Sunday, 13 September 2015

Cutting out JC virus

Wollebo HS, Bellizzi A, Kaminski R, Hu W, White MK, Khalili K.
CRISPR/Cas9 System as an Agent for Eliminating Polyomavirus JC Infection.PLoS One. 2015 ;10(9):e0136046.

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease of the central nervous system (CNS) caused by reactivation of the human polyomavirus JCV gene expression and its replication in oligodendrocytes, the myelin producing cells in the brain. Once a rare disease seen in patients with lymphotproliferative and myeloproliferative disorders, PML has been seen more frequently in HIV-1 positive/AIDS patients as well as patients undergoing immunomodulatory therapy due for autoimmune disorders including multiple sclerosis, rheumatoid arthritis, and others. As of now there is no cure for PML and in most cases disease progression leads to death within two years. Similar to other polyomaviruses, the JCV genome is small circular double stranded DNA that includes coding sequences for the viral early protein, T-antigen, which is critical for directing viral reactivation and lytic infection. Here, we employ a newly developed gene editing strategy, CRISPR/Cas9, to introduce mutations in the viral genome and, by inactivating the gene encoding T-antigen, inhibit viral replication. We first used bioinformatics screening and identified several potential targets within the JCV T-antigen gene that can serve as sites for the creation of guide RNAs (gRNAs) for positioning the Cas9 nuclease on the designated area of the viral genome for editing. Results from a series of integrated genetic and functional studies showed that transient or conditional expression of Cas9 and gRNAs specifically targets the DNA sequences corresponding to the N-terminal region of T-antigen, and by introducing mutation, interferes with expression and function of of the viral protein, hence suppressing viral replication in permissive cells. Results from SURVEYOR assay revealed no off-target effects of the JCV-specific CRISPR/Cas9 editing apparatus. These observations provide the first evidence for the employment of a gene editing strategy as a promising tool for the elimination of the JCV genome and a potential cure for PML.

We have all heard of knockout mice where we get rid of a gene of interest. But can we get rid of genes in humans? Well bacteria do just that when they are infected with a virus. The have evolved a mechanism to cut out the virus from the bacterial genome.
We (the royal we that is) have harnessed this capacity and we have worked out how to knock out genes from the genome so we can use this system to knockout genes. This system is known as CRISPR or crisper.



CRISPRs (clustered regularly interspaced short palindromic repeats) are segments of prokaryotic (bacterial) DNA containing short repetitions of base sequences. Each repetition is followed by short segments of "spacer DNA" from previous exposures to a bacterial virus or plasmid.

The CRISPR/Cas system is a prokaryotic immune system that confer resistance to foreign genetic elements such as plasmids and phages (viruses that i nfect bacteria) and provides a form of acquired immunity. CRISPR spacers recognize and cut these exogenous genetic elements in a manner analogous to RNAi in eukaryotic organisms.CRISPRs are found in approximately 40% of sequenced bacteria genomes

The CRISPR/Cas system has been used for gene editing (adding, disrupting or changing the sequence of specific genes) and gene regulation in species throughout the tree of life.By delivering the Cas9 protein and appropriate guide RNAs into a cell, the organism's genome can be relatively cheaply cut at any desired location.

Cas9 is a nuclease, an enzyme specialized for cutting DNA. It has two active cutting sites (HNH and RuvC), one for each strand of the DNA's double helix. The team demonstrated that they could disable one or both sites while preservingCas9's ability to home in on its target DNA. Jinek combined tracrRNA and spacer RNA into a "single-guide RNA" molecule that, mixed with Cas9, could find and cut the correct DNA targets


So can you use CRISPR to remove JC virus. This is what they hope, but is not this going to be easy to do this in humans. Is this a start? 

7 comments:

  1. This reads almost as science fiction, although robust and target-specific genome editing may already be a reality

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  2. If you believe MS is caused by EBV why not cut to the chase and target EBV virus instead of JC?

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  3. "As of now there is no cure for PML and in most cases disease progression leads to death within two years."

    Why is it that neuros tell MS patients that PML is survivable when all other immunologists admit a PML diagnosis is grim? So many Tysabri patients seem misinformed about the real long term consequences of PML, which is far more crippling and fatal when you extend out to 24 months.

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  4. Could be a solution for those who are JC positive and more aggressive use DMT as natalizumab in peace ... I read a while ago one JC virus theory as an external causative agent of MS, I'm just not able to locate here where I read this . I would bedding such "approach"?

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  5. You'd think Biogen would be all over this, since it addresses the concerns with Tysabri, Tecfidera, etc.

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  6. if Crispr can edit out JC virus, why not just edit out the MS gene?

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    Replies
    1. There is not such a thing as an MS gene...youu have maybe 400-500 gene variants that can contribute to your susceptibility, get rid of the most important MS gene and you will probably die from infection as you won't be able to recognise them

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