The development of encapsulated cell technologies as therapies for neurological and sensory diseases.

Cell encapsulation therapies involve the implantation of cells that secrete a therapeutic factor to provide clinical benefits. The transplanted cells are protected from immunorejection via encapsulation in a semipermeable membrane. This treatment strategy was originally investigated as a method for protecting pancreatic islets from immunorejection, thus allowing them to secrete insulin as a chronic treatment for diabetes. Since then a significant body of work has been conducted in developing cell encapsulation therapies to treat a variety of different diseases. Many of these conditions involve neurodegeneration, such as Alzheimer's and Parkinson's disease, as cell encapsulation therapies have proven to be particularly suitable for delivering therapeutics to the central nervous system. This is mainly because they offer chronic delivery of a therapeutic and can be implanted proximal to the affected tissue, bypassing the blood brain barrier, which is impermeable to many agents. Whilst these therapies are not yet widely available in the clinic, promising results have been obtained in several advanced clinical trials and further developmental work is currently underway. This review specifically examines the development of encapsulated cell therapies as treatments for neurological and sensory diseases and evaluates the challenges that are yet to be overcome before they can be made available for clinical use.