(BOSTON) — Harvard-affiliated scientists say they have been able to keep a monkey alive for two years with a genetically engineered pig kidney. Although preliminary, transplant experts say this research is an important milestone in the search for an alternative source of organs.

Scientists are hopeful that one day, genetically modified organs grown in pigs may be able to significantly extend the life of people with end-stage organ failure.

In recent months, other high-profile research teams at New York University and the University of Alabama at Birmingham announced successful transplants of genetically modified pig-kidneys into brain dead human donors. But those experiments ended after a few weeks.

“Duration of survival has been an Achilles heel of genetically modified pig organs to date due to a combination of rejection and opportunistic infections,” said Dr. Peter Chin-Hong, director of the transplant infectious disease program at University of California, San Francisco.

This new research, published in Nature, represents the longest period of time that scientists have been able to keep a non-human primate research animal alive.

“This proof-of-concept study provides real hope that transplantation of porcine [pig] donor kidneys into humans is very much on the horizon,” Chin-Hong said.

Still, experts cautioned that this new research was preliminary, and the idea of pig-grown organs is likely several years away from becoming a reality.

“If ultimately proved successful in human organ recipients – which is still years away at this point – this could be one of the key advances needed to make xenotransplantation a reality in clinical practice,” said Dr. Josh Levitsky, president of the American Society of Transplantation.

The new research was led by eGenesis, a company co-founded by Harvard geneticist George Church. In a press release, scientists at eGenesis said the new research will help lay the groundwork for formal clinical trials.

In prepared remarks, eGenesis CEO Michael Curtis, PhD, said the company is focused on “improving long-term survival for transplant recipients from months to years.”

Eventually, the hope is that transplant doctors will be able to use genetically modified pig organs instead of solely relying on deceased human organ donors.

“Among all solid organs transplanted, kidneys are most sought after, expected to increase in demand further, and there is a significant shortfall of organs leading to premature deaths,” Chin-Hong said.

Every day, 17 people die waiting on the organ transplant list, according to the Health Resources & Services Administration. There are currently more than 100,000 people waiting on the national transplant list and a new person is added to the list every 10 minutes.

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