For the first time, researchers have been able to produce a sheep embryo that has a small amount of human genetic code. The scientific breakthrough was announced at the American Association for the Advancement of Science meeting in Texas this week. This could be very important for future medical technologies as researchers hope one day to grow human body parts for organ donation from genetically engineered animals.

“Even today the best-matched organs, except if they come from identical twins, don’t last very long because with time the immune system continuously is attacking them,” said Dr Pablo Ross from the University of California, Davis, who is part of the team working towards growing human organs in other species, in a media briefing reported by the Guardian.

To be exceedingly clear, the embryos weren’t half human/half sheep, they were not created on a whim and without regulation, and were all actually destroyed within four weeks of their creation.

The team inserted adult human stem cells inside an early-stage sheep embryo, and they followed its development over 28 days. “About one in 10,000 cells in these sheep embryos are human,” explained Ross.

While this ratio is a tiny 0.01 percent, it is much higher than scientists have previously been able to achieve for pig-human chimeras. That was closer to one human cell in every 100,000 pig cells. Sheep and pigs are used because their organs are roughly the right size to be transplanted into humans. But to actually develop an organ, the embryos would need to have about 1 percent of human cells, so we're still a while off.

There have been ethical concerns about this threshold. Some people worry that by humanizing the cellular composition of animals it could be possible to create a human-faced pig or a sheep with a human mind. The team has shown that they are capable of focusing the human cells to be able to construct specific organs.

“We have published several papers showing we can target the region, so we can avoid human cells differentiating into the human brain or human gonads,” Dr Hiro Nakauchi of Stanford University, who is also part of the team.

The road to having animals as potential organ donors is still extremely long and the challenges are not easy to overcome. For research alone, the team is planning on requesting permission to keep the embryos for longer than the current threshold of 28 days, but that’s not in any way a certainty that their approach could actually lead to a viable transplant solution.

That said, it’s important to keep working at it. In the United States alone, 117,000 people are currently on an organ donor waiting list and 22 people die each day waiting for a transplant.

[H/T: Guardian]