What's next after CRISPR clears hurdle in quest to transplant pig organs into humans?

Transplanting animal organs into humans is an attractive approach, but the risk of immune rejection or catching a virus from the organ has been a significant roadblock. eGenesis used CRISPR to address the latter concern.

CRISPR splashed into headlines this week, but not for its potential to treat genetic disease. Scientists at Cambridge, Massachusetts-based eGenesis have used the gene-editing technology to inactivate a family of viruses in pigs, which could pave the way for transplanting animal organs into humans.

There is a significant shortage of human organs and tissues for transplant—more than 116,000 people are waiting for a lifesaving organ transplant, according to the Department of Health and Human Services. Xenotransplantation, using animal organs for human transplant, could go a long way towards solving this problem.

Xenotransplantation is not a new idea, but it comes with significant obstacles to scientists working on it, including the risk of cross-species virus transmission. Porcine Endogenous Retrovirus (PERV), found in the pig genome, can infect human cells, for example. Once infected, these cells can pass the virus onto other cells.

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To combat this, the researchers at eGenesis used CRISPR to cut the retrovirus out of the genome in primary cells taken from pigs. They then cloned the cells, creating retrovirus-free pig embryos that were implanted into surrogate sows. The piglets were the first to be born without active PERVs, and the team will monitor them for any long-term side effects. The findings are published in the journal Science.

Several other research groups are investigating different ways to overcome challenges in xenotransplantation. One idea involves growing human organs in animals, rather than transplanting animal organs into humans. Researchers from Stanford University and the University of Tokyo reversed diabetes in mice by transplanting mouse pancreatic cells they had grown in rats. This method might allow for the creation of custom organs that are a genetic match to the recipient, eliminating the need for lifelong immunosuppression.

In a different tack, Salk Institute scientists developed embryos containing cells from both humans and pigs. While these human-pig chimeras were not allowed to fully develop, they could be useful for drug development and regenerative medicine. The Salk team will try to use CRISPR to create pigs that lack certain organs and use human cells to fill in the gaps.

Back in March, eGenesis raised $38 million to back its mission to make xenotransplantation “a routine and lifesaving medical procedure,” it said at the time. The biotech landed on pigs as the best animal to use because of how similar they are to humans in size and physiology.

Eliminating PERV from pig embryos is just one piece of the puzzle. Next, eGenesis plans to use gene editing to tackle immune rejection of transplanted organs.