Immunotherapy in prion disease

Transmissible spongiform encephalopathies (TSEs), also known as prion diseases, describe a group of fatal neurodegenerative disorders affecting both humans and animals. Accumulation of misfolded prion proteins is the pathological hallmark of these disorders; such accumulation occurs in lymphoreticular tissue prior to CNS involvement in scrapie, experimental models and human variant Creutzfeldt-Jakob disease. Lymphoreticular accumulation of misfolded prion protein has not been demonstrated in human sporadic or genetic forms of TSE. Once clinical symptoms develop, all prion disorders have a rapidly progressive and lethal course, and no effective therapy exists. In the past 10 years, antibody-based immunotherapy has been considered for other neurodegenerative disorders associated with protein misfolding and, therefore, might also be an effective approach to prevention or treatment of prion disease. Self-tolerance to endogenous prion protein is, however, a major challenge to the development of effective immunotherapy, as is the risk of adverse effects from active immunization. This Review summarizes the evidence that immunization could slow disease progression or increase lifespan in animal models of prion diseases. The therapeutic potential of these strategies in treating patients with prion diseases is also discussed.