A Pig Kidney Just Worked Inside a Human for 271 Days
A gene-edited pig kidney just kept a man alive and off dialysis for 271 days, shattering every record in xenotransplantation. With FDA approval for an expanded trial in hand, eGenesis is turning science fiction into a real answer for the 90,000 Americans stuck on the kidney transplant waiting list.
Tim Andrews spent two years tethered to a dialysis machine. Three days a week, every week, for hours at a stretch. Then a surgeon at Massachusetts General Hospital handed him a kidney from a pig, and he didn't need dialysis again for nine months.
That pig kidney functioned for 271 days. It's the longest a gene-edited animal organ has ever worked inside a living human being. And it just changed the math on one of medicine's most stubborn problems.
The Kidney Crisis Nobody Talks About
About 90,000 Americans sit on the kidney transplant waiting list right now. Last year, roughly 28,000 got a transplant. You can do that math yourself; it's not pretty.
But the real number is even worse. Only about 1 in 8 people with kidney failure ever make it onto the waiting list in the first place. The rest just stay on dialysis, which is brutal: five-year survival on dialysis hovers around 35%. A kidney transplant pushes that above 80%.
Every day, about 11 people on the kidney waiting list die. The average wait stretches beyond three years, and in some parts of the country it can hit a decade. We don't have a treatment problem. We have a supply problem. There simply aren't enough human kidneys to go around.
So what if the kidneys didn't have to come from humans at all?
Building a Better Pig
eGenesis, a biotech company spun out of Harvard geneticist George Church's lab, has been working on that exact question. Their approach is almost absurdly ambitious: take a pig, rewrite its DNA with CRISPR gene-editing tools, and create organs that a human body won't immediately destroy.
The engineering involved is staggering. The pig that produced Tim Andrews' kidney had 69 individual genetic edits. Those edits fall into three categories, and each one solves a different problem.
First, eGenesis knocked out three sugar molecules on the surface of pig cells. Think of these sugars as name tags that scream "I'm foreign!" to your immune system. Removing them is like peeling off the name tags so the bouncer doesn't notice the pig kidney snuck into the club.
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Second, they inserted seven human genes into the pig's DNA. These genes help regulate blood clotting, calm down inflammation, and keep the complement system (your body's chemical defense network) from going haywire against the transplanted organ.
Third, and this is where eGenesis really differentiates itself: they inactivated approximately 59 copies of porcine endogenous retroviruses (PERVs) baked into the pig genome. These are ancient viral sequences that could theoretically jump from pig cells to human cells. Shutting them all down is an enormous safety precaution.
The result is an organ called EGEN-2784: a pig kidney redesigned, at the genetic level, to coexist with a human body.
Nine Months Without Dialysis
Tim Andrews, 67, from New Hampshire, received his EGEN-2784 kidney at MGH in January 2025. The kidney started working immediately. No extended dialysis after surgery. He went home, got his energy back, and lived a normal life.
For 271 days, that pig kidney filtered his blood, managed his metabolism, and kept him off the machine that had dominated his life for two years. He reported major improvements in energy and quality of life.
The graft wasn't perfect forever. Toward the end, doctors noticed persistent proteinuria, which means protein was leaking into his urine, a sign of ongoing injury to the kidney. After 271 days, surgeons removed the pig kidney, and Tim returned to dialysis while remaining on the waiting list for a human organ.
That detail matters enormously. The pig kidney served as a bridge: it bought Tim months of normal life while he waited for a human organ. For the thousands of people who die every year on the transplant waiting list, a nine-month bridge could be the difference between life and death.
He's Not the Only One
A second patient, Bill Stewart, 54, received an EGEN-2784 kidney on June 14, 2025. He was discharged about a week after surgery. As of early 2026, he had been off dialysis for more than 200 days and counting.
Two patients is not a clinical trial. It's a proof of concept. But it's a proof of concept that seemed impossible just a few years ago. In 2021, the first pig kidneys transplanted into brain-dead humans lasted only 54 to 77 hours. We've gone from days to months in under five years.
The FDA Opens the Door
eGenesis didn't just set a survival record. The company also secured FDA clearance for a Phase 1/2/3 clinical trial of EGEN-2784 in patients with end-stage kidney disease. This is big: it means the FDA looked at the data, weighed the risks, and decided the science is mature enough to test in a structured, multi-patient study.
The trial design is notable for how aggressive it is. It's what's called a "seamless" Phase 1/2/3, meaning eGenesis can move through safety evaluation and efficacy testing under a single protocol without starting over at each phase. The primary evaluation window is 24 weeks (about six months) post-transplant, with lifelong follow-up after that.
Eligibility criteria: patients must be 50 or older, dependent on dialysis, and actively listed on a kidney transplant waiting list. In other words, exactly the population that's running out of time.
The expanded access study at MGH (which produced the Tim Andrews and Bill Stewart cases) was limited to three patients. This new trial is designed to be multi-center, meaning more hospitals, more patients, and more data. The exact number of sites hasn't been announced yet.
The Competition Is Real
eGenesis isn't alone in this race. United Therapeutics, through its subsidiary Revivicor, has its own gene-edited pig kidney product called UKidney. Their approach uses fewer edits (10 versus eGenesis' 69), but the FDA has also approved their clinical trial, called EXPAND, at NYU Langone.
The EXPAND trial started with an initial plan for six transplants, with potential expansion to 50 patients. It targets patients aged 55 to 70 on hemodialysis for at least six months.
NYU performed the first combined heart pump and pig kidney transplant in a living patient back in April 2024. That patient died in July 2024, though the failure appeared linked to hemodynamic complications rather than the kidney itself. A subsequent UKidney recipient at NYU had the organ removed in April 2025 after an unrelated infection caused graft failure.
The scoreboard, for now: eGenesis holds the record for longest function (271 days). United Therapeutics has the larger planned trial. Both have FDA-cleared paths forward. This is a genuine two-horse race, and the competition should accelerate progress for patients.
What Could Go Wrong
Let's be honest about the risks, because they're significant.
Durability is unproven. The best result so far is nine months. Human kidney transplants from deceased donors routinely last a decade or more. Nobody knows yet whether pig kidneys can get anywhere close to that. The proteinuria that ended Tim Andrews' graft function suggests chronic injury processes that scientists haven't fully solved.
Immunosuppression is heavy. Reports from early cases describe patients taking enormous quantities of medication to keep their bodies from attacking the foreign organ. If pig kidneys require more toxic or costly immunosuppression than human transplants, the value proposition gets complicated.
The sample size is tiny. We're talking about single-digit patients worldwide. Outcomes have ranged from weeks to nine months. That kind of variability makes it hard to draw confident conclusions.
Manufacturing is complex. Breeding gene-edited, pathogen-free pigs in designated facilities, retrieving organs, and preserving them for transplant is an expensive, capital-intensive supply chain. Early organs will likely cost six figures each.
And there's always the wildcard: public perception. A highly publicized death linked to xenotransplantation could slow adoption, even if the science is sound.
Why This Matters More Than You Think
Zoom out for a second. The kidney transplant waiting list kills people every day. Dialysis costs Medicare over $50 billion per year. Models show that if we simply got better at listing eligible patients (without increasing organ supply), median wait times would jump from about 33 months to over 52 months. We'd need 11,000 additional kidneys per year just to prevent things from getting worse.
There is no realistic path to closing that gap with human donors alone. Living donation has barely budged in a decade. About 20% of recovered kidneys deemed viable are discarded and never transplanted.
Xenotransplantation isn't a moonshot anymore. It's an engineering problem with a clear clinical need, regulatory buy-in, and two well-funded companies racing to solve it. The 271-day milestone proves that gene-edited pig kidneys can sustain human life for meaningful periods. The question has shifted from "can this work?" to "how long can we make it last?"
That's a much better question to be asking. And for the 90,000 people on the waiting list, it might be the most important question in medicine.
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