Gene editing may make pig-to-human organ transplants a reality

James Marshall
August 11, 2017

Remnants of ancient viral infections, genes from porcine endogenous retroviruses-known by their unfortunate acronym-are scattered throughout the pig genome, and could infect a person who one day receives a pig's heart, lung, or kidney as a replacement or temporary organ. Major religious groups have concluded that pig organs are OK for live-saving transplants, although some Jewish and Muslim leaders believe dialysis is sufficient for patients with renal failure. "This is a great step forward for xenotransplantation", says Joachim Denner of the Robert Koch Institute in Germany.

The team plans to make pigs that are altered to a greater extent, to make them more immunologically similar to people. And even with PERVs off the table, pigs will require other modifications so that their organs won't be rejected by the human immune system or cause other harms. "If you need to knock [these viruses] out, this is the way to do it, no question", he says.

Every day, about 22 people die because they don't get the replacement organs they desperately need. Pig organs, meanwhile, can grow to a conveniently human size.

PERVs have been shown to infect human cells and previous research has shown the horizontal transfer of PERVs among human cells. But those are small numbers of cells within a protective capsule, Denner notes. The retroviruses don't harm pigs, but would make xenotransplants, cross-species transplants, impossible.

Gene editing has been generating plenty of buzz recently.

Then CRISPR came along. In 2015, they co-founded the company eGenesis to focus on engineering transplantable organs, and Yang became the company's chief scientific officer. "The real breakthrough will be when people are moving around for years with pig organs, only then will we really know that it's safe and effective". Another team has previously altered pigs so their cells lack a certain sugar molecule on their surface that provokes immune rejection.

Piglets cloned from the genetically modified cells were found to be free from all Pervs. In a lab dish the pig viruses infected human cells, and those infected cells were able to infect other human cells that had not been directly exposed to pig cells.

Egenesis, a startup that raised $US38 million in March, just successfully used the gene-editing tool CRISPR to knock out a key virus in piglets. They inserted the edited genetic material into pig eggs to create embryos, which were implanted in sows and developed into piglets, reports New Scientist.

Numerous porcine embryos and fetuses cloned in the CRISPR experiments died before birth or shortly after, but scientists ended up with 15 living female piglets, the oldest now 4 months old.

Other reports by Click Lancashire

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