Pig organs are similar in size and function to our own, and people are less squeamish about harvesting body parts from an animal raised for meat than they would be about a primate’s. Yet one major hurdle that has continued to vex any such cross-species transplants, or xenotransplants, has been the threat of transmitting viruses that can infect people and pigs alike.

Scientists in Massachusetts announced that by using the CRISPR–Cas9 gene-editing system they were able to inactivate all 25 viruses in the pig genome, yielding seemingly healthy piglets and moving research one step closer to a future of xenotransplantation.