Bridge to human transplant

A 66-year-old American patient with end-stage renal disease lived for 271 days without dialysis using a genetically modified pig kidney before receiving a human donor organ. Tim Andrews developed terminal kidney failure following type 2 diabetes and entered an experimental protocol authorized by the US Food and Drug Administration at Massachusetts General Hospital in Boston. Details of the procedure, led by Dr. Leonardo V. Riella, were published on 3 September 2026 in the medical journal The Lancet. Andrews faced an estimated seven-year wait for a compatible human kidney, while the average life expectancy for patients on dialysis is five years.

Andrews described the procedure as a path toward regaining daily autonomy away from dialysis equipment.

“Hope is the most important thing of all, a chance to get off that machine and live your life.”

Clinical course and complications

Surgeons transplanted the porcine organ in January 2025 from a miniature pig bred in a pathogen-free facility. Scientists introduced 69 genetic modifications into the animal genome to suppress human immune rejection and deactivate endogenous porcine viruses. The organ began functioning immediately after surgery. Two weeks into recovery, Andrews experienced a mild T-cell-mediated cellular rejection episode, which clinicians managed by adjusting immunosuppressive medications. The kidney maintained normal blood filtration for six months until complications emerged following a bacterial infection.

To treat the infection, physicians reduced immunosuppressive dosages, which contributed to microvascular inflammation, tissue clotting, and thrombotic microangiopathy. The xenograft failed after 271 days of function and was surgically removed in October 2025. Andrews returned to dialysis for 82 days until an allograft from a deceased human donor became available in January 2026. The human kidney functioned immediately, and 231 days of follow-up observation showed no pre-existing immune sensitization from the pig kidney and no transmission of porcine pathogens.

Addressing the donor shortage

The trial demonstrated the feasibility of using porcine organs as a temporary bridge to keep patients alive and healthy enough for subsequent allotransplantation. In the United States, approximately 100,000 people are currently registered on kidney transplant waiting lists, but surgeons perform only about 25,000 kidney transplants annually. In the United Kingdom, more than 7,000 patients await kidney donations. For Andrews, physicians estimated a 9% probability of receiving a human kidney within five years, compared to a 40% probability of dying or being removed from the list.

The 271-day duration exceeded a previous xenotransplantation in 2024, in which a 53-year-old American woman survived over two months with a genetically edited pig kidney. Pigs serve as the primary animal model for xenotransplantation because their organs match human physiological dimensions and breeding can occur in controlled, pathogen-screened environments.

Patients on waitlist100,000

Transplants performed per year25,000

Patients on waitlist

100000 patients

Transplants performed per year

25000 patients

Data from the article text

Dr. Leonardo Riella noted the broader objective of developing alternatives for patients facing long transplant queues.

“We are working hard to provide hope and we firmly believe that xenotransplantation can offer an alternative for patients who do not have a living donor.”