Xenotransplantation

Pigs are of particular interest for xenotransplants because the animals are close to human size, are easily raised in captivity, and have large litters. They’re already routined killed for food and they’re less genetically related to humans than nonhuman primates, which reduces disease transmission risks and some researchers’ ethical concerns.

Xenotransplantation can include the insertion of any organ, tissue, cells or fluids from any nonhuman animal into a human. This US Food and Drug Administration graphic about pig-to-human applications shows different possibilities, including the exploration of using pig pancreatic cells for treating diabetes.

The first successful use of a pig heart valve in a human was reported in 1965. This 2015 video details why humans have been able to use pig animal valves for so long with good results and how that differs from what’s needed for whole organ transplants.

Pigs are the current first choice for xenotransplantation procedures, yet such work gives some researchers and animal welfare advocates pause. Concerns include that pigs would have a poor quality of life since the animals must live in a strictly-controlled, hyper-clean environment to avoid risky pathogens.

David Bennett Sr., the world’s first genetically modified pig heart transplant recipient, explained his reasoning to his University of Maryland Medical Center care team in 2022 regarding why he accepted a pig organ: He was dying and ineligible for a human heart transplant so this was a last-ditch effort, he said. He died two months after receiving the heart.

Originally a bacterial defense system against viruses, CRISPR uses guide RNA and a protein called Cas9 to identify and cut specific DNA sequences. Scientists can repurpose this system to switch off faulty genes, insert new ones to treat genetic diseases, or modify organs grown in other animals so that they appear less foreign to a human immune system.

Early reported xenotransplantation attempts included 17th century efforts in France to transfuse blood from animals into humans. The poor results prompted France to issue a xenotransplantation ban. In the 19th century, researchers tried animal-to-human skin grafts from species including sheep, rabbits, dogs, cats, rats, chickens, and pigeons.

In October 2025, Tim Andrews had his gene-edited pig kidney removed because it was no longer working well. He had the transplanted organ for 271 days—surpassing the prior record of a patient who functioned with one for 130 days. Andrews remains on the kidney transplant wait list to receive a donated kidney from a human, but he has a particularly hard-to-match blood type, making it challenging to get the organ.

Ten donated kidneys are thrown away daily even though thousands of people are awaiting a kidney transplant. Listen to a kidney doctor and a 2012 economics Nobel laureate discuss why this happens and how the organ transplantation system may be improved. Transplant centers are penalized for low transplant survival rates, they note, and that contributes to why hospitals may decide certain organs are just too risky to use.

Researchers studying the death of David Bennett Sr., the first gene-edited pig heart transplant patient, discovered potential factors that may have contributed to his demise. One finding is that there was a latent virus, called porcine cytomegalovirus (PCMV), in the pig heart, which may have contributed to dysfunction of the transplant.