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The short version

  • Tim Andrews survived nine months with a genetically edited pig kidney, setting a new duration record for xenotransplantation and avoiding dialysis during that period.
  • The experimental organ failed due to vascular damage following an MRSA infection, but it successfully kept the patient alive until a human donor kidney became available.
  • Researchers report no evidence that prior exposure to pig organs negatively impacts subsequent acceptance of human kidneys, validating the bridge-to-transplant strategy.

A genetically modified pig kidney has sustained a human patient for nine months, marking the longest duration recorded for such an experimental procedure. The case involves Tim Andrews, a 68-year-old resident of New Hampshire who suffered from end-stage kidney disease. Before the transplant, Andrews relied on dialysis to filter waste from his blood, a treatment that severely limited his mobility and energy levels. He volunteered for the high-risk procedure at Massachusetts General Hospital in Boston, viewing it as a final opportunity to contribute to medical science despite his poor prognosis.

In January 2025, surgeons implanted a kidney from a Yucatan miniature pig into Andrews. The donor animal had undergone 69 specific genetic edits designed to minimize the risk of transmitting porcine viruses and to reduce the likelihood of immune rejection by the human host. Following the surgery, Andrews reported significant improvements in his quality of life. He was able to walk freely without being tethered to medical equipment and experienced a return of energy that had been absent for years.

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The transplant maintained function for 271 days, allowing Andrews to remain off dialysis during this critical waiting period. However, complications arose approximately six months post-surgery when he contracted a bacterial infection caused by methicillin-resistant Staphylococcus aureus, commonly known as MRSA. To combat the infection, medical staff reduced his immunosuppressive medications, which are essential for preventing organ rejection. This adjustment inadvertently led to damage in the blood vessels of the pig kidney, eventually resulting in organ failure.

Despite the eventual loss of the animal organ, medical teams consider the intervention a success because it bridged the gap between dialysis dependence and human transplantation. After the pig kidney was removed, Andrews returned to dialysis for three months. In January 2026, he received a donated human kidney. He has since resumed active pursuits including swimming, cycling, kayaking, and fishing, expressing gratitude for the additional time gained through the experimental procedure.

This case follows an earlier attempt in March 2024, when surgeons at the same hospital transplanted a genetically modified pig kidney into Richard Slayman, a 62-year-old man with end-stage kidney disease. Slayman passed away 52 days after the procedure due to cardiac issues that appeared unrelated to the transplant itself. The contrast between these two cases highlights both the potential and the unpredictability of xenotransplantation as a clinical strategy.

Leonardo Riella, the lead author of the study published in The Lancet and medical director for kidney transplantation at Mass General Brigham, described the nine-month survival as remarkable. While the pig kidney did not serve as a permanent solution, it carried the majority of the waiting time required before a human organ became available. This outcome validates the concept that animal organs can effectively extend patient survival during periods of donor scarcity.

David Mulligan, a surgeon at Yale School of Medicine who was not involved in the research, noted that the case proves the feasibility of using pig kidneys as temporary measures. The broader implication is that xenotransplantation could alleviate pressure on the national transplant waiting list, which currently includes nearly 110,000 individuals in the United States alone. Kidneys are a particularly urgent target due to the disruptive nature of dialysis and the high demand for donor organs.

Since Andrews’ procedure, Riella’s team has performed five additional pig kidney transplants. One patient, whose case is pending publication, has already exceeded the nine-month benchmark set by Andrews. These accumulating data points suggest that temporary exposure to pig organs does not adversely affect a patient’s ability to accept a human kidney later. Mike Curtis, president and CEO of eGenesis, which developed the genetically modified organs used in these trials, stated that initial concerns about cross-reactivity have not materialized.

The success of these bridge transplants offers a potential pathway for managing the global organ shortage. By keeping patients stable and healthy while they wait for human donors, xenotransplantation could reduce mortality rates among those on waiting lists. As more data emerges from ongoing trials, researchers aim to refine genetic editing techniques to further improve organ longevity and safety profiles.

Andrews’ experience underscores the personal stakes involved in medical innovation. His willingness to participate in an experimental trial with uncertain outcomes has contributed valuable insights into the viability of xenotransplantation. The medical community continues to monitor long-term effects and seek ways to mitigate risks such as infection and vascular damage, aiming to make this technology a standard option for patients in critical need.

Sources behind this briefing

Go to the original reporting

  • Smithsonian Magazine↗A Genetically Modified Pig Kidney Kept a Man Alive for a Record Nine Months, Allowing Him to Wait for a Donated Human Organ