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Protective cellular immune correlates against pandemic influenza:

implications for universal vaccines

2nd WHO Meeting on development and clinical trials of

broadly protective influenza vaccines 5th – 7th May 2014, Geneva

Professor Ajit Lalvani FMedSci Chair of Infectious Diseases

Respiratory Infection Section National Heart and Lung Institute Imperial College London

NIHR Health Protection Research Unit in Respiratory Infection Imperial College London & Public Health England

Can we learn from natural resistance to pandemic flu?

• In a pandemic, global population is antibody-naïve and highly susceptible to infection with the antigenically-shifted strain

• Yet the majority of people who get infected experience minimal or no symptoms……

• ……these optimal clinical outcomes during a pandemic are more common in those with prior seasonal flu

J Infect Dis 2006 Bull WHO 1959

Heterosubtypic immunity

• Heterosubtypic immunity (HSI) against influenza: immunity induced

by one influenza subtype confers protection against infection or

disease caused by an antigenically-shifted previously un-encountered

influenza virus

Role for cross-reactive T cells to conserved core proteins supported by:

- animal models (since Schulman & Kilbourne J Bacteriol 1965) - human experimental challenge model (McMichael et al NEJM 1983)

Key questions for universal influenza vaccine development

• Do unexposed, antibody-naïve individuals harbour T cells

that cross-recognise new pandemic strains?

• If so, do T cells mediate heterosubtypic protection against

naturally-acquired symptomatic pandemic flu?

• Which T cell subset is associated with protection against

symptoms?

Protective correlate to guide rational design and

evaluation of universal flu vaccine

NB: these questions can only be answered during a pandemic when a new viral strain spread through a susceptible antibody-niave population.

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Unique natural experiment

Study population recruited at start of pandemic

91 conserved CD8 epitopes from core proteins:

PB1, M1, NP

A/England/195/2009 – pH1N1 strain

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IFN-γ IL-2 IFN-γ/IL-2 dual

Predicted CD8 epitopes from PB1, M1 and NP proteins (9-mers)

Ex vivo enumeration of major Functional T cell subsets

Pre-existing pH1N1 flu-specific T cells at baseline

Live pH1N1 virus

Conserved CD8 epitopes from PB1, NP, M1

Sridhar et al. Eur J Immunol 2012

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Study population recruited at start of pandemic Cohort of 342 yielded 25 precisely-defined cases of incident pH1N1 flu

Sridhar et al, Nature Medicine 2013

Frequencies of pre-existing IFNg/IL-2 total cytokine-secreting CD8+ T-cells associated with

limited symptom severity

Sridhar et al, Nature Medicine 2013

Significantly higher frequency of IFNg+IL-2- subset of CD8+ T-cells associated with limited symptoms

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Higher frequency of IFNg+IL-2- subset of CD8+ T-cells associated with lower symptom scores

Live pH1N1 virus CD8 conserved epitopes

Heterosubtypic IFNg+IL-2- CD8+ T-cells are associated with prevention of viral shedding

Sridhar et al, Nature Medicine 2013

Each 10-fold increase in the frequency of pH1N1 virus-specific T cells confers a 7-fold decrease in

risk of developing influenza illness with fever

Sridhar et al, Nature Medicine 2013

The protection-associated CD8+IFNg+IL-2- T cell subset has a late-effector CD45RA+CCR7-phenotype and

lung-homing (CCR5+) and cytotoxic capacity

Sridhar et al, Nature Medicine 2013

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Conclusions

• First cellular immune correlate of protection against influenza illness following natural infection • In absence of antibody, cross-reactive CD8+ T-cells limit illness severity and virus shedding with a new reassortant pandemic virus strain • This cellular correlate provides rationale and a surrogate marker for design and evaluation of broadly protective T-cell inducing influenza vaccines

Implications for universal influenza vaccine development

Target antigens and epitopes for

inclusion in vaccine

+

protection-associated

T cell subset to be induced

= blueprint for vaccine and surrogate marker

Respiratory Infections, Imperial College London Collaborators at Public Health England

Conflict of interest statement: AL is named inventor on a patent covering development and evaluation of T cell-based universal influenza vaccines Lalvani et al, J Exp Med 1997

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Discussion

Community cohort study provided mild to moderately symptomatic infection. Will these CD8 T-cells work against more severe disease? How long do these T-cells last following infection? This is a correlate in peripheral blood. Do these cells exist in the lung? Will vaccine-induced protection be the same as naturally-acquired protection?

Study Definitions

• Seroconversion = 4 fold titre rise in paired serum sample

• Infection = Nasal swab +ve AND/OR Seroconversion without H/o pandemic vaccination

• Asymptomatic Infection = Individuals with seroconversion BUT NO ILI reported in survey and answered >75% of surveys

• Symptomatic infection = Individuals reporting at least one ILI.

• Total symptom score = weighted summed score of five canonical influenza symptoms (fever, myalgia, sore throat, headache, cough).

Evidence for T cell-mediated heterosubtypic immunity in humans is restricted to

experimental challenge studies

pre-challenge CTL responses

(Wilkinson et al., 2012 Nat Med )

pre-challenge CD4+ responses

In the absence of antibodies to challenge strains

CD8 T cells mediate hetersubtypic immunity against influenza disease in animal models

J Bacteriol 1965

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Flourescence-linked Immunospot

Casey et al, PLoS ONE 2010

33 pH1N1 sero-negative individuals

30/33 individuals had a IFN-γ only response

22/33 individuals had a IL-2 only response

Cross-reactive T cells are detectable in majority of sero-negative individuals

Sridhar et al. EJI 2012

T cell responses to pandemic H1N1 • Circulating, influenza-specific memory T cells cross-reactive

with pH1N1 prevalent in healthy individuals naïve to pH1N1

Sridhar S, Begom S et al. EJI 2012

N = 35

Predominantly of IFN-γ+IL-2- cytokine secreting profile detected by fluorescence-immunospot

These pre-existing cells could mediate protection against pH1N1 disease

What is the phenotype and functional attribute of these cells?

0.5

million

deaths

5 million new symptomatic

cases p.a.

60% asymptomatic infection

Preventing pandemics with T cells

1.4

million

deaths

9 million new cases p.a.

2 billion infected

T cell-based

diagnosis & targeted

treatment of latent TB TB FLU T cell-based

risk-stratification

and vaccination to prevent

influenza illness