Scientists attempting to harvest human organs in pigs create human-pig embryo

Nicola Davis and Kevin Rawlinson, The Guardian, 6 June 2016

Scientists trying to grow human organs inside pigs in an attempt to tackle a shortage of donors have successfully created part-human, part-pig embryos, it has been reported.

Researchers at the University of California, Davis combined human stem cells and pig DNA and allowed the embryos to mature for 28 days, before terminating the experiment and analysing the tissue.

They believe the animals, which if they had been carried to term would have developed a human internal organ, but would have looked and behaved like any other pig. The goal is that in the future, similar animals could potentially act as a ready source of organs for life-saving transplants.

To create the “chimeric” embryos, the scientists used a gene-editing technique known as Crispr to knock out a section of the pig’s DNA necessary for the embryo to develop a pancreas.

Human induced pluripotent (iPS) stem cells were then injected into the pig embryo. These are cells that have the potential to develop into any tissue type in the resulting foetus. Although genetically foreign, they are not rejected by the pig embryo because its immune system has not yet developed.

Instead the human cells would be expected to follow the chemical cues from the pig embryo to develop into different tissues in the foetus. In most cases they are outcompeted by the pig embryo’s own cells but in the case of the pancreas there are no pig cells to compete with. Hence the embryo goes on to develop a pancreas derived from the injected human cells.

“You are basically creating a vacuum, a hole, so that the human cells respond to the right cues, they make a pancreas. The pig cells can’t. But what we don’t know, and this is what they need to look at, is whether the human cells can also contribute substantially to other tissues, and particularly they are worried about the brain,” said Robin Lovell-Badge, a geneticist at the Francis Crick Institute in London.

It was reported earlier this year that scientists had begun attempts to create the embryos, but there has been opposition from authorities. In September last year, the US National Institutes of Health said it would not back research into “chimeras” until it knew more about the implications.

It cited fears that the presence of human cells could affect the animal’s brain and behaviour, potentially making it more human. Prof Pablo Ross, the reproductive biologist leading the research, sought to calm those fears, saying there was a “very low potential for a human brain to grow”.

It is not the first attempt to create chimeras. Among the previous experiments, scientists using different techniques were able to produce a mouse with a rat’s pancreas, and mice with livers almost completely composed of human cells.

“The whole idea of making chimeras, mixing different animal species or human-animal, has been around for decades,” said Lovell-Badge.

But Peter Stevenson, from Compassion in World Farming, told the BBC’s Panorama programme: “I’m nervous about opening up a new source of animal suffering. Let’s first get many more people to donate organs.”