The transplantation of pig organs into humans is a step closer to becoming a reality after researchers showed the organs can function long-term in baboons.

The transplanting of organs from one species to another, known as xenotransplantation, has been the subject of research for many years. Proponents say it could help get around a shortage of human organs.

However, there are numerous hurdles to overcome, from viruses that could infect recipients – something researchers have recently been using gene-editing tools to tackle – to preventing rejection of the organs, as well as ethical considerations.

Researchers say they have made a major move forward by significantly increasing the survival time of baboons whose hearts have been replaced with those of pigs.

It is not the first time pig organs, including hearts, have been transplanted into monkeys. Previous work has showed that a pig heart can function for more than two and a half years when transplanted into the abdomen of a baboon – although the baboon kept its own heart to pump blood around its body.

But when it comes to actually keeping baboons alive, pig hearts had only done the job for a maximum of 57 days – and that was only achieved in one animal.

Now, writing in the journal Nature, researchers from Germany, Sweden and Switzerland report they have broken through this barrier, with one baboon surviving with a pig heart for more than six months.

After initially disappointing results, the team refined the transplant procedure, switching from preserving donor hearts in cold storage to keeping them at 8C (46.4F) with fluids containing oxygen, hormones, red blood cells and nutrients circulating through them. They also found it was necessary to give the monkeys drugs to prevent the piglet heart from growing too large and medication to lower their blood pressure to match that of pigs.

“Hearts of pigs grow rapidly – even if they are out of the body of a pig – and we could stop that growth,” said the surgeon Bruno Reichart, a co-author of the study from Ludwig Maximilian University of Munich, noting that if the heart is too big it cannot function properly.

The results from five baboons show that while one had to be put down soon after transplant, two lived healthily for three months with no sign of problems – at which point the team put them down – while the remaining two baboons were followed for 195 and 182 days respectively before they were put down.

Reichart said that if financial backing were secured to allow the team to carry out further research, including using “cleaner” donor animals, clinical trials could begin in humans in about three years. So far, the team’s work has been supported by the German government.

Writing in an accompanying article, Christoph Knosalla from the German Heart Centre in Berlin said the International Society for Heart and Lung Transplantation previously suggested clinical trials of pig organ transplants could be on the cards once at least 10 primates, and 60% of recipients, were shown to have survived for three months or longer.

Bruce Whitelaw, a professor of animal biotechnology at the Royal (Dick) school of veterinary studies at the University of Edinburgh, said that while scientists had also been working to grow human organs inside pigs and sheep, that technology was still in its early stages and transplanting pig organs was a more immediate possibility. He said the main barriers to clinical trials now appeared to be practical rather than technical.

“In a world where we don’t have enough organs to transplant and people are dying because of that, then anything that can increase the number of organs is to be welcomed,” he said.