U of T researchers' low-cost pinprick test measures COVID-19 immunity in under one hour

Igor Stagljar made his career building molecular tools to combat cancer. But when the pandemic hit last March, he aimed his expertise at a new adversary: SARS-CoV-2.

Stagljar is a professor of biochemistry and molecular genetics in the Donnelly Centre for Cellular and Biomolecular Research at the University of Toronto’s Temerty Faculty of Medicine. Last spring, with support from U of T’s Toronto COVID-19 Action Fund, Stagljar and his team began developing a new method for measuring immunity to coronavirus in those who recovered from COVID-19.

They are now ready to reveal their creation: a pinprick test that accurately measures the concentration of coronavirus antibodies in blood in under one hour. And it’s cheap – costing a toonie or about tenth of current tests.

Their method is detailed in a study published this week in the journal Nature Communications.

“Our assay is as sensitive as, if not better than, any other currently available assay in detecting low levels of IgG antibodies and its specificity – also known as false-positive rate – is as good as the best antibody test on the market,” said Stagljar, who collaborated with public health agencies and blood banks from across Canada to have the test validated on blood samples taken from former COVID-19 patients.

Read about the new test in the Globe and Mail

Serological tests detect antibodies, which are protein molecules in blood that recognize and neutralize Sars-CoV-2 to prevent infection. Such tests are seen as a key tool for public health experts to manage the ongoing pandemic because it allows them to measure population immunity.

According to a January report by the national COVID-19 Immunity Task Force, the majority of Canadians remain vulnerable to coronavirus infection with less than two per cent testing positive for antibodies.

Population-level studies can also help reveal the duration of coronavirus immunity across patients who had different experiences of disease – from asymptomatic to severe. They also have the potential to reveal the threshold antibody level needed for protection after natural infection and vaccination.

“That level is still to be determined, but we do know that people who have been infected with SARS-CoV-2 have very diverse levels of antibodies, and it would not be surprising to find that below some baseline level they might not be protective,” said Zhong Yao, senior research associate in Stagljar’s lab and co-inventor of the testing method.

Several serological tests have received regulatory approval. At present, ELISA (enzyme-linked immunosorbent assay)-based methods are considered the gold standard when it comes to measuring antibody concentration as a strength of individual immune response. But the ELISA approach requires several laboratory steps that take six hours to complete, making it unsuitable for rapid diagnostics. On the other hand, simpler methods using test strips, similar to pregnancy tests, provide fast results but are not quantitative and are less reliable.

The new method is called SATiN, which stands for Serological Assay based on split Tripart Nanoluciferase. It is the first COVID-19 serology test that uses highly sensitive protein complementation chemistry in which a light-emitting luciferase protein is reconstituted from separate fragments as test readout.

Luciferase is initially supplied in fragments that cannot not glow on their own. One piece is attached on the viral spike protein, which antibodies bind to in order to neutralise the virus, while another is hooked to a bacterial protein that antibodies also interact with. By binding simultaneously to the coronavirus spike protein and the bacterial protein, the antibody helps lock luciferase pieces together into a whole molecule. The result is a flash of light that can be detected and converted into antibody concentration by a plate reader instrument. All reagents can be prepared from scratch and in bulk, helping to keep costs down.

Stagljar is now working with U of T’s intellectual property office and Toronto Innovation Acceleration Partners to find industry partners that could help make the method widely available. He is also collaborating with Prabhat Jha, director of the Centre for Global Health Research at St. Michael’s Hospital and a professor at U of T’s Dalla Lana School of public Health, who is leading a long-term study to establish duration of immunity across 10,000 Canadians. In another project, Stagljar is working with Allison McGeer, senior clinician scientist at Sinai Health System and a professor at Dalla Lana and the Temerty Faculty of Medicine, to assess antibody levels in people after vaccination.

“It’s really useful to have that quantitative ability to know what someone’s antibody status is – whether it’s from a past infection or a vaccination,” Stagljar said. “This will be of crucial importance for the next stage of the pandemic, especially now when governments of all countries started with mass vaccinations with recently approved anti-COVID-19 vaccines.”