FDA-Authorized Trial Tests Gene-Edited Pig Kidney Transplants in Living Patients

In early November, in an operating room at NYU Langone Health in New York City, surgeons connected the blood vessels of a man with failing kidneys to an organ grown inside a genetically engineered pig.

The patient, whose identity has not been released, was not part of a last-ditch emergency or an experimental one-off. He became the first participant in a formally regulated U.S. clinical trial testing whether a gene-edited pig kidney can function as a routine treatment for human kidney failure—and eventually win approval from the Food and Drug Administration.

First FDA-authorized “registration” trial

The study, known as the EXPAND trial, is the first FDA-authorized clinical trial of a gene-edited pig kidney in living patients explicitly designed to support a future marketing application. The experimental graft, branded “UKidney” by its developer, United Therapeutics Corp., carries 10 genetic modifications intended to help a pig organ behave more like a human one and avoid rapid rejection.

“This marks a transformative moment in transplant medicine,” Dr. Robert Montgomery, the surgeon who led the operation and director of the NYU Langone Transplant Institute, said in a statement when the trial was announced. He said the work “offers new hope to the thousands of Americans currently on the kidney transplant waiting list.”

United Therapeutics disclosed that the first transplant under the EXPAND protocol took place Nov. 3, 2025, at NYU Langone after the FDA cleared the company’s investigational new drug application earlier in the year. The company has described the study as a “phase 1/2/3” or “phaseless” registration trial, a design meant to roll early safety testing and later efficacy evaluation into one continuous program.

Who is eligible—and how the trial will expand

Under the trial’s initial phase, up to six adults between ages 55 and 70 with end-stage renal disease can receive a UKidney transplant at two U.S. centers. All must have been on hemodialysis for at least six months and either be considered medically ineligible for a human kidney or judged unlikely to receive one within five years. A 12-week pause is required between the first and second transplants to allow close safety review.

If the first six cases meet predefined safety and performance benchmarks—including patient survival, kidney function and absence of severe rejection at 24 weeks—the company and regulators could allow the trial to expand to roughly 50 participants and additional hospitals.

From compassionate use to conventional clinical evidence

The launch of EXPAND marks a shift in xenotransplantation, the decades-old effort to use animal organs in humans. Over the past four years, several U.S. teams have transplanted pig hearts and kidneys into people under expanded access or compassionate-use rules, which allow experimental interventions in patients with no other options. Those procedures generated global headlines but were not structured as conventional drug trials.

NYU, in particular, has been at the forefront of such work. Montgomery’s group performed the world’s first transplant of a gene-edited pig kidney into a brain-dead person in 2021, then repeated the procedure several times in deceased donors. In 2024 and 2025, the team implanted pig kidneys into at least two living patients under emergency exemptions. One of those recipients, Alabama resident Towana Looney, lived with a pig kidney for about 130 days before the organ was removed after an unrelated infection, and she returned to dialysis.

At Massachusetts General Hospital, surgeons using organs from a different line of heavily engineered pigs developed by Boston-area startup eGenesis reported a man who lived 271 days with a pig kidney before the organ was removed last fall, the longest documented survival for such a transplant.

Those cases showed that pig kidneys can work in humans for months, but they also exposed weaknesses: undetected viral infections, complex rejection patterns and uncertainty about long-term risks. They also did not follow the structure or data standards the FDA requires for approving medical products.

By contrast, EXPAND is intended from the outset to generate the kind of evidence package the agency would need to consider a biologics license application for UKidney. United Therapeutics executive Leigh Peterson called the first transplant in the trial “a watershed moment” for the company’s effort to broaden access to transplantable organs.

What’s genetically changed in the “UKidney” pigs

The UKidney grafts are derived from pigs engineered with 10 specific DNA changes.

Four pig genes are knocked out:

• GGTA1, B4GALNT2, and CMAH, which produce sugar molecules that provoke a fierce human immune response
• GHR (growth hormone receptor), intended to control organ growth

Six human genes are added:

• Two that help regulate the complement system, which can attack foreign tissue
• Two that modulate coagulation, aiming to reduce clotting on the organ’s surface
• One that eases oxidative stress
• CD47, a “don’t eat me” signal that discourages immune cells from destroying the graft

Unlike some experimental pig organs developed by other companies, the UKidney pigs do not have their endogenous retroviruses removed. Instead, the program relies on high-biosecurity breeding, extensive pathogen testing of donor animals and intensive post-transplant surveillance for viruses such as porcine cytomegalovirus and porcine endogenous retroviruses. Recipients will be monitored for life for signs of zoonotic infection.

Regulators see that surveillance as critical because any virus that jumps from pig tissues into people could pose a broader public health problem, not just an individual one. The FDA has required long-term follow-up and detailed consent language that makes clear recipients may be asked to submit to testing for years and face restrictions on donating blood or tissues.

Why the stakes are high: kidney shortage and dialysis burden

The hope driving such precautions is the prospect of easing a chronic organ shortage that has resisted decades of policy and clinical reforms. More than 105,000 people in the United States are currently on organ transplant waiting lists, and nearly 90,000 of them need a kidney, according to federal data. Despite a record 48,149 organ transplants performed nationwide in 2024, thousands of patients die or become too sick to receive an organ each year.

Kidney failure also falls unevenly across the population. Federal statistics show that more than 808,000 people in the U.S. live with end-stage renal disease, and Black Americans are more than four times as likely as White Americans to develop it. They make up about 30% of the ESRD population despite representing roughly 14% of the country overall.

Dialysis—the fallback treatment when kidneys fail—can sustain life but ties patients to machines for hours several times a week and is associated with high mortality, cardiovascular complications and poor quality of life. Most ESRD care is covered by Medicare regardless of age, making it one of the program’s most expensive chronic conditions.

Ethical, cultural and cost questions

Montgomery has argued publicly that if xenotransplantation can be made safe and reliable, pig organs might eventually exceed human ones in availability and performance. In a December interview, he said pig organs could one day be “superior to human ones,” offering more predictable function and eliminating the wait for a suitable donor.

Not everyone shares that optimism. Animal welfare advocates have questioned the ethics of raising sentient animals solely as sources of organs. Religious and cultural concerns are also likely; pigs are considered unclean in some faith traditions, potentially affecting which patients will accept such transplants. Health policy analysts warn that any approved xenograft would almost certainly enter the market as a high-priced, patented product, raising questions about who could afford access and how insurers and government programs would respond.

United Therapeutics, based in Silver Spring, Maryland, and Massachusetts-based eGenesis are among several companies aiming to build what amounts to an industrial supply chain for transplant organs. Both are pursuing multiple organ types. The FDA has separately cleared trials of gene-edited pig livers used externally as a temporary support system for failing human livers.

For now, however, all of those ambitions hinge on the experiences of a handful of patients like the anonymous man at NYU Langone. His new kidney is being watched as closely as any in modern transplant history—each lab value, biopsy and viral test a data point in a larger calculation about whether medicine is ready to cross a permanent species line.

“This thing is moving in the right direction,” Montgomery told reporters recently, noting that dialysis remains a safety net if the pig organs fail. Whether it keeps moving—from an extraordinary surgery in one operating room to a standard option for the tens of thousands of people living on dialysis—will depend on what happens to him and the small group of volunteers who agree to follow.