Proposed algorithm for approval of human TSE tests in Europe.

Current Regulatory Position in Europe Variant CJD assays will need to be CE marked but are not currently on Annex 2A of the In Vitro Diagnostic Medical Devices Directive (98/79/EC). UK Committee on the Microbiological Safety of Blood, Tissues and Organs (MSBTO) has made a request that they be added through the Medicines and Healthcare products Regulatory Agency to the European Commission. Likely to years. Likely public pressure to implement any first generation assays in the meantime.

UK + Irish Blood Services Prion Assay Working Group To act as the primary point of contact within UK and Irish Blood Services for manufacturers developing prion assays. To provide expertise and advice to manufacturers on the laboratory and clinical development requirements for prion assays. To liase with UK operational services on all matters regarding approval of prion assays for use. To ensure that appropriate decision-making bodies are kept appraised of the technology. To prepare a technical specification and route to evaluation.

Difficulties with PrP TSE detection Assume infectivity in human blood is 1-10 ID/ml during the incubation period Studies of infected hamster brain suggests a ratio of about 10 5 molecules of PrP TSE / infectious unit. If the correlation is correct, the level of infectivity in blood corresponds to about 10 6 molecules / ml.

Caveats around PrP TSE detection Recent studies indicate that the infectivity associated with the proteinase-resistant form of PrP is principally found in polymeric aggregates of particle size range of kDa, or about molecules of PrP TSE. 1 ml of blood containing 10 infectious doses could contain as little as molecules of PrP TSE Not yet known if abnormal but proteinase-sensitive forms of PrP are infectious. If so, calculation of the number of molecules of PrP TSE in a unit of infectivity may seriously underestimate the actual number of molecules correlated with a single infectious unit.

Impact of Sensitivity and Specificity negative predictive value: % positive predictive value: 0.98%

Impact on donors and the blood supply Management of positives –to tell or not to tell…. –to bleed or not to bleed... How to separate the true and false positives (direct impact) Implications of true positivity - will the donor develop clinical variant CJD or not? Psychological and social impact on donor Indirect impact on donor recruitment and retention

Impact of pre-symptomatic testing for Huntingdon’s Chorea Formalised protocol of pre-screen counselling where those at risk have the opportunity to explore what a positive result may mean for them and their family. Majority of people choose not to be tested. Of those who test positive, 2% experience a ‘catastrophic event’ (suicide, attempted suicide, psychiatric hospitalisation) Literature also reports significant levels of personal stress and family / social breakdown. These figures are considered to be comparatively low.

Proposed evaluation algorithm

TSE-infected animal blood samples Systematic library of samples for samples of: –whole blood, red cells, buffy coat, plasma –separated according to standard protocols –well characterised from a variety of TSE infected and control animals such as: –scrapie-infected, BSE-infected and normal control mice and hamsters –scrapie-infected, BSE-infected and normal control sheep –BSE-infected and normal control cattle –CWD-infected and normal control deer / elk –TSE-infected primates

Proposed evaluation algorithm

Human blood samples Peripheral blood samples from patients with CJD Peripheral blood samples from patients ‘presumed infected’ with CJD Peripheral blood samples from patients ‘potentially a risk of CJD for public health purposes’.

Proposed evaluation algorithm

Test Assessment Facility 5,000 UK and 5,000 US whole blood donations aliquots of red cells, buffy coat and plasma aimed to be a comparative specificity panel not sized to give accurate epidemiological data