On a farm in the southern US state of Virginia, David Ayares and his research team are breeding genetically modified pigs to transplant their organs into human patients. Revivicor, the biotech company Ayares leads, is at the forefront of xenotransplantation research — the implantation of animal organs into humans — aimed at solving a chronic organ shortage with thousands of Americans die every year.

Andrew Caballero-Reynolds / AFP—Getty Images