A woman has lived with a pig kidney for more than nine months without needing dialysis, a record-setting achievement.

The woman underwent the operation at Massachusetts General Hospital on November 22 last year. As of Thursday, the kidney has been functioning for 285 days, according to Cambridge, Massachusetts-based eGenesis, the biotech company that used Crispr gene editing to make the organ fit for human transplantation. Previously, the record for a person living with a transplanted pig kidney was 271 days, set by Tim Andrews.

Most people in need of a kidney transplant wait three to five years on average to receive one, though it can take longer depending on blood type and other factors. While they wait, patients often need dialysis, in which a person’s blood vessels are hooked up to a machine that removes excess fluid and waste from the bloodstream. Dialysis typically requires four-hour sessions three times a week and can damage blood vessels over time, making the procedure hard on the body.

Pig kidneys could offer an alternative until a human organ is available. Pig organs are similar in size and function to human organs and are being investigated as a way to ease the shortage of human donor organs. To make them more suitable for humans, scientists are genetically editing them to prevent immediate rejection and reduce the risk of pig viruses being passed on to transplant patients.

Patients' health gets worse the longer they're on dialysis, “and their odds of getting a human transplant aren't rising fast enough to meet their declining health,” says Mike Curtis, CEO of eGenesis. The company used Crispr to remove certain pig genes that could cause an immune response and add a handful of human genes.

“What we saw with Mr. Andrews was a radical improvement in his overall health while he was on the pig kidney versus if he had stayed on chronic dialysis,” Curtis says.

The woman who has crossed the nine-month mark is the fifth person to receive an eGenesis kidne...