A team of Swiss-German researchers has developed a method of testing for neutralizing antibodies against SARS-CoV-2 that creates a result in half the time of traditional tests.

A conventional neutralization test to determine immunity to SARS-CoV-2 usually takes two to three days and has to be carried out with infectious coronaviruses in a lab resorting to biosafety level 3. Now, a team from the University of Bern, in cooperation with colleagues from Ruhr-Universität Bochum (RUB), have developed a test which takes only 18 hours and does not have elevated biosafety requirements.

<strong>Disguising a benign virus as SARS-CoV-2</strong>

To be able to detect antibodies against SARS-CoV-2 in serum samples from covid-19 sufferers, the researchers used another virus that does not disperse. They exchanged the envelope protein of the virus to the spike protein of this novel coronavirus, which mediates virus entry and infection. "As a consequence, the viruses could be recognized by antibodies against Sars-Cov-2," explains lead author Toni-Luise Meister by Ruhr-Universität Bochum. "The antibodies bind to the viruses which were changed in this way and neutralize them that no more can penetrate cells."

<strong>Luminescence helps determine resistance</strong>

Since the virus pseudotyped in this way can not spread in host cells, no elaborate biosafety precautions are essential for the test. To be able to find out the amount of antibodies, the researchers genetically modified the virus to ensure that green fluorescent protein and a luciferase, an enzyme from fireflies, will be generated by infected cells. "After a single round of infection, we can then determine how many cells show green fluorescence," says lead author Ferdinand Zettl in the Institute of Virology and Immunology at Bern. The green fluorescence is a sign of infection with all the pseudotyped virus. The green cells the researchers are finding, the further neutralizing antibodies exist which obstructed the virus. Additionally, a luminometer may be utilized to read the luminescence signal made by the luciferase enzyme--another way of evaluating the test.

<strong>Quick and reliable</strong>

In order to check the reliability and comparability with the traditional neutralization test, the researchers employed it to blood samples from covid-19 patients. "The direct contrast revealed a fantastic correlation between the two test systems," explains corresponding writer Professor Stephanie Pfänder, PhD, from the Department of Molecular and Medical Virology in RUB. Compared to 56 hours to the traditional test, the new evaluation is much quicker, with only 18 hours to this test outcome. "Another fantastic benefit is that it may be performed in virtually all medical labs, because no sophisticated security precautions are necessary," points outside Gert Zimmer, PhD, in the Institute of Virology and Immunology from Bern, corresponding author of the study.

<strong>Reference</strong>

1 Zettl F, Meister TL, Vollmer T, et al. Rapid quantification of SARS-CoV-2-neutralizing antibodies using propagation-defective vesicular stomatitis virus pseudotypes. <em>Vaccines</em>, 2020;8(3):386. doi: <span style="color: #ff6600;"><a style="color: #ff6600;" href="http://dx.doi.org/10.3390/vaccines8030386">3390/vaccines8030386</a>.</span>