A groundbreaking xenotransplantation experiment just reached a new milestone. Tim Andrews lived with a genetically engineered pig kidney for nearly nine months - the longest such transplant on record - before surgeons at Massachusetts General Hospital removed it on October 23. The achievement marks a significant step forward in addressing the critical organ shortage that leaves 90,000 Americans waiting for kidneys.
The biotech world just witnessed its most successful xenotransplantation to date. Tim Andrews, a 67-year-old New Hampshire man, lived with a genetically engineered pig kidney for nearly nine months before declining function forced its removal at Massachusetts General Hospital last week.
Andrews received the pig kidney on January 25 after spending over two years on dialysis. His rare blood type meant an even longer wait than the typical three-to-five years most kidney patients face. But this wasn't just about one patient - it was about proving that cross-species organ transplants could work at scale.
The numbers tell the story of why this matters. Nearly 90,000 Americans are waiting for kidney transplants right now, while the US managed just 28,000 procedures in 2024. The gap between supply and demand keeps widening, pushing researchers toward increasingly bold solutions.
eGenesis, the Cambridge biotech company that engineered Andrews' kidney, used CRISPR technology to make 69 genetic modifications to their donor pig. They removed harmful pig genes and added human ones, creating what they hoped would be a more compatible organ. The extensive editing represents a different approach from competitors like Revivicor, a subsidiary of United Therapeutics, which used single-digit gene modifications in earlier trials.
Andrews became the fourth person worldwide to receive a pig kidney, and his outcome dramatically outperformed the others. Richard Slayman, the first recipient at Mass General, died in May 2024 after nearly two months. Lisa Pisano at NYU Langone had her pig kidney removed after less than two months due to failure - she later passed away. Towana Looney, also at NYU Langone, lived with her pig kidney for just over four months before rejection forced its removal.
The pattern was troubling, but Andrews changed the trajectory. His kidney showed early signs of cellular rejection just two weeks post-surgery, but Leonardo Riella, Mass General's medical director for kidney transplantation, successfully treated it with adjusted immunosuppressants. "Off and on, we have had to adjust his medications. It's definitely more intense than a regular human transplant," Riella told WIRED in July.
The intensive medication management paid off. Andrews was discharged on February 1 and lived normally for months - a crucial proof point that pig organs could provide meaningful quality of life, not just biological function.
Two more patients have since received pig kidneys: one in China and 54-year-old Bill Stewart at Mass General, bringing the total to six worldwide. The field is moving fast, with each procedure informing the next.
eGenesis isn't calling this a failure. "The life-supporting function provided by the donor organ highlights the possibilities for patients around the world who are desperately waiting for a transplant," the company said in a statement. They're framing nine months of function as validation of their heavily-edited approach.
The genetic editing debate is far from settled. While eGenesis uses 69 modifications, Revivicor's earlier attempts used just one or ten edits. The optimal number remains an open question that could determine which company dominates this emerging market.
Mass General isn't slowing down - they plan another pig kidney transplant before year-end. Each iteration generates more data about rejection patterns, optimal immunosuppression protocols, and patient selection criteria.
Andrews' nine-month success represents real progress in xenotransplantation, even though the kidney ultimately failed. His case proves that heavily gene-edited pig organs can provide sustained function and meaningful quality of life. As Mass General prepares its next procedure and companies refine their genetic modifications, we're watching the early stages of what could become a massive new organ supply chain. For the 90,000 Americans waiting for kidneys, each month of additional function brings hope that animal organs might eventually bridge the transplant gap.
