Xenotransplantation: Pig Kidney Success

The medical community recently witnessed a historic event that could reshape the future of organ transplants. Surgeons at Massachusetts General Hospital successfully transplanted a genetically edited pig kidney into a living human patient. This breakthrough offers new hope to the hundreds of thousands of patients currently languishing on organ waiting lists.

The Landmark Procedure at Mass General

In March 2024, a surgical team at Massachusetts General Hospital (MGH) in Boston performed a four-hour surgery that marked a world first. The recipient was Richard “Rick” Slayman, a 62-year-old man suffering from end-stage kidney disease. While surgeons had previously tested pig kidneys in brain-dead recipients, Slayman was the first living patient to undergo the procedure with the goal of extending his life.

The surgery was led by Dr. Tatsuo Kawai, the director of the Legorreta Center for Clinical Transplant Tolerance. Following the operation, the medical team reported immediate success. The pig kidney began producing urine and filtering waste products almost immediately, turning pink as blood began to flow through it. This immediate function is a critical indicator of surgical success, as human kidneys from deceased donors often take days to “wake up” and function properly.

Slayman was discharged from the hospital on April 3, 2024, just two weeks after the surgery. He was able to go home without the need for dialysis, marking a significant victory for xenotransplantation.

The Science: Not Just Any Pig

The kidney used in this transplant did not come from a standard farm animal. It was provided by eGenesis, a biotechnology company based in Cambridge, Massachusetts. The organ came from a donor pig that had undergone massive genetic engineering to make it compatible with the human body.

Using the gene-editing tool CRISPR-Cas9, scientists made 69 distinct genomic edits to the donor pig. These modifications were essential to prevent the human immune system from attacking the foreign organ immediately.

Specific Genetic Modifications

The edits performed by eGenesis can be broken down into three specific categories:

• Removing Pig Genes: Three specific genes responsible for producing sugars (glycans) on the surface of pig cells were “knocked out.” These sugars usually trigger a rapid and violent rejection by the human immune system.
• Adding Human Genes: Seven human transgenes were inserted into the pig’s DNA. These genes produce proteins that help regulate inflammation and blood clotting, effectively “camouflaging” the organ so the human body recognizes it as less foreign.
• Viral Inactivation: Perhaps the most extensive editing involved the inactivation of porcine endogenous retroviruses (PERVs). These are viral elements naturally embedded in the pig genome. While harmless to pigs, there is a theoretical risk they could jump to humans. The scientists inactivated 59 of these viral genes to eliminate the risk of infection.

Why This is a Critical Solution

The driving force behind this research is 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 waiting for an organ transplant. The vast majority of these patients are waiting for a kidney.

The statistics highlight a dire reality:

• Roughly 17 people die every day in the U.S. while waiting for an organ transplant.
• The average wait time for a kidney can range from three to five years depending on the region.
• Dialysis, while life-saving, is physically exhausting and expensive, costing the U.S. healthcare system billions annually.

If xenotransplantation becomes a standard medical practice, it could provide an unlimited supply of organs. This would essentially eliminate the waiting list and allow patients to receive a transplant before their health deteriorates significantly.

The Outcome and What Comes Next

While the surgery was a technical success, the long-term results highlighted the complexity of this frontier. Richard Slayman passed away in May 2024, roughly two months after the transplant. However, it is vital to note the statement released by the transplant team: they found “no indication” that the transplant itself was the direct cause of his death. Slayman had a history of Type 2 diabetes and hypertension, which are significant comorbidities.

His survival for two months off dialysis provided invaluable data to researchers. It proved that a genetically modified organ could sustain human life and perform critical biological functions without immediate hyperacute rejection.

The Second Case: Lisa Pisano

Following the MGH success, surgeons at NYU Langone Health performed a similar procedure on Lisa Pisano in April 2024. Pisano faced heart failure and kidney failure. She received a mechanical heart pump and a gene-edited pig kidney (also utilizing a thymic gland transplant to help immune acceptance).

While the organ functioned initially, it had to be removed after 47 days due to poor blood flow related to her heart pump mechanism, rather than outright organ rejection. These early cases are technically “compassionate use” experiments granted by the FDA, meant for patients who have exhausted all other options.

Looking Toward Clinical Trials

Before pig kidneys can become a standard treatment like hip replacements or stents, rigorous clinical trials are necessary. The FDA requires more consistent data from primate studies and these initial human compassionate use cases before approving large-scale human trials.

Biotech companies like eGenesis and Revivicor (which provided the heart for the 2022 David Bennett transplant) are currently working to refine the immunosuppression drug regimens used alongside these organs. The goal is to move from “compassionate use” to Phase 1 clinical trials, which could begin as early as 2025 or 2026.

Frequently Asked Questions

Did the patient’s body reject the pig kidney? In Richard Slayman’s case, he did experience a mild episode of cellular rejection roughly one week after surgery. However, doctors successfully treated this with standard adjustments to his medication, and the kidney continued to function until his death.

Is it safe to use animal organs? The biggest safety concerns are rejection and the transfer of animal viruses (zoonosis). The gene editing performed by eGenesis specifically targets the retroviruses (PERVs) to minimize infection risks. The FDA monitors these procedures closely to ensure public safety.

How much does a pig kidney transplant cost? Because these are currently experimental procedures covered by research grants and hospital funding, there is no commercial price tag yet. However, the cost is expected to be comparable to standard human transplants eventually, potentially saving money long-term by removing the high costs of ongoing dialysis.

When will this be available to the general public? It will likely take several years. Researchers need to prove that these organs can last for years, not just months. If clinical trials proceed smoothly, limited availability for high-risk patients could occur within the next decade.