The Organ Factory: How Pig Kidneys Entered the Clinical Trial Era

A half-century of scientific failure just became the most consequential clinical trial in transplant history.

By Carry and Conquer Publications

On November 3, 2025, surgeons at NYU Langone Health performed the first transplant under the EXPAND study (NCT06878560), sponsored by United Therapeutics Corporation (Nasdaq: UTHR). The patient received a UKidney, an investigational porcine organ carrying 10 targeted genomic edits, making this not another emergency compassionate-use experiment but the first regulated, FDA-cleared clinical trial of a gene-edited pig organ in a living human. For private equity, venture capital, and biotech strategists watching the regenerative medicine space, this moment represents a structural inflection: the organ shortage problem, which kills roughly 17 Americans per day, may have found a working engineering solution that is now enrolling patients.

The Machine Under the Hood

The UKidney is derived from pigs raised in a designated pathogen-free facility and carries a precise set of genetic instructions written by United Therapeutics' subsidiary Revivicor. Six human genes have been inserted into the pig genome to improve immunological compatibility, signaling the human body to accept rather than attack the incoming organ. Four porcine genes are inactivated, or knocked out, to strip away surface antigens that would otherwise trigger immediate immune assault. The result is a kidney that looks and functions like a pig organ but presents a partially humanized molecular surface to the recipient's immune system.

United Therapeutics' lead rival, eGenesis (Series D, $191 million, September 2024), takes an even more aggressive editing approach: its EGEN-2784 product carries 69 genomic edits, including modifications that inactivate porcine endogenous retroviruses embedded throughout the pig genome to eliminate any potential cross-species infection risk. That the two dominant players have converged on meaningfully different edit profiles, 10 versus 69, reflects a field still negotiating the tradeoff between simplicity and comprehensiveness. Both now have FDA-cleared IND applications. Both are enrolling patients.

The EXPAND trial begins with a cohort of six patients across two transplant centers, with a mandatory 12-week wait between the first and second surgeries. An independent data monitoring committee will review safety and efficacy data after the initial cohort before the protocol expands to up to 50 participants. The study is designed as a seamless phase 1/2/3 combination trial, sometimes referred to as phaseless, to accelerate the pathway toward a Biologics License Application rather than cycling through discrete approval phases. That structural choice is itself a signal: United Therapeutics is not testing a hypothesis, it is building a regulatory filing.

The Man Who Made It Happen

Dr. Robert Montgomery, H. Leon Pachter Professor of Surgery at NYU Grossman School of Medicine and director of the NYU Langone Transplant Institute, is the trial's primary investigator and the person who performed the world's first gene-edited pig-to-human organ transplant on September 25, 2021. That procedure, done on a neurologically deceased patient, was followed by five more xenotransplant studies in deceased individuals before Montgomery's team moved to living recipients. In total, NYU Langone had performed nine xenotransplant surgeries before the EXPAND trial launched, including two with pig hearts and four with gene-edited pig kidneys.

Montgomery's perspective on organ scarcity is not purely clinical. He is a heart transplant recipient himself, having survived seven cardiac arrests before reaching the top of the transplant list in 2018. He has said his children have inherited his cardiac condition, meaning they will likely need transplants of their own. That personal stake gives his advocacy for xenotransplantation a dimension that goes beyond the professional. "We performed the first gene edited pig-to-human kidney transplant on September 25th, 2021," Montgomery wrote in a message following the EXPAND launch. "I don't think any of us thought there would be two FDA approved trials beginning less than 4 years after that landmark event."

The trial's participation criteria reveal how seriously the team is taking both scientific rigor and patient selection. Enrollees must be between 55 and 70 years old, must have been on hemodialysis for at least six months, and must be screened using a crossmatch assay to confirm immunological compatibility with the UKidney. Patients with severe cardiovascular disease, advanced neurological conditions, uncontrolled diabetes, or histories of medical noncompliance are excluded. This is not a last-resort cohort; it is a carefully selected one.

The Case File Before the Trial

The compassionate-use cases that preceded EXPAND were not uniformly encouraging, but they were instructive in ways that changed the science. In April 2024, Lisa Pisano, a 54-year-old woman from New Jersey with combined heart and kidney failure who was ineligible for conventional organ transplants, received a UKidney alongside a left ventricular assist device at NYU Langone. The pig kidney functioned for roughly the first month, enabling her to come off dialysis and stabilize her cardiovascular function. A series of low-blood-pressure episodes damaged the organ, it was removed after 47 days, and Pisano died in hospice care that July. The same month, Massachusetts General Hospital performed the first pig kidney transplant in a living patient: Richard Slayman, 62, received an eGenesis kidney with 69 edits in March 2024 and died about seven weeks later of causes unrelated to the transplant.

The most significant compassionate-use outcome came in November 2024, when Montgomery's team transplanted a UKidney into Towana Looney, a 53-year-old grandmother from Alabama who had donated a kidney to her mother in 1999 and later developed kidney failure from preeclampsia. She had been on dialysis since 2016 and was listed as highly sensitized, making a conventional match unlikely. The pig kidney allowed her to live dialysis-free for 130 days. By late February 2025, she had returned home to Alabama with normal kidney function. The kidney was ultimately removed in April 2025 after an unrelated infection compromised her renal function, and she returned to dialysis. But 130 dialysis-free days, from a pig kidney, in a living patient, represents the longest recorded survival following a pig-to-human kidney xenotransplantation.

These outcomes, imperfect as they are, constitute the clinical foundation on which the EXPAND trial rests. Researchers noted that healthier patients, enrolled earlier in their disease course before dialysis-related complications accumulate, are likely to produce cleaner data on durability.

The Market That Has No Supply

The scale of the problem EXPAND is working against is not contested. More than 90,000 Americans are currently on the kidney transplant waitlist. Roughly 26,000 kidney transplants took place in the U.S. last year, leaving a structural gap that has persisted for decades because the supply of deceased donor kidneys grows far more slowly than demand. Fewer than 1 percent of registered organ donors die in circumstances that allow for deceased organ donation, a biological constraint that cannot be engineered away. Meanwhile, over 557,000 patients in the U.S. are on dialysis to manage kidney failure, a treatment that costs Medicare approximately $36 billion per year and is associated with progressive cardiovascular damage, immunosuppression, and shortened life expectancy.

For investors tracking biopharma and medical devices, the market geometry is straightforward: if xenotransplantation achieves clinical viability, it addresses a captive patient pool with no other durable solution, at price points that would justify extraordinary valuation multiples. United Therapeutics, which operates as a public benefit corporation and trades on Nasdaq, generated over $2 billion in annual revenue from its pulmonary arterial hypertension drug franchise before the xenotransplantation program became a public focus. The EXPAND study's eventual BLA pathway is intended to establish UKidney as a standalone commercial product, not a research curiosity.

The competitive field is still small but consolidating quickly. eGenesis raised $191 million in September 2024, the largest xenotransplantation financing round to date, specifically to advance EGEN-2784 toward a clinical trial. That trial, targeting 33 patients over roughly two and a half years, is now also enrolling. The next generation of pigs under development by both companies and academic collaborators carries as many as 69 genomic edits, and nonhuman primate experiments with those organs have produced survival times of one to two years.

What Comes After Phase One

The trial's structure is designed to produce data that regulators can act on without a multi-year gap between phases. After the initial six-patient cohort clears its independent safety review, United Therapeutics plans to amend the protocol to expand enrollment to 50 patients across additional transplant centers and prepare the underlying package for a BLA submission. Efficacy endpoints include participant survival rate, UKidney survival rate, change in measured glomerular filtration rate, and quality-of-life improvements at 24 weeks post-transplant. Patients who receive a UKidney will be followed for the remainder of their lives, with ongoing monitoring for organ function and zoonotic infections.

The Biologics License Application framework, if successful, would allow UKidney to be prescribed and reimbursed as an approved medical product rather than delivered under an expanded access exemption. That shift from exception to standard of care is the transition the field has been building toward since 2021. Dr. Leigh Peterson, Executive Vice President of Product Development and Xenotransplantation at United Therapeutics, called the EXPAND launch a watershed moment for the company's broader mission of widening access to transplantable organs. Regulators, academic centers, and the industry are now all operating from the premise that xenotransplantation is not hypothetical.

Richard Knight, medical director of transplant diagnostics at Thermo Fisher Scientific, who has followed the field for decades, put the 2025 moment in context: "I've been in the field for decades, and I remember when I started as a young surgeon in transplantation, xenotransplantation was a field that you pursued in the lab using small animals, and the barriers seemed insurmountable. Lots of good researchers gave up, but this year, the progress has been amazing."

The most durable questions now are not about whether pig kidneys can function in living humans. They are about scale. Hundreds or thousands of these procedures would need to be performed annually to make meaningful inroads into the waitlist. Manufacturing infrastructure, pricing, and reimbursement pathways have not yet been stress-tested at anything approaching that volume. For the investors, operators, and healthcare strategists paying attention, that gap between proven science and built capacity is the next large problem. And it is, historically, where the carries get made.