The novel coronavirus SARS-CoV-2 that causes the COVID-19 disease, emerged in
2019 and caused
a world-wide pandemic. With COVID-19 still spreading and vaccination efforts underway, there
is an urgent need for high quality tests to conduct dependable serology and epidemiology
studies.
A serological test, also known as an antibody test, searches for antibodies
against the
SARS-CoV-2 virus in an individual's blood. There are two types of antibody tests for
detecting SARS-CoV-2-induced immune response.
The first type of antibody tests investigate a general immunogenic response by
detecting
either the total antibody response or the isotype-specific response to infection. A number
of ELISA and lateral flow rapid tests are on the market allowing users to detect such
general binding antibodies.
The second type of antibody tests detect only the portion of the antibodies
that can
interfere with the binding of the virus to the human cells and deter subsequent infection.
These are termed neutralization antibody tests. The gold standard for such tests is the
virus neutralization assay (VNT). It requires handling the live SARS-CoV-2 virus and
monitoring its interaction with human cells in presence of a sample to determine if the
sample contains antibodies that can prevent the virus from binding (neutralizing
antibodies). This assay is well-established and has been used for investigating patients'
immune response to a variety of infectious diseases. However, VNT is tedious and
time-consuming, taking 2-4 days to complete and requiring a high level of expertise. Due to
the use of a live virus, the VNT test can only be conducted in a specialized biosafety level
3 (BSL3) containment facility. An alternative to the VNT is a test that uses a
non-infectious virus such as lentivirus expressing the viral protein of interest. Such a
pseudovirus-based virus neutralization test (pVNT) can be performed in BSL2 level safety
environment. However, pVNT is also time-consuming and suffers from many of the shortcomings
of the VNT – such as higher experimental variability, the requirement for a high level of
expertise, and significant time to obtain results.
To overcome the shortcomings of VNT and pVNT, Professor Lin-Fa Wang's lab at
Duke-NUS Medical
School established a novel approach - the surrogate virus neutralization test (sVNT). The
sVNT detects NAbs without the need to use live virus or cells and can be completed in 1-2
hours in a BSL2 lab. The sVNT assay uses purified receptor binding domain (RBD) from the
SARS-CoV-2 viral spike (S) protein and the host cell receptor ACE2. The test is designed to
mimic the virus-host interaction by direct protein-protein interaction in a test tube or an
ELISA plate well. This highly specific interaction can then be neutralized, i.e., blocked by
the NAbs in patient or animal sera in the same manner as in a conventional VNT.
