Standards for the assay of Creutzfeldt-Jakob disease specimens

Assessment of the Zoonotic Potential of Atypical Scrapie Prions in Humanized Mice Reveals Rare Phenotypic Convergence but Not Identity With Sporadic Creutzfeldt-Jakob Disease Prions

BACKGROUND

Atypical/Nor98 scrapie (AS) is an idiopathic infectious prion disease affecting sheep and goats. Recent findings suggest that zoonotic prions from classical bovine spongiform encephalopathy (C-BSE) may copropagate with atypical/Nor98 prions in AS sheep brains. Investigating the risk AS poses to humans is crucial.

METHODS

To assess the risk of sheep/goat-to-human transmission of AS, we serially inoculated brain tissue from field and laboratory isolates into transgenic mice overexpressing human prion protein (Met129 allele). We studied clinical outcomes as well as presence of prions in brains and spleens.

RESULTS

No transmission occurred on the primary passage, with no clinical disease or pathological prion protein in brains and spleens. On subsequent passages, 1 isolate gradually adapted, manifesting as prions with a phenotype resembling those causing MM1-type sporadic Creutzfeldt-Jakob disease in humans. However, further characterization using in vivo and in vitro techniques confirmed both prion agents as different strains, revealing a case of phenotypic convergence. Importantly, no C-BSE prions emerged in these mice, especially in the spleen, which is more permissive than the brain for C-BSE cross-species transmission.

CONCLUSIONS

The results obtained suggest a low zoonotic potential for AS. Rare adaptation may allow the emergence of prions phenotypically resembling those spontaneously forming in humans.

Experimental Bovine Spongiform Encephalopathy in Squirrel Monkeys: The Same Complex Proteinopathy Appearing after Very Different Incubation Times

Incubation periods in humans infected with transmissible spongiform encephalopathy (TSE) agents can exceed 50 years. In humans infected with bovine spongiform encephalopathy (BSE) agents, the effects of a “species barrier,” often observed when TSE infections are transmitted from one species to another, would be expected to increase incubation periods compared with transmissions of same infectious agents within the same species. As part of a long-term study investigating the susceptibility to BSE of cell cultures used to produce vaccines, we inoculated squirrel monkeys (Saimiri sp., here designated SQ) with serial dilutions of a bovine brain suspension containing the BSE agent and monitored them for as long as ten years. Previously, we showed that SQ infected with the original “classical” BSE agent (SQ-BSE) developed a neurological disease resembling that seen in humans with variant CJD (vCJD). Here, we report the final characterization of the SQ-BSE model. We observed an unexpectedly marked difference in incubation times between two animals inoculated with the same dilution and volume of the same C-BSE bovine brain extract on the same day. SQ-BSE developed, in addition to spongiform changes and astrogliosis typical of TSEs, a complex proteinopathy with severe accumulations of protease-resistant prion protein (PrP^TSE), hyperphosphorylated tau (p-tau), ubiquitin, and α-synuclein, but without any amyloid plaques or β-amyloid protein (Aβ) typical of Alzheimer’s disease. These results suggest that PrP^TSE enhanced the accumulation of several key proteins characteristically seen in human neurodegenerative diseases. The marked variation in incubation periods in the same experimental TSE should be taken into account when modeling the epidemiology of human TSEs.

Prion potentiation after life-long dormancy in mice devoid of PrP

Prions are neurotropic pathogens composed of misfolded assemblies of the host-encoded prion protein PrP^C which replicate by recruitment and conversion of further PrP^C by an autocatalytic seeding polymerization process. While it has long been shown that mouse-adapted prions cannot replicate and are rapidly cleared in transgenic PrP^0/0 mice invalidated for PrP^C, these experiments have not been done with other prions, including from natural resources, and more sensitive methods to detect prion biological activity. Using transgenic mice expressing human PrP to bioassay prion infectivity and RT-QuIC cell-free assay to measure prion seeding activity, we report that prions responsible for the most prevalent form of sporadic Creutzfeldt-Jakob disease in human (MM1-sCJD) can persist indefinitely in the brain of intra-cerebrally inoculated PrP^0/0 mice. While low levels of seeding activity were measured by RT-QuIC in the brain of the challenged PrP^0/0 mice, the bio-indicator humanized mice succumbed at a high attack rate, suggesting relatively high levels of persistent infectivity. Remarkably, these humanized mice succumbed with delayed kinetics as compared to MM1-sCJD prions directly inoculated at low doses, including the limiting one. Yet, the disease that did occur in the humanized mice on primary and subsequent back-passage from PrP^0/0 mice shared the neuropathological and molecular characteristics of MM1-sCJD prions, suggesting no apparent strain evolution during lifelong dormancy in PrP^0/0 brain. Thus, MM1-sCJD prions can persist for the entire life in PrP^0/0 brain with potential disease potentiation on retrotransmission to susceptible hosts. These findings highlight the capacity of prions to persist and rejuvenate in non-replicative environments, interrogate on the type of prion assemblies at work and alert on the risk of indefinite prion persistence with PrP-lowering therapeutic strategies.

Improving the Predictive Value of Prion Inactivation Validation Methods to Minimize the Risks of Iatrogenic Transmission With Medical Instruments

Prions are pathogenic infectious agents responsible for fatal, incurable neurodegenerative diseases in animals and humans. Prions are composed exclusively of an aggregated and misfolded form (PrP^Sc) of the cellular prion protein (PrP^C). During the propagation of the disease, PrP^Sc recruits and misfolds PrP^C into further PrP^Sc. In human, iatrogenic prion transmission has occurred with incompletely sterilized medical material because of the unusual resistance of prions to inactivation. Most commercial prion disinfectants validated against the historical, well-characterized laboratory strain of 263K hamster prions were recently shown to be ineffective against variant Creutzfeldt-Jakob disease human prions. These observations and previous reports support the view that any inactivation method must be validated against the prions for which they are intended to be used. Strain-specific variations in PrP^Sc physico-chemical properties and conformation are likely to explain the strain-specific efficacy of inactivation methods. Animal bioassays have long been used as gold standards to validate prion inactivation methods, by measuring reduction of prion infectivity. Cell-free assays such as the real-time quaking-induced conversion (RT-QuIC) assay and the protein misfolding cyclic amplification (PMCA) assay have emerged as attractive alternatives. They exploit the seeding capacities of PrP^Sc to exponentially amplify minute amounts of prions in biospecimens. European and certain national medicine agencies recently implemented their guidelines for prion inactivation of non-disposable medical material; they encourage or request the use of human prions and cell-free assays to improve the predictive value of the validation methods. In this review, we discuss the methodological and technical issues regarding the choice of (i) the cell-free assay, (ii) the human prion strain type, (iii) the prion-containing biological material. We also introduce a new optimized substrate for high-throughput PMCA amplification of human prions bound on steel wires, as translational model for prion-contaminated instruments.

Quaking-induced conversion of prion protein on a thermal mixer accelerates detection in brains infected with transmissible spongiform encephalopathy agents

Detection of misfolded prion protein, PrPTSE, in biological samples is important to develop antemortem tests for transmissible spongiform encephalopathies (TSEs). The real-time quaking-induced conversion (RT-QuIC) assay detects PrPTSE but requires dedicated equipment and relatively long incubation times when applied to samples containing extremely low levels of PrPTSE. It was shown that a microplate shaker with heated top (Thermomixer-C) accelerated amplification of PrPTSE in brain suspensions of 263K scrapie and sporadic Creutzfeldt-Jakob disease (sCJD). We expanded the investigation to include TSE agents previously untested, including chronic wasting disease (CWD), macaque-adapted variant CJD (vCJD) and human vCJD, and we further characterized the assays conducted at 42°C and 55°C. PrPTSE from all brains containing the TSE agents were successfully amplified using a truncated hamster recombinant protein except for human vCJD which required truncated bank vole recombinant protein. We compared assays conducted at 42°C on Thermomixer-C, Thermomixer-R (without heated top) and on a fluorimeter used for RT-QuIC. QuIC on Thermomixer-R achieved in only 18 hours assay sensitivity similar to that of RT-QuIC read at 60 hours (or 48 hours with sCJD). QuIC on Thermomixer-C required 24 hours to complete and the endpoint titers of some TSEs were 10-fold lower than those obtained with RT-QuIC and Thermomixer-R. Conversely, at 55°C, the reactions with sCJD and CWD on Thermomixer-C achieved the same sensitivity as with RT-QuIC but in shorter times. Human vCJD samples tested at higher temperatures gave rise to high reactivity in wells containing normal control samples. Similarly, reactions on Thermomixer-R were unsuitable at 55°C. The main disadvantage of Thermomixers is that they cannot track formation of PrP fibrils in real time, a feature useful in some applications. The main advantages of Thermomixers are that they need shorter reaction times to detect PrPTSE, are easier to use, involve more robust equipment, and are relatively affordable. Improvements to QuIC using thermal mixers may help develop accessible antemortem TSE tests.

Both murine host and inoculum modulate expression of experimental variant Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSEs) are infections that are experimentally transmissible to laboratory animals. TSE agents (prions) can be serially passaged in the same animal species. The susceptibility of mice to infection with specific TSE agents can be unpredictable and must be established empirically. We challenged wild-type C57BL/6 and RIIIS/J mice and transgenic mice overexpressing bovine prion protein (TgBo110) with a human brain infected with variant Creutzfeldt-Jakob disease (vCJD) agent and pooled brains of macaques experimentally infected with human vCJD agent (first-passage macaque vCJD). The human vCJD brain yielded a wide range of infectivity titres in different mouse models; TgBo110 mice were the most sensitive. In contrast, infectivity titres of macaque vCJD brain were similar in all three murine models. The brains of RIIIS/J mice infected with both human and macaque vCJD had mild or no vacuolation, while infected C57BL/6 and TgBo110 mice had spongiform degeneration with vacuolation. Abnormal prion protein (PrP^TSE) extracted from the brains of vCJD-infected TgBo110 mice displayed different glycosylation profiles and had greater resistance to denaturation by guanidine hydrochloride than PrP^TSE from infected wild-type mice or from either inoculum. Those histopathological features of TSE and physical properties of PrP^TSE in mice with experimental vCJD were intrinsic to the host, even though we also observed differences between wild-type mice infected with either agent, suggesting a modulatory effect of the inoculum. This study compared three widely used mouse models infected with two different vCJD inocula. The results show that the host plays a major role in manifestations of experimental TSEs.

Rapid Testing for Creutzfeldt-Jakob Disease in Donors of Cornea

BACKGROUND

Creutzfeldt-Jakob disease (CJD) has been accidentally transmitted by contaminated corneal transplants. Eye donors are not ordinarily tested for CJD, in part because an easy test is not available. We propose a relatively simple postmortem procedure to collect brain samples without performing full autopsy and show that a test currently marketed for veterinary diagnosis would offer an effective screening test.

METHODS

We selected 6 brains from confirmed cases of human sporadic CJD and sampled each in triplicate (18 specimens), 28 control brains of individuals with non-CJD neurodegenerative diseases and 10 normal brains. We also applied a procedure involving retro-orbital puncture after enucleation and biopsied the frontal lobes and optic nerves of a macaque experimentally infected with variant CJD. All samples were tested with the IDEXX HerdChek BSE-Scrapie Ag Kit to detect the abnormal prion protein, PrP.

RESULTS

The test discriminated between control and CJD-infected brains. All 18 infected brain samples diluted to 0.1%, except one, showed signals above cutoff, and a number of samples were reactive at even higher dilutions. These results suggest the test could detect the low concentrations of PrP probably present in brains of donors at early stages of CJD. Our collection procedure obtained sufficient macaque brain and optic nerve tissues to detect PrP.

CONCLUSIONS

We showed that a commercial test combined with rapid sample collection might offer a practical solution to screen brains of cornea donors for evidence of CJD. Such a test might enhance safety of corneal transplants and some other tissue-derived products.

Blood reference materials from macaques infected with variant Creutzfeldt-Jakob disease agent

BACKGROUND

Variant Creutzfeldt-Jakob disease (vCJD) is a fatal neurodegenerative infection that can be transmitted by blood and blood products from donors in the latent phase of the disease. Currently, there is no validated antemortem vCJD blood screening test. Several blood tests are under development. Any useful test must be validated with disease-relevant blood reference panels.

STUDY DESIGN AND METHODS

To generate blood reference materials, we infected four cynomolgus macaques with macaque-adapted vCJD brain homogenates. Blood was collected throughout the preclinical and clinical phases of infection. In parallel, equivalent blood was collected from one uninfected macaque. For each blood collection, an aliquot was stored as whole blood and the remainder was separated into components. Aliquots of plasma from terminally ill macaques were assayed for the presence of PrP(TSE) with the protein misfolding cyclic amplification (PMCA) method. Infectivity of the macaque brain homogenate used to infect macaques was titrated in C57BL/6 and RIII J/S inbred wild-type mice.

RESULTS

We sampled blood 19 times from the inoculated monkeys at various stages of the disease over a period of 29 months, generating liters of vCJD-infected macaque blood. vCJD was confirmed in all inoculated macaques. After PMCA, PrP(TSE) was detected in plasma from infected monkeys, but not from uninfected animals. Both mouse models were more sensitive to infection with macaque-adapted vCJD agent than to primary human vCJD agent.

CONCLUSION

The macaque vCJD blood panels generated in this study provide a unique resource to support vCJD assay development and to characterize vCJD infectivity in blood.

Human tonsil-derived follicular dendritic-like cells are refractory to human prion infection in vitro and traffic disease-associated prion protein to lysosomes

The molecular mechanisms involved in human cellular susceptibility to prion infection remain poorly defined. This is due, in part, to the absence of any well characterized and relevant cultured human cells susceptible to infection with human prions, such as those involved in Creutzfeldt-Jakob disease. In variant Creutzfeldt-Jakob disease, prion replication is thought to occur first in the lymphoreticular system and then spread into the brain. We have, therefore, examined the susceptibility of a human tonsil-derived follicular dendritic cell-like cell line (HK) to prion infection. HK cells were found to display a readily detectable, time-dependent increase in cell-associated abnormal prion protein (PrP(TSE)) when exposed to medium spiked with Creutzfeldt-Jakob disease brain homogenate, resulting in a coarse granular perinuclear PrP(TSE) staining pattern. Despite their high level of cellular prion protein expression, HK cells failed to support infection, as judged by longer term maintenance of PrP(TSE) accumulation. Colocalization studies revealed that exposure of HK cells to brain homogenate resulted in increased numbers of detectable lysosomes and that these structures immunostained intensely for PrP(TSE) after exposure to Creutzfeldt-Jakob disease brain homogenate. Our data suggest that human follicular dendritic-like cells and perhaps other human cell types are able to avoid prion infection by efficient lysosomal degradation of PrP(TSE).

Red-backed vole brain promotes highly efficient in vitro amplification of abnormal prion protein from macaque and human brains infected with variant Creutzfeldt-Jakob disease agent

Rapid antemortem tests to detect individuals with transmissible spongiform encephalopathies (TSE) would contribute to public health. We investigated a technique known as protein misfolding cyclic amplification (PMCA) to amplify abnormal prion protein (PrP^TSE) from highly diluted variant Creutzfeldt-Jakob disease (vCJD)-infected human and macaque brain homogenates, seeking to improve the rapid detection of PrP^TSE in tissues and blood. Macaque vCJD PrP^TSE did not amplify using normal macaque brain homogenate as substrate (intraspecies PMCA). Next, we tested interspecies PMCA with normal brain homogenate of the southern red-backed vole (RBV), a close relative of the bank vole, seeded with macaque vCJD PrP^TSE. The RBV has a natural polymorphism at residue 170 of the PrP-encoding gene (N/N, S/S, and S/N). We investigated the effect of this polymorphism on amplification of human and macaque vCJD PrP^TSE. Meadow vole brain (170N/N PrP genotype) was also included in the panel of substrates tested. Both humans and macaques have the same 170S/S PrP genotype. Macaque PrP^TSE was best amplified with RBV 170S/S brain, although 170N/N and 170S/N were also competent substrates, while meadow vole brain was a poor substrate. In contrast, human PrP^TSE demonstrated a striking narrow selectivity for PMCA substrate and was successfully amplified only with RBV 170S/S brain. These observations suggest that macaque PrP^TSE was more permissive than human PrP^TSE in selecting the competent RBV substrate. RBV 170S/S brain was used to assess the sensitivity of PMCA with PrP^TSE from brains of humans and macaques with vCJD. PrP^TSE signals were reproducibly detected by Western blot in dilutions through 10^-12 of vCJD-infected 10% brain homogenates. This is the first report showing PrP^TSE from vCJD-infected human and macaque brains efficiently amplified with RBV brain as the substrate. Based on our estimates, PMCA showed a sensitivity that might be sufficient to detect PrP^TSE in vCJD-infected human and macaque blood.

A closer look at prion strains: characterization and important implications

Prions are infectious proteins that are responsible for transmissible spongiform encephalopathies (TSEs) and consist primarily of scrapie prion protein (PrP^Sc), a pathogenic isoform of the host-encoded cellular prion protein (PrP^C). The absence of nucleic acids as essential components of the infectious prions is the most striking feature associated to these diseases. Additionally, different prion strains have been isolated from animal diseases despite the lack of DNA or RNA molecules. Mounting evidence suggests that prion-strain-specific features segregate with different PrP^Sc conformational and aggregation states.

Strains are of practical relevance in prion diseases as they can drastically differ in many aspects, such as incubation period, PrP^Sc biochemical profile (e.g., electrophoretic mobility and glycoform ratio) and distribution of brain lesions. Importantly, such different features are maintained after inoculation of a prion strain into genetically identical hosts and are relatively stable across serial passages.

This review focuses on the characterization of prion strains and on the wide range of important implications that the study of prion strains involves.

Candidate cell substrates, vaccine production, and transmissible spongiform encephalopathies

Transmissible spongiform encephalopathy (TSE) agents have contaminated human tissue-derived medical products, human blood components, and animal vaccines. The objective of this study was to determine the potential susceptibility to infection of 5 cell lines used or proposed for manufacture of biological products, as well as other lines. Cell lines were exposed to the infectious agents of sporadic and variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy (BSE). Exposed cultures were tested for TSE-associated prion protein (PrP(TSE)) and TSE infectivity by assay in rodents and nonhuman primates. No PrP(TSE) or infectivity has been detected in any exposed cell line under study so far. Animals inoculated with BSE brain homogenate developed typical spongiform encephalopathy. In contrast, animals inoculated with cells exposed to the BSE agent remained asymptomatic. All cell lines we studied resisted infection with 3 TSE agents, including the BSE agent.

Biochemical and strain properties of CJD prions: complexity versus simplicity

Prions, the agents responsible for transmissible spongiform encephalopathies, are infectious proteins consisting primarily of scrapie prion protein (PrP(Sc)), a misfolded, β-sheet enriched and aggregated form of the host-encoded cellular prion protein (PrP(C)). Their propagation is based on an autocatalytic PrP conversion process. Despite the lack of a nucleic acid genome, different prion strains have been isolated from animal diseases. Increasing evidence supports the view that strain-specific properties may be enciphered within conformational variations of PrP(Sc). In humans, sporadic Creutzfeldt-Jakob disease (sCJD) is the most frequent form of prion diseases and has demonstrated a wide phenotypic and molecular spectrum. In contrast, variant Creutzfeldt-Jakob disease (vCJD), which results from oral exposure to the agent of bovine spongiform encephalopathy, is a highly stereotyped disease, that, until now, has only occurred in patients who are methionine homozygous at codon 129 of the PrP gene. Recent research has provided consistent evidence of strain diversity in sCJD and also, unexpectedly enough, in vCJD. Here, we discuss the puzzling biochemical/pathological diversity of human prion disorders and the relationship of that diversity to the biological properties of the agent as demonstrated by strain typing in experimental models.

The octarepeat region of the prion protein is conformationally altered in PrP(Sc)

Background

Prion diseases are fatal neurodegenerative disorders characterized by misfolding and aggregation of the normal prion protein PrP^C. Little is known about the details of the structural rearrangement of physiological PrP^C into a still-elusive disease-associated conformation termed PrP^Sc. Increasing evidence suggests that the amino-terminal octapeptide sequences of PrP (huPrP, residues 59–89), though not essential, play a role in modulating prion replication and disease presentation.

Methodology/Principal Findings

Here, we report that trypsin digestion of PrP^Sc from variant and sporadic human CJD results in a disease-specific trypsin-resistant PrP^Sc fragment including amino acids ∼49–231, thus preserving important epitopes such as the octapeptide domain for biochemical examination. Our immunodetection analyses reveal that several epitopes buried in this region of PrP^Sc are exposed in PrP^C.

Conclusions/Significance

We conclude that the octapeptide region undergoes a previously unrecognized conformational transition in the formation of PrP^Sc. This phenomenon may be relevant to the mechanism by which the amino terminus of PrP^C participates in PrP^Sc conversion, and may also be exploited for diagnostic purposes.

Pathogen safety of plasma-derived products - Haemate P/Humate-P

Summary.  Plasma‐derived factor VIII (FVIII) and von Willebrand Factor (VWF)/FVIII concentrates have been successfully used to treat haemophilia since the late 1960s. These products are derived from pools of plasma donations that may contain viral contaminants – including hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV) – and may therefore present a transmission risk to recipients. To ensure the safety of Haemate^® P/Humate‐P^®, a plasma‐derived VWF/FVIII concentrate, donors of plasma are carefully selected and all donations are screened for viral antigens (HBV), virus‐specific antibodies (HIV‐1/2, HCV) and genomic material [hepatitis A virus, HBV, HCV, HIV‐1 and high titres of human parvovirus B19 (B19V)]. As a quality control measure, plasma pools for fractionation are only released for further processing when non‐reactivity has been demonstrated in serological and genome amplification assays. The manufacturing process for plasma‐derived products, especially the fundamental procedure of pasteurization, is effective in inactivating and/or removing a wide variety of viruses that may potentially be present despite the screening process. This has been demonstrated in virus validation studies using a range of different viruses. New emerging infectious agents, including prions, which potentially pose a threat to recipients of plasma derivatives, are also the subject of safety evaluations. The multiple precautionary measures that are inherent in the overall production process of Haemate P/Humate‐P have resulted in an excellent safety record, documented during 25 years of clinical use, and will help to maintain the high safety margin in the future.

Prominent and persistent extraneural infection in human PrP transgenic mice infected with variant CJD

BACKGROUND

The evolution of the variant Creutzfeldt-Jakob disease (vCJD) epidemic is hazardous to predict due to uncertainty in ascertaining the prevalence of infection and because the disease might remain asymptomatic or produce an alternate, sporadic-like phenotype.

METHODOLOGY/PRINCIPAL FINDINGS

Transgenic mice were produced that overexpress human prion protein with methionine at codon 129, the only allele found so far in vCJD-affected patients. These mice were infected with prions derived from variant and sporadic CJD (sCJD) cases by intracerebral or intraperitoneal route, and transmission efficiency and strain phenotype were analyzed in brain and spleen. We showed that i) the main features of vCJD infection in humans, including a prominent involvement of the lymphoid tissues compared to that in sCJD infection were faithfully reproduced in such mice; ii) transmission of vCJD agent by intracerebral route could lead to the propagation of either vCJD or sCJD-like prion in the brain, whereas vCJD prion was invariably propagated in the spleen, iii) after peripheral exposure, inefficient neuroinvasion was observed, resulting in an asymptomatic infection with life-long persistence of vCJD prion in the spleen at stable and elevated levels.

CONCLUSION/SIGNIFICANCE

Our findings emphasize the possibility that human-to-human transmission of vCJD might produce alternative neuropathological phenotypes and that lymphoid tissue examination of CJD cases classified as sporadic might reveal an infection by vCJD-type prions. They also provide evidence for the strong propensity of this agent to establish long-lasting, subclinical vCJD infection of lymphoreticular tissues, thus amplifying the risk for iatrogenic transmission.

Characterization of prion protein (PrP)-derived peptides that discriminate full-length PrPSc from PrPC

On our initial discovery that prion protein (PrP)-derived peptides were capable of capturing the pathogenic prion protein (PrP(Sc)), we have been interested in how these peptides interact with PrP(Sc). After screening peptides from the entire human PrP sequence, we found two peptides (PrP(19-30) and PrP(100-111)) capable of binding full-length PrP(Sc) in plasma, a medium containing a complex mixture of other proteins including a vast excess of the normal prion protein (PrP(C)). The limit of detection for captured PrP(Sc) was calculated to be 8 amol from a approximately 10(5)-fold dilution of 10% (wt/vol) human variant Creutzfeldt-Jakob disease brain homogenate, with >3,800-fold binding specificity to PrP(Sc) over PrP(C). Through extensive analyses, we show that positively charged amino acids play an important, but not exclusive, role in the interaction between the peptides and PrP(Sc). Neither hydrophobic nor polar interactions appear to correlate with binding activity. The peptide-PrP(Sc) interaction was not sequence-specific, but amino acid composition affected binding. Binding occurs through a conformational domain that is only present in PrP(Sc), is species-independent, and is not affected by proteinase K digestion. These and other findings suggest a mechanism by which cationic domains of PrP(C) may play a role in the recruitment of PrP(C) to PrP(Sc).

Reference materials for the evaluation of pre-mortem variant Creutzfeldt-Jakob disease diagnostic assays

BACKGROUND AND OBJECTIVES

A standard panel of materials is needed for the evaluation of assays being developed for the diagnosis of variant Creutzfeldt-Jakob disease.

MATERIALS AND METHODS

Tissues from human and animals incubating transmissible spongiform encephalopathy disease have been prepared, aliquoted and where possible characterized by in vitro methods.

RESULTS

A standardized preparation of materials has been generated.

CONCLUSIONS

Large-scale preparations of tissues and blood fractions can be used to directly compare the sensitivities of assays using different formats.

Direct detection of disease associated prions in brain and lymphoid tissue using antibodies recognizing the extreme N terminus of PrPC

A simple diagnostic test is described for the detection of TSE in bovine, ovine and human brain and lymphoid tissue that obviates the use of proteinase K as a discriminating reagent. The immunoassay utilises high affinity anti-peptide antibodies that appear blind to the normal isoform of prion protein (PrP(C)). These reagents have been produced with novel N-terminal chimeric peptides and we hypothesise that the retention and stability of the extreme N-terminus of PrP in the disease-associated aggregate makes it an operationally specific marker for TSE. Accordingly, the assay involves homogenisation of the tissue directly in 8M guanidine hydrochloride, a simple one-step capture of PrP(Sc) followed by detection with a europium-labelled anti-PrP(C) antibody. This rapid assay clearly differentiates between levels of disease-associated PrP extracted from brain and lymphoid tissues taken from confirmed TSE positive and negative cattle and sheep. The assay can also be used to detect PrP(Sc) in cases of vCJD.

Blood safety: Opportunities and challenges addressed through Critical Path research at FDA

New scientific discoveries and technologies create opportunities for medical and public health advancement through development of innovative products. However, novel products and technologies bring new challenges to regulation. FDA recently established a 'Critical Path' research initiative to modernize regulatory science concepts and tools to meet the challenges of the 21st century. Central to this initiative is the concept that regulatory science is distinct from the 'discovery' science that generates ideas for development of new drugs, biologics, or medical devices. In this article, the authors discuss the concepts of FDA 'Critical Path' research and review examples of such research performed in the Office of Blood Research and Review within the Center for Biologics Research and Evaluation at FDA to illustrate how the 'Critical Path' research is being used to address opportunities and challenges impacting blood and blood products.:

Application of an immunocapillary electrophoresis assay to the detection of abnormal prion protein in brain, spleen and blood specimens from patients with variant Creutzfeldt–Jakob disease

Sensitive and specific detection of abnormal prion protein in blood could provide a diagnostic test or screening assay for animal and human prion diseases. Here, the application of an immunocapillary electrophoresis (ICE) method developed for sheep scrapie to brain, spleen and blood from patients with Creutzfeldt–Jakob disease (CJD) is described. The assay involves organic-solvent extraction, a competitive immunoassay using fluorescently labelled synthetic prion protein peptides and polyclonal antibodies specific for those sequences, and analysis by capillary electrophoresis using laser-induced fluorescence detection. The test was evaluated by using clinical blood specimens from patients with variant (n=5) or sporadic (n=4) CJD and patients initially suspected of having CJD who were given an alternative diagnosis (n=6). In this context, the ICE assay was specific, but incompletely sensitive (55 %). The method was unable to detect abnormal prion protein in variant CJD brain or spleen reference materials due to its loss during the extraction process.

Protease-resistant prion protein in lymphoreticular tumors of variant Creutzfeldt-Jakob disease mice

We report protease-resistant prion protein (PrPres) in spontaneous lymphoreticular tumors of mice infected with the agent of variant Creutzfeldt-Jakob disease (vCJD). PrPres may accumulate in lymphoreticular system tumors of asymptomatic persons with vCJD. The statistical power of estimates of vCJD prevalence might be increased by expanding screening to include samples of lymphoreticular neoplasms.

Detection of type 1 prion protein in variant Creutzfeldt-Jakob disease

Molecular typing of the abnormal form of the prion protein (PrP(Sc)) has come to be regarded as a powerful tool in the investigation of the prion diseases. All evidence thus far presented indicates a single PrP(Sc) molecular type in variant Creutzfeldt-Jakob disease (termed type 2B), presumably resulting from infection with a single strain of the agent (bovine spongiform encephalopathy). Here we show for the first time that the PrP(Sc) that accumulates in the brain in variant Creutzfeldt-Jakob disease also contains a minority type 1 component. This minority type 1 PrP(Sc) was found in all 21 cases of variant Creutzfeldt-Jakob disease tested, irrespective of brain region examined, and was also present in the variant Creutzfeldt-Jakob disease tonsil. The quantitative balance between PrP(Sc) types was maintained when variant Creutzfeldt-Jakob disease was transmitted to wild-type mice and was also found in bovine spongiform encephalopathy cattle brain, indicating that the agent rather than the host specifies their relative representation. These results indicate that PrP(Sc) molecular typing is based on quantitative rather than qualitative phenomena and point to a complex relationship between prion protein biochemistry, disease phenotype and agent strain.

An immunoassay for the pathological form of the prion protein based on denaturation and time resolved fluorometry

Concern about the possible secondary spread of variant Creutzfeldt-Jakob disease (vCJD) through blood transfusion and blood products has increased the need for a sensitive and rapid test for the identification of PrP(Sc) in specimens collected non-invasively from living persons. Furthermore, an accurate estimate of the prevalence of pre-clinical vCJD in the British population would be possible if there were such a test that could be applied to specimens available readily (e.g. blood and urine). As a first step towards that goal, we have developed a simple and sensitive test for the detection of PrP(Sc) in peripheral tissues and brain of vCJD patients, based on the differential extraction of PrP(Sc) with guanidine hydrochloride. The prion protein (PrP) isoforms are extracted sequentially from homogenized tissue by applying two different concentrations of this chaotropic agent. Each extraction yields a fraction of the PrP isoforms with different solubilities in guanidine hydrochloride. Quantitation of the two fractions (relatively insoluble or relatively soluble) using time resolved fluorescence (DELFIA) as a reporter system allows differentiation between PrP(Sc) infected and non-infected tissues. The assay has a detection limit of 10 pg PrP, is robust and could be automated.

Computerized morphometric analysis of pathological prion protein deposition in scrapie-infected hamster brain

Transmissible spongiform encephalopathies (TSEs or prion diseases) are characterized by a constellation of typical though variable pathological changes in the brain. Deposition of disease-associated abnormal prion protein (PrP(Sc)) is the pathological feature of TSEs most consistent and accessible for quantification. However, the evaluation of PrP(Sc) deposits detected by immunohistochemical techniques has been traditionally based on arbitrarily assigned semiquantitative scores. This approach is limited by its subjectivity and bias, yielding considerable variability. In this study, we used MetaMorph 6.1 image analysis software for quantitative analysis of immunostained PrP(Sc) deposits in the CNS of hamsters infected with the 263K strain of scrapie agent. Computerized morphometric analysis (CMA) allowed unambiguous detection of even minimal amounts of immunostained PrP(Sc). CMA values for intensity of staining and area stained correlated well with semiquantitative scores, providing reproducible quantitative data and objective criteria for analyzing PrP(Sc) deposition. CMA provides a simple and reliable method for improved and consistent diagnosis of TSEs that may also be used to quantify other immunostained biomarkers.

Diagnosis of human prion disease

With the discovery of the prion protein (PrP), immunodiagnostic procedures were applied to diagnose Creutzfeldt-Jakob disease (CJD). Before development of the conformation-dependent immunoassay (CDI), all immunoassays for the disease-causing PrP isoform (PrPSc) used limited proteolysis to digest the precursor cellular PrP (PrPC). Because the CDI is the only immunoassay that measures both the protease-resistant and protease-sensitive forms of PrPSc, we used the CDI to diagnose human prion disease. The CDI gave a positive signal for PrPSc in all 10-24 brain regions (100%) examined from 28 CJD patients. A subset of 18 brain regions from 8 patients with sporadic CJD (sCJD) was examined by histology, immunohistochemistry (IHC), and the CDI. Three of the 18 regions (17%) were consistently positive by histology and 4 of 18 (22%) by IHC for the 8 sCJD patients. In contrast, the CDI was positive in all 18 regions (100%) for all 8 sCJD patients. In both gray and white matter, approximately 90% of the total PrPSc was protease-sensitive and, thus, would have been degraded by procedures using proteases to eliminate PrPC. Our findings argue that the CDI should be used to establish or rule out the diagnosis of prion disease when a small number of samples is available as is the case with brain biopsy. Moreover, IHC should not be used as the standard against which all other immunodiagnostic techniques are compared because an immunoassay, such as the CDI, is substantially more sensitive.