Genetically Engineered Pig Kidneys Show Success In Human Transplant Trials At Massachusetts Hospital

BOSTON — Genetically engineered pig kidneys have been successfully transplanted into five patients at Massachusetts General Hospital, marking a significant milestone in the decades-long effort to use animal organs to address a persistent shortage of human transplant organs, according to results from an ongoing clinical trial.

The five patients underwent xenotransplantation, the process of transplanting organs between species, since March 2024, according to U.S. biotechnology company eGenesis, which developed the genetically modified pig kidneys used in the procedures. In three of the five patients, the transplanted organs continued functioning for more than eight months without triggering rejection or requiring the patient to return to dialysis.

Leonardo Riella, director of kidney transplantation at Massachusetts General Hospital, who led the eGenesis clinical trials, described the scale of the challenge the research aims to address.

"The organ shortage is the greatest crisis we have right now in transplantation," Riella said.

Mike Curtis, chief executive of eGenesis, characterized the results as a meaningful advance toward the company's broader goal of expanding access to transplantation.

"It's amazing to see the progress," Curtis said. "Our goal is to make transplantation available to patients when they need it, without being constrained by the limited supply of human donor organs."

The pig kidneys used in the trial were grown in Yucatan miniature pigs, a breed selected in part because their organs are similar in size to human organs. Researchers genetically engineered the pigs to remove three specific pig proteins most likely to trigger immune rejection in human recipients, while adding seven human genes intended to improve compatibility between the transplanted organ and the recipient's body. Researchers also manipulated the porcine DNA to inactivate viruses that could otherwise pose an infection risk to transplant recipients.

Riella said the animal organs are initially envisioned as a bridge therapy, helping patients avoid dialysis while they wait for a human donor kidney to become available, rather than as a permanent, standalone replacement for human organ transplants at this stage.

"As a bridge to get patients off dialysis while they wait for a human donor kidney," Riella said, describing the initial intended use of the pig kidneys. He added that the approach could eventually serve "as a destination therapy in its own right" if ongoing trials succeed in establishing long-term safety and durability for the procedure.

One of the five patients, Tim Andrews, whose case was detailed in a study published in The Lancet medical journal, lived with a pig kidney for nearly nine months without requiring dialysis, after receiving the transplant at age 66. The organ eventually began to fail, though doctors found no signs of immune rejection had caused the decline. Andrews subsequently received a kidney from a deceased human donor. Follow-up testing showed that having lived with the pig kidney beforehand did not make it more difficult for the subsequent human donor kidney to function successfully in his body.

Curtis said the U.S. Food and Drug Administration has authorized an expanded clinical trial involving 33 patients with renal failure, set to begin early next year across as many as 10 transplant centers throughout the United States. EGenesis is targeting marketing approval for the pig kidney treatment by the end of 2029. The company is also collaborating with Japanese partner PorMedTec to begin kidney xenotransplantation trials in Japan starting in 2028, according to Curtis.

David Crosby, chief research officer at the renal charity Kidney Research UK, described the results as encouraging while cautioning that significant additional research remains necessary before the approach can be fully evaluated against existing treatment options.

Crosby called the breakthrough "an exciting prospect" but said further research was needed to determine whether the xenotransplantation approach ultimately proves "safer and better" for patients compared with spending years on dialysis while awaiting a conventional human organ transplant.

Xenotransplantation research has moved through repeated cycles of optimism and disappointment since serious scientific investigation into the field began in the 1980s. Researchers and industry officials say recent advances in animal cloning, genetic engineering and immunology have meaningfully improved the field's prospects compared with earlier decades, when similar research repeatedly failed to produce durable clinical results.

Curtis said public squeamishness and ethical objections to breeding animals specifically for organ transplantation have also diminished over time, as the field has produced increasingly tangible clinical outcomes for patients facing organ failure.

"Hard to sustain ... when you look at the outcomes for our patients," Curtis said, describing his view of moral objections to xenotransplantation given the results seen in the current trial.

Much of the earlier history of xenotransplantation research focused on heart transplants rather than kidneys, but kidney xenografts have since emerged as the area closest to achieving formal clinical approval. Curtis pointed to a key practical advantage kidneys hold over hearts in this context.

"A big advantage of the kidney is that if the transplant fails we can safely return the patient to dialysis," Curtis said. "If the transplanted heart fails, there's not much you can do."

Despite that advantage favoring kidney research, both eGenesis and a separate leading U.S. xenotransplant company, United Therapeutics, are continuing to pursue research involving both organ types. The FDA has separately approved a small trial of xenotransplanted hearts led by United Therapeutics, indicating continued institutional interest in expanding the approach beyond kidneys alone.

The results from the Massachusetts General Hospital trials add to a small but growing body of clinical evidence suggesting genetically engineered animal organs may eventually offer a viable supplement to the existing human donor organ system, which has long struggled to meet demand from patients suffering from kidney failure and other organ-related illnesses. With an expanded 33-patient trial set to begin early next year across multiple U.S. transplant centers, researchers are hoping to build a larger evidentiary base to support the therapy's eventual path toward regulatory approval later this decade.

For patients like Andrews, whose experience illustrated both the potential and current limitations of the technology, the trial results offer a tangible example of how genetically modified pig organs might eventually help bridge the gap between diagnosis of organ failure and the long wait many patients currently face for a compatible human donor organ, even as researchers caution that substantial additional evidence will be needed before the approach becomes a widely available treatment option.