Pig kidneys stored for a year regain function after deep freeze

Scientists have rewarmed pig kidneys that were cooled to -150°C, stored for more than a year and then shown to function again. The organs regained their colour, restored blood flow and produced urine after being tested on perfusion machines and transplanted into pigs, according to reporting from MIT Technology Review. ¹

The result is an important step towards organ banking, but it is not a human-transplant breakthrough yet. The work has been shared as a bioRxiv preprint and has not been peer-reviewed. The researchers also found signs of injury in the rewarmed kidneys, and the animals were monitored for only two hours after transplantation. ¹²

Turning an organ glass-like

The team first loads a kidney with cryoprotectants, chemicals that help prevent ice crystals from forming. It then infuses the organ with iron oxide nanoparticles. Those particles can be heated by an electromagnetic field, allowing the researchers to warm the kidney more evenly than a conventional thawing process. ¹

The approach builds on earlier work with rat kidneys, which the team had rewarmed after storage periods of up to 100 days. Pig kidneys are a more demanding test because they are around the same size as human kidneys, while a rat kidney weighs roughly one gram and a pig kidney around 100 grams. ¹

Once the pig kidneys reached about -120°C, they entered a vitrified, glass-like state. The team then cooled them to roughly -150°C and stored a small number for days, weeks and, in one case, just over a year. The researchers had to modify the cryoprotectant mixture because the formula used for the rat experiments did not perform as well in the larger organs. ¹

A working organ, not a finished treatment

The rewarmed kidneys were flushed to remove the cryoprotectants and nanoparticles before testing. On perfusion machines, they regained a healthy colour and produced urine. In transplanted pigs, they also produced urine, although at around two-thirds of the expected amount. The year-stored kidney produced urine immediately when placed on a perfusion machine. ¹

That distinction matters. Producing urine and restoring blood flow show that the organs can recover key functions, but they do not prove that a rewarmed kidney can sustain an animal for the long term. The researchers say the next steps include longer monitoring in pigs and work on less toxic cryoprotectants. They also plan experiments involving human kidneys, which remain a separate challenge. ¹²

A successful organ-banking system could eventually give doctors more time to match organs to recipients and prepare patients for transplantation. At present, human organs have a much shorter preservation window, typically around 24 to 36 hours according to the report. ¹

Our opinion

This is a genuine milestone, but the headline should stop short of promising frozen human organs on demand. The strongest evidence is that a large mammalian organ can be cooled, stored for a year and brought back to measurable function. The biggest caveat is equally clear: the kidneys were injured, produced less urine than expected and were not shown to support life over an extended period. That makes this a compelling proof of concept, not a ready-made transplant service.