Chinese surgeons have transplanted a liver from a genetically modified pig into a brain-dead person, showing that the liver can function in a human and extending a strategy previously attempted with the heart and kidneys.

The pig liver produced bile and albumin — key indicators of liver function — and maintained a stable blood flow with no signs of immunological rejection, the researchers announced on Wednesday. The experiment ended after 10 days when the recipient’s family requested the body.

The results, published in the research journal Nature, suggest that gene-modified pig livers can survive in humans, bolstering hopes that pigs could someday become sources of human organs for patients with organ failure — a long-standing goal thwarted by immune rejection.

However, hepatobiliary surgeon Lin Wang at the Xijing Hospital, Fourth Military Medical University in Xi’an, China, who led the research, himself cautioned that it was still unclear whether the gene-modified pig liver could support a patient with liver failure. “It is our dream to make this happen — but currently we cannot say whether the pig liver could support a patient with severe liver failure,” Wang said. “In the future, we will try to answer: how long (can) the pig liver survive and support the human body.”

Lin and his colleagues transplanted a liver from a Bama miniature pig in which six genes had been edited into an adult human recipient who was diagnosed as brain-dead in the study supervised by their hospital’s ethics committee.

The gene edits included removing genes involved in immune rejection and inserting human genes to enhance compatibility. The surgeons transplanted the pig liver on March 10, 2024, and stopped the experiment on March 20, 2024, when the recipient’s family requested the body.

Medical researchers have described the Chinese study as a fresh milestone towards the goal of xenotransplantation, or cross-species transplants. Peter Friend, professor of transplantation at the University of Oxford in the UK, said the insertion of a small xeno-liver without disrupting the existing liver is an “elegant surgical technique”.

“But the presence of the brain dead person’s native liver means that we cannot extrapolate the extent to which this xenograft (pig liver) would have supported a patient in liver failure,” Friend cautioned in a statement released by the UK’s Science Media Centre.

At least three kidney transplants have been performed in the US since 2021 — one with up to 61 days follow-up in brain-dead patients, said Rafael Matesanz, the founder of Spain’s National Transplant Organisation.

Ivan Fernandez Vega, professor of pathological anatomy at the University of Oviedo, Spain, said more studies were required. “Only basic liver functions, albumin synthesis and bile secretion, were assessed, with no data on complex liver functions such as drug metabolism, detoxification, or immune functions,” Vega said.