Infectious disease researchers at Fred Hutchinson Cancer Research Center have used a gene editing approach to remove latent herpes simplex virus 1, or HSV-1, also known as oral herpes. In animal models, the findings show at least a 90 percent decrease in the latent virus, enough researchers expect that it will keep the infection from coming back.
The study, published August 18 in Nature Communications, used two sets of genetic scissors to damage the virus’s DNA, fine-tuned the delivery vehicle to the infected cells, and targeted the nerve pathways that connect the neck with the face and reach the tissue where the virus lies dormant in individuals with the infection.
“This is the first time that scientists have been able to go in and actually eliminate most of the herpes in a body,” said senior author Dr. Keith Jerome, professor in the Vaccine and Infectious Disease Division at Fred Hutch.
“We are targeting the root cause of the infection: the infected cells where the virus lies dormant and are the seeds that give rise to repeat infections.”
Most research on herpes has focused on suppressing the recurrence of painful symptoms, and Jerome said that his team is taking a completely different approach by focusing on how to cure the disease.
“The big jump here is from doing this in test tubes to doing this in an animal,” said Jerome, who also leads the Virology Division at UW Medicine.
“I hope this study changes the dialog around herpes research and opens up the idea that we can start thinking about cure, rather than just control of the virus.”
Two-thirds of the world population under the age of 50 have HSV-1, according to the World Health Organization. The infection primarily causes cold sores and is lifelong.
In the study, the researchers used two types of genetic scissors to cut the DNA of the herpes virus. They found that when using just one pair of the scissors the virus DNA can be repaired in the infected cell.
But by combining two scissors – two sets of gene-cutting proteins called meganucleases that zero in on and cut a segment of herpes DNA – the virus fell apart.
“We use a dual meganuclease that targets two sites on the virus DNA,” said first author Martine Aubert, a senior staff scientist at Fred Hutch.
“When there are two cuts, the cells seem to say that the virus DNA is too damaged to be repaired and other molecular players come in to remove it from the cell body.”
The dual genetic scissors are introduced into the target cells by delivering the gene coding for the gene-cutting proteins with a vector, which is a harmless deactivated virus that can slip into infected cells.
The researchers injected the delivery vector into a mouse model of HSV-1 infection, and it finds its way to the target cells after entering the nerve pathways.
The researchers found a 92% reduction in the virus DNA present in the superior cervical ganglia, the nerve tissue where the virus lies dormant.
The reductions remained for at least a month after the treatment and is enough the researchers say to keep the virus from reactivating.
The team did other comparisons to fine-tune the gene editing approach:
- Gene cuts with meganucleases were more efficient that with CRISPR/Cas9.
- Refining the vector delivery mechanism, they found the adeno-associated virus (AAV) vector that was the most efficient at getting the gene edits to cells infected with the virus.
The researchers are pursuing a similar strategy for herpes simplex 2, which causes genital herpes. They expect it to take at least 3 years to move toward clinical trials.
“This is a curative approach for both oral and genital HSV infection,” Aubert said. “I see it going into clinical trials in the near future.”
Infection with herpes simplex virus (HSV) has been recognized since antiquity in humans, however, the first in vitro cultivation of HSV was assayed in 1925 . Since 1968, herpes simplex type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) have been distinguished from each other by different clinical manifestations and tropism .
HSV belongs to Herpesviridae, which is a broad family of enveloped-DNA viruses that induce numerous clinically substantial syndromes in both adults and neonates. Several factors including viral entrance, the nature of the disease, and degree of host immune competency could affect the induced syndromes [3,4].
HSV-1 is generally associated with oral or facial infection and encephalitis, while HSV-2 is accountable for genital herpes, which is an important sexually transmitted disease .
Moreover, infection with HSV-2 can cause recurrent, painful genital lesions and is often connected with negative psychosocial consequences such as shame, anxiety, and depression. Furthermore, infection with HSV-2 was observed to be a high-risk factor for potential HIV infection, as well as invasive cervical carcinoma .
Several reports have declared that HSV is involved in various ocular diseases, including stromal keratitis, endotheliitis and neurotrophic keratopathy [4–7]. The current existant treatment of HSV infection relies mainly on the use of acyclovir (ACV) and related synthetic nucleoside analogs.
Unfortunately, the rigorous utilization of these drugs has led to the establishment of undesirable effects as well as drug-resistant strains [8,9]. Although imperative efforts were taken to develop a vaccination, no vaccines have been validated or marketed for effective prevention of the infection to date.
Therefore, the development of new antiviral medications has earned much attention in recent decades [10,11]. While many anti-HSV drugs have already been developed and engaged in the treatment of HSV infections, the search for different sources of anti-HSV drugs is a great task for many researchers and healthcare providers to conquer challenges with drug resistance .
Thus, it is an important concern to open new gates to search for new therapeutic agents that perform with different mechanisms of action than nucleoside analogs. Nature is a very rich source of these molecules.
Epidemiology and Pathogenesis of HSV Infection
It’s acknowledged that HSV endures for the lifetime of the host in the form of latent infection in the peripheral neurons . After infection begins, reactivation can be systematically triggered by re-entering the lytic phase of replication to create a progeny virus for spreading .
However, during latent infection, the viral lytic genes are largely down-regulated, and their promoters are joined into repressive heterochromatin (Figure 1).
Consequently, reactivation necessitates viral lytic gene expression to be created by silenced promoters in the absence of viral proteins . During primary infection, HSV penetrates through breaks in the skin or mucosa and subsequently attaches to and accesses epithelial cells and starts replication.
It’s taken up by free sensory nerve endings placed at the dermis, and the nucleocapsid containing the viral genome is transferred by retrograde axonal flow to the nucleus in the sensory ganglion [16,17]. Skin symptoms include vesicular lesions on an erythematous base.
Lesions drive to the focal damage of the epithelial layer and a widespread infiltrate of inflammatory cells elaborates in the surrounding rim and the underlying dermal layer [15,18]. It has been estimated that 10–30% of new infections are symptomatic.
After recovering from the initial infection, HSV perseveres latently in the sensory ganglion for the life of the host. Regularly, the virus reactivates from the latent state and moves back down the sensory nerves to the skin or mucosal surface [15,19].
Viral shedding can appear either in the presence of lesions as a clinical reactivation or with very moderate or no symptoms as subclinical reactivation. Shedding from mucosal surfaces drives transmission to other sexual partners and, in some cases, infection with HSV can be transferred from mother to infant at delivery [20,21].
REFERENCE LINK : doi:10.3390/v12020154
More information: Martine Aubert et al, Gene editing and elimination of latent herpes simplex virus in vivo, Nature Communications (2020). DOI: 10.1038/s41467-020-17936-5