Wanted: Antibodies against the coronavirus

For some time now, everyone has been talking about antibody tests that can detect infection by the SARS-CoV-2 corona virus. Sure, it would be a fine thing to know if one has already undergone an infection and our immune system has already produced antibodies against the invader. These antibodies recognize the virus very specifically and initiate a defense. The hope of being immune to the pandemic as a result is high. 

In record time, suppliers from around the world have brought such antibody tests to market. For the most part, however, these had a stumbling block: they delivered many false positive results. This means that the test result actually says that one has formed antibodies against the virus - but this is not correct. The person concerned is then lulled into a false sense of security that he or she can no longer fall ill. 

A good test must meet at least two criteria: On the one hand, it must be as "sensitive" as possible, i.e. it must be sensitive to the presence of antibodies against the virus and be able to detect them even in the smallest quantities. On the other hand, however, a high "specificity" is also required: the test must find exactly the molecules it is looking for - and not substances that only look similar. The reason that the two criteria are not easy to meet is that there are related (much more harmless) corona viruses with which we have already come into contact and have therefore formed antibodies. One has to make sure that a test really finds the current, dangerous corona viruses.

The biggest problems with false positive test results have so-called "rapid tests", which show a result very quickly, without the need for special equipment or expertise. Much better are laboratory tests that require special equipment and give a result after a few hours. Unclear results can also be clarified with so-called "neutralization tests". These are the "gold standard" among antibody tests: they can really prove whether a person being treated has actually formed antibodies that "neutralize" the virus, i.e. kill it. However, they require highly specialized laboratories because intact viruses have to be multiplied - only three virology laboratories in Austria are authorized to do this.

The problem with most laboratory tests is that they require special technical equipment. That was the starting point for a consortium of Austrian research institutes. "The consortium's goal was to develop an ELISA test as an alternative to platform tests, which can only be performed in specially equipped laboratories, that can also be done in normal medical diagnostic laboratories with standard equipment and provide equally good results," reports biotechnologist Otto Doblhoff-Dier, vice rector for research at the University of Veterinary Medicine Vienna (Vetmeduni Vienna). "The test should be easy to perform and robust, and the starting materials should be readily available."

Supported by a sponsor from Austrian industry, partners have spontaneously come together who have cooperated well on a regular basis in the past. In addition to Vetmeduni Vienna, these are the University of Natural Resources and Life Sciences Vienna (BOKU), the Medical University of Vienna (MedUni Vienna) and two application-oriented partners - a manufacturer of diagnostics and the AIT Austrian Institute of Technology - to enable rapid implementation in practice. "In this cooperation, almost everything runs through networks of trust," notes Doblhoff-Dier. This has also enabled rapid and targeted cooperation despite all the constraints imposed by the Corona crisis. 

In the consortium, each partner does what it is particularly good at: BOKU is in close contact with Florian Krammer, an Austrian researcher who is working on a similar test at the Icahn School of Medicine at Mount Sinai in New York. "We have modified the concept somewhat and adapted it to our expression systems," says Reingard Grabherr, head of the Department of Biotechnology at BOKU. The antigens used are parts of viral proteins that are recognized by the patients' antibodies. "The goal is to produce the antigens as high quality, clean and in large quantities as possible," Grabherr said. The researchers have succeeded in doing so; they can now produce the two antigens agreed upon in the consortium in sufficient quantities in bacteria and mammalian cells, respectively, in the laboratory. The advantage of this approach, which (unlike all other available tests) uses two antigens, is that the results are much more accurate: Thus, there are fewer false positive (and false negative) results.

Researchers at Vetmeduni Vienna are currently working on establishing an ELISA test. This is a standard test that can be performed in all medical laboratories and provides a result in three hours at the latest. These tests, which are being developed to production readiness by a corporate partner, are being evaluated at MedUni Vienna. "We have a very large bank of serum samples - both from pre-Covid times and from Covid cases," reports Christoph Binder, Professor at the Clinical Institute of Laboratory Medicine. "As soon as our commercial partner has a prototype ready, we will test about 1500 samples under real clinical laboratory conditions and compare them with results from other platforms." That should happen as early as the next few weeks. What is already clear is that "our antigens have very good specificity data," says Binder. If everything goes according to plan, the regulatory performance evaluation review should be completed before the summer - then the new test can be used routinely.

In addition to the ELISA test, the two antigens are also used in a second test platform: At AIT, a so-called "multiplex procedure" was adapted for the Covid-19 antibody tests, which was originally developed in the Research Studio Austria "PepPipe" for the analysis of proteins. This special test goes far beyond the possibilities of other tests: on the one hand, it can be used to check considerably more different properties of the antigens, and also several different antibodies. Specifically, in addition to antibodies of the IgG class, which are responsible for the specific immune response, the binding of IgM antibodies (which provide a rapid but more non-specific immune response) is also measured. "In total, we measure 22 parameters in one test," explains Martin Jung, head of the AIT Competence Unit Molecular Diagnostics. This provides a much more complete picture of how the immune system defends itself against infection. 

On the other hand, the multiplex test provides quantitative information: it can be used to determine an antibody titer. "That's the big advantage of our test," Jung says. However, there is no advantage without a disadvantage: the multiplex test requires very specialized equipment; it can only be used in specialized laboratories. AIT already performs the tests in cooperation with the laboratory Dr. Kosak, Dr. Reckendorfer and Partners. "We are open to other partners," says Jung.

The research consortium already has further ideas about the direction in which the antibody tests can and should be developed in the future - with the aim of obtaining the most precise information possible about the nature of the immune response in the event of a Covid 19 infection. This knowledge is immensely important in order to be able to better deal with the pandemic in the future. Because the virus will not leave us so quickly.