Pig-human chimeras point way to growing human transplant organs

Scientists have found a possible way to grow human organs and tissues using the embryo of a pig to transplant into people. They used gene-editing technology to alter mouse embryos – deleting some genes that are critical for the development of a particular organ, such as the heart, pancreas or eyes.

Dr Jun Wu, from the Salk Institute in the United States and the lead author of the research, said it was the first time they had successfully generated a human-pig chimeric embryo. “This is long enough for us to try to understand how the human and pig cells mix without raising ethical concerns about mature chimeric animals”, said co-author Professor Juan Carlos Izpisua Belmonte from Salk Institute.

The cells made up just a tiny part of each embryo, and producing any organs this way is far in the future. To that end, a study published today in the journal Cell accomplished an important first step-growing pig embryos that contain human cells.

Embryos that are less than 0.001% human – and the rest pig – have been made and analysed by scientists.

The first step was to see whether human cells could even grow in another species.

For one, aspects of the technology make some people uneasy, said Jason Robert, a bioethicist at Arizona State University. It’s an important question in the field of organ transplantation, since a worldwide shortage of most organs-including hearts, lungs, livers and kidneys-means many people who desperately need them won’t receive them and will face nearly certain death.

Animal-human hybrids can be used as sources for organs to transplant, for blood and for immune system products.

A four-week-old human-pig embryo. The idea has been around since the 70s, and folks have long voiced concerns about humans contracting animal diseases, and animal rights. Such combinations had been successfully created earlier with mice and rats, but larger animals like pigs would be needed to make human-sized organs.

In the second part of the study, the scientists moved on to introduce humans’ cells into pig embryos.

Other uses include insights into early human development and disease onset, and providing a realistic drug-testing platform. But he said the bigger point – that human stem cells are powerful, and research needs to proceed cautiously – is well taken.

“What they have created is the ability to place “ticking time-bombs” inside cells that contribute to specific organs in a rat, mouse or pig body”.

“If we saw contributions, we’d need to inactivate the human cells from going there”, Wu said. Aside from the symbolic and philosophical questions that come from mixing human and animal genetics, there is a fear that stem cells could one day be used to create an animal with a human brain.

“I think the paper is well done”. The scientific trick appears to be the use of intermediate-stage stem cells – but this still remains inefficient at various levels.

Only one human cell existed for every 100,000 pig cells, an incredibly small ratio, but the success will open doors for further research and development. “You can imagine if you’re driving your auto and enter into a highway [that] is filled with pig embryonic cells, which are going three times faster than you. you have to adjust your speed and timing perfectly so you don’t cause any accidents”.