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Authors: D. Lapuente et al.

Link to paper: https://www.medrxiv.org/content/10.1101/2020.05.09.20091447v1

Journal/ Pre-Print: MedRxiv

Tags: Immunology/Immunity, Clinical/ Diagnostics

Research Highlights 

1. Development of a flow cytometric assay to test for IgG and IgM against SARS-CoV-2 spike protein

2. Specific and sensitive identification of seropositive individuals

3. No cross-reactivity with antibodies against other coronaviruses e.g. common cold CoVs

Summary 

The authors developed a diagnostic tool based on flow cytometry for identification of seropositive individuals by expressing the SARS-CoV-2 spike protein in a cell line. Specific IgG or IgM from patient sera that bind to these cells are then labelled with a secondary antibody and MFI recorded. Patients with PCR-confirmed SARS-CoV-2 were 100% positive for IgG and the majority positive for IgM, whereas all but two uninfected individuals tested negative. Sera from patients with confirmed endemic infection by other human coronaviruses did not test positive in this assay. Comparison with commercially available kits showed this assay to be more sensitive than ELISA and CLIA, correctly identifying more positive individuals.

Impact for SARS-CoV2/COVID19 research efforts

Develop diagnostic tools for SARS-CoV2/COVID19

Study Type

· In vitro study

· Patient Case study

Strengths and limitations of the paper

Novelty: Even though reliable tests for antibody detection are already available, the authors provide another method that is independent of kit availability and may be more sensitive.

Standing in the field: Antibodies against S1 are thought to be most protective, justifying their focus on this one viral protein.

Appropriate statistics: No statistics used, but flow cytometry gating and MFI comparisons are appropriately controlled

Viral model used: pCG1_CoV_2019-S plasmid encoding the codon-optimized sequence of the SARS-CoV96 2 S protein

Translatability: Might have potential in antibody detection in regions with restricted ELISA kit availability

Main limitations: Creating S1-expressing HEK293T cells and the subsequent flow cytometric analysis might outweigh the advantage of not having to purchase a kit.

They do not address whether the two pre-COVID-19 sera that tested positive were false positives or whether it’s a cross-reaction with something they didn’t test for that might be protective against SARS-CoV-2.