| Summary: | Current influenza vaccines have reduced immunogenicity and are of uncertain efficacy in older adults. We assessed the safety and immunogenicity of MVA-NP+M1, a viral-vectored influenza vaccine designed to boost memory T cell responses, in a group of older adults.Thirty volunteers (aged 50-85) received a single intramuscular injection of MVA-NP+M1 at a dose of 1·5×10(8) plaque forming units (pfu). Safety and immunogenicity were assessed over a period of one year. The frequency of T cells specific for nucleoprotein (NP) and matrix protein 1 (M1) was determined by interferon-gamma (IFN-γ) ELISpot, and their phenotypic and functional properties were characterized by polychromatic flow cytometry. In a subset of M1-specific CD8(+) T cells, T cell receptor (TCR) gene expression was evaluated using an unbiased molecular approach.Vaccination with MVA-NP+M1 was well tolerated. ELISpot responses were boosted significantly above baseline following vaccination. Increases were detected in both CD4(+) and CD8(+) T cell subsets. Clonality studies indicated that MVA-NP+M1 expanded pre-existing memory CD8(+) T cells, which displayed a predominant CD27(+)CD45RO(+)CD57(-)CCR7(-) phenotype both before and after vaccination.MVA-NP+M1 is safe and immunogenic in older adults. Unlike seasonal influenza vaccination, the immune responses generated by MVA-NP+M1 are similar between younger and older individuals. A T cell-inducing vaccine such as MVA-NP+M1 may therefore provide a way to circumvent the immunosenescence that impairs routine influenza vaccination.ClinicalTrials.gov NCT00942071.
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