Published:
2/3/2021

The Frederick National Laboratory (FNL) is providing scientists across the country with a key antigen used in antibody tests for the coronavirus after finding that the antigen is exceptionally sensitive and can be made rapidly and at low cost. This helps meet a pressing need for accurate testing.

3D model of SARS-CoV-2
3D model of SARS-CoV-2 created at the MRC Laboratory of Molecular Biology using electron cryo-tomography (cryo-ET) data analysed by John Briggs’ group and collaborators, published in Nature.
This model of an authentic virus particle reveals positions, conformations and orientations of the spike proteins on the virion membrane (blue). RBD = Receptor Binding Domain.

The antigen, a protein, is used in blood tests to show whether a person has antibodies to the COVID-19 virus, indicative of a previous infection. Antibody testing helps determine how many people have been infected by the novel coronavirus, even if they had no symptoms or known exposure. This is essential for knowing how far the virus has spread into communities and how long people may stay protected after recovering.

The study by FNL and National Institute of Health (NIH) scientists described a method of protein production that yields a reagent that is nearly 100 percent sensitive to antibodies to the virus and can be made rapidly and inexpensively in batch quantities to meet the urgent demand for accurate testing.

The scientific report, published in Protein Expression and Purification, details the production process that results in the highly sensitive reagent so other scientists can follow the recipe. And FNL investigator Dominic Esposito, Ph.D., who led the study, said FNL is also providing the reagent directly to other scientists for their antibody tests.

The research study examined part of the so-called spike protein on the surface of the SARS-CoV-2 virus that is used to infect target cells and cause disease. A part of that spike protein — the receptor binding domain (RBD) — is commonly used in a type of antibody test, an enzyme-linked immunosorbent assay or ELISA. There are different ways to manufacture RBD, but there was a pressing need for the protein to be high in sensitivity and ample in quantity.

The research group investigated a number of factors involved in protein production, such as the genetic elements, cell-culture variables, and purification processes for two commonly used RBDs, one provided by Mt. Sinai’s Icahn School of Medicine and the other by the Ragon Institute of Massachusetts General Hospital. They also tried processing the protein in large batches.

The scientists found that the Ragon RBD benefitted most from fine-tuning the production process, with a sensitivity in the ELISA double that of other versions and a four-fold increase in protein production yield. They attributed the high sensitivity to a protein used to “tag” RBD. In this case, the tag was added by the Ragon laboratory for an unrelated purpose and its function in aiding sensitivity was purely serendipitous, Esposito said.

“We don’t really know why it works,” Esposito said. “Does it help orient the protein? Does it present better to the antibodies?” Either way, it clearly plays an important role, he said.

With this information in hand, Esposito’s group began supplying RBD to the trans-NIH Serosurvey, a large study to determine how many adults in the United States who have not been tested for the virus, or who have not tested positive, still have antibodies to the virus. The survey will show how far the virus has spread undetected – revealing the true magnitude of the pandemic. And it will help inform public health strategies.

Esposito said FNL is also providing the reagent to other NIH institutes and government agencies, as well as public health organizations overseas.

“This is the kind of thing Frederick National Laboratory should be doing as a national laboratory and scientific resource for the nation,” Esposito said.

Other members of the research team include Jennifer Mehalko, Matthew Drew, Kelly Snead, John-Paul Denson, Vanessa Wall, Troy Taylor, Simon Messing, and William Gillette from FNL and Kaitlyn Sadtler of the National Institute for Biomedical Imaging and Bioengineering, who is also the lead investigator for the trans-NIH Serosurvey.

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