Reliable Antibodies Testing for SARS-CoV-2

In this interview, Poncho Meisenheimer, VP of R&D at Promega, talks to News-Medical Life Sciences about the importance of having the reliability for SARS-CoV-2 antibody tests.

Can you give us a brief introduction to SARS-CoV-2 Antibody tests and the importance of its reliability?

A SARS-CoV-2 antibody test, or serological test, is used to detect antibodies which are made by your immune system in response to a threat, such as a specific virus. These blood tests can provide a history of infection in individuals, monitor population-based prevalence of disease, assess disease stage, and guide vaccine development.

An antibody test with a high sensitivity (Positive Percent Agreement - PPA) means the assay will generate a lower number of false negative results which is important when these tests are used for identifying previously infected persons. False negatives pose several risks including lack of patient isolation or protection which might lead to further spread, prescription of improper therapeutic treatments, and inaccuracies in contact tracing and surveillance studies.

 

Image Credit:Shutterstock/Kateryna Kon

What is the difference between RT-PCR and antibody tests?

PCR-based testing is used to identify an active SARS-CoV-2 infection in individuals by directly detecting the presence of the virus’ genetic material (RNA). Whereas antibody testing is used to identify our body’s immune response to either an active or past infection from the SARS-CoV-2 virus. The development of specific and sensitive tests of both types is critical.

In terms of antibody detection, what role does the severity of illness play?

In patient samples, antibody response has been found to vary with different clinical manifestations and disease severity1-7. Data reports from several research studies demonstrate that many patients with severe COVID-19 related symptoms produce higher antibody levels than patients with mild to moderate disease during a similar time period. Therefore, the sensitivity (PPA) of an antibody test is often higher in hospitalized patients, who are more likely to have more severe symptoms as a result of the virus.

What is the concept and underlying technology behind the Lumit™ Dx SARS-CoV-2 Immunoassay?

Using our new Lumit™ Technology, we developed a qualitative IVD test intended to detect antibodies to SARS-CoV-2. The Lumt™ Dx immunoassay is comprised of two protein fragments – one part SARS-CoV-2-specific protein and the other part a subunit of NanoBiT® Luciferase (SmBiT or LgBiT). In the presence of serum or plasma containing antibodies to SARS-CoV-2, the protein fragments are drawn into close proximity by the antibody to form an active luminescent enzyme.

Image Credit:Shutterstock/Dotted Yeti

In terms of antibody testing for SARS-CoV-2, what are some of the strengths behind this approach?

Besides being fast and simple, the binding interactions of our assay all occur in a homogeneous solution. This is a vast improvement over the heterogeneous interactions with antibodies that are typical of ELISA assays, which can lead to background interference due to anomalies in surface interactions.

On the other hand, what are some of the main limitations and implications of antibody tests?

At this time, the true clinical utility of antibody tests for SARS-CoV-2 is actively being studied. Researchers do not yet know if the presence of antibodies implies an individual is immune to a virus in the future. Nor do they know exactly how long antibodies truly last in the body or if we elicit long-term antibody responses upon reinfection with the virus.

How would you say the Lumit™ Dx Immunoassay differs from other antibody detection methods (such as conventional ELISA methods)?

Conventional ELISA methods involve multiple incubation and wash steps often leading to inconsistent data, include multiple antibody and detection steps often decreasing specificity and increasing background noise, and can take hours to obtain results.

The Lumit™ Dx SARS-CoV-2 Immunoassay eliminates the need for all washes, reducing the protocol to just a few simple steps. This means less hands-on time, allowing a lab to move through the workflow faster and go from sample to results in less than an hour. The workflow does not require specialized plates or an investment in large lab equipment, rather just a luminescent-capable microplate reader is needed. Also, the assay can be easily automated on most major liquid handlers to accommodate testing of large sample sets. Our Field Support Specialists have scientific, technical and programmatic expertise in working with Promega-developed (MaxprepTM) and third-party liquid handler platforms and are available to optimize and support any lab workflow.

In addition, the Lumit™ Dx SARS-CoV-2 Immunoassay detects human antibodies against the Receptor Binding Domain (RBD) antigen within the S1 subunit of the SARS-CoV-2 Spike (S) protein, unlike many antibody tests on the market that detect antibodies against the Nucleocapsid (N) protein. Research has demonstrated that the Spike (S) protein may offer better sensitivity than the Nucleocapsid (N) protein for measuring SARS-CoV-2-specific antibodies8. Also, many researchers have demonstrated that antibodies produced against the Spike (S) protein, many specifically produced against the RBD domain, are capable of viral neutralization and are targeted in treatment and vaccine development efforts9-14.

Lastly, our data was generated using true community samples with a wide spectrum of disease severity, which is more representative of what a clinical serology lab will observe when testing “outpatients”. Many antibody tests on the market today did not stratify their sample cohorts in this way to obtain the clinical performance for their assay.

Image Cresit:Shutterstock/narci5

Can you tell us about how Promega used their expertise in Bioluminescence and how they have incorporated novel bioluminescent technology in Lumit™?

Promega has been a pioneer in bioluminescent technology since 1990, beginning with Firefly-based Technologies, then Renilla-based Technologies and more recently our NanoLuc®-based Technologies. Unlike fluorescence, bioluminescence is unaffected by excitation wavelength overlap, fluorescent chemicals in media, and background fluorescence.

The Lumit™ Technology enables bioluminescence-based detection of specific antigens or antibodies, simplifying immunoassay protocols and accelerating time to results. Based on our award-winning15-16 NanoBiT® complementation system, Lumit™ Technology powers sensitive and accurate immunoassays for research and diagnostic applications.

We continue to grow our expertise in this space, identifying innovative and novel ways to infuse our bioluminescent technologies across various applications for research, pharma and clinical laboratories.

What is the strategy behind using a Community Cohort for Clinical Performance, and what are some of the challenges that come alongside this method?

For prevalence testing and population screening, antibody tests can be used to identify individuals who were not hospitalized and may not have had a known SARS-CoV-2 infection. Additionally, the clinical performance of our assays shows that antibody response can increase with symptom severity. For these reasons, we chose to gather samples from individuals within the community who had recovered from confirmed cases of COVID-19 (but had not necessarily required hospitalization). This cohort provided a challenge because the symptoms and level of infection in these individuals were more mild, which likely impacted the amount of antibodies produced. Therefore, the benefit of working locally was that we had real-world samples that were a representation of a typical community, and thus gave us more realistic data as we optimized the sensitivity for our antibody test.

Image credit:Shutterstock/ NicoElNino

In terms of availability, where is the Lumit™ Dx SARS-CoV-2 Immunoassay currently available?

The Lumit™ Dx SARS-CoV-2 Immunoassay is available in the U.S. We plan to make the assay available in Europe and the United Kingdom in early 2021. We are also exploring opportunities to release the assay in other parts of the world so we encourage labs to contact Promega to discuss making that possible.

Where can our readers go to find out more?

Please visit www.promega.com/AntibodyTest to learn more about the Lumit™ Dx SARS-CoV-2 Immunoassay. Visit www.promega.com/LumitTechnology to learn more about LumitTM Technology.

About Poncho Meisenheimer

Poncho Meisenheimer is a trained chemist and VP of R&D at Promega. He has worked for 19 years in luminescent drug discovery tool development and assay development, but he is just one mind in a much larger scientifically talented team that developed the Lumit™ Dx SARS-CoV-2 Immunoassay. As the public crisis stabilizes, all these team members will return to tool development for infectious disease, oncology, biologics, cellular analysis, and life science research.

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