VaxArray for hemagglutinin and neuraminidase potency testing of influenza vaccines

An ELISA-based assay for determining haemagglutinin potency in egg, cell, or recombinant protein derived influenza vaccines

Background

The current compendial assay for haemagglutinin antigen potency in influenza vaccine is the single radial immunodiffusion (SRID) which is time consuming and can lead to delays in release of vaccine. We previously described an alternate capture and detection enzyme linked immunoassay (ELISA) that utilizes sub-type specific, sub-clade cross-reactive monoclonal antibodies (mAbs) that are haemagglutination inhibiting (HAI) and correlate with SRID. The aim of this study is to determine the applicability of ELISA across current platforms for quantitation of seasonal quadrivalent vaccine.

Methods

A single mAb capture and detection ELISA was employed to quantitate hemagglutinin (HA) derived from different vaccine platforms and host organisms and compared to SRID and a polyclonal antibody based ELISA.

Results

We selected mAbs that displayed appropriate characteristics for a stability indicating potency assay which reacted to avian, insect and mammalian derived HA. Qualification of the homologous mAb assay against egg and cell derived HA demonstrated performance similar to that of the SRID however, superiority in sensitivity and specificity against strains from both influenza B/Victoria and B/Yamagata lineages. Analysis of drifted strains across multiple seasons demonstrated continued utility of this approach, reducing the need to develop reagents each season. With modification of the assay, we were able to accurately measure HA from different platforms and process stages using a single calibrated reference standard. We demonstrated the accuracy of ELISA when testing vaccine formulations containing selected adjuvants at standard and higher concentrations. Accelerated stability analysis indicated a strong correlation in the rate of degradation between the homologous mAb ELISA and SRID but not with ELISA utilizing polyclonal antisera. Further, we demonstrated specificity was restricted to the trimeric and oligomeric forms of HA but not monomeric HA.

Conclusion

We believe this homologous mAb ELISA is a suitable replacement for the SRID compendial assay for HA antigen quantitation and stability assessment. Identification of suitable mAbs that are applicable across multiple vaccine platforms with extended sub-type reactivity across a number of influenza seasons, indicate that this assay has broad applicability, leading to earlier availability of seasonal and pandemic vaccines without frequent replacement of polyclonal antisera that is required with SRID.

Rapid Identity and Quantity CQA Test for Multivalent mRNA Drug Product Formulations

The COVID-19 pandemic highlighted mRNA as a promising platform for vaccines and therapeutics. Many of the analytical tools used to characterize the critical quality attributes of mRNA are inherently singleplex and are not necessarily optimal from a labor and cost perspective. Here, we demonstrate the feasibility of a multiplexed platform (VaxArray) for efficient identity verification and concentration determination for both monovalent and multivalent mRNA formulations. A model system comprising mRNA constructs for influenza hemagglutinin and neuraminidase was used to characterize the analytical performance metrics for a VaxArray mRNA assay. The assay presented herein had a time to result of less than 2 h, required no PCR-based amplification nor extraction of mRNA from lipid nanoparticles, and exhibited high construct specificity that enabled application to the bivalent mixture. The sensitivity for influenza hemagglutinin and neuraminidase mRNA was sub-µg/mL, which is vaccine-relevant, and the average accuracy (%recovery of a check standard) and precision were 104 ± 2% and 9 ± 2%, respectively.

Development of functionally relevant potency assays for monovalent and multivalent vaccines delivered by evolving technologies

A potency or potency-indicating assay is a regulatory requirement for the release of every lot of a vaccine. Potency is a critical quality attribute that is also monitored as a stability indicator of a vaccine product. In essence, a potency measurement is a test of the functional integrity of the antigen and is intended to ensure that the antigen retains immunocompetence, i.e., the ability to stimulate the desired immune response, in its final formulation. Despite its central importance, there is incomplete clarity about the definition and expectation of a potency assay. This article provides a perspective on the purpose, value, and challenges associated with potency testing for vaccines produced by new technologies. The focus is on messenger RNA vaccines in the light of experience gained with recombinant protein-based vaccines, which offer the opportunity to directly correlate in vitro antigenicity with in vivo immunogenicity. The challenges with developing immunologically relevant in vitro assays are discussed especially for multivalent vaccine products, the importance of which has been reinforced by the ongoing emergence of SARS-CoV-2 variants of concern. Immunoassay-based release of multivalent vaccine products, such as those containing multiple antigens from different variants or serotypes of the same virus, require antibodies that are selective for each antigen and do not significantly cross-react with the others. In the absence of such exclusively specific antibodies, alternative functional assays with demonstrable correlation to immunogenicity may be acceptable. Initiatives for geographically distributed vaccine technology facilities should include establishing these assay capabilities to enable rapid delivery of vaccines globally.

Broad Reactivity Single Domain Antibodies against Influenza Virus and Their Applications to Vaccine Potency Testing and Immunotherapy

The antigenic variability of influenza presents many challenges to the development of vaccines and immunotherapeutics. However, it is apparent that there are epitopes on the virus that have evolved to remain largely constant due to their functional importance. These more conserved regions are often hidden and difficult to access by the human immune system but recent efforts have shown that these may be the Achilles heel of the virus through development and delivery of appropriate biological drugs. Amongst these, single domain antibodies (sdAbs) are equipped to target these vulnerabilities of the influenza virus due to their preference for concave epitopes on protein surfaces, their small size, flexible reformatting and high stability. Single domain antibodies are well placed to provide a new generation of robust analytical reagents and therapeutics to support the constant efforts to keep influenza in check.

Multiplexed, microscale, microarray-based serological assay for antibodies against all human-relevant coronaviruses

Rapid, sensitive, and precise multiplexed assays for serological analysis during candidate COVID-19 vaccine development would streamline clinical trials. The VaxArray Coronavirus (CoV) SeroAssay quantifies IgG antibody binding to 9 pandemic, potentially pandemic, and endemic human CoV spike antigens in 2 h with automated results analysis. IgG antibodies in serum bind to the CoV spike protein capture antigens printed in a microarray format and are labeled with a fluorescent anti-species IgG secondary label. The assay demonstrated excellent lower limits of quantification ranging from 0.3 to 2.0 ng/mL and linear dynamic ranges of 76 to 911-fold. Average precision of 11 % CV and accuracy (% recovery) of 92.5 % over all capture antigens were achieved over 216 replicates representing 3 days and 3 microarray lots. Clinical performance on 263 human serum samples (132 SARS-CoV-2 negatives and 131 positives based on donor-matched RT-PCR and/or date of collection) produced 98.5 % PPA and 100 % NPA.

Neuraminidase, the Forgotten Surface Antigen, Emerges as an Influenza Vaccine Target for Broadened Protection

For 50 years it has been known that antibodies to neuraminidase (NA) protect against infection during seasonal and pandemic influenza outbreaks. However, NA is largely ignored in the formulation and standardization of our current influenza vaccines. There are a number of factors that contributed to this antigen being forgotten, including the lack of an easily performed test to measure NA antibody. With the availability of that test, it has been possible to show its independent contribution to protection in various situations. The challenge now is to make it possible to include known amounts of NA in investigational vaccines or to routinely measure NA content in licensed vaccines. Vaccines containing optimal amounts of NA may be particularly useful when there are antigenic changes, either drift or shift, in the hemagglutinin because NA immunity offers broad protection. It is now time to remember the NA as we work toward improved influenza vaccines.

Hemagglutinin Quantitative ELISA-based Potency Assay for Trivalent Seasonal Influenza Vaccine Using Group-Specific Universal Monoclonal Antibodies

The assurance of vaccine potency is important for the timely release and distribution of influenza vaccines. As an alternative to Single Radial Immunodiffusion (SRID), we report a new quantitative enzyme-linked immunosorbent assay (ELISA) for seasonal trivalent influenza vaccine (TIV). The consensus hemagglutinin (cHA) stalks for group 1 influenza A virus (IAV), group 2 IAV, and influenza B virus (IBV) were designed and produced in bacterial recombinant host in a soluble form, and monoclonal antibodies (mAbs) were generated. The group-specific ‘universal’ mAbs (uAbs) bound to various subtypes of HAs in the same group from recombinant hosts, embryonated eggs, and commercial vaccine lots. The calibration curves were generated to assess the sensitivity, specificity, accuracy, and linear dynamic range. The quantitative ELISA was validated for the potency assay of individual components of TIV- H1, H3, and IBV- with good correlation with the SRID method. This new assay could be extended to pandemic or pre-pandemic mock-up vaccines of H5 of group 1 and H7 virus of group 2, and novel HA stalk-based universal vaccines.

A neuraminidase potency assay for quantitative assessment of neuraminidase in influenza vaccines

Neuraminidase (NA) immunity leads to decreased viral shedding and reduced severity of influenza disease; however, NA content in influenza vaccines is currently not regulated, resulting in inconsistent quality and quantity of NA that can vary from manufacturer to manufacturer, from year to year, and from lot to lot. To address this problem, we have developed an assay for NA quantification that could be used by the industry to move toward developing influenza vaccines that induce a predictable immune response to NA. The VaxArray Influenza Seasonal NA Potency Assay (VXI-sNA) is a multiplexed sandwich immunoassay that relies on six subtype-specific monoclonal antibodies printed in microarray format and a suite of fluor-conjugated “label” antibodies. The performance of the assay as applied to a wide range of influenza vaccines is described herein. The assay demonstrated high NA subtype specificity and high sensitivity, with quantification limits ranging from 1 to 60 ng/mL and linear dynamic ranges of 24–500-fold. When compared to an enzymatic activity assay for samples exposed to thermal degradation conditions, the assay was able to track changes in protein stability over time and exhibited good correlation with enzyme activity. The assay also demonstrated excellent analytical precision with relative error ranging from 6 to 12% over day-to-day, user-to-user, and lot-to-lot variation. The high sensitivity and reproducibility of the assay enabled robust detection and quantification of NA in crude in-process samples and low-dose, adjuvanted vaccines with an accuracy of 100 ± 10%.

Influenza vaccines that contain neuraminidase (NA) are associated with lower disease severity and better prognosis in vaccinated individuals, but the amount and quality of NA present in vaccines remains difficult to determine. Here, Rose Byrne-Nash and colleagues present the VaxArray Influenza Seasonal NA Potency Assay (VXI-sNA), a multiplexed sandwich immunoassay for the quantification of NA of all subtypes and for the determination of its potency. Featuring multiple NA subtype-specific antibodies printed in microarray format, the VXI-sNA showed high precision, dynamic range and reproducibility, and its results correlated well with NA enzymatic activity. This method is a step forward towards standardization of NA quantification for the assessment of stability, batch-to-batch variation and immunogenicity of NA in influenza vaccine formulations, and may help to develop influenza vaccines that trigger predictable immune responses to NA for increased protection against influenza infections.