Naturally prion resistant mammals: A utopia?

Each known abnormal prion protein (PrP^Sc) is considered to have a specific range and therefore the ability to infect some species and not others. Consequently, some species have been assumed to be prion disease resistant as no successful natural or experimental challenge infections have been reported. This assumption suggested that, independent of the virulence of the PrP^Sc strain, normal prion protein (PrP^C) from these ‘resistant’ species could not be induced to misfold. Numerous in vitro and in vivo studies trying to corroborate the unique properties of PrP^Sc have been undertaken. The results presented in the article “Rabbits are not resistant to prion infection” demonstrated that normal rabbit PrP^C, which was considered to be resistant to prion disease, can be misfolded to PrP^Sc and subsequently used to infect and transmit a standard prion disease to leporids. Using the concept of species resistance to prion disease, we will discuss the mistake of attributing species specific prion disease resistance based purely on the absence of natural cases and incomplete in vivo challenges. The BSE epidemic was partially due to an underestimation of species barriers. To repeat this error would be unacceptable, especially if present knowledge and techniques can show a theoretical risk. Now that the myth of prion disease resistance has been refuted it is time to re-evaluate, using the new powerful tools available in modern prion laboratories, whether any other species could be at risk.     

Lipopolysaccharide induced conversion of recombinant prion protein

The conformational conversion of the cellular prion protein (PrP^C) to the β-rich infectious isoform PrP^Sc is considered a critical and central feature in prion pathology. Although PrP^Sc is the critical component of the infectious agent, as proposed in the “protein-only” prion hypothesis, cellular components have been identified as important cofactors in triggering and enhancing the conversion of PrP^C to proteinase K resistant PrP^Sc. A number of in vitro systems using various chemical and/or physical agents such as guanidine hydrochloride, urea, SDS, high temperature, and low pH, have been developed that cause PrP^C conversion, their amplification, and amyloid fibril formation often under non-physiological conditions. In our ongoing efforts to look for endogenous and exogenous chemical mediators that might initiate, influence, or result in the natural conversion of PrP^C to PrP^Sc, we discovered that lipopolysaccharide (LPS), a component of gram-negative bacterial membranes interacts with recombinant prion proteins and induces conversion to an isoform richer in β sheet at near physiological conditions as long as the LPS concentration remains above the critical micelle concentration (CMC). More significant was the LPS mediated conversion that was observed even at sub-molar ratios of LPS to recombinant ShPrP (90–232).     

Insoluble cellular prion protein and its association with prion and Alzheimer diseases

The soluble cellular prion protein (PrP^C) is best known for its association with prion disease (PrD) through its conversion to a pathogenic insoluble isoform (PrP^Sc). However, its deleterious effects independent of PrP^Sc have recently been observed not only in PrD but also in Alzheimer disease (AD), two diseases which mainly affect cognition. At the same time, PrP^C itself seems to have broad physiologic functions including involvement in cognitive processes. The PrP^C that is believed to be soluble and monomeric has so far been the only PrP conformer observed in the uninfected brain. In 2006, we identified an insoluble PrP^C conformer (termed iPrP^C) in uninfected human and animal brains. Remarkably, the PrP^Sc-like iPrP^C shares the immunoreactivity behavior and fragmentation with a newly-identified PrP^Sc species in a novel human PrD termed variably protease-sensitive prionopathy. Moreover, iPrP^C has been observed as the major PrP species that interacts with amyloid β (Aβ) in AD. This article highlights evidence of PrP involvement in two putatively beneficial and deleterious PrP-implicated pathways in cognition and hypothesizes first, that beneficial and deleterious effects of PrP^C are attributable to the chameleon-like conformation of the protein and second, that the iPrP^C conformer is associated with PrD and AD.Key words: prion protein, prion disease, cognition, cognitive deficit, insoluble prion protein, Alzheimer disease, variably protease-sensitive prionopathy, dementia, memory     

Anti-PrP antibodies detected at terminal stage of prion-affected mouse

The causative agent of prion diseases is the pathological isoform (PrP^Sc) of the host-encoded cellular prion protein (PrP^C). PrP^Sc has an identical amino acid sequence to PrP^C; thus, it has been assumed that an immune response against PrP^Sc could not be found in prion-affected animals. In this study, we found the anti-prion protein (PrP) antibody at the terminal stage of mouse scrapie. Several sera from mice in the terminal stage of scrapie reacted to the recombinant mouse PrP (rMPrP) molecules and brain homogenates of mouse prion diseases. These results indicate that mouse could recognize PrP^C or PrP^Sc as antigens by the host immune system. Furthermore, immunization with rMPrP generates high titers of anti-PrP antibodies in wild-type mice. Some anti-PrP antibodies immunized with rMPrP prevent PrP^Sc replication in vitro. The mouse sera from terminal prion disease have several wide epitopes, although mouse sera immunized with rMPrP possess narrow epitopes.     

Pressure-assisted dissociation and degradation of “proteinase K-resistant” fibrils prepared by seeding with scrapie-infected hamster prion protein

The crucial step for the fatal neurodegenerative prion diseases involves the conversion of a normal cellular protein, PrP^C, into a fibrous pathogenic form, PrP^Sc, which has an unusual stability against heat and resistance against proteinase K digestion. A successful challenge to reverse the reaction from PrP^Sc into PrP^C is considered valuable, as it would give a key to dissolving the complex molecular events into thermodynamic and kinetic analyses and may also provide a means to prevent the formation of PrP^Sc from PrP^C eventually in vivo. Here we show that, by applying pressures at kbar range, the “proteinase K-resistant” fibrils (rHaPrP^res) prepared from hamster prion protein (rHaPrP [23–231]) by seeding with brain homogenate of scrapie-infected hamster, becomes easily digestible. The result is consistent with the notion that rHaPrP^res fibrils are dissociated into rHaPrP monomers under pressure and that the formation of PrP^Sc from PrP^C is thermodynamically controlled. Moreover, the efficient degradation of prion fibrils under pressure provides a novel means of eliminating infectious PrP^Sc from various systems of pathogenic concern.     

Rapid, high-throughput detection of PrPSc by 96-well immunoassay

Prion diseases are emerging infectious disorders that affect several mammalian species including humans. The transmissible agent is comprised of PrP^Sc, a misfolded isoform of the normal host-encoded prion protein PrP^C. Immunodetection of PrP^Sc is often utilized for prion disease diagnosis and tracking spread of the infectious agent through the host. We have developed a rapid, high-throughput 96-well immunoassay, which is specific for the detection of PrP^Sc. This assay has PrP^Sc detection limits similar to western blot and is advantageous because of its comparatively shorter running time, smaller start-up and operation costs and large sample capacity.Key words: prion disease, immunodetection, PrP^Sc     

Insoluble cellular prion protein and its association with prion and Alzheimer diseases

The soluble cellular prion protein (PrP^C) is best known for its association with prion disease (PrD) through its conversion to a pathogenic insoluble isoform (PrP^Sc). However, its deleterious effects independent of PrP^Sc have recently been observed not only in PrD but also in Alzheimer disease (AD), two diseases which mainly affect cognition. At the same time, PrP^C itself seems to have broad physiologic functions including involvement in cognitive processes. The PrP^C that is believed to be soluble and monomeric has so far been the only PrP conformer observed in the uninfected brain. In 2006, we identified an insoluble PrP^C conformer (termed iPrP^C) in uninfected human and animal brains. Remarkably, the PrP^Sc-like iPrPC shares the immunoreactivity behavior and fragmentation with a newly-identified PrP^Sc species in a novel human PrD termed variably protease-sensitive prionopathy. Moreover, iPrP^C has been observed as the major PrP species that interacts with amyloid β (Aβ) in AD. This article highlights evidence of PrP involvement in two putatively beneficial and deleterious PrP-implicated pathways in cognition, and hypothesizes first, that beneficial and deleterious effects of PrPC are attributable to the chameleon-like conformation of the protein and second, that the iPrP^C conformer is associated with PrD and AD.     

The Extent of Protease Resistance of Misfolded Prion Protein Is Highly Dependent on the Salt Concentration

Transmissible spongiform encephalopathies are neurodegenerative diseases caused by prions in mammals. An aberrantly folded protein (PrP^Sc) is the main component of these proteinaceous infectious particles. Prions exhibit strong resistance to protease digestion, which is typically exploited for biochemical discrimination from its native cellular form (PrP^C). This classical feature has been partially challenged by the isolation of sizeable amounts of protease-sensitive PrP^Sc isoforms that self-propagate in vivo. Here, we report that the degree of PrP^Sc protease resistance is highly dependent on the concentration of salt in the solution. Similar changes were observed in PrP^Sc obtained from different strains and species. Strikingly, the effect of salt is reversible and is associated with changes on the size of PrP^Sc particles, but surprisingly, the more protease-sensitive species consists of a larger size. These findings shed light on the mechanistic aspects of prion proteolysis and should be considered when assessing samples of biomedical relevance.     

Transgenic Rabbits Expressing Ovine PrP Are Susceptible to Scrapie

Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative diseases affecting a wide range of mammalian species. They are caused by prions, a proteinaceous pathogen essentially composed of PrP^Sc, an abnormal isoform of the host encoded cellular prion protein PrPC. Constrained steric interactions between PrP^Sc and PrP^C are thought to provide prions with species specificity, and to control cross-species transmission into other host populations, including humans. Transgenetic expression of foreign PrP genes has been successfully and widely used to overcome the recognized resistance of mouse to foreign TSE sources. Rabbit is one of the species that exhibit a pronounced resistance to TSEs. Most attempts to infect experimentally rabbit have failed, except after inoculation with cell-free generated rabbit prions. To gain insights on the molecular determinants of the relative resistance of rabbits to prions, we generated transgenic rabbits expressing the susceptible V¹³⁶R¹⁵⁴Q¹⁷¹ allele of the ovine PRNP gene on a rabbit wild type PRNP New Zealand background and assessed their experimental susceptibility to scrapie prions. All transgenic animals developed a typical TSE 6–8 months after intracerebral inoculation, whereas wild type rabbits remained healthy more than 700 days after inoculation. Despite the endogenous presence of rabbit PrP^C, only ovine PrP^Sc was detectable in the brains of diseased animals. Collectively these data indicate that the low susceptibility of rabbits to prion infection is not enciphered within their non-PrP genetic background.     

Chemically Induced Accumulation of GAGs Delays PrPSc Clearance but Prolongs Prion Disease Incubation Time

Prion diseases are a group of fatal neurodegenerative diseases affecting humans and animals. The only identified component of the infectious prion is PrP^Sc, an aberrantly folded isoform of PrP^C. Glycosaminoglycans, which constitute the main receptor for prions on cells, play a complex role in the pathogenesis of prion diseases. For example, while agents inducing aberrant lysosomal accumulation of GAGs such as Tilorone and Quinacrine significantly reduced PrP^Sc content in scrapie-infected cells, administration of Quinacrine to prion-infected subjects did not improve their clinical status. In this study, we investigated the association of PrP^Sc with cells cultured with Tilorone. We found that while the initial incorporation of PrP^Sc was similar in the treated and untreated cells, clearance of PrP^Sc from the Tilorone-treated cells was significantly impaired. Interestingly, prolonged administration of Tilorone to mice prior to prion infection resulted in a significant delay in disease onset, concomitantly with in vivo accumulation of lysosomal GAGs. We hypothesize that GAGs may complex with newly incorporated PrP^Sc in lysosomes and further stabilize the prion protein conformation. Over-stabilized PrP^Sc molecules have been shown to comprise reduced converting activity.     

Generation of antisera to purified prions in lipid rafts

Prion diseases are fatal neurodegenerative disorders caused by prion proteins (PrP). Infectious prions accumulate in the brain through a template-mediated conformational conversion of endogenous PrP^C into alternately folded PrP^Sc. Immunoassays toward pre-clinical detection of infectious PrP^Sc have been confounded by low-level prion accumulation in non-neuronal tissue and the lack of PrP^Sc selective antibodies. We report a method to purify infectious PrP^Sc from biological tissues for use as an immunogen and sample enrichment for increased immunoassay sensitivity. Significant prion enrichment is accomplished by sucrose gradient centrifugation of infected tissue and isolation with detergent resistant membranes from lipid rafts (DRMs). At equivalent protein concentration a 50-fold increase in detectable PrP^Sc was observed in DRM fractions relative to crude brain by direct ELISA. Sequential purification steps result in increased specific infectivity (DRM >20-fold and purified DRM immunogen >40-fold) relative to 1% crude brain homogenate. Purification of PrP^Sc from DRM was accomplished using phosphotungstic acid protein precipitation after proteinase-K (PK) digestion followed by size exclusion chromatography to separate PK and residual protein fragments from larger prion aggregates. Immunization with purified PrP^Sc antigen was performed using wild-type (wt) and Prnp^0/0 mice, both on Balb/cJ background. A robust immune response against PrP^Sc was observed in all inoculated Prnp^0/0 mice resulting in antisera containing high-titer antibodies against prion protein. Antisera from these mice recognized both PrP^C and PrP^Sc, while binding to other brain-derived protein was not observed. In contrast, the PrP^Sc inoculum was non-immunogenic in wt mice and antisera showed no reactivity with PrP or any other protein.Key words: prion, scrapie, Prnp0/0 mice, purification methodology, antibody, antisera, lipid-rafts, detergent resistant membranes, neuroscience, immunization, diagnostic     

PrP N-terminal domain triggers PrP(Sc)-like aggregation of Dpl

Transmissible spongiform encephalopathies are fatal neurodegenerative disorders thought to be transmitted by self-perpetuating conformational conversion of a neuronal membrane glycoprotein (PrP^C, for “cellular prion protein”) into an abnormal state (PrP^Sc, for “scrapie prion protein”). Doppel (Dpl) is a protein that shares significant biochemical and structural homology with PrP^C. In contrast to its homologue PrP^C, Dpl is unable to participate in prion disease progression or to achieve an abnormal PrP^Sc-like state. We have constructed a chimeric mouse protein, composed of the N-terminal domain of PrP^C (residues 23-125) and the C-terminal part of Dpl (residues 58-157). This chimeric protein displays PrP-like biochemical and structural features; when incubated in presence of NaCl, the α-helical monomer forms soluble β-sheet-rich oligomers which acquire partial resistance to pepsin proteolysis in vitro, as do PrP oligomers. Moreover, the presence of aggregates akin to protofibrils is observed in soluble oligomeric species by electron microscopy.     

Sialylation of Prion Protein Controls the Rate of Prion Amplification,the Cross-Species Barrier,the Ratio of PrPSc Glycoform and Prion Infectivity

The central event underlying prion diseases involves conformational change of the cellular form of the prion protein (PrP^C) into the disease-associated, transmissible form (PrP^Sc). PrP^C is a sialoglycoprotein that contains two conserved N-glycosylation sites. Among the key parameters that control prion replication identified over the years are amino acid sequence of host PrP^C and the strain-specific structure of PrP^Sc. The current work highlights the previously unappreciated role of sialylation of PrP^C glycans in prion pathogenesis, including its role in controlling prion replication rate, infectivity, cross-species barrier and PrP^Sc glycoform ratio. The current study demonstrates that undersialylated PrP^C is selected during prion amplification in Protein Misfolding Cyclic Amplification (PMCAb) at the expense of oversialylated PrP^C. As a result, PMCAb-derived PrP^Sc was less sialylated than brain-derived PrP^Sc. A decrease in PrP^Sc sialylation correlated with a drop in infectivity of PMCAb-derived material. Nevertheless, enzymatic de-sialylation of PrP^C using sialidase was found to increase the rate of PrP^Sc amplification in PMCAb from 10- to 10,000-fold in a strain-dependent manner. Moreover, de-sialylation of PrP^C reduced or eliminated a species barrier of for prion amplification in PMCAb. These results suggest that the negative charge of sialic acid controls the energy barrier of homologous and heterologous prion replication. Surprisingly, the sialylation status of PrP^C was also found to control PrP^Sc glycoform ratio. A decrease in PrP^C sialylation levels resulted in a higher percentage of the diglycosylated glycoform in PrP^Sc. 2D analysis of charge distribution revealed that the sialylation status of brain-derived PrP^C differed from that of spleen-derived PrP^C. Knocking out lysosomal sialidase Neu1 did not change the sialylation status of brain-derived PrP^C, suggesting that Neu1 is not responsible for desialylation of PrP^C. The current work highlights previously unappreciated role of PrP^C sialylation in prion diseases and opens multiple new research directions, including development of new therapeutic approaches.     

Brain delivery of AAV9 expressing an anti-PrP monovalent antibody delays prion disease in mice

Prion diseases are caused by a conformational modification of the cellular prion protein (PrP^C) into disease-specific forms, termed PrP^Sc, that have the ability to interact with PrP^C promoting its conversion to PrP^Sc. In vitro studies demonstrated that anti-PrP antibodies inhibit this process. In particular, the single chain variable fragment D18 antibody (scFvD18) showed high efficiency in curing chronically prion-infected cells. This molecule binds the PrP^C region involved in the interaction with PrP^Sc thus halting further prion formation. These findings prompted us to test the efficiency of scFvD18 in vivo. A recombinant Adeno-Associated Viral vector serotype 9 was used to deliver scFvD18 to the brain of mice that were subsequently infected by intraperitoneal route with the mouse-adapted scrapie strain RML. We found that the treatment was safe, prolonged the incubation time of scrapie-infected animals and decreased the burden of total proteinase-resistant PrP^Sc in the brain, suggesting that scFvD18 interferes with prion replication in vivo. This approach is relevant for designing new therapeutic strategies for prion diseases and other disorders characterized by protein misfolding.     

Recombinant Prion Protein Refolded with Lipid and RNA Has the Biochemical Hallmarks of a Prion but Lacks In Vivo Infectivity

During prion infection, the normal, protease-sensitive conformation of prion protein (PrP^C) is converted via seeded polymerization to an abnormal, infectious conformation with greatly increased protease-resistance (PrP^Sc). In vitro, protein misfolding cyclic amplification (PMCA) uses PrP^Sc in prion-infected brain homogenates as an initiating seed to convert PrP^C and trigger the self-propagation of PrP^Sc over many cycles of amplification. While PMCA reactions produce high levels of protease-resistant PrP, the infectious titer is often lower than that of brain-derived PrP^Sc. More recently, PMCA techniques using bacterially derived recombinant PrP (rPrP) in the presence of lipid and RNA but in the absence of any starting PrP^Sc seed have been used to generate infectious prions that cause disease in wild-type mice with relatively short incubation times. These data suggest that lipid and/or RNA act as cofactors to facilitate the de novo formation of high levels of prion infectivity. Using rPrP purified by two different techniques, we generated a self-propagating protease-resistant rPrP molecule that, regardless of the amount of RNA and lipid used, had a molecular mass, protease resistance and insolubility similar to that of PrP^Sc. However, we were unable to detect prion infectivity in any of our reactions using either cell-culture or animal bioassays. These results demonstrate that the ability to self-propagate into a protease-resistant insoluble conformer is not unique to infectious PrP molecules. They suggest that the presence of RNA and lipid cofactors may facilitate the spontaneous refolding of PrP into an infectious form while also allowing the de novo formation of self-propagating, but non-infectious, rPrP-res.     

Isolation of Soluble and Insoluble PrP Oligomers in the Normal Human Brain

The central event in the pathogenesis of prion diseases involves a conversion of the host-encoded cellular prion protein PrP^C into its pathogenic isoform PrP^{Sc 1}. PrP^C is detergent-soluble and sensitive to proteinase K (PK)-digestion, whereas PrP^Sc forms detergent-insoluble aggregates and is partially resistant to PK^2-6. The conversion of PrP^C to PrP^Sc is known to involve a conformational transition of α-helical to β-sheet structures of the protein. However, the in vivo pathway is still poorly understood. A tentative endogenous PrP^Sc, intermediate PrP* or "silent prion", has yet to be identified in the uninfected brain⁷.Using a combination of biophysical and biochemical approaches, we identified insoluble PrP^C aggregates (designated iPrP^C) from uninfected mammalian brains and cultured neuronal cells^{8, 9}. Here, we describe detailed procedures of these methods, including ultracentrifugation in detergent buffer, sucrose step gradient sedimentation, size exclusion chromatography, iPrP enrichment by gene 5 protein (g5p) that specifically bind to structurally altered PrP forms¹⁰, and PK-treatment. The combination of these approaches isolates not only insoluble PrP^Sc and PrP^C aggregates but also soluble PrP^C oligomers from the normal human brain. Since the protocols described here have been used to isolate both PrP^Sc from infected brains and iPrP^C from uninfected brains, they provide us with an opportunity to compare differences in physicochemical features, neurotoxicity, and infectivity between the two isoforms. Such a study will greatly improve our understanding of the infectious proteinaceous pathogens. The physiology and pathophysiology of iPrP^C are unclear at present. Notably, in a newly-identified human prion disease termed variably protease-sensitive prionopathy, we found a new PrP^Sc that shares the immunoreactive behavior and fragmentation with iPrP^{C 11, 12}. Moreover, we recently demonstrated that iPrP^C is the main species that interacts with amyloid-β protein in Alzheimer disease¹³. In the same study, these methods were used to isolate Abeta aggregates and oligomers in Alzheimer''s disease¹³, suggesting their application to non-prion protein aggregates involved in other neurodegenerative disorders.     

Brain delivery of AAV9 expressing an anti-PrP monovalent antibody delays prion disease in mice

Prion diseases are caused by a conformational modification of the cellular prion protein (PrP^C) into disease-specific forms, termed PrP^Sc, that have the ability to interact with PrP^C promoting its conversion to PrP^Sc. In vitro studies demonstrated that anti-PrP antibodies inhibit this process. In particular, the single chain variable fragment D18 antibody (scFvD18) showed high efficiency in curing chronically prion-infected cells. This molecule binds the PrP^C region involved in the interaction with PrP^Sc thus halting further prion formation. These findings prompted us to test the efficiency of scFvD18 in vivo. A recombinant Adeno-Associated Viral vector serotype 9 was used to deliver scFvD18 to the brain of mice that were subsequently infected by intraperitoneal route with the mouse-adapted scrapie strain RML. We found that the treatment was safe, prolonged the incubation time of scrapie-infected animals and decreased the burden of total proteinase-resistant PrP^Sc in the brain, suggesting that scFvD18 interferes with prion replication in vivo. This approach is relevant for designing new therapeutic strategies for prion diseases and other disorders characterized by protein misfolding.     

PrPST,a Soluble,Protease Resistant and Truncated PrP Form Features in the Pathogenesis of a Genetic Prion Disease

While the conversion of PrP^C into PrP^Sc in the transmissible form of prion disease requires a preexisting PrP^Sc seed, in genetic prion disease accumulation of disease related PrP could be associated with biochemical and metabolic modifications resulting from the designated PrP mutation. To investigate this possibility, we looked into the time related changes of PrP proteins in the brains of TgMHu2ME199K/wt mice, a line modeling for heterozygous genetic prion disease linked to the E200K PrP mutation. We found that while oligomeric entities of mutant E199KPrP exist at all ages, aggregates of wt PrP in the same brains presented only in advanced disease, indicating a late onset conversion process. We also show that most PK resistant PrP in TgMHu2ME199K mice is soluble and truncated (PrP^ST), a pathogenic form never before associated with prion disease. We next looked into brain samples from E200K patients and found that both PK resistant PrPs, PrP^ST as in TgMHu2ME199K mice, and “classical” PrP^Sc as in infectious prion diseases, coincide in the patient''s post mortem brains. We hypothesize that aberrant metabolism of mutant PrPs may result in the formation of previously unknown forms of the prion protein and that these may be central for the fatal outcome of the genetic prion condition.     

Co-existence of Distinct Prion Types Enables Conformational Evolution of Human PrPSc by Competitive Selection

The unique phenotypic characteristics of mammalian prions are thought to be encoded in the conformation of pathogenic prion proteins (PrP^Sc). The molecular mechanism responsible for the adaptation, mutation, and evolution of prions observed in cloned cells and upon crossing the species barrier remains unsolved. Using biophysical techniques and conformation-dependent immunoassays in tandem, we isolated two distinct populations of PrP^Sc particles with different conformational stabilities and aggregate sizes, which frequently co-exist in the most common human prion disease, sporadic Creutzfeldt-Jakob disease. The protein misfolding cyclic amplification replicates each of the PrP^Sc particle types independently and leads to the competitive selection of those with lower initial conformational stability. In serial propagation with a nonglycosylated mutant PrP^C substrate, the dominant PrP^Sc conformers are subject to further evolution by natural selection of the subpopulation with the highest replication rate due to its lowest stability. Cumulatively, the data show that sporadic Creutzfeldt-Jakob disease PrP^Sc is not a single conformational entity but a dynamic collection of two distinct populations of particles. This implies the co-existence of different prions, whose adaptation and evolution are governed by the selection of progressively less stable, faster replicating PrP^Sc conformers.     

Safety,specificity and immunogenicity of a PrPSc-specific prion vaccine based on the YYR disease specific epitope

Prions are a novel form of infectivity based on the misfolding of a self-protein (PrP^C) into a pathological, infectious isomer (PrP^Sc). The current uncontrolled spread of chronic wasting disease in cervids, coupled with the demonstrated zoonotic nature of select livestock prion diseases, highlights the urgent need for disease management tools. While there is proof-of-principle evidence for a prion vaccine, these efforts are complicated by the challenges and risks associated with induction of immune responses to a self-protein. Our priority is to develop a PrP^Sc-specific prion vaccine based on epitopes that are uniquely exposed upon misfolding. These disease specific epitopes (DSEs) have the potential to enable specific targeting of the pathological species through immunotherapy. Here we review outcomes of the translation of a prion DSE into a PrP^Sc-specific vaccine based on the criteria of immunogenicity, safety and specificity.