Reiner de Vries conducting a liver supercooling experiment Jeffrey Andree, Reinier de Vries and Korkut Uygun

The length of time that a liver can be kept outside the body has been extended to a day and a half by a new “supercooling” method, which for the first time has let human organs be safely stored at sub-zero temperatures.

The technique, which lowers the organ’s temperature below zero without forming damaging ice crystals, could boost the number of liver transplants carried out and could also be used on other organs, says Reinier de Vries of Harvard Medical School in Boston.

There is a shortage of organs available for transplant, with about 14,000 people on the liver waiting list in the US, for example. A big problem is that when an organ becomes available from someone who has died, it can only be stored outside the body, at 4 degrees C, for a short time – up to 12 hours in the case of livers – which limits how far it can be transported. “It’s a race against the clock,” says de Vries.


His team has developed a method for cooling livers down to -4 degrees C without them freezing. The organ is connected to a machine that perfuses it with chemicals to lower the freezing point, and air is removed from the storage bag, to avoid ice crystals forming at air-liquid contact points.

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The method was tested on three human livers that had been made available for transplant but weren’t in good enough condition to use. After the sub-zero storage and rewarming, all three organs seemed to recover well when they were perfused with blood at body temperature, as they started making bile.

As the organs are not frozen they cannot be kept below zero indefinitely, but de Vries says they will now try extending the storage period past a day and a half. It could also be used with hearts and kidneys, although lungs would be more difficult because they are filled with air. “The larger the volume of the organ, the more difficult it becomes. Human livers are the largest solid organ.”

Some livers for transplant are already kept on a similar machine that perfuses them with blood at body temperature, but only for up to 24 hours. Andy Self of OrganOx, the Oxford-based manufacturer of one such device, says being able to keep them outside the body for longer would give “logistical advantages”. “But with cold storage, there’s no way of assessing how that liver will perform after transplant.”

Journal reference: Nature Biotechnology, DOI: 10.1038/s41587-019-0223-y