T-cell immunity to influenza A viruses.

Influenza infection remains a global threat to human health. Influenza viruses are normally controlled by antibodies specific for the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Standard influenza vaccines are aimed at inducing these antibodies, but they must be administered annually and can be rendered ineffective since different strains circulate from year to year and vary considerably in their individual HA and NA profiles. Influenza-specific T cells have been shown to be protective in animal models and typically recognize the more conserved internal influenza proteins. Improving our understanding of influenza-specific T-cell responses, including immunodominance, specific epitope sequences, strain-related epitope variation, host/virus interaction, and the balance between immunity versus immunopathology, will be important to improve future T-cell-based vaccines, which promise broader strain coverage and longer-lasting protection than current standard vaccines.