# Presentation: 498859

## Labeling Claims for TSE Reduction Studies with Blood Processing Filters

- Jaro Vostal, M.D., Ph.D.
- Division of Hematology, OBRR

## Conversion of PrPc to PrPsc

- Vostal  10/2005

**Normal prion **
**protein (PrPc)**

**Pathologic prion protein (PrPsc)**

**Protease resistant**
**less soluble**

**Accumulated PrPsc**
**and neurotoxicity**

**Altered conformations  **
**of PrPc**

**TSE infectivity present**

## Transport of TSE from peripheral inoculum to the CNS 

- Vostal  10/2005

- spleen

- stomach

**CNS**

**neuron**

**CNS**

- Transport of TSE from peripheral inoculum to the CNS

## BSE transmission by blood transfusionHouston, F.  et al. Lancet 2000Hunter, N. et al. J. Gen Virology, 2002

**Asymptomatic**
**BSE infected sheep**

**Healthy sheep**

**BSE infected sheep**

**Blood transfusion**

- BSE transmission by blood transfusionHouston, F.  et al. Lancet 2000Hunter, N. et al. J. Gen Virology, 2002

**X**

**X**

## Epidemiological evidence for vCJD transmission by blood transfusion in humansLlewelyn, C.A. et al, Lancet 363: 417-421, 2004Peden, A.H. et al. Lancet 364: 527-529, 2004

- The UK National CJD surveillance system identified individuals (48 total, 17 alive) who received blood products from 15 donors who later became diagnosed as vCJD cases
- 2 living recipients were subsequently diagnosed with vCJD
- 1 developed and died from symptoms of vCJD
- 1 died for unrelated cause and was unsymptomatic for vCJD but had PrPres identified in spleen
- Both received non-leukoreduced red cells

## Issues to consider for validation of devices and processes used to reduce TSE infectivity in human blood 

- Distribution of TSE infectivity in blood
- Cell-associated
- Intracellular vs extracellular
- Free floating in plasma
- Physical attributes of infectivity (aggregates, fibrils, microvesicles)
- Interaction of the individual units of infectivity with the devices
- Distribution during and after processing
- (microparticle generation)

## Steps to validate TSE reduction efficacy claims

- In vitro spiking studies of TSE infectivity into human blood
- Detection of infectivity by surrogate markers (PrPres) or by bioassay
- Endogenous TSE infectivity in an animal model
- Detection of infectivity by bioassay

## Predictive value of animal models for human situation

- Comparability of animal blood to human blood
- Cell type number, size and physical properties of blood cells
- Interaction of animal and human blood cells with different materials
- Transmissibility or infectivity of a TSE agent may be influenced by
- Strain of  agent used
- The dose of agent
- Distribution of infectivity in blood
- Distribution of normal prion ?

## Hematologic values for various species

| Species | RBC count x 106/ uL | RBC MCV (fL) | WBC
Count x 103/ uL | Platelet x 103/ uL |
| --- | --- | --- | --- | --- |
| Sheep | 10-13 | 35 | 4-12 | 500 |
| Golden Hamster | 6-7 | 60-70 | 5-10 | 500-800 |
| Mouse | 9-11 | 50 | 7-12 | 250-500 |
| Human | 4-5 | 86-98 | 4-11 | 150-450 |

- Schalm, O.W. Veterinary Hematology, 2nd ed. Lea & Febiger, Philadelphia 1965
- Harrison, Principles of Internal Medicine, 17th ed. McGraw-Hill, 1994

## PrPc expression on blood cells of different speciesVostal, J.G. and Holada, K. Transf Med Rev. 15: 268-281, 2001

## Validation of TSE infectivity reduction is only one part of the evaluation process

- TSE reduction devices also need to be evaluated for their impact on transfusion product quality
- Evaluation of red cells, platelets or plasma
- FDA follows a standardized evaluation approach to each transfusion product based on previous experience with devices that process transfusion products (e.g. leukoreduction filters)

## Leukoreduction: the process of reducing the total number of leukocytes in a transfusion component

- Methods:filtration of blood products or collection of products by  apheresis
- Use of leukoreduced blood products has been associated with reduction of
- febrile non hemolytic transfusion reactions
- Alloimmunization
- Cytomegalovirus (CMV)
- No claims by manufacturers for their devices beyond meeting the criteria for leukoreduction
- US       <5x106 leukocytes per transfusion product
- Europe <1x106 leukocytes per transfusion product

## Validation of Leukoreduction Filters-Efficacy

- Quantitation of leukocytes in particular blood product before and after filtration
- Whole blood, red cells, platelets, plasma
- Define timing of leukoreduction from time of collection
- Explore effects of temperature on filtration efficacy (room vs cold temperatures)
- Validation specific for particular anticoagulant

## Validation of Leukoreduction Filters-Safety

- Biocompatibility and integrity of materials
- Effect on cellular products
- In vitro recovery (85%)
- Hemolysis at end of storage (<1%)
- In vivo recovery of radiolabelled cells (platelets and red cells)
- Plasma –
- Levels and function of plasma proteins
- Complement activation

## FDA proposal for validating a claim of reducing TSE infectivity in human blood products

- Demonstrate reduction of _endogenous_ TSE infectivity by bioassay in two animal models (rodent and sheep)
- Use full scale blood unit and leukoreduction filter
- TSE infectivity from BSE or vCJD strain
- Reduction of PrPsc in blood product will be considered supportive but not sufficient for a claim
- Study performed at two separate sites to minimize issues of cross contamination and differences in laboratory practice
- Study size sufficient to support statistically valid conclusion

## Question 1:Are the FDA’s proposed minimal criteria for validation of TSE infectivity reduction by filtration adequate and appropriate?Please comment on the following points 

- A) Rationale for the use of specific animal models to study the properties of blood-borne TSE infectivity (Are experiments in rodents sufficient, or should experiments also be done in sheep?)
- B) Is it necessary that each experiment should be done at two separate laboratory sites (i.e. to ensure reproducibility, and accuracy of clearance)?
- C) General description of informative scaled-down processes for reducing TSE infectivity in blood

## Question 1:Are the FDA’s proposed minimal criteria for validation of TSE infectivity reduction by filtration adequate and appropriate?Please comment on the following points

- D) Levels of clearance acceptable for claims of reduced TSE infectivity in blood components as used in clinical settings
- E) Estimated logs of clearance of TSE infectivity required to conclude that blood filters have effectively removed infectivity from blood components
- F) Methodology appropriate to use in evaluating TSE agent clearance (bioassays for infectivity, Western blot or other assay for prion proteins, other methods)

## Question 2: Does the  FDA’s proposed labeling for a filter meet the appropriate criteria for a claim of reduction of TSE infectivity in blood or blood components?

*A) This filter (device) has been shown to reduce TSE infectivity in blood from an infected animal model.  *
*                                          **or*
*B) This filter (device) has been shown to reduce transmission of TSE infectivity by transfusion in an animal model.*
*                                        **and  (A+C or B+C) *
*C) Due to lack of feasibility, studies have not been performed to validate this claim in a human population. *