Pig Kidneys Stored at -150°C for Over a Year Successfully Rewarmed and Restored to Function, Advancing Organ Banking

Pig kidneys stored at an ultralow temperature for months—one for more than a year—have been thawed, rewarmed, and shown to function again, according to scientists who say the feat could be a step toward long-term “organ banking” for transplantation.

The organs were cooled to around -150 °C, a range cold enough to halt biological activity. Rather than freezing in the usual sense, the kidneys were placed into a vitrified, glass-like state designed to avoid the ice crystals that can shred delicate tissue. After storage, the team rewarmed the kidneys, evaluated them on perfusion machines, and transplanted them into pigs. The organs reportedly regained healthy color and produced urine—two basic indicators that blood flow and filtration had resumed.

Erik Finger, a transplant surgeon at the University of Minnesota who co-led the work, said the outcome exceeded his expectations. He described leaving the operating room after the final transplant convinced the achievement marked a turning point for the field. The study has been posted to the preprint server bioRxiv and has not yet undergone peer review. Researchers also emphasize that the kidneys are not flawless, and the work has not yet proven the organs can keep an animal alive over extended periods.

Even so, outside experts characterize the results as a major milestone. Cryobiologist Peter Kilbride, who was not involved in the study, said groups have struggled for years to reach the point of demonstrating functional recovery in an intact organ. Harvard Medical School biomedical engineer Korkut Uygun, also not part of the research, called the approach a potential pathway to indefinite organ storage—an advance he said could transform transplantation.

The stakes are high. Tens of thousands of transplants are performed each year in the United States, and the procedures are estimated to have delivered roughly 2 million years of added life over the past quarter century. Yet organ scarcity persists, and logistics remain unforgiving: once a donor organ becomes available, it typically must reach a compatible recipient and be transplanted within about 24 to 36 hours under current preservation methods.

Longer storage could ease multiple bottlenecks at once. With more time, clinicians could better match donors and recipients and coordinate transport. It might also help reduce rejection risk by allowing doctors to prepare recipients’ immune systems in advance. Today, transplant recipients generally require lifelong immunosuppressive drugs to prevent rejection—medications that can carry significant side effects and raise the risk of infections and cancer. Finger summed up the promise of the concept: instead of patients waiting on an unpredictable organ supply, organs could be held in reserve for patients.

The underlying challenge is that vitrification is routine for small biological samples—such as eggs, sperm, and embryos—but extremely difficult for whole organs. Cryoprotectant chemicals can prevent ice formation, yet they are often highly toxic at the concentrations needed. Meanwhile, large tissues are hard to cool quickly and evenly, and just as hard to rewarm uniformly; uneven heating can crack vitrified tissue or cause localized damage.

To tackle the rewarming problem, Finger collaborated with University of Minnesota bioengineer John Bischof and colleagues on a strategy that distributes heat throughout the organ. After loading a kidney with cryoprotectant, the team infused it with iron oxide nanoparticles that are inert to cells. During rewarming, an electromagnetic field is applied. As the field’s radiofrequency alternates between two states, the nanoparticles flip to align with it, releasing heat within the tissue. By tuning the field’s power, the researchers can control heating and aim for rapid, even warming across the whole organ.

Why it matters

If organs can be safely stored for months or years, transplant medicine could shift from emergency logistics to planned, optimized care, affecting patients on waiting lists and the hospitals that serve them. The approach could improve matching and coordination and may eventually reduce rejection by enabling pre-transplant immune preparation. The next critical tests will be peer review, longer-term survival studies, and demonstration that the method can be replicated in human organs.