This article talks about how scientists are using new gene editing technology to disrupt and potentially destroy viral DNA. In this case scientists at Kyoto University used the CRISPR Cas-9 system to disrupt the DNA. The article first describes briefly what the CRISPR Cas-9 does. CRISPR stands for clustered regularly interspaced palindromic repetitions. Basically, it is a section of DNA, first discovered in bacteria, that can be utilized as a defense mechanism to protect a cell from viral infection. The CRISPR Cas-9 system is an RNA guided (or guide-RNA, aka gRNA) nuclease system. Let’s first take a look at what happens when a cell becomes infected by a virus. For example, we can look at the human immunodeficiency virus (HIV). HIV is a retrovirus meaning (among other things) it is a single-stranded RNA virus which incorporates itself into the host cells DNA through reverse transcriptase. HIV is interesting because of it’s ability to lie completely dormant for so many years. For simplicities sake lets say that the virus infects the cell and begins to attack immediately. In the large majority of these cases the host cell will die, however, if the host cell manages to survive it can do something very interesting and useful-assuming our cell has the CRISPR Cas-9 system. The CRISPR system will basically send out proteins that can read the amino acid sequence of the viral DNA. It then imbeds these copied sequences back into it’s own DNA code. Many short guide RNA strands can now be made. These strands will go off and associate with their matching sequence on the viral DNA. Lastly, an enzyme called Cas-9 will come and bind to these sites and make a double stranded cut in the viral DNA. After many of these double stranded cuts have been made in the viral DNA, the virus can no longer make many of it’s proteins and can no longer function correctly. What’s even more important is that this virus can not replicate itself so it cannot re-infect this cell, or any other cell in the organism. And, perhaps most importantly for our cell, because the viral DNA has been sequenced into this CRISPR region of it’s own DNA, all of this cells daughter cells will be immune to this virus. The CRISPR Cas-9 system then, is like a permanent vaccine that the cell gives to itself and all its descendants.
The researchers at Kyoto University attempted to edit and block the HIV virus that can lie dormant in the host cell sometimes referred to as a latent reservoir (LTR). Anti-retroviral therapy is able to keep active replication of HIV in check. The problem is that the LTR is always there and until now, has been resistant to therapy. The researchers report that when LTR-targeting CRISPR Cas-9 components were transfected into fighter T cells (the cells that HIV infects), the expression of LTR was significantly reduced. The researchers also report that the CRISPR Cas-9 may be a very useful tool in curing HIV.
Brief Introduction into CRISPR Cas-9