Mass General Performs Second Pig Kidney Transplant as FDA Clears Trials

A 54-year-old man from New Hampshire is recovering after receiving an experimental gene-edited pig kidney on June 14 at Massachusetts General Hospital, hospital officials said Monday, marking another milestone as regulators prepare to launch human trials of animal-to-human organ transplants.

Bill Stewart, an athletic trainer from Dover, said he volunteered in part to "contribute to the science of it," and was easing back into desk duties after the procedure. Stewart, whose kidneys failed because of high blood pressure and who had spent two years on dialysis, said the transplant has freed him of the time and energy demands of dialysis.

The operation at Mass General follows earlier experimental xenotransplants and comes as the Food and Drug Administration has approved eGenesis, a pig organ producer, to begin a controlled study of gene-edited pig kidney transplants. The approval and recent procedures aim to address a persistent shortage: more than 100,000 people are on the U.S. transplant list, most awaiting kidneys, and thousands die while waiting for a donor organ.

Mass General kidney specialist Dr. Leonardo Riella, who will help lead the new clinical trial, said the program has learned from prior attempts and is adjusting patients' anti-rejection medications when needed. "Right now we have a bottleneck," Riella said, noting that xenotransplantation could help reduce the shortfall of available human organs.

The Mass General team has previously reported that a different New Hampshire recipient, Tim Andrews, has remained off dialysis for seven months after receiving a pig kidney, surpassing the earlier known post-transplant survival of 130 days for a gene-edited pig organ. That 130-day case involved an Alabama woman whose pig kidney was removed after rejection returned her to dialysis. Those earlier procedures and other initial experiments, which included two pig heart and two pig kidney transplants, were often performed in critically ill patients and were of limited duration.

Stewart said he sought out Andrews for advice before enrolling and was aware of the experimental nature of the procedure. Because some potential living donors were not compatible and his blood type could mean a wait of up to seven years for a deceased donor match, he applied to be a candidate for Mass General's transplant program.

Riella said Stewart's anti-rejection regimen was adjusted early after the transplant to address a concern, and Andrews has required similar medication tailoring. He cautioned that it is too soon to predict how long pig kidneys ultimately will function in humans, but said even temporary function that allows people to avoid dialysis and await a human organ would be valuable. "A year, hopefully longer than that — that's already a huge advantage," Riella said.

The eGenesis trial will offer gene-edited pig kidney transplants to 30 people age 50 or older who are on the transplant list, according to the team. Another company, United Therapeutics, has also received FDA approval to begin enrolling patients in a similar study.

Scientists have been altering genes in pigs to make their organs more compatible with the human immune system, aiming to reduce the risk that the organs will be immediately attacked and destroyed after transplantation. Research groups in multiple countries, including a recent announcement from Chinese researchers about a kidney xenotransplant with limited public details, have contributed to the evolving body of experience.

Clinicians and researchers say careful clinical trials will be needed to determine safety, durability and the best ways to manage immune suppression in recipients. For patients like Stewart, who said he had "always been a little bit of a science nerd," participating in early-stage procedures offers a potential treatment option where conventional donor organs are scarce.

Mass General and regulators plan to use the upcoming studies to gather systematic data on outcomes, immune response and potential complications, which proponents say could eventually expand treatment options for people with organ failure. For now, the procedures remain experimental and closely monitored as investigators work to translate animal-organ science into reproducible clinical benefit.