Self-Amplifying mRNA Vaccines Expressing Multiple Conserved Influenza Antigens Confer Protection against Homologous and Heterosubtypic Viral Challenge
BALB/c mice were immunized i.m. twice, 8 weeks apart, with PBS, 0.1 μg of SAM(NP), SAM(M1), SAM(M1-NP), or with 0.2 μg of SAM(NP)+SAM(M1). Four weeks after the second immunization, mice were infected with PR8 virus. NP-specific CD8 T cells recruited in the lungs after the infection were characterized by flow cytometry. (a) Numbers of NP-specific CD8+ T cells. Data are from individual mice (depicted as dots), while solid lanes indicate the mean±SD. (b) Cumulative frequency of Ag-specific, cytokine-secreting CD8+ T cells, indicated as absolute number per lung. The color code represents the different combinations of cytokine produced by the respective cells after in vitro stimulation with medium (m), NP147-155 peptide (NP), or M1 peptide pool (M1), as indicated. (c) Absolute number of NP-specific CD8+ T cells positive (black bar) or not (grey bar) for CD107a. Data derived from two independent and merged experiments. Statistical analyses were performed using the Mann-Whitney U test. *p<0.05; **p<0.01 compared to the PBS-treated group.