Clinical And Analytical Performance Of An Automated Serological Test That Identifies S1/S2 Neutralizing IgG In Covid-19 Patients Semiquantitatively

  1. Fabrizio Bonelli
  2. Antonella Sarasini
  3. Claudia Zierold
  4. Mariella Calleri
  5. Alice Bonetti
  6. Chiara Vismara
  7. Frank Blocki
  8. Luca Pallavicini
  9. Alberto Chinali
  10. Daniela Campisi
  11. Elena Percivalle
  12. Anna Pia DiNapoli
  13. Carlo Federico Perno
  14. Fausto Baldanti

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Abstract

BACKGROUND

In the Covid-19 pandemic, highly selective serological testing is essential to define exposure to SARS-CoV-2 virus. Many tests have been developed, yet with variable speed to first result, and of unknown quality, particularly when considering the prediction of neutralizing capacity.

OBJECTIVES/METHODS

The LIAISON ® SARS-CoV-2 S1/S2 IgG assay was designed to measure antibodies against the SARS-CoV-2 native S1/S2 proteins in a standardized automated chemiluminescent assay. Clinical and analytical performance of the test were validated in an observational study using residual samples (>1500) with positive or negative Covid-19 diagnosis.

RESULTS

The LIAISON ® SARS-CoV-2 S1/S2 IgG assay proved highly selective and specific, and offers semiquantitative measures of serum or plasma levels of anti-S1/S2 IgG with neutralizing activity. The diagnostic sensitivity was 91.3% and 95.7% at >5 or ≥15 days from diagnosis respectively, and 100% when assessed against a neutralizing assay. The specificity ranged between 97% and 98.5%. The average imprecision of the assay was <5 % coefficient of variation. Assay performance at 2 different cut-offs was evaluated to optimize predictive values in settings with different % disease prevalence. CONCLUSIONS. The automated LIAISON ® SARS-CoV-2 S1/S2 IgG assay brings efficient, sensitive, specific, and precise serological testing to the laboratory, with the capacity to test large amounts of samples per day: first results are available within 35 minutes with a throughput of 170 tests/hour. The test also provides a semiquantitative measure to identify samples with neutralizing antibodies, useful also for a large scale screening of convalescent plasma for safe therapeutic use.

IMPORTANCE

With the worldwide advance of the COVID-19 pandemic, efficient, reliable and accessible diagnostic tools are needed to support public health officials and healthcare providers in their efforts to deliver optimal medical care, and articulate sound demographic policy. DiaSorin has developed an automated serology based assay for the measurement of IgG specific to SARS CoV-2 Spike protein, and tested its clinical performance in collaboration with Italian health care professionals who provided access to large numbers of samples from infected and non-infected individuals. The assay delivers excellent sensitivity and specificity, and is able to identify samples with high levels of neutralizing antibodies. This will provide guidance in assessing the true immune status of subjects, as well as meeting the pressing need to screen donors for high titer convalescent sera for subsequent therapeutic and prophylactic use.

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  1. ScreenIT

    SciScore for 10.1101/2020.05.19.105445: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementIRB: The protocol for this study (de-identified remainders) was determined to be exempt under existing ethics committee regulations.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.
    Cell Line Authenticationnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    SARS-CoV-2 S1/S2 IgG chemiluminescent assay is a recently developed assay from DiaSorin designed to detect IgG antibodies in the serum or plasma of subjects and patients exposed to the SARS-CoV-2 virus.
    detect IgG
    suggested: None
    Experimental Models: Cell Lines
    SentencesResources
    Recombinant fusion antigens were expressed in human cells (HEK-293) to ensure proper folding, oligomer formation and glycosylation, providing capture moieties more similar to the viral Spike proteins, as processed by natural cellular cleavage (20-22): this distinguishes the DiaSorin CLIA from commonly used ELISAs where the antigens are presented on plastic plate surfaces, and are susceptible to significant denaturation consequent to passive adsorption to these hydrophobic surfaces (23, 24).
    HEK-293
    suggested: None
    Briefly, 50 μl of diluted serum (4-fold serial dilutions from 1:10 to 1:640) were added to an equal volume of viral suspension (tissue culture infectious dose 50 of a SARS-CoV2 strain isolated from a symptomatic patient), incubated, and then combined with Vero-E6 cells.
    Vero-E6
    suggested: None
    Software and Algorithms
    SentencesResources
    Statistical analyses: The statistical program R 3.5 and MedCalc 19.2 were utilized for all analyses presented.
    MedCalc
    suggested: (MedCalc, RRID:SCR_015044)

    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: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    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.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2020.05.19.105445 on bioRxiv