FDA Clears First Clinical Trials of Gene‑Edited Pig Kidneys for Human Transplant

The U.S. Food and Drug Administration has approved the first clinical trials to transplant genetically modified pig organs into living human patients, regulators and developers said, marking a step toward broader testing of xenotransplantation as a response to the nation’s severe organ shortage.

Massachusetts-based eGenesis and Mass General Brigham in Boston will provide gene‑edited pig kidneys to 30 people age 50 and older who are on dialysis and on the human organ transplant waiting list, according to the companies and physicians involved. The approval follows a series of one-off compassionate‑use transplants in the United States that tested the approach in critically ill patients.

The trial will use kidneys designated EGEN‑2784 that have been modified with gene‑editing technologies such as CRISPR/Cas9. Developers say the edits remove or alter pig genes that can trigger rapid immune rejection, inactivate porcine viruses that could infect humans, and add human genes intended to improve compatibility with the human immune system.

All prior U.S. transplants of animal organs into living humans were authorized under so‑called compassionate‑use provisions designed for patients with immediate life‑threatening conditions and no comparable treatments. Those isolated procedures yielded data and experience that regulators cited in clearing the formal clinical trial, which is intended to assess safety and efficacy in a broader, more stable patient population.

"Right now we have a bottleneck" in the supply of human organs for transplantation, said Dr. Leonardo Riella, a kidney specialist at Mass General who will help lead the trial. More than 100,000 people are registered on the U.S. transplant waiting list, most of them seeking kidneys; thousands die each year while waiting for a compatible organ, and wait times can stretch to seven years.

Experts and developers emphasize that the trials will monitor for known risks of transplantation, including rejection and infections, and will require patients to take immunosuppressive drugs. Rejection can occur within days, months or years after a transplant, and prior experimental pig organ implants have survived for varying lengths of time. An earlier case in Alabama saw a pig kidney function for 130 days before being removed after signs of rejection, while another patient in New Hampshire remained off dialysis for about seven months after receiving a gene‑edited pig kidney.

Bill Stewart, 54, of New Hampshire, is the most recent U.S. patient to receive a gene‑edited pig kidney and was reported to be recovering well after a June 14 operation. Tim Andrews, also of New Hampshire, has remained free of dialysis for a record seven months following his transplant. Richard Slayman, who in 2024 became the first person to survive following an animal‑to‑human organ transplant, lived for two months after his procedure before dying; his case and others have provided physicians with clinical observations that informed the design of the new study.

Mike Curtis, chief executive officer of eGenesis, said the trial represents "a new frontier in medicine and demonstrates the potential of genome engineering to change the lives of millions of patients globally suffering from kidney failure." Another U.S. developer, United Therapeutics, has received FDA authorization to begin enrolling patients in a similar study and is preparing to start its trial.

Gene‑editing in xenotransplantation typically targets multiple issues at once: reducing or eliminating molecules on pig cells that provoke a human immune attack, removing endogenous retroviruses known as PERVs that could pose viral risks, and adding human regulatory genes to reduce coagulation and inflammatory mismatches. Researchers say these multilayered edits are intended to improve initial compatibility and prolong graft survival, but long‑term durability in humans remains unproven.

Earlier notable milestones include a 2022 heart transplant using a genetically modified pig heart and experimental lung and heart implants in other settings; those efforts involved very ill patients and were short‑lived. Chinese researchers have recently announced a lung xenotransplant with few published details. The mixed outcomes of these early cases prompted some investigators to shift from enrolling the sickest patients to studying organ recipients who are more stable, a change the FDA cited as part of the rationale for broader clinical testing.

The FDA's approval of the trial establishes a formal framework for data collection, safety monitoring and regulatory oversight that advocates say is needed before the approach could be considered for routine clinical use. Investigators will be required to report graft function, infectious complications, immune responses and survival outcomes as part of the study protocol.

Officials caution that it is too early to predict how long gene‑edited pig kidneys might last in humans. "A year, hopefully longer than that — that's already a huge advantage," Dr. Riella said, adding that even temporary graft function that frees patients from dialysis would represent substantial clinical benefit while they await a human organ.

The trial comes amid intense efforts worldwide to develop alternatives to human donor organs, including improved organ preservation, living donor programs, bioengineered tissues and other xenogeneic approaches. Scientists and ethicists say careful, transparent reporting and long‑term follow‑up will be essential to address safety, infectious‑disease and ethical considerations tied to cross‑species transplantation.

The eGenesis–Mass General Brigham study is expected to begin enrollment soon; investigators said participants will be followed closely and that additional details on eligibility, monitoring and endpoints will be provided as the trial opens. Regulators and researchers plan to use the findings to determine whether gene‑edited pig organs can safely expand the supply of transplantable kidneys and reduce deaths among patients with end‑stage kidney disease.