Promising New Rapid COVID-19 Serological Test Data Released

Antibodies responding to covid-19 coronavirus, illustration
Illustration of antibodies (red and blue) responding to an infection with the new coronavirus SARS-CoV-2 (purple). The virus emerged in Wuhan, China, in December 2019, and causes a mild respiratory illness (covid-19) that can develop into pneumonia and be fatal in some cases. The coronaviruses take their name from their crown (corona) of surface proteins, which are used to attach and penetrate their host cells. Once inside the cells, the particles use the cells' machinery to make more copies of the virus. Antibodies bind to specific antigens, for instance viral proteins, marking them for destruction by other immune cells.

Testing for COVID-19 continues to be too little too late in the United States. Many groups are working on closing the testing gap, by innovating new tests for both the presence of the virus and antibodies. A robust serological test that would detect neutralizing antibodies to SARS-CoV-2 could be used to help determine the infection rate, amount of herd immunity in the community, and vaccine efficacy during clinical trials and after large-scale vaccination. A new report describes a SARS-CoV-2 surrogate virus neutralization test that detects total immunodominant neutralizing antibodies targeting the viral spike (S) protein receptor-binding domain in an isotype- and species-independent manner.

This work is published in Nature Biotechnology in the article, “A SARS-CoV-2 surrogate virus neutralization test based on antibody-mediated blockage of ACE2–spike protein–protein interaction.

The surrogate VNT (sVNT) detects neutralizing antibodies (NAbs) “without the need for any live virus or cells and can be completed in 1–2 h in a BSL2 laboratory.” The sVNT is capable of detecting the functional NAbs that can block the binding of the coronavirus spike protein to the angiotensin-converting enzyme 2 (ACE2) host receptor, which mimics the virus-host interaction.

Using purified receptor-binding domain (RBD) from the S protein and the host cell receptor ACE2, the authors wrote that their test is “designed to mimic the virus–host interaction in an ELISA plate well.” This RBD–ACE2 interaction can be neutralized by specific NAbs in patient or animal sera.

The sVNT was developed by scientists from Duke-NUS Medical School, in collaboration with the National Centre for Infectious Diseases (NCID), Agency for Science, Technology and Research (A*STAR)’s Institute of Molecular and Cell Biology (IMCB) Singapore, and GenScript Biotech.

The scientists in Singapore and China validated the test across two patient cohorts, with a sample size of 250 from China and 375 from Singapore, and found it achieved 99.93% specificity and 95–100% sensitivity and differentiated antibody responses to several human coronaviruses.

Infection or immunity to the virus is diagnosed by the presence of NAbs in a patient’s blood sample, which would block the RBD-ACE2 interaction. Antibody tests, such as the conventional virus neutralization test (cVNT) and the pseudovirus-based virus neutralization test (pVNT), remain the only platforms for detecting NAbs. However, both require live viruses and cells, highly skilled operators, and days to obtain results. Other assays, such as the enzyme-linked immunosorbent assay (ELISA) detect binding antibodies (BAbs) but are unable to differentiate between BAbs and NAbs.

The sVNT can also measure NAbs from different animals in a species-independent manner. It can, therefore, be a powerful tool to investigate the role of animals in the transmission of COVID-19 from natural reservoirs to intermediate hosts.

“It is an increasingly critical clinical question about what proportion of patients with COVID-19 develop antibodies to COVID-19, how long it lasts, and whether antibodies protect patients from reinfection. Neutralizing antibody is the gold-standard serological platform to determine this,” noted David Lye, MBBS, director, Infectious Disease Research and Training Office (IDRTO), and senior consultant, NCID. “The sVNT developed by Prof Wang,” he continued, “makes it accessible to all hospital laboratories, and is a great advance in COVID-19 serological assays.”

“We are excited about the results of Dr. Wang’s work and are looking forward to expanding global access to cPass,” said David Martz, vice president of new product management in the life science group at GenScript. “We believe that cPass is a faster and more effective test than traditional virus neutralization assays and will prove an invaluable tool for researchers searching for clues to herd immunity and vaccine efficacy.”

“We have filed for EUA approval from the FDA,” continued Martz, “and are ramping up production capacity quickly to accommodate global requests for access to these unique research assays.”

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