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 non-

orthogonal processes] to give a total log10 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, 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

TSE Spike Plasma

Cryoprecipitation Cryoprecipitate(FVIII)

Cryopoor Plasma Supernatant

Albumin, IGIV, A1PI, etc.

TSE Clearance Evaluation: Spiking Model

Plasma from TSE-infected animal

Cryoprecipitation Cryoprecipitate(FVIII)

Cryopoor Plasma Supernatant

Albumin, IGIV, A1PI, etc.

TSE Clearance Evaluation: Endogenous Infection model

TSE Clearance Studies

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 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 PrPsc (microsomal spike) by Depth Filtration – Influence of Starting Materials and

FilterStarting Material Depth Filter Reduction 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

OBRR Actions to Minimize Risk of TSE Agents in Blood Products – TSE

ClearanceTSEAC (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 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

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.