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CHIRON Submission To FDA TSE Advisory Committee Meeting

CHIRON Submission To FDA TSE Advisory Committee Meeting. 19 September 2006 Gaithersburg, MD David Peretz M.Sc., D.Sc. Senior Scientist. Presentation Outline. Review vCJD assay development progress Review assay performance data Review proposed validation process.

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CHIRON Submission To FDA TSE Advisory Committee Meeting

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  1. CHIRON Submission To FDA TSE Advisory Committee Meeting 19 September 2006 Gaithersburg, MD David Peretz M.Sc., D.Sc. Senior Scientist

  2. Presentation Outline • Review vCJD assay development progress • Review assay performance data • Review proposed validation process

  3. Challenges in Assay Development • Issues and Implications… • Biology Unknown levels and prevalence of prions in vCJD donations • Disease models Questionable relevance of rodent models • Sample Availability < 30 human vCJD samples available, and small volumes • Confirmation Test None available in vitro • Sensitivity goal Nucleic acid test model not applicable • Incidence Declining incidence raises question about continued testing • Realism Atypical infectious disease test

  4. Development Assumptions and Rationale Analyte Specificity • Assay was developed to detect human PrPSc presuming this to be both the cause and biochemical marker of the disease (Prusiner et al. Science 1982, Bueler et al. Cell 1993, Legname et al. Science 2004) Assay Sensitivity • Sensitivity requirements based on rodent studies, human transmission to primates and transgenic mice, using the following criteria: (Bolton et al. Arch. Biochem. Biophes. 1987, Taguchi et al. Am. J. Patho. 2003, Brown et al. J. Lab. Clin. Med. 2001) • 1LD50 = 0.1pg = 4.3 attomole Syrian hamster PrPSc • 1LD50 = 0.1-10 nl 10% CJD brain homogenate Initial Analytical Studies • Spiking experiments with animal and human tissues into plasma • Detection limit of endogenously animal infected blood Clinical Validation Studies • Establish clinical sensitivity and specificity • Confirm with an assay which is as sensitive

  5. Assay Format Capture PrPSc in plasma Dissociation and Condition Transfer Supernatant ELISA - Detection ELISA - Capture Level of Selection > 1000 fold

  6. CHIRON Analytical Sensitivity for Capture and Detection of vCJD Human PrPSc Spiked in plasma rPrP ELISA alone Complete Assay 1pg PrP=43amol Performance Exceeds Benchmarks and Approaches the Limit of Detection Required for Blood Screening

  7. Initial Specificity of Prion Assay on Normal Human Plasma Samples

  8. Proposed Pre-Clinical Confirmation Process • PSR-1 Selects PrPSc and Infectivity • Pull-down material is PK resistant, demonstrated • Pull-down material is infectious, ongoing study • Proof of Principle • Detection of PrPSc in sheep plasma, ongoing study • 100 disease samples • 100 Australian negatives • Biology of PrPSc in Blood • Time course in Syrian hamster , ongoing study • 300 animals

  9. Proposed Clinical Validation Process • Clinical Specificity • Donor samples • 5000 UK (high prevalence) • 5000 US (low prevalence) • Hospitalized patients • 100 non-neurodegenerative (non-ND) patients • 100 ND patients • Interfering substances • Bilirubin, Rheumatoid factor, Human anti-mouse antibodies, etc • Clinical Sensitivity • All available vCJD plasma samples • >40 Symptomatic sCJD plasma samples • Validation • Commercial validated assay with similar/better sensitivity • Research assay with similar/better sensitivity

  10. Recommendation/Proposal • With currently available data, rodent infectivity studies appear unlikely to add value, given: • Persuasive evidence for transmission of vCJD by blood transfusion • Proven correlation between PrPSc and infectivity in multiple tissues • The variability of prion biology between species • PrPSc levels vary (Brown et al. J. Lab. Clin. Med. 2001) • Levels of infectivity vary (Brown et al. J. Lab. Clin. Med. 2001) • Incubation period can exceed life span (Race et al. J. Virol. 2001) • An assay which reliably demonstrated PrPSc detection in disease progression models • An assay which was specific in separating vCJD positives from normal human PrP • An assay with surrogate specificity validated with a confirmatory test for PrPSc • Since assay validation will require defined standards: • Encourages the allocation of government funding to support generation of surrogate reference materials and a confirmatory assay • Surrogate reference material could be blood derived from a time-course in animals • Confirmatory assay could be WB or PMCA or cell culture or another technique • Intent is for manufacturers to calibrate their assays against the confirmatory assay

  11. The CHIRON Team David Peretz, MSc, DSc, Senior Scientist, R&D W. Andrew Heaton, MD, VP/Chief Medical Officer Alisha J. McReynolds, Associate, Regulatory Affairs Rainer Ziermann, PhD, Director, Scientific Affairs

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