Doctors in China say they transplanted a genetically modified pig liver into a 71-year-old man who lived 171 days after the procedure, and 38 of those days were with the pig organ in place – a first to be published in a peer-reviewed journal.

Scientists have had early success transplanting genetically modified pig kidneys and hearts into humans, and pig livers have been transplanted into people who were brain-dead. But experts in the field of xenotransplantation – using animal organs in people – have had some concerns about whether the liver would be a good candidate for such a procedure.

“Everyone always says, ‘oh, liver is too complicated to transplant, compared to the heart or kidney,’ but after this, in the future, I think people will think differently. I think liver is good if we can get enough human genes in the pig,” said Dr. Beicheng Sun, president of the First Affiliated Hospital of Anhui Medical University and a co-author of the new study.

Unlike hearts and kidneys that have more narrow functions, the liver is more complicated to replace with a pig organ because it’s large and has a dual blood supply and multiple functions. The liver filters blood, removes toxins and waste, processes nutrients, detoxifies harmful substances like alcohol and drugs, produces bile to help with digestion, produces proteins that help blood clot and plays an important role in regulating blood sugar.

A transplanted pig liver given to a brain-dead patient in China in March 2024 was removed at their family’s request 10 days after surgery. There had been no signs of immune rejection or accumulation of inflammation.

Experts say the new study, published Thursday in the Journal of Hepatology, suggests that pig-to-human liver transplantation shows promise for use as a bridge to help a human who has a serious liver condition live long enough for enough of their own liver to recover or for a donor human liver to became available.

“In the future, maybe the left side can get a real chance to regenerate, and in that case, we would remove the graft, and that would be enough to support the life, or at least we know we can wait one or two months for a graft from a human that could save his life. I think this is a very key finding,” Sun said.

With more than 100,000 people on organ transplant waiting lists in the US alone and more than 9,000 waiting for a liver transplant, the demand for human organs far outpaces the supply. Livers are the second biggest need after kidneys, according to the US Health Resources & Services Administration. Scientists have been exploring alternatives for decades, including using pig organs because of their similarity to human organs.

The man had initially been hospitalized for hepatitis B-related cirrhosis, a condition in which scar tissue replaces healthy tissue, impairing the function of the liver and sometimes leading to liver failure. He also had a large tumor in the right lobe of his liver, but efforts to shrink the tumor with a high concentration of chemotherapy targeted to its blood supply were unsuccessful.

In some cases like this, surgeons can surgically remove a part of the liver, but the researchers behind the new study said that what was left of the man’s liver would probably have been too small to meet his metabolic needs.

After almost three weeks in the hospital, the man developed severe abdominal pain, and tests showed that the tumor was in danger of rupturing. Doctors tested family members to see whether they could donate liver tissue, but no one was a good match, so a gene-edited pig liver was considered the only remaining option that could save the man’s life. He and his daughter discussed the experiment with the doctors and agreed to proceed.

“We need to have great respect for this patient and their family,” Sun said. “The patient provides such a special contribution to the field of this science, and we need to be grateful for all of these patients who have made such a big contribution to this field.”

Doctors removed the tumor and the transplanted the genetically modified pig liver onto what was left of the man’s liver.

The transplant seemed successful. Right away, the pig liver turned red, and bile – which helps remove waste products and aids in the absorption of fats – started draining from the external bile duct, with secretion progressively increasing over time. Within the first day, there was a significant increase in other liver function indicators, and there were no initial signs of inflammation or rejection.

But by day 25, the patient’s heart started showing progressive signs of stress. Tests on day 28 and 33 showed inflammatory changes related to the transplant, and doctors swapped out some of the immune-weakening drugs. But there were other signs that the transplant wasn’t working as well as it did at first, suggesting that the man had developed a condition called xenotransplantation-associated thrombotic microangiopathy, in which microscopic blood clots damage small blood vessels and organs.

On day 37, the man’s blood pressure plummeted and his heart rate increased, and he was in and out of consciousness. At that point, his own liver was considered capable of functioning enough to keep his body going, so doctors removed the pig organ on day 38. The man’s liver continued to function well afterward.

On day 135, the man developed upper gastrointestinal bleeding, and he died of this bleeding 171 days after the transplant procedure.

Dr. Heiner Wedemeyer, a professor and chairman of the Department of Gastroenterology, Hepatology, Infectious Diseases and Endocrinology at Hannover Medical School in Germany who co-authored an editorial that was published alongside the study Thursday, wrote that the experiment showed “a cause for cautious optimism” as well as a “reminder of how far the field must still travel.”

“It’s really groundbreaking,” Wedemeyer told CNN. “For me as a transplant hepatologist, it really opens completely new views and ideas.”

Wedemeyer said he saw a patient Wednesday morning who had acute liver failure and did not qualify for transplantation with a human organ because of some cancer issues.

“If I would have had, at this stage, use of a pig liver to bridge her – because she may need three, four, five, six, seven weeks to recover with her own liver – I would have done this,” he said. “A pig liver gives us completely new opportunities, and that can really be promising for our patients.” (CNN)

• Doctors at the First Affiliated Hospital of Anhul Medical University in China transplanted a liver from a pig into a 71-year-old man in May 2024. Courtesy Dr. Beicheng Sun