Vaxfectin, a cationic lipid-based adjuvant for protein-based influenza vaccines.

Mice were immunized either with unadjuvanted seasonal trivalent influenza vaccine (TIV) or TIV formulated with Vaxfectin, a cationic lipid-based adjuvant. Increasing doses of Vaxfectin resulted in increased hemagglutination-inhibition or anti-TIV ELISA antibody titers, with up to a 200-fold increase obtained with 900 microg of Vaxfectin. A >or=10-fold dose-sparing effect was demonstrated with Vaxfectin formulations. Vaxfectin preferentially increased IgG2 titers compared to IgG1 titers, resulting in a balanced IgG isotype distribution. Lower doses of Vaxfectin (30 microg) did not enhance antibody responses, but increased the number of IFN-gamma secreting T-cells by up to 18-fold. The data demonstrate that Vaxfectin enhances Th1 responses with protein-based seasonal influenza vaccine, and suggest that cellular or humoral immune responses may be preferentially induced by modifying the Vaxfectin:antigen ratio in the vaccine formulation.