Abstract
To enable benchmarking of immunogenicity between candidate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines, there is a need for standardized, validated immunogenicity assays. In this article, we report the design and criteria used to validate immunogenicity assays and the outcome of the validation of serologic and functional assays for the evaluation of functional immune response and antibody titers in human serum. A quantitative cell-based microneutralization (MNT) assay, utilizing a reference standard, for detecting anti-SARS-CoV-2 spike protein-neutralizing antibodies in human serum and Meso Scale Discovery’s multiplex electrochemiluminescence (MSD ECL) assay for immunoglobulin G (IgG) antibodies to SARS-CoV-2 spike, nucleocapsid, and receptor-binding domain (RBD) proteins were assessed for precision, accuracy, dilutional linearity, selectivity, and specificity using pooled human serum from coronavirus disease 2019 (COVID-19)-confirmed recovered donors. Both assays met prespecified acceptance criteria for precision, relative accuracy, dilutional linearity, selectivity, and specificity. Both assays demonstrated high specificity for the different SARS-CoV-2 antigens or virus tested, and no significant cross-reactivity with seasonal coronaviruses. An evaluation to compare the neutralizing activity in the MNT assay to the IgG measured using the MSD ECL assay showed a strong correlation between the presence of neutralizing activity and amount of antibodies against the spike and RBD proteins in sera from both convalescent and vaccinated individuals. Finally, the MNT assay was calibrated to the WHO reference standard to enable reporting of results in international units, thus facilitating comparison of immunogenicity data generated by different assays and/or laboratories. The MSD ECL assay has previously been calibrated. In conclusion, these validated assays for the evaluation of functional immune response and antibody titers following SARS-CoV-2 vaccination could provide a relatively simple standardized approach for accurately comparing immune responses to different vaccines and/or vaccination regimens.
Highlights
The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019, and the start of the subsequent coronavirus disease 2019 (COVID-19) pandemic [1], led to a rapid international vaccine development response [2, 3]
To ensure the accelerated development and availability of multiple vaccines globally, there is an urgent need for laboratory assays that would enable “bridging” or comparison of efficacy between candidate vaccines [7]. To address this need for standardized validated immunogenicity assays, we developed and validated two assays to be used in combination to evaluate the immunogenicity of SARS-CoV-2 vaccines using human serum samples
We describe the design and criteria used to validate these immunogenicity assays and report the outcomes of the validation of these assays in terms of precision, accuracy, dilutional linearity, selectivity, and specificity, as well as a comparison of performance between the MNT and Meso Scale Discovery (MSD) ECL assays in human serum samples from COVID-19 convalescent and vaccinated individuals, which were known to contain anti-SARS-CoV-2 antibodies
Summary
The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019, and the start of the subsequent coronavirus disease 2019 (COVID-19) pandemic [1], led to a rapid international vaccine development response [2, 3]. By the end of 2020, more than 170 potential SARS-CoV-2 vaccines were in preclinical development and more than 60 were undergoing clinical evaluation [2]. Both the World Health Organization (WHO) and the US Food and Drug Administration (FDA) have published considerations and guidance for the development and evaluation of SARS-CoV-2 vaccines [4, 5]. The guidance stipulates that preclinical studies and clinical trials of vaccines should include evaluation of humoral, cellular, and functional immune responses. The FDA Guidance for Industry “Development and Licensure of Vaccines to Prevent COVID-19” notes that assays utilized for the evaluation of immunogenicity should demonstrate suitability for their intended purposes and be validated before use in pivotal clinical trials [5]
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