Introduction
Serum neutralization corresponds protection against viral infection
after vaccination or natural infection. However, high levels of mutation
observed in viral glycoprotein of different variants could prevent
effective protection provided by neutralization serum. Therefore,
immediate determination of serum neutralization potency against
different variants is crucial (Wu et al., 2020). Particularly, new
variants have begun to emerge for disease caused by global infection
with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) since
2019. It has been reported that mutations on the major neutralization
target of these variants alter serum-neutralizing activity induced by
early strains or vaccines (Kuzmina et al., 2021; Robbiani et al., 2020).
Some of these mutations can provide an escape from immune response by
decreasing monoclonal antibody (mAb) neutralization (Liu et al., 2021).
Due to the high risk of SARS-CoV-2 infection, cultivation of authentic
viruses requires laboratories with at least level 3 biological safety
(BSL3) equipped with negative pressure systems. This limitation prevents
to perform neutralization assays in many research centers, which only
has BSL2 laboratories. Pseudotyped virus neutralization assay is an
alternative method based on packaging a reliable replication-defective
pseudovirus with Spike protein to mimic the entry of the authentic
virus. Thereby, pseudoviruses can be contained in BSL2 conditions to
perform neutralization assays (Chen and Zhang, 2021; Li et al., 2018).
In the broad extent, pseudoviruses can be utilized in
seroepidemiological studies, vaccine and monoclonal antibody
development, screening of viral entry inhibitors, and fundamental
virological methods (Ou et al., 2020). Several convenient pseudotyped
virus for SARS-CoV-2 have been reported, such as human immunodeficiency
virus (HIV)-based lentiviral particles (Donofrio et al., 2021), murine
leukemia virus (MLV)-based retroviral particles (Chen and Zhang, 2021),
or vesicular stomatitis virus (VSV)-based systems (Nie et al., 2020;
Salazar-García et al., 2022) with higher performance for evaluating the
efficacy of therapeutic drugs and vaccines (Salazar-García et al.,
2022). The results of such pseudovirus neutralization tests are very
closely correlated to those of authentic virus measurements. Also,
tracking the changes in Spike glycoprotein using pseudovirus
neutralizing assays is relatively easy (Schmidt et al., 2020).
From the beginning of the pandemic, DNA sequencing data of virus
glycoproteins is utilized to identify individual mutations in SARS-CoV-2
(Schrörs et al., 2021). One of the first variants called B.1.1.7 was
first emerged in the United Kingdom and had multiple mutations in the
target regions of neutralizing antibodies such as receptor binding
domain and N-terminal domain of Spike. SubsequentlyB.1.351 variant has
been identified in South Africa with additional mutations. B.1.1.7 and
B.1.351 variants share key mutations in the RBD (N501Y, D614G), but
B.1.351 has additional changes causing widespread escape from mAbs
(E484K, K417N) (Harvey et al., 2021; Zhou et al., 2021).
In this paper, we evaluated human convalescent plasma with different
serum neutralizing activities using pseudotyped VSV-ΔG virus carrying
Spike variants (Wuhan strain, B.1.1.7, and B.1.351). First, we
made a series of point mutations in Spike sequence of SARS-CoV-2 to
obtain global variants. Second, we generated pseudotyped viruses
usingSpike of ancestoral Wuhan strain and two variants and utilized to
evaluate neutralization activity of human serum samples. Neutralization
assay using Spike pseudotyped VSV-ΔG virus was found to correlate with
plaque assay using SARS-CoV-2 authentic virus. Additionally, Spike
pseudotyped VSV-ΔG virus was sufficient to discriminate serum responses
against different variants of the virus.