Pig-kidney transplants enter clinical trials: first patient treated in the EXPAND study

On 3 November 2025 United Therapeutics announced that the first transplant in the EXPAND clinical trial had been performed at NYU Langone Health in New York, by a team led by surgeon Robert Montgomery. The patient received a kidney from a pig with ten gene edits: six human genes added to help the body accept the organ, and four pig genes inactivated to reduce the risk of rejection and limit organ growth.

Why it matters

Earlier pig-kidney transplants in living patients were done one by one, under the FDA's expanded access programme. EXPAND is a formal trial that combines phases 1, 2 and 3 and is meant to support an application for FDA approval. The first stage includes six transplants at two centres; participants are 55 to 70 years old, have been on haemodialysis for at least six months and have no other severe illnesses. Each patient is followed for 24 weeks and then for life, including for infections passed on from the animal. In September 2025 the FDA also cleared a similar trial by eGenesis, for patients aged 50 or older who depend on dialysis and are on the transplant waiting list.

What happened to earlier patients

At Massachusetts General Hospital (MGH), Tim Andrews, aged 66, received a gene-edited pig kidney from eGenesis on 25 January 2025. According to a paper published in The Lancet in September 2026, the kidney worked for 271 days without the patient needing dialysis, the longest period reported so far. The organ then developed small-vessel injury and inflammation and lost function; in January 2026 the patient received a kidney from a deceased human donor. No transmission of pig pathogens was detected. A second MGH patient, Bill Stewart, had surgery on 14 June 2025 and went home a week later.

At NYU Langone, the pig kidney of a woman transplanted in November 2024 was removed in April 2025 after it stopped working properly because of complications from an unrelated infection; she returned to dialysis.

What it means for patients

The pig kidney remains an experimental treatment, offered in US clinical trials with strict entry criteria. Long-term durability, the causes of late graft loss, the best immunosuppression regimen and the infection risk are still unknown. The authors of the Lancet paper describe xenotransplantation, for now, as a possible "bridge" to a human kidney; safety and durability must be shown before it can become a long-term solution.