Adenovectored RSV prefusion glycoprotein + soluble glycoprotein combination immunization establishes persistent opsonophagocytic antibody response through IgG3

Abstract

Introduction: Respiratory syncytial virus (RSV) causes significant lower-respiratory-tract disease in high-risk groups. A phase IIb trial showed that a combination vaccine of Ad26-vectored prefusion RSV F (Ad26.preF) plus soluble prefusion F protein (SpreF) was 80 % protective, yet the longevity and functionality of these humoral responses are unknown.

Methods: Sera from vaccinated adults were analyzed 12 months after the primary dose and 28 days after a homologous booster at 1 year. IgG subclasses, isotypes, Fc-γ receptor (FcγR) binding, and Fc-dependent effector functions including opsinophagocytosis against RSV-F subtypes A and B were quantified via Systems Serology.

Results: A single dose generated durable immunity: IgG3-driven opsonophagocytic activity and broad FcγR engagement (via IgG1, IgG2, and IgG3) persisted through 12 months without appreciable decay. The booster did not increase antibody titres, FcγR binding, or functional activity, indicating that the primary response had already plateaued.

Discussion: One dose of Ad26.preF + SpreF elicits a long-lasting, functionally potent humoral response that is not further enhanced by a booster at 12 months, suggesting limited benefit from early re-vaccination. Continued follow-up will clarify the duration of protection and inform booster timing in vulnerable populations.

Keywords: RSV; adenovirus vector; antibody; prefusion glycoprotein; vaccine.

Figure 1

The AD26.preF/SpreF protein combination vaccine establishes a longitudinally preserved IgG3 response to RSV/A F and RSV/B F. (A) Treatment schematic. The participants had serum drawn immediately before vaccination with combinatorial vaccine AD26.preF/SpreF protein. The serum samples were subsequently collected on days 29, 365, and 393. A subset of participants who received an initial AD26.preF/SpreF protein was boosted with a second dose of the same combination vaccine on day 365. (B) Univariate comparisons of baseline (black), placebo-treated (gray), or AD26.preF/SpreF protein-vaccinated (gold) participants at the indicated timepoints for IgG1, IgG2, IgG3, and IgG4 against RSV F subtype A. (C) The same as (B) but for RSV F subtype B. Statistical comparisons were done using an initial Wilcox test followed by a Bonferroni correction for multiple comparisons. Comparisons were made for recipients of AD26.preF/SpreF protein against placebo at the same timepoint. Bonferroni-corrected p-values (q-values) were represented above the timepoints with *q < 0.05, **q < 0.01, and ***q < 0.001; comparisons whose q-value was ≥ 0.05 were left unlabeled. Data was plotted as a box and whisker showing median, interquartile ranges, and ranges. Individual data points were superimposed on each box and whisker plot. Values were plotted as binding mean fluorescence units (MFI) quantified as arbitrary units (A.U.) via multiplexed flow cytometry.

Figure 2

The AD26.preF/SpreF protein induces an acute FcγR-binding repertoire against both RSV/A F and RSV/B F. (A) Univariate comparisons of baseline (black), placebo-treated (gray), or AD26.preF/SpreF protein-vaccinated (gold) participants at the indicated timepoints for FcγRIIA, FcγRIIB, FcγRIIIA, and FcγRIIIB against RSV F subtype A. (B) Same as (A) but for RSV-F subtype B. Statistical comparisons were done using an initial Wilcox test followed by a Bonferroni correction for multiple comparisons. Comparisons were made for recipients of AD26.preF/SpreF protein against placebo at the same timepoint. Bonferroni-corrected p-values (q-values) were represented above the timepoints with *q < 0.05, **q < 0.01, and ***q < 0.001; comparisons whose q-value was ≥ 0.05 were left unlabeled. Data was plotted as a box and whisker showing median, interquartile ranges, and ranges. Individual data points were superimposed on each box and whisker plot. Values were plotted as binding mean fluorescence units (MFI) quantified as arbitrary units (A.U.) via multiplexed flow cytometry.

Figure 3

The AD26.preF/SpreF protein induces a significant opsinophagocytic response and coordinated humoral profiles for over 1 year. (A) Antibody-dependent cellular phagocytosis (ADCP) was quantified at baseline (black), placebo-treated (gray), or AD26.preF/SpreF protein-vaccinated (gold) participants at the indicated timepoints for RSV/A F (left) and RSV/B F (right). (B) Antibody-dependent neutrophil phagocytosis (ADNP) was quantified at baseline (black), placebo-treated (gray), or AD26.preF/SpreF protein-vaccinated (gold) participants at the indicated timepoints for RSV/A F (left) and RSV/B F (right). (C) Correlation ribbon wheel to show statistically significant Spearman’s correlations (q-value < 0.05) between humoral features at day 29 post-vaccination with AD26.preF/SpreF protein. (D) Same as (C) but for correlations at day 393, the last draw date for recipients of the AD26.preF/SpreF protein (single dose); the legend for Spearman’s correlation coefficient value is shown in the bottom right. Comparisons were made for recipients of AD26.preF/SpreF protein against placebo at the same timepoint. Bonferroni-corrected p-values (q-values) were represented above the timepoints with *q < 0.05, **q < 0.01, and ***q < 0.001; comparisons whose q-value was ≥ 0.05 were left unlabeled. Data was plotted as a box and whisker showing median, interquartile ranges, and ranges. Individual data points were superimposed on each box and whisker plot. Values were plotted as the defined phagoscore, which is a measurement of opsinophagocytosis of fluorescent beads.

Figure 4

Boosting with AD26.preF/SpreF protein demonstrated negligible effects on AD26.preF/SpreF protein-primed recipients. (A) Multivariate clustering using partial least squares discriminate analysis (PLSDA) of individuals at baseline (black), day 393 single dose (gold), and day 393 boosted (red). Baseline humoral profiles were used instead of placebo for multivariate clustering to improve model separation. (B) (Rows 1 and 2) Univariate comparisons of placebo-treated (gray), single-dose AD26.preF/SpreF protein-vaccinated (gold), or boosted (red) participants at the indicated timepoints for IgG1 and FcγRIIA against RSV/A F (left) and RSV/B F (right). (Row 3) ADNP for placebo-treated (gray), single-dose AD26.preF/SpreF protein-vaccinated (gold), or boosted (red) participants at the indicated timepoints for RSV/A F (left) and RSV/B F (right). Bonferroni-corrected p-values (q-values) were represented above the timepoints with *q < 0.05, **q < 0.01, and ***q < 0.001; comparisons whose q-value was ≥ 0.05 were labeled as n.s. for not significant. Data was plotted as a box and whisker showing median, interquartile ranges, and ranges. Individual data points were superimposed on each box and whisker plot.