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The 37/67 kDa laminin receptor (LRP/LR) acts as a receptor for prions providing a promising target for the treatment of prion diseases. Recently, we selected anti-LRP/LR single-chain antibodies (scFvs) and proved a reduction of the peripheral PrP Sc propagation by passive immunotransfer into scrapie-infected mice. Here, we report the development of an in vivo gene delivery system based on adeno-associated virus (AAV) vectors expressing scFvs-S18 and -N3 directed against LRP/LR. Transduction of neuronal and non-neuronal cells with recombinant (r)AAV serotype 2 vectors encoding scFv-S18, -N3 and -C9 verified the efficient secretion of the antibodies. These vectors were administered via stereotactic intracerebral microinjection into the hippocampus of C57BL/6 mice, followed by intracerebral inoculation with 10 % RML at the same site 2 weeks post-injection of rAAV. After 90 days post-infection, scFv-S18 and -N3 expression resulted in the reduction of peripheral PrP Sc propagation by approximately 60 and 32 %, respectively, without a significant prolongation of incubation times and survival. Proof of rAAV vector DNA in spleen samples by real-time PCR strongly suggests a transport or trafficking of rAAV from the brain to the spleen, resulting in rAAV-mediated expression of scFv followed by reduced PrP Sc levels in the spleen most likely due to the blockage of the prion receptor LRP/LR by scFv.Prion diseases are fatal lethal neurodegenerative diseases affecting humans and animals (for review see Weissmann, 2004;Zuber et al., 2007a). None of the affected individuals can be treated or cured effectively (Ludewigs et al., 2007;Vana et al., 2007;Weissmann & Aguzzi, 2005). The abnormal form of the prion protein, PrP Sc , is frequently associated with infectivity and propagates mainly in the brain and the lymphoreticular system (LRS). Accumulation of the aggregated PrP Sc leads to neuronal death. PrP Sc is distinct from the host protein PrP c by its biochemical properties such as proteinase K sensitivity and insolubility, but harbours the same amino acid sequence. The generation of PrP Sc from PrP c involves conformational changes accompanied by modifications in the secondary structure of the protein (for review see Aguzzi & Weissmann, 1998;Prusiner, 1998;Weissmann, 2004).The 37/67 kDa laminin receptor (LRP/LR) is a multifunctional protein (i) playing an important role in cell adhesion, movement and growth of many cell types, (ii) acting as a receptor for some subtypes of adeno-associated 3These authors contributed equally to this work. (Morel et al., 2005). The fact that LRP levels are increased in organs of the LRS and central nervous system (CNS), such as spleen and brain, of infected animals (Rieger et al., 1997) strongly suggests that this receptor is not only essential for prion uptake after oral infection but also plays an important role for PrP Sc propagation and prion pathogenesis in the peripheral nervous system, including the LRS and CNS. Additionally, several laminin receptor isoforms have been found in mouse bra...

Prion diseases are lethal for both humans and animals, and affected individuals die after several months following a rapid disease progression. Although researchers have attempted for decades to develop effective therapeutics for the therapy of human prion disorders, until now no efficient drug has been available on the market for transmissible spongiform encephalopathy (TSE) treatment or cure. Approximately 200 patients worldwide have died or suffer from variant Creutzfeldt-Jakob disease (CJD). Incidences for sporadic and familial CJD are approximately 1.5-2 per million per year and one per 10 million per year, respectively, in Europe. This review summarizes classical and modern trials for the development of effective anti-TSE drugs, introduces potential effective delivery systems, such as lentiviral and adeno-associated virus systems for antiprion components, including antibodies and siRNAs, and presents vaccination trials. Most of the antiprion drugs target prion protein PrP(c) and/or PrP(Sc). Alternative targets are receptors and coreceptors for PrP, that is, the 37/67-kDa laminin receptor and heparan sulfate proteoglycanes. We review clinical trials for the treatment of TSEs and describe hindrances and chances for a breakthrough in therapy of prion disorders.

1. Prion diseases are a group of rare, fatal neurodegenerative diseases, also known as transmissible spongiform encephalopathies (TSEs), that affect both animals and humans and include bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep, chronic wasting disease (CWD) in deer and elk, and Creutzfeldt-Jakob disease (CJD) in humans. TSEs are usually rapidly progressive and clinical symptoms comprise dementia and loss of movement coordination due to the accumulation of an abnormal isoform (PrP(Sc)) of the host-encoded prion protein (PrP(c)). 2. This article reviews the current knowledge on PrP(c) and PrP(Sc), prion replication mechanisms, interaction partners of prions, and their cell surface receptors. Several strategies, summarized in this article, have been investigated for an effective antiprion treatment including development of a vaccination therapy and screening for potent chemical compounds. Currently, no effective treatment for prion diseases is available. 3. The identification of the 37 kDa/67 kDa laminin receptor (LRP/LR) and heparan sulfate as cell surface receptors for prions, however, opens new avenues for the development of alternative TSE therapies.