Measurement of Influenza Neuraminidase Inhibition Titers by Enzyme-Linked Lectin Assay (ELLA)

Maryna Eichelberger

Division of Viral Products CBER, OVRR, US-FDA

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Broad protection by NA-specific antibodies

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Schulman, Khakpour, Kilbourne, J. Virol. 2:778, 1968

N1-specific antibodies provide significant heterologous protection

• Prior infections with seasonal influenza A/H1N1 virus reduced illness and epidemic of pandemic H1N1: Couch et al. Clin. Infect. Dis. 2012

• Seasonal N1 induce antibodies that cross-react with 2009 H1N1pdm virus that contribute to protection: Marcelin et al. PLoS 2011

• Seasonal N1(DNA vaccine) protects some mice against lethal challenge with H5N1: Sandbulte et al., PLoS Medicine, 2008

• NA of 2009 H1N1pdm (VLP) protects against H5N1: Easterbrook et al., Virology, 2012

• Monoclonal antibodies with specificity for conserved N1 epitopes protect mice against lethal challenge with seasonal H1N1, 2009 pandemic H1N1 and H5N1 viruses: Wan et al., J Virol, 2013

Assays to measure NA inhibiting antibody titers Traditional Thiobarbituric acid (TBA) method • Chemical conversion of sialic acid to chromophore • Warren (1959) and Aminoff (1961) • Webster and Laver (1967): assay used to determine NI titers

WHO: Methods for Influenza surveillance Miniaturized TBA method • Sandbulte et al., 2009 Enzyme-linked lectin assay (ELLA) • Peanut agglutinin (PNA) binds to residual terminal galactose • Lambre et al, 1990 • Cate et al., Vaccine, 2010

ELLA is a practical method suitable for determination of NI titers in human sera - Couzens et al., J Virol Methods, 2014

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Protein Sugars Galactose Sialic acid

2. Add in standard amount of virus/NA with sera dilutions

Protein Sugars Galactose Sialic acid

NA

3. Add in PNA-HRPO

Protein Sugars Galactose::PNA-HRPO

4. Add in substrate (OPD)

Protein Sugars Galactose::PNA-HRPO

OPD

Signal

Overview of ELLA to determine NI titers

1. Coat plates with fetuin

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ELLA and mini-TBA are comparable Ferret antisera Human antisera

N1 N2

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Elements to ensure accuracy of NI assay

• Substrate – Should mimic ‘bulk’ of natural substrate

• Fetuin • Cell surface glycoproteins

• Source of NA – Purified NA – Detergent disrupted virus – Whole virus or VLPs: mismatched HA

– Classical reassortment – Reverse genetics

H6/PR8 NA Reassortant Virus

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Heat-treatment of control serum reduces non-specific NI activity when using H6 reassortants

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0%

10%

20%

30%

40%

50%

60%

70%

5 10 20 40 80 160 320 640

untreated

F/T

56 C

56 C F/T

Per

cent

inhi

bitio

n of

NA

activ

ity

Serum dilution

Virus diln (log2)

0.00.51.01.52.02.53.0

2 3 4 5 6 7 8 9 10 11 12

A490

nm

H6N1NC/99

Virus diln (log2)

Activity (µU/ml) 888 444 222 111 56 28 14 7 3.5 1.8 0.9

0.0

0.5

1.0

1.5

2.0

2.5

3.0

2 3 4 5 6 7 8 9 10 11 12

A499

0nm

H6N2WI/05

Activity (µU/ml) 494 247 123 62 31 16 8 4 2 1 0.5

Titration of antigen to identify dilution to use in the assay

~10 µU/ml NA activity is added per well

Influenza Neuraminidase Inhibition Assay Standardization

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CONSISE international study of the ELLA NA inhibition assay Goals:

• Determine the reproducibility of ELLA when conducted in different labs

• Evaluate the benefit of a serum standard • Facilitate establishment of ELLA in ‘new’ labs • Identify ELLA reagents/steps to improve assay performance

CONSISE – labs participating in ELLA study

Paul-Ehrlich-Institute, Germany

Univ of Hong Kong Hong Kong

Public Health England, UK

China CDC, China

CBER, FDA, USA

NIAID, NIH, USA

Novavax, USA

NIH, Portugal

Valladolid NIC, Spain

WHO Influenza Collaborating Centre, Australia

Istituto Superiore di Sanita, Italy

Univ of Melbourne, Australia

National Institute for Biological Standards and Control (NIBSC), UK University of Kent, UK

Erasmus Medical Center, The Netherlands

Naval Medical Research Center, USA

Naval Health, USA

Swedish Inst for Communicable Dis Control, Sweden

University of Bergen, Norway

Siriraj Hospital, Mahidol Univerisity,

Thailand

National Institute of Virology, India

CDC, USA

Univ of Michigan, USA

Focus Diagnostics, USA

Health Canada, Canada

Baxter, Austria Cantacuzino Institute, Romania

GSK, Germany

SJCRH, USA

Institut Pasteur Cambodia

Baylor Univ, USA

Institut Pasteur, Algeria

Natl Microbiol Lab, Canada

Beijing Inst for Microbiol/Epidemiology,

China

BC CDC, Canada

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Labs in blue: experienced Labs in black: new to ELLA Labs underlined: submitted data

Study plan

Perform the ELLA in different laboratories on a single set of 12 samples; measure NA inhibition titers against N1 of

A/BR/59/2007 (H1N1) and N2 of A/UR/716/2007 (H3N2)

– A single SOP used with either OPD or TMB as substrate; data generated with alternate assays run in parallel were compared

– 12 samples representing a range of titers were selected for the study; 1 sample was repeated (within assay variability); assay run on 3 different days by the same operator (intra-lab variability)

– One sample (transgenic bovine plasma, Sanford) was intended to be used as a standard

– H6N1 and H6N2 reassortant viruses were BPL-inactivated and used in-house to confirm suitability before distribution

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Data Submitted

• 50% end point titers • IC50 (non-linear regression) as secondary measure • Assay conditions/reagents

Data received for interim analysis discussed at workshop/webinar

Data received for final analysis received from 15 experienced

labs and 8 labs “new” to ELLA Each lab identified by letter code

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Workshop to discuss preliminary study results and assay steps

Friday 19th September, 2014; NIH campus and Webinar

The workshop presentations are available from the CONSISE website https://consise.tghn.org/about/international-meetings/

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Data Analysis (1)

• Intra-lab assay variability (repeat sample in each assay) – 69 of 71 N1 assays (97%) and 68 of 71 N2 assays (96%) had a 2-fold

or lower difference in titer of samples S001 and S010

• Intra-lab assay repeatability (12 samples run in assays on 3 different days) – the percentage of samples with a ≥4-fold difference in IC50 titer

against H6N1 is 1.1% – the percentage of samples with a ≥4-fold difference in IC50 titer

against H6N2 is 5.3%

• Inter-lab variability (data generated by 15 experienced labs) – the mean %GCV across 12 samples for end point titers against the

N1 antigen was 112% and against the N2 antigen was 82 %

Statistical analyses performed by Yonghong Gao (BARDA)

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Data Analysis (2) • Impact of a standard on NI titer and variability

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N1 N2

GMT %GCV GMT %GCV

Sample Abs Rel Abs Rel Abs Rel Abs Rel

1 817 1079 95 69 680 742 60 43

2 121 160 168 0 3293 3592 96 60

3 23 31 111 49 31 34 84 57

4 70 92 98 65 42 45 98 106

5 110 145 123 50 46 50 75 47

6 9 12 87 69 9 10 64 52

7 22 29 90 65 34 38 74 53

8 11 15 96 55 147 160 74 0

9 418 551 114 54 18 20 114 73

10 857 1131 116 56 737 804 84 54

11 64 85 119 53 295 321 80 43

12 661 873 130 61 187 204 80 58

Data Analysis (3)

• Comparison of variability in assay conducted by experienced vs 8 laboratories who recently established the assay – %GCV was lower for new labs!

• Evaluation of factors that contribute to ELLA variability – Use of different substrates (OPD vs TMB): no impact on variability – Background signal: significant difference in NI titers for N1antigen – Signal strength: significant difference in NI titers for N2 antigen – Antigen dilution: critical element (lower titers if too much antigen)

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Assay improvements

• Define the standard amount of antigen to use in the assay more clearly

• Update assay buffer to stipulate pH that optimizes NA activity • Establish conditions that allow shorter incubation time • Use of alternate NA sources e.g., VLPs

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Acknowledgements My laboratory Laura Couzens

Jin Gao Charu Sharma

CONSISE organization

Maria van Kerkhove John Wood

CONSISE Study steering committee

CONSISE Study participants

BARDA Funds

Yonghong Gao Mario Barro

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