Scientists grow Human-pig hybrid embryo in US

Scientists have grown a hybrid species which has human and pig DNA by injecting human stem cells into the embryo of a pig.

The so-called chimera embryo has been hailed as a breakthrough that could overcome the problem of organ shortages.

But some experts say the development raises huge ethical issues, especially if any of the cells produced were from the brain or reproductive organs.

An American team started by trying to forge an embryo that combined rats and mice to see if stem cells could be turned into replacement organs.

They went on to make a human-cow embryo but decided to use pigs in follow-up procedures as they were easier and cheaper to use, according to The Scientist website.

The team implanted the resulting embryos back into pigs and found some had grown and now had human cells.

Many of them, however, ended up underdeveloped.

According to the team from the Salk Institute of Biological Studies, the success was limited because humans and pigs are not closely related and have widely differing gestation periods.

Jun Wu, a staff scientist at the Salk Institute, told The Scientist: “One of the reasons might be the timing.

“You can imagine if you’re driving your car and enter into a highway 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.”

Despite the failures, some of the human stem cells turned into muscle cells and the beginnings of some organs including the pancreas and liver.

The team intend to continue finessing their technique and were buoyed by the success of another study, in Japan, this week which successfully implanted a mouse pancreas, generated in a rat, back into a mouse.

That organ, Nature reported, remained healthy for more than a year and helped treat a mouse with diabetes.

Juan Carlos Izpisua Belmonte, the leader of the Salk study, said the risk that chimera brain cells or reproductive organ cells would be created would be minimal as they have ways to prevent it happening in the laboratory.