Scientists report reviving pig kidneys after more than a year in ultra-cold storage

What Happened

University of Minnesota scientists say they have revived pig kidneys after storing them in an ultra-cold, glass-like state for months, including one kidney kept for more than a year.

After being rewarmed, tested on machines and transplanted into pigs, the kidneys regained their color and produced urine, according to a report by MIT Technology Review. The researchers described those outcomes as key signs that the organs were functioning.

The work was led by Erik Finger, a University of Minnesota transplant surgeon, and John Bischof, a bioengineer at the university. The findings were posted on the preprint server bioRxiv and have not yet been evaluated through peer review.

Finger told MIT Technology Review that he had not initially expected the method to work. After the team completed its last transplant, he said, “This is a big deal.”

How the Process Works

The technique is based on vitrification, a preservation process that cools biological material into a glass-like state rather than allowing damaging ice crystals to form. Vitrification is already used for eggs, sperm and embryos, but applying it to whole organs is considerably more difficult.

The Minnesota team used cryoprotectants, chemical compounds that act like antifreeze, to reduce ice formation in the kidneys. Such chemicals can be toxic, however, and large organs are difficult to cool and rewarm uniformly.

To address the rewarming problem, the researchers infused the kidneys with iron oxide nanoparticles. When exposed to an electromagnetic field, the particles generate heat throughout the organ. The researchers can adjust the field's power to control the heating rate, increasing it after the kidney reaches minus 120 degrees Celsius.

According to MIT Technology Review, the procedure involved loading a pig kidney with cryoprotectants for about two hours, then pumping nanoparticles through it for roughly seven to eight minutes. The organ was then cooled with nitrogen vapor to about minus 150 degrees Celsius.

Why It Matters

Human organs generally can be preserved for only about 24 to 36 hours, according to MIT Technology Review. That narrow window can make it difficult to transport a donated organ, complete compatibility testing and match it with a recipient.

Longer-term organ storage could potentially allow doctors to hold organs until an appropriate recipient is ready rather than racing to move an organ within hours. It might also provide more time to prepare recipients and their immune systems before transplantation.

“With real organ banking, instead of the patients waiting for the organ, it’s the organs that are waiting for the patients,” Finger told the publication.

Peter Kilbride, a cryobiologist and cofounder of Kyros Kairos who was not involved in the work, called the reported result a breakthrough after years of failed attempts to reach this stage. Korkut Uygun, a Harvard Medical School biomedical engineer and surgery professor who also was not involved, said the work could make indefinite organ banking possible.

Background

The researchers previously reported vitrifying rat kidneys in a study published in 2023. In that work, rat kidneys were stored for as long as 100 days before being rewarmed and transplanted into rats.

Pig kidneys represent a more demanding test because they are much larger. MIT Technology Review reported that rat kidneys weigh about 1 gram, compared with roughly 100 grams for pig kidneys. Pig kidneys are also similar to human kidneys in size and appearance, making them a useful research model.

The team had to modify the cryoprotectant mixture used for rat kidneys because it did not work as effectively in pig organs, Bischof told the publication.

What Happens Next

The reported results are an early step, not evidence that frozen organs are ready for clinical use. The researchers have not shown that the revived pig kidneys can sustain life over the long term, and the approach has not been demonstrated in human organs.

Peer review will be an important next test for the findings. Researchers would also need to establish that organs preserved this way can safely recover durable function and that the chemicals and nanoparticles do not cause unacceptable harm before the technique could be considered for human transplantation.