Xenotransplantation, the process of using organs from one species in another, is gaining traction in the medical field as advancements in technology pave the way for new possibilities. Tim Andrews, a resident of New Hampshire, faced a dire situation with failing kidneys and saw little hope of receiving a human transplant in time. However, after learning about Richard Slayman, who underwent a xenotransplant in 2024, Andrews reached out to the medical team at Mass General Hospital (MGH) in Massachusetts.
On January 25th, surgeons at MGH performed a groundbreaking operation, transplanting a genetically modified pig kidney into Andrews. This organ functioned for 271 days, setting a new record for such procedures. While both Andrews and Slayman received their transplants under exceptional compassionate grounds, the field of xenotransplantation is moving towards wider clinical applications. In September, the Food and Drug Administration (FDA) granted approval to eGenesis, the company responsible for Andrews”s kidney, to initiate full-scale clinical trials for pig kidneys. United Therapeutics, known for producing pig organs via its subsidiary Revivicor, received similar permissions in February.
The global demand for organ transplants is staggering, with less than 10% of those needing a transplant receiving one, according to the Global Observatory on Donation and Transplantation. In the United States, approximately 13 individuals die daily while waiting for organ donations. The scarcity of available organs has also led to a black market, where patients pay exorbitant amounts for questionable sources. Pigs, with their rapid breeding capabilities and organ sizes that closely resemble human organs, are seen as a viable solution to this shortage. Their biological similarities to humans reduce ethical concerns associated with using primates.
Despite the promise of xenotransplantation, progress has been gradual. A pioneering study in 1995 by Jeffrey Platt, a surgeon at the University of Michigan, marked the beginning of pig organ transplants into monkeys. Recent advancements have largely been attributed to CRISPR technology, which enables precise editing of pig genomes to enhance organ compatibility with humans. One of the significant challenges in transplantation is the risk of organ rejection, where the recipient”s immune system identifies the new organ as foreign. This issue is amplified with cross-species transplants, requiring extensive immunosuppressant medication that carries risks of infections and other side effects.
Companies like Revivicor and eGenesis use advanced genetic editing techniques to create pigs with modified genes that minimize immune responses. By disabling several pig genes responsible for strong immune reactions and incorporating human genes that help reduce rejection and blood clotting issues, they aim to produce suitable organ donors. The resulting genetically edited pigs have shown promise in monkey trials, but human results have been mixed. Andrews”s case highlights the complexities of managing rejection; although he initially managed to control rejection with medication, he ultimately had to return to dialysis after his kidney”s function declined.
Looking ahead, both eGenesis and Revivicor are optimistic about their upcoming trials and the potential for improved treatments. Eledon, a collaborating firm, is testing a new anti-rejection drug, tegoprubart, which may offer fewer side effects than existing medications. Revivicor is also investigating ravulizumab, a drug currently used for autoimmune disorders.
In addition to kidney transplants, research is expanding to other organs. Revivicor has conducted two heart transplants from pigs and is preparing to trial its “UThymoKidney,” which combines pig kidneys with porcine thymus tissue to potentially enhance immune tolerance. Meanwhile, eGenesis has received approval for a pig-liver perfusion system, which would keep the organ functioning outside the body while connected to a patient”s circulatory system, offering a temporary solution until a suitable human organ becomes available.
As of now, Tim Andrews is not the only patient with a pig kidney; Bill Stewart, an athletics coach, received his transplant in June. MGH plans to perform additional transplants later this year, marking a significant step forward in the field of xenotransplantation.
Correction (October 29, 2025): This article has been updated to clarify that the FDA granted approval to United Therapeutics rather than Revivicor.
