If scientists can develop safe immunosuppressants that always work, then many people with type 1 diabetes may choose to have pancreas transplants. Until then, many doctors think islet transplants are a better option. Islets are clusters of cells in the pancreas that make insulin. In people with type 1 diabetes, islet cells are destroyed. Only 1-2% of the pancreas is made up of islet cells.
In pancreatic islet transplantation, cells are taken from a donor pancreas and transferred into another person. Once implanted, the new islets begin to make and release insulin. Researchers hope that islet transplantation will help people with type 1 diabetes live without daily injections of insulin.
The Edmonton Protocol
In the 1970s, islet transplant experiments were conducted with great success in laboratory mice. The excitement that those experiments generated soon turned to frustration, as initial attempts to reproduce that success in humans were largely disappointing. For many years progress was slow, and few transplant recipients were able to stay diabetes-free for more than a few months before the transplanted islet cells failed. But in recent years, scientists have begun to make rapid advances in transplant technology, and some of the most exciting new research comes to us from researchers at the University of Alberta in Edmonton, Canada. These scientists have used a new procedure called the Edmonton Protocol to treat patients with type 1 diabetes.
In this procedure, researchers use specialized enzymes to remove islets from the pancreas of a deceased donor. For an average-size person (70 kg), a typical transplant requires about 1 million islets, equal to two donor organs. Because the islets are extremely fragile, transplantation occurs immediately after they are removed.
The transplant itself is easy and takes less than an hour to complete. The surgeon uses ultrasound to guide placement of a small plastic tube (catheter) through the upper abdomen and into the liver. The islets are then injected through the catheter into the liver. The patient will receive a local anesthetic. If a patient cannot tolerate local anesthesia, the surgeon may use general anesthesia and do the transplant through a small incision.
It takes some time for the cells to attach to new blood vessels and begin releasing insulin. The doctor will order many tests to check blood glucose levels after the transplant, and insulin may be needed until control is achieved.
Benefits and Risks
Immunosuppressive or anti-rejection drugs are needed to keep the transplanted islets functioning. Researchers do not fully know what long-term effects these drugs may have. Also, although the early results of the Edmonton Protocol are very encouraging, more research is needed to answer questions about how long the islets will survive and how often the transplantation procedure will be successful.
However, transplanting islet cells has several advantages over transplanting a pancreas. First, unlike the pancreas transplant, an islet transplant is a minor surgical procedure, is less expensive, and is probably safer. Second, scientists may learn how to protect these cells from attack by the immune system. Several methods are already under study. If successful, the person with an islet transplant would not need to take immunosuppressants. Surgery would then be safer and more effective for many people with type 1 diabetes.
There is also continuing research on the transplantation of animal islets. Because the supply of human islets is severely limited, even the most successful method of human islet transplantation could only cure a small fraction of the people with diabetes through existing sources of human islets from donor pancreases. If islets from animal sources (for example, pigs) could be made to work successfully, a cure would be available for everyone. But transplants between species involve a whole new set of problems when it comes to regulating the body's immune response, so much work will still have to be done to make that a possibility.