Ten Gene Edits or Six? What 271 Days With a Pig Kidney Really Proved

Roughly 110,000 people are currently waiting for organ transplants in the United States alone, most of them for kidneys. Someone joins that list every seven minutes, and about 12 people die each day still waiting. Xenotransplantation — transplanting organs from pigs into humans — has suddenly become a real candidate for closing that gap. In October 2025, a genetically engineered pig kidney kept a New Hampshire man off dialysis for 271 days, setting a new record. But the kidney was eventually removed from his body. A record-setting success, and a rejection problem still unsolved — how far has pig-to-human transplantation actually come?

271 Days, Then Removal

On January 25, 2025, Tim Andrews, 67, received EGEN-2784, a genetically engineered pig kidney developed by the biotech company eGenesis. According to the company, the kidney carries three classes of modification: removal of three glycan antigens that are targets for rejection, addition of seven human genes to improve immune and blood-clotting compatibility, and inactivation of viruses embedded in the pig genome (endogenous retroviruses). Counting the viral inactivations, the review paper discussed below puts the total at 69 edits. After the transplant, Andrews lived dialysis-free for more than seven months. But on October 27, 2025, the kidney was removed and Andrews returned to dialysis; the same review attributes the removal to protein leaking continuously into the urine. The 271 days between transplant and removal stand as the longest a pig kidney has functioned inside a human body.

Around the same time, NYU Langone Health launched a separate trial called EXPAND, using a pig kidney called UKidney — developed by a company affiliated with United Therapeutics, carrying ten total edits: six added human genes and four inactivated pig genes. Pig kidneys built on different design philosophies by different companies are now being tested in humans in parallel, at multiple medical centers.

What Keeps Triggering Rejection

A review published in Frontiers in Immunology in December 2025 lays out the recurring problem in pig-to-human kidney transplants. The central obstacle, the authors write, is chronic antibody-mediated rejection: over time, the immune system keeps producing antibodies against the pig tissue, causing tiny blood clots to form in the vessels. Suppressing the immune system more aggressively can hold off rejection, but it also raises the risk of infection — and infections themselves can trigger rejection, creating a difficult balancing act.

The review also notes that damage which normally takes years to appear in a standard human-to-human kidney transplant can show up within months in a xenograft. Seen in that light, the 271-day record marks how far this race against time has come — not the finish line.

Is More Gene Editing Always Better?

Development teams have made different design choices about how many genes a pig kidney needs to have edited. Counting only the edits aimed at rejection and clotting, the eGenesis kidney and the United Therapeutics-affiliated kidney both carry ten — a mix of added human genes and disabled pig genes. By contrast, the kidney a team at Xijing Hospital in China transplanted into a 69-year-old woman carries just six such edits (three antigens removed and three human genes added). Even so, at the time the review was written, it was reported to have been functioning for almost eight months.

That the six-edit and ten-edit kidneys both reached the eight-to-nine-month range suggests the number of edits alone does not determine how long a graft survives. The review states that even with ideal genetic modification, chronic antibody-mediated rejection and clotting damage in small vessels eventually become the predominant causes of failure. Because engineering and breeding these pigs is slow and costly, the question of how much editing is truly necessary has direct implications for how quickly the technology could scale.

Why Everyone Is Racing to Trial This Now

The urgency traces back to the organ shortage itself. Of the roughly 110,000 people on the US transplant waiting list, most need kidneys, and about 12 die each day while waiting. In response, the FDA cleared investigational new drug applications for both eGenesis and the United Therapeutics-affiliated program around 2025, and human trials are now underway simultaneously at multiple medical centers — an unusual pace for a field this new. Kidneys aren't the only target: genetically engineered pig hearts have already been transplanted into human patients as well, and xenotransplantation is increasingly seen as a broader answer to organ scarcity, not just a kidney-specific fix.

The 271-day record shows that a pig organ can, for a stretch of time, genuinely function inside a human body. But it also exposes a harder truth: no matter how many genes get edited, the rejection response triggered by crossing the species barrier hasn't been fully tamed yet. On present results, xenotransplantation looks less like a replacement for kidney transplantation than a bridge — buying patients months, perhaps a year, of freedom from dialysis while they wait for a human donor. To stand alongside ordinary kidney transplantation, future trials will need to show that the chronic rejection now appearing within months can be pushed out to years.