Genetically Modified Pig Kidney Works in US Man for Record 271 Days, Offering New Hope for Organ Transplants

By Michael Isa · Published September 4, 2026

A genetically modified pig kidney has functioned inside a US man for a record 271 days, marking a breakthrough in xenotransplantation and offering fresh hope to thousands of patients waiting for human donor organs.

Tim Andrews, who had end-stage kidney disease, received the genetically engineered pig kidney at Massachusetts General Hospital in January 2025. The organ continued to provide sufficient kidney function for about nine months, allowing him to remain dialysis-free while he waited for a human kidney.

The milestone, documented by researchers at Mass General Brigham and published in The Lancet, represents the longest dialysis-free survival reported following a pig-kidney transplant in a living human. Andrews also became the first reported patient to move successfully from a pig-kidney transplant to a subsequent human kidney transplant. (Mass General Brigham News)

How Did a Pig Kidney Work Inside a Human?

The achievement was made possible by extensive genetic engineering.

Ordinary pig organs are not compatible with the human immune system. Without modification, a transplanted pig kidney would be attacked rapidly by the recipient's immune system, potentially causing catastrophic rejection.

The kidney used for Andrews was developed by biotechnology company eGenesis and carried 69 genetic edits. These modifications were designed to overcome some of the major biological barriers that have historically prevented animal organs from being safely transplanted into humans. (eGenesis)

The genetic modifications fell into three broad categories.

First, scientists removed three pig genes responsible for producing sugar molecules that can trigger powerful human immune reactions. Eliminating these targets helps reduce the risk of hyperacute rejection, in which the recipient's immune system can destroy a transplanted organ almost immediately.

Second, researchers inserted seven human genes designed to improve compatibility between the pig kidney and the human body. These genes help regulate immune responses, inflammation, blood clotting and other biological processes involved in transplant rejection.

Third, scientists inactivated porcine endogenous retroviruses, or PERVs, embedded in the pig genome. The goal is to reduce the possibility of viruses being transmitted from the animal organ to the human recipient.

Together, these modifications essentially transformed the pig kidney into a much more human-compatible organ.

The Kidney Allowed Andrews to Escape Dialysis

For patients with end-stage kidney disease, dialysis can become a regular and demanding part of life. The treatment filters waste and excess fluid from the blood when the kidneys can no longer perform that function adequately.

Andrews had been dependent on dialysis before receiving the pig kidney. The xenotransplant provided functioning kidney tissue and allowed him to live without dialysis for 271 days.

For researchers, this is particularly significant because xenotransplantation does not necessarily have to replace human transplantation immediately. Instead, genetically modified animal organs could initially serve as a temporary bridge for patients waiting for a human donor.

That approach could potentially give patients additional time while protecting them from prolonged dialysis and its associated burdens. Mass General Brigham describes Andrews' case as evidence that genetically engineered pig kidneys may be able to sustain kidney function while preserving the possibility of a later human transplant.

Why Did Pig Kidney Eventually Fail?

Despite its record performance, the pig kidney was not a permanent solution.

After functioning for 271 days, the kidney's performance began to decline, and surgeons removed it on October 23, 2025. Earlier reports said doctors observed signs of rejection during the transplant period, but these were treated by adjusting Andrews' immunosuppressive medication.

Later, damage developed in the kidney's blood vessels, accompanied by inflammation and declining function. Researchers reported that there was no clear evidence that antibodies were directly attacking the organ, leaving the precise reason for its eventual failure unresolved. (Punch Newspapers)

After the pig kidney was removed, Andrews returned to dialysis for 82 days before receiving a human donor kidney in January 2026. The human kidney subsequently functioned well, making his case particularly important for researchers studying xenotransplantation as a bridge to conventional transplantation.

A Potential Solution to Organ Shortage

The significance of Andrews' experience extends beyond a single patient's treatment.

Kidneys are among the most sought-after organs for transplantation, while the number of available human donors remains far below demand. In the United States, more than 90,000 people have been reported to be on the kidney transplant waiting list, while only around 25,000 kidney transplants are performed annually.

This gap means some patients spend years waiting for a suitable organ. For people whose health deteriorates while waiting, the shortage can have devastating consequences.

Genetically modified pigs could potentially provide a more readily available source of transplantable organs because pigs can be bred and their organs prepared under controlled conditions.

The technology, however, remains experimental. Researchers still need to establish whether pig kidneys can function safely and reliably for much longer periods, whether complications can be consistently controlled and whether the approach can ultimately become suitable for widespread clinical use.

The Next Stage of Pig-to-Human Transplants

The field is now moving toward larger clinical studies.

eGenesis has announced that the US Food and Drug Administration has cleared a Phase 1/2/3 clinical trial known as RESTORE, involving 33 patients with kidney failure who are between 50 and 70 years old and waiting for a human donor kidney. The company expects the study to begin in the first quarter of 2027.

Meanwhile, researchers have already reported additional patients receiving genetically engineered pig kidneys, suggesting that science is progressing beyond isolated experimental cases.

Interestingly, Andrews' 271-day record has already been surpassed by another patient: eGenesis reported that a woman receiving a genetically engineered pig kidney at Massachusetts General Hospital has remained dialysis-independent for more than nine months. This means Andrews' record is already being challenged as researchers push toward longer-lasting xenotransplants.

What the Breakthrough Means for the Future

Tim Andrews' experience does not mean pig kidneys are ready to replace human donor kidneys. Instead, it demonstrates something potentially more important: a genetically engineered animal organ can sustain a human being for an extended period while keeping open the possibility of a later human transplant.

For patients facing years of dialysis and uncertain waiting times, that could eventually become a transformative option.

The 271-day milestone therefore represents more than a record. It is evidence that decades of research into xenotransplantation, genetic engineering and transplant immunology may finally be moving toward a practical solution to one of medicine's most persistent problems, the shortage of human organs.

If future trials demonstrate that these organs can remain functional for a year or longer with manageable risks, genetically modified pig kidneys could become an important part of the global transplant system.

For now, Andrews' case stands as a landmark in the journey from experimental animal-to-human transplantation toward a future in which an organ shortage may no longer determine how long a patient must wait for a chance at a new life.