Xenotransplantation

Xenotransplantation (pronounced zee-no-tran-splan-TAY-shin) is when non-human cells, tissues, or organs are used to treat medical conditions in humans. More people need organs than what is available. On average, seventeen people die each day in the United States waiting for an organ transplant. Finding other sources for organs is critical to save lives.

Xenotransplantation is an experimental treatment. It is only allowed in extremely rare and serious cases. The FDA has not yet allowed clinical trials to begin. These trials will be important to show if this procedure is truly safe and effective.

Most research has transferred vital organs, such as the kidney, heart, or liver, from one animal to a different type of animal. Some research has also used animal cells or tissues to treat other serious conditions like epilepsy, chronic intractable pain, Huntington’s disease, Parkinson’s disease, type 1 diabetes, and severe burns. This article will focus on organ transplantation.

Xenotransplantation is a broad term that includes many different treatment methods. For kidney transplants, the general concept is simple – transfer a working kidney from an animal into a person. Pigs are the most promising source of animal kidneys. This is because pigs:

• are widely available
• have kidneys that are similar in size to humans
• have a low risk of transferring disease

The pigs used for this procedure are raised in a laboratory for this purpose. Their genes are edited to better match human genes. This helps lower the risk of rejection in humans. Rejection is when the body attacks the new organ. The person receiving the xenotransplant will still need to take anti-rejection medications.

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. Clinical trials in humans have not yet started. However, a few operations have been done in rare cases with special permission from the FDA and ethics review boards:

• A person without brain function received two kidneys from a pig. Afterward, he was monitored for 74 hours. The kidneys appeared to continue filtering the blood and making urine. Also, the body did not reject the kidneys.
• An additional two people without brain function also received kidneys from pigs. Afterward, they were monitored for 54 hours. These people had similar results - kidneys continued filtering blood, making urine, and no rejection.
• A severely ill man received a heart from a pig. After the surgery, he lived for two more months. His body never rejected the heart. His exact cause of death is unclear. Doctors found a small amount of a pig-specific virus in the heart after he died. This may have been a factor in his death.

These cases show that it is possible to use some animal organs in humans without causing rejection.

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 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, 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 pig kidneys transferred to humans can maintain basic functions. These include filtering waste from the blood and making urine. However, the human kidney has many other important roles. It is not yet clear if transplanted animal kidneys can do all the same things.

Human research is needed to address these concerns. More safety concerns may come up as this research continues, which will also need to be addressed.

Xenotransplantation also raises many ethical issues. Below are some of the key issues that have been identified:

• Patient privacy: People volunteering in this research will be monitored for a long time, possibly for life. This can lead the person to feel like their health is on display for others. Family, friends, and other direct contacts may also need to be monitored if there is concern about an animal infection spreading.
• Psychological harm: Some people may not accept a person’s choice to receive a xenotransplant or engage in this research. Sadly, the patient may experience taunting, bullying, or other abuse from others.
• Fair distribution of organs: Using animal organs can increase the number of organs available for transplant. This can shorten the waitlist and increase the number of lives saved. However, how do we ensure organs are offered to patients fairly? Who decides which patient gets a human kidney and who gets one from a pig?
• Animal welfare: These animals are raised in a laboratory. This sterile environment helps decrease the risk of infection for humans. However, this environment may not support the animal’s overall wellbeing. Also, the animal’s genes are edited to lower the risk of organ rejection in humans. Using animals in this way to benefit humans is an ongoing debate.
• Religious and cultural considerations: The most promising source for animal kidneys is the pig. However, some religions and cultures may have strict rules against humans interacting with pigs. Exceptions to save a person’s life usually exist, but still another topic of ongoing debate.

United States Food & Drug Administration Center for Biologics Evaluation and Research
https://www.fda.gov/vaccines-blood-biologics/xenotransplantation

This content is provided for informational use only and is not intended as medical advice or as a substitute for the medical advice of a healthcare professional.