Population Screening for Variant Creutzfeldt-Jakob Disease Using a Novel Blood Test

Abstract

IMPORTANCE Our study indicates a prototype blood-based variant Creutzfeldt-Jakob disease (vCJD) assay has sufficient sensitivity and specificity to justify a large study comparing vCJD prevalence in the United Kingdom with a bovine spongiform encephalopathy–unexposed population. In a clinical diagnostic capacity, the assay’s likelihood ratios dramatically change an individual’s pretest disease odds to posttest probabilities and can confirm vCJD infection. OBJECTIVES To determine the diagnostic accuracy of a prototype blood test for vCJD and hence its suitability for clinical use and for screening prion-exposed populations. DESIGN, SETTING, AND PARTICIPANTS Retrospective, cross-sectional diagnostic study of blood samples from national blood collection and prion disease centers in the United States and United Kingdom. Anonymized samples were representative of the US blood donor population (n = 5000), healthy UK donors (n = 200), patients with nonprion neurodegenerative diseases (n = 352), patients in whom a prion disease diagnosis was likely (n = 105), and patients with confirmed vCJD (n = 10). MAIN OUTCOME AND MEASURE Presence of vCJD infection determined by a prototype test (now in clinical diagnostic use) that captures, enriches, and detects disease-associated prion protein from whole blood using stainless steel powder. RESULTS The assay’s specificity among the presumed negative American donor samples was 100% (95% CI, 99.93%-100%) and was confirmed in a healthy UK cohort (100% specificity; 95% CI, 98.2%-100%). Of potentially cross-reactive blood samples from patients with nonprion neurodegenerative diseases, no samples tested positive (100% specificity; 95% CI, 98.9%-100%). Among National Prion Clinic referrals in whom a prion disease diagnosis was likely, 2 patients with sporadic CJD tested positive (98.1% specificity; 95% CI, 93.3%-99.8%). Finally, we reconfirmed but could not refine our previous sensitivity estimate in a small blind panel of samples from unaffected individuals and patients with vCJD (70% sensitivity; 95% CI, 34.8%-93.3%). CONCLUSIONS AND RELEVANCE In conjunction with the assay’s established high sensitivity (71.4%; 95% CI, 47.8%-88.7%), the extremely high specificity supports using the assay to screen for vCJD infection in prion-exposed populations. Additionally, the lack of cross-reactivity and false positives in a range of nonprion neurodegenerative diseases supports the use of the assay in patient diagnosis.

Factors intrinsic and extrinsic to blood hamper the development of a routine blood test for human prion diseases

“…This assay was shown to be more efficient than IP with antibodies, and allowed the detection of PrP TSE in human whole blood spiked with high dilutions (up to 10 210 ) of vCJD-infected brain homogenate, and in the whole blood of 15 of 21 symptomatic patients with vCJD H. Abdel-Haq with 71.4 % sensitivity and 100 % specificity. This assay was recently validated by the same research group, using a larger number of samples, including healthy and potentially crossreactive patient populations (Jackson et al, 2014). This validation study not only confirmed the previously determined specificity and sensitivity of the assay for vCJD infection in blood, but also identified 2 of 105 patients who were positive for sCJD, indicating that this assay was also sensitive for significantly lower levels of prion infectivity, such as those associated with sCJD (Jackson et al, 2014).…”

“…This assay was recently validated by the same research group, using a larger number of samples, including healthy and potentially crossreactive patient populations (Jackson et al, 2014). This validation study not only confirmed the previously determined specificity and sensitivity of the assay for vCJD infection in blood, but also identified 2 of 105 patients who were positive for sCJD, indicating that this assay was also sensitive for significantly lower levels of prion infectivity, such as those associated with sCJD (Jackson et al, 2014). However, this assay is still limited by its insufficient sensitivity for the detection of asymptomatic individuals with vCJD who are subclinical carriers, or at the preclinical stage of the disease.…”

“…However, based on the fact that PrP TSE from vCJD-infected brain homogenate spiked into whole blood can be detected with good sensitivity at dilution of 10 210 , hypothetically, it should be possible to detect prions in the blood of vCJD patients at the preclinical stage of the disease (Edgeworth et al, 2011). Moreover, given that other blood tests based on different principles showed similar behaviour, but that not all blood samples obtained from clinically affected subjects tested positive for PrP TSE (Terry et al, 2009;Bannach et al, 2012;Jackson et al, 2014;Lacroux et al, 2014), the sensitivity of the tests is unlikely to be the only factor responsible for the failed detection of PrP TSE . Rather, it may be related to the variable presence of factors intrinsic and extrinsic to blood that differentially affect the concentration and/or detection of PrP TSE in blood as compared to other tissues.…”

First Demonstration of Transmissible Spongiform Encephalopathy-associated Prion Protein (PrPTSE) in Extracellular Vesicles from Plasma of Mice Infected with Mouse-adapted Variant Creutzfeldt-Jakob Disease by in Vitro Amplification

“…Recently, infectivity was reported in the plasma of two out of four patients affected by sporadic CJD (sCJD) (11). Although similar levels of PrP TSE have been detected in spleens, tonsils, and lymph nodes of vCJD and sCJD patients by Western blotting (12), the identification of this protein in the blood of individuals afflicted with the latter by various methods, including PrP TSE capture coupled to direct immunodetection of surface-bound material (6), capillary electrophoresis (13), and protein misfolding cyclic amplification (PMCA) coupled to surrounding optical fiber immunoassay (12), has been highly elusive for decades, with only two cases recently reported (8). Nevertheless, extensive epidemiological data continue to provide no evidence of human-to-human transmission of sCJD through blood transfusion (14).…”

Bioassay of prion-infected blood plasma in PrP transgenic Drosophila

“…However, the occurrence of vCJD cases caused by administration of prion-infected human blood has highlighted the realistic opportunity for the development of a blood-based diagnostic test for this condition. Recent developments have shown promise with the detection of vCJD-positive blood samples from clinical vCJD cases by immuno-biochemical selection of disease-associated PrP, without the use of PK [42,43], and by detection of PK-resistant PrPSc following PMCA [44]. Since transmissibility is a defining hallmark of prion diseases, it will be important to develop a reasonably rapid and versatile confirmatory prion infectivity bioassay to supplement these biochemical-based prion diagnostic assays.…”