Liver transplants: pre-transplant preservation period extended

The Parliamentary Information Office of the Parliamentary Yearbook reports on the development of a new “supercooling” technique which extends the amount of time that rat livers can remain viable outside the body prior to transplantation. If successful in humans, the new technique could more than triple the amount of storage time for organs, opening up the possibility of world-wide allocation of donor organs.

Organ transplants are one of the miracles of modern medicine.  The procedure helps around 3,000 people in the UK take on a new lease of life each year.  Despite this, organ shortage is a universal problem and there are currently around 10,000 people in the UK in need of a transplant. Figures from NHS Blood and Transplant indicate that up to 1,000 people die each year due to a shortage of donor organs, the equivalent of 3 people per day.

Over the course of the last century, organ transplantation has overcome major technical limitations. However, one of the main challenges for organ transplantation remains the fact that once the supply of oxygen and nutrients to an organ is cut off, its cells begin to deteriorate by the hour. This means that the process of organ matching, allocation and transplant is time critical.

To assist with this, scientists have developed preservation solutions that enable organs to be stored outside the body whilst preserving function, but only for a very limited period of time. Extending this window of opportunity would provide many benefits. Consequently, current research in this area has been directed at techniques to improve organ preservation.

A new technique has recently been demonstrated which may improve the practice of organ storage for transplantation.  The new system - developed at the Massachusetts General Hospital (MGH) in Boston, USA, - allowed the successful transplantation of rat livers after preservation for as long as four days, more than tripling the amount of time organs can currently be preserved.

Using current technology livers can be preserved outside the body for a maximum of 24 hours.  This technology relies on a combination of cold temperatures and a chemical solution which prevents the liver tissue from dying during transit.

The new system uses protective solutions and machine perfusion, but crucially it involves a specific protocol for “supercooling” organs to below freezing temperatures. The procedure - which so far has only been tested on rats - has recently been described in Nature Medicine. 

For the procedure, donor livers taken from rats were attached to a machine perfusion (an artificial body that supports basic organ function) and flushed with a mixture of 2 protective solutions. In the first instance the livers were cooled to 4^oC. The organs were then submerged in the protective solution mix and cooled to -6^oC.  They were subsequently stored at this temperature for either 72hr (3 days) or 96 hours (4 days).  At the end of this time organ temperature was gradually increased to 4^oC. The organs were machine-perfused with solution once again at room temperature for three hours.  The organs were then transplanted into healthy rats which were monitored for a period of 3 months.

The results showed that all the animals that received organs that had been super cooled for 72 hours remained healthy at the end of 3 month follow up period.  The survival rate for rats that had received livers stored for 96 hours was 58%.

The researchers note that further work is needed before the approach can be applied to humans.  However, the study has important implications for the future of organ transplantation.  The longer donated organs can be stored, the better the chances of finding best patient match; the longer period also extends the time which doctors and patients have to prepare for surgery.

Senior co-author Yarmin Yarmush, founding director of Massachusetts General Hospital Centre for Engineering in Medicine and a faculty member of Harvard Medical School, commented on this in a press release on the hospital’s website.  He said: “By reducing the damage that can occur during preservation and transportation, our supercooling protocol may permit the use of livers currently considered marginal - something we will be investigating - which could further reduce the long waiting lists for transplants.”