Cytotoxic T lymphocyte responses to a liposome-adjuvanted influenza A virus vaccine in the elderly.

This randomized double-blind study evaluated cytotoxic T lymphocyte (CTL) responses of elderly volunteers after parenteral immunization with either liposome-adjuvanted (n = 23) or control subvirion (n = 26) vaccine containing detergent-split influenza A/Taiwan/1/86 (H1N1) virus. Peripheral blood mononuclear cells obtained 0, 2, and 12 weeks after vaccination were stimulated in vitro with influenza A (H1N1) virus-infected autologous cells and then assayed for influenza virus-specific cytotoxicity using autologous virus-infected target cells. CTL responses to vaccination exhibited influenza A virus heterosubtypic cross-reactivity and were mediated primarily by CD8+ effector cells. Anti-influenza virus CTL activity was enhanced to a significantly greater extent by the liposome vaccine than by the control subvirion vaccine. It remains to be established whether the advantage of a liposomal formulation in terms of an improved CTL response is relevant to vaccine protective efficacy.