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After ‘Absurdly Long’ 100-Day Freeze, Rat Kidneys Were Successfully Transplanted

Nanoparticles can allow long-term freezing of transplant organs

Illustration of a snowman holding a kidney.

Thomas Fuchs

Thousands of donated organs are discarded every year. As soon as one becomes available, doctors race to find a compatible recipient—but transplantation time lines are measured in hours, and many organs still can't be used. Now researchers publishing in Nature Communications have successfully preserved rat kidneys for 100 days before thawing and transplanting them into other rats.

Scientists have cryogenically preserved organs for decades via vitrification: cooling them so quickly that ice cannot form and rupture cells. But thawing them quickly enough to avoid damage has proved nearly impossible. “If the outside heats faster than the middle, you get thermal stress—like when you drop an ice cube in water and you hear it crack,” says study author Erik Finger, a transplant surgeon at the University of Minnesota. “You could basically put a crack right through the middle of the organ and make it not function.”

For the new study, just before vitrification the team flooded the rat kidneys' vasculature with iron oxide nanoparticles and a newly developed cryoprotective solution that can preserve the organs at extremely low temperatures. After 100 days, they thawed the organs with an alternating magnetic field, which caused the nanoparticles to oscillate and evenly warm the tissue. The researchers then flushed the nanoparticles and cryoprotective solution out of the organs before replacing the rats' native kidneys with these transplants. The recipients were able to live without medical support.

Only one previous study successfully rewarmed and transplanted a vitrified organ in any animal, and the rabbit kidney in question had been vitrified for roughly 10 minutes—and it performed poorly after transplantation. Drastically extending the preservation period and developing a new method for warming was a “crowning achievement” for the researchers, says Gloria Elliott, president and chief science officer for the Organ Preservation Alliance. “No one has been able to do a good job of reproducing that,” Elliott adds. “So it's been a long time coming.”

Human organs are bigger than rat organs, but Finger is optimistic this technology will translate because of how the nanoparticles uniformly heat an organ from within. New York University surgery resident David Andrijevic, who revived dead pigs' organs while working as a research scientist at Yale University, says this study completely changes the field of transplantation. He adds that “100 days is absurdly long.”

Finger's group hopes to start human organ trials within the next six months. Scaling up will be a challenge, Finger says, but long-term organ banking would be invaluable for the 100,000 people on the organ transplant waiting list. “For each organ recipient who does not know when the transplant might come,” he says, “you can say, ‘What's in the freezer?’ and pick out what's best for this particular patient today.”