The Denison and Baric teams, with lead authors Michelle Becker, Ph.D., of Vanderbilt, and Rachel Graham Ph.D., of UNC, determined that not being able to grow the virus represented a critical gap in the ability to rapidly identify and respond to new pathogens.
To address this vulnerability, the team decided to use synthetic biology to recover a non-cultivatable virus.
"The idea is, here's the virus, or the virus group, that we think became SARS-CoV," Denison said. "Let's see if we can synthetically recover the bat virus and test it in cultured cells and in animal models let the bat virus show us the pathways that it may have used to become a human pathogen.
"Then we would have a viable candidate virus to test for diagnostics, vaccines and treatment."
The investigators used published SARS-like bat coronavirus sequences to establish a "consensus" genome sequence "the best bet for a virus genome that would be viable," Denison said. They then used commercial DNA synthesis and reverse genetics to "build" the consensus viral genome and several variations.
The consensus synthetic SARS-like bat CoV did not initially grow in culture. But substitution of a single small region from human SARS-CoV the Spike protein receptor binding domain that is critical for viral entry into human cells allowed the new chimeric SARS-like bat CoV to grow well in monkey cells (commonly used to study human SARS-CoV).
"It was a tremendous surprise that such a small region of SARS-CoV was sufficient to allow the bat virus to move from zero growth to very efficient growth in cells," Denison said.
The chimeric virus also grew well in mouse cells modified to express the receptor for SARS-CoV and in primary human airway epithelial cells. It grew poorly in mice, but a single additional change in the Spike region
|Contact: John Howser|
Vanderbilt University Medical Center