Can Pig Organs Save Human Lives?

A kidney began filtering blood inside a 62-year-old man at Massachusetts General Hospital in March 2024. The organ did not come from another human but from a genetically engineered Yucatan miniature pig. The surgery was the first transplant of a gene-edited pig kidney into a living human. The donor kidney contained 69 genomic modifications intended to improve its compatibility with the human body. The procedure marked a major step towards making xenotransplantation—the transplantation of cells, tissues, or organs between species—a viable clinical treatment beyond just experimental research.

The reason for pursuing xenotransplantation is simple: there are not enough human organs for everyone who needs one. A healthy kidney needs to filter waste from the blood, regulate water and electrolytes such as sodium and potassium, and help maintain the body’s chemical balance. This makes kidney failure, a condition in which the kidneys can no longer adequately filter their blood, especially significant because patients are often forced to depend on dialysis while waiting for a transplant. Dialysis is a process that removes waste products and excess fluid from the blood, but it requires repeated treatment, can be extremely costly over time, and does not fully replace every function of a healthy kidney. The shortage of donor organs can leave patients waiting while their health deteriorates. Therefore, researchers hope that pigs could eventually provide a more predictable supply of kidneys rather than making patients depend entirely on the limited supply of available human organs.

Pigs are promising donors partly because their kidneys are similar to human kidneys in both size and function. A transplanted kidney must take over the regulatory functions of a healthy human kidney, making this functional similarity especially important. Recent pig-to-human transplants have shown that genetically modified pig kidneys can maintain electrolytes, minerals that help regulate fluid balance, within the ranges required by the human body. The more difficult part, though, is convincing the human immune system not to attack the organ. 

Pig cells carry molecules on their surfaces that human antibodies recognize as foreign. Without genetic modification, these differences can cause hyperacute rejection, an extremely rapid immune response that can destroy a transplanted organ soon after blood begins flowing through it. Modern gene editing allows researchers to modify donor pigs before transplantation by removing pig genes associated with immune incompatibility and inserting human genes intended to improve compatibility with the recipient.  

CRISPR-Cas9, a gene-editing tool that allows scientists to alter specific sections of DNA, has made it possible to perform numerous genetic changes in the same donor animal. In the kidney transplanted at Massachusetts General Hospital in 2024, scientists deleted three major pig glycan antigens, inserted seven human genes, and inactivated porcine endogenous retroviruses (PERVs) as part of 69 genomic modifications. These changes target some of the major biological risks of xenotransplantation. Glycan antigens are carbohydrate structures on cell surfaces that can attract an immune response, and PERVs are viral sequences naturally present in pig DNA. Researchers monitor them because retroviruses from animal donors are a potential source of cross-species infection in xenotransplantation.

However, not every research group uses the same genetic strategy. In November 2025, NYU Langone Health announced the first surgery in its EXPAND clinical trial, which tested gene-edited pig kidneys in patients with end-stage kidney disease. The trial used a pig kidney called the UKidney, which came from a pig with 10 edits: six human genes were added, and four pig genes were inactivated to reduce rejection risk and moderate organ growth. By comparison, the kidney used in the 2024 Massachusetts General Hospital transplant had 69 edits, including seven inserted human genes. One of these genes, CD46, helps regulate the complement system, a part of the immune system that can attack foreign cells and contribute to organ rejection. The contrast between 69 edits and 10 edits demonstrates that scientists are still determining which genetic changes are necessary for a pig organ to function safely over the long term.

Gene editing, however, does not entirely prevent rejection. The recipient of the 2024 Massachusetts General Hospital pig kidney developed T-cell-mediated rejection within the first week after transplantation. T-cells are immune cells that recognize and attack cells they perceive as foreign. After researchers intensified the patient's immunosuppressive treatment, the rejection episode responded to therapy, although innate immune activation persisted. 

That creates a second challenge: patients need powerful immunosuppressive drugs to keep their immune systems from attacking the transplanted kidney. Immunosuppression protects the organ, but weakening the immune response can leave a patient more vulnerable to infection. Xenotransplantation raises an additional concern known as zoonotic infection, in which an infectious agent passes from an animal to a human. The FDA warns that xenotransplantation could expose recipients to both known and previously unrecognized infectious agents, including retroviruses that may remain inactive before causing disease later. Researchers therefore raise donor pigs in controlled environments, screen them for pathogens, genetically mitigate some of the viral risks, and closely monitor transplant recipients. So far, researchers involved in the Massachusetts General Hospital program report that their monitoring protocols have not detected pig-derived infections in their xenotransplant recipients.

Despite these challenges, the field has now moved into formal clinical trials. NYU Langone’s EXPAND study is designed to evaluate the safety and effectiveness of gene-edited pig kidneys in patients with end-stage kidney disease. Trial participants are monitored for kidney function, survival, quality of life, rejection, and infection. After transplantation, participants undergo an initial 24-week follow-up and then continue to be monitored for the rest of their lives for results including kidney function and zoonotic infections. As of July 2026, two formal pig-kidney clinical trials are underway, marking a shift from isolated experimental surgeries to more organized clinical research. 

The central question, therefore, is no longer whether a pig kidney can function inside a person. Researchers now need to know how long it can function, if rejection can be controlled without dangerously suppressing the immune system, and if unexpected infections or other complications might emerge over time. Xenotransplantation also raises several ethical questions about breeding genetically modified pigs for use as organ donors, and which patients should receive an experimental kidney rather than remain on dialysis or wait for a human organ.

For now, a pig kidney is not the perfect replacement for a healthy human donor kidney. Researchers do not have enough long-term evidence to know whether these organs may function safely for years. That is why current research is comparing pig-kidney transplantation with dialysis, especially for patients who may not receive a human kidney in time. If genetically engineered pig kidneys prove to be durable and safe, xenotransplantation could one day shift reliance away from the limited donor supply and toward a more predictable source of organs.