Coronavirus particles, illustration - SARS-CoV-2 virus
Credit: KATERYNA KON/SCIENCE PHOTO LIBRARY/Getty Images

A test of SARS-CoV-2 immunity status has been developed that measures the ability of the viral spike protein to bind the human ACE2 receptor. The first of its kind, the pin prick test is powered by a protein-complementation strategy using the fluorescent luciferase protein from a deep-water shrimp. The binding of the spike protein to human ACE2 gives off a glow of light that is captured by a luminometer instrument.

The researchers who developed it expect the test to become a valuable tool for deciding who needs a booster and when, which will help save lives and avoid future lockdowns.

The study was led by Igor Stagljar, a professor of biochemistry and molecular genetics, at the Donnely Centre for Cellular and Biomolecular Research, at Temerty Faculty of Medicine, and Shawn Owen, an associate professor of pharmaceutics and pharmaceutical chemistry, at the University of Utah.  The journal Nature Communications published their findings.

“Our method, which we named Neu-SATiN, is as accurate as, but faster and cheaper than, the gold standard, and it can be quickly adapted for new variants as they emerge,” he said.

Neu-SATiN stands for Neutralization Serological Assay based on split Tri-part Nanoluciferase, and it is a newer version of SATiN, which monitors the complete IgG pool, which they developed last year.

“The truth is we don’t yet know how frequent our shots should be to prevent infection,” said Stagljar. “To answer these questions, we need rapid, inexpensive and quantitative tests that specifically measure SARS-CoV-2 neutralizing antibodies, which are the ones that prevent infection.”

When a patient blood sample is added into the proprietary mixture, neutralizing antibodies bind the spike protein, preventing it from contacting ACE2. Consequently, in such cases, luciferase remains in pieces, with an accompanying drop in light signal. The plug and play method can be adapted to different variants within a couple of weeks by engineering variant mutations into the spike protein.

The researchers applied Neu-SATiN to blood samples collected from 63 patients with different histories of COVID-19 infection and vaccination up to November 2021. Patient neutralizing capacity was assessed against the original Wuhan strain and the variants, Alpha, Beta, Gamma, Delta and Omicron.

“We thought it would be important to monitor people that have been vaccinated to see if they still have protection and how long it lasts,” said Owen, who did his postdoctoral training in the Donnelly Centre with distinguished bioengineer and University Professor Molly Shoichet. “But we also wanted to see if you were vaccinated against one variant, does it protect you against another variant?”

The neutralizing antibodies were found to last about three to four months when their levels would drop by about 70 per cent irrespective of infection or vaccination status.

The data match those from a recent U.K. study, which showed that both neutralizing antibodies and cellular immunity, a type of immunity provided by memory T cells, from either infection, vaccination, or both, offered no protection from catching Omicron. In a surprising twist, the U.K. group also found that infections with Omicron boosted immunity against earlier strains, but not against Omicron itself, for reasons that remain unclear.

“There will be new variants in the near future for sure,” Stagljar said. “Monitoring and boosting immunity with respect to circulating variants will become increasingly important and our method could play a key role in this since it is fast, accurate, quantitative and cheap.”

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