CD8+ T immune cells that are present prior to infection and are specific for influenza virus are associated with reduced severity of influenza-associated illness in people who have been naturally infected. These findings, reported online this week in Nature Medicine, provide support for the development of influenza vaccines aimed at enhancing T cell responses.

Vaccines against influenza induce a strong but short-lived antibody response that frequently lacks the ability to neutralize viral strains that are not components of the vaccine.As a result, the emergence of a new influenza strain not targeted by the vaccine, such as that seen during the 2009 H1N1 pandemic, can result in widespread infection with potentially severe outcomes.The role of longer-lived, cross-reactive CD8+ T cells that are produced by the in protecting against illness after natural influenza infection and in the absence of virus-specific antibodies has been less clear.

Ajit Lalvani and colleagues analyzed CD8+ T cell responses in individuals infected with the 2009 pandemic virus (pH1N1) and found that in the absence of neutralizing antibodies to pH1N1, pre-existing CD8+ T cells specific for highly conserved viral peptides were associated with reduced severity of symptoms and nasal shedding of pH1N1.The findings suggest that new influenza vaccines should promote the development of cross-reactive CD8+ T cells-in addition to antibodies-in order to protect against influenza-associated illness from future pandemics as well as from annual seasonal influenza.