Covid-19 antibody test developed to be scalable

Scientists have developed an antibody test for the virus that causes Covid-19 that they say is more accurate and can handle a larger number of donor samples at lower overall cost than standard antibody tests currently in use.

 In the short term, the test, developed by researchers at the University of Texas at Austin in collaboration with Houston Methodist and other institutions, can be used to accurately identify the best donors for convalescent plasma therapy and measure how well candidate vaccines and other therapies evoke an immune response.

According to the researchers, additional uses coming later that are likely to have the biggest societal impact are to assess relative immunity in those previously infected by the SARS-CoV-2 virus and identify asymptomatic individuals with high levels of neutralising antibodies against the virus.

“This is potentially game-changing when it comes to serological testing for Covid-19 immunity,” said Jason Lavinder, a research associate in the Cockrell School of Engineering. “We can now use highly scalable, automated testing to examine antibody-based immunity to Covid-19 for hundreds of donors in a single run. With increased levels of automation, limited capacity for serological testing can be rapidly addressed using this approach.”

The standard of Covid-19 antibody testing measures the amount of virus neutralising (VN) antibodies circulating in the blood because this closely correlates with immunity. But this version of antibody testing is not widely available because it’s technically complex. This requires days to set up, run, and interpret, and needs to be performed in a biosafety level 3 laboratory.

The research team, therefore, looked to another type of test, called ELISA assays, that can be implemented and performed with relative ease in a high-throughput fashion and are widely available and extensively used in clinical labs across the world.

The ELISA tests, or enzyme-linked immunosorbent assays, look at whether antibodies against specific SARS-CoV-2 proteins are present and produce a quantitative measure of those antibodies.

The goal of the study was to test the hypothesis that levels of antibodies that target two regions of the virus’s spike protein – spike ectodomain (ECD) and receptor-binding domain (RBD) – are correlated with virus neutralising antibody levels.

This makes these more accessible, easier-to-perform ELISA tests a surrogate marker to identify plasma donors with antibody levels above the recommended US Food and Drug Administration (FDA) threshold for convalescent plasma donation.

As part of the study, the researchers used the new test to evaluate 2,814 blood samples used in an ongoing study of convalescent plasma therapy. Houston Methodist became the first academic medical centre in the US to transfuse plasma from recovered individuals into Covid-19 patients.

The team found that the ELISA tests had an 80 per cent probability or greater of comparable antibody level to VN levels at or above the FDA-recommended levels for Covid-19 convalescent plasma. These results affirm that all three types of tests could potentially serve as a quantitative target for therapeutic and prophylactic treatments.