Fig. 4.

Mouse immunogenicity studies of a lipid nanoparticle formulated self-amplifying RNA (LNP/RNA) candidate vaccine encoding RSV-F. Groups of eight mice were vaccinated intramuscularly (i.m.) on days 0 and 21 with naked self-amplifying RNA (0.01–1 μg), self-amplifying RNA formulated in lipid nanoparticles (LNP/RNA, 0.01–10 μg), or viral replicon particles (VRPs, 1 × 10⁶ IU). Sera were collected on day 35, and F-specific IgG (A), IgG1 (B), and IgG2a (C) titers were determined by ELISA. Dots depict measurements from individual mice and solid lines, the geometric mean titers of eight mice per group. Dotted lines indicate the limit of 25 for quantification. For determination of GMTs, a titer <25 was assigned a value of 5. (D) Frequencies of RSV-F antigen-specific, cytokine-producing CD8⁺4⁻ T cells in spleens of BALB/c mice vaccinated on days 0 and 21 with RNA, RNA/LNP, or VRP. Spleens were collected 4 wk after the second vaccination and pooled (four spleens per pool) before antigen stimulation in vitro and flow cytometry analysis. Error bars indicate the 95% confidence upper limits. No IL2⁺ TNFα⁺, IL2⁺IFNγ⁺, IL2⁺, or IL5⁺ CD8 T cells were detected. Serum IgG titers 2 wk after the first vaccination can be found in Fig. S3. NS, not significant.