Xenotransplantation, the transplanting of organs or tissue from one species into another, has moved in the past few years from a long-running experiment to the edge of formal clinical trials, with pigs as the donor of choice. The short answer to whether pig organs can be transplanted into humans is that they have been, in a small number of people, with outcomes ranging from a few weeks to many months. Nobody has yet shown that the approach can match a human donor organ, and the field is clear about that. What has changed is how long the organs last and how carefully the studies are now being run.

Why do researchers want animal organs at all?

The reason is arithmetic. More than 100,000 people are on the transplant waiting list in the United States, and thousands die each year before an organ arrives. Dialysis keeps kidney patients alive but carries a heavy burden of its own. A reliable supply of organs from animals would, if it worked, ease that shortage.

Pigs became the favored source for practical reasons. They breed quickly, they can be raised in controlled, clean facilities, and they can be genetically edited. Researchers also use them because their organs are of broadly similar size to human ones, an observation based on general anatomy rather than anything in the sources consulted for this article. Primates are closer to humans genetically, but they are slow to breed, scarce and carry viruses that could more easily infect people, and their use raises stronger ethical objections.

Is this a new idea?

No. It is more than a century old, and for most of that time it failed. In 1905, slices of rabbit kidney were placed in a child with kidney disease. In February 1963, surgeons in Minneapolis grafted a baboon kidney into a woman whose own kidneys were failing. It worked briefly. Her body rejected it five days later, and she died the following month.

At Tulane in 1963 and 1964, surgeons gave primate kidneys to several dying patients. One recipient of a chimpanzee kidney, Jefferson Davis, left the hospital in December 1964 after six weeks. In a larger series of 13 transplants, one recipient survived nine months. A chimpanzee heart placed in a patient in 1964 failed within two hours.

The best-known early case is Baby Fae, an infant who received a baboon heart on 26 October 1984. She died on 15 November from rejection, which has mainly been attributed to a mismatch between her blood type and the baboon’s.

What goes wrong when a pig organ meets a human body?

Rejection, in several forms. The fastest is hyperacute rejection. Pig cells carry a sugar called alpha-gal that humans do not make, and human blood contains natural antibodies against it. The antibodies bind, trigger a cascade of blood proteins called complement, and cause clotting and tissue death within minutes to hours.

If that is avoided, a slower antibody-driven attack, called acute vascular rejection, can follow in two to three days. T cells and natural killer cells can also assault the graft, and over a longer span the blood vessels can narrow in a process akin to chronic rejection of ordinary transplants. Blood clotting problems add to the difficulty: transplanted kidneys can disrupt coagulation, and livers have caused a severe drop in platelets in experiments.

Researchers fight back with gene editing. They knock out the pig gene that makes alpha-gal, and add human genes that restrain complement, such as CD55, CD46 and CD59. In 2020 the FDA approved pigs engineered not to produce alpha-gal sugars. Patients also receive immune-suppressing drugs, and as the cases below show, getting that regimen right is still a work in progress.

Which patients have received pig organs?

Most were gravely ill and received the organs through special compassionate-use permission.

  • September 2021: A gene-edited pig kidney was attached to a brain-dead person at NYU Langone. The only edit was removal of alpha-gal. No immediate rejection was seen.
  • January 2022: David Bennett Sr. received a heart from a pig with 10 genetic modifications at the University of Maryland. He died about two months later.
  • September 2023: Lawrence Faucette received a pig heart at the same hospital and died on 30 October 2023, with signs of rejection.
  • March 2024: Richard Slayman, whose human kidney had failed, received a pig kidney with 69 edits at Massachusetts General Hospital. He died a few months later of causes that were reported as unrelated, with no apparent rejection of the organ.
  • April 2024: Lisa Pisano received a pig kidney and a mechanical heart pump at NYU Langone. The kidney was removed in late May after poor blood flow and medication damaged it.
  • 2025: Tim Andrews and Bill Stewart received pig kidneys at Massachusetts General. Andrews kept his kidney for 271 days, a record for a pig organ at that time, before it was removed in October 2025 because of rejection. He received a human kidney in January 2026. Stewart’s operation took place on 14 June 2025, and he was reported to be doing well when the news broke that September.
  • August 2025: A pig lung was transplanted into a brain-dead recipient, a study of feasibility, not a treatment.

An Alabama woman’s pig kidney lasted 130 days before rejection forced its removal and she went back to dialysis. That figure stood as the record until Andrews.

Are there clinical trials now?

Yes. In early 2025 the FDA cleared the first clinical trials of pig kidney transplants in people with kidney failure, for two companies: United Therapeutics and eGenesis.

The designs differ. United Therapeutics uses pigs with 10 gene edits, six human genes added and four pig genes removed, and planned to begin with six patients, with the option of expanding to 50. Early participants were described as people who had been on dialysis for at least six months and had no other serious medical problems. eGenesis uses pigs with 69 edits, most of them intended to inactivate viruses. Its study involves 30 people aged 50 or older who are on dialysis and on the transplant list.

Operations are staged with months between them so that doctors can learn from each one before continuing. Each patient is monitored for 24 weeks and followed for life, including for any infection that might pass from pig to person. The FDA has required lifelong monitoring of recipients since 2006.

What about viruses?

Pigs carry porcine endogenous retroviruses, or PERVs, which are embedded in their DNA. Most breeds have around 50 copies, and some can produce infectious virus. In lab experiments, certain PERVs can infect human cells.

Researchers have used CRISPR to disable all the PERV copies in pig cells, which stopped infection of human cells in culture. That is a laboratory result. According to the reviewed summary, no experimental pig xenotransplant has so far shown PERV transmission to a person. Screening donor pigs and monitoring recipients remain central to the trials.

Because this risk reaches beyond the patient to the public, the trials include long-term follow-up. It is a reason regulators move slowly even when a transplant looks successful.

How long can a pig kidney last, and what would count as success?

So far, the longest reported pig organ function in a living person is in the range of 271 days, in Andrews. By comparison, the record for a chimpanzee kidney cited in the sources is 273 days, so the two are nearly level. A deceased-donor human kidney commonly lasts many years, so pig organs are not yet competitive on that measure.

Doctors involved say even a year would be a meaningful benefit, because it could keep a patient off dialysis until a human kidney becomes available. Others note that the experiments are new, and the worst case is that the organ is removed and the patient returns to dialysis. Numbers in this field change quickly, and one summary from September 2025 still listed a shorter record, so any single figure should be read with its date in mind. The best measure will come from the trials.

What do ethicists and regulators say?

Three kinds of objection come up. Animal welfare groups question whether it is acceptable to breed heavily edited pigs for spare parts. Public health experts point to the infection risk described above. And bioethicists ask about consent, since recipients must agree to lifelong surveillance and, under the FDA’s 2006 requirements, give up the right to withdraw from monitoring.

Governments have reacted differently over time. Australia declared an 18-year moratorium on animal-to-human transplantation in 2005, then repealed it in 2009. Oversight now tends to be case by case, with institutional review boards and agency approval for each study. Cost is an open question as well: the source material says nothing about what a pig kidney might cost, and prices would depend heavily on how the industry scales.

Common questions

Why pigs and not monkeys?

Pigs are easy to breed, can be raised in clean facilities, and can be gene-edited. Primates raise stronger ethical concerns, reproduce slowly and carry viruses closer to human ones.

Do patients become part pig?

No. The organ is a pig organ made more compatible through gene edits, and the person’s own cells and genes are unchanged.

Has a pig heart worked long term?

Not yet. The two living recipients of pig hearts, in 2022 and 2023, died after about two months and about six weeks respectively.

Is it legal?

Experimental xenotransplants have been done under FDA permission, first as individual compassionate-use cases and then within trials cleared in 2025. Rules differ by country.

Will it replace human donors?

That is not established. The more modest hope is a bridge that helps patients survive until a human organ is available, or a supplement to the donor system.

What to remember

Pig organs have been transplanted into living people, and the best kidney results now run to several months. The challenges are rejection, immune suppression and virus risk, and the answer to how well it will work will come from the clinical trials that began in 2025. Heart results have been brief. Claims that pig organs will end the transplant shortage are predictions. For now, this is a promising experiment, not a standard treatment.

Sources