Abstract
Quantitative and robust serology assays are critical measurements underpinning global COVID-19 response to diagnostic, surveillance, and vaccine development. Here, we report a proof-of-concept approach for the development of quantitative, multiplexed flow cytometry-based serological and neutralization assays. The serology assays test the IgG and IgM against both the full-length spike antigens and the receptor binding domain (RBD) of the spike antigen. Benchmarking against an RBD-specific SARS-CoV IgG reference standard, the anti-SARS-CoV-2 RBD antibody titer was quantified in the range of 37.6 µg/mL to 31.0 ng/mL. The quantitative assays are highly specific with no correlative cross-reactivity with the spike proteins of MERS, SARS1, OC43 and HKU1 viruses. We further demonstrated good correlation between anti-RBD antibody titers and neutralizing antibody titers. The suite of serology and neutralization assays help to improve measurement confidence and are complementary and foundational for clinical and epidemiologic studies.
Highlights
The same number of MagPlexAvidin, SeroMap, or MagPlex-C microbeads were conjugated with the same amount of a receptor binding domain (RBD) (Ragon). mAb S562-109 spiked in a negative serum (NIST standard reference material (SRM) 909c) and positive plasma control (NIBSC convalescent plasma code: 20/130) diluted in PBT buffer served
The signal-to-noise ratio from SeroMap beads was higher from the positive plasma control, but lower from the mAb S562-109 positive control when compared to the MagPlex-C beads
While our serological assays utilize the MagPlex-C beads commonly used on the Luminex platform, our assays use the flow cytometry platform instead of more specialized Luminex equipment
Summary
Robust and quantitative serological and neutralization assays are key measurements for assessing the complex patient responses to SARS-CoV-2, the coronavirus that causes COVID-19 [1]. Serological assays are critical for measuring the individual and the population exposure to COVID-19. Serological assays are fundamental for the measurement of complex humoral immune responses to SARS-CoV-2. Current serology results are highly variable [6], in part due to a lack of well characterized, globally traceable reference materials needed for assay validation and control. As a part of the hierarchy of the global standardization of serologic testing, a robust, quantitative reference assay is urgently needed to support various responses to the pandemic
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