Facing a shortage of organs needed by tens of thousands of patients, scientists have been studying pig organs as a potential solution. Genetically modified to suit humans and transplanted in the same way as human organs, the hope has been that they would function as well as those transplanted from human donors. But human bodies keep rejecting them.

A new study published November 13 in Nature provides new hope. In it, an international team of physicians detail how they prevented a human’s body from rejecting a pig organ—not once, but twice—for the first time ever.