A patient with end-stage kidney disease has become the first known person to receive a human kidney after previously living with a genetically engineered pig kidney. The case offers new evidence that animal organs could one day serve as temporary support for patients waiting for a suitable human donor.
Tim Andrews remained dialysis-free for 271 days after receiving a pig kidney at Massachusetts General Hospital. When the experimental organ eventually failed, it was removed. He returned to dialysis briefly before receiving a deceased-donor human kidney 82 days later.
The details, published in The Lancet’s first-in-human study, show that the human kidney functioned immediately and that the earlier xenotransplant did not appear to interfere with the subsequent procedure.
Table of Contents
First Patient to Move From Pig to Human Kidney
Andrews, from Concord, New Hampshire, was 66 when surgeons transplanted the pig kidney on January 25, 2025. He had end-stage kidney disease and had spent more than two years undergoing dialysis.
His chances of receiving a human kidney quickly remained limited. Andrews had no suitable living donor, and his type O blood group made finding a compatible deceased donor more difficult. He had also experienced significant health complications, including a heart attack in July 2023.
According to the Harvard Medical School report on the case, Andrews is the first documented xenotransplant recipient to progress successfully to a human kidney transplant.
Pig Kidney Provided 271 Days Without Dialysis
The transplanted pig kidney began functioning immediately, allowing Andrews to stop dialysis for the first time in more than two years. He was discharged from the hospital one week after the operation.
For Andrews, the procedure meant more than improved laboratory results. It temporarily removed the exhaustion, scheduling demands and physical strain associated with regular dialysis. The kidney supported him for 271 days, representing the longest peer-reviewed period of dialysis-free survival following a pig-kidney transplant in a living person at the time of the report.
The procedure was performed under the FDA’s Expanded Access pathway, which permits patients with serious or life-threatening conditions to receive investigational treatments when comparable alternatives are unavailable.
How the Pig Kidney Was Genetically Engineered
The kidney was provided by biotechnology company eGenesis and came from a pig carrying 69 genomic modifications. Researchers used CRISPR-based editing to make the organ more compatible with the human body.
Three pig genes responsible for producing carbohydrate antigens were disabled. These antigens can cause the human immune system to attack pig tissue almost immediately.
Scientists also inserted seven human genes intended to regulate immune responses, inflammation, blood clotting and other interactions between the organ and the recipient’s bloodstream. Copies of porcine endogenous retroviruses embedded in the pig’s genome were inactivated to reduce concerns about animal-to-human viral transmission.
Despite these changes, the kidney was still biologically foreign. Andrews, therefore, required powerful immunosuppressive medicines and extensive medical monitoring.
Doctors Successfully Treated Early Rejection
A biopsy conducted 14 days after transplantation identified T-cell-mediated rejection. This occurs when immune cells recognise transplanted tissue as foreign and start attacking it.
Doctors treated the episode, and the kidney continued working for several months. Andrews was closely monitored for declining renal function, antibody development, rejection and possible transmission of pig-derived microorganisms.
Researchers reported that no pig pathogen was detected in the patient. While encouraging, that result reflects the experience of a single individual and does not establish the broader infectious safety of xenotransplantation.
The kidney’s continued function after early rejection nevertheless showed that an immune attack on a pig organ can, under certain circumstances, be controlled.
Why the Experimental Kidney Eventually Failed
The pig kidney remained relatively stable for approximately six months. Andrews then developed a bacterial infection, forcing doctors to reduce his immunosuppressive treatment.
Reducing the medication helped address the immediate infection risk but left the transplanted organ more exposed to immune injury. Inflammation subsequently appeared in the kidney’s smallest blood vessels.
The damage progressed to thrombotic microangiopathy, a condition involving injured blood-vessel linings and microscopic clots. As the vascular injury worsened, the kidney gradually lost its ability to function.
Doctors ultimately removed the organ after 271 days, and Andrews temporarily returned to dialysis. The failure highlighted a central challenge facing xenotransplantation: preventing rejection while avoiding dangerous levels of immune suppression.
Human Kidney Worked Immediately After Transplant
Eighty-two days after the pig kidney was removed, Andrews received a human kidney from a deceased donor. The new organ began functioning immediately.
Doctors were particularly concerned about sensitisation. Exposure to foreign tissue can cause a recipient to develop antibodies that attack future donor organs, potentially making it harder to find a compatible human kidney.
However, researchers found no evidence that the pig kidney had produced sensitisation that could undermine the human transplant. The new kidney continued functioning during 231 days of reported follow-up.
This outcome suggests that receiving a pig kidney does not necessarily disqualify a patient from later receiving a human organ, a critical requirement if xenotransplantation is to be used as temporary support.
Pig Kidneys Could Become a Bridge for Patients
The case does not demonstrate that pig kidneys are ready to permanently replace human organs. Instead, it supports a more immediate possibility: using them as a bridge between kidney failure and conventional transplantation.
A genetically engineered pig kidney could free selected patients from dialysis while they remain on the waiting list for a human donor kidney. Such an approach could improve daily life and provide additional time for a suitable organ to become available.
The need remains substantial. The US federal transplant system continues to report a major gap between the number of patients requiring organs and the number available. Kidneys account for most transplant demand.
What Comes Next for Xenotransplantation
Andrews’ case is an important clinical milestone, but it remains a single-patient study. Researchers must determine whether they can safely reproduce similar results across larger groups with different ages, medical histories, and immune profiles.
Future studies will need to improve immunosuppressive strategies, limit microvascular injury and establish the long-term risk of infection. Scientists must also determine whether further genetic modifications can help pig kidneys survive for years rather than months.
For Andrews, the experimental kidney was not a permanent solution. It did, however, provide nine months without dialysis and carried him safely to a functioning human transplant. That successful transition may be one of xenotransplantation’s most practical early uses.
