For people with end-stage kidney disease, a kidney transplant can offer a life beyond the exhausting routine of dialysis. But there is one major problem: there are not enough human donor kidneys to meet demand. A remarkable new case from the US is now raising the possibility that a genetically modified pig kidney could one day help bridge that gap.

Tim Andrews, who was 66 when he underwent the experimental procedure, lived for 271 days without dialysis after receiving a genetically edited pig kidney in January 2025. When the animal kidney eventually failed, doctors removed it and Andrews returned temporarily to dialysis. In January 2026, he received a dead-donor human kidney.

The case, reported by researchers from Massachusetts General Hospital and colleagues in The Lancet, is significant for two reasons. It represents the longest reported dialysis-free survival following a pig-kidney xenotransplant in a living person and, for the first time, demonstrates that such a transplant can act as a "bridge" to a subsequent human kidney transplant.

The development does not mean pig kidneys are ready to replace human donor organs. But it marks an important step in a field that has struggled for decades with immune rejection, infection risks and organ durability.

What happened to Tim Andrews?

Andrews had end-stage kidney disease and faced a difficult wait for a suitable human kidney. He received a kidney from a genetically modified Yucatan miniature pig under an FDA Expanded Access Investigational New Drug application.

The transplanted kidney began functioning immediately. Andrews did not require dialysis for 271 days, giving him several months free from a treatment that normally has to be performed repeatedly each week in patients with kidney failure.

The pig kidney was eventually removed after its function deteriorated. Researchers found microvascular injury and inflammation in the graft. Immunosuppression had also been reduced after about six months because Andrews developed an infection, an important factor in understanding the eventual graft failure.

Andrews subsequently spent a period back on dialysis before receiving a dead-donor human kidney in January 2026. Importantly, the human kidney functioned immediately, and follow-up found no evidence that the earlier pig transplant had sensitised him against the human organ. No pig-derived pathogens were detected.

Why use a genetically edited pig kidney?

Pig organs are being studied because their size and physiology make them comparatively suitable for human transplantation. The major obstacle is the human immune system, which recognises a pig organ as foreign and can mount a powerful rejection response.

Scientists therefore modify the pig's genome before transplantation.

The kidney used in this programme carried 69 genomic edits. Three major pig glycan antigens that can trigger human antibody responses were removed; seven human genes were introduced to make the organ more compatible with the human immune system; and porcine endogenous retroviruses (PERVs) were inactivated to reduce the risk of pig-to-human viral transmission.

Earlier research published in Nature showed that kidneys from pigs carrying these modifications could provide prolonged kidney function in non-human primates, supporting their progression towards human studies. The approach is therefore not simply about transplanting an ordinary pig kidney. It involves combining gene editing, intensive immunosuppression, infection surveillance and highly controlled donor-animal conditions.

Why 271 days matters

This is not the first pig kidney to be transplanted into a human. In March 2024, Massachusetts General Hospital performed the world's first transplant of a genetically edited pig kidney into a living human recipient. That patient survived 52 days before dying from cardiac causes unrelated to the kidney; the transplanted organ was functioning at the time.

Another major milestone came in 2025, when a gene-edited pig kidney functioned in a living recipient for 271 days. The new Lancet report adds something particularly important: the kidney was not merely able to sustain life temporarily. It successfully served as a bridge until a human donor kidney became available.

That distinction could matter enormously if xenotransplantation eventually becomes clinically available.

Could pig kidneys reduce the need for dialysis?

That is one of the biggest potential advantages. Kidney transplantation generally provides better survival and quality of life than remaining on dialysis, according to the WHO. Yet shortages of donor organs mean many patients spend prolonged periods waiting while continuing dialysis.

The WHO says more than 150,000 solid-organ transplants are performed globally each year, representing less than 10% of estimated global need. It also identifies xenotransplantation as one of the approaches being investigated to address organ shortages, while stressing that animal organs are not yet a replacement for human donation.

India faces the same fundamental problem. According to the National Organ and Tissue Transplant Organisation (NOTTO), India recorded 18,911 organ transplants in 2024, including 3,403 involving dead donors. Kidney transplantation accounted for 10,140 procedures in January-September 2024 alone, with the majority coming from living donors. 

A reliable supply of genetically engineered pig kidneys could, in theory, provide an additional source of organs, either as a long-term transplant or, more immediately, as a temporary solution while a patient waits for a human kidney.

What are the remaining concerns?

The biggest question is durability. Andrews' experience shows that a genetically engineered kidney can function for many months, but it also demonstrates that maintaining the organ over the long term remains difficult. Microvascular injury and inflammation ultimately led to graft failure. Researchers say the case provides clues for improving gene editing, immunosuppression and monitoring.

There are also concerns about infection, immune rejection, the long-term effects of immunosuppressive drugs and whether results seen in a handful of highly selected patients can be reproduced in larger populations.

The evidence is still extremely limited. Andrews represents one patient, without a comparison group, and the transplant was performed under intensive specialist monitoring. The researchers themselves emphasise that further clinical trials are required before xenotransplantation can become routine care. 

The significance of the Tim Andrews case lies less in the idea of a "pig kidney replacing a human kidney" and more in what it demonstrates about the future of transplantation.

For 271 days, a genetically edited animal kidney performed enough of the work of a human kidney to keep a patient with end-stage kidney disease off dialysis. When a human organ eventually became available, the patient was able to transition successfully to it.

That makes xenotransplantation potentially more than a scientific curiosity. It could become a bridge between kidney failure and a human transplant, if researchers can make these organs safer, more durable and reliably compatible with the human immune system. For now, however, human organ donation remains indispensable. The pig kidney may eventually help close the gap, but it has not yet eliminated it.

Read More: Putting Pig Organs In People Is OK In The US, But Growing Human Organs In Pigs Is Not - Why Is That?



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