Dose-dependent serological profiling of AdCLD-CoV19-1 vaccine in adults

Abstract

AdCLD-CoV19-1, a chimeric adenovirus-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine, was previously reported to elicit robust antibody responses in mice and non-human primates after a single dose. In this study, we conducted a systems serology analysis to investigate changes in humoral immune responses induced by varying doses of the AdCLD-CoV19-1 vaccine in a phase I clinical trial. Serum samples from participants receiving either a low or a high dose of the vaccine were analyzed for antibody features against prototype SARS-CoV-2 spike (S) domains (full-length S, S1, S2, and receptor binding domain), as well as Fc receptor binding and effector functions. While both low- and high-dose vaccines induced robust humoral immune responses following vaccination, the quality of antibody features differed between the dose groups. Notably, while no significant difference was observed between the groups in the induction of most S1-specific antibody features, the high-dose group exhibited higher levels of antibodies and a stronger Fc receptor binding response specific to the S2 antigen. Moreover, univariate and multivariate analyses revealed that the high-dose vaccine induced higher levels of S2-specific antibodies binding to FcγR2A and FcγR3B, closely associated with antibody-dependent neutrophil phagocytosis (ADNP). Further analysis using the Omicron BA.2 variant demonstrated that the high-dose group maintained significantly higher levels of IgG and FcγR3B binding to the S2 antigen and exhibited a significantly higher ADNP response for the S2 antigen compared with the low-dose group. These findings underscore the importance of considering diverse humoral immune responses when evaluating vaccine efficacy and provide insights for optimizing adenovirus vector-based SARS-CoV-2 vaccine doses.IMPORTANCEOptimization of vaccine dose is crucial for eliciting effective immune responses. In addition to neutralizing antibodies, non-neutralizing antibodies that mediate Fc-dependent effector functions play a key role in protection against various infectious diseases, including coronavirus disease 2019. Using a systems serology approach, we demonstrated significant dose-dependent differences in the humoral immune responses induced by the AdCLD-CoV19-1 chimeric adenovirus-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine, particularly against the SARS-CoV-2 spike 2 domain. These findings highlight the importance of assessing not only neutralizing antibody titers but also the quality and functionality of antibody responses when evaluating vaccine efficacy.

Keywords: SARS-CoV-2; adenovirus vector-based vaccine; effector function; spike protein; systems serology.

Fig 1

Overall humoral immune responses across the two dose groups post-vaccination. Violin plots (representing medians, interquartile ranges, minima, and maxima) showing the antibody levels in the low- and high-dose groups on days 0 and 28. Individuals were vaccinated on day 0 with two different doses. Dots represent the participants (n = 20). (A) Anti-SARS-CoV-2 S IgG titers were measured as log10 binding antibody units/mL (BAU/mL) using ELISA. (B) Log10 titers of neutralizing antibodies against SARS-CoV-2 measured using the FRNT assay. For the comparison of changes in antibody levels, a Mann–Whitney U test was performed. The P value is indicated in the figure. (C) Polar plots depicting the mean percentile of prototype SARS-CoV-2-specific antibody features for the two dose groups on days 0 and 28. Percentile rank scores were determined for each antibody feature across all individuals. The colors represent the following feature groups: light-yellow, antibody-dependent functional assays; orange, FcR profiling; and light green, antibody isotypes and subclasses. The SARS-CoV-2 FS antigen was used for the functional assays. SARS-CoV-2 FS, S1, S2, and RBD antigens were used for antibody and FcR profiling. ****P < 0.0001.

Fig 2

Differences in antibody architecture between the two groups on day 28 post-vaccination. Violin plots illustrating univariate comparisons of antibody profiling specific to prototype SARS-CoV-2 FS, S1, S2, and RBD between the low- and high-dose groups on day 28. Data are presented as geometric mean fluorescence intensity (GMFI). The analyzed antibody isotypes and subclasses are (A) IgG, (B) IgG1, (C) IgG2, (D) IgG3, (E) IgA1, and (F) IgM, which are specific to four different antigens. The two groups were compared using the Mann–Whitney U test. The P values are shown in the figure. *P < 0.05, **P < 0.01, and ***P < 0.001.

Fig 3

Differences in FcR architecture between the two dose groups on day 28 post-vaccination. Violin plots showing univariate comparisons of FcR profiling specific to prototype SARS-CoV-2 FS, S1, S2, and RBD between the low- and high-dose groups on day 28. FcR binding for (A) FcγR2A, (B) FcγR2B, (C) FcγR3A, (D) FcγR3B, and (E) FcRn is expressed as GMFI. The two groups were compared using the Mann–Whitney U test. The P values are shown in the figure. *P < 0.05 and **P < 0.01.

Fig 4

Fc-mediated effector functions of the two dose groups on day 28 post-vaccination. (A) Violin plots showing univariate comparisons of four Fc-mediated effector functions specific to prototype SARS-CoV-2 FS between the low-dose and high-dose groups on day 28. Measurements are presented as GMFI for C3 deposition, indicating ADCD; as phagocytosis scores for ADCP and ADNP; and as the percentage of CD107a-positive cells, representing ADNKA. (B) The ADNP results for the low- and high-dose groups on day 28 with S1 and S2 antigens are shown as violin plots. The two groups were compared using the Mann–Whitney U test. The P values are shown in the figure. *P < 0.05.

Fig 5

Multivariate analysis of the two dose groups post-vaccination. A sPLS-DA was performed using antibody feature data from the two dose groups on day 28. (A) Sample plot with 0.95 ellipse confidence level illustrating the separation of antibody features between individuals in low- and high-dose groups. Colors indicate the dose groups: blue indicates the high-dose group and orange indicates the low-dose group. (B) ROC curve and AUC for the model containing components 1 and 2. The AUC value, calculated to compare the two dose groups, was 0.8974. (C) The antibody features that significantly contributed to the differentiation between the high-dose group (blue, pointing left) and the low-dose group (orange, pointing right) are shown and ranked by the loading score for component 1. (D) A co-correlation network was constructed based on three selected features from the loading plot for X-variate 1 using Spearman’s rank correlation. Only correlations with |r| > 0.7 to at least one of the highlighted features in gray are displayed.

Fig 6

Profiling assays and ADNP of the two dose groups on day 28 post-vaccination against the Omicron BA.2 variant. Violin plots showing univariate comparisons of profiling assays and ADNP specific to Omicron BA.2 FS, S1, and S2 between the low- and high-dose groups on day 28. Antibody features of (A) IgG, (B) FcγR2A, and (C) FcγR3B are expressed as GMFI. (D) The ADNP results are presented as phagocytosis scores. The two groups were compared using the Mann–Whitney U test. The P values are shown in the figure. *P < 0.05.