"Pigs' organs are the right size for human transplantation, and they work similarly to human organs," said Lord Winston, head of the Institute of Reproductive and Developmental Biology at Hammersmith Hospital in London.

According to Natural News.com, health professionals have attempted to transplant organs from animals into humans before, but research in the field dropped off in the late 1990s when early transplant attempts were rejected and attacked by recipients' bodies as foreign tissue. Concerns over the possibility that transplants could facilitate the spread of diseases from animals to humans also contributed to a drop in the field's popularity.

Now Winston and colleagues from Imperial College want to revive the idea by breeding pigs that contain six human genes, in order to decrease the chances that the pigs' organs will be rejected by human bodies. They have formed a company called Atazoa that has successfully created transgenic pig sperm, but their research stalled due to strict British regulations over transgenic animals.

"One of the biggest problems in Britain is the regulatory framework. It's been very difficult to get this sort of animal work going," Lord Winston said.

The researchers initially had to wait 13 months before they were licensed to genetically modify the pigs, then were told that regulations prohibited breeding genetically modified animals on agricultural land.

In response, Atazoa has moved its research to the United States, which has drastically fewer regulations concerning genetic research on animals. The researchers will breed the pigs with genetically modified sperm in Missouri, and hope to produce a fully modified animal within the next two years. After that, they hope to begin clinical trials to demonstrate that the genetically engineered organs are safe for human transplant.