Roughly 90,000 people are on the U.S. kidney transplant waiting list at any given time, and a meaningful share will die or be delisted before a human organ becomes available. That shortage, not novelty, is why the FDA has cleared two separate companies to put gene-edited pig kidneys into living humans on a prospective basis for the first time in medical history.
United Therapeutics announced FDA clearance of its investigational new drug application for the UKidney xenotransplantation trial in February 2025, and performed the first transplant under its EXPAND study, the first clinical trial evaluating xenotransplantation in end-stage renal disease, in late 2025. United Therapeutics The EXPAND protocol is registered to run until 2075, reflecting how long-term this evidence program is designed to be. ClinicalTrials.gov eGenesis received its own IND clearance for a kidney transplant program in September 2025, building on an existing expanded access compassionate use cohort. eGenesis The Associated Press covered the first EXPAND transplant, performed at NYU Langone, as the start of the first formal clinical trial of its kind. AP News
What makes the pig kidney survive a human immune system?
Both companies use pigs with multiple gene edits: knockouts of genes that produce sugar antigens the human immune system attacks on contact, and insertions of human complement-regulatory and coagulation genes to reduce hyperacute rejection risk. United Therapeutics' organ, marketed as the "10 GE" kidney, carries ten such edits. This is not a single edit, it is a stacked genetic engineering program refined over more than a decade of nonhuman primate data before ever reaching a human recipient.
What are these trials actually measuring?
Three things, in order of clinical priority.
- Graft survival at defined intervals. Early compassionate-use patients survived weeks to months. A trial-grade result needs to show graft function extending past a year in a meaningful fraction of patients.
- Rejection episodes and the immunosuppression regimen required to prevent them. If patients need immunosuppression far more aggressive than standard transplant protocols, the net clinical benefit shrinks even if the organ itself survives.
- Infection risk, specifically the theoretical risk of porcine endogenous retrovirus transmission, which the gene-editing programs are specifically designed to inactivate.
Why regulators are moving unusually fast here
Xenotransplantation is one of the few areas where FDA has publicly supported prospective human trials despite an evidence base built almost entirely on compassionate use cases rather than the traditional animal-to-Phase-1-to-Phase-2 ladder. The rationale is straightforward: dialysis carries its own five-year mortality burden, and a terminal patient facing that reality changes the risk calculus that governs first-in-human review. This is a case where desperate unmet need is doing real regulatory work, not just providing a marketing narrative.
What has to happen before this reaches ordinary patients
Even a strongly positive EXPAND readout will not put xenotransplant kidneys into standard nephrology practice quickly. Manufacturing capacity for gene-edited, pathogen-free source pigs is small and expensive. Long-term outcomes data, meaning multi-year graft survival across a broader population than a first cohort of critically ill patients, will take years to accumulate given the trial's own 2028 primary completion target. And payers have no existing reimbursement pathway for a xenograft, which will need its own coding and coverage determination separate from human-donor transplant codes.
The takeaway
This is one of the few genuinely novel therapeutic modalities moving through FDA review right now, not an incremental device iteration. The near-term signal to watch is not headlines about the first transplant, that milestone has passed, it is the first published one-year graft survival data out of EXPAND, expected as the trial's early cohort matures. That number, not the initial procedure, will determine whether xenotransplantation becomes a real answer to the organ shortage or remains a compassionate-use bridge for a small number of patients.
