A major milestone in transplant medicine suggests that genetically engineered pig kidneys could serve as temporary lifesaving organs for patients waiting for human donors. Two people who previously received gene-edited pig kidneys have now successfully received human kidney transplants, easing a major concern that exposure to an animal organ might make patients more likely to reject a human organ later.
The development provides some of the strongest evidence yet that xenotransplantation—the transplantation of organs between different species—could help address the severe shortage of donor kidneys.
One of the patients, Tim Andrews, received a genetically engineered pig kidney at Massachusetts General Hospital in January 2025. Andrews, who had end-stage kidney disease, lived with the organ for 271 days without requiring dialysis, the longest dialysis-free period reported at the time for a living human recipient of a pig kidney.
The pig kidney initially functioned immediately. Andrews experienced an early episode of T-cell-mediated rejection, but doctors successfully treated it. After approximately six months, physicians reduced his immunosuppressive medication because of an infection. The kidney later developed inflammation and damage to small blood vessels, eventually causing it to fail.
Andrews returned to dialysis temporarily before receiving a kidney from a deceased human donor in January 2026.
Crucially, the new human kidney began functioning immediately, and doctors found no evidence that the previous pig transplant had sensitized his immune system in a way that endangered the human organ. That result addresses one of the important uncertainties surrounding xenotransplantation.
A second recipient of an eGenesis pig kidney has also successfully transitioned to a human donor kidney, providing additional evidence that receiving a genetically engineered animal organ does not necessarily prevent a conventional transplant later.
The achievement changes how scientists may think about the immediate purpose of pig organs.
Researchers ultimately hope genetically engineered pig kidneys could become permanent replacements for failing human kidneys. But reaching that goal requires proving that the organs can function safely for years. In the meantime, doctors increasingly see another possibility: using pig kidneys as a “bridge” to human transplantation.
That could be enormously valuable because dialysis places significant physical strain on patients. People with kidney failure can spend hours connected to dialysis machines several times each week while waiting years for a suitable human organ. Some deteriorate so severely during that period that they become too sick to receive a transplant; others die while waiting.
A pig kidney capable of functioning for months—or eventually years—could allow patients to leave dialysis while remaining on the human-organ waiting list.
The organs used by Mass General Brigham are produced by biotechnology company eGenesis. The pigs undergo extensive genetic engineering intended to make their organs more compatible with the human body. Scientists remove or modify genes that can provoke powerful immune reactions, add human genes that improve compatibility and disable potentially dangerous viruses embedded within the pig genome.
Since March 2024, five patients with kidney failure have received eGenesis pig kidneys through the FDA’s Expanded Access pathway. Three achieved sustained kidney function for more than eight months without dialysis.
The field is also moving toward larger and more systematic testing. eGenesis expects to begin an FDA-cleared clinical trial in early 2027, ultimately involving up to 33 patients at multiple transplant centers. Other companies, including United Therapeutics, are also developing genetically modified pig organs.
Significant challenges remain. Scientists must improve immunosuppression, prevent vascular injury and rejection, monitor potential infections and determine whether animal organs can survive reliably over much longer periods. The number of patients treated so far also remains extremely small.
Nevertheless, these cases represent an important shift. Xenotransplantation no longer exists only as a theoretical solution to the organ shortage. Doctors now have evidence that a pig kidney can function inside a living person for many months, free that patient from dialysis and still leave the door open for a successful human transplant afterward.
The long-term ambition remains even greater: creating a reliable supply of genetically engineered organs so patients no longer have to wait years for another person to donate one.
For now, however, the latest results demonstrate a potentially transformative intermediate step: pig kidneys may be able to keep patients healthier and dialysis-free while buying them the most precious resource in transplant medicine—time to wait for a human organ.
