A genetically modified pig’s kidney kept a man with organ failure off dialysis for nine months while he waited for a suitable human donor’s kidney to become available. This suggests pig kidneys could act as a temporary measure amid lengthy organ waiting lists, but they may also work as a permanent replacement one day.

“I think it’s incredible in terms of the science behind it and what they’ve achieved,” says at Imperial College London, who wasn’t involved in the work.

For people with severe kidney disease, where these organs are failing and dialysis is needed, a kidney transplant provides the best chance of survival and better quality of life. However, demand for donor organs exceeds supply.

One possible solution is xenotransplantation, the transfer of organs from other animals into humans. In January 2022, a pig heart was transplanted into a person for the first time, but the recipient died several months later, possibly due to the presence of a pig virus. A pig liver transplant also occurred last year.

A pig’s kidney was transplanted into a living person for the first time in 2024. The recipient, Richard Slayman, aged 62, died 52 days later from cardiac-related causes. In the latest development, Tim Andrews, a 66-year-old man with end-stage kidney failure, opted to receive a kidney from a pig to avoid dialysis while he waited for a suitable human organ.

at Mass General Brigham hospital in Boston and his colleagues transplanted the kidney, which came from a Yucatan miniature pig, into Andrews in January 2025. The organ had been genetically modified to improve compatibility with the human immune system, such as by removing some sugars that we produce antibodies against and adding seven human genes.

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The transplant was initially a success, and Andrews – who also received immunosuppression drugs to stop his body rejecting the organ – came off dialysis and resumed normal life. However, after about six months, he was admitted to hospital with a methicillin-resistant Staphylococcus aureus (MRSA) infection, which most antibiotics can’t kill.  

Riella and his colleagues reduced the immunosuppression drugs Andrews was on, but then damage started to develop in the kidney’s blood vessels. This progressed to organ failure, and the kidney was removed a record 271 days after transplantation. “He had a kidney that lasted nine months, which is mind-blowing,” says Riella.

Andrews went back onto dialysis for about three months, before finally receiving a suitable human kidney in January 2026. This marks the first time a pig kidney has been used as a temporary bridge to a human transplant.

“Such transplants may allow patients to avoid going through dialysis, which is so important because it causes so much wear and tear to the body,” says Riella. “Hopefully, maybe 15 years from now, pig kidneys will compete with a human kidney transplant, but you’re not there yet.”

2024 saw the first living people to receive pig kidney transplants

Three people in the US received a genetically modified pig kidney in 2024, marking another step towards animal-to-human organ transplants becoming routine

The procedure is experimental, and Riella couldn’t give an estimate of how much it might cost. But in the US, there are about 600,000 people on dialysis, which can cost about $100,000 a year per individual, he says.

Riella says the team has now done five such transplants and two more case reports will be published this year, including one of a person who has already beaten Andrews’s record of nine months with a functioning pig kidney.

“I think these will be carried out more widely in the future, but it’ll be a little while,” says Willicombe, largely due to their probable high cost. Scientists should also continue researching artificial kidneys, as well as ways to regenerate damaged organs and optimise donated ones, she says.

Transplanting organs from non-human animals into people could revolutionise medicine, potentially saving . Scientists have previously experimented with giving people pig hearts and kidneys, and have now reported transplanting the animal’s liver into a living person for the first time.

“This is really, really groundbreaking,” says at Hannover Medical School in Germany, who wasn’t involved in the procedure. “The patient was close to dying, but due to the transplant, he survived for half a year.”

The liver’s complexity meant such surgeries had only been , with signs of success. “The heart is just a muscle pumping blood,” says Wedemeyer. “The kidney is also easy, because it needs only to clear things from the body. But the liver is different because it produces so many different proteins involved in so many metabolic processes.”

The heart and kidney transplants in living people similarly showed signs of early success, but complications later arose. With the heart transplant, this was linked to it possibly transferring over a pig virus.

Now, at Anhui Medical University in China and his colleagues have reported the transplantation of a pig’s liver into a 71-year-old man. The recipient’s liver function was considered too poor for a conventional transplant to have a good chance of success, due to a large tumour and heavy scarring from a hepatitis B infection. Thousands of people die each year waiting for a liver transplant, so each procedure must be carefully justified, says Sun.

The man still required some form of transplant, though, as his tumour could have fatally ruptured at any moment, says Sun. With the recipient’s permission, in May 2024, Sun and his team replaced the right part of his liver, containing the tumour, with one from an 11-month-old miniature pig. The five-hour operation involved them connecting blood vessels from the pig’s liver with those in the left side of his own organ.

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To prevent the liver being rejected by his immune system, three genes were deactivated in the pig and seven genes were introduced, so the organ functioned more like a human one. The man also took immune-suppressing drugs, and the team carefully checked that the liver wasn’t infected with any porcine viruses.

Almost immediately, the liver began secreting bile, a fluid the organ produces to help break down fat from food. Within weeks, the recipient’s levels of bile and albumin – a protein made by the liver that prevents too much fluid leaking from blood vessels – had increased to healthy amounts, says Sun.

But about a month after the procedure, he developed life-threatening clots in his blood vessels, forcing the team to remove the transplant. That was probably partly caused by it excessively activating part of the recipient’s immune system and producing abnormal levels of some blood-clotting proteins, which healthy livers also make. This is probably more likely to occur with pig transplants, due to how different the animal is to a human, says Sun.

The man lived for about another five months, with just the left side of his liver, then died from stomach bleeding, which is , says Sun. Both Sun and Wedemeyer say the bleeding was probably unrelated to the transplant.

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Despite the man’s death, the procedure can still be considered a partial success, because he probably otherwise would have died soon after his tumour was removed, says Wedemeyer. What’s more, the recipient’s own liver partly regenerated while the transplant was functioning well, which is probably why he lived for months after it was removed, he says.

This procedure has furthered our understanding of xenotransplantation, raising the possibility that pig livers could buy time for those waiting for human transplants, says Wedemeyer. They could even enable remaining liver tissue to regenerate enough that people no longer need the procedure, says Sun.

But it will probably be at least a decade before pig livers can be used to permanently replace human ones, says Sun. We first need to substantially reduce the risk of complications, for instance through further genetic modifications, says Sun.

A computational model that could rapidly design a blood vessel network for any 3D-printed organ may take us a step closer to transplanting artificial livers, kidneys or hearts without the need for a donor.

People with organ failure often require organ transplants, but is being met. To fill this need, scientists are developing ways to 3D-print organs in the lab. But these require blood vessel networks to stay alive, and existing experimental methods for designing these take days or even weeks.

To address this, at Stanford University in California and her colleagues built a computational model that can design these networks for any organ based on a mathematical law that describes how blood vessels branch into smaller ones in the body.

They tested their approach by having the model design a network of 25 vessels for a 1-centimetre-wide ring-shaped structure that had been 3D-printed from kidney cells, which it did in just a few minutes.

The team then printed the vessel network into the ring using cold gelatin particles, before heating it to 37°C (98.6°F), which melted the gelatin and left a network of hollow, 1-millimetre-wide channels that mimicked blood vessels. The researchers then continuously pumped a liquid containing oxygen and nutrients through the channels to simulate normal blood flow.

A week later, there were around 400 times more alive cells in the ring compared with an identical ring of kidney cells without the vessels, which the team had also bathed in the blood-like fluid.

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“We could keep the cells alive that were in close proximity to the vessels,” says Marsden. Those that were further away died because it isn’t yet possible to print the smaller, more highly branched vessels that are needed to supply nutrients to those regions, she says. The team is exploring ways to address this.

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“They’re definitely pushing the boundary of what’s possible,” says at Paris-Saclay University in France. The approach could one day allow scientists to design the vessel network for a full-sized organ in hours, rather than days or weeks, he says. “Vessel [networks] designed in this way could be used in the future to replace, or at least complement, organs that could be grown in the lab.”

First, the researchers need to develop ways to print these blood vessel networks into large organs. If all goes well, Marsden says they hope to test 3D-printed organs in pigs within about five years.

Instead of administering general anaesthesia, which is the default for such an operation, doctors gave a spinal anaesthesia, similar to that used during Caesarean sections. The transplant took less than 2 hours.

Nicholas was completely aware and awake during his surgery, but experienced “no sensation whatsoever” and was able to talk with the surgeons about the different milestones they reached during the procedure.

After a successful operation on 24 May, he was discharged the next day, walking out of Northwestern Memorial Hospital. The normal stay there for kidney transplant patients is two to three days.

This new option may increase access to transplantation for people who are at high risk of complications from general anaesthesia, while also decreasing time spent in hospital. ⁠

When children with heart failure await transplants, they typically stay at the hospital for months to years, tethered to a bulky blood-pumping device. But an implantable heart pump could allow them to wait at home.

Regulators in the US and Europe have approved one device, the Berlin Heart, for long-term use in younger children awaiting a heart transplant. But this life-saving tool comes with limitations, says at Stanford University in California. It attaches to the heart via two large tubes, hindering children’s movement. Berlin Heart also requires that children remain in hospital so they can be monitored for risks like stroke and infection.

Almond and his colleagues tested a newer device, the Jarvik 2015, in seven children with heart failure between 7 months and 7 years old. It can be implanted into the heart and connects to an external battery pack worn at the waist. The device works by pumping blood from the heart’s left ventricle into the main vessel that sends blood throughout the body.

The researchers implanted the pump during open-heart surgery, monitoring children in hospital afterwards. On average, children used it for 115 days. All seven survived and five received heart transplants. Of the other two, one spontaneously recovered while the other switched to a device that also supports right ventricle function after their heart’s right side failed, unrelated to the Jarvik 2015. One child experienced a severe stroke, a known risk of cardiac assistive devices.

Most children didn’t experience any pain with the device and they were able to engage in most activities. “With less material outside the body and not being tethered to a large pump, that child is actually able to be a bit more free and move around,” says Almond.

Larger trials must investigate whether the pump could enable children to wait for a transplant at home, says Almond. Children in the US typically wait three to 12 months for a transplant, while those in Europe may wait up to two years.

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“The Berlin Heart is very successful, bridging patients to transplant, and we’ve become quite expert in the use of it,” says at Boston Children’s Hospital. “[But] we hope that new devices will be able to allow children be discharged home, like adults.”

Surgeons have successfully transplanted a pig kidney into a 62-year-old man living with end-stage kidney disease. The recipient, Richard Slayman, is recovering well and is expected to be discharged from the hospital soon, mere days after the surgery.

Is this the first ever pig kidney transplant?

This is the first time a pig kidney has been transplanted into a living human, which makes it a significant milestone in the field of xenotransplantation, or the transfer of animal organs to humans.

“The success of this transplant is the culmination of efforts by thousands of scientists and physicians over several decades,” said at Massachusetts General Hospital in a . “Our hope is that this transplant approach will offer a lifeline to millions of patients worldwide who are suffering from kidney failure.”

Strictly speaking, however, this isn’t the first ever pig-to-human kidney transplant. The procedure has been performed five times in the past, all in people who were declared brain-dead and kept on life support. The most recent of these took place in July 2023 by Robert Montgomery at NYU Langone Health and his colleagues. That kidney functioned for more than a month without signs of rejection or infection.

When did the surgery take place?

Kawai and his colleagues performed the surgery on 16 March. The procedure lasted 4 hours, and the kidney began producing urine and the waste product creatinine soon after, according to reporting by . Slayman has also been able to stop dialysis, a further indication of the kidney’s proper functioning.

Where did the pig kidney come from?

The organ was provided by the pharmaceutical company eGenesis, which breeds pigs that have been genetically engineered to carry certain human genes and to lack a particular set of pig genes that are harmful to humans. These genetic modifications reduce the likelihood of transplant rejection, when the immune system attacks the organ and causes it to fail. Slayman is also receiving a cocktail of immune-suppressing drugs to further lower this risk. So far, there is no sign of rejection and Slayman is able to walk on his own. His doctors hope to discharge him from the hospital soon.

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What do we know about the recipient?

Slayman has type 2 diabetes, high blood pressure and kidney disease. He had previously received a human kidney from a donor in December 2018. However, the organ showed signs of failure approximately five years later. He started dialysis in May of last year, but experienced complications, requiring visits to the hospital every two weeks. This had a serious impact on his quality of life while he awaited a second transplant.

More than are waiting for an organ transplant, of whom 17 die each day. The US Food and Drug Administration authorised the experimental transplant for Slayman due to a lack of other treatment options.

“I saw it not only as a way to help me, but a way to provide hope for the thousands of people who need a transplant to survive,” said Slayman in a statement.

Have there been xenotransplant procedures involving other organs?

Only two other people have undergone a xenotransplant, both of whom received a genetically modified pig heart. The first, a man named David Bennett, passed away two months later, potentially due to complications from a pig virus called porcine cytomegalovirus. As such, scientists genetically inactivated this and similar viruses in the pig that Slayman’s kidney came from.

The second recipient, a man named Lawrence Faucette, died from transplant rejection six weeks afterwards.