Cell-Mediated Immune Response to Influenza Using Ex Vivo Stimulation and Assays of Cytokine and Granzyme B Responses.

The antibody response to vaccination has been the industry and regulatory standard for evaluating influenza vaccine efficacy. Although antibodies are an important defense mechanism providing sterilizing immunity, in older adults, the cellular immune response is also needed for clinical protection against the serious complications of influenza. Thus, the demonstration of enhanced antibody responses as a strategy for advancing new influenza vaccines through the standard clinical development pipeline may fail to translate to enhanced protection in the older population. In peripheral blood mononuclear cells (PBMC) challenged with live influenza virus, an increase in the interferon-γ:interleukin-10 (IFN-γ:IL-10) ratio and the level of the cytolytic mediator, granzyme B (GrzB), correlates with protection against influenza in vaccinated older adults. This chapter provides detailed methods for measuring these cell-mediated immune responses, which have been validated according to the International Conference on Harmonisation (ICH) guidelines. These immune correlates could be combined with antibody responses to improve the prediction of enhanced protection in vaccine trials in the older population.