Almost all of us carry one form or another of herpes virus, and the consequences can be far worse than the occasional cold sore. Herpes viruses also cause shingles and can be implicated in blindness, birth defects and even cancer – and as yet, we can’t rid ourselves of them.
One of our best ways to combat herpes viruses is by blocking the enzyme they need to copy their DNA so that they can replicate. But although this can keep the level of virus in your body down, it cannot wipe out the infection. Worse, it doesn’t work on dormant herpes viruses that are waiting inside our cells for the right time to flare up again.
But gene editing may allow us to destroy these latent viruses. Robert Jan Lebbink at the University Medical Center Utrecht, the Netherlands, and his colleagues are developing a therapy that might safely clear certain herpes viruses from the body by messing with their DNA.
Lebbink’s team have been experimenting with CRISPR, the gene-editing technique that can be used to cut DNA at precise points in a sequence. When carried out on DNA inside an organism or virus, the DNA snip is usually repaired, but this process often introduces mutations or errors at this cut site.
This means gene editing can help destroy dormant viruses. When CRISPR is used to cut viral DNA in two or more important places, there is a good chance that the DNA will not be repaired properly, leaving the virus unable to function.
When they tried this technique on monkey or human cells infected with Epstein-Barr virus (EBV, pictured above) – a herpes virus that causes glandular fever and is associated with a range of cancers – they found that cutting the DNA in one spot reduced viral activity by about 50 per cent, while cutting it in two places led to 95 per cent of dormant viruses being lost from the cells.
Viruses that can establish a latent relationship with the host are capable of causing disease. Examples of viruses include the Herpes Simplex Virus 1 (also dubbed HSV 1) and retroviruses . The latter group of viruses includes the Human Immunodeficiency Viruses (HIVs ) that are the most likely cause of acquired immunodeficiency syndrome (AIDS ).
Herpesviruses infect the majority of the human population and can cause significant morbidity and mortality. Herpes simplex virus (HSV) type 1 causes cold sores and herpes simplex keratitis, whereas HSV-2 is responsible for genital herpes. Human cytomegalovirus (HCMV) is the most common viral cause of congenital defects and is responsible for serious disease in immuno-compromised individuals. Epstein-Barr virus (EBV) is associated with infectious mononucleosis and a broad range of malignancies, including Burkitt’s lymphoma, nasopharyngeal carcinoma, Hodgkin’s disease, and post-transplant lymphomas. Herpesviruses persist in their host for life by establishing a latent infection that is interrupted by periodic reactivation events during which replication occurs. Current antiviral drug treatments target the clinical manifestations of this productive stage, but they are ineffective at eliminating these viruses from the infected host. Here, we set out to combat both productive and latent herpesvirus infections by exploiting the CRISPR/Cas9 system to target viral genetic elements important for virus fitness. We show effective abrogation of HCMV and HSV-1 replication by targeting gRNAs to essential viral genes. Simultaneous targeting of HSV-1 with multiple gRNAs completely abolished the production of infectious particles from human cells. Using the same approach, EBV can be almost completely cleared from latently infected EBV-transformed human tumor cells. Our studies indicate that the CRISPR/Cas9 system can be effectively targeted to herpesvirus genomes as a potent prophylactic and therapeutic anti-viral strategy that may be used to impair viral replication and clear latent virus infection.
Herpesviruses are large DNA viruses that are carried by almost 100% of the adult human population. Herpesviruses include several important human pathogens, such as herpes simplex viruses (HSV) type 1 and 2 (causing cold sores and genital herpes, respectively), human cytomegalovirus (HCMV; the most common viral cause of congenital defects, and responsible for serious disease in immuno-compromised individuals), and Epstein-Barr virus (EBV; associated with infectious mononucleosis and a wide range of malignancies). Current antiviral drug treatments are not effective in clearing herpesviruses from infected individuals. Therefore, there is a need for alternative strategies to combat these pathogenic viruses and prevent or cure herpesvirus-associated diseases. Here, we have assessed whether a direct attack of herpesvirus genomes within virus-infected cells can inactivate these viruses. For this, we have made use of the recently developed CRISPR/Cas9 genome-engineering system to target and alter specific regions within the genome of these viruses. 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.
SOURCES- New Scientist, PLOS