Kidney Xenotransplantation

Kidney xenotransplantation (pronounced zee-no-trans-plan-TAY-shin) is a procedure of transplantating a genetically-modified pig kidney, also known as a xenokidney, into a human recipient.

The demand for donor kidneys far exceeds supply. Over 90,000 people in the U.S. are waiting for a kidney transplant. Kidneys from pigs could be a new source of organs, offering faster access to life-saving transplants.

Kidney xenotransplantation is currently an experimental treatment. It has only been approved in extremely rare and serious cases. 

In 2025, after decades of research, the U.S. Food and Drug Administration (FDA) approved the first human clinical trials to begin. Trials will be important to show if this procedure is truly safe and effective for treating kidney failure.

• Pig kidneys are similar in size and function compared to human kidneys.
• Pig kidneys may be able to fulfill many of the same functions as the human kidney (this will be further explored in clinical trials)
  • Remove natural waste products and extra water from the body
  • Help maintain your blood pressure
  • Balance important vitamins and minerals
• The pig kidney is expected to last about 30 years. This is similar to an allotransplant (human donor kidney)

Pig kidneys used for kidney xenotransplantation are genetically modified. This means changing the genes of the pig so the organs can work more safely in a human body. It also lowers the risk of organ rejection. This is done before the pig is born, and the pigs are then raised in highly controlled, clean environments.

Genetic modification helps by:

• Removing pig genes that cause strong immune reactions in humans
• Adding human genes that make the xenokidney look more "friendly" to the immune system
• Eliminating viruses that pigs naturally carry, which could be risky for humans

Clinical trials, beginning in 2025, will be a slow and steady process to ensure this is a safe and effective treatment for people with kidney failure.

Clinical trials will begin with a very small group of patients. As more data is collected, these trials may expand to larger numbers of patients.

It is not yet known if and when kidney xenotransplantation will be more widely available.

There will be multiple sites conducting the first trials, including:

• Massachusetts General Hospital
• New York University – Langone
• Johns Hopkins

The list may expand as trials progress

Many studies have been done in animals over the past several decades. Most of these studies transferred pig organs into baboons. Baboons are used because they have a genetic makeup that is very close to humans. These studies showed that transplanting organs across animal species is possible. 

The FDA has allowed clinical trials in humans to begin in 2025. Before this step could happen, a few operations were done with special permission from the FDA and ethics review boards. These early cases have shown kidney xenotransplant to be a promising path forward and worth studying in clinical trials.

Clinical trials will show us if kidney xenotransplantation is safe for humans. There are known and unknown risks that will be better understood with these trials.

The most common safety concerns are:

• Infection risk: All transplants come with the risk of infection. Many steps are taken to lower this risk as much as possible. The risk of infection from an animal organ - called zoonotic (pronounced zow-uh-naa-tuhk) infection - may be higher than the risk from a human organ. This is because the organ may contain animal-specific germs. The risk of these germs spreading among humans is also a serious concern.
• Organ rejection: All transplants also come with the risk of the body rejecting the new organ. Transplants from animals have a higher risk because animals have a different genetic code. To lower this risk for xenotransplanted organs, researchers make small changes to the animal’s DNA to better match human genes. Finding the right genetic code to prevent rejection and the long-term impact of these gene edits are important.
• Fulfilling all the kidney’s roles: Early evidence shows that xenokidneys can maintain basic functions. These include filtering waste from the blood and making urine. However, the human kidney has many other important roles. Clinical trials will explore whether the xenokidney can replace all of these important functions.