Human-pig hybrid created in lab to help grow donor organs

The embryo was terminated before the potential chimerical animal could be born

The animal was much more like a pig than a human

Scientists have created a hybrid of a human and a pig in a lab.

The embryo was terminated before the potential “chimera” animal could be born. But it is a pioneering development all the same, suggesting that it might be possible to create such embryos and leave them until they are born.

The scientists hope that they can ultimately grow functional organs and tissues that can then be used for transplants. Such chimeras might also be used for things like drug-testing, since they would react in the same way humans do.

The scientists report in the paper published in the scientific journal Cell that the efforts to grow embryos containing pig and human DNA had proved harder than they anticipated. Even after decades of attempts, scientists are struggling to make stem cells in petri dishes become fully functional adult cells, let alone three-dimensional tissues and organs of the kind that might be needed.

“It’s like when you try to duplicate a key. The duplicate looks almost identical, but when you get home, it doesn’t open the door. There is something we are not doing right,” said Professor Izpisua Belmonte. “We thought growing human cells in an animal would be much more fruitful. We still have many things to learn about the early development of cells.”

But the researchers still want to do more work to improve the efficiency of the combined embryos.

“At this point, we wanted to know whether human cells can contribute at all to address the ‘yes or no’ question,” said Juan Carlos Izpisua Belmonte, the study’s lead investigator. “Now that we know the answer is yes, our next challenge is to improve efficiency and guide the human cells into forming a particular organ in pigs.”

This photograph shows injection of human iPS cells into a pig blastocyst (Juan Carlos Izpisua Belmonte)

The researchers started by creating a rat and mouse chimera by introducing rat cells into mouse embryos and letting them grow. Such research has been successful, and led in 2010 to a mouse that had pancreatic tissue formed out of rat cells.

Such work uses gene editing tools to delete specific genes that are important for the creation of organs, while the egg grows. As it does so, rat cells are injected and the embryos then use them to fill the gap.

“The rat cells have a functional copy of the missing mouse gene, so they can out-compete mouse cells in occupying the emptied developmental organ niches,” said staff scientist Jun Wu. As the organism grew, the rat cells are used where the mouse cells couldn’t be, and so created the tissues that made up the heart, eye or pancreas.

That same technique could then be used to combine the human and pig cells.