The U.S. FDA has granted emergency use authorization (EUA) to Genscript USA Inc. for its Cpass SARS-CoV-2 Neutralization Antibody Detection Kit, the first commercially available test to detect neutralizing antibodies in individuals previously infected with the novel coronavirus. The serology test measures levels of neutralizing antibodies in samples from patients recovering from COVID-19 as well as people vaccinated against the SARS-CoV-2 virus, and can also be used to screen animals for possible infection.

To date, the FDA has issued EUAs for more than 50 serology tests, but those only detect the presence of binding antibodies – not whether antibodies are capable of protecting against viral infection.

Based on an enzyme-linked immunosuppressant assay, Cpass detects neutralizing antibodies regardless of whether they are IgG, IgM or IgA istotype, from blood plasma or serum drawn from a vein.

Current testing is performed using live virus assays, which require biosafety level 3 labs and take several days or more to yield results. By contrast, Genscript said the test utilizes pure proteins that can be produced in a more reproducible way than conventional methods for measuring neutralizing antibodies. Moreover, Cpass is compatible with manual, automated and high-throughput immunoassay workflows, enabling turnaround times of as little as one hour.

“Unlike commercially available antibody-based tests that are routinely used for detecting prior exposure to the virus, the Cpass can assess both prior exposure and the presence of neutralizing antibodies in convalescent patients,” said David Martz, vice president of new product management in Genscript’s Life Science Group.

“The Cpass kit is also a valuable tool for assessing vaccine performance,” he added. “When vaccine companies start phase II or III trials, a standardized test that can detect neutralizing antibodies will be needed for a large cohort of patients to evaluate the efficacy of vaccines within different populations and regions.”

High sensitivity, specificity

To support the EUA, Genscript provided the FDA with data comparing Cpass’ performance with a real-time polymerase chain reaction (RT-PCR) test and with two plaque reduction neutralization test titers, PRNT50 and PRNT90. Using RT-PCRF as the comparator, Cpass demonstrated sensitivity of 94% and specificity of 96.5%. The Cpass test showed 100% sensitivity and specificity when using the PRNT titers.

The testing strategy was also validated in two COVID-19 patient cohorts in Singapore and China, with sample sizes of 375 and 250, respectively. The study, published in Nature Biotechnology in July, directly compared the clinical performance of Cpass and a cell- and virus-based detection test, with results showing Cpass was able to detect neutralizing antibodies from patients with 95% to 100% sensitivity and 99.93% specificity.

Piscataway, N.J.-based Genscript has already launched Cpass for countries that accept the CE mark, including all countries in Europe and many in Asia Pacific and Africa, Martz told BioWorld. It also has regulatory approval from Singapore’s Health Sciences Authority.

With COVID-19 cases again rising globally, the company has “the capacity to produce millions of tests per month, and we can quickly scale up as needed,” he said

Positive response

Reaction to news of the EUA has been “very positive,” according to Martz. “We expect rapidly increasing demand as more studies are performed and more vaccines enter later-stage studies. The effect will be to greatly increase demand for a high volume of testing for neutralizing antibodies in the thousands of samples from extended time-based studies.

He highlighted that Cpass is the only FDA-authorized test for neutralizing antibodies that can handle the increase in volumes that is anticipated over the coming months.

Tim Stenzel, director of the Office of In Vitro Diagnostics and Radiological Health in the FDA’s Center for Devices and Radiological Health, said the test could help scientists gain more insight into the role antibodies play in combating COVID-19, but cautioned against using the results as a sign they can forego wearing masks, social distancing and other precautionary behaviors.

“There are still many unknowns about what the presence of SARS-CoV-2 antibodies may tell us about potential immunity, but today’s authorization gives us another tool to evaluate those antibodies as we continue to research and study this virus,” he said. “Patients should not interpret results as telling them they are immune, or have any level of immunity, from the virus.

Genscript has not yet set a price point for Cpass in the U.S., Martz said. As the first test of its type to get the FDA’s nod, discussions with insurers about reimbursement are still in early stages.