Development of a blood screning assay for diagnosis of prion diseases in humans
For many decades, Creutzfeldt-Jakob disease (CJD) was thought to be transmissible among humans only via contact with infectious nervous system tissue. However, recently it was shown that variant Creutzfeldt-Jakob disease (vCJD) is transmissible by blood donation. The transmission of the disease occurred in the incubation period of the donors, which demonstrates that this route is highly efficient. Precautionary measures such as leucodepletion and donor deferral increase the costs of blood and blood products, reduce the donor population, and might lead to shortage of available blood products.
Undetected subclinically infected blood donors bear a great risk for secondary vCJD transmission, persistence and or even spread of vCJD epidemic within the human population. This demonstrates the urgent need for a screening method, which is applicable and repeatable in easily accessible tissues and fluids such as blood.
There is a need to identify new biochemical markers, since conventional tests require brain autopsy or biopsy and surrogate markers are often positive in advanced disease stages only. A test in blood would be more favourable for diagnostic purposes and as a screening assay in blood donors. It needs to reflect disease pathology in the early stages and therefore be able to indicate a prion infection. The tests may be based on PrPSc detection or on surrogate markers reflecting the reaction of the organism to the disease process.
The development of such assays requires the study of cell culture systems and animal experiments under controlled conditions. They have to be verified on human biological samples, which are collected at early disease stages. The goal is the development of a test using multimodal approaches such as detection of disease-specific early markers or abnormal protein aggregation. This work will be directed towards the identification of specific interacting partners on a protein, mRNA and DNA level.
The amplification of the abnormal prion protein by PMCA (Protein Misfolding Cyclic Amplification) is one of the most challenging methods. Particularly with regard to the prevention of artefacts, this method demands much effort to achieve accuracy in discriminating between the normal and abnormal prion protein. Furthermore, the identification of putative prion protein interaction partners may include a risk potential. The instability of some proteins and the occurrence of high abundant proteins, which can mask other proteins, are possible sources for the production of unspecific artefacts. Due to the sensitivity to protein degradation of human fluids, the storage and handling of the samples must be consistent.
The aim is the development of easy applicable tests for prion diseases in humans and potentially in animals. A suitable blood test can be used for diagnostic purposes, whereas a screening assay will be a relevant tool for the analysis of blood samples.
The table on the left gives an overview on the Work Packages in this study.
Results of the project on diagnostic markers can be used by public health services and blood banks for blood donor testing. They may be also used by the medical community for individual diagnosis in suspected cases of human spongiform encephalopathies. In addition, the results can be used in potential studies on the treatment of human CJD and can be used in the protocols for monitoring of disease activity or progress.