SARS-CoV-2 antibody test: expertise of Austrian universities

Whereas the current PCR test looks directly for SARS-CoV-2 DNA, an antibody test tells us whether someone has previously been infected by the novel coronavirus and whether their immune system has responded to this infection by producing antibodies against it. Reliable mass antibody tests are important tools for gathering information about the spread of the coronavirus and about the unrecorded number of infections. Because, with antibody testing it is also possible to identify people who have had the infection without having any symptoms. In this way, antibody tests can help to forecast more accurately the level of immunity within the population and to take more targeted measures to limit the spread of the disease. In view of the anticipated licensing of vaccines, antibody tests are also an important tool for checking the success of vaccination.

Common basis for test system
Austrian virologist Florian Krammer (Icahn School of Medicine at Mount Sinai, New York/USA) recently developed a serological test for identifying SARS-CoV-2 antibodies in the blood. Based on this, three Austrian universities – BOKU, Vetmeduni Vienna and MedUni Vienna – came together in the spring of 2020 to generate a serological test that was capable of specifically and sensitively detecting SARS-CoV-2 antibodies in the blood and could also be deployed in small laboratories.

Together with scientists from the University of Natural Resources and Applied Life Sciences Vienna (BOKU), Vienna University of Veterinary Medicine developed the basis for this antibody test. This involved investigating the technical and clinical aspects of establishing an antibody test. Development of the test system was greatly accelerated by the close collaboration between immunologists and biochemists from Vetmeduni Vienna and experts from BOKU and MedUni Vienna, as well as the financial support of an Austrian industrial sponsor. "The strength and rapid success of the consortium is down to the fact that each partner contributed its specialist know-how required for the design, testing and validation of this test system," says Wilhelm Gerner from the Institute of Immunology at Vetmeduni Vienna. This made it possible to develop a high-quality test method very quickly.

Proteins for Austria-wide antibody test
The University of Natural Resources and Applied Life Sciences formed a cross-departmental consortium made up of scientists from the Department of Biotechnology (DBT) and the Department of Applied Genetics and Cell Biology (DAGZ), with the aim of rapidly providing high-quality SARS CoV-2 proteins (antigens) for test development. The DBT has wide-ranging expertise and the necessary infrastructure for small or large-scale expression (production) of recombinant proteins in various production systems, e.g. mammalian and insect cells or microbial organisms such as bacteria and yeasts, and cleaning of these proteins. The DAGZ supplements this expertise with the production of recombinant proteins in plants and the targeted modification of their sugar structures.

"Over the last few months we have been driven by scientific curiosity and our desire to help to develop different versions of these antigens, as well as additional antigen candidates, and to test these for their suitability for use in an antibody test," emphasises Reingard Grabherr from BOKU's Department of Biotechnology. BOKU established complex cleaning processes and analytical methods to guarantee that the antigens can be reproducibly manufactured with a particularly high level of purity. Many external partners praised the high quality of the antigens produced at BOKU, since this will significantly improve the accuracy and reliability of any tests based on them.

ELISA expertise at Vetmeduni Vienna
Vienna University of Veterinary Medicine contributed its expertise in the design and setting up of new ELISA test systems. Enzyme-Linked Immunosorbent Assays (ELISA) are able to identify highly specific proteins such as antibodies, for example. The ELISA that has been developed is able to detect antibodies against SARS-CoV-2 from samples from infected patients and is available in two different versions. One version of the test looks for the presence of antibodies against the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. The second version detects antibodies against the nucleoprotein (NP). The test that targets the NP reacts more sensitively in the early stages of the immune response, whereas the test kit that targets RBD correlates better with the immunity of patients in the main and late phase of the immune response.

Biobank is an important resource
In order to test the quality and robustness of the two tests in a clinical diagnostic laboratory, MedUni Vienna, led by the Department of Laboratory Medicine, contributed its extensive expertise in the validation of diagnostic tests. In order to determine the specificity and sensitivity of an antibody test, i.e. how many false positives or false negatives it generates, it is necessary to test a large number of well characterised serum samples that were collected before the pandemic and/or come from patients with a confirmed Covid-19 diagnosis. Here, MedUni Vienna was able to draw on its extensive collection of samples in the biobank and an Austria-wide laboratory medicine network.

High quality and versatile test system
Ultimately, the early and close collaboration between the academic partners and the industrial partner Technoclone was able to bring the antibody test onto the market in record time. The newly established test system has important advantages over the existing antibody tests, as Wilhelm Gerner explains: "The antibody test can be performed by any certified laboratory with a standard ELISA reader. As well as this, the test system allows quantification of antibodies in the samples. It is therefore possible to conduct accurate chronological studies of antibody titers." Another application might be for the testing of vaccines in the future. Most of the vaccines currently in development only incorporate areas from the spike protein of SARS-CoV-2. By establishing two separate systems for detecting antibodies against the RBD from the spike protein and against the nucleoprotein, it will be possible to investigate in future vaccine studies whether vaccinated people only develop antibodies against the RBD (reaction to the vaccine) or whether an immune response to circulating SARS-CoV-2 also occurs in the background. If this were the case, antibodies would also be formed to the nucleoprotein. This would provide important information about the protective effect of the vaccines.