For the first time mouse pancreases have developed in rats, with islet cells used to cure mouse diabetes. This raises hopes we could grow human organs in pigs

Organs made to order? Manfred Weis/Getty

TRANSPLANT waiting lists could become a thing of the past if we could find a way to grow human organs inside other animals. Now mouse pancreases have been grown inside rats – a first step towards a ready supply of organs for transplant.

When small parts of these organs were transplanted into mice with diabetes, it reversed their disease. This finding raises the prospect that someone needing a new liver, for instance, could have what is essentially their own organ grown to order inside a specially conceived piglet, within a year of providing a small skin sample. Pigs or sheep make the best candidates, because their organs are a similar size to ours.

Donor organs are in short supply. Only around 3 in 1000 people die in a way that makes them suitable as organ donors. In the UK, nearly a third of people who need an organ wait more than two years in poor health, and one in 10 die while on the waiting list.


The shortage has prompted research into creating organs in the lab. Many of these methods involve stem cells, which can be encouraged to form most types of tissue using different mixtures of chemical cues and signalling molecules. However, growing large organs with complex three-dimensional structures and their own blood supply has proved far from easy.

Instead, Hiromitsu Nakauchi at the University of Tokyo, Japan, and his team used rat embryos as living incubators. They began by genetically modifying parent rats so their offspring would be unable to make their own pancreas. A few days after conception, they injected mouse stem cells into the tiny rat embryos, which developed as normal, except their pancreases mostly comprised mouse cells.

Once the rats reached adulthood, the team removed the pancreases and implanted clusters of these pancreatic cells into mice with diabetes. These clusters, or islets, restored the blood glucose levels of the mice to normal for over a year (Nature, DOI: 10.1038/nature21070).

This is the first time this kind of inter-species organ generation has successfully treated a medical condition. “It proved those pancreatic islets must be very functional,” says Nakauchi.

“This is the first time this kind of inter-species organ generation has treated a medical condition”

That doesn’t mean doing the same with whole organs in pigs and people is imminent, though. The team used clusters of cells, instead of transplanting whole pancreases, partly because the procedure is relatively easy.

As humans and pigs are less genetically similar than rats and mice, the growing organ might be attacked by the piglet’s immune system. The team found that the islet clusters contained some rat cells from other tissues, but that the mouse immune system seemed to kill these without harming the pancreas cells. However, this may be more dangerous if a whole, large organ is transplanted.

While the approach was used to cure mice with diabetes, people can already be treated with insulin. So the technique may prove more important for treating other diseases. New organs are more urgently needed for people with failing hearts, livers, lungs and kidneys, says Nakauchi.

So far, his team has managed to modify rats so they don’t grow a liver, so it should be possible to grow mouse liver cells for transplant in a similar way to the islet cells. But getting rid of the heart is likely to be more difficult, he says.

There are also ethical issues. Because the technique would involve inserting human cells into pig embryos, the adult animals could have some human brain cells. Does that mean we should give those pigs greater moral consideration? Ethicists will need to tackle such issues as research into such human-pig chimeras continues, says Bernhard Hering at the University of Minnesota. “We are crossing a crucial line here. But exciting papers always come with new questions.”

Researchers may be able to avoid creating pig-human brains by using human stem cells that have been genetically altered so they are incapable of forming brain tissue.

This article appeared in print under the headline “Can pigs grow human organs?”