The removal of HIV DNA from the genomes of live animals has been reported in the journal Gene Therapy. Mice and rats were engineered to have HIV DNA incorporated into the genome of every cell and were treated with a CRISPR-Cas9 system designed to target a segment of the virus. After two weeks, viral DNA had been successfully targeted in all of the mouse tissue types. The researchers say that in principle their technique could be developed towards use in humans, but that more more animal work is needed.
Dr. Keith R. Jerome, Member, Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, and Professor and Head, Virology Division, Department of Laboratory Medicine, University of Washington:
Expertise: gene therapy for latent HIV infection, pathogen-host interactions during chronic viral infections
“This is an important study that marks the next step toward using HIV DNA excision from the host genome as part of a curative strategy.
“While this is an important and elegant advance, it’s important to remember that these were transgenic animals in which the HIV sequence was artificially introduced into every cell in the body. The next step may be more difficult – showing that this approach can work against an actual infection with HIV. It will be difficult because we know HIV is expert at finding hiding places within the body.
The real issue going forward is delivery – this paper is yet another demonstration of the tremendous promise of CRISPR-Cas9, but can the AAV (Adeno Associated Virus) used in this study or other delivery methods get it to the memory T cells where latent HIV hides? And if so, can Cas9 be delivered to almost every latently infected T cell, which will be required if we are to achieve a cure?”
Dr. Warner C. Greene, Director, Gladstone Institute of Virology and Immunology, Nick and Sue Hellmann Distinguished Professor of Translational Medicine, University of California, San Francisco.
Expertise: HIV pathogenesis, molecular mechanisms of HIV latency
“This is an interesting paper that provides data on the utility of CRISPR-Cas9 system delivered by adeno-associated virus (AAV) to cleave HIV DNA in an HIV-1 transgenic mouse (in this animal, the HIV transgene is present in every cell). They see evidence of cleavage of HIV DNA in vitro and more importantly in vivo. Perhaps not surprisingly, the effect is only partial.
A concern that surrounds this approach is whether there will be any off-target effects of CRISPR-Cas9 payload; obviously deletion of an important cellular gene could be devastating. They suggest that off target effects have not been observed thus far, but this issue of safety plagues all of these types of approaches.
“Evidence of in vivo cleavage is encouraging but the real issue is whether this approach can be used to eliminate the one infectious latent provirus that is present at a frequency of 1 cell in a 1 million in infected individuals. Presumably, without being able to selectively target the latently infected cell, the AAV-CRISPR-Cas9 will infect all of the cells. We can only hope it will only act in the cell containing its target, which is a big if.
“While interesting, this is the first baby step on a long journey to the clinic. There is considerable interest in gene editing for a number of clinical applications with CRISPR-Cas9 the current darling of the field. That said, HIV latency is a tough target for the gene editing approach because we have no current method to target the therapeutic to the latently infected cell. In the final analysis, a truly effective anti-latency treatment must be safe, simple, effective, and scalable to the developing world where HIV is hitting the hardest.”
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http://geneticexperts.org
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