Scientists reverse pig organ rejection twice in human patient

Over 61 days, a team at NYU Langone did something no one had managed before: they transplanted a genetically modified pig kidney into a human patient and stopped the body's immune system from rejecting it—not once, but twice.

The breakthrough matters because right now, more than 108,000 people in the United States are waiting for an organ transplant. Last year, fewer than half of them got one. Pig organs, genetically engineered to look less foreign to the human immune system, could help close that gap. But there's been a persistent problem: human bodies keep attacking them.

This study, published in Nature in November, shows that rejection isn't inevitable—it's just a problem we can now solve.

The research team, led by Robert Montgomery at NYU Langone's Transplant Institute, worked with a brain-dead patient whose family had donated their body to science. What made this experiment different wasn't just that they succeeded twice, but how they succeeded. The team conducted daily biopsies, blood tests, and fluid samples—creating what Montgomery calls "probably the most deeply studied human in history." This constant monitoring let them catch rejection five days earlier than standard methods would have.

That early detection mattered. When they spotted the immune system attacking, they used existing medications to reverse it. Both times, the kidney returned to normal function.

At the cellular level, the researchers discovered exactly why rejection happens. The pig kidney expressed higher levels of genes that human immune systems flag as foreign. T cells—white blood cells that patrol for invaders—also played a bigger role in the attack than anyone had realized. Once they understood the mechanism, they could interrupt it.

"From a physiological standpoint, it just does its thing," Montgomery told CNN. "The kidney is capable of doing most of the things that a human kidney can do."

Muhammad Mohiuddin, who led the first pig-human transplant in 2022, called this "the first evidence of how to reverse rejection." Minnie Sarwal, a transplant surgeon at UC San Francisco, described the 61 days of stable kidney function as "novel proof of concept."

The next phase is already underway. Montgomery's team is testing these immune-suppression techniques in 20 additional patients to confirm the findings work beyond a single case. If they do, the implications are significant: shorter wait times, more organs available, and a way to help people who might otherwise spend years on dialysis or die waiting.

The pig kidney didn't just survive in a human body. It worked.