Diagnostic Breakthroughs

Researchers Develop Scalable Antibody Test to Detect COVID-19 Immunity

Scalable, accurate assays capable of not only COVID-19 detection but actual immunity to the virus will be critical for social distancing, virus surveillance and treatment. And now researchers at the University of North Carolina-Chapel Hill (UNC) believe they have developed such a test and that it can be ramped up and made available to test thousands of blood samples at laboratories that do not have the resources of commercial laboratories and large academic medical centers.

The Diagnostic Challenge

People can carry COVID-19 infection without exhibiting symptoms. Currently, COVID-19 testing is being performed only on the symptomatic. Testing all individuals, regardless of symptoms, would require assays capable of detecting not only the presence of COVID-19 antibodies but also their antibody levels. Unfortunately, assays for measuring neutralizing antibodies take about three days to complete and typically require special high-containment facilities necessary for safely working with infectious viruses.

The UNC Test

The new UNC test was developed from scratch by a team of researchers designated as emergency employees when the campus was shut down due to the pandemic. The team designed new antigens and used a large panel of SARS-CoV-2 patients and human and animal control samples.

The UNC researchers, who published their work in Science Immunology, created a simplified experimental assay, a blood test to pinpoint SARS-CoV-2 antibodies that target one unique piece of the SARS-CoV-2 spike protein called a receptor binding domain, or RBD. Their RBD-based antibody test is capable of measuring the levels of that domain, which correlates to the levels of the all-important neutralizing antibodies that provide immunity.

The UNC assay is extremely specific for antibodies to the virus that causes COVID-19, which is not the case for some currently available antibody tests. The RBD of the spike protein in SARS-CoV-2 is not shared among other known human or animal coronaviruses. For example, when the researchers tested blood collected from people exposed to other coronaviruses, none had antibodies to the RBD of SARS-CoV-2.

In other words, the antibodies produced by individuals exposed to the virus that cause COVID-19 are highly specific to SARS-CoV-2. This means that if these antibodies are present, that individual has been exposed to the virus that causes COVID-19.

From day nine after the onset of symptoms and thereafter, the UNC assay allowed the researchers to accurately identify RBD-based antibodies to SARS-CoV-2. “Our results strongly support the use of RBD-based antibody assays for population-level surveillance and as a correlate of the neutralizing antibody levels in people who have recovered from SARS-CoV-2 infections,” noted co-senior author Aravinda de Silva, professor of microbiology and immunology and member of the UNC Institute for Global Health and Infectious Diseases.

Takeaway

The results strongly support the viability of using RBD-based antibody assays for population-level surveillance and as a correlate of the neutralizing antibody levels in people who have recovered from SARS-CoV-2 infections. To make it happen, UNC is further streamlining the test into an inexpensive assay that could be completed in about 70 minutes, rather than the current four to five hours.

 “We don’t see our research as a means to replace commercial tests,” according to a UNC researcher. “Commercial tests are critical, especially for making decisions about the clinical management of individual patients. But it’s too early in the pandemic to know if the commercial assays are suitable for identifying people who experienced very mild or no disease after infection or if the assays tell us anything about protective immunity, as researchers are still learning about this virus.”

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