A genetically modified kidney from a pig has kept a 66-year-old American man with kidney failure alive for a record nine months and successfully acted as a 'bridge' to a human transplant in a world first, doctors say.

Gene-edited pig kidneys could offer a lifeline to patients stuck waiting for a human donor.

Tim Andrews, 67, from New Hampshire, US, lived with the animal organ for nine months before later receiving a human donation.