Islet transplantation success
(From Nature Medicine Biomedical News)
A newly developed transplantation protocol has made it possible for patients with Type I diabetes to achieve sustained insulin independence. Although most Type I diabetics are treated with insulin injections, islet cell transplantation has been pursued as a treatment for patients with uncontrollable serum glucose concentrations. However, this approach has failed in practice, as only 8% of patients receiving pancreatic islet transplantation remain insulin-independent for up to 1 year, because of difficulties in obtaining a sufficient number of beta cells and graft rejection. Furthermore, current immunosuppressive regimens include steroids such as glucocorticoids, which induce insulin resistance. In an article to be published in the 27 July New England Journal of Medicine, Shapiro et al. describe a glucocorticoid-free immunosuppressive strategy involving the drugs tacrolimus, sirolimus and daclizumab, which prevent IL-2 signaling and T-cell activation. Islet cells isolated from cadaver pancreata were transplanted, through the main portal vein, into seven patients who received the new immunosuppressive drug combination. All seven patients were able to discontinue insulin therapy for an average of 12 months and did not experience acute cellular rejection.
"This is a very important study," said Terry Strom of Beth Israel Hospital in Boston. "It means that it is possible to obtain transplantable islets." Another new aspect of the study was that the patients required a second dose before achieving therapeutic insulin independence. "It will be important to determine why the first injection of islets is not effective, and why a second dose is required," said Strom. "It may be that during the early time period that the patient is still becoming immunosuppressed, the islets cannot survive the combined autoimmune response along with the allograft response." Strom added that the success of this approach creates an attractive area for investigation into tolerance induction, a therapeutic approach that would allow patients receive transplants without undergoing long-term immunosuppression. |
