Islet cell transplantation involves isolating the insulin producing islet cells from a donor pancreas before transplanting them into the recipient. The indications for who would be considered for islet cell transplantation are similar to those for whole pancreas transplants.
Islet cell clusters within the pancreas contain the beta cells responsible for insulin production. They make up only a tiny proportion of the whole pancreas. Many doctors consider isolating them by chemical digestion prior to transplantation a much better option for the treatment of Type 1 diabetes. The resulting islet cell material makes the surgery much easier and it can even be performed under local anesthetic. The isolated islets can be injected through a catheter into the liver where they grow and in time start to make and release insulin. The procedure may take less than an hour to complete.
As with whole pancreas transplants one of the main problems relates to the lack of organ donors. In the case of islet transplantation it has even proved necessary to isolate islets from the pancreas of two donors in order to provide sufficient cells for a successful transplant. This is because islets are extremely fragile and can be easily destroyed by the digestion process, by the environment into which they are transported and by the drugs used in preventing their rejection by the recipient’s immune system.
After many years of frustrating research a ray of hope was offered by the publication of a relatively successful clinical trial obtained using the so called Edmonton protocol from the transplant team in Canada. The success in demonstrating that a high proportion of their patients were free from insulin injections post procedure was thought to offer the possibility of a cure of Type 1 diabetes. It was the breakthrough that patients were waiting for. Unfortunately, the results did not stand the test of time as more and more patients reverted back to needing insulin injections as the transplant failed. The science behind the research, however, can be considered to be a resounding success and has provided a platform for much more investment into this area.
To put this area of clinical research into some perspective it is worthwhile reconsidering the worldwide burden of diabetes. The supply of human islets is very limited, and even if successful, any human islet transplant programme could only cure a tiny fraction of the people with diabetes from existing sources of donor pancreases. For this reason there are active research groups who are trying to obtain islets from animals such as pigs where perhaps the supply could outstrip the demand.
Transplants between species is called xenotransplantation and although results are quite encouraging this area throws up a whole new set of problems, not least serious ethical considerations.
The scientific barrier as to how to prevent rejection of the transplanted cells also remains a complicated issue and it is why stem cell research could be so important. The ultimate scientific dream would be to engineer transplantable cells with the capacity not only to make insulin but also escape the immune attack of the recipient.
These problems continue to hamper our long-term success in this area.