Watching SARS-CoV-2 spread in animal models in real time

Date:
September 27, 2021
Source:
Texas Biomedical Research Institute
Summary:
New 'reporter viruses' developed by researchers make it much easier
to observe SARS-CoV-2 and its variants in cells and live animals in
the lab, enabling faster screening of potential anti-viral drugs,
vaccines and neutralizing antibodies.



FULL STORY ==========================================================================
A version of SARS-CoV-2, the virus that causes COVID-19 disease, has
been successfully modified to glow brightly in cells and animal tissues, providing a real-time way to track the spread and intensity of viral
infection as it happens in animal models, researchers at Texas Biomedical Research Institute (Texas Biomed) report in the journal The Proceedings
of the National Academy of Sciences (PNAS).


==========================================================================
"Now we can track where the virus goes in animal models for COVID-19,"
said virologist Luis Martinez-Sobrido, Ph.D., a Professor at Texas Biomed,
and senior paper author. "Being able to see how the virus progresses,
and which organs and cell types it specifically targets, will be a big
help for understanding the virus and optimizing anti-viral drugs and
vaccines." In addition to tracking the virus, Martinez-Sobrido and his collaborators have already begun using the reporter viruses to screen how
well neutralizing antibodies work against different variants of concern,
as recently reported in the Journal of Virology.

Turning up the lights To make the reporter virus, Martinez-Sobrido
and his team combined several advanced molecular biology tools to add
the genetic sequence for the fluorescent or bioluminescent "reporter"
proteins to the virus genetic code. As the virus's code is replicated
and transcribed, so too is the code for the glowing proteins.

In an earlier study, the team replaced one of the virus's genes with the
gene for the glowing proteins, but this resulted in a very dim signal --
the gene was not expressed enough to be easily detected in animals. To
turn up the brightness, the researchers had to figure out how to get
the virus to produce larger quantities of the reporter proteins.



========================================================================== Their solution: they inserted the reporter gene next to a different
gene in SARS-CoV-2, specifically, the gene coding for the nucleocapsid
protein. "It's the most expressed protein in SARS-CoV-2," said molecular biologist Chengjin Ye, Ph.D., a member of Martinez-Sobrido's lab. This
time, the signal was so bright, "it almost blinded me when I looked
through the fluorescent microscope," he said.

Faster screens The reporter proteins work in cells and live animal models,
in combination with imaging systems that detect the wavelengths of light emitted by the proteins.

Being able to observe viral load and location visually offers many
advantages over other methods. It is much simpler and faster, saving
time and materials.

"Instead of needing a large team to screen 2,000 compounds to see if
they work against the virus, one person could do that with a reporter
virus in a few hours," Ye said.

It also enables tracking the virus in the same animal throughout the
course of infection and treatment, reducing the number of animals needed
to gain similar insights.



========================================================================== Tracking variants The team adapted the reporter viruses to express
different colored proteins attached to SARS-CoV-2 variants of
concern, which they described in a separate paper in the Journal of
Virology. Critically, this approach has enabled them to test how well
a neutralizing antibody works against two variants in one test well,
at the same time.

"This is a significant advantage for saving time and resources,
especially with so many basic materials like plastics and reagents in
such high demand and limited supply due to the pandemic," says Kevin
Chiem, Ph.D. candidate and member of Martinez-Sobrido's lab. "As new
variants emerge, we can easily adapt the system and quickly screen
for how well antibodies work against them." Powerful and accurate
Importantly, the group demonstrated the reporter viruses behave the same
as a wild-type version of the virus. This is thanks to the fact they
did not remove any viral genes, and because they designed the reporter
protein to immediately separate from the virus's nucleocapsid protein so
it functions normally. Their research shows reporter protein brightness correlates well with viral load, although protein accumulation can occur
over several days leading to a slightly stronger signal in some cases.

The advancement relies on several powerful techniques, including reverse genetics techniques to generate recombinant SARS-CoV-2, which link
together pieces of genetic code to produce the full virus.

Martinez-Sobrido and his team have shared their recombinant SARS-CoV-2
and the noninfectious precursor materials, called plasmids, with more
than 100 labs around the world. They can now share the reporter viruses
with qualified labs with biocontainment safety level (BSL)-3 access,
which is necessary to work with SARS-CoV-2, to help to combat the still
ongoing COVID-19 pandemic.

"We feel is it is our responsibility to share these new tools and
technologies with other researchers around the world to help bring the
pandemic to an end as quickly as possible," Martinez-Sobrido said.

Collaborators on these projects include Jun-Gyu Park, Jesus A. Silvas,
Desarey Morales Vasquez, and Jordi B. Torrelles at Texas Biomed;
Julien Sourimant and Richard K. Plemper at The Center for Translational Antiviral Research at Georgia State University; Michelle J. Lin and
Alexander L. Greninger at University of Washington; James J. Kobie,
Mark R. Walter and Michael S.

Piepenbrink at University of Alabama at Birmingham; and Juan Carlos de
la Torre at The Scripps Research Institute.

========================================================================== Story Source: Materials provided by
Texas_Biomedical_Research_Institute. Note: Content may be edited for
style and length.


========================================================================== Journal References:
1. Chengjin Ye, Kevin Chiem, Jun-Gyu Park, Jesus A. Silvas, Desarey
Morales
Vasquez, Julien Sourimant, Michelle J. Lin, Alexander L. Greninger,
Richard K. Plemper, Jordi B. Torrelles, James J. Kobie, Mark
R. Walter, Juan Carlos de la Torre, Luis Martinez-Sobrido. Analysis
of SARS-CoV- 2 infection dynamic in vivo using reporter-expressing
viruses.

Proceedings of the National Academy of Sciences, 2021; 118 (41):
e2111593118 DOI: 10.1073/pnas.2111593118
2. Kevin Chiem, Desarey Morales Vasquez, Jesus A. Silvas, Jun-Gyu Park,
Michael S. Piepenbrink, Julien Sourimant, Michelle J. Lin,
Alexander L.

Greninger, Richard K. Plemper, Jordi B. Torrelles, Mark
R. Walter, Juan C. de la Torre, James K. Kobie, Chengjin Ye, Luis
Martinez-Sobrido. A bifluorescent-based assay for the identification
of neutralizing antibodies against SARS-CoV-2 variants of concern
in vitro and in vivo.

Journal of Virology, 2021; DOI: 10.1128/JVI.01126-21
3. Kevin Chiem, Desarey Morales Vasquez, Jun-Gyu Park, Roy Neal
Platt, Tim
Anderson, Mark R. Walter, James J. Kobie, Chengjin Ye, Luis
Martinez- Sobrido. Generation and Characterization of Recombinant
SARS-CoV- 2 Expressing Reporter Genes. Journal of Virology, 2021;
95 (7) DOI: 10.1128/JVI.02209-20 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210927121236.htm

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