As more COVID-19 antibody testing becomes available, one question has been on everybody’s mind: Does the presence of antibodies to SARS-CoV-2, the virus responsible for the global pandemic, mean that people are protected from future infection? To that end, Genscript Biotech Corp., of Piscataway, N.J., has applied for emergency use authorization (EUA) with the U.S. FDA to market a test that specifically recognizes neutralizing antibodies to SARS-CoV-2.

According to Genscript, the Cpass SARS-CoV-2 Neutralization Antibody Detection Kit is the first test submitted to the agency for approval to detect neutralizing antibodies to the coronavirus that does not use live virus, meaning it could be used safely in standard hospital and clinic labs. That sets it apart from traditional virus neutralization tests, which employ live virus and cells and must be performed in a biosafety containment facility.

“Genscript’s Cpass kit would be a valuable tool in our fight against the SARS-CoV-2 outbreak, providing laboratories with a fast, accurate method of testing for neutralizing antibodies against the virus,” said David Martz, Genscript’s vice president of new product management for life sciences. “We believe that the Cpass test kit could be critical in assessing herd immunity, durability of protective immune response and efficacy of SARS-CoV-2 vaccine candidates.”

Mimics interaction between virus and cell

The test detects neutralizing antibodies regardless of whether they are IgG, IgM or IgA isotype. It is performed using blood plasma or serum drawn from a vein and involves the use of an enzyme-linked immunosorbent assay, which is widely used in serological tests. Genscript said the kit is compatible with manual, automated and high-throughput immunoassay workflows.

“We detect neutralizing antibodies by mimicking the interaction between the virus and the cell,” Martz told BioWorld. “For the virus to enter the cell, the receptor-binding domain of the spike protein on the virus needs to interact with the ACE2 receptors on the human cell. Antibodies present in the serum or plasma that can prevent this binding would prevent the virus’ entry into the cell and are referred to as neutralizing antibodies.

“By using the interacting proteins instead of live virus or live cells, we can reproduce this reaction and, therefore, are able to detect these neutralizing antibodies in a very efficient, fast and more automatable way, compared to conventional virus neutralization assays.”

The Cpass kit, which leverages technology invented by Wang Linfa, director of Duke-National University of Singapore’s emerging infectious diseases program, has been validated with samples from patients in the PROTECT clinical trial, a prospective, multicenter study to detect novel pathogens and characterize emerging infections, coordinated by Singapore’s National Centre for Infectious Diseases. Singapore’s Health Sciences Authority has approved the test for clinical use.

The company has conducted several studies of Cpass in the U.S., Singapore and China, with overall sensitivity of 93.8% and specificity of 99.4%. In the data that was submitted for the FDA EUA, the test demonstrated a sensitivity of 94% and specificity of 96.5%, Martz said.

CE mark, HSA approvals

The EUA filing comes less than two weeks after Genscript won CE-IVD marking for its Cpass test.

“We are launching worldwide, and the RUO [research use only] kit is available for purchase globally,” Martz said. Commercialization efforts in CE-mark countries and Singapore are already underway, and the company is working with partners to launch in additional countries that require their own regulatory approvals.

The U.S. rollout of the Cpass test will begin after EUA approval. Martz didn’t disclose what sort of testing capacity the company is projecting for its COVID-19 neutralizing antibody test, but seemed confident that it can fulfill the required need.

“Genscript has developed the kit in a way that we can scale up the production to meet potential demand,” he said.

In the meantime, Martz said the company is collaborating with some academic groups that are working with vaccine companies and is looking for additional partners in this area.

Others are working on tests to identify immunity to SARS-CoV-2. Quanterix Corp. announced recently researchers had developed a COVID-19 antibody with 1,000 times the sensitivity of current tests using its Simoa bead-based immunoassay platform. The blood-based test detects and measures IgG, IgM and IGA antibodies against four immunogenic viral proteins associated with SARS-CoV-2, showing seroconversion as early as one day after the onset of symptoms with less than a microliter of plasma. Patients who test positive with the IgG test would be followed up wit a multiplex assay to gain more insight on the level of antibodies they have across different categories and whether those antibodies are effective in preventing infection.

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