All the cool techniques people are developing with CRISPR-Cas9 are great and all, but sometimes a repurposed natural genetic system just has to go back to its roots. If CRISPR was originally a virus defense system in bacteria, why not forget about all this genome engineering whatnot for a minute and just use it to fight deadly viruses in humans?
That’s the reasoning behind a new article from a group at the Salk Institute, who pitted CRISPR against HIV. HIV is particularly hard to fight because it integrates into target cell genomes, where it can lie in wait, safe from standard drugs. What we really need to get rid of HIV is some way to specifically target its DNA sequence inside cells… oh wait, CRISPR!
CRISPR v HIV: Battle of the Acronyms
Other groups have used CRISPR against hepatitis and HIV, but the new paper is the most thorough report so far of CRISPR’s efficacy against full-length HIV. Hsin-Kai Liao and others from the Belmonte lab first targeted Cas9 against an integrating, GFP reporter virus. Cas9 was expressed in human HEK293 cells, which were then infected with the virus. Cas9 reduced the number of GFP-positive cells by up to 72%, indicating they were protected from infection, and the protection worked whether or not the virus had integrated.
Ferreting out Latent HIV
The real challenge in HIV, though, is getting rid of viruses already integrated and hiding inside cells. The team tested Cas9 against these particularly dastardly proviruses by using cells with pre-integrated reporter viruses. Fourteen day after transient Cas9 transfection, about half the cells were GFP-free, and a second round of Cas9 expression cured about half of the remainder. This could be good for potential therapies, since multiple low-dose treatments may have fewer side effects for the patient.
To make Cas9 an even more efficient HIV fighter, the group screened different target sites in the HIV genome and targeted two sites at once. With these improved versions, they not only cut the number of cells expressing viral GFP by 90%, they also saw about 4 times more cells surviving and thriving, suggesting the cells really had kicked the virus.
HIV-immune Hematopoietic Stem Cells
To test the system in even more relevant situations, the group stably integrated Cas9 into a human T-cell line and bathed them in HIV. Again, Cas9 protected the cells, even though most control cells were GFP-positive and/or dead within 14 days. Finally, they stably integrated Cas9 into human stem cells, differentiated them into white blood cells, and showed 90% immunity to HIV. These results suggest that where our own immune system fails, at least against HIV, maybe we can help it with one stolen from bacteria.
Read more about how we’ve hijacked CRISPR to fight HIV in Nature Communications, March 2015
Do some more HIV fighting with Hu et al. in PNAS, August 2014