Fig. 2: IgG subclass responses and FcγR engagement of antibodies induced by Ad26.RSV.preF/RSV preF protein combinations in naïve mice.

Naïve female BALB/c mice were immunized at Week 0 and Week 6 with Ad26.RSV.preF (1 × 10⁸, 1 × 10⁹, or 1 × 10¹⁰ vp; n = 6 in each group), RSV preF protein (0.15, 1.5, or 15 µg; n = 6 each), or Ad26.RSV.preF combined with RSV preF protein at varying dose levels (n = 13 each). IgG1 (a) and IgG2a (b) preF-binding antibody titers, expressed as relative potency titer, were measured in serum by ELISA at Week 8. Horizontal lines indicate mean antibody responses per group, and the dotted line indicates the LOD, specified as the titer of the sample with the highest titer in the formulation buffer control group. Serum obtained at Week 8 from mice immunized with the highest vaccine concentration (Ad26.RSV.preF [1 × 10¹⁰ vp] and RSV preF protein [15 ug], alone or in combination) was pooled and used to measure FcγRIV activation in an ADCC reporter assay (c), expressed as RLU. Total IgG binding to RSV F-expressing target cells (d) was measured by fluorescence using AF488-conjugated goat anti-mouse IgG. Average of duplicate measurements is shown. Statistical comparisons were made across dose by ANOVA for potentially censored measurements (Tobit model) with Bonferroni correction for multiple comparisons (at an overall significance level of α = 0.05). Ad26, adenovirus type 26; ADCC, antibody-dependent cellular cytotoxicity; ELISA, enzyme- linked immunosorbent assay; FcγR, Fcγ receptor; FcγRIV, Fcγ receptor IV; IgG, immunoglobulin G; LOD, limit of detection; ns, not significant; preF, prefusion conformation-stabilized RSV F protein; Rel. Pot., relative potency; RLU, relative light units; RSV, respiratory syncytial virus; vp, viral particles.