Association between SARS-CoV-2 Neutralizing Antibodies and Commercial Serological Assays

  1. Mei San Tang
  2. James Brett Case
  3. Caroline E Franks
  4. Rita E Chen
  5. Neil W Anderson
  6. Jeffrey P Henderson
  7. Michael S Diamond
  8. Ann M Gronowski
  9. Christopher W Farnsworth

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Abstract

Background

Commercially available SARS-CoV-2 serological assays based on different viral antigens have been approved for the qualitative determination of anti-SARS-CoV-2 antibodies. However, there are limited published data associating the results from commercial assays with neutralizing antibodies.

Methods

Sixty-six specimens from 48 patients with PCR-confirmed COVID-19 and a positive result by the Roche Elecsys Anti-SARS-CoV-2, Abbott SARS-CoV-2 IgG, or EUROIMMUN SARS-CoV-2 IgG assays and 5 control specimens were analyzed for the presence of neutralizing antibodies to SARS-CoV-2. Correlation, concordance, positive percent agreement (PPA), and negative percent agreement (NPA) were calculated at several cutoffs. Results were compared in patients categorized by clinical outcomes.

Results

The correlation between SARS-CoV-2 neutralizing titer (EC50) and the Roche, Abbott, and EUROIMMUN assays was 0.29, 0.47, and 0.46, respectively. At an EC50 of 1:32, the concordance kappa with Roche was 0.49 (95% CI; 0.23–0.75), with Abbott was 0.52 (0.28–0.77), and with EUROIMMUN was 0.61 (0.4–0.82). At the same neutralizing titer, the PPA and NPA for the Roche was 100% (94–100) and 56% (30–80); Abbott was 96% (88–99) and 69% (44–86); and EUROIMMUN was 91% (80–96) and 81% (57–93) for distinguishing neutralizing antibodies. Patients who were intubated, had cardiac injury, or acute kidney injury from COVID-19 infection had higher neutralizing titers relative to those with mild symptoms.

Conclusions

COVID-19 patients generate an antibody response to multiple viral proteins such that the calibrator ratios on the Roche, Abbott, and EUROIMMUN assays are all associated with SARS-CoV-2 neutralization. Nevertheless, commercial serological assays have poor NPA for SARS-CoV-2 neutralization, making them imperfect proxies for neutralization.

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  1. Version published to 10.1093/clinchem/hvaa211
  2. ScreenIT

    SciScore for 10.1101/2020.07.01.182220: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementIRB: Specimens: This study was approved by the Institutional Review Board of Washington University in St. Louis.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.
    Cell Line Authenticationnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    The Abbott SARS-CoV-2 IgG assay was performed on an i2000 Abbott Architect (Abbott Diagnostics) and detects IgG antibodies against the viral nucleocapsid protein.
    viral nucleocapsid protein.
    suggested: None
    Plates were then washed and incubated with 1 µg/mL anti-S antibody (CR3022) (19) and HRP-conjugated goat anti-Human IgG.
    anti-S
    suggested: None
    CR3022
    suggested: None
    anti-Human IgG
    suggested: None
    Experimental Models: Cell Lines
    SentencesResources
    Indicated dilutions of plasma were incubated with 102 focus forming units (FFU) of SARS-CoV-2 for 1h at 37°C before addition of the antibody virus complex to Vero E6 monolayers at 37°C for 1h.
    Vero E6
    suggested: None
    Software and Algorithms
    SentencesResources
    Mortality and intubation were determined by physician encounter notes, acute kidney injury (AKI) was defined using RIFLE criteria of 2-fold increase in serum creatinine and urine output less than 5 mL/kg/hr, cardiac injury was defined as a troponin I concentration > 0.03 ng/mL (Abbott Diagnostics).
    Abbott
    suggested: (Abbott, RRID:SCR_010477)
    The Abbott SARS-CoV-2 IgG assay was performed on an i2000 Abbott Architect (Abbott Diagnostics) and detects IgG antibodies against the viral nucleocapsid protein.
    Abbott Architect
    suggested: (Abbott ARCHITECT i1000sr System, RRID:SCR_019328)
    All statistical analyses were performed with GraphPad Prism 8 (GraphPad).
    GraphPad Prism
    suggested: (GraphPad Prism, RRID:SCR_002798)
    GraphPad
    suggested: (GraphPad Prism, RRID:SCR_002798)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    There are several limitations associated with this study. The true sensitivity and specificity of neutralizing titers in PCR-confirmed SARS-CoV-2 infected patients could not be accurately determined because specimens were pre-selected for serological positivity by commercially available immunoassays. This approach was chosen given the highly manual nature of testing for neutralizing antibodies and the primary goal of comparing neutralizing antibody titers to commercial assays. Furthermore, while the neutralizing assay utilized is robust and reproducible, it has not been validated for clinical use. In contrast to other studies, this assay uses an infectious strain of SARS-CoV-2 as opposed to pseudotyped rhabodoviruses or lentiviruses that heterologously express the SARS-CoV-2 spike protein. Furthermore, the relatively small number of patients tested means that potentially subtle differences in PPA, NPA, and concordance between the three assays could not be distinguished as a result of wide, overlapping confidence intervals. Finally, while others have demonstrated that neutralizing titers appear as early as d10 post-onset of symptoms, it is possible that assessing patients at later time points (i.e., d28) would reveal a higher concordance. While the majority of patients tested serially had neutralizing titers that peaked by d14-15, future studies are needed at later timepoints to correlation with commercial assays at later timepoints. This includes several months after infectio...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • No funding statement was detected.
    • No protocol registration statement was detected.

    About SciScore

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  3. Version published to 10.1101/2020.07.01.182220v1 on bioRxiv