# Presentation: 522949

## 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 Clearance Evaluation:  Spiking Model

***Cryoprecipitation*****	****	****	****	****	****Cryo**_**precipitate**_
**	****	****	****	****	****	****	****(FVIII)**
**	****	****	****	****	****	****	**
**	****	****	****Cryopoor Plasma **_**Supernatant**_**	****	**
**	****	****	**
**	****	****	****Albumin, IGIV, **
**	****	****	****A1PI, etc.**

_**TSE Clearance Evaluation:  Spiking Model**_

- High titer;
- caveat

## TSE Clearance Evaluation:  Endogenous 

***Cryoprecipitation*****	****	****	****	****	****Cryo**_**precipitate**_
**	****	****	****	****	****	****	****(FVIII)**
**	****	****	****	****	****	****	**
**	****	****	****Cryopoor Plasma **_**Supernatant**_**	****	**
**	****	****	**
**	****	****	****	****Albumin, IGIV, **
**	****	****	****	****A1PI, etc.**

_**TSE Clearance Evaluation:  Endogenous **_
**	****	**_**Infection model**_

- Low titer;
- Relevance;
- Limitations

## 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 Filter

_**Starting Material**_**	****	****	**_**Depth Filter**_**	**_**Reduction Factor (log**__**10**__**)**_
**	****	****	****	****	****	**
**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 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 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) 

- 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

## 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.

## 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.