Human-sheep hybrids could pave way for diabetes cure
Human-sheep hybrids have been created by scientists for the first time, opening the door to organs being grown inside the farmyard animals for use in transplants or to cure diabetes.
A team at Stanford University successfully grew embryos inside a surrogate for three weeks which had both sheep and human cells.
It is the first stage toward growing an unlimited supply of human organs for transplants and even providing a cure for Type 1 diabetes.
The next step is to implant human stem cells into sheep embryos which have been genetically modified so they cannot grow a pancreas, in the hope that human DNA will fill in the missing code.
If successful a human pancreas should appear inside the animal's body. The team is about to apply for permission from regulators to lengthen their experiment to 70 days to see if the human cells really can create an organ.
Speaking at the American Association for the Advancement of Science's annual meeting in Texas, lead researcher Dr Hiro Nakuachi said he believed that organs grown in animals would be available for transplant within the next five to ten years.
"We have already generated a mouse pancreas in rats and then transplanted those into a diabetic mouse and were able to show almost a complete cure without any immunosuppressants," he said.
"When it comes to human-sheep, it seems more difficult. So we would like to proceed a little longer and this time use organ-deficient embryos.
"It could take five years or it could take 10 years, but I think eventually we will be able to do this."
Britain is facing a transplant shortage crisis because medicine has advanced to such a degree that many more lives are being saved, so there are fewer donor organs available.
Last year, researchers from the Salk Institute in the US created human-pig hybrids, but no lab has yet succeeded in growing an organ.
Previously scientists had hoped that pig or sheep organs could be used directly because they are roughly the same size as a human. However, they were always rejected. The new approach gets round the rejection problem because it uses stem cells directly from a human patient.
Sheep also have similar heart and lungs to humans, and their embryos have previously been shown to form chimeras with goat embryos, creating geeps. The process is also more efficient than in pigs. Transplanting around 40 to 50 embryos into pig surrogates leads to a maximum of 14 piglets, while transferring three to four sheep embryos brings yields of up to three foetuses.
Dr Pablo Ross, who works with Dr Nakauchi, added: "The sheep is a good model for many human conditions.
"The size of the sheep organs is similar to human size, some of the organs are physiologically similar and a lot of cardiovascular research is done in sheep because they have some similarities to humans in terms of heart shape."
To make the hybrids, scientists transplanted human stem cells into pre-implantation embryos of sheep. The embryos were allowed to grow for a week before being implanted into a surrogate sheep. Current rules ban labs from allowing the survival of hybrids beyond 21 days, so the surrogate animal was slaughtered after three weeks.
British scientists said it would be groundbreaking if the team managed to grow an organ inside an animal.
Professor Ludovic Vallier at the Wellcome - MRC Cambridge Stem Cell Institute said: "It would definitely be a world first if Hiro could demonstrate that he can generate a human organ in the sheep."
However, Robin Lovell-Badge, of the Francis Crick Institute in London, warned the resulting organs may still be rejected by the body.