A 66-year-old New Hampshire man with end-stage kidney disease spent 271 days living off a gene-edited pig kidney before doctors at Massachusetts General Brigham replaced it with a human organ from a deceased donor in January, a case doctors say shows the experimental procedure can serve as a bridge rather than a permanent fix. Tim Andrews of Barrington, New Hampshire, received the pig kidney transplant in January 2025 and stopped dialysis entirely during that stretch, before ultimately receiving the human kidney about a year later.
According to WCVB Boston, Andrews said he is doing well and has now gone a little over 280 days since his human kidney transplant. Massachusetts General Brigham doctors confirmed the genetically edited pig kidney bought him time while he waited for a human organ to become available, a case that WCVB reports marks the longest anyone has lived with a pig kidney since the world's first such procedure in 2024.
Dr. Leonardo Riella, a surgeon at Mass General Brigham, said the case demonstrated that patients receiving a pig kidney may not become sensitized and face no major limitations to later receiving a human transplant. Pig transplantation, he said, may not prevent or limit a patient's access to a human kidney down the line — a finding that reframes the animal organ as a stopgap rather than a competitor to the traditional donor pipeline.
Why Andrews Needed a Bridge in the First Place
Before the procedure, Andrews faced more than a 40% chance of dying or being removed from the transplant waitlist, compared with just a 9% chance of receiving a human kidney within five years, according to The Guardian. End-stage kidney disease patients on dialysis generally face a five-year mortality rate exceeding 50%, the outlet reports, underscoring the stakes behind his decision to pursue an experimental option. According to the National Institutes of Health's 2025 United States Renal Data System Annual Data Report, the adjusted mortality rate among people with end-stage kidney disease was 132.5 per 1,000 person-years. The report also says more than half of people died within five years of starting treatment for end-stage kidney disease, and over 75% died within 10 years.
The pig kidney, designated EGEN-2784, functioned immediately after surgery but began showing damage to its blood vessels around six months in, ultimately leading to organ failure at day 271. Notably, no pig viruses or retroviruses were detected throughout the entire duration of the transplant, per a report from Radio Royal, addressing a safety concern that has long shadowed xenotransplantation research. According to the U.S. Food and Drug Administration's PHS Guideline on Infectious Disease Issues in Xenotransplantation, xenotransplantation trials require formal responsibility for designing and monitoring the studies. The U.S. Food and Drug Administration's xenotransplantation guidance addresses infectious-disease risks associated with porcine donor animals and explains how sponsors should assess those risks.
The Company Behind the Engineered Organ
EGEN-2784 was developed by Cambridge-based biotechnology firm eGenesis, which used CRISPR-Cas9 gene editing to make 69 modifications designed to prevent immune rejection and block virus transmission, according to CGTlive. The company's platform works by inactivating porcine endogenous retroviruses while inserting human transgenes to boost compatibility with human recipients.
The case builds on a program that began in March 2024, when 62-year-old Richard “Rick” Slayman became the world's first living recipient of a gene-edited pig kidney at Massachusetts General Hospital under FDA compassionate use rules — a milestone Hoodline covered at the time. Slayman lived with the organ for 52 days before dying of a sudden cardiac arrhythmia that doctors determined was unrelated to organ rejection, according to MedPage Today. Mass General Brigham has since performed additional pig kidney xenotransplants on 54-year-old Bill Stewart in June 2025 and 56-year-old Molly Falco in November 2025 under an FDA-approved expanded access pilot study, according to Riella.
A Path Toward Formal Clinical Trials
The U.S. Food and Drug Administration has since cleared an Investigational New Drug application allowing eGenesis to launch a Phase 1/2/3 clinical trial evaluating EGEN-2784 kidneys in dialysis-dependent patients aged 50 and older with end-stage kidney disease, according to CRISPR Medicine News. That clearance marks a shift from individual compassionate-use cases toward a structured, multi-patient clinical evaluation. eGenesis isn't alone in the race — biotechnology firm United Therapeutics received its own FDA clearance in February 2025 to begin Phase 1/2/3 trials for a competing gene-edited porcine kidney product called UKidney, per CGTlive.
The bridge option could eventually be available to more than 90,000 Americans currently on the kidney transplant waitlist, per WCVB's report. Figures from the Organ Procurement and Transplantation Network show that just 27,573 kidney transplants were performed nationwide in 2025, according to UNOS, while an average of 12 to 13 people on the waitlist die each day. Mass General Brigham's institutional ties to transplant medicine run deep: surgeons at Brigham and Women's Hospital performed the world's first successful human organ transplant, a kidney, back in 1954, according to Mass General Giving.
