Nature and Impact of Influenza Antigen Specific T Cell Responses on Disease in an In Vivo Human Challenge Model.

Session VI – John Oxford

Title of Contribution: Nature and Impact of Influenza Antigen Specific T Cell Responses on Disease in an In Vivo Human Challenge Model.

Author(s): T M A Wilkinson1, J S Oxford3, A J Mann3, X Xu2, C Li2, B Nicholas1, K Staples1, C Dumont3, R Lambkin-Williams3 and A Gilbert3
Affiliation(s): 1. Division of Infection, Inflammation and Repair, Southampton University School of Medicine, Southampton, UK. 2. MRC Human Immunology Unit, University of Oxford, UK. 3. Retroscreen Virology Ltd. UK

Abstract:
Despite current vaccination strategies influenza remains an important cause of worldwide morbidity and mortality. Rapid antigenic drift of surface epitopes necessitates constant adjustment to conventional vaccines to ensure appropriate coverage of circulating strains.
Novel vaccines targeting internal viral proteins, which tend to be more highly conserved between strains, and generate T cell immunity, may offer opportunity to provide protection against the majority of influenza viruses and potentially cover against a pandemic pathogen. These T cell vaccines are in development, however, knowledge of clinically relevant protective T cell influenza immunity is limited and has proven difficult to study effectively in the field. We therefore designed an in vivo influenza human challenge study using a clinically relevant H3N2 influenza A strain to investigate the relationship between the prevalence of pre-existing virus specific T cells, clinical indicators of disease and viral shedding in a population of healthy volunteers.
17 volunteers (9 male), median age 25 years (range 18 to 42), with normal lung function and no history of respiratory disease were screened for protective H3N2 serology and candidates with HA titres <10 HAI were recruited for viral challenge. PBMC derived T cell responses to specific virus proteins were determined using a pan-influenza genome peptide stimulation matrix and ELISPOT interferon-γ assay.
The final challenge cohort of 17 was divided into four groups each inoculated nasally with a different titre of with GMP grade H3N2 influenza A. Twice daily records of symptoms, physical examination and nasal wash for viral shedding were taken. Repeat T cell assays were performed on day 7 and post quarantine on day 28. All volunteers received oseltamivir prior to discharge. No serious adverse events were recorded.
Baseline influenza T cell responses were detected in 15 of the 17 volunteers; NP and Matrix proteins were immunodominant at baseline. 14 of 17 inoculated volunteers manifested influenza symptoms, and viral shedding was demonstrated in 13 volunteers by cell culture assay, most of which peaked on day 2 or 3. Marked T cell responses – 3 to 4 fold rises in proportion and magnitude of response, were seen at day 7 to immunodominant proteins along with an increased spectrum of protein responses.  Relationships between T cell IFN-γ responses to viral proteins and illness severity will be presented.
The improved understanding of human T cell driven immunity to influenza and its impact on disease gained by this novel experimental approach will inform on the development of improved vaccines offering an important opportunity to improve preventative strategies against this enduring pathogen.