Anti-B19 screening for safe cellular blood products for at–risk patients

Anti-B19 screening for safe cellular blood products for at–risk patients

SoGAT XVIII, USA, May 24-25th, 2005

Harry Bos on behalf of Project Group Parvo B19 Safe Blood Components (Theo Cuijpers, Marco Koppelman, John Jongerius, Maarten Koot, et al.)

SoGAT, May 25th, 2005

Parvovirus B19

Small non enveloped virus; 23 nm.

Single-stranded DNA genome; approx. 5500 nucl.Encoding 3 proteins:

•VP1: ± 5% of capsid•VP2: ± 95% of capsid•NS1: non-structural for viral replication

Erythrovirus •Highly thropic for erythroid progenitor cells

Infected cells undergo lysis caused by expression of NS1•Decline in red blood cell count and haemoglobin


Clinical manifestation of infection

Epidemiology

- Seroprevalence in adults world-wide approx. 50-80%

- Seroconversion rate for adults is about 0.8% per year

Healthy individuals

- Erythema infectiosum (fifth disease) - Chills- Headache- Rash

- No clinical symptoms


Risk groups for B19 infections

Women during second trimester of pregnancy

- Intra uterine fetal death (10%)

- Hydrops fetalis (3%)

Patients with congenital or acquired haemolytic anaemia

Cellular immunodeficient patients

- Aplastic crisis

- Prolonged bone marrow damage and aplasia

- Bone marrow transplantation


Health Council of the Netherlands*

B19 may cause serious complications in risk groups

B19 can be transmitted by blood tranfusion

B19 infection in healthy individuals:

- Formation of protective Antibodies

- Sometimes persistance of B19 virus for some time

B19 safe blood components from:

- Donors with IgG Antibodies

- Interval at least six months

*) Council of the Netherlands Bloodproducts and Parvovirus B19. 2002; publication no. 2002/07


Health Council of the Netherlands

Plasma products

The risk-group approach can not be used for plasma products

because of their large-scale production and use.

Approach for blood derivatives:

- Lowering the load in manufacturing pools by NAT screening and removal of high load units (>5 x 106 IU/ml)


Estimation of demand of Parvo safe blood products in the Netherlands

Erythrocyte concentrates 54,800 (8%)

Plasma 9,950 (8%)

Thrombocyte concentrates 11,000 (22%) equivalent to

56,000 donor units

Delivery of thrombocyte concentrates is the determing factor in the number of donors to be screened

for B19

Total numbers of donors to be screened: 250,000

= 50% of the donorpopulation


B19 IgG antibody screening

Screening Assay:

- Biotrin Parvovirus B19 Sandwich ELISA

- α-VP2 IgG

- FDA cleared B19 ELISA

Automation of the screening assay:

- Automatic pipetting device: Tecan Genesis

- ELISA back-end processor: Ortho Summit Processor


OD/CO for reactive α-Parvo B19 result 25,500 donations first time tested

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0-0.5

0.5-1

1-1.5

1.5-2

2-2.5

2.5-3

3-3.5

3.5-4

4-4.5

4.5-5

5-5.5

5.5-6

6-6.5

6.5-7

7-7.5

7.5-8

8-8.5

8.5-9

9-9.5

9.5-10

>10

OD/CO class

% o

f tot

al d

onat

ions

Reactive OD/CO > 1.0 80.1 %Reactive OD/CO > 1.5 78.7%


Status Anti-parvo B19 Testing April 1st, 2005

Reactive OD/CO > 1.5 75.4 %

First time tested

Realised number244,572

Reactive (OD/CO > 1.5)184,468

Firist and second time tested

Reactive (OD/CO > 1.5)124,932

Desired number first and second time reactives 125,000


Status demand of Parvo safe cellular blood products in the Netherlands, April 1th, 2005

Explicit demand of hospitals:

Division Northeast < 10

Division Southeast 15

Division Southwest 16

Division Northwest 10-20 thrombocyte concentrates weekly

) The Parvo status of the product is printed standard on the label of the bloodproduct


Limitations of the B19 screening method

A) False positive reactions

- 1 donor: low pos OD/CO ratio

B) Persistance of B19 virus in infected donors for a period of more than six months

- 2 donors: high pos OD/CO ratio, low B19 DNA load

Remark: Blood products will probably not be infectious, because the high titer of B19 antibodies will neutralise the virus present in a low concentration.


Persistent B19 infection (B)Donor 1

Time Course for IgG, IgM & the B19-DNA viral load

0

2

4

6

8

10

0 100 200 300 400 500

Time (Days) Post Infection

B19

-VP2

(O

D/C

O)

110100100010000100000100000010000000

B19

DN

A V

ial

load

(IU

/ml)

IgM IgGViral Load


Alternative Screening Based on Natural History of Infection.

Further R&D on the testing system in place.• Follow up of acute infected donors found in plasma-

screening

• Sensitive B19 NAT of 5000 donations 6 month bleeding (2nd IgG anti-Parvo screening). % False positive rate IgG test?

Possible Consequences• Extension of the 6 month-interval period to the

length of the observed viremic period

• Parvo-NAT screening of donation for safe product

• IgM and IgG screening of donation for the safe product

• Or combination of these approaches


Projects under consideration to improve the screening method

- Determine the false positive rates of the different brands of IgG anti-Parvo assays

- Determine the in vitro neutralising effect of B19 antibodies (e.g. α-VP1, α-VP2, α-NS1), using cohort of follow up samples of acute infected individuals.


Conclusions

Parvo B19 safe blood components can be derived from donors with IgG Antibodies tested at an interval of at least six months.

Parvo B19 safe cellular blood products can be in case of a transfusion used for risk groups for B19 infection. This approach will reduce serious complications due to transfusion related B19 infection.

Further research is in consideration to improve the screening method.

Anti-B19 screening for safe cellular blood products for at–risk patients

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