Thanks to a new supercooling technique, researchers at Harvard Medical School (HMS) have found a way to triple the time a donor organ can remain viable as it waits to be transplanted into a host.
For a study published in Nature Biotechnology, the team managed to cool donor livers to sub-zero Celsius temperatures without freezing the organs – effectively allowing them to stay in suspended animation. This means they remain viable for 27 hours as opposed to the nine hours that traditional methods* enable.
The study’s authors hope that this could expand the availability of livers for transplantation, boost organ donor efficiency, reduce time restraints facing medical professionals, and – importantly – increase the number of procedures, therefore cutting the number of people on the transplant waiting list. In the US, shortages mean that only around 36,500 of the 730,000 or so people needing a donor organ each year receive the life-saving treatment they need.
The new technique allowed researchers to supercool the livers to sub-zero temperatures of -6°C (21.2°F) without damaging the tissue. This increases the amount of time the organs remain viable outside a human body to more than a day, the researchers say. The 27 hours of viability means there is enough time for the organ to be shipped anywhere in the US – and even further afield.
Before the supercooling, another technique called machine perfusion is used to evenly distribute a preservative solution that protects the livers and prevents them from freezing, in part by minimizing air-liquid interfaces. Machine perfusion was used to thaw the livers (and take them out of suspended animation) just prior to transplant surgery. Within that window, the donor organs can be transported at -4°C (24.8°F).
Before applying the technique to human livers, the team succeeded in “supercooling” rat livers. Despite doubts that they could reap the same results in larger organs, the researchers were able to scale up the process 200 times by using a combination of technologies, lead author Reiner de Vries, HMS research fellow in surgery, said in a statement.
The researchers note that though the livers remained viable, there were differences in energy charge, oxygen uptake, and apoptosis after the treatment that should be further investigated to improve the process. And while using human livers makes the study clinically relevant, they recommend long-term survival experiments involving supercooled livers and swine (or an alternative large animal model) before it can be trialed in humans.
“A lot of times when an organ becomes available, there may not be a good match nearby – so in terms of allocation, when you add that extra amount of time, that means you can search a wider distance which means you have a better chance of not only finding a good match, but an excellent match,” said Shannon Tessier, HMS instructor in surgery. “And that means that you have less organ discard, get more organs to recipients, and those organs are better matched to the recipients, meaning that organ can have a longer life within the recipient.”
*The method currently used involves storing donor organs on ice in a preservative solution. The temperature is kept between 4 and 8°C (or 39.2 and 46.4°F) – any cooler and the organ is compromised, experiencing damage akin to a deep frostbite. After approximately nine hours outside the human body, the tissue of the organ becomes damaged beyond repair and cannot be transplanted into a new host.