines and biotherapeutics to identify the extent to which animal-based testing methods are described. The aim is to recommend where updates to these documents can lead to an increased and more harmonised adoption of 3Rs principles (i.e. Replacement, Reduction and Refinement of animal tests) in the quality control and batch release testing requirements for vaccines and biotherapeutics. Improved adoption of 3Rs principles and non-animal testing strategies will help to reduce the delays and costs associated with product release testing. Developing recommendations that are widely applicable by both the manufacturers and national regulatory authorities for vaccines and biological therapeutics globally requires a detailed understanding of how different organisations view the opportunities and barriers to better integration of the 3Rs. To facilitate this, we developed and distributed a survey aimed at individuals who work for national regulatory authorities (NRAs) and/or national control laboratories (NCLs). In this paper, we present the key findings from this survey and how these will help inform the recommendations for wider integration of 3Rs approaches by WHO in their guidance documents applicable to the quality control and batch release testing of vaccines and biotherapeutics.

Variability of in vivo potency assays of whole-cell pertussis, inactivated polio, and meningococcal B vaccines

For the batch release of vaccines, potency release assays are required. Non-animal in vitro tests have numerous advantages and are preferred; however, several vaccines are still released using in vivo assays. Their major drawback is the inherent variability with its practical implications. We quantified the variability of in vivo potency release assays for whole-cell pertussis, inactivated polio and meningococcal B (MenB) vaccines which showed large CV (Coefficient of Variation) ranging from 34% to 125%. As inherent variability might potentially be attributed to the highly variable immune system between individual animals, we evaluated the antibody titres to four MenB antigens in 344 individual outbred mice. These varied strongly, with more than 100-fold differences in antibody titres in responsive mice. Furthermore, within individual mice there was generally no correlation between the strengths of the responses to the four antigens. A mouse with a very low or no response to one antigen in many cases exhibited a strong response to another antigen. The large differences between individual animals is likely a considerable contributor to the inherent variability of in vivo potency assays. Our data again support the notion that it is preferred to move away from in vivo potency assays for monitoring batch to batch consistency as part of vaccine batch release testing.

A universal UHPLC-CAD platform for the quantification of polysaccharide antigens

Several glycoconjugate-based vaccines against bacterial infections have been developed and licensed for human use. Polysaccharide (PS) analysis and characterization is therefore critical to profile the composition of polysaccharide-based vaccines. For PS content quantification, the majority of Ultra High Performance Liquid Chromatography (UHPLC) methods rely on the detection of selective monosaccharides constituting the PS repeating unit, therefore requiring chemical cleavage and tailored development: only a few methods directly quantify the intact PS. The introduction of charged aerosol detector (CAD) technology has improved the response of polysaccharide analytes, offering greater sensitivity than other detector sources (e.g., ELSD). Herein, we report the development of a universal UHPLC-CAD method (UniQS) for the quantification and quality evaluation of polysaccharide antigens (e.g., Streptococcus Pneumoniae, Neisseria meningitidis and Staphylococcus aureus). This work laid the foundation for a universal UHPLC-CAD format that could play an important role in future vaccine research and development helping to reduce time, efforts, and costs.

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.

COVID-19 in early 2023: Structure, replication mechanism, variants of SARS-CoV-2, diagnostic tests, and vaccine & drug development studies

Coronavirus Disease-19 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome-coronaviruses-2 (SARS-CoV-2), a highly pathogenic and transmissible coronavirus. Most cases of COVID-19 have mild to moderate symptoms, including cough, fever, myalgias, and headache. On the other hand, this coronavirus can lead to severe complications and death in some cases. Therefore, vaccination is the most effective tool to prevent and eradicate COVID-19 disease. Also, rapid and effective diagnostic tests are critical in identifying cases of COVID-19. The COVID-19 pandemic has a dynamic structure on the agenda and contains up-to-date developments. This article has comprehensively discussed the most up-to-date pandemic situation since it first appeared. For the first time, not only the structure, replication mechanism, and variants of SARS-CoV-2 (Alpha, Beta, Gamma, Omicron, Delta, Epsilon, Kappa, Mu, Eta, Zeta, Theta, lota, Lambda) but also all the details of the pandemic, such as how it came out, how it spread, current cases, what precautions should be taken, prevention strategies, the vaccines produced, the tests developed, and the drugs used are reviewed in every aspect. Herein, the comparison of diagnostic tests for SARS-CoV-2 in terms of procedure, accuracy, cost, and time has been presented. The mechanism, safety, efficacy, and effectiveness of COVID-19 vaccines against SARS-CoV-2 variants have been evaluated. Drug studies, therapeutic targets, various immunomodulators, and antiviral molecules applied to patients with COVID-19 have been reviewed.

Development of an In Vitro Test Method to Replace an Animal-Based Potency Test for Pertactin Antigen in Multivalent Vaccines

There is increasing interest to replace animal-based potency assays used routinely to test vaccines, since they are highly variable, are costly, and present ethical concerns. The development of relevant in vitro assays is part of the solution. Using pertactin (PRN) antigen as an example in DTaP-IPV (diphtheria, tetanus, acellular pertussis, and inactivated poliovirus) vaccines, a PRN antigenicity ELISA was developed using two monoclonal antibodies with a high affinity to unique PRN epitopes, relevance to human immune responses, and evidence of functionality. The ELISA measured consistent PRN antigenicity between the vaccine lots and was validated to demonstrate its accuracy, precision, linearity, and specificity. Notably, the PRN antigenicity ELISA was more sensitive than the mouse-based potency test and could more effectively differentiate between degraded and intact vaccine lots compared to the in vivo test. From these studies, the PRN antigenicity ELISA is proposed as an in vitro replacement for the in vivo potency test for PRN in DTaP-IPV-based formulations. Important considerations in this study included comprehensive antibody characterization, testing of multiple vaccine lots, method validation, and comparison to animal-based potency. Together, these factors form part of an overall strategy that ensures reliable and relevant in vitro assays are developed to replace animal tests.

The consistency approach for the substitution of in vivo testing for the quality control of established vaccines: practical considerations and progressive vision

The aim of this letter is to share the discussions and proposals made by the VAC2VAC consortium on how to support the deployment of the "Consistency Approach" for quality control of established vaccines and thus facilitate the substitution of in vivo testing. This work answers specific questions about " what does a control strategy according to the consistency testing look like" and " how to submit a control strategy defined according to the consistency testing". Some topics were answered in a very straightforward manner. This was the case when the deployment of the consistency approach and the corresponding changes in vaccines control strategy was supported by the generic application of procedures already described in regulatory guidelines/requirements and related to the establishment or change in the control strategy of vaccines. The application of other procedures required more specific attention and some were deeply debated before reaching a proposal. The key outcomes of this work are that robust science must be used to develop a substitution strategy and generate supportive data packages. And this good science can best occur with good scientific collaboration between the different parties involved. Therefore, early interaction between manufacturers and competent authorities before and during dossier submission is critical to success. The consistency approach, when approved and in place, will ensure vaccine products of assured quality reach the patient in a more efficient manner than when relying on in vivo testing. Adapting the mindset was one of the major hurdles to a progressive vision but there is now consensus between manufacturers and competent authorities to foster the elimination of in vivo testing for routine vaccine release testing.

Integrating 3Rs approaches in WHO guidelines for the batch release testing of biologicals: Responses from a survey of vaccines and biological therapeutics manufacturers

The UK National Centre for the Replacement, Refinement, and Reduction of Animals in Research (NC3Rs) has been tasked by the World Health Organization (WHO) to review the extent to which animal-based testing methods are described in their manuals, guidelines and recommendations for vaccines and biotherapeutics. The aim is to identify and recommend where updates to these documents can lead to an increased and more harmonised adoption of 3Rs principles (i.e. Replacement, Reduction and Refinement of animal tests) in the quality control and batch release testing requirements for vaccines and biotherapeutics. Developing recommendations that are widely applicable by both the manufacturers and national regulatory authorities for vaccines and biologicals globally requires a detailed understanding of how different organisations view the opportunities and barriers to better integration of the 3Rs. To facilitate this, we developed and distributed a survey aimed at vaccine and biotherapeutics manufacturers in July 2021. In this paper, we present the key findings from this survey and how these will help inform the recommendations for wider integration of 3Rs approaches by WHO in their guidance documents applicable to the quality control and batch testing of vaccines and biotherapeutics.

Accelerating Global Deletion of the Abnormal Toxicity Test for vaccines and biologicals. Planning common next steps. A workshop Report

This online workshop Accelerating Global Deletion of the Abnormal Toxicity Test for vaccines and biologicals. Planning common next steps was organized on October 14th, 2021, by the Animal Free Safety Assessment Collaboration (AFSA), the Humane Society International (HSI), the European Federation of Pharmaceutical Industries and Associations (EFPIA), in collaboration with the International Alliance of Biological Standardization (IABS). The workshop saw a participation of over a hundred representatives from international organizations, pharmaceutical industries and associations, and regulatory authorities of 28 countries. Participants reported on country- and region-specific regulatory requirements and, where present, on the perspectives on the waiving and elimination of the Abnormal Toxicity Test. With AFSA, HSI, EFPIA and IABS representatives as facilitators, the participants also discussed specific country/global actions to further secure the deletion of ATT from all regulatory requirements worldwide.

Mass Spectrometry-Based Quantification of the Antigens in Aluminum Hydroxide-Adjuvanted Diphtheria-Tetanus-Acellular-Pertussis Combination Vaccines

Vaccines undergo stringent batch-release testing, most often including in-vivo assays for potency. For combination vaccines, such as diphtheria-tetanus-pertussis (DTaP), chemical modification induced by formaldehyde inactivation, as well as adsorption to aluminum-based adjuvants, complicates antigen-specific in-vitro analysis. Here, a mass spectrometric method was developed that allows the identification and quantitation of DTaP antigens in a combination vaccine. Isotopically labeled, antigen-specific internal standard peptides were employed that permitted absolute quantitation of their antigen-derived peptide counterparts and, consequently, the individual antigens. We evaluated the applicability of the method on monovalent non-adjuvanted antigens, on final vaccine lots and on experimental vaccine batches, where certain antigens were omitted from the drug product. Apart from the applicability for final batch release, we demonstrated the suitability of the approach for in-process control monitoring. The peptide quantification method facilitates antigen-specific identification and quantification of combination vaccines in a single assay. This may contribute, as part of the consistency approach, to a reduction in the number of animal tests required for vaccine-batch release.

Regulation of Clostridium tetani Neurotoxin Expression by Culture Conditions

BACKGROUND

Ensuring consistency of tetanus neurotoxin (TeNT) production by Clostridium tetani could help to ensure consistent product quality in tetanus vaccine manufacturing, ultimately contributing to reduced animal testing. The aim of this study was to identify RNA signatures related to consistent TeNT production using standard and non-standard culture conditions.

METHODS

We applied RNA sequencing (RNA-Seq) to study C. tetani gene expression in small-scale batches under several culture conditions.

RESULTS

We identified 1381 time-dependent differentially expressed genes (DEGs) reflecting, among others, changes in growth rate and metabolism. Comparing non-standard versus standard culture conditions identified 82 condition-dependent DEGs, most of which were specific for one condition. The tetanus neurotoxin gene (tetX) was highly expressed but showed expression changes over time and between culture conditions. The tetX gene showed significant down-regulation at higher pH levels (pH 7.8), which was confirmed by the quantification data obtained with the recently validated targeted LC-MS/MS approach.

CONCLUSIONS

Non-standard culture conditions lead to different gene expression responses. The tetX gene appears to be the best transcriptional biomarker for monitoring TeNT production as part of batch-to-batch consistency testing during tetanus vaccine manufacturing.

Integrating 3Rs approaches in WHO guidelines for the batch release testing of biologicals

Animal testing has long been integral to the development of biologicals, including vaccines. The use of animals can provide important information on potential toxicity, insights into their mechanism of action, pharmacokinetics and dynamics, physiologic distribution, and potency. However, the use of these same methods is often adopted into the post-licensure phase of the product life cycle for the monitoring of product qualities, such as potency or safety, as part of their routine batch release. The UK National Centre for the Replacement, Refinement, and Reduction of Animals in Research (NC3Rs) and the World Health Organization (WHO) are collaborating on a project to review animal-based testing methods described in WHO manuals, guidelines and recommendations for biologicals to identify where updates can lead to a more harmonised adoption of 3Rs principles (i.e. Replacement, Reduction, and Refinement of animal tests) in batch release testing requirements. An international working group consisting of more than 30 representatives from pharmaceutical and biotechnology companies, national control laboratories and regulatory bodies is performing this review. This project aims to address concerns about inconsistencies in the guidance for the scientifically justified use of animal methods required for the post-licensure quality control and batch release testing of biologicals, and the near absence of recommendations for the application of 3Rs principles within the relevant guidelines. Improved adoption of 3Rs principles and non-animal testing strategies will help to reduce the delays and costs associated with product release testing and help support faster access to products by the global communities who need them most urgently.

Structural Alterations of Antigens at the Material Interface: An Early Decision Toolbox Facilitating Safe-by-Design Nanovaccine Development

Nanomaterials have found extensive interest in the development of novel vaccines, as adjuvants and/or carriers in vaccination platforms. Conjugation of protein antigens at the particle surface by non-covalent adsorption is the most widely used approach in licensed particulate vaccines. Hence, it is essential to understand proteins' structural integrity at the material interface in order to develop safe-by-design nanovaccines. In this study, we utilized two model proteins, the wild-type allergen Bet v 1 and its hypoallergenic fold variant (BM4), to compare SiO2 nanoparticles with Alhydrogel® as particulate systems. A set of biophysical and functional assays including circular dichroism spectroscopy and proteolytic degradation was used to examine the antigens' structural integrity at the material interface. Conjugation of both biomolecules to the particulate systems decreased their proteolytic stability. However, we observed qualitative and quantitative differences in antigen processing concomitant with differences in their fold stability. These changes further led to an alteration in IgE epitope recognition. Here, we propose a toolbox of biophysical and functional in vitro assays for the suitability assessment of nanomaterials in the early stages of vaccine development. These tools will aid in safe-by-design innovations and allow fine-tuning the properties of nanoparticle candidates to shape a specific immune response.

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.

Variability of in vivo potency tests of Diphtheria, Tetanus and acellular Pertussis (DTaP) vaccines

For batch release of legacy vaccines such as DTaP, in vivo potency release assays are required. We quantified the variability of in vivo potency release assays for four DTaP (Diphtheria, Tetanus, acellular Pertussis) products of different manufacturers. With their large CV (Coefficients of Variance) ranging from 16% to 132%, these in vivo assays are of limited value to ensure their potency is consistent and similar to the clinical batches used for the marketing authorisation. Our data show that, although individual potency test results show high variability, the DTaP batches are manufactured with great consistency, because repeated potency testing yields similar averages for the different batches. The economic impact of variability of in vivo tests is significant since it may result in the need for greater amount of antigen than may be required or for repeating a test. For monitoring the consistency of potency, in vitro assays are superior to in vivo assays. Animal-free potency determination is common practice for newly developed vaccines under modern GMP quality systems. However, replacement of in vivo potency tests for legacy vaccines like DTaP is challenging and would require a 'reverse characterisation' strategy in which the antigens are further characterised at the level of drug substance and drug product to identify critical quality attributes (CQA) that can be tested with in vitro assays. Based on these an updated set of release tests without animal tests can be proposed. Our data can serve as benchmark for the innovative methods.

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.

Degradomics-Based Analysis of Tetanus Toxoids as a Quality Control Assay

Currently, batch release of toxoid vaccines, such as diphtheria and tetanus toxoid, requires animal tests to confirm safety and immunogenicity. Efforts are being made to replace these tests with in vitro assays in a consistency approach. Limitations of current in vitro assays include the need for reference antigens and most are only applicable to drug substance, not to the aluminum adjuvant-containing and often multivalent drug product. To overcome these issues, a new assay was developed based on mimicking the proteolytic degradation processes in antigen-presenting cells with recombinant cathepsin S, followed by absolute quantification of the formed peptides by liquid chromatography-mass spectrometry. Temperature-exposed tetanus toxoids from several manufacturers were used as aberrant samples and could easily be distinguished from the untreated controls by using the newly developed degradomics assay. Consistency of various batches of a single manufacturer could also be determined. Moreover, the assay was shown to be applicable to Al(OH)₃ and AlPO₄-adsorbed tetanus toxoids. Overall, the assay shows potential for use in both stability studies and as an alternative for in vivo potency studies by showing batch-to-batch consistency of bulk toxoids as well as for aluminum-containing vaccines.

Animal testing for vaccines. Implementing replacement, reduction and refinement: challenges and priorities

Transition to in vitro alternative methods from in vivo in vaccine release testing and characterization, the implementation of the consistency approach, and a drive towards international harmonization of regulatory requirements are most pressing needs in the field of vaccines. It is critical for global vaccine community to work together to secure effective progress towards animal welfare and to ensure that vaccines of ever higher quality can reach the populations in need in the shortest possible timeframe. Advancements in the field, case studies, and experiences from Low and Middle Income Countries (LMIC) were the topics discussed by an international gathering of experts during a recent conference titled "Animal Testing for Vaccines - Implementing Replacement, Reduction and Refinement: Challenges and Priorities". This conference was organized by the International Alliance for Biological Standardization (IABS), and held in Bangkok, Thailand on December 3 and 4 2019. Participants comprised stakeholders from many parts of the world, including vaccine developers, manufacturers and regulators from Asia, Europe, North America, Australia and New Zealand. In interactive workshops and vibrant panel discussions, the attendees worked together to identify the remaining barriers to validation, acceptance and implementation of alternative methods, and how harmonization could be promoted, especially for LMICs.

Novel Formaldehyde-Induced Modifications of Lysine Residue Pairs in Peptides and Proteins: Identification and Relevance to Vaccine Development

Formaldehyde-inactivated toxoid vaccines have been in use for almost a century. Despite formaldehyde's deceptively simple structure, its reactions with proteins are complex. Treatment of immunogenic proteins with aqueous formaldehyde results in heterogenous mixtures due to a variety of adducts and cross-links. In this study, we aimed to further elucidate the reaction products of formaldehyde reaction with proteins and report unique modifications in formaldehyde-treated cytochrome c and corresponding synthetic peptides. Synthetic peptides (Ac-GDVEKGAK and Ac-GDVEKGKK) were treated with isotopically labeled formaldehyde (¹³CH₂O or CD₂O) followed by purification of the two main reaction products. This allowed for their structural elucidation by (2D)-nuclear magnetic resonance and nanoscale liquid chromatography-coupled mass spectrometry analysis. We observed modifications resulting from (i) formaldehyde-induced deamination and formation of α,β-unsaturated aldehydes and methylation on two adjacent lysine residues and (ii) formaldehyde-induced methylation and formylation of two adjacent lysine residues. These products react further to form intramolecular cross-links between the two lysine residues. At higher peptide concentrations, these two main reaction products were also found to subsequently cross-link to lysine residues in other peptides, forming dimers and trimers. The accurate identification and quantification of formaldehyde-induced modifications improves our knowledge of formaldehyde-inactivated vaccine products, potentially aiding the development and registration of new vaccines.

Recent advances, approaches and challenges in targeting pathways for potential COVID-19 vaccines development

During the COVID-19 pandemic in a modern era, there is a global consensus on the need for the rapid development of a vaccine against SARS-CoV-2 for effective and sustainable control. Developing these vaccines is fundamental to public health. This urgent need is supported by the scientific explosion in structural and genomic biology that facilitates the urgent development of an ideal COVID-19 vaccine, using new pathways to facilitate its large-scale development, testing, and manufacture. Here, we summarize the types of COVID-19 candidate vaccines, their current stage in early testing in human clinical trials, and the challenges for their implementation.

Formaldehyde treatment of proteins enhances proteolytic degradation by the endo-lysosomal protease cathepsin S

Enzymatic degradation of protein antigens by endo-lysosomal proteases in antigen-presenting cells is crucial for achieving cellular immunity. Structural changes caused by vaccine production process steps, such as formaldehyde inactivation, could affect the sensitivity of the antigen to lysosomal proteases. The aim of this study was to assess the effect of the formaldehyde detoxification process on the enzymatic proteolysis of antigens by studying model proteins. Bovine serum albumin, β-lactoglobulin A and cytochrome c were treated with various concentrations of isotopically labelled formaldehyde and glycine, and subjected to proteolytic digestion by cathepsin S, an important endo-lysosomal endoprotease. Degradation products were analysed by mass spectrometry and size exclusion chromatography. The most abundant modification sites were identified by their characteristic MS doublets. Unexpectedly, all studied proteins showed faster proteolytic degradation upon treatment with higher formaldehyde concentrations. This effect was observed both in the absence and presence of glycine, an often-used excipient during inactivation to prevent intermolecular crosslinking. Overall, subjecting proteins to formaldehyde or formaldehyde/glycine treatment results in changes in proteolysis rates, leading to an enhanced degradation speed. This accelerated degradation could have consequences for the immunogenicity and the efficacy of vaccine products containing formaldehyde-inactivated antigens.

Harnessing the power of novel animal-free test methods for the development of COVID-19 drugs and vaccines

The COVID-19-inducing virus, SARS-CoV2, is likely to remain a threat to human health unless efficient drugs or vaccines become available. Given the extent of the current pandemic (people in over one hundred countries infected) and its disastrous effect on world economy (associated with limitations of human rights), speedy drug discovery is critical. In this situation, past investments into the development of new (animal-free) approach methods (NAM) for drug safety, efficacy, and quality evaluation can be leveraged. For this, we provide an overview of repurposing ideas to shortcut drug development times. Animal-based testing would be too lengthy, and it largely fails, when a pathogen is species-specific or if the desired drug is based on specific features of human biology. Fortunately, industry has already largely shifted to NAM, and some public funding programs have advanced the development of animal-free technologies. For instance, NAM can predict genotoxicity (a major aspect of carcinogenicity) within days, human antibodies targeting virus epitopes can be generated in molecular biology laboratories within weeks, and various human cell-based organoids are available to test virus infectivity and the biological processes controlling them. The European Medicines Agency (EMA) has formed an expert group to pave the way for the use of such approaches for accelerated drug development. This situation illustrates the importance of diversification in drug discovery strategies and clearly shows the shortcomings of an approach that invests 95% of resources into a single technology (animal experimentation) in the face of challenges that require alternative approaches.

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.

A next-generation sequencing based method for determining genetic stability in Clostridium tetani vaccine strains

Production of tetanus and other clostridial vaccines highly depends on the stable and reproducible production of high toxin levels. This creates a need to ensure the genetic stability of seed strains. We developed a two-stage method for improved assessment of the genetic stability of Clostridium seed strains. This method is based on next-generation sequencing (NGS) of strain DNA and mapping the sequence reads to a reference sequence. The output allows analysis of global genome consistency followed, if necessary, by detailed expert judgement of potential deviations at the gene level. The limit of detection of our method is an order of magnitude better than that of the currently established pulsed-field gel electrophoresis (PFGE). Improved genetic characterization of bacterial seed lots will have a positive impact on the characterization of the production process. This will be a first step towards applying the consistency approach to vaccine batch release of established vaccines. This can contribute to the reduction and ultimately replacement of routinely used animal tests in vaccine production. This work was carried out as part of the Innovative Medicines Initiative 2 (IMI2) project VAC2VAC (Vaccine batch to vaccine batch comparison by consistency testing).

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.

Incidental induction of secondary bowel disorders in guinea pigs during a batch safety test of veterinary vaccines

Veterinary vaccines are subjected to a safety testing using laboratory animals via intraperitoneal injection per batch. From April 2010 to March 2011, 7 guinea pigs in 4 batch tests exhibited unrecoverable weight loss and/or were found dead. Six guinea pigs had developed intussusception, whereas another one had developed an intestinal obstruction consequent to adhesion. A histopathology revealed that these lesions were associated with inflammatory foci. Other animals than the 7 guinea pig also developed similar inflammatory foci but did not develop bowel disorders. In the retesting of these batches, animals did not exhibited clinical signs, though inflammatory foci were detected. The clinical signs, detected in the primary test, might be due to bowel disorders secondary to an inflammatory response, rather than toxicity.

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.

Identity, Structure and Compositional Analysis of Aluminum Phosphate Adsorbed Pediatric Quadrivalent and Pentavalent Vaccines

Purpose

The goal of this study is to set an empirical baseline to map the structure-function relation of the antigens from the commercialized vaccine products.

Methods

To study the structural changes of protein antigens after adsorption several analytical tools including DLS, FTIR, Fluorescence, LD, and SEM have been used.

Results

All antigens have shown wide range of hydrodynamic diameter from 7 nm to 182 nm. Upon adjuvantation, the size distribution has become narrow, ranging from 10 to 12 μm, and has been driven by the derived diameter of aluminum phosphate (AlPO₄) adjuvant. Further to examine size and morphology of adsorbed antigens, SEM has been used. The SEM results have demonstrated that the AlPO₄ adjuvant suspension and adsorbed proteins consist of submicron particles that form a continuous porous surface. Diphtheria Toxoid (DT), Tetanus Toxoid (TT), and chemically-modified Filamentous Haemagglutinin (FHA) have shown surface adsorption to AlPO_4. Secondary structure alpha-helix and beta-sheet content of DT and TT has increased after adsorption to AlPO₄ adjuvant as shown by FTIR, whereas no significant changes were noted for other protein antigens. The results from Intrinsic Fluorescence have shown a structural rearrangement in DT and TT, consistent with the FTIR results. Multivalent vaccine product identity has been determined by FTIR as unique fingerprint spectrum.

Conclusion

The globular proteins such as DT and TT have shown changes in secondary structure upon adsorption to AlPO₄, whereas fibrillar protein FHA has not been affected by adsorption. FTIR can be used as a lean technique to confirm product identity at different manufacturing sites.

Monocyte-activation test to reliably measure the pyrogenic content of a vaccine: An in vitro pyrogen test to overcome in vivo limitations

Pyrogen content is one of the critical quality attributes impacting the safety of a product, and there is an increasing need for assays that can reliably measure this attribute in vaccines. The Limulus amebocyte lysate (LAL) assay and the rabbit pyrogen test (RPT) are the canonical animal-based pyrogen tests currently used to release vaccines; however, there are several drawbacks associated with these tests when applied to Bexsero, intrinsically pyrogenic product, containing a meningococcal Outer Membrane Vesicle component. While the RPT, as applied to Bexsero at its given dilution, ensures safe vaccine, it is highly variable and prone to false positive results. On the other hand, the LAL assay although quantitative, can detect only endotoxin pyrogens and is not sufficient for monitoring the safety of Bexsero, which contains both LPS and non-endotoxin pyrogens. Being aware of these limitations of the RPT and LAL when applied to Bexsero, the Monocyte Activation Test (MAT) which is sensitive to both endotoxin and non-endotoxin based pyrogens has been developed as an alternative pyrogen test. Here, the development and the validation of a MAT assay adapted from the European pharmacopoeia for Bexsero, is described. The MAT assay is then used for monitoring the safety and consistency of Bexsero vaccines at release, providing great advantages in terms of reduced variability with respect to RPT, reduction of animal use, in line with the 3Rs principle concerning the protection of animals and faster time to market. In addition the correlation of the MAT to the RPT has been demonstrated supporting the replacement of the in vivo method and the potential application of the assay to other intrinsically pyrogenic vaccines.

Raman spectroscopy-based identification of toxoid vaccine products

Vaccines are complex biomedicines. Manufacturing is time consuming and requires a high level of quality control (QC) to guarantee consistent safety and potency. An increasing global demand has led to the need to reduce time and cost of manufacturing. The evolving concepts for QC and the upcoming threat of falsification of biomedicines define a new need for methods that allow the fast and reliable identification of vaccines. Raman spectroscopy is a non-destructive technology already established in QC of classical medicines. We hypothesized that Raman spectroscopy could be used for identification and differentiation of vaccine products. Raman maps obtained from air-dried samples of combination vaccines containing antigens from tetanus, diphtheria and pertussis (DTaP vaccines) were summarized to compile product-specific Raman signatures. Sources of technical variance were emphasized to evaluate the robustness and sensitivity in downstream data analysis. The data management approach corrects for spatial inhomogeneities in the dried sample while offering a proper representation of the original samples inherent chemical signature. Reproducibility of the identification was validated by a leave-one-replicate-out cross-validation. The results highlighted the high specificity and sensitivity of Raman measurements in identifying DTaP vaccine products. The results pave the way for further exploitation of the Raman technology for identification of vaccines in batch release and cases of suspected falsification.

A light-based identification method offers a fast, reliable and non-destructive method to analyze vaccines. Using vaccines for tetanus, diphtheria, and pertussis, a German research team led by the Paul Ehrlich Institute and University of Jena and Leibniz-IPHT showed that Raman spectroscopy — which identifies substances based on how they scatter laser light — is able to identify distinctive signatures of vaccines. In their experiments, Raman spectroscopy was sensitive enough to detect subtle differences in vaccine formulation, such as the specific combination of vaccine and adjuvant components. However, a data analytics technique was required to correct for sample quality variation caused by their preparation. Raman spectroscopy already sees use in classical medicines, and its application to vaccines could help to reduce the time and cost of quality control while benefitting the unmet need for rapid analysis of vaccine quality and identity.

One science-driven approach for the regulatory implementation of alternative methods: A multi-sector perspective

EU regulations call for the use of alternative methods to animal testing. During the last decade, an increasing number of alternative approaches have been formally adopted. In parallel, new 3Rs-relevant technologies and mechanistic approaches have increasingly contributed to hazard identification and risk assessment evolution. In this changing landscape, an EPAA meeting reviewed the challenges that different industry sectors face in the implementation of alternative methods following a science-driven approach. Although clear progress was acknowledged in animal testing reduction and refinement thanks to an integration of scientifically robust approaches, the following challenges were identified: i) further characterization of toxicity pathways; ii) development of assays covering current scientific gaps, iii) better characterization of links between in vitro readouts and outcome in the target species; iv) better definition of alternative method applicability domains, and v) appropriate implementation of the available approaches. For areas having regulatory adopted alternative methods (e.g., vaccine batch testing), harmonised acceptance across geographical regions was considered critical for broader application. Overall, the main constraints to the application of non-animal alternatives are the still existing gaps in scientific knowledge and technological limitations. The science-driven identification of most appropriate methods is key for furthering a multi-sectorial decrease in animal testing.

Drivers and barriers in the consistency approach for vaccine batch release testing: Report of an international workshop

Safety and potency assessment for batch release testing of established vaccines still relies partly on animal tests. An important avenue to move to batch release without animal testing is the consistency approach. This approach is based on thorough characterization of the vaccine, and the principle that the quality of subsequent batches is the consequence of the application of consistent production of batches monitored by a GMP quality system. Efforts to implement the consistency approach are supported by several drivers from industry, government, and research, but there are also several barriers that must be overcome. A workshop entitled "Consistency Approach, Drivers and Barriers" was organized, which aimed to discuss and identify drivers and barriers for the implementation of the 3Rs in the consistency approach from three different perspectives/domains (industry, regulatory and science frameworks). The workshop contributed to a better understanding of these drivers and barriers and resulted in recommendations to improve the overall regulatory processes for the consistency approach. With this report, we summarise the outcome of this workshop and intend to offer a constructive contribution to the international discussion on regulatory acceptance of the consistency approach.

A collaborative study of an alternative in vitro potency assay for the Japanese encephalitis vaccine

The use of inactivated Japanese encephalitis (JE) vaccines has been ongoing in East Asia for 40 years. A mouse immunogenicity assay followed by a Plaque Reduction Neutralization (PRN) Test (PRNTest) is currently recommended for each lot release of the vaccine by many national authorities. We developed an alternative in vitro ELISA to determine the E antigen content of the Japanese encephalitis virus to observe the 3Rs strategy. A collaborative study for replacing the in vivo potency assay for the Japanese encephalitis vaccine with the in vitro ELISA assay was confirmed comparability between these two methods. The study demonstrated that an in vitro assay could perform faster and was more convenient than the established in vivo PRNTest. Moreover, this assay had better precision and reproducibility compared with the conventional in vivo assay. Additionally, the content of antigen determined using the in vitro ELISA correlated well with the potency of the in vivo assay. Furthermore, this method allowed discrimination between individual lots. Thus, we propose a progressive switch from the in vivo assay to the in vitro ELISA for JE vaccine quality control.

A simple method for measuring porcine circovirus 2 whole virion particles and standardizing vaccine formulation

Porcine Circovirus 2 (PCV2) is involved in porcine circovirus-associated disease, that causes great economic losses to the livestock industry worldwide. Vaccination against PCV2 proved to be very effective in reducing disease occurrence and it is currently performed on a large scale. Starting from a previous model concerning Foot-and Mouth Disease Virus antigens, we developed a rapid and simple method to quantify PCV2 whole virion particles in inactivated vaccines. This procedure, based on sucrose gradient analysis and fluorometric evaluation of viral genomic content, allows for a better standardization of the antigen payload in vaccine batches. It also provides a valid indication of virion integrity. Most important, such a method can be applied to whole virion vaccines regardless of the production procedures, thus enabling meaningful comparisons on a common basis. In a future batch consistency approach to PCV2 vaccine manufacture, our procedure represents a valuable tool to improve in-process controls and to guarantee conformity of the final product with passmarks for approval. This might have important repercussions in terms of reduced usage of animals for vaccine batch release, in the framework of the current 3Rs policy.

Correlation between ToBI test and in vivo titration for diphtheria and tetanus

Alternatives to animal testing for quality control of biologicals have been a goal since 1959. Instituto Butantan has been developing such methods for quality control of biologicals for human use (vaccines and hyperimmune equine sera) for the last 13 years. In this paper we compare the modified ToBI test and the in vivo seroneutralization test to assess immunogenicity of diphtheria and tetanus vaccines and hyperimmune sera. Data from the last 10 years were statistically analyzed to compare the results for in vivo and in vitro titrations (diphtheria, n = 525 and tetanus, n = 455). The agreement between the tests depended on the serum titer range. For both diphtheria and tetanus components, the correlation and concordance coefficient was higher as the serum titer increased. Overall, the in vitro/in vivo titer ratio did not vary systematically over the range of measurements. These results indicate that although the in vitro ToBI test is not completely able to replace the in vivo serum titration, it is a useful tool to guide the tests during the production process, which can reduce the number of animals used for lot release.

[Reduction of animal experiments in experimental drug testing]

In order to ensure the quality of biomedical products, an experimental test for every single manufactured batch is required for many products. Especially in vaccine testing, animal experiments are traditionally used for this purpose. For example, efficacy is often determined via challenge experiments in laboratory animals. Safety tests of vaccine batches are also mostly performed using laboratory animals. However, many animal experiments have clear inherent disadvantages (low accuracy, questionable transferability to humans, unclear significance). Furthermore, for ethical reasons and animal welfare aspects animal experiments are also seen very critical by the public. Therefore, there is a strong trend towards replacing animal experiments with methods in which no animals are used ("replacement"). If a replacement is not possible, the required animal experiments should be improved in order to minimize the number of animals necessary ("reduction") and to reduce pain and suffering caused by the experiment to a minimum ("refinement"). This "3R concept" is meanwhile firmly established in legislature. In recent years many mandatory animal experiments have been replaced by alternative in vitro methods or improved according to the 3R principles; numerous alternative methods are currently under development. Nevertheless, the process from the development of a new method to its legal implementation takes a long time. Therefore, supplementary regulatory measures to facilitate validation and acceptance of new alternative methods could contribute to a faster and more consequent implementation of the 3R concept in the testing of biomedical products.

Development and validation of a serological potency test for the release of Leptospira vaccines--requirements in the European Union

Both European Pharmacopoeia Monograph 01/2008:0447 "Canine Leptospirosis vaccine (inactivated)" and the more recent Monograph 01/2008:1939 "Bovine Leptospirosis vaccine (inactivated)" explicitly allow for a sero-response test to assess batch potency. Test setup and requirements for in vivo and in vitro validation are described. Furthermore, the two main strategies to assess batch potency and their specific demands are addressed.

Development of Leptospira in vitro potency assays: EU/industry experience and perspectives

Nobivac® Lepto (MSD Animal Health) is a non-adjuvanted canine leptospirosis vaccine containing inactivated whole cells of Leptospira interrogans serogroup Canicola serovar Portlandvere and L. interrogans serogroup Icterohaemorrhagiae serovar Copenhageni. The current standard in vivo potency test is a hamster challenge test associated with major drawbacks such as animal suffering and poor reproducibility. Here, the quantification of antigenic mass by ELISA as a new in vitro potency test is described, supporting the 3Rs concept (replacement, reduction, and refinement of animal tests) and in accordance with European Pharmacopoeia Monograph 0447 (Canine Leptospirosis Vaccine [Inactivated]). The two corresponding sandwich ELISAs are based on monoclonal antibodies specific for immunodominant leptospiral lipopolysaccharide epitopes. Protection in passive immunization experiments demonstrate that these monoclonal antibodies recognize key protective antigens in currently licensed human and veterinary whole cell Leptospira vaccines. The high precision and robustness renders the two ELISAs much more reliable correlates of potency in dogs than the hamster potency test. The recent approval of these assays for a new canine leptospirosis vaccine is an important contribution to the 3Rs in quality control testing of Leptospira vaccines.

Physicochemical and immunochemical assays for monitoring consistent production of tetanus toxoid

The detoxification of tetanus toxin by formaldehyde is a crucial step in the production of tetanus toxoid. The inactivation results in chemically modified proteins and it determines largely the ultimate efficacy and safety of the vaccine. Currently, the quality of tetanus toxoid lots is evaluated in potency and safety tests performed in animals. As a possible alternative, this article describes a panel of in vitro methods, which provides detailed information about the quality of tetanus toxoid. Ten experimental lots of tetanus toxoid were prepared using increasing concentrations of formaldehyde and glycine to obtain tetanus toxoids having differences in antigenicity, immunogenicity, residual toxicity and protein structure. The structural properties of each individual toxoid were determined using immunochemical and physicochemical methods, including biosensor analysis, ELISA, circular dichroism, TNBS assay, differential scanning calorimetry, fluorescence and SDS-PAGE. The quality of a tetanus toxoid lot can be assessed by these set of analytical techniques. Based on antigenicity, immunogenicity and residual toxicity data, criteria are formulated that tetanus toxoids lot have to meet in order to have a high quality. The in vitro methods are a valuable selection of techniques for monitoring consistency of production of tetanus toxoid, especially for the detoxification process of tetanus toxin.

Non-animal replacement methods for human vaccine potency testing: state of the science and future directions

NICEATM and ICCVAM convened an international workshop to review the state of the science of human and veterinary vaccine potency and safety testing methods, and to identify opportunities to advance new and improved methods that can further reduce, refine, and replace animal use. This report addresses methods and strategies identified by workshop participants for replacement of animals used for potency testing of human vaccines. Vaccines considered to have the highest priority for future efforts were (1) vaccines for which antigen quantification methods are already developed but not validated, (2) vaccines/components that require the largest number of animals, (3) vaccines that require an in vivo challenge test, and (4) vaccines with in vivo tests that are highly variable and cause a significant number of invalid tests. Vaccine potency tests identified as the highest priorities for replacement were those for diphtheria and tetanus, pertussis (whole cell and acellular), rabies, anthrax, polio vaccine (inactivated) and complex combination vaccines based on DT or DTwP/aP. Research into understanding the precise mechanism of protection afforded by vaccines and the identification of clinically relevant immunological markers are needed to facilitate the successful implementation of in vitro testing alternatives. This report also identifies several priority human vaccines and associated research objectives that are necessary to successfully implement in vitro vaccine potency testing alternatives.

Bridging the Gap Between Validation and Implementation of Non-Animal Veterinary Vaccine Potency Testing Methods

Simple Summary

Many vaccines are tested for quality in experiments that require the use of large numbers of animals in procedures that often cause significant pain and distress. Newer technologies have fostered the development of vaccine quality control tests that reduce or eliminate the use of animals, but the availability of these newer methods has not guaranteed their acceptance by regulators or use by manufacturers. We discuss a strategic approach that has been used to assess and ultimately increase the use of non-animal vaccine quality tests in the U.S. and U.K.

Abstract

In recent years, technologically advanced high-throughput techniques have been developed that replace, reduce or refine animal use in vaccine quality control tests. Following validation, these tests are slowly being accepted for use by international regulatory authorities. Because regulatory acceptance itself has not guaranteed that approved humane methods are adopted by manufacturers, various organizations have sought to foster the preferential use of validated non-animal methods by interfacing with industry and regulatory authorities. After noticing this gap between regulation and uptake by industry, we began developing a paradigm that seeks to narrow the gap and quicken implementation of new replacement, refinement or reduction guidance. A systematic analysis of our experience in promoting the transparent implementation of validated non-animal vaccine potency assays has led to the refinement of our paradigmatic process, presented here, by which interested parties can assess the local regulatory acceptance of methods that reduce animal use and integrate them into quality control testing protocols, or ensure the elimination of peripheral barriers to their use, particularly for potency and other tests carried out on production batches.