Prion diseases: immunotargets and therapy

Jennifer T Burchell, Peter K Panegyres

Transmissible spongiform encephathalopathies or prion diseases are a group of neurological disorders characterized by neuronal loss, spongiform degeneration, and activation of astrocytes or microglia. These diseases affect humans and animals with an extremely high prevalence in some species such as deer and elk in North America. Although rare in humans, they result in a devastatingly swift neurological progression with dementia and ataxia. Patients usually die within a year of diagnosis. Prion diseases are familial, sporadic, iatrogenic, or transmissible. Human prion diseases include Kuru, sporadic, iatrogenic, and familial forms of Creutzfeldt-Jakob disease, variant Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, and fatal familial insomnia. The causative agent is a misfolded version of the physiological prion protein called PrP(Sc) in the brain. There are a number of therapeutic options currently under investigation. A number of small molecules have had some success in delaying disease progression in animal models and mixed results in clinical trials, including pentosan polysulfate, quinacrine, and amphotericin B. More promisingly, immunotherapy has reported success in vitro and in vivo in animal studies and clinical trials. The three main branches of immunotherapy research are focus on antibody vaccines, dendritic cell vaccines, and adoptive transfer of physiological prion protein-specific CD4(+) T-lymphocytes. Vaccines utilizing antibodies generally target disease-specific epitopes that are only exposed in the misfolded PrP(Sc) conformation. Vaccines utilizing antigen-loaded dendritic cell have the ability to bypass immune tolerance and prime CD4(+) cells to initiate an immune response. Adoptive transfer of CD4(+) T-cells is another promising target as this cell type can orchestrate the adaptive immune response. Although more research into mechanisms and safety is required, these immunotherapies offer novel therapeutic targets for prion diseases.