Combat HIV via the CRISPR system

With permission from NPG

It look like a real "cure" is underway for AIDS, a disease used to be one of the most fearsome one of the modern era. Just recently, Sangamo Biosciences received FDA approval to carry out clinical trials with zinc-finger nucleases to knock out the virus receptor on normal human hemopoietic stem cells. Now, it seems that the bacterial defense system, the CRISPR, could also be utilized to combat viral infection in human cells. In a recent paper, a group from La Jolla, CA developed a CRISPR strategy to attack invading HIV, making the antiviral tool expressing cells resistant to infection.

The authors first transduced 293T cells with replication incompetent lentiviruses carrying a GFP as a target for CRISPR. Not surprisingly disruption of GFP was readily detectable in Cas9/gRNA expressing cells. Novelty here is that it seems Cas9 can target the pre-integration viral genome, i.e. the human chromosomal environment is not required for action (as assayed by non-integrating lentiviruses). This is quite plausible, since the original bacterial CRISPR system indeed inactivates viral and plasmid DNA sequences, which have not been integrated into the host. Interestingly, CRISPR was able to be active in a high copy number system, projecting its usefulness in transgene animal models, where multiple copies of the transgene is present.

Also not surprisingly CRISPR was able to target HIV viral sequences in 293T.CD4.CCR5 cells, latently infected human T cell lines and differentiated human pluripotent stem cells. However, primary human T-cells were conferred only partially resistant to HIV infection.

This study is in correlation with other studies demonstrating antiviral effect of CRISPR against hepatitis B virus, papillomavirus, herpes simplex virus. I'm not sure how these findings are translatable to human clinical trials.

Full text of the paper here: Liao HK, Gu Y, Diaz A, Marlett J, Takahashi Y, Li M, Suzuki K, Xu R, Hishida T, Chang CJ, Esteban CR, Young J, Izpisua Belmonte JC. Use of the CRISPR/Cas9
system as an intracellular defense against HIV-1 infection in human cells. Nat Commun. 2015 Mar 10;6:6413. doi: 10.1038/ncomms7413.

Rare hemoglobin disorders remain major target diseases to be corrected with genome editing systems

Recently, Sangamo Biosciences received green light from FDA to start clinical trials on beta-thalassemia. In their approach, finc-finger nucleases shall disrupt transcriptional regulators to switch the production from mutated adult hemoglobin back to normal fetal hemoglobin. Now, another company, Editas Medicine reported successful in vivo gene repair for sickle cell anemia at the Keystone Symposium for Genomic Instability and DNA Repair in Whistler, British Columbia, Canada. This hereditary hemoglobinopathy is characterized by a mutation in the hemoglobin beta (HBB) gene leading to abnormal red blood cell morphology under certain circumstances. The presented mechanism for gene repair is thought to be gene conversion, i.e. self-repair of the CRISPR targeted allele utilizing a different, but closely related gene as a repair template. The efficiency and precise mechanism remains a question. “These data suggest gene conversion as a possible new approach to genomic repair for certain kinds of genetic mutations,” said Katrine Bosley, chief executive officer, Editas Medicine. “While the results are early and further work is needed to see if this approach could be used therapeutically, the data exemplify Editas’ commitment to explore and develop the full potential of genome editing to treat a broad range of genetically driven diseases.”
Source: http://www.editasmedicine.com/documents/Editas%20Keystone%20Data%20PR%20030115%20FINAL%20.pdf