Scientists say they have, for the first time, revived pig kidneys that were cooled to -150 °C and stored in a freezer for months, with one organ kept in a glass-like state for more than a year. After rewarming, testing in machines and transplanting into pigs, the kidneys regained their color and produced urine, key signs that they were working. The team hopes the findings can eventually be replicated with human organs.
The research, led by Erik Finger, a transplant surgeon at the University of Minnesota, and John Bischof, a bioengineer at the same institution, was shared on the preprint server bioRxiv and has not yet been peer-reviewed.
"Ten years ago ... I wouldn't say I had high hopes it was actually going to work," Finger said. "After we did the last transplant, I walked out of the room and said, 'This is a big deal.'"
The kidneys, which are similar in size to human ones, were vitrified, a process that turns biological material into something like glass at ultra-low temperatures. Vitrification is already used to store eggs, sperm and embryos, but whole organs are far harder to preserve. Cryoprotectant chemicals can prevent damaging ice crystals, but they tend to be toxic, and it is difficult to cool and rewarm large tissues evenly.
The results were greeted with caution but enthusiasm by others in the field. "Thank God that someone's actually managed to do it in one organ and prove that it works," said Peter Kilbride, a cryobiologist and cofounder of Kyros Kairos, who was not involved in the research. "For years, people have been trying and failing to get to this step. Finally, we've got this breakthrough."
Korkut Uygun, a biomedical engineer and professor of surgery at Harvard Medical School, who was also not involved, said: "Their work is amazing and will enable us to truly, indefinitely bank organs. It is a revolutionary time for transplantation."
The researchers acknowledged that the kidneys are not perfect and have yet to be shown to sustain life over the long term. But the ability to bank organs for long periods could address two major challenges in transplantation: the shortage of available organs and the current limit of 24 to 36 hours for preserving human organs before transplant. Long-term banking would also give doctors more time to match organs to recipients and potentially prepare recipients' immune systems beforehand.
"With real organ banking ... instead of the patients waiting for the organ, it's the organs that are waiting for the patients," Finger said.
Analysis
Why This Matters
- Organ transplantation is constrained by a severe shortage of available organs and a preservation window of only 24 to 36 hours, which makes matching and delivery a race against time.
- The ability to bank organs indefinitely would let doctors match organs to recipients more carefully and potentially prepare recipients' immune systems in advance, reducing the lifelong reliance on immunosuppressive drugs.
- If the approach transfers to human organs, it could mark a turning point for transplant medicine, but the findings are preliminary and not yet peer-reviewed.
Background
Transplanted organs must typically be used within hours of being removed from a donor, which limits how far they can travel and how much time there is to find the best match. Recipients also face lifelong courses of immunosuppressive drugs, which carry side effects and raise the risk of infections and cancer.
Cryopreservation has long worked for small biological materials such as eggs, sperm and embryos, using vitrification to turn cells into a glass-like state. Whole organs are far more challenging because ice crystals can destroy tissue, the chemicals used to prevent them are toxic, and large organs must be cooled and rewarmed uniformly. This study is the first to demonstrate that a whole organ can be stored frozen and then show signs of working after rewarming and transplant.
Key Perspectives
Researchers: Erik Finger and John Bischof describe the work as a milestone. "After we did the last transplant, I walked out of the room and said, 'This is a big deal,'" Finger said.
Cryobiologists and transplant researchers: Peter Kilbride called it a long-awaited breakthrough, while Korkut Uygun said it could enable organs to be banked indefinitely, calling it "a revolutionary time for transplantation."
Critics and skeptics: The study has not been peer-reviewed, the kidneys are not perfect, and the researchers have not yet demonstrated that the revived organs can sustain life over the long term. Whether the technique scales to human organs remains unproven.
What to Watch
- Peer review of the bioRxiv preprint and any independent replication of the results.
- Whether the researchers can demonstrate long-term survival in transplanted animals.
- Progress toward applying the same vitrification and rewarming method to human-sized organs.