CRISPR/Cas9 against herpesviruses
Biologists have learned how to purify the genome from herpesviruses
The CRISPR/Cas9 genetic modification system helped to clear infected cells of herpesviruses. The report on the work is published by the journal PLoS Pathogen (van Diemen et al., CRISPR/Cas9-Mediated Genome Editing of Herpesviruses Limits Productive and Latent Infections).
An extensive group of herpesviruses includes not only HSV-1 and HSV-2 causing oral and genital herpes, but also pathogens of many other diseases: chickenpox viruses, Epstein–Barr and others. They are distinguished by their ability to long latent, latent preservation in the host genome, with individual outbreaks of the "acute" phase, during which the virus multiplies and spreads to new cells. This strategy has provided herpesviruses with an extraordinary spread – it is believed that almost the entire population of the Earth is their carriers.
There are quite effective means that stop the vital activity of herpesviruses in the acute phase of reproduction. But there are no targeted drugs that can "expel" the virus hidden in the body: this requires removing its DNA hidden among the host's own genes. This possibility is provided by new technologies of genetic modification based on the bacterial CRISPR/Cas9 system. For the first time, the staff of Robert Jan Lebbink from the University Medical Center in Utrecht managed to test this method on herpesviruses.
The authors selected herpesviruses of type 1 (herpes simplex virus, HSV-1), type 4 (Epstein–Barr virus, EBV) and type 5 (human cytomegalovirus, HCMV) as targets. For certain parts of their DNA, guiding RNA molecules were created, thanks to which Cas9 nucleases are able to recognize them in the host genome and cut them.
Experiments conducted on cultures of human Vero cells, as well as on animals, have shown that even an incision in one section of viral DNA reduces the number of infected cells by about half, and two incisions lead to almost complete removal of viruses. So, for EBV, this decrease was 40-60 percent and 95 percent, respectively. The HCMV virus was successfully inactivated already with one "incision", but HSV-1 turned out to be more resistant and required an attack using two guide RNAs.
The authors tested various variants of guide RNAs, showing that molecules that bind to different genes or simply to different parts of the same gene may have different effectiveness. In particular, in experiments on HCMV, it was shown that an attack on genes that are extremely important for the reproduction of the virus creates a powerful selection pressure and leads to the appearance of mutant forms with an altered DNA sequence at the binding site of the guide RNA. Therefore, the use of such an editing procedure will require special measures and techniques, as when prescribing antibiotics.
"Our work shows that using the CRISPR/Cas9 system, it is possible to effectively influence the genomes of herpesviruses in terms of prevention and treatment, to suppress virus replication and remove latent infection," the authors conclude (in a press release Towards a cure for herpesviruses: Targeting infection with CRISPR/Cas9 – VM).
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01.07.2016