SARS-CoV-2 Surrogate Virus Neutralization Test
1. The surrogate neutralization test is capable of measuring majority neutralizing Abs against SARS2 RBD regardless of isotype (IgG, IgM, IgA), unlike standard ELISAs reported by other groups.
2. The correlation study between the infectious virus-based virus neutralization test (VNT) and the RBD-hACE2-based sVNT shows that they are positively correlated.
3. sVNT was tested against corona-related strains (SARS1, MERS, 229/NL63 and OC43) and a slight cross-reactivity was detected against the serum of SARS-CoV patients. However, the neutralizing capacity of the SARS-CoV-2 sera was statistically significantly higher than that of SARS-CoV.
This paper reports a SARS-CoV-2 surrogate virus neutralization (sVNT) assay, which assays for total neutralizing antibodies in an isotype and species-independent manner, using a proficient ELISA that detects region-specific abs. RBD of the Spike protein that blocks ACE2 binding. sVNT provides a rapid (2 h) BSL2 assay with high specificity (100%) and sensitivity up to 95-100% (depending on cut-off stringency). This assay has been validated against sera of different coronaviruses, including SARS1, MERS, 229/NL63, and OC43. Since most available diagnostic tests are isotype-specific, this test has the advantage of measuring the total amount of neutralizing activity in SARS-CoV-2 sera.
Impact for SARS-CoV2/COVID19 research efforts
Develop diagnostic tools for SARS-CoV-2/COVID19: a competitive ELISA using ACE2 as a substrate, HRP-conjugated SARS-CoV-2 S RBD protein, and convalescent serum from CoVid-19 patients.
Type of Study
In vitro study
Strengths and limitations of the article
- New: A novel and rapid diagnostic test that can be performed on BSL2 to test the neutralizing ability of SARS-CoV-2 S protein RBD-specific antibodies in patient serum.
- Appropriate statistics: ~125 patients or controls in two cohorts. Kruskal-Wallis test/Dunn’s multiple comparisons test. There are few descriptive statistics in the document and the results are limited to numbers.
- The viral model used: Different hCOV viruses were used, including SARS1 and MERS. Also 229, NL63 or OC. Sera from different species were also tested: rabbits and ferrets.
- Translatability: Laboratory ELISA (BSL2).
- Main limitations: Immunogenic epitopes are not only found in RBD but also in other regions of protein S and also protein N. This test will only determine those antibodies against epitopes found in the SARS protein RBD. -CoV-2 that blocks ACE2 binding, thus missing other potentially beneficial effects of antibody binding (eg, opsonization) or indirect effects of binding reported by other groups
- The assay does not discriminate between antibody classes and therefore cannot report the stage of infection (i.e., IgM = acute infection, IgG = class change later in infection) or whether the response is high avidity/ low affinity or low avidity/high affinity.
- Clinical patient details are sparse and time points are widely clustered, common limitations in the current situation.
- There is no information on the quality of the recombinant proteins they are using (all the proteins are reagents of commercial origin).