A pig kidney kept a living man alive

Surgeons at Massachusetts General Hospital transplanted a kidney from a pig carrying 69 genetic edits into a living man in March 2024; he went home two weeks later.

The number in the organ

Sixty-nine is the count of genomic edits carried by the pig whose kidney was transplanted into Richard Slayman at Massachusetts General Hospital on March 16, 2024. The edits were described in detail by Anand and colleagues at eGenesis in Nature in October 2023. They fall into three groups. Three pig genes that produce glycan antigens, sugars on the cell surface that human antibodies attack within minutes, were knocked out. Seven human transgenes, which regulate complement, coagulation and inflammation, were inserted at a single genomic site. And 59 copies of porcine endogenous retrovirus embedded in the pig genome were inactivated to remove the risk that they could cross into a human recipient. The donor line was a Yucatan miniature pig, chosen because its organs are close to human size, with blood type O to avoid ABO incompatibility. The editing was done with CRISPR-Cas9.

Why the pig had to be edited

The Nature paper tested the design in cynomolgus monkeys. Kidneys from pigs carrying only the three glycan knockouts survived a median of 24 days. Kidneys that also carried the seven human transgenes survived a median of 176 days, a difference the authors report as statistically significant. The longest-surviving graft functioned for 758 days. In laboratory tests, edited pig kidney endothelial cells modulated inflammation to a degree the authors describe as indistinguishable from human endothelial cells.

Before a living patient, there were the deceased. In 2022 Robert Montgomery and colleagues at NYU Langone reported in the New England Journal of Medicine that kidneys from pigs lacking the alpha-gal antigen, transplanted into two brain-dead recipients maintained on ventilators, began making urine within moments of reperfusion and showed no hyperacute or antibody-mediated rejection on biopsies over a 54-hour study. Estimated glomerular filtration rate rose from 23 to 62 in one recipient and from 55 to 109 in the other.

March 16, 2024

Slayman was 62, from Weymouth, Massachusetts, with end-stage kidney disease from long-standing type 2 diabetes and hypertension. According to the hospital's announcement, he had spent seven years on dialysis before receiving a human kidney from a deceased donor in December 2018. That kidney began to fail in 2023, and he returned to dialysis in May of that year. The U.S. Food and Drug Administration granted a single-patient Expanded Access Protocol, the compassionate-use pathway, in late February 2024. The surgery took four hours. His immunosuppression included two investigational agents, tegoprubart and ravulizumab, alongside standard drugs. The hospital's announcement placed the national transplant waiting list at more than 100,000 people, with 17 dying each day while waiting, and its own kidney waiting list at more than 1,400.

The clinical report, by Tatsuo Kawai, Leonardo Riella and colleagues, appeared in the New England Journal of Medicine in 2025. The xenograft functioned immediately. Creatinine fell promptly and progressively, and dialysis was no longer needed. On day 8 a biopsy showed T-cell-mediated rejection, which was reversed with intensified immunosuppression. He was discharged on April 3, 2024, 18 days after surgery.

Day 52

On May 11, 2024, Mass General announced that Slayman had died suddenly. The transplant team's statement said it had no indication that the death was the result of the transplant. The NEJM report gives the cause: sudden cardiac death on post-transplant day 52, with autopsy showing severe coronary artery disease and ventricular scarring. Kidney function had been sustained to that point, and the autopsy found no evident rejection of the xenograft. His family's statement said the procedure had given them seven more weeks with him.

What came after

On November 25, 2024, Montgomery's team at NYU Langone transplanted a kidney from a Revivicor pig carrying ten gene edits into Towana Looney, a 53-year-old woman from Alabama who had been on dialysis for eight years and had earlier donated a kidney to her mother. The organ was removed on April 4, 2025, after 130 days, because of acute rejection; she returned to dialysis.

On January 25, 2025, Mass General transplanted a second eGenesis kidney, this time into Tim Andrews, a 66-year-old man from New Hampshire who had been on dialysis for more than two years. The procedure was carried out under an FDA-authorized multi-patient expanded access study; according to Harvard's account of the surgery, the authorization covered a three-patient study at Mass General, with two further transplants planned for 2025. A third recipient, also from New Hampshire, received a kidney in June 2025 and was reported by the hospital in October to be faring well. According to the hospital, the kidney was removed on October 23, 2025, after 271 days, because its function was declining. Andrews returned to dialysis and, according to eGenesis, received a human kidney on January 13, 2026. Each living recipient to date has kept a pig kidney longer than the one before: 52 days, 130 days, 271 days.

The waiting list

The Organ Procurement and Transplantation Network's 2024 annual report, published in the American Journal of Transplantation, records 27,660 kidney transplants in the United States in 2024, the highest number on record, against 143,982 adult candidates listed during the year. One candidate in ten had been waiting five years or longer. The federal donation site organdonor.gov placed the national transplant waiting list at 109,817 people in its 2026 snapshot, with kidneys the most commonly needed organ and the majority of the list, and reported that twelve people die each day while waiting.

What the story does and does not show

The NEJM report describes one patient followed for 52 days. The kidney worked, a rejection episode was reversed, and the recipient died of heart disease that predated the operation. That is evidence that a 69-edit pig kidney can sustain a living human for weeks. It is not evidence about months or years, and there was no comparison group.

Across the three living recipients described here, the longest a pig kidney has remained in place is 271 days, and each organ was ultimately lost to rejection or declining function or outlived by the patient's other conditions. All three transplants were performed under compassionate-use or expanded-access authorization, not in a completed clinical trial. The story's slide saying Slayman went home two weeks later understates the interval by four days. The slide's figure of more than 90,000 Americans waiting for a kidney is consistent with the official totals above but is not a number this article could verify from a primary source at a single date. The waiting list is real, the edits are real, and the organ functioned. Whether a pig kidney can replace dialysis for years remains an open question in a study that has, so far, enrolled a handful of people.

Sixty-nine edits, and the organ worked.