Organ Transplants from Pigs to Humans

The medical community is currently witnessing a pivotal shift in transplant medicine. With over 100,000 Americans on the national transplant waiting list and 17 people dying every day while waiting, the supply of human organs simply cannot meet the demand. Xenotransplantation, the process of transplanting organs from animals to humans, has moved from theoretical science to clinical reality. Recent surgeries involving genetically modified pig organs suggest a future where the donor list might become obsolete.

The Recent Breakthroughs in Xenotransplantation

For decades, the idea of using animal organs for humans failed because the human immune system immediately attacked the foreign tissue. However, 2022 through 2024 marked a series of historic milestones that proved this barrier could be broken.

The First Living Kidney Recipient

In March 2024, Massachusetts General Hospital achieved a global first. Surgeons transplanted a genetically edited pig kidney into Richard “Rick” Slayman, a 62-year-old man with end-stage kidney disease. Slayman, who had previously received a human kidney that failed, was facing a difficult future on dialysis.

The surgery was successful, and the kidney began producing urine and filtering waste almost immediately. Slayman was discharged from the hospital two weeks later. While he sadly passed away in May 2024, his medical team noted that there was no indication his death was a result of the transplant. This case provided critical data proving a modified pig kidney could function inside a living human for weeks without hyper-acute rejection.

Heart Transplants at University of Maryland

Prior to the kidney breakthrough, the University of Maryland Medical Center made headlines with cardiac xenotransplantation.

• David Bennett (2022): The first patient to receive a genetically modified pig heart. He lived for two months after the surgery.
• Lawrence Faucette (2023): The second patient to undergo the procedure. He survived for six weeks, engaging with family and undergoing physical therapy before his immune system eventually rejected the organ.

These surgeries were performed under the FDA’s “compassionate use” authorization, which is granted only when a patient has a life-threatening condition and no other treatment options.

The Science: Why Pigs and How It Works

You might wonder why scientists chose pigs over primates, which are genetically closer to humans. The answer lies in biology and logistics. Pigs have organs that are roughly the same size as human organs. They are also easy to breed and reach adult size in just six months, making them a scalable solution for the organ shortage.

The Role of CRISPR and Genetic Editing

A standard pig organ would be rejected by a human body in minutes. To solve this, biotech companies like eGenesis and Revivicor (a subsidiary of United Therapeutics) use CRISPR-Cas9 gene-editing technology to “humanize” the pig organs.

For the kidney transplanted into Rick Slayman, eGenesis performed 69 specific genomic edits:

1. Removing Harmful Genes: Scientists knocked out three genes involved in the production of certain sugars (such as alpha-gal) that trigger immediate immune rejection in humans.
2. Adding Human Genes: They inserted seven human genes that help regulate inflammation and blood clotting, tricking the recipient’s body into recognizing the organ as “self.”
3. Viral Safety: The team inactivated 59 retroviruses embedded in the pig genome (known as PERVs) to eliminate the risk of transmitting animal diseases to humans.

Addressing the Global Organ Shortage

The primary driver for this research is the desperate lack of human donors. In the United States alone, the Health Resources & Services Administration (HRSA) reports that more than 85% of patients on the waiting list need a kidney.

The average wait time for a human kidney can be three to five years. During this time, patients must undergo dialysis multiple times a week. Dialysis is a life-sustaining treatment, but it is physically taxing and only does a fraction of the work a healthy kidney does.

If xenotransplantation becomes FDA-approved for general use, it would effectively create an unlimited supply of organs. This would allow doctors to perform transplants preventatively rather than waiting for patients to reach critical organ failure.

Challenges and Future Outlook

Despite the excitement, significant hurdles remain before you see these procedures in your local hospital.

Rejection and Infection Risks

Even with genetic modification, the human immune system is incredibly efficient at identifying foreign invaders. The deaths of early recipients like David Bennett involved complex factors, potentially including latent viruses or delayed rejection mechanisms that doctors are still learning to manage.

The Path to Clinical Trials

The surgeries performed so far were one-off cases for patients with no other hope. The next step is for companies like eGenesis to launch formal clinical trials. These trials will need to demonstrate that pig organs can keep a human alive and healthy for a significant period—likely a year or more—to be considered a viable alternative to human dialysis or transplantation.

Ethical Considerations

The use of animals for organ harvesting raises ethical questions regarding animal welfare. However, proponents argue that because pigs are already widely raised for food (millions are processed annually in the US alone), raising a smaller number specifically for life-saving medical procedures is ethically justifiable. Strict regulations oversee the housing and care of these medical-grade animals to ensure they are pathogen-free and treated humanely.

Frequently Asked Questions

Are pig transplants available to the public now? No. Currently, these procedures are experimental and only authorized by the FDA for specific, individual emergency cases under “compassionate use.” Formal clinical trials are required before they become a standard treatment option.

Why did the first heart transplant patient die? David Bennett lived for two months. While the exact cause was complex, researchers found evidence of a porcine virus (PCMV) in the heart, which may have contributed to inflammation and heart failure. This prompted stricter screening protocols for subsequent donors.

How much does a genetically modified pig organ cost? There is no set market price yet. However, the cost of a transplant is expected to be high initially but potentially lower than the long-term costs of dialysis, which costs Medicare tens of thousands of dollars per patient every year.

Can you live a normal life with a pig organ? The goal is for recipients to live normal lives. However, like human organ recipients, they will likely need to take immunosuppressant drugs for the rest of their lives to prevent rejection.