The hearts of genetically modified pigs could be transplanted into humans to solve the shortage of organ donors, scientists believe.
Researchers successfully grafted a pig heart into a baboon more than a year ago and it is still functioning, they report today.
Until now, organs transplanted into primates have only lasted for a maximum of six months before being rejected.
But scientists have tweaked the DNA of pigs so that their hearts are more compatible with primates and humans.
“The developments may instil a new ray of hope for thousands of patients waiting for human donor organs,” said Muhammad Mohiuddin of the Cardiothoracic Surgery Research Programme at the National Heart, Lung, and Blood Institute in the US.
“If successful, this method could change the current transplant paradigm, eliminating the shortage of donor organs including hearts, livers, kidneys, intestine, as well as insulin producing cells for treatment of diabetes.”
At present people needing a heart transplant must wait until a suitable donor heart becomes available. Last year 145 operations were carried out at seven hospitals in Britain.
However, only eight out of 10 people in the UK receive the transplant they needed because of a lack of suitable donors. Many adults and children are forced to wait more than a year for a new heart.
Those on waiting lists have to use an artificial heart but these are not perfect and have issues with power supplies, infection, and both clotting and haemolysis, the break down of red blood cells.
Transplantation using an animal organ, or xenotransplantation, has been proposed as an option to save human lives, but the challenge has been to stop hosts rejecting donor hearts.
However researchers found that the pig hearts were alive and functioning well more than year after being grafted in place.
Pigs were chosen because their anatomy is compatible with humans and they have a rapid breeding cycle. Pig valves are already swapped for human heart valves.
Critics claim that because the life cycle of pigs is shorter than humans they will need to be replaced. They could also pass on diseases.
But through genetic changes, the scientists have added several human genes to the pig genome as well as removing genes which trigger a dangerous immune response in humans.
Grafts from these genetically engineered pigs are less likely to be seen as foreign, thus reducing the immune reaction against them.
Chris Mason, professor of regenerative medicine at University College London, said: “The fact is you have got lots of people waiting for heart transplants and if you could have a supply of hearts off the shelf then that is clearly beneficial.
“Heart failure is a really horrible condition so anything that could improve quality of life is of great value.
“I think we are a long way off from being able to genetically engineer a whole heart though stem cells so this could provide a good stop-gap.”
The genetic modifications also mean that fewer immunosuppressive drugs are needed which are often responsible for complications. When Christiaan Barnard attempted the first heart transplant in 1967 it was the drugs which killed his patient as his immune system was so weak he died from pneumonia.
The experiments involved using these genetically engineered pig hearts, transplanted in the abdomen of baboons alongside their actual hearts.
The next step is to use hearts from the same pigs to test their ability to provide full life support by replacing the original baboon heart.
Dr Mohiuddin said; “Based on the data from long-term surviving grafts, we are hopeful that we will be able to repeat our results in the life-supporting model.”
Prof Peter Weissberg, the medical director of the British Heart Foundation said: “I think this stands a high chance of happening but it is still a very long way off.
“There were similar projects happening in the 1990s but they ground to a halt because they struggled to deal with the problems of rejection.
“There is a shortage of organs so this could be potentially promising and we already use pig valves in heart surgery.
“But there is a long way to go. They still have to prove this would work in humans.”
The study was presented at the 94th American Association for Thoracic Surgery annual meeting in Toronto.