A copycat who can help in the search for COVID-19 vaccine candidates

Due to the current global COVID-19 crisis, the whole world is desperately searching for a vaccine. To develop a suitable serum, research must first understand how the virus enters our bodies. We now know that SARS-CoV-2 attaches itself to the ACE2 receptor with the receptor binding domain (RBD) of the spike protein. If this interaction is blocked with a neutralising antibody, the virus cannot enter into the cell.

To find such an antibody, a neutralisation test (virus neutralisation test, VNT) is traditionally carried out. This involves using the pathogenic virus in a cell culture to test whether the antibodies are actually capable of neutralising SARS-CoV-2. However, this procedure requires a biosafety level 3 and takes several days. Although there are now many immunoassays that can also test for neutralising antibodies, the specificity is not sufficient and therefore neutralisation tests must still be carried out.

A promising alternative is Genscript's cPass Neutralization Antibody Detection Kit. The cPass kit mimics a VNT without using pathogenic viruses. It is capable of measuring functional neutralizing antibodies (NAbs) within one hour. Due to its format, the test is scalable and can be automated at high sample throughput.

Since only about 3% of the total antibodies produced by the immune response are neutralizing antibodies, the cPass kit has a significant advantage over many other immunoassays. It detects only circulating neutralizing antibodies. Many of the tests currently available on the market simply bind to all binding antibodies. Therefore these antibody tests do not show any neutralizing function.

Furthermore, the current ELISAS often require a secondary antibody that is isotype and species dependent. The cPass test is not limited to human samples and can be applied to any species.

FDA approval for drug evaluation is still pending and therefore the VNT remains the gold standard for the time being. However, the cPass test can help scientists use automated systems to narrow down the number of targets before performing time-consuming neutralization tests. The cPass test could also be used to determine the extent to which the population or certain groups have already had contact with Sars-CoV-2 (screening studies).