Measuring SARS-CoV-2 neutralizing antibody activity using pseudotyped and chimeric viruses
diagnostics immunology/immunity therapeutics virology
Authors:Schmidt et al.
Link to paper: https://doi.org/10.1101/2020.06.08.140871
Key Words: Immunology/Immunity, Virology, Therapeutics, Diagnostics
Different high-throughput antibody neutralization assays are described, all are SARS-CoV-2 spike-pseudotyped, HIV-1 (2 and 3 plasmid constructs that are replication-defective), VSV and a replication-competent chimeric VSV/SARS-CoV-2.
Convalescent plasma neutralization titers obtained with the pseudotyped virus were well correlated (~0.6) with titers obtained using authentic SARS-CoV-2.
A panel of 15 human monoclonal antibodies selected on the basis of neutralization potency using an HIV-1 pseudotype virus (IC50 values ranging between 3ng/mL and 60ng/mL), potently neutralized pseudotyped viruses and authentic SARS-CoV-2.
The authors describe high-throughput and rapid SARS-CoV-2 antibody neutralization assays based on pseudotyped and chimeric viruses, which they validate using a panel of convalescent plasma and human receptor binding domain (RBD)-specific monoclonal antibodies. They generate and validate HIV-1-based SARS-CoV-2 S pseudotyped virions, VSV-based SARS-CoV-2 S pseudotyped virions and a replication competent VSV/SARS-CoV2 chimeric virus. The use of dual GFP and NanoLuc reporters in pseudotyped viral genomes allows for a rapid and flexible assessment of neutralizing activity, either microscopically, by flow cytometry or NanoLuc luciferase assays. They go on to show that each surrogate virus-based assay could correctly identify the most potent neutralizing human monoclonal antibodies as compared to authentic SARS-CoV-2 and measurements of neutralizing activity correlated well with measurements using authentic virus.
Impact for SARS-CoV2/COVID19 research efforts
Understand the immune response to SARS-CoV2/COVID19
Develop diagnostic tools for SARS-CoV2/COVID19
In vitro study
Strengths and limitations of the paper
Novelty: Instead of just describing a particular surrogate Ab neutralisation test, they construct and compare multiple surrogate neutralization assays used for evaluation of neutralizing antibody activity. These assays are reported in a previous publication by the same groups (Robbiani et al. 2020).
Standing in the field:Similar high-throughput neutralization assays have been described previously, on individual basis.
Appropriate statistics: Yes, as far as we can judge.
Viral model used:Convalescent plasma from COVID-19 infected individuals
Translatability:The assays are high-throughput, rapid and convenient and can be executed in a standard BSL-2 laboratory.
Main limitations: The authors were very diligent in discussing the limitations of their own work in the discussion. One potential limitation that is not mentioned is that they do not measure the expression of TMPRSS2 protease (needed to prime the SARS2 Spike) in their chosen expression cell lines. As a result, we do not know in what way the infection rates have been affected, if at all.
As noted by the authors, pseudotyped and chimeric viruses do not recapitulate the authentic virus completely (e.g. spike density on the surface), which could affect the measured potency of some neutralizing antibodies.