Genetically Modified Pig-to-Human Kidney Xenotransplant

The organ transplant waiting list has grown steadily for decades, and kidney disease sits at its center. Fewer than 25,000 renal transplants are performed annually in the United States against a waiting list that has exceeded 90,000 patients. Xenotransplantation, using animal organs as a source, had been attempted sporadically since the 1960s, but every attempt foundered on hyperacute rejection: the human complement system recognized alpha-1,3-galactose residues on pig endothelial cells and destroyed the graft within minutes to hours. Genetic modification offered a theoretical escape from that barrier, but the step from preclinical primate work to a human recipient had not been taken.

In September 2021, Robert Montgomery and colleagues at NYU Langone surgically attached the kidney of an alpha-1,3-galactosyltransferase (GGTA1) knockout pig to the femoral vessels of a brain-dead human recipient being maintained on life support, with consent from the family. The organ was positioned outside the abdominal cavity, on the thigh, to allow direct observation. Over 54 hours it produced urine, excreted creatinine, and showed no signs of hyperacute rejection. The result was notable both for what happened and for what did not happen: the complement cascade never fired, and the graft remained viable.

The donor pig carried a single gene knockout, the simplest genetic modification available at that stage. Within months, teams at NYU and the University of Alabama at Birmingham under Jayme Locke were working with pigs carrying up to 10 genetic edits, including removal of additional pig antigens and insertion of human complement-regulatory, coagulation, and immune-modulatory genes. In a separate 2021 experiment, Locke's UAB team transplanted a pair of these 10-gene pig kidneys into a brain-dead patient, which functioned for 77 hours without rejection. The field moved from proof-of-concept to iterative refinement within a single year.

Subsequent years brought more challenging tests. In 2022 a pig heart was transplanted into a living patient at the University of Maryland; it functioned for nearly two months before the patient died. The graft's failure involved both an immune rejection response and reactivation of a latent porcine virus (porcine cytomegalovirus), a finding that pushed transplant programs toward more thorough pathogen screening of donor animals. In March 2024, Tatsuo Kawai's team at Massachusetts General Hospital performed the first transplant of a gene-edited pig kidney into a living patient, under a single-patient compassionate-use authorization from the FDA, with a second such transplant following in January 2025. Chronic kidney disease affects roughly 37 million Americans, and xenotransplantation is one of the few approaches that could increase the absolute supply of transplantable organs rather than optimize allocation of an unchanged supply.