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 Cryop
recipitate (FVIII) Cryopoor
Plasma Supernatant Albumin, IGIV,
A1PI, etc.
High titer caveat
7
TSE Clearance Evaluation Endogenous
Infection model
Plasma from TSE-infected animal Cryoprecipitati
on Cryoprecipitate (FVIII) C
ryopoor Plasma Supernatant Albumin,
IGIV, A1PI, etc.
Low titer Relevance Limitations
8
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

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 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 (IGIV) Seitz K200 2.8 Foster et. al., Vox
Sang 78 86-95, 2000 Fr I supernatant (IGIV,
albumin) Supra P80 (albumin) Supra P80 1.1 Fr V supernatant
(albumin) Prp-sc spike Supra P80 2.4 Vey
et al, Biologicals 30187-96, 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 38810-6
• 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
  2253-56
• Foster, PR et al. Assessment of the potential of
  plasma fractionation processes to remove
  causative agents of transmissible spongiform
  encephalopathy. Vox Sanguinis 2000 7886-95
• 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 421497-1500
• Vey, M et al. Purity of spiking agent affects
  partitioning of prions in plasma protein
  purification. Biologicals 2002 30187-96
• 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 83137-45
• Van Holten, RW et al. Removal of prion challenge
  from an immune globulin preparation by use of a
  size-exclusion filter. Transfusion 2002
  42973-4.
• Van Holten RW et al. Evaluation of depth
  filtration to remove prion challenge from an
  immune globulin preparation. Vox Sang 2003
  8520-4.

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 84176-87.
• Burnouf T et al. Nanofiltration of single plasma
  donations feasibility study. Vox Sang 2003
  84111-119.
• 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 8692-9.