TSE Clearance in Plasma Derivatives TSE Advisory Committee

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

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

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 nonorthogonal processes] to give a total log 10 reduction value

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”)

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

TSE Clearance Evaluation: Spiking Model TSE Spike Plasma Cryoprecipitation Cryoprecipitate (FVIII) Cryopoor Plasma Supernatant Albumin, IGIV, A 1 PI, etc.

TSE Clearance Evaluation: Endogenous Infection model Plasma from TSE-infected animal Cryoprecipitation Cryoprecipitate (FVIII) Cryopoor Plasma Supernatant Albumin, IGIV, A 1 PI, etc.

TSE Clearance Studies Steps studied: • Et. OH precipitation • PEG precipitation • Salt precipitation • Depth filtration • Nanofiltration • Column chromatography Clearance relies upon: • Partitioning (nonrobust? ) • Additiveness of steps (demonstrated) • Appropriate scaledown • Relevance of model

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

Specificity of Process: Clearance Pr. Psc (microsomal spike) by Depth Filtration – Influence of Starting Materials and Filter Starting Material Depth Filter Reduction Factor (log 10) Fr V (albumin) Seitz KS 80 > 4. 9 Fr V (albumin) CUNO Delipid 1 2. 3 S I + III (IGIV) Millipore AP 20 <1 Fr II (IGIV) Seitz K 200 > 2. 8 Foster et. al. , Vox Sang 78: 86 -95, 2000 Fr I supernatant (IGIV, albumin) Supra P 80 <1 Fr V supernatant (albumin) Supra P 80 > 1. 1 Fr V supernatant (albumin) – Prp-sc spike Supra P 80 > 2. 4 Vey et al, Biologicals 30: 187 -96, 2002

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

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

TSE Clearance and Risk Assessment • TSE clearance a critical variable in risk assessments for v. CJD • 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

Published TSE Clearance Studies for Plasma Derivatives (1) 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 2. 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 3. 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 4. 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 5. 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 6. 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

Published TSE Clearance Studies for Plasma Derivatives (2) 7. Cai, K et al. Solvent-dependent precipitation of prion protein. Biochem Biophys. Acta 2002 1597: 28 -35 8. 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 9. Vey, M et al. Purity of spiking agent affects partitioning of prions in plasma protein purification. Biologicals 2002 30: 187 -96 10. 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 11. 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. 12. Van Holten RW et al. Evaluation of depth filtration to remove prion challenge from an immune globulin preparation. Vox Sang 2003 85: 20 -4.

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. 14. Burnouf T et al. Nanofiltration of single plasma donations: feasibility study. Vox Sang 2003 84: 111 -119. 15. Gregori, et al. Partitioning of TSE infectivity during ethanol fractionation of human plasma. Biologicals 2004 32: 1 -10. 16. 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.