Islet transplantation is a treatment for diabetes that has the potential to normalize glucose levels and prevent the development of complications. In spite of the simplicity of the concept and the urgent need to provide such a treatment to patients, there has been a frustrating lack of progress. This perspective delves into the scientific and political impediments to success. The scientific barriers are the need to find a satisfactory source of insulin-producing tissue and the requirement to prevent this tissue from being destroyed by immune rejection and autoimmunity. The problems and potential of allografts, xenografts, and the development of cell lines are discussed. Multiple approaches to the prevention of immune destruction are considered, including immunobarrier devices, immunosuppression, development of tolerance, and genetic manipulation. The political barriers discussed include the problems of high expectations, the controversy surrounding targeted research, the balance between basic and applied research, the roles of industry and academia, the concerns about xenotransplantation, and the difficulties in developing a planned approach to the problem.

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