69 Gene Edits, 9 Months, One Pig Kidney: The Xenotransplant Scorecard
Six people have received genetically engineered pig organs. Three died. The longest-surviving recipient lived dialysis-free for nine months, then got a human kidney. Two companies are now racing through FDA trials with radically different gene-editing strategies. Here is every case, every outcome, and the $50 billion question underneath it all.
Seventeen people die every day in the United States waiting for an organ transplant. More than 100,000 are on the national waiting list. Roughly 90,000 of them need kidneys. Last year, only 22,000 deceased-donor kidney transplants were performed. The arithmetic is brutal: for every kidney transplanted, four people keep waiting. Many of them are dying.
The idea of using animal organs to close that gap is older than most people realize. In 1984, a 12-day-old infant named Baby Fae received a baboon heart at Loma Linda University Medical Center. She survived 21 days. For the next three decades, xenotransplantation remained a concept that sounded plausible in grant proposals and implausible everywhere else.
Then CRISPR happened. Between 2022 and 2026, six living humans received genetically engineered pig organs. Three of them died. One had her kidney removed after immune rejection. One set a world record for survival. And two biotech companies are now running FDA-approved clinical trials, each with a fundamentally different theory about how many gene edits a pig needs before its kidney can live inside a person.
The Complete Scorecard
| Patient | Organ | Date | Gene Edits | Pig Source | Days Functional | Outcome |
|---|---|---|---|---|---|---|
| David Bennett Sr., 57 | Heart | Jan 2022 | 10 | Revivicor | 60 | Died. Porcine cytomegalovirus found in organ post-mortem. |
| Rick Slayman, 62 | Kidney | Mar 2024 | 69 | eGenesis | ~61 | Died. Cardiac causes. MGH stated unrelated to transplant. Kidney was functioning. |
| Lisa Pisano, 54 | Kidney | Apr 2024 | 10 | United Therapeutics | 47 | Kidney removed (blood flow issues). Died July 2024. |
| Towana Looney, 53 | Kidney | Dec 2024 | 10 | United Therapeutics | 130 | Kidney removed. Immune rejection. Back on dialysis. |
| Tim Andrews, 66 | Kidney | Jan 2025 | 69 | eGenesis | ~270 | Kidney removed Oct 2025. World record: 9 months. Received human donor kidney Jan 2026. |
| Bill Stewart, 54 | Kidney | Jun 2025 | 69 | eGenesis | Ongoing* | Dialysis-free. Third eGenesis patient. |
*As of latest public reports. Days are approximate based on published dates.
Six patients. Three genetic engineering platforms. Survival durations ranging from 47 days to 9 months. What stands out is the trajectory: from David Bennett's 60 days in 2022 to Tim Andrews' 270 in 2025. That is a 4.5x improvement in survival duration in three years. In genomics terms, that is the kind of iteration rate you see in sequencing technology, not in transplant medicine.
69 Edits vs. 10: Two Philosophies of Pig Engineering
The two companies leading xenotransplantation have adopted sharply different engineering strategies. The gap is not minor. It is a 7x difference in the number of genetic modifications.
eGenesis (Cambridge, MA) makes 69 gene edits across three classes: (1) elimination of three glycan antigens that trigger hyperacute rejection, (2) insertion of seven human transgenes that regulate immune response, reduce inflammation, improve coagulation compatibility, and modulate complement activation, and (3) inactivation of porcine endogenous retroviruses (PERVs) embedded in the pig genome. eGenesis is the only company addressing all three categories. They raised $191 million in September 2024 and received FDA IND clearance for a Phase 1/2/3 trial in September 2025.
United Therapeutics (Nasdaq: UTHR) takes a leaner approach with its UKidney: 10 gene edits total. Six human genes are added to facilitate immunological acceptance. Four pig genes are knocked out to reduce rejection risk and moderate organ growth. Notably, United Therapeutics does not inactivate PERVs. Their first clinical transplant in the EXPAND trial (NCT06878560) was performed at NYU Langone on November 3, 2025.
The philosophical difference is real. eGenesis treats the pig genome as a codebase that needs extensive refactoring before deployment. United Therapeutics treats it more like a patch: fix the critical compatibility bugs, ship, and iterate. Both approaches have produced functional kidneys in humans. Whether the extra 59 edits explain eGenesis' longer survival times (270 days vs. 130) or whether patient selection and surgical technique matter more is unanswerable at N=6.
The Bridge Nobody Expected
Tim Andrews' story contains the most consequential data point in the entire scorecard. After his eGenesis pig kidney was removed in October 2025, he received a human donor kidney on January 13, 2026. He is the first person in history to undergo a successful allotransplant (human-to-human) after a xenotransplant (pig-to-human).
That sequence matters more than the 9-month record. It suggests pig kidneys could function as a bridge to human transplant rather than a permanent replacement. For the 90,000 people on the kidney waitlist, a bridge organ that keeps them alive and off dialysis for months while they wait for a human donor changes the calculus entirely. Andrews had O-positive blood, which meant a 5-10 year estimated wait. He had a 9% chance of receiving a human kidney within five years, according to eGenesis. Statistically, there was a 49% chance he would be removed from the waitlist due to illness or death before a kidney became available.
He got one in 12 months.
The $50 Billion Problem
About 555,000 Americans are on dialysis. Average annual cost per patient runs roughly $90,000 under Medicare (per USRDS data). That puts total U.S. dialysis spending at approximately $50 billion per year. A kidney transplant costs roughly $400,000 upfront but saves about $35,000 annually compared to dialysis over the long term.
Run the numbers on even modest xenotransplant penetration:
| Scenario | Patients Served | Annual Dialysis Savings | Waitlist Deaths Averted |
|---|---|---|---|
| 10% of waitlist backlog | 9,000 | $810 million/year | ~620/year |
| 25% of waitlist backlog | 22,500 | $2.0 billion/year | ~1,550/year |
| 50% of waitlist backlog | 45,000 | $4.1 billion/year | ~3,100/year |
Calculation: 17 deaths/day x 365 = 6,205 annual waitlist deaths. Dialysis savings assume $90K/yr per patient redirected from dialysis to functioning transplant. These are gross savings; they do not account for xenotransplant procedure costs, immunosuppression, or monitoring, none of which have been publicly priced at scale.
Neither eGenesis nor United Therapeutics has disclosed expected per-unit pricing for a pig kidney. But the economics of dialysis create an enormous incentive. Every patient removed from dialysis saves Medicare $90,000 per year. A pig kidney that functions for even one year before needing replacement or bridging to a human kidney is cost-effective against the counterfactual.
What David Bennett's Death Taught Everyone
The first case on the scorecard remains the most instructive. David Bennett received a pig heart from Revivicor (a subsidiary of United Therapeutics) in January 2022 at the University of Maryland. He survived 60 days. Post-mortem analysis revealed porcine cytomegalovirus (PCMV) in the transplanted heart, a pathogen that should have been detected during pre-transplant screening.
That single finding reshaped the field. Screening protocols were overhauled. eGenesis went further: their 69-edit approach includes inactivation of porcine endogenous retroviruses (PERVs) that are integrated into the pig genome itself. PERVs cannot be screened out because they are part of the pig's DNA. They must be edited out, nucleotide by nucleotide. eGenesis claims to be the only company making this class of edit.
United Therapeutics does not inactivate PERVs. Their position, implied by the design of UKidney, is that the risk is manageable through screening and monitoring rather than genomic deletion. This is not an unreasonable position, as no PERV transmission to humans has been documented in any xenotransplant case to date. But the absence of evidence is not evidence of absence, and the history of cross-species viral transmission (HIV originated in chimpanzees; influenza regularly jumps from pigs) suggests vigilance is warranted over timescales longer than the 270-day record currently available.
Strongest Counterargument
Six patients is not a dataset. It is an anecdote collection. Comparing eGenesis' 270-day survival to United Therapeutics' 130-day record and attributing the difference to gene-edit count requires ignoring every confounding variable: patient age, baseline health, surgical team experience, immunosuppression protocols, comorbidities, and sheer luck. Rick Slayman received an eGenesis kidney with 69 edits and died from cardiac causes two months later. Towana Looney received a United Therapeutics kidney with 10 edits and had 130 functional days. Single-patient outcomes in different institutions with different protocols are not head-to-head comparisons.
More fundamentally, the history of xenotransplantation is littered with premature optimism. Baby Fae's 21-day survival in 1984 generated enormous excitement that led nowhere for 38 years. The current generation of pig organs may face failure modes that only emerge at longer time horizons: chronic rejection, subclinical viral reactivation, or immune tolerance decay that does not manifest until year two or three. The longest observation period in a living human is 270 days. We know nothing about what happens at 365, or 730, or 1,825.
Limitations
This analysis aggregates publicly available data from press releases, hospital statements, and news reports. No patient medical records were reviewed. Survival durations are approximate, based on published dates. Immunosuppression regimens differ across institutions and are not standardized; comparing outcomes across different protocols is inherently limited. Cost projections use aggregate Medicare/USRDS data and do not account for individual variation in dialysis costs, comorbidity-related expenses, or the currently unknown cost of xenotransplant procedures at scale. Long-term outcomes beyond 270 days are entirely unknown. The small sample size (N=6) makes any statistical inference impossible.
The Bottom Line
Pig-to-human organ transplantation has gone from a sci-fi concept to two competing FDA clinical trials in four years. The survival curve is improving fast: 60 days to 270 days in three iterations. A patient has now successfully bridged from a pig kidney to a human kidney, proving the concept that matters most for the 90,000 people on the waitlist. eGenesis and United Therapeutics are running their Phase 1/2/3 trials now, with first data expected in 2026-2027. If even 10% of the waitlist backlog can be served, that is 620 lives per year and $810 million in dialysis savings. The gene-editing question (69 edits vs. 10) will only be answered by the trials. The organ shortage question has a clearer answer: 17 people died today. Another 17 will die tomorrow. The pig kidneys are not perfect, but they are real, and they are here.