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

Kinetics of Abnormal Prion Protein in Blood of Transgenic Mice Experimentally Infected by Multiple Routes with the Agent of Variant Creutzfeldt-Jakob Disease

Transmissible spongiform encephalopathies (TSEs) or prion diseases are characterized by the accumulation in affected tissues of the abnormal prion protein PrP^TSE. We previously demonstrated PrP^TSE in the blood of macaques experimentally infected with variant Creutzfeldt-Jakob disease (vCJD), a human TSE, months to years prior to clinical onset. That work supported the prospect of using PrP^TSE as a blood biomarker to detect vCJD and possibly other human TSEs before the onset of overt illness. However, our results also raised questions about the origin of PrP^TSE detected in blood early after inoculation and the effects of dose and route on the timing of the appearance of PrP^TSE. To investigate these questions, we inoculated vCJD-susceptible transgenic mice and non-infectable prion protein-knockout mice under inoculation conditions resembling those used in macaques, with additional controls. We assayed PrP^TSE in mouse blood using the protein misfolding cyclic amplification (PMCA) method. PrP^TSE from the inoculum cleared from the blood of all mice before 2 months post-inoculation (mpi). Mouse PrP^TSE generated de novo appeared in blood after 2 mpi. These results were consistent regardless of dose or inoculation route. We also demonstrated that a commercial ELISA-like PrP^TSE test detected and quantified PMCA products and provided a useful alternative to Western blots.

Abnormal prion protein, infectivity and neurofilament light-chain in blood of macaques with experimental variant Creutzfeldt-Jakob disease

Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative infections. Variant Creutzfeldt-Jakob disease (vCJD) and sporadic CJD (sCJD) are human TSEs that, in rare cases, have been transmitted by human-derived therapeutic products. There is a need for a blood test to detect infected donors, identify infected individuals in families with TSEs and monitor progression of disease in patients, especially during clinical trials. We prepared panels of blood from cynomolgus and rhesus macaques experimentally infected with vCJD, as a surrogate for human blood, to support assay development. We detected abnormal prion protein (PrP^TSE) in those blood samples using the protein misfolding cyclic amplification (PMCA) assay. PrP^TSE first appeared in the blood of pre-symptomatic cynomolgus macaques as early as 2 months post-inoculation (mpi). In contrast, PMCA detected PrP^TSE much later in the blood of two pre-symptomatic rhesus macaques, starting at 19 and 20 mpi, and in one rhesus macaque only when symptomatic, at 38 mpi. Once blood of either species of macaque became PMCA-positive, PrP^TSE persisted through terminal illness at relatively constant concentrations. Infectivity in buffy coat samples from terminally ill cynomolgus macaques as well as a sample collected 9 months before clinical onset of disease in one of the macaques was assayed in vCJD-susceptible transgenic mice. The infectivity titres varied from 2.7 to 4.3 infectious doses ml^-1. We also screened macaque blood using a four-member panel of biomarkers for neurodegenerative diseases to identify potential non-PrP^TSE pre-symptomatic diagnostic markers. Neurofilament light-chain protein (NfL) increased in blood before the onset of clinical vCJD. Cumulatively, these data confirmed that, while PrP^TSE is the first marker to appear in blood of vCJD-infected cynomolgus and rhesus macaques, NfL might offer a useful, though less specific, marker for forthcoming neurodegeneration. These studies support the use of macaque blood panels to investigate PrP^TSE and other biomarkers to predict onset of CJD in humans.

Non-human primates in prion diseases

The fascinating history of prion diseases is intimately linked to the use of nonhuman primates as experimental models, which brought so fundamental and founding information about transmissibility, pathogenesis, and resistance of prions. These models are still of crucial need for risk assessment of human health and may contribute to pave a new way towards the moving field of prion-like entities which now includes the main human neurodegenerative diseases (especially Alzheimer's and Parkinson's diseases).

Body-first Parkinson's disease and variant Creutzfeldt-Jakob disease - similar or different?

In several neurodegenerative disorders, proteins that typically exhibit an α-helical structure misfold into an amyloid conformation rich in β-sheet content. Through a self-templating mechanism, these amyloids are able to induce additional protein misfolding, facilitating their propagation throughout the central nervous system. This disease mechanism was originally identified for the prion protein (PrP), which misfolds into PrP^Sc in a number of disorders, including variant Creutzfeldt-Jakob disease (vCJD) and bovine spongiform encephalopathy (BSE). More recently, the prion mechanism of disease was expanded to include other proteins that rely on this self-templating mechanism to cause progressive degeneration, including α-synuclein misfolding in Parkinson's disease (PD). Several studies now suggest that PD patients can be subcategorized based on where in the body misfolded α-synuclein originates, either the brain or the gut, similar to patients developing sporadic CJD or vCJD. In this review, we discuss the human and animal model data indicating that α-synuclein and PrP^Sc misfolding originates in the gut in body-first PD and vCJD, and summarize the data identifying the role of the autonomic nervous system in the gut-brain axis of both diseases.

Preclinical Detection of Prions in Blood of Nonhuman Primates Infected with Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) is caused by prion infection with bovine spongiform encephalopathy and can be transmitted by blood transfusion. Protein misfolding cyclic amplification (PMCA) can detect prions in blood from vCJD patients with 100% sensitivity and specificity. To determine whether PMCA enables prion detection in blood during the preclinical stage of infection, we performed a blind study using blood samples longitudinally collected from 28 control macaques and 3 macaques peripherally infected with vCJD. Our results demonstrate that PMCA consistently detected prions in blood during the entire preclinical stage in all infected macaques, without false positives from noninfected animals, when using the optimized conditions for amplification of macaque prions. Strikingly, prions were detected as early as 2 months postinoculation (>750 days before disease onset). These findings suggest that PMCA has the potential to detect vCJD prions in blood from asymptomatic carriers during the preclinical phase of the disease.

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.

Unexpected prion phenotypes in experimentally transfused animals: predictive models for humans?

The recently reevaluated high prevalence of healthy carriers (1/2,000 in UK) of variant Creutzfeldt-Jakob Disease (v-CJD), whose blood might be infectious, suggests that the evolution of this prion disease might not be under full control as expected. After experimental transfusion of macaques and conventional mice with blood derived from v-CJD exposed (human and animal) individuals, we confirmed in these both models the transmissibility of v-CJD, but we also observed unexpected neurological syndromes transmissible by transfusion: despite their prion etiology confirmed through transmission experiments, these original cases would escape classical prion diagnosis, notably in the absence of detectable abnormal PrP with current techniques. It is noteworthy that macaques developed an original, yet undescribed myelopathic syndrome associating demyelination and pseudo-necrotic lesions of spinal cord, brainstem and optical tract without affecting encephalon, which is rather evocative of spinal cord disease than prion disease in human medicine. These observations strongly suggest that the spectrum of human prion diseases may extend the current field restricted to the phenotypes associated to protease-resistant PrP, and may notably include spinal cord diseases.

Lack of Transmission of Chronic Wasting Disease to Cynomolgus Macaques

Chronic wasting disease (CWD) is a fatal prion disease that can infect deer, elk, and moose. CWD was first recognized in captive deer kept in wildlife facilities in Colorado from 1967 to 1979. CWD has now been detected in 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland. It is currently unknown if humans are susceptible to CWD infection. Understanding the health risk from consuming meat and/or products from CWD-infected cervids is a critical human health concern. Previous research using transgenic mouse models and in vitro conversion assays suggests that a significant species barrier exists between CWD and humans. To date, reported epidemiologic studies of humans consuming cervids in areas where CWD is endemic have found no evidence to confirm CWD transmission to humans. Previously, we reported data from ongoing cross-species CWD transmission studies using two species of nonhuman primates as models. Squirrel monkeys (SM) and cynomolgus macaques (CM) were inoculated by either the intracerebral or oral route with brain homogenates from CWD-infected deer and elk containing high levels of infectivity. SM were highly susceptible to CWD infection, while CM were not. In the present study, we present new data for seven CWD-inoculated CM euthanized 11 to 13 years after CWD inoculation and eight additional uninoculated control CM. New and archival CM tissues were screened for prion infection by using the ultrasensitive real-time quaking-induced conversion (RT-QuIC) assay, immunohistochemistry, and immunoblotting. In this study, there was no clinical, pathological, or biochemical evidence suggesting that CWD was transmitted from cervids to CM.IMPORTANCE Chronic wasting disease (CWD) is a fatal prion disease found in deer, elk, and moose. Since it was first discovered in the late 1960s, CWD has now spread to at least 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland. Eradication of CWD from areas of endemicity is very unlikely, and additional spread will occur. As the range and prevalence of CWD increase, so will the potential for human exposure to CWD prions. It is currently unknown if CWD poses a risk to human health. However, determining this risk is critical to preventing a scenario similar to that which occurred when mad cow disease was found to be transmissible to humans. In the present study, we used cynomolgus macaque monkeys as a surrogate model for CWD transmission to humans. After 13 years, no evidence for CWD transmission to macaques was detected clinically or by using highly sensitive prion disease-screening assays.

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.

Advancing Public Health Using Regulatory Science to Enhance Development and Regulation of Medical Products: Food and Drug Administration Research at the Center for Biologics Evaluation and Research

Center for Biologics Evaluation and Research enhances and supports regulatory decision-making and policy development. This work contributes to our regulatory mission, advances medical product development, and supports Food and Drug Administration’s regulatory response to public health crises. This review presents some examples of our diverse scientific work undertaken in recent years to support our regulatory and public health mission.

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.

Ten-year follow-up of two cohorts with an increased risk of variant CJD: donors to individuals who later developed variant CJD and other recipients of these at-risk donors

BACKGROUND

Transmission of variant Creutzfeldt-Jakob disease (vCJD) through blood transfusion is implicated in three deaths and one asymptomatic infection. Based on this evidence, individuals assessed to be at increased risk of vCJD through donating blood transfused to individuals who later developed vCJD, or through being other recipients of such donors, are followed up to further understand the risks of vCJD transmission through blood.

OBJECTIVES

To provide a ten-year follow-up of these at-risk cohorts.

METHODS

Blood donors to patients who later died from vCJD were identified by the Transfusion Medicine Epidemiological Review (TMER) study. A reverse risk probability assessment quantified the risk of blood transfusion or exposure through diet as the source of vCJD in the recipients. Donors to these recipients, and these donors' other recipients, with a probability risk above 1%, are classified as at increased risk of vCJD for public health purposes. These cohorts are monitored for any vCJD occurrences.

RESULTS

A total of 112 donors and 33 other recipients of their donated blood have been classified as at increased risk. After 2397 and 492 vCJD-free years of follow-up, respectively, no deaths in either at-risk cohort were of vCJD-related causes.

CONCLUSIONS

The at-risk cohorts have survived disease-free far longer than the estimated incubation time for dietary-acquired vCJD (donors) and transfusion-acquired disease (other recipients). However, due to our still limited understanding of, and a lack of a reliable test for, asymptomatic vCJD infection, public health follow-up is necessary for continued monitoring of at-risk cohorts.

Distinctive properties of plaque-type dura mater graft-associated Creutzfeldt-Jakob disease in cell-protein misfolding cyclic amplification

There are two distinct subtypes of dura mater graft-associated Creutzfeldt-Jakob disease (dCJD) with methionine homozygosity at codon 129 of the PRNP gene. The majority of cases is represented by a non-plaque-type (np-dCJD) resembling sporadic CJD (sCJD)-MM1 or -MV1, while the minority by a plaque-type (p-dCJD). p-dCJD shows distinctive phenotypic features, namely numerous kuru plaques and an abnormal isoform of prion protein (PrP(Sc)) intermediate in size between types 1 and 2. Transmission studies have shown that the unusual phenotypic features of p-dCJD are linked to the V2 prion strain that is associated with sCJD subtypes VV2 or -MV2. In this study, we applied protein misfolding cyclic amplification (PMCA) using recombinant human prion protein as a substrate and demonstrated that p-dCJD prions show amplification features that are distinct from those of np-dCJD. Although no amplification of np-dCJD prions was observed with either 129 M or 129 V substrate, p-dCJD prions were drastically amplified with the 129 V substrates, despite the PRNP codon 129 incompatibility between seed and substrate. Moreover, by using a type 2 PrP(Sc)-specific antibody not recognizing PrP(Sc) in p-dCJD, we found that type 2 products are generated de novo from p-dCJD prions during PMCA with the 129 V substrates. These findings suggest that our cell-PMCA is a useful tool for easily and rapidly identifying acquired CJD associated with the transmission of the V2 CJD strain to codon 129 methionine homozygotes, based on the preference for the 129 V substrate and the type of the amplified products.