Islet cell transplants

The pancreas produces enzymes to digest food as well as the hormones glucagon and insulin to control blood glucose. The hormones are produced in parts of the pancreas called the islets or islets of Langerhans. The α cells produce glucagon when blood glucose falls. This stimulates the liver to release glucose into the blood. The β cells produce insulin when blood glucose is high. If the problem lies only with the cells that produce insulin it is not necessary to transplant a whole pancreas.

As with transplantation of a whole pancreas, the reason for an islet cell transplant is type 1 diabetes with failed control. The procedure is still considered experimental and there are few centres that perform them.

A pancreas is taken from a dead donor. The first step is to extract and purify the islet cells. Often, two or more donor organs are needed to supply enough islet cells.

When the cells have been separated, a surgeon directs a tube through an opening made in the abdomen to the portal vein. This is a large blood vessel leading to the liver. Islet cells are injected through this tube to the liver where they are taken up in the small blood vessels. The liver is more accessible than the pancreas and so the procedure is easier. The cells settle in the liver and produce insulin well.

The procedure usually takes less than an hour and is followed by about two days in hospital. Sometimes the infusions need to be repeated for an adequate result. Sometimes the process needs to be repeated at a later date. This requires an additional donor organ and a further stay in hospital. Risks include bleeding and blood clots.

Type 1 diabetes is caused by the body’s own immune system destroying the insulin secreting cells of the pancreas. It can also destroy the transplanted cells.

Because this is a transplant, suppression of the immune system is required to prevent rejection. This makes the body more susceptible to infection. The drugs used to prevent rejection usually include steroids such as prednisolone and this pushes up blood glucose. This may mean that it is not possible to stop insulin completely but it should be possible to use less and to have better diabetic control.

If you are on a waiting list for an islet cell transplant you must continue to do your utmost to control your diabetes as well as you can. This includes control of blood pressure and blood cholesterol.

Success of the procedure is improving as years go by but it is far from perfect. In a study of 36 patients published in 2006, more than 40% were off insulin completely after one year but by 3 years that figure was down to 17%. Still needing some insulin does not mean that the operation has been a failure. Less insulin may be required with better control of the diabetes and hence a lower risk of complications of the disease.

Dr Tony Woolfson MB BS DM MRCP(UK)
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