Scientists launch a test that determines the number of neutralising antibodies against SARS-CoV-2 within a much shorter period of time than previous methods.
To determine immunity to SARS-CoV-2, the strain of coronavirus that causes COVID-19, and the effectiveness of potential vaccines, the number of neutralising antibodies in the blood of recovered or vaccinated individuals need to be determined.
A traditional neutralisation test usually takes two to three days and must be carried out with infectious coronaviruses in a laboratory complying with biosafety level 3. A Swiss-German research team has launched a new test that takes only 18 hours and doesn’t require high biosafety requirements.
The test was developed at the Institute of Virology and Immunology (IVI) of the University of Bern and the Swiss Federal Office for Food Safety and Animal Health and evaluated in cooperation with colleagues from the Ruhr-University Bochum using serum samples from COVID-19 patients.
The researchers have published their report in the journal, “Vaccines” on the 15th of July 2020.
In order to detect antibodies against SARS-CoV-2, the researchers used another virus that doesn’t propagate. They exchanged the envelope protein of this virus for the spike protein of the novel coronavirus, which mediates virus entry and infection.
“As a result, the viruses can be identified by antibodies against SARS-CoV-2,” said lead author Toni-Luise Meister. “The antibodies bind to the viruses that have been altered in this way and neutralise them so that no longer can penetrate the host cells.”
Since the pseudovirus [a virus produced naturally or artificially for research purposes] can’t propagate in host cells, no elaborate biosafety precautions are necessary for the test.
In order to determine the amount of antibodies, the researchers genetically modified the virus so that green fluorescent protein and luciferase, an enzyme from fireflies, were produced by the infected cells.
Ferdinand Zettle from the Institute of Virology and Immunology in Bern said: “After a single round of infection, we can then determine how many cells show green fluorescence.”
The green fluorescence is an indicator of infection with the pseudotyped virus. The less green cells the researchers are finding, the more neutralizing antibodies are present which blocked the virus.
In addition, a luminometer [an instrument that measures visible light coming from a sample] may be used to read the luminescence signal produced by the luciferase enzyme.
In order to check the reliability and comparability with the conventional neutralisation test, the researchers applied it to blood samples from COVID-19 patients.
Professor Stephanie Pfänder from the Department of Molecular and Medical Virology at RUB said: “The direct comparison showed a good correlation between the two test systems.
Compared to 56 hours for the conventional test, the new test is much faster, with only 18 hours needed to produce the results.
Dr. Gert Zimmer from the Institute of Virology and Immunology in Bern said: “Another great advantage is that the test can be carried out in almost all medical labs, because no sophisticated safety precautions are necessary.”