Surgeons and researchers behind the first pig-to-human kidney transplant hailed it on Thursday (March 21) as a major breakthrough that could benefit countless patients on dialysis or languishing on transplant waitings lists.

Richard Slayman, a 62-year-old man who has end-stage renal disease, became the first human to receive a new kidney from a genetically modified pig, in a four-hour surgery, performed on March 16, doctors from Massachusetts General Hospital in Boston announced.

Slayman of Weymouth, Massachusetts, is recovering well and expected to be discharged soon, the hospital said.

Slayman had received a transplant of a human kidney at the same hospital in 2018 after seven years on dialysis, but the organ failed after five years and he had resumed dialysis treatments.

The kidney was provided by eGenesis of Cambridge, Massachusetts, from a pig that had been genetically edited to remove genes that could be harmful to a human recipient and add certain human genes to improve compatibility. The company also inactivated certain viruses inherent to pigs that have the potential to infect humans.

EGenesis CEO Mike Curtis, told Reuters that the company had been testing genetically edited transplants on primates for several years, and was therefore confident it could work successfully on a living human patient.

Drugs used to help prevent rejection of the pig organ by the patient's immune system included an experimental antibody called tegoprubart, developed by Eledon Pharmaceuticals.

The surgery marks progress in xenotransplantation – the transplanting of organs or tissues from one species to another.

According to the United Network for Organ Sharing, more than 100,000 people in the U.S. await an organ for transplant, with kidneys in the greatest demand.