Ancient Retroviruses can be Excised from Pig DNA

I used to work in a lab that had the very ambitious goal of engineering animals to grow human organs and serve as the ultimate workhorse of organ transplantation. This required the manipulation of embryos isolated from various animals and some nuanced and drawn out genetic manipulations that I never fully grasped. However, implicit to this method of generating organs was the production of human organs in animals rather than using animal organs to transplant into humans. Using pig organs, or even tissues, to make heart valves or even serve as a human heart presents some problems. Host-graft rejection and immune response to even parts of pig organs are the defensive responses that make such a transplant challenging, but another adverse viral consideration lies in PERVs, porcine endogenous retroviruses. These sequences have been though to contribute to tissue rejection because the viruses are expressed when put in humans. The article uses CRISPR-Cas 9 to excise these sequences and has been shown to be effective because the regions that need to be treated are localized. I thought that this could be used to excise the proviruses of chronic viruses affecting humans, like herpesviruses or HIV. However, this method works only when the genetics in need of alteration aren't everywhere, like in grafts, rather than every single T cells and dendritic cell. Still, this article exemplifies the way in which CRISPR can change how we combat viruses.

-Andrew

Source: http://www.sciencemag.org/news/2017/08/crispr-slices-virus-genes-out-pigs-will-it-make-organ-transplants-humans-safer