Changes in sperm engineering have allowed scientists to dramatically reduce the chances of transplanted pig organs being rejected by human patients.

A new technique suggests the success rate could be improved from 4% to 88%, according to the journal Proceedings of the National Academy of Sciences.

Until now researchers have relied on injecting a human gene into fertilised pig eggs to create animals whose organs can be harvested for use by humans.

The possibility of generating transgenic pigs efficiently and reproducibly will... be an advantage for creating multitransgene pig donor animals Marialuisa Lavitrano

But too often the animals fail to pick up the human gene and the organs have only been successful in 4% of cases.

But a team led by Marialuisa Lavitrano, at the University of Milano-Bicocca in Italy, have found that by modifying the DNA in pig sperm, rather than in the eggs, they can dramatically reduce the chances of organs being rejected.

Of 93 piglets produced from the treated sperm, 57% had the human gene in their organs.

When two unsuccessful fertilisations were excluded from the total of eight carried out, the success rate rose as high as 88%.

Furthermore the gene, called hDAF, was functional in multiple organs, including the heart, lung and kidney.

Laboratory tests showed that pig cells with the human protein produced by the gene were resistant to attack by the human immune system.

Ms Lavitrano's team had previously demonstrated the technique, sperm-mediated gene transfer (SMGT), on mice.

'High efficiency'

They wrote: "The pig is the most likely donor animal for xenotransplantation of organs, but may well require multiple transgenes to be a satisfactory donor for humans.

"Given the high efficiency of transgenesis, SMGT could greatly facilitate the production of such pigs."

The scientists made use of sperm's ability naturally to pick up DNA from the environment.

Fresh pig sperm was incubated in a medium that contained the human DNA.

The sperm naturally incorporated the human gene, which was then passed on to offspring after fertilisation.

The researchers added: "The possibility of generating transgenic pigs efficiently and reproducibly will, hopefully, not only be an advantage for creating multitransgene pig donor animals, but also enable strategies to fulfil many of the promises originally expected from the introduction of transgenic livestock."