The scientists successfully rid 37 pigs of viruses hiding in their DNA, overcoming one of the big barriers to transplanting pig organs to people.
The team at eGenesis admits preventing pig organs from being rejected by the human body remains a huge challenge
But experts said it was a promising and exciting first step.
The study, published in the journal Science, started with skin cells from a pig.
Tests identified 25 Pervs - porcine endogenous retroviruses - hidden in the pig's genetic code.