The researchers used a gene editing technique called CRISPR–Cas9 (more commonly referred to as CRISPR). CRISPR uses the natural defense mechanisms of bacteria to target specific pieces of DNA in a genome, allowing scientists to essentially crop out — and potentially replace — individual sequences. The possibilities with CRISPR are basically endless, but the technique is still in its infancy. When scientists recently tried to use the method to edit the genomes of human embryos, for example, they had a very low success rate in deleting the genes they wanted to delete, and had a whole mess of erroneously deleted genes to boot.
In the new study, a team led by Harvard University's George Church — one of the pioneers of the CRISPR technique — used gene editing to remove all the copies of porcine endogenous retroviruses (or PERVs) from their pig cells' DNA. These PERVs could potentially infect a human who received a pig organ transplant, so getting rid of them is essential, but they can't be bred out of a pig's genome using more traditional tactics. That's why doctors have some success transplanting pieces of pig organs — like skin and heart valves — into humans, but have yet to attempt entire organs.
According to the researchers, the 62 cuts they made (which is by far the greatest number ever made on one genome using CRISPR) didn't seem to inadvertently scramble anything else up. They haven't been tested in a human transplant yet, but in a petri dish, human cells showed a 1000-fold reduction in PERV transmission with the edited pig cells.
Since the group has apparently edited ten times more genes than have ever successfully been edited on a single genome with CRISPR, other scientists will no doubt be eager to study their techniques.
The next step for pig transplants is to create actual embryos with the edited genomes. Nature reports that Church has co-founded a biotech company called eGenesis to perfect the process, and that their edited embryos are almost ready to be implanted and brought to term.