Transmissible Spongiform Encephalopathies are a family of progressive, invariably fatal neurological disorders. Unlike more conventional infectious diseases, TSEs appear to be caused by a new family of infectious agents, a misfolded self protein (PrPd) capable of altering the conformation of the normal self protein (PrPc) and thereby inducing self- replication. Most importantly, these agents do not appear to contain specific nucleic acid, and therefore all diagnostic techniques rely upon identification of the conformationally unique form. As a result, all successful post-mortem diagnostics to date rely upon the use of monoclonal antibodies. Although blood is clearly infectious and capable of transmitting disease, identification of PrPd within the blood of affected humans and experimental animals has been difficult. As a result, there is currently no approved antemortem diagnostic assay for TSE infection of either animals or humans. We propose to capitalize on the exquisite specificity of antibody-based diagnostics and the sensitivity of the Polymerase Chain Reaction to validate a PrPd-specific Immuno-PCR assay for TSEs. To accomplish this goal, we will (a) define the sensitivity of the Immuno-PCR assay for PrPd obtained from brain and lymphoid tissues of affected sheep;(b) Define the presence of PrPd within the blood of clinical end-stage scrapie-affected sheep and (c) Map the appearance of PrPd within the blood of experimentally infected animals throughout the course of infection. This work is novel, in that it capitalizes on the strengths of both nucleic-acid and protein-based assays. RTI has a track record in translational research on TSEs, and has established a partnership with PrionCyte to accomplish these goals. Following successful Phase I studies, we anticipate confirming these results in additional species through Phase II studies.
The United States collects approximately 15 million units of whole blood each year from an estimated 8 million volunteers (American Red Cross, www.pleasegiveblood.org/education/faq.php). Given the long asymptomatic and diagnostically-invisible incubation period of TSEs, FDA regulations now ban blood donations by individuals at risk for incubating variant CJD (vCJD), resulting in an estimated drop in already limited blood donations of approximately 500,000 units (www.americasblood.org). Identification of additional native cases of BSE, or the appearance of native cases of vCJD could result in further threats to the US blood supply. There is therefore an immediate and significant need for a highly sensitive, blood-based test for infectivity in transmissible spongiform encephalopathies.
