A potentially lifesaving treatment for some of 800,000 Americans suffering from kidney disease just took a step toward becoming a reality. For more than a month, a pig kidney has been functioning inside a person. It is the longest period of time that a gene-edited pig kidney has continued working in a human.

Maurice “Mo” Miller is the 57-year-old man on whom the transplant was performed, reports The Associated Press. After he was declared brain-dead, his sister gave permission for his body to be used in the experimental xenotransplantation.

On July 14, doctors at NYU Langone Health removed both human kidneys and replaced them with a single kidney from a genetically modified pig. The kidney immediately began producing urine and looked “even better than a human kidney,” said Dr. Robert Montgomery, director of NYU Langone’s transplant institute.

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Kidney disease in the U.S.

According to the National Kidney Foundation, there are more than 100,000 patients in the United States waiting for kidney transplants, with a median wait time of 3.6 years. More than 3,000 people are added to the waiting list every month, but almost 400 die each month while waiting. About 26,000 people received a kidney transplant in 2022.

Dialysis can keep patients with kidney failure alive, but the gold standard treatment is an organ transplant, reports The New York Times. “A lot of folks think dialysis is an appropriate alternative, but people die on dialysis,” said Dr. Jayme Locke, director of the University of Alabama Comprehensive Transplant Institute and lead researcher on another pig-to-human kidney transplant experiment.

Montgomery, himself the recipient of a heart transplant, is acutely aware of the need for transplantable organs. “There are simply not enough organs available for everyone who needs one,” he said in the NYU Langone press release. These experiments in donor bodies are crucial to moving toward live clinical trials.

Overcoming rejection

NYU Langone notes that the “first hurdle to overcome in xenotransplants is preventing hyperacute rejection, which typically occurs just minutes after an animal organ is connected to the human circulatory system.”

Those rejection issues are overcome by using genetic modification to better match organs to human bodies. In the case of the monthlong functioning pig kidney, a single gene modification was made, which knocks out the hyperacute rejection gene. That genetic modification was combined with embedding the pig’s thymus gland under the outer layer of the kidney. Previous genetically engineered pig organ transplants have incorporated up to 10 genetic modifications.

Additionally, standard transplant immunosuppression medications are being used, along with “enhanced screening of porcine cytomegalovirus (pCMV) in the donor pig” as pCMV may affect organ performance and potentially trigger organ failure. No pCMV was detected after 32 days, reports NYU Langone.

What’s next?

The pig kidney experiment at NYU Langone will continue for another month, “with permission from the family, ethics committee approval and continued support from United Therapeutics,” the parent company responsible for producing the genetically altered pigs.

Both The Associated Press and The New York Times report that the Food and Drug Administration are in discussions with researchers on whether to allow rigorous trials of pig heart or kidney transplants to begin in live volunteer patients.