Fig. 5: Humoral and cellular immunogenicity measured in African green monkey serum.
Female African green monkeys were pre-exposed i.n. with RSV Memphis 37 (7.5 × 105 pfu) at Week –19 and immunized intramuscularly with Ad26.RSV.preF (1 × 1011 vp; n = 11); RSV preF protein (150 µg; n = 4); or a combination of Ad26.RSV.preF (1 × 1011 vp) with RSV preF protein (15, 50, or 150 µg; n = 7 in each group) at Week 0 with homologous boost immunization at Week 60. RSV CL57 VNT, expressed as log2 IC50, were measured in serum samples; dots represent mean VNT per group; error bars indicate SD (a). LOD was determined as 3×SD above mean VNT of Week –19 serum samples and indicated by a dotted line. RSV preF IgG-binding titers, expressed as log10 endpoint titers, were measured by ELISA in serum samples (b). Dots represent mean titers per group; error bars indicate SD. LOD was determined as log10 of the inverse of the lowest serum dilution. PBMCs were obtained before immunization (but after pre-exposure) and after immunization at Weeks 2, 7, 9, 15, and 72 for measurements of cellular immune responses by IFN-γ ELISpot (c), expressed as SFU/106 PBMCs. Each dot represents geometric mean responses per group, and error bars indicate 95% CIs. LOD was set at 50 SFU/106 PBMCs. Measurement of the animal showing the highest SFU counts at Weeks 2, 7, and 9 (in the group receiving Ad26.RSV.preF/RSV preF protein [15 μg]) is missing at Week 15 due to too many spots. Ad26, adenovirus type 26; CI, confidence interval; EC50, 50% effective concentration; ELISA, enzyme-linked immunosorbent assay; ELISpot, enzyme-linked immune absorbent spot; FFL, firefly luciferase; IC50, half-maximum inhibitory concentration; IFN-γ, interferon-γ; IgG, immunoglobulin G; i.n., intranasally; LOD, limit of detection; PBMC, peripheral blood mononuclear cell; pfu, plaque-forming units; preF, prefusion conformation-stabilized RSV F protein; RSV, respiratory syncytial virus; SD, standard deviation; SFU, spot-forming units; VNT, virus neutralization titers; vp, viral particles.
