Pig Kidney Transplant: A Historic Medical Milestone

In March 2024, the medical community witnessed a groundbreaking event that could eventually save thousands of lives. Surgeons at Massachusetts General Hospital performed the first successful transplant of a genetically edited pig kidney into a living human patient. This procedure represents a major leap forward in the field of xenotransplantation and offers new hope for patients suffering from end-stage kidney failure.

The Patient and the Procedure

The recipient of this historic transplant was Richard “Rick” Slayman, a 62-year-old manager at the Massachusetts Department of Transportation. Slayman had been battling Type 2 diabetes and hypertension for years, leading to End-Stage Renal Disease (ESRD). He had previously received a human kidney transplant in 2018, but that organ began to fail five years later, forcing him back onto dialysis.

Dialysis had become increasingly difficult for Slayman due to complications with his vascular access. Facing a long wait for another human donor and diminishing quality of life, his doctors proposed an experimental alternative. On March 16, 2024, a team led by Dr. Tatsuo Kawai and Dr. Nahel Elias performed the four-hour surgery.

The results were immediate and visually striking to the surgical team. Once blood flow was restored to the pig kidney, it turned pink and began producing urine right away. This immediate function is a critical indicator of success in transplant surgery. Slayman recovered well enough to be discharged from the hospital just two weeks later, marking a monumental achievement for the team at Mass General.

The Science: Inside the Genetically Edited Organ

Transplanting an organ from one species to another, known as xenotransplantation, has historically failed because the human immune system immediately recognizes the animal tissue as foreign and destroys it. To overcome this biological barrier, the kidney used in Slayman’s surgery was not an ordinary pig kidney.

The organ was provided by eGenesis, a biotechnology company based in Cambridge, Massachusetts. Scientists at eGenesis used CRISPR-Cas9 gene-editing technology to make 69 specific genomic changes to the donor pig.

Key Genetic Modifications

• Removal of Harmful Genes: The team knocked out three specific pig genes responsible for producing sugars that are toxic to the human body. These sugars usually trigger hyperacute rejection, where the immune system attacks the organ within minutes.
• Addition of Human Genes: They inserted seven human transgenes. These genes help regulate pathways involved in inflammation and blood coagulation, essentially camouflaging the kidney so the human body accepts it.
• Viral Inactivation: One of the biggest risks in xenotransplantation is the potential transfer of animal viruses to humans. The researchers inactivated 59 porcine endogenous retroviruses (PERVs) in the pig’s genome to eliminate the risk of infection.

Addressing the Global Organ Shortage

This breakthrough is significant because of the severe shortage of human organs available for transplant. According to the United Network for Organ Sharing (UNOS), more than 100,000 people in the United States are currently on the waiting list for a lifesaving organ transplant. The vast majority of these patients are waiting for kidneys.

The statistics are grim:

• Roughly 17 people die every day in the U.S. while waiting for an organ.
• The average wait time for a kidney can range from three to five years depending on the region.
• Hundreds of thousands of patients rely on dialysis to stay alive, a treatment that is physically exhausting and costly.

If pig kidneys become a viable option, they could provide an unlimited supply of organs. This would effectively eliminate the waiting list. Doctors envision a future where xenotransplantation serves as a bridge to keep patients healthy while they wait for a human kidney, or perhaps even as a permanent destination therapy.

From Brain-Dead Studies to Living Patients

Before the surgery on Richard Slayman, researchers had only tested pig kidney transplants in non-human primates or in humans who had been declared brain-dead.

In late 2021 and throughout 2022, surgical teams at NYU Langone Health and the University of Alabama at Birmingham connected genetically modified pig kidneys to brain-dead recipients maintained on ventilators. These experiments were crucial. They proved that the human body would not immediately reject the organs and that the kidneys could filter waste effectively for several days or weeks.

However, a living patient presents a much more complex environment. A living patient has an active, dynamic immune system and metabolic needs that a brain-dead host does not. The success of the Mass General surgery provided the first real-world data on how a pig kidney functions in a fully active human body.

Challenges and the Path Forward

While the surgery was a technical success, the path forward involves rigorous scrutiny. Sadly, Richard Slayman passed away in early May 2024, approximately two months after the transplant. Massachusetts General Hospital released a statement clarifying that there was no indication his death was the result of the transplant itself.

Slayman’s bravery has provided scientists with invaluable data. The FDA allowed this specific procedure under the “Expanded Access” protocol, often called “compassionate use.” This rule allows patients with life-threatening conditions to access experimental treatments when no other options exist.

For this to become a standard medical treatment, large-scale clinical trials are necessary. Researchers must determine:

1. Long-term survival rates: Can a pig kidney function for years?
2. Immunosuppression protocols: What specific drug cocktails are best to prevent rejection without leaving the patient too vulnerable to infection?
3. Cost and accessibility: How will insurance providers handle the costs of genetically engineered organs?

The events of 2024 have moved the timeline for xenotransplantation forward by years. What was once viewed as a theoretical possibility is now a clinical reality undergoing active refinement.

Frequently Asked Questions

Why are pigs used for organ transplants instead of monkeys? Pigs are preferred over primates for several reasons. Their organs grow to human size quickly (within six months), they are already raised for food on a massive scale, and there are fewer ethical concerns regarding their use compared to non-human primates. Additionally, pigs can be bred in sterile environments to reduce infection risks.

Did the patient reject the kidney? While Richard Slayman did experience a mild rejection episode roughly a week after surgery, doctors were able to reverse it using standard steroid treatments and adjustments to his medication. The kidney returned to normal function shortly after. Rejection is a common occurrence even in human-to-human transplants.

Is this procedure available to the public now? No. This procedure is still highly experimental. It is not available to the general public or those currently on the transplant waiting list. It will likely take several years of clinical trials and FDA review before it becomes a standard treatment option.

What is the difference between this and the pig heart transplants? The pig heart transplants performed at the University of Maryland Medical Center involved a different organ and slightly different genetic modifications. While both the heart and kidney recipients survived the initial surgeries, the physiology of the kidney is more complex regarding waste filtration and hormone production. Success in kidney transplants is often viewed as a “gateway” to broader xenotransplantation because dialysis exists as a backup if the organ fails, unlike with heart transplants.