Validation and performance of a multiplex serology assay to quantify antibody responses following SARS-CoV-2 infection or vaccination

Seasonal human coronavirus humoral responses in AZD1222 (ChaAdOx1 nCoV-19) COVID-19 vaccinated adults reveal limited cross-immunity

Background

Immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is now widespread; however, the degree of cross-immunity between SARS-CoV-2 and endemic, seasonal human coronaviruses (HCoVs) remains unclear.

Methods

SARS-CoV-2 and HCoV cross-immunity was evaluated in adult participants enrolled in a US sub-study in the phase III, randomized controlled trial (NCT04516746) of AZD1222 (ChAdOx1 nCoV-19) primary-series vaccination for one-year. Anti-HCoV spike-binding antibodies against HCoV-229E, HCoV-HKU1, HCoV-OC43, and HCoV-NL63 were evaluated in participants following study dosing and, in the AZD1222 group, after a non-study third-dose booster. Timing of SARS-CoV-2 seroconversion (assessed via anti-nucleocapsid antibody levels) and incidence of COVID-19 were evaluated in those who received AZD1222 primary-series by baseline anti-HCoV titers.

Results

We evaluated 2,020/21,634 participants in the AZD1222 group and 1,007/10,816 in the placebo group. At the one-year data cutoff (March 11, 2022) mean duration of follow up was 230.9 (SD: 106.36, range: 1-325) and 94.3 (74.12, 1-321) days for participants in the AZD1222 (n = 1,940) and placebo (n = 962) groups, respectively. We observed little elevation in anti-HCoV humoral titers post study-dosing or post-boosting, nor evidence of waning over time. The occurrence and timing of SARS-CoV-2 seroconversion and incidence of COVID-19 were not largely impacted by baseline anti-HCoV titers.

Conclusion

We found limited evidence for cross-immunity between SARS-CoV-2 and HCoVs following AZD1222 primary series and booster vaccination. Susceptibility to future emergence of novel coronaviruses will likely persist despite a high prevalence of SARS-CoV-2 immunity in global populations.

Validation and Suitability Assessment of Multiplex Mesoscale Discovery Immunogenicity Assay for Establishing Serological Signatures Using Vaccinated, Non-Vaccinated and Breakthrough SARS-CoV-2 Infected Cases

Antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are multi-targeted and variable over time. Multiplex quantitative serological assays are needed to provide accurate and robust seropositivity data for the establishment of serological signatures during vaccination and or infection. We describe here the validation and evaluation of an electro-chemiluminescence (ECL)-based Mesoscale Discovery assay (MSD) for estimation of total and functional IgG relative to SARS-CoV-2 spike, nucleocapsid and receptor binding (RBD) proteins in human serum samples to establish serological signatures of SARS-CoV-2 natural infection and breakthrough cases. The 9-PLEX assay was validated as per ICH, EMA, and US FDA guidelines using a panel of sera samples, including the NIBSC/WHO reference panel (20/268). The assay demonstrated high specificity and selectivity in inhibition assays, wherein the homologous inhibition was more than 85% and heterologous inhibition was below 10%. The assay also met predetermined acceptance criteria for precision (CV < 20%), accuracy (70-130%) and dilutional linearity. The method's applicability to serological signatures was demonstrated using sera samples (n = 45) representing vaccinated, infected and breakthrough cases. The method was able to establish distinct serological signatures and thus provide a potential tool for seroprevalence of SARS-CoV-2 during vaccination or infection.

Silver Nanocluster-Tagged Electrochemiluminescence Immunoassay with a Sole and Narrow Triggering Potential Window

The commercialized electrochemiluminescence (ECL) immunoassay is carried out by holding luminophore Ru(bpy)32+ at a given potential. Designing an electrochemiluminophore with a narrow triggering potential window is strongly anticipated to decrease the electrochemical cross-talk and improve the flux of the commercialized ECL immunoassay in a potential-resolved way. Herein, L-penicillamine-capped silver nanoclusters (LPA-AgNCs) are facilely synthesized and utilized as tags to perform the ECL immunoassay with a sole and narrow triggering potential window of 0.24 V by employing hydrazine (N2H4) as a coreactant. The maximum ECL emission of the LPA-AgNCs/N2H4 system is located ca. +1.27 V. Upon immobilizing LPA-AgNCs onto the electrode surface via forming a sandwich immunocomplex, the ECL of LPA-AgNCs/N2H4 can be utilized to sensitively and selectively determine human carcinoembryonic antigen from 0.5 to 1000 pg/mL with a low limit of detection of 0.1 pg/mL (S/N = 3). This work might open a way to screen electrochemiluminophores for the multiple ECL immunoassay in a potential-resolved way.

Longitudinal nucleocapsid antibody testing reveals undocumented SARS-CoV-2 infections in patients with lung cancer

Patients diagnosed with lung cancer (LC) exhibit increased susceptibility to SARS-CoV-2 infection. Rodilla et al. monitor the levels of plasma anti-nucleocapsid antibodies within a cohort of fully vaccinated LC patients and reveal that the actual infection rate is nearly twice the documented rate, indicating a significant prevalence of unreported cases.

Assay Harmonization Study To Measure Immune Response to SARS-CoV-2 Infection and Vaccines: a Serology Methods Study

The Coronavirus disease 2019 (COVID-19) pandemic presented the scientific community with an immediate need for accurate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology assays, resulting in an expansion of assay development, some without following a rigorous quality control and validation, and with a wide range of performance characteristics. Vast amounts of data have been gathered on SARS-CoV-2 antibody response; however, performance and ability to compare the results have been challenging. This study seeks to analyze the reliability, sensitivity, specificity, and reproducibility of a set of widely used commercial, in-house, and neutralization serology assays, as well as provide evidence for the feasibility of using the World Health Organization (WHO) International Standard (IS) as a harmonization tool. This study also seeks to demonstrate that binding immunoassays may serve as a practical alternative for the serological study of large sample sets in lieu of expensive, complex, and less reproducible neutralization assays. In this study, commercial assays demonstrated the highest specificity, while in-house assays excelled in antibody sensitivity. As expected, neutralization assays demonstrated high levels of variability but overall good correlations with binding immunoassays, suggesting that binding may be reasonably accurate as well as practical for the study of SARS-CoV-2 serology. All three assay types performed well after WHO IS standardization. The results of this study demonstrate there are high performing serology assays available to the scientific community to rigorously dissect antibody responses to infection and vaccination. IMPORTANCE Previous studies have shown significant variability in SARS-CoV-2 antibody serology assays, highlighting the need for evaluation and comparison of these assays using the same set of samples covering a wide range of antibody responses induced by infection or vaccination. This study demonstrated that there are high performing assays that can be used reliably to evaluate immune responses to SARS-CoV-2 in the context of infection and vaccination. This study also demonstrated the feasibility of harmonizing these assays against the International Standard and provided evidence that the binding immunoassays may have high enough correlation with the neutralization assays to serve as a practical proxy. These results represent an important step in standardizing and harmonizing the many different serological assays used to evaluate COVID-19 immune responses in the population.

One year safety and immunogenicity of AZD1222 (ChAdOx1 nCoV-19): Final analysis of a randomized, placebo-controlled phase 1/2 trial in Japan

BACKGROUND

Long duration trial data for two-dose COVID-19 vaccines primary series' are uncommon due to unblinding and additional doses. We report one-year follow-up results from a phase 1/2 trial of AZD1222 (ChAdOx1 nCoV-19) in Japan.

METHODS

Adults (n = 256) seronegative for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) were stratified by age, 18-55 (n = 128), 56-69 (n = 86) and ≥70-year-old (n = 42), and randomized 3:1 to AZD1222 or placebo. Safety, immunogenicity, and exploratory efficacy data were collected until study Day 365.

RESULTS

Safety was consistent with previous reports. In AZD1222 vaccinees, humoral responses against SARS-CoV-2 steadily declined over time. By Day 365, anti-SARS-CoV-2 spike-binding (spike) and receptor-binding domain (RBD) mean antibody titers remained above Day 15 levels and pseudovirus neutralizing antibodies were undetectable in many participants.

CONCLUSIONS

AZD1222 is immunogenic and well tolerated in Japanese adults. Expected waning in anti-SARS-CoV-2 humoral responses was observed; spike and RBD antibody titers remained elevated. (ClinicalTrials.gov: NCT04568031).

Development, Validation, and Utilization of a Luminex-Based SARS-CoV-2 Multiplex Serology Assay

SARS-CoV-2 antibody testing is important for seroprevalence studies and for evaluating vaccine immune responses. We developed and validated a Luminex bead-based multiplex serology assay for measuring IgG levels of anti-SARS-CoV-2 antibodies against full-length spike (S), nucleocapsid (N), and receptor-binding domains (RBDs) of wild-type, RBD N501Y mutant, RBD E484K mutant, RBD triple mutant SARS-CoV-2 proteins, Sars-CoV-1, MERS-CoV, and common human coronaviruses, including SARS-CoV-2, OC43, 229E, HKU1, and NL63. Assay cutoff values, sensitivity, and specificity were determined using samples from 160 negative controls and 60 PCR-confirmed, SARS-CoV-2-infected individuals. The assay demonstrated sensitivities of 98.3%, 95%, and 100% and specificities of 100%, 99.4%, and 98.8% for anti-(S), -N, and -RBD, respectively. Results are expressed as IgG antibody concentrations in BAU/mL, using the WHO international standard (NIBSC code 20/136) for anti-SARS-CoV-2 IgG antibodies. When the multiplex assay was performed and compared with singleplex assays, the IgG antibody measurement geometric mean ratios were between 0.895 and 1.122, and no evidence of interference was observed between antigens. Lower and upper IgG concentration limits, based on accuracy (between 80% and 120%), precision (percent relative standard deviation, ≤25%), and sample dilutional linearity (between 75% and 125%), were used to establish the assay range. Precision was established by evaluating 24 individual human serum samples obtained from vaccinated and SARS-CoV-2-infected individuals. The assay provided reproducible, consistent results with typical coefficients of variation of ≤20% for all assays, irrespective of the run, day, or analyst. Results indicate the assay has high sensitivity and specificity and thus is appropriate for use in measuring SARS-CoV-2 IgG antibodies in infected and vaccinated individuals. IMPORTANCE The SARS-CoV-2 pandemic resulted in the development and validation of multiple serology tests with variable performance. While there are multiple SARS-CoV-2 serology tests to detect SARS-CoV-2 antibodies, the focus is usually either on only one antigen at a time or multiple proteins from only one SARS-CoV-2 variant. These tests usually do not evaluate antibodies against viral proteins from different SARS-CoV-2 variants or from other coronaviruses. Here, we evaluated a multiplex serology test based on Luminex technology, where antibodies against multiple domains of SARS-CoV-2 wild type, SARS-CoV-2 mutants, and common coronavirus antibodies are detected simultaneously in a single assay. This Luminex-based multiplex serology assay can enhance our understanding of the immune response to SARS-CoV-2 infection and vaccination.

Utility of Roche Elecsys anti-SARS-CoV-2 S in ascertaining post-vaccine neutralizing antibodies

With widespread global COVID-19 vaccine coverage, a scalable, cost-effective, and standardized tool to ascertain post-vaccine immunity is a dire need. Neither clinical evaluations of vaccine efficacy, nor live virus antibody neutralization assays fulfill these criteria. Commercially available anti-S binding immunological assays have the potential to fill this gap, but need to be systematically evaluated for their utility to serve as surrogates for the aforementioned, widely accepted tools of determining vaccine efficacy. In this study, we evaluated an anti-S binding immunological assay (Roche Elecsys Anti-SARS-CoV-2 S) by utilizing two hundred and fifty-five archived serum specimens, either pre-pandemic, or those exposed to natural infections or vaccines with their neutralizing titers pre-determined through a live virus, pseudotyped antibody neutralization assay. Roche Elecsys Anti-SARS-CoV-2 S demonstrated good sensitivity (98%) and specificity (99%), just as has been reported in some other previously conducted studies using this assay. Only a mild correlation, however, with the live virus pseudotyped lentivirus antibody neutralization assay (Spearman's r = 0.26) was observed. We conclude that, as such, Elecsys Anti-SARS-CoV-2 S has a high sensitivity and specificity for detecting anti-SARS-CoV-2 S proteins, though the assay does not always correlate well with live virus assays for quantitative outcomes.

AZD1222-induced nasal antibody responses are shaped by prior SARS-CoV-2 infection and correlate with virologic outcomes in breakthrough infection

The nasal mucosa is an important initial site of host defense against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, intramuscularly administered vaccines typically do not achieve high antibody titers in the nasal mucosa. We measure anti-SARS-CoV-2 spike immunoglobulin G (IgG) and IgA in nasal epithelial lining fluid (NELF) following intramuscular vaccination of 3,058 participants from the immunogenicity substudy of a phase 3, double-blind, placebo-controlled study of AZD1222 vaccination (ClinicalTrials.gov: NCT04516746). IgG is detected in NELF collected 14 days following the first AZD1222 vaccination. IgG levels increase with a second vaccination and exceed pre-existing levels in baseline-SARS-CoV-2-seropositive participants. Nasal IgG responses are durable and display strong correlations with serum IgG, suggesting serum-to-NELF transudation. AZD1222 induces short-lived increases to pre-existing nasal IgA levels in baseline-seropositive vaccinees. Vaccinees display a robust recall IgG response upon breakthrough infection, with overall magnitudes unaffected by time between vaccination and illness. Mucosal responses correlate with reduced viral loads and shorter durations of viral shedding in saliva.

Robust humoral and cellular recall responses to AZD1222 attenuate breakthrough SARS-CoV-2 infection compared to unvaccinated

Background

Breakthrough severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in coronavirus disease 2019 (COVID-19) vaccinees typically produces milder disease than infection in unvaccinated individuals.

Methods

To explore disease attenuation, we examined COVID-19 symptom burden and immuno-virologic responses to symptomatic SARS-CoV-2 infection in participants (AZD1222: n=177/17,617; placebo: n=203/8,528) from a 2:1 randomized, placebo-controlled, phase 3 study of two-dose primary series AZD1222 (ChAdOx1 nCoV-19) vaccination (NCT04516746).

Results

We observed that AZD1222 vaccinees had an overall lower incidence and shorter duration of COVID-19 symptoms compared with placebo recipients, as well as lower SARS-CoV-2 viral loads and a shorter median duration of viral shedding in saliva. Vaccinees demonstrated a robust antibody recall response versus placebo recipients with low-to-moderate inverse correlations with virologic endpoints. Vaccinees also demonstrated an enriched polyfunctional spike-specific Th-1-biased CD4+ and CD8+ T-cell response that was associated with strong inverse correlations with virologic endpoints.

Conclusion

Robust immune responses following AZD1222 vaccination attenuate COVID-19 disease severity and restrict SARS-CoV-2 transmission potential by reducing viral loads and the duration of viral shedding in saliva. Collectively, these analyses underscore the essential role of vaccination in mitigating the COVID-19 pandemic.

Performance and validation of an adaptable multiplex assay for detection of serologic response to SARS-CoV-2 infection or vaccination

Measurement of quantitative antibody responses are increasingly important in evaluating the immune response to infection and vaccination. In this study we describe the validation of a quantitative, multiplex serologic assay utilising an electrochemiluminescence platform, which measures IgG against the receptor binding domain (RBD), spike S1 and S2 subunits and nucleocapsid antigens of SARS-CoV-2. The assay displayed a sensitivity ranging from 73 to 91% and specificity from 90 to 96% in detecting previous infection with SARS-CoV-2 depending on antigenic target and time since infection, and this assay highly correlated with commercially available assays. The within-plate coefficient of variation ranged from 3.8-3.9% and the inter-plate coefficient of variation from 11 to 13% for each antigen.

Distinct Antibody Responses to Endemic Coronaviruses Pre- and Post-SARS-CoV-2 Infection in Kenyan Infants and Mothers

Pre-existing antibodies that bind endemic human coronaviruses (eHCoVs) can cross-react with SARS-CoV-2, which is the betacoronavirus that causes COVID-19, but whether these responses influence SARS-CoV-2 infection is still under investigation and is particularly understudied in infants. In this study, we measured eHCoV and SARS-CoV-1 IgG antibody titers before and after SARS-CoV-2 seroconversion in a cohort of Kenyan women and their infants. Pre-existing eHCoV antibody binding titers were not consistently associated with SARS-CoV-2 seroconversion in infants or mothers; however, we observed a very modest association between pre-existing HCoV-229E antibody levels and a lack of SARS-CoV-2 seroconversion in the infants. After seroconversion to SARS-CoV-2, antibody binding titers to the endemic betacoronaviruses HCoV-OC43 and HCoV-HKU1, and the highly pathogenic betacoronavirus SARS-CoV-1, but not the endemic alphacoronaviruses HCoV-229E and HCoV-NL63, increased in the mothers. However, eHCoV antibody levels did not increase following SARS-CoV-2 seroconversion in the infants, suggesting the increase seen in the mothers was not simply due to cross-reactivity to naively generated SARS-CoV-2 antibodies. In contrast, the levels of antibodies that could bind SARS-CoV-1 increased after SARS-CoV-2 seroconversion in both the mothers and infants, both of whom were unlikely to have had a prior SARS-CoV-1 infection, supporting prior findings that SARS-CoV-2 responses cross-react with SARS-CoV-1. In summary, we found evidence of increased eHCoV antibody levels following SARS-CoV-2 seroconversion in the mothers but not the infants, suggesting eHCoV responses can be boosted by SARS-CoV-2 infection when a prior memory response has been established, and that pre-existing cross-reactive antibodies are not strongly associated with SARS-CoV-2 infection risk in mothers or infants.