Harvard Researchers Succeed In Destroying Both Latent And Active Herpes Virus In Human Cells Using Gene Editing
To date, the the herpes
simplex virus, commonly known as the cold sore virus, is a devious microbe that is hard to destroy and eradicate in infected humans.
The virus enters the body through regions lined with mucous membranes ie mouth, nose and genitals but quickly establishes lifelong viral hideouts inside nerve cells. After initial infection, the virus lurks dormant only to be reawakened periodically to cause outbreaks marked by the eruption of cold sores or blisters. In a handful of people, the consequences of viral re-awaking can be devastating, including blindness and brain inflammation.
Although antiviral medications can prevent recurrent outbreaks, but they are not always effective, so for decades, researchers have sought a solution that would quiet the virus for good.
In a breakthrough research using human fibroblast cells infected with herpes
simplex virus (HSV
), researchers at Harvard Medical School have successfully used CRISPR-Cas9 gene editing
to disrupt not only actively replicating virus but also the far-harder to reach dormant pools of the virus, demonstrating a possible strategy for achieving permanent viral control.
The research findings were published in the journal eLife
Dr David Knipe, the Higgins Professor of Microbiology and Molecular Genetics in the Blavatnik Institute at Harvard Medical School and lead investigator for the study told Thailand Medical
News, "This is an exciting first step, one that suggests it is possible to permanently silence lifelong infections but much more work remains to be done."
Significantly, the research represents the first successful instance of disrupting latent viral reservoirs through gene editing
. Latent reservoirs are notoriously impervious to antiviral medications and have also proven hard to gene-edit.
The study also identify the mechanisms by which actively replicating virus becomes uniquely vulnerable to gene editing
. These very mechanisms may also explain why latent forms of the virus are less amenable to this technique.
Most importantly , the experiments reveal that the DNA of an actively replicating virus is more exposed to the Cas9 enzyme, the molecular scissors in the CRISPR-Cas9 gene-editing
system. This is because actively replicating viruses have fewer protective histones that wrap around their DNA to shield it.
Dr Knipe added, "The absence of protective histones makes the DNA more accessible and easier to cut, so it's essentially identified HSV
's Achilles heel.
The study findings offer a model system for using gene editing
in a localized way to disrupt active replication in specific sites. However, Knipe cautions, the arch-challenge of delivering gene-editing
therapy to neurons, where the virus hides and enters a state of dormancy remains to be solved, Knipe added.
Almost 70% of the world population harbors the v
irus according to the World Health Organization. While most infections are asymptomatic, in a handful of people HSV
can cause serious damage. It can infect the eyes, a condition known as herpes keratitis, and lead to blindness. In people with compromised immune systems, HSV
can cause brain inflammation. In newborns, the virus can cause disseminated, systemic disease and brain inflammation and can be fatal in a quarter of infected babies.
Hence, one early therapeutic use of this technique could involve local and limited gene-editing
of the epithelial cells in the mouth, eyes or genitals of people with established HSV
infections as a way to prevent the virus from causing active outbreaks at vulnerable sites, Knipe said.
Dr Knipe added, "If you want to prevent corneal infections, for example, you might be able to use CRISPR-Cas9 editing
in the corneal cells to prevent new infections or prevent the virus from reactivating or reduce the reactivation. People who have recurrent herpes keratitis infection of the cornea start to go blind after a while because of the reactivation and the resulting inflammation that causes clouding of the cornea."
The great advantage of limited, localized gene-editing
is avoiding the widespread, possible off-target effects that might inadvertently alter the DNA of cells other than those intended.
Dr Knipe concluded, "We still have a long way to go in ensuring hyperprecision and safety of new gene-editing
tools so local editing could offer a safer, more limited first step."
Reference : Hyung Suk Oh et al. Herpesviral lytic gene functions render the viral genome susceptible to novel editing by CRISPR/Cas9, eLife (2019). DOI: 10.7554/eLife.51662