Transplanting pig organs into humans may be much safer than previously thought, a study suggests.
There are concerns about putting animal organs into humans
There is a worldwide shortage of human organs for transplants. Many people believe organs from animals, especially pigs, could be a viable alternative.
However, studies have suggested that transplanting these organs into humans could pose a major health risk.
But this latest study, published in the Journal of Clinical Investigation, suggests the risk is very low.
Yong-Guang Yang and colleagues at Harvard Medical School transplanted cells from humans and pigs into mice.
They found that the human and pig cells were able to co-exist alongside each other.
Previous studies have suggested that viruses found in pig cells can infect human cells.
These viruses, called porcine endogenous retroviruses or PERVs, are harmless in pigs.
However, there are concerns that they could pose a serious health risk to humans.
This latest study suggests that this may be less of a problem than previously thought.
The scientists transplanted pig bone marrow cells into the mice. The cells did not contain a strain of PERVs known to be able to infect human cells.
These pig cells were able to co-exist safely with the human cells for the 25 weeks of the study.
The scientists described their findings as encouraging. They said the results raise the possibility of using pig organs in human transplants.
However, Dr Jonathon Stoye, head of virology at the UK's National Institute for Medical Research, suggested the results should be interpreted cautiously.
"What this paper shows is that carefully selected source animals do not seem to transmit PERVs. It is important not to generalise."
But speaking to BBC News Online, he added: "This takes us a step closer. However, the emphasis must be on not using any random pig but carefully choosing the source animals."
In the UK, the government would have to approve transplants using animal organs before they can go ahead.
Ministers have set up the UK Xenotransplantation Interim Regulatory Authority (UKXIRA) to advise them on such issues.
The authority regularly reviews the latest scientific research in this area.