Tim Andrews, a 66-year-old man, survived for 271 days with a genetically modified pig kidney before receiving a human transplant in January. this experimental procedure at Mass General Brigham provided a critical alternative to dialysis for a patient with a rare blood type.
The 271-Day Bridge to a Human Organ
For Tim Andrews, the experimental pig kidny was not a permanent cure but a survival mechanism. According to a paper published in the Journal of American Society of Nephrology, the organ functioned for nine months, allowing Andrews to recover from a state of extreme weakness where he had previously been unable to walk. The pig kidney eventually failed after blood clots formed in the organ's vessels, necessitating its removal and a brief return to dialysis.
The success of the subsequent human kidney transplant in January is perhaps the most significant clinical finding. Mike Curtis, CEO of eGenesis,noted that the previous exposure to pig tissue did not appear to alter how Tim Andrews' body responded to the human organ. This suggests that xenotransplantation does not necessarily sensitize a patient or create barriers to receiving a traditional human transplant later.
Addressing the 90,000-Person U.S. Waiting List
The urgency of this research is underscored by the dire statistics provided by the United Network for Organ Sharing, which notes that roughly 90,000 people are currently on the U.S. kidney transplant waiting list. With an average of 11 people dying every day while waiting for a donor, the demand for viable organs far outstrips the supply.
Dr. Leonardo Riella of Mass General Brigham emphasizes that for many patients, the alternative to a transplant is dialysis, which he describes as causing immense "wear and tear ." The goal of using a pig kidney as a "bridge" is to keep patients healthy enough to survive until a matching human donor becomes available, rather than allowing them to deteriorate to a point where they are too sick for any surgery.
How eGenesis Modified the Pig Genome
The organ used in the Tim Andrews case was produced by the biotechnology firm eGenesis. To make the transplant viable, the pig underwent extensive genetic editing designed to inactivate endogenous viruses within the pig genome and prevent the human immune system from immediately rejecting the foreign tissue.
This genetic tailoring is what allowed the organ to function for nearly 300 days . While the blood clots that eventually ended the experiment highlight the remaining technical hurdles, the ability of a gene-edited organ to sustain human life for several months represnts a significant leap from earler attempts in the field.
Lessons from Rick Slayman and the 33-Patient Trial
The path to this milestone has been marked by both progress and tragedy. In March 2024, Mass General Brigham transplanted a pig kidney into Rick Slayman, who died within two months due to a cardiac event that appeared unrelated to the organ itself... Similarly, early pig heart transplants in 2022 resulted in recipients who died shortly after the procedure.
Despite these losses, as a statement from eGenesis reported, three of the five patients in the current expanded access program have lived with their pig kidneys for more than eight months. This data has provided the confidence for eGenesis to plan a formal clinical trial involving 33 patients next year. Dr. Muhammad Mohiuddin of the University of Maryland School of Medicine, who spent decades researching xenotransplantation in primates, notes that the transition to human application has moved faster than many in the scientific community ever imagined.
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