Quantitative, Epitope-specific, Serological Screening of COVID-19 Patients Using a Novel Multiplexed Array-based Immunoassay Platform

Following the COVID-19 pandemic outbreak in late 2019, a large number of antibody tests were developed for use in seroprevalence studies aimed at determining the extent of current or previous SARS-CoV-2 virus infections in a given population. The vast majority of these tests are qualitative and use a single target for antibody detection, incorporating either full-length or truncated versions of the nucleocapsid (N) or spike (S) proteins from SARS-CoV-2. Importantly, mono-epitope tests – whether qualitative or quantitative - are unable to localise antibody binding or characterise the distribution and titres of epitope recognition by anti-SARS-CoV-2 antibodies within an individual or across a population. However, it seems plausible that if such information were available, it may correlate with the presence of potent, high-titre, neutralising antibodies that afford protection again imminent re-infection, as well as with the likelihood of developing a memory B-cell response that would provide more durable protection. We have developed a novel, quantitative, multi-antigen, multiplexed, array-based immunoassay platform, ‘ImmuSAFE COVID+’ (ImmuSAFE) comprising 6 functionally validated domains or regions of the N protein of SARS-CoV-2 expressed using Sengenics’ KREX technology. This array platform enables determination of both the position and breadth of anti-SARS-CoV-2 antibody responses following natural infection or vaccination. To validate our platform, 100 serum samples (confirmed sero-positive COVID-19 cases, n=50; pre-pandemic HIV positive controls, n=50) were tested for IgG seropositivity to the N antigen, yielding 100% specificity and 100% sensitivity. All 50 cases showed positive antibody reactivity towards at least one N protein epitope, whilst all 50 controls showed antibody reactivity below threshold values. Broad variation was also observed in the magnitude and breadth of antibodies present, represented as an Epitope Coverage score (EPC). A positive correlation was observed between increasing age and EPC values, with individuals under 40 years old having a mean EPC score of 3.1, whilst individuals above the age of 60 had a mean EPC of 5.1. This finding may have broad implications for the natural history of COVID-19 disease in different individuals. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study is funded by Malaysia Automotive, Robotics & IoT Institute (MARii), an agency under the Ministry of International Trade and Industry (MITI). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Institute for Medical Research, Ministry of Health, Malaysia. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The data that support the findings of this study are available from the Institute of Medical Research (IMR), Ministry of Health, Malaysia, but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of Institute for Medical Research, Ministry of Health, Malaysia.