Herpesviruses are responsible for an array of infections and diseases, including cold sores, shingles, genital herpes, and even some forms of cancer. Now, new research reveals how a revolutionary genome-editing technique called CRISPR/Cas9 could eliminate these viruses once and for all.
Researchers say the CRISPR/Cas9 gene-editing tool shows promise for the elimination of herpesviruses.
Study co-author Ferdy R. van Diemen, of the University Medical Center Utrecht, the Netherlands, and colleagues recently published their findings in the journal PLOS Pathogens.
CRISPR/Cas9 is a novel system that enables researchers to target and alter the genome of an organism, either by cutting out, adding, or replacing parts of DNA strands.
This gene-editing tool has caused much excitement in the medical world, with researchers claiming the technology could help treat a variety of diseases.
Earlier this year, for example, a study published in the journal Science revealed how CRISPR/Cas9restored muscle function in mouse models of Duchenne muscular dystrophy.
For this latest study, van Diemen and colleagues set out to investigate whether CRISPR/Cas9 could be an effective tool to eradicate herpesviruses from human cells.
There are a total of eight herpesviruses that are known to infect humans. Once a person is infected with one or more of these viruses, they lay dormant in the host cells for life; the viruses can reactivate at any point and cause symptoms.
The researchers focused on three herpes viruses: herpes simplex virus type 1 (HSV-1), human cytomegalovirus (HCMV), and Epstein-Barr virus (EBV).
HSV-1 is a cause of cold sores and HSV keratitis – an infection of the eye’s cornea. HCMV can cause birth defects, and EBV can cause mononucleosis and some cancers – such as Burkitt’s lymphoma.
Firstly, the researchers adapted the CRISPR/Cas9 technology to include guide RNAs (gRNAs), which are molecule sequences that help target important parts of the viral genome.
On applying the technology to lymphoma cells infected with EBV, the researchers found that the gRNAs were able to target certain EBV DNA sequences in the latent phase, and this triggered the development of mutations at these regions.
These mutations cause loss of EBV function and lead to instability of viral DNA molecules, the team explains.
By using two specific gRNAs to target a gene crucial to EBV function, the researchers found they were able to eliminate around 95 percent of latent EBV from the lymphoma cells.
The researchers then applied the modified CRISPR/Cas9 tool to lymphoma cells infected with HCMV, and they found that certain gRNAs impaired HCMV replication in cells during the active phase.
However, they also identified HCMV variants that managed to escape the gene-editing technique, meaning that CRISPR/Cas9 would need to be applied to multiple HCMV sites at the same time to prevent resistant HCMV genomes from arising.
Findings ‘open new avenues for treatment of herpesviruses’
Finally, they tested the adapted CRISPR/Cas9 tool on lymphoma cells infected with HSV-1. Despite the rapid replication of this virus – relative to HCMV – the team found that certain gRNAs reduced HSV-1 replication in the active phase.
On combining two rGNAs that were able to target two HSV-1-related genes, the team was able to halt HSV-1 replication completely.
However, during the latent phase, the researchers found they were unable to use the CRISPR/Cas9 system to edit the HSV-1 genome.
Still, van Diemen and colleagues believe their findings indicate that CRISPR/Cas9 shows promise as an effective tool for the eradication of herpesviruses:
“By targeting sites in the genomes of three different herpesviruses (HSV-1, HCMV, and EBV), we show complete inhibition of viral replication and in some cases even eradication of the viral genomes from infected cells.
The findings presented in this study open new avenues for the development of therapeutic strategies to combat pathogenic human herpesviruses using novel genome-engineering technologies.”