Gene-edited pig kidneys sustain patients past nine months in US clinical trials

Extending survival past nine months

A female patient at Massachusetts General Hospital has lived with a gene-edited pig kidney for 285 days without requiring dialysis, setting a record for animal-to-human organ transplants. The procedure took place on 22 November 2025 under the expanded access pathway of the Food and Drug Administration, which permits experimental interventions for patients facing life-threatening conditions with no standard alternatives. The organ was developed by Cambridge-based biotechnology firm eGenesis, which used Crispr gene editing to modify porcine DNA for human compatibility. The patient represents the fifth individual to receive an eGenesis kidney. eGenesis chief executive Mike Curtis explained the rationale for providing xenotransplants to patients facing severe declines on dialysis.

What we saw with Mr. Andrews was a radical improvement in his overall health while he was on the pig kidney versus if he had stayed on chronic dialysis.

The first bridge to a human transplant

The clinical data follows the case of Tim Andrews, a 66-year-old New Hampshire resident whose treatment details were published in The Lancet. Andrews suffered from end-stage renal disease caused by type 2 diabetes and faced a 9% chance of securing a human kidney within five years, compared to a greater than 40% risk of dying or removal from the transplant registry. In January 2025, surgical teams at Mass General Brigham implanted a kidney from a Yucatan miniature pig named Wilma. The organ functioned for 271 days, allowing Andrews to manage household activities and walk his dog before decreasing renal function required its removal in October 2025. Following a brief return to dialysis, Andrews received a kidney from a deceased human donor, establishing the first documented use of a xenotransplant as a temporary bridge.

Andrews reflected on the personal impact of regaining kidney function after his prolonged illness.

I was alive, and I hadn't been in a long time.

Shortages in donor organ registries

The xenotransplantation trials address severe structural imbalances between organ demand and donor availability. In the United States, approximately 100,000 individuals remain on waiting lists for kidney transplants, while medical centers perform around 25,000 transplants annually. In the United Kingdom, more than 7,000 patients await kidney donations. Typical wait times range from three to five years, though patients can wait up to seven years depending on blood type and matching criteria. Routine dialysis demands four-hour sessions three times per week, a regimen that progressively damages blood vessels and yields an average patient survival of five years.

Andrews noted the psychological and physical strain associated with extended waiting periods on dialysis.

Hope is the biggest thing, the chance to be free from the machine and live your life.

Genetic engineering and safety modifications

Making porcine kidneys viable in human recipients requires extensive genomic modification to prevent hyperacute rejection and viral transmission. Before transplantation, eGenesis applied 69 Crispr gene edits to Wilma the pig, knocking out porcine genes that trigger human immune responses, adding human genes, and disabling endogenous retroviruses. Earlier efforts yielded shorter survival times, including the first living pig kidney recipient in 2024, who died after 52 days from unrelated cardiac issues. Prior to these trials, xenograft survival in living human recipients had not exceeded two months. Mass General Brigham and eGenesis continue to evaluate xenotransplants under regulatory pathways to stabilize patients while deceased donor kidneys remain unavailable.