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Islet Cell Transplantation More Successful than Previously Thought
Scott Gottlieb, New YorkBritish Medical Journal, August 5, 2000; Permission granted for reprint
Islet cell transplantation as a means of alleviating or even curing the symptoms of type I diabetes mellitus may be more successful than previously believed, according to a new study.
The progress of the technique is likely to be impeded, however, as a result of a shortage of pancreases, the primary source of islets.
Previously, the success rate in transplanting pancreatic islet cells has been low, perhaps because of the toxic effects of immunosuppressive drugs on the islets. In this study, glycated haemoglobin values became normal in a series of seven patients with type I diabetes mellitus who underwent islet cell transplants.
Their glycated haemoglobin levels remained normal for a median of 11.9 months after they received allogenic islets by transcutaneous injection into the portal vein. Unlike in previous attempts at islet cell transplantation, which used glucocorticoids, in this series immunosuppression consisted of the drugs sirolimus, tacrolimus, and daclizurnab (New England Journal of Medicine 2000;343:230-8).
Islet cell transplantation has previously been viewed as less promising than transplantation of the whole pancreas, largely because of a poorer success rate (about 8% v 80-90%).
More than 16 million Americans have diabetes, which ranks as the sixth leading cause of death in the United States. Currently, the only candidates for transplantation are people with type I (insulin dependent) diabetes. It is believed that if vast supplies of islet cells were available, transplantation could be extended to those with type 2 (non-insulin dependent) diabetes.
The problem with islet cell transplantation is that a donor pancreas is offered for islet cell transplantation only after it has been turned down for use as a whole organ transplant. However, as a source of islet cells, a pancreas has to be used within 12 hours, so delays in decision making can render a donor organ useless.
These delays may pose a problem in a 10 centre clinical trial of the new transplantation technique used in the current trial (the Edmonton protocol), which is scheduled to begin in September.
Earlier this month President Clinton named the 10 centres -- six in the United States, three in Europe, and one in Edmonton, Canada -- that will participate in a trial aimed at reproducing the current results in other settings. In the trial, 40 type 1 diabetic aged 18-65 years will receive islet cell transplants.
The enrollment criteria include a five-year history of type 1 diabetes and one of the following: brittle diabetes, hypoglycaemic unawareness, at least one hypoglycaemic reaction in the previous 18 months, progressive secondary complications, or failure of intensive insulin managemet.
The lead author of the article in the New England Journal of Medicine, Dr. James Shapiro, professor of surgery at the University of Alberta in Edmonton, said that the result of previous trial, many of which failed, suggest that it is the steroids that damage the transplanted islet cells.
On obstacle to the new technique will be obtaining donor organs for the procedure. Even if organs are made available for islet cell transplantation, any transplant centres have concerns about whether funding is available to pay for the cost of recovering organs for the procedure. Professor Shapiro said that the cost of obtaining a pancreas can be as high as $22,000 in the United States.
http://www.bmj.com
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