SARS-CoV-2 assays to detect functional antibody responses that block ACE2 recognition in vaccinated animals and infected patients
clinical diagnostics immunology/immunity vaccines virology
Authors:Walker et al.
Link to paper:https://doi.org/10.1101/2020.06.17.158527
Journal/ Pre-Print:BioRxiv
Tags: Immunology/Immunity, Clinical/ Diagnostics, Vaccines, Virology
Research Highlights
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Developed a competitive ELISA to test for antibodies which inhibit SARS-CoV-2 spike protein RBD interaction with ACE2, which has the potential to test for vaccine efficacy.
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In mice, antibodies had greater ACE2 inhibition for S1+S2 compared to only S1 for SARS-CoV-2 spike protein.
Summary
The authors tested a competitive ELISA assay with bound SARS-CoV-2 spike protein, with competition between ACE2 and purified IgG or sera from vaccinated animal models (mice, rabbits, guinea pigs, rhesus macaques) and Covid-19 patients. The animals were vaccinated with the INO-4800 vaccine, and naive animals (mock saline vaccination) and Day 0 sera were used as negative controls. Healthy human pre-pandemic samples were used as a negative control. There was no blinding used in the study.
Impact for SARS-CoV2/COVID19 research efforts
Develop diagnostic tools for SARS-CoV2/COVID19
Others: Also suggests tool could be used to test efficacy of the vaccines
Study Type
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In vitro study
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In vivo study (e.g. mouse, NHP)
Strengths and limitations of the paper
Novelty:New tool to detect antibodies from sera which inhibit RBD-ACE2 interaction of SARS-CoV-2
Standing in the field:Another antibody assay, ELISA-based
Appropriate statistics:Some statistics, but lacking and poorly explained
Viral model used:SARS-CoV-2 spike protein (S1+S2) and S1, SARS-CoV-2 pseudovirus
Translatability:Might be useful as an antibody test, including for vaccine efficacy investigation
Main limitations:
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No blinding of samples before experiments, and previous vaccine study in animal models which was referenced also had no blinding.
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No descriptions of repeats, or mention of duplicates or triplicates for ELISAs
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Low numbers of animals for each test
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Barely anything done with SPR assay - did not use purified IgG or sera to validate assay
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No rationale for the steps taken in the study and unclear descriptions and figures
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No comparison between their competitive ELISA and a sandwich ELISA to show sera/purified IgG/ACE2 binding to SARS-CoV-2 RBD, matrix effects, and quantification.