TSE Clearance in Plasma Derivatives

1. TSE Clearance in Plasma Derivatives TSE Advisory Committee February 8, 2005 Dorothy Scott, M.D. DH/OBRR/CBER/FDA

2. TSE Clearance Studies and Risk Assessment • Clearance is an important factor in overall risk estimation • Clearance by manufacturing process CAN be tested in scaled-down studies • Viral clearance studies paradigm applied

3. Paradigm: Validation of Virus Removal/inactivation Includes: • Scaling down process steps • Spiking appropriate steps with high titer of infectious agent (actual or model) • Determination reduction factors for each step • Summing reduction factors [from non-orthogonal processes] to give a total log10 reduction value

4. Studies of Clearance of TSE Agents • Source of infectivity • Brain preparations from experimentally infected animals with human/animal TSE agents • Blood from experimentally infected animals • Form infectious agent • Brain homogenate • Subcellular fractions • Membrane-free infectious material (e.g. fibrils) • Blood and blood fractions • * Alterations in form during manufacturing (“conditioning”)

5. Measures of Clearance • Assays to measure outcomes • In vivo infectivity – laborious, expensive, long-term experiments, but considered most relevant and most sensitive • In vitro - measurements of PrPSc • Bridging in vivo to in vitro results scientific controversy exists

6. TSE Clearance Evaluation: Spiking Model TSE Spike Plasma Cryoprecipitation Cryoprecipitate (FVIII) Cryopoor Plasma Supernatant Albumin, IGIV, A1PI, etc. High titer; caveat

7. TSE Clearance Evaluation: Endogenous Infection model Plasma from TSE-infected animal Cryoprecipitation Cryoprecipitate (FVIII) Cryopoor Plasma Supernatant Albumin, IGIV, A1PI, etc. Low titer; Relevance; Limitations

8. Steps studied: EtOH precipitation PEG precipitation Salt precipitation Depth filtration Nanofiltration Column chromatography Clearance relies upon: Partitioning (non-robust?) Additiveness of steps (demonstrated) Appropriate scale-down Relevance of model TSE Clearance Studies

9. TSE Clearance and Individual Manufacturing Processes • Manufacturing processes are highly individual • Rigorous demonstrations of TSE clearance need to be based upon the specific manufacturing process

10. Specificity of Process: Clearance PrPsc (microsomal spike) by Depth Filtration – Influence of Starting Materials and Filter Starting MaterialDepth FilterReduction Factor (log10) Fr V (albumin) Seitz KS80 > 4.9 Fr V (albumin) CUNO Delipid 1 2.3 S I + III (IGIV) Millipore AP20 < 1 Fr II (IGIV) Seitz K200 > 2.8 Foster et. al., Vox Sang 78: 86-95, 2000 Fr I supernatant (IGIV, albumin) Supra P80 < 1 Fr V supernatant (albumin) Supra P80 > 1.1 Fr V supernatant (albumin) – Prp-sc spike Supra P80 > 2.4 Vey et al, Biologicals 30:187-96, 2002

11. OBRR Actions to Minimize Risk of TSE Agents in Blood Products – TSE Clearance TSEAC (2/2003) endorsed FDA consideration of labeling claims for TSE clearance in plasma derivatives, based upon specific demonstration of TSE removal during manufacturing • TSE clearance study submissions encouraged by OBRR • Submissions received, evaluations in progress

12. FDA Requests for Submission TSE Clearance Data • Voluntary • Best current methods • Model selection not restricted but needs to be justified • 3 Logs clearance for “non-robust” steps considered significant • Science-in-evolution

13. TSE Clearance and Risk Assessment • TSE clearance a critical variable in risk assessments for vCJD • Clearance can be tested on a laboratory scale, with caveats (spike relevance, model agents, etc.) • Data can be provided for risk assessments: specific study of product provides best approximation of clearance • Clearance studies, and advances in these study methods could improve precision of risk estimates

14. Published TSE Clearance Studies for Plasma Derivatives (1) • Brown, P et al. The distribution of infectivity in blood components and plasma derivatives in experimental models of transmissible spongiform encephalopathy. Transfusion 1998 38:810-6 • Brown, P et al. Further studies of blood infectivity in an experimental model of transmissible spongiform encephalopathy, with an explanation of why blood components do not transmit CJD in humans. Transfusion 1999 39: 1169-78 • Lee, DC et al. Monitoring plasma processing steps with a sensitive Western blot assay for the detection of prion protein. J. Virol. Meth. 2000 84: 77-89 • Foster, PR et al. Assessment of the potential of plasma fractionation processes to remove causative agents of transmissible spongiform encephalopathy. Transfusion Science 2000 22:53-56 • Foster, PR et al. Assessment of the potential of plasma fractionation processes to remove causative agents of transmissible spongiform encephalopathy. Vox Sanguinis 2000 78:86-95 • Lee, DC et al. A direct relationship between the partitioning of the pathogenic prion protein and transmissible spongiform encephalopathy infectivity during the purification of plasma proteins. Transfusion 2001 41: 449-55

15. Published TSE Clearance Studies for Plasma Derivatives (2) • Cai, K et al. Solvent-dependent precipitation of prion protein. Biochem Biophys. Acta 2002 1597: 28-35 • Stenland, JS et al. Partitioning of human and sheep forms of the pathogenic prion protein during the purification of therapeutic proteins from human plasma. Transfusion 2002 42:1497-1500 • Vey, M et al. Purity of spiking agent affects partitioning of prions in plasma protein purification. Biologicals 2002 30:187-96 • Reichl, HE et al. Studies on the removal of a BSE-derived agent by processes used in the manufacture of human immunoglobulin. Vox Sanguinis 2002 83:137-45 • Van Holten, RW et al. Removal of prion challenge from an immune globulin preparation by use of a size-exclusion filter. Transfusion 2002 42:973-4. • Van Holten RW et al. Evaluation of depth filtration to remove prion challenge from an immune globulin preparation. Vox Sang 2003 85:20-4.

16. Published TSE Clearance Studies for Plasma Derivatives (3) 13. Trejo, SR, et al. Evaluation of virus and prion reduction in a new intravenous immunoglobulin manufacturing process. Vox Sang 2003 84:176-87. • Burnouf T et al. Nanofiltration of single plasma donations: feasibility study. Vox Sang 2003 84:111-119. • Gregori,et al. Partitioning of TSE infectivity during ethanol fractionation of human plasma. Biologicals 2004 32: 1-10. • Foster, PR et al. Distribution of a bovine spongiform encephalopathy-derived agen over ion-exchange chromatography used in the preparation of concentrates of fibrinogen and factor VIII. Vox Sang 2004 86:92-9.