Scientists Reverse Human Rejection of Pig Organ Transplant for First Time Ever

A new study reversed transplant rejection twice, uncovering the reasons for transplant rejection on a cellular level

Mary Randolph - Staff Contributor

November 18, 2025 12:10 p.m.

A team of doctors at NYU Langone transplanted a pig kidney into a brain-dead patient and reversed its rejection twice during the 61-day study. Joe Carrotta / NYU Langone

Facing a shortage of organs needed by tens of thousands of patients, scientists have been studying pig organs as a potential solution. Genetically modified to suit humans and transplanted in the same way as human organs, the hope has been that they would function as well as those transplanted from human donors. But human bodies keep rejecting them.

A new study published November 13 in Nature provides new hope. In it, an international team of physicians detail how they prevented a human’s body from rejecting a pig organ—not once, but twice—for the first time ever.

Fun Fact: Livers and kidneys are just the beginning

When it comes to transplanting organs, livers and kidneys are just the beginning. Everything from the human eye to heart valves and knee cartilage can be transplanted between humans—but animal organ transplantation is still relatively young compared to the field of transplantation itself.

Scientists transplanted a kidney on a brain-dead patient whose body had been donated to science. Over the 61-day experiment, the patient’s body rejected the transplant twice. Both times, doctors reversed the rejection with existing medication, returning the kidney to successful function.

“It’s a huge step forward,” Robert Montgomery, lead author of the study and director of the NYU Langone Transplant Institute, where the research was conducted, tells ABC News’ Mary Kekatos. “As we move forward, I do believe that we will be in a position in the next few years where gene-edited pig organs will be an alternative to human organs.”

“In my mind, this is the first evidence of how to reverse rejection,” Muhammad Mohiuddin, a surgeon at the University of Maryland School of Medicine who led the first pig-human transplant in 2022 and was not involved in the study, tells Nature’s Rachel Fieldhouse.

The team could understand and reverse the rejections so successfully because of the daily research they conducted on the patient, tracking his organ activity on a cellular level. This tracking allowed researchers to catch both organ rejections five days earlier than they would have otherwise, ABC reports.

“We could really get a very dense set of data points from doing biopsies, taking blood samples, body fluid samples and create an atlas of what that immune response looks like,” Montgomery tells the outlet. “And that’s what’s really unique about the study. I think that this is probably the most deeply studied human in history.”

From their analyses of the patient’s blood, the researchers pinpointed specific cells and antibodies causing rejections. The pig organ expressed higher levels of genes that human immune systems consider foreign substances, they found, prompting an immune response. T cells—white blood cells that react to germs and unknown invaders—also play a larger role in rejection than previously thought, Montgomery tells Nature.

The study, which researchers chose to end at the 61-day mark, marks the longest time a pig organ has survived in a brain-dead patient and signals hope for future application of this method, Minnie Sarwal, a surgeon who co-directs the University of California San Francisco’s kidney and pancreas transplant program, tells CNN‘s Jen Christensen.

“Sixty-one days of stable renal function is novel proof of concept, and I think it confirms that genetically engineered pig kidneys can sustain physiological function in human circulation,” Sarwal tells the outlet.

Such breakthroughs could cut wait times for patients in need, the researchers hope. Currently, more than 108,000 people in the United States are waiting for an organ transplant, according to the United Network for Organ Sharing (UNOS). Less than half that number received a transplant in 2024.

Montgomery’s team will now test immune suppression techniques for pig transplants in 20 additional patients, Montgomery tells CNN, so these findings can be replicated in more than a single patient.

Despite the challenges presented by the body’s immune response to the pig organs, the researchers conclude, “a minimally gene-edited pig kidney can support long-term life-sustaining physiologic functions in a human.”

Knowing that “will give us a sense of relief moving forward in the clinical trials…to know that when you put a pig kidney in a human, from a physiological standpoint, it just does its thing,” Montgomery tells CNN. “The [pig] kidney is capable of doing most of the things that a human kidney can do.”

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