Islets are clusters of cells in the pancreas that produce insulin and other hormones. When islets are destroyed, the body cannot make insulin and a person develops Type 1 diabetes. Researchers believe that transplanting islet cells to provide the needed insulin might be a cure for Type 1 diabetes.
At present, islet transplantation is an experimental therapy. Scientists have made progress toward islet transplantation over the past 25 years, but still face many barriers in attempting to use islet cell transplants, in particular, as a cure for diabetes.
Two major areas of research are methods of obtaining a sufficient number of cells to transplant and preventing rejection of transplanted cells.
Getting enough islet cells to transplant. Early findings show that about 1 million islet cells have to be transplanted to make enough insulin so that insulin injections will no longer be necessary. The number of people who could benefit from transplants is larger than the number of human organ donors available each year, so researchers around the world are studying the use of islet cells from fetal tissue or other such as pigs.
Preventing Rejection . . .
Rejection is the biggest problem with any transplant. The immune system is programmed to destroy "foreign" invaders such as bacteria and viruses. However, the system also destroys "invited foreigners," such as transplanted islet cells.
Large doses of medicines, called immunosuppressants, are necessary to stop the immune system from rejecting the transplant. For most people, the risks of using immunosuppressants are greater than the benefits of transplantation. (However, people with diabetes who must take these medications because of kidney transplants for end-stage renal disease can benefit from simultaneous pancreas transplant.)
Researchers are trying to develop methods of transplanting islet cells to reduce or eliminate the need for immunosuppression and the risk of rejection. Immunoisolation methods separate the islets from the immune system of the patient by coating cells or encapsulating them into microscopic containers. Immunoalteration tries to change the surface of islet cells so that the patient's immune system does not notice or attack them.
The Diabetic Newsletter  courtesy of NIDDK