Pig kidneys that were “frozen” for a year have been brought back to life
Pig kidneys that were cooled to -150 °C and stored in a freezer for months have been successfully rewarmed and shown to work again for the first time, say scientists. They hope to replicate the findings with human organs.
Scientists successfully preserved pig kidneys at -150°C for up to a year, then rewarmed and revived them to function again. The kidneys, which are similar in size to human ones, regained their color and produced urine after being transplanted into pigs or tested on perfusion devices. One kidney stored for just over a year performed as well as fresher ones, producing urine immediately upon rewarming. The breakthrough was announced by researchers from the University of Minnesota, led by transplant surgeon Erik Finger and bioengineer John Bischof. The findings, shared on the preprint server bioRxiv in October 2026, have not yet been peer-reviewed but are considered a major milestone in organ preservation.
Organ transplantation saves lives but faces critical challenges, including a severe shortage of available organs and a narrow time window of 24 to 36 hours for preservation. In the U.S. alone, tens of thousands of transplants occur annually, saving an estimated 2 million years of life over the past 25 years. Current preservation methods require organs to be transplanted quickly, leaving little time for matching donors to recipients. Additionally, patients must take lifelong immune-suppressing drugs to prevent organ rejection, which increases infection and cancer risks. Long-term organ banking could address these issues by allowing organs to be stored indefinitely, giving doctors more time to find the best match and potentially reducing rejection risks by preparing recipients' immune systems in advance.
The process used to freeze the kidneys is called vitrification, which cools tissues to an ultra-low temperature (-120°C or lower) so quickly that they turn into a glass-like state instead of forming damaging ice crystals. This technique is already used to preserve smaller biological samples like eggs, sperm, and embryos. However, vitrifying whole organs is far more complex due to their size and structure. Scientists use cryoprotectants—chemicals similar to antifreeze—to prevent ice formation, but these chemicals can be toxic. The challenge lies in evenly cooling and rewarming large organs without causing damage. The researchers added iron oxide nanoparticles to the cryoprotectant solution, which can be activated with an electromagnetic field to generate heat during rewarming, ensuring uniform and controlled heating.
After vitrification, the kidneys are stored at -150°C and can remain frozen for months or even over a year. To revive them, the team removes the cryoprotectants and nanoparticles, then rewarms the organs using the electromagnetic field. The process is carefully controlled to avoid damage. Once rewarmed, the kidneys are tested in two ways: placed on perfusion devices, which provide nutrients and assess function outside the body, or transplanted into pigs for short-term monitoring. In both cases, the kidneys regained blood flow and produced urine, though at about two-thirds the expected volume. One kidney stored for over a year performed exceptionally well, producing urine immediately upon rewarming. The researchers observed that the kidneys 'pink up,' indicating restored blood flow and viability.
While the breakthrough is significant, the rewarmed kidneys showed signs of injury, likely caused by the cryoprotectants. The damage raises questions about whether these organs could support life long-term. Experts like Greg Fahy, a pioneer in cryobiology, note that the experiments don’t yet prove the kidneys could sustain a pig’s life for extended periods. The team plans to test the kidneys in pigs over longer durations and explore ways to repair the damage. They are also developing less toxic cryoprotectants and plan to conduct similar experiments with human kidneys. The ultimate goal is to create a reliable system for banking organs indefinitely, which could transform transplantation by making organs available on demand for emergencies like drug overdoses or gunshot wounds.
The research was led by Erik Finger, a transplant surgeon, and John Bischof, a bioengineer, both at the University of Minnesota. Their work was praised by experts in the field. Peter Kilbride, a cryobiologist and cofounder of Kyros Kairos, called it a historic breakthrough after years of failed attempts. Korkut Uygun, a biomedical engineer at Harvard Medical School, described it as revolutionary for transplantation, enabling 'indefinitely banking organs.' Kevin Myer, CEO of LifeGift, an organ procurement organization in Texas, emphasized the potential to store organs for a year or longer, which could save lives in urgent cases. The findings were shared on *bioRxiv* in October 2026 and have not yet undergone peer review, but the scientific community views them as a major step forward.
