FDA greenlights first diagnostic test for COVID-19 antibodies that block the virus from entering cells

The FDA has authorized what it describes as the first COVID-19 diagnostic test that detects whether a person has the specific antibodies known to block the coronavirus from entering and infecting human cells.

These neutralizing antibodies are seen as a strong biomarker of potential immunity against the disease—compared to other antibodies created by the body, which have only been used as evidence of previous exposure to the virus.

The commercial diagnostic kit developed by GenScript is designed to provide a test result within one hour. However, it is still unknown how long these neutralizing antibodies can last within the body, and how many are needed to provide protection against the novel coronavirus.

“The ability to detect neutralizing antibodies can help us gain additional insight into what the existence of antibodies may mean for patients as we continue the fight against COVID-19,” said Tim Stenzel, director of the FDA’s Office of In Vitro Diagnostics and Radiological Health. 

“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,” Stenzel added. “Patients should not interpret results as telling them they are immune, or have any level of immunity, from the virus.”

Previously, measuring virus-neutralizing antibodies required the use of live samples of the coronavirus—a difficult task performed in specialized laboratories equipped with high-level biocontainment hardware to prevent the spread of potentially lethal pathogens.

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But GenScript’s assay, developed with Duke-National University of Singapore Medical School, mimics the neutralization process using safer materials. It combines recombinant protein fragments of the coronavirus’ receptor binding domain—which the virus uses to unlock and enter human cells—with an enzyme derived from horseradish roots. 

"Unlike commercially available antibody-based tests that are routinely used for detecting prior exposure to the virus, the cPass kit can assess both prior exposure and the presence of neutralizing antibodies in convalescent patients," said David Martz, vice president of new product management for GenScript’s life sciences group. 

"The cPass kit is also a valuable tool for assessing vaccine performance,” Martz said. “When vaccine companies start phase 2 or 3 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."