Fig. 6: Enhanced lung protection following immunization with the combined FPM2e:LNP vector.

Balb/c mice were i.n immunized with 3 doses with 5 μg FPM2e, FPM2e:LNP, or FPM2e:LNPPEG at 10 days apart and survival and weight loss was monitored following a challenge infection with 4× LD50 of the mouse adapted ×47 (a) or PR8 (b) influenza A virus strains. The percent of surviving mice (left panels) and body weight loss (right panels) are given of groups of 10 mice and one representative experiment of 3 giving similar results is shown. c Representative images of the gross pathology of the lung in the different groups of mice at 7 days post infection with the PR8 strain. d Detection of M2e-tetramer-specific CD4⁺ T cells in the lung of immunized and PR8-challenged mice. Representative FACS dot plots of M2e-tetramer⁺ CD4⁺ T cells in the different groups from one representative experiment out of 3 giving similar results (left panel). The percentage (middle panel) and absolute number (right panel) of antigen primed M2e⁺ tetramer CD4⁺ T cells are given as means ± SD in the different groups of 5 mice and one representative experiment is shown out of 3 giving similar results. e Percent of surviving mice (left panel) and body weight loss (middle panel) following depletion of CD4⁺T cells and challenge infection with 4× LD50 of PR8 virus strain. FACS plot showing successful depletion of CD4⁺ T cells in lungs (right panel). f Anti-M2e antibodies assessed in the different treatment groups: serum titers of IgG1(left panel) or IgG2a (middle panel) or IgA titers (right panel) in BAL were determined by ELISA after the PR8 infection and given as mean log₁₀ titers ± SD of 3 independent experiments. Statistical significance was calculated by unpaired t test and p values are given as *p < 0.05; **p < 0.01; ***p < 0.005; ****p < 0.0001.