Quantitative, multiplexed, targeted proteomics for ascertaining variant specific SARS-CoV-2 antibody response

Determining the protection an individual has to SARS-CoV-2 variants of concern (VoC) will be crucial for future immune surveillance and understanding the changing immune response. As further variants emerge, current serology tests are becoming less effective in reflecting neutralising capability of the immune system. A better measure of an evolving antigen-antibody immune response is needed. We describe a multiplexed, baited, targeted-proteomic assay for direct detection of multiple proteins in the SARS-CoV-2 anti-spike antibody immunocomplex. This enables a more sophisticated and informative characterisation of the antibody response to vaccination and infection against VoC. Using this assay, we detail different and specific responses to each variant by measuring several antibody classes, isotypes and associated complement binding. Furthermore, we describe how these proteins change using serum from individuals collected after infection, first and second dose vaccination. We show complete IgG1 test concordance with gold standard ELISA (r>0.8) and live virus neutralisation against Wuhan Hu-1, Alpha B.1.1.7, Beta B.1.351, and Delta B.1.617.1 variants (r>0.79). We also describe a wide degree of heterogeneity in the immunocomplex of individuals and a greater IgA response in those patients who had a previous infection. Significantly, our test points to an important role the complement system may play particularly against VoC. Where we observe altered Complement C1q association to the Delta VoC response and a stronger overall association with neutralising antibodies than IgG1. A detailed understanding of an individual’s antibody response could benefit public health immunosurveillance, vaccine design and inform vaccination dosing using a personalised medicine approach.\n\n### Competing Interest Statement\n\nThe authors have submitted an intellectual property claim for using the platform for clinical applications.\n\n### Funding Statement\n\nThis work is (partly) funded by the NIHR GOSH BRC, TMSRG UCL and The Peto Foundation. RJB, DMA and AMK are supported by UKRI MR/W020610/1. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR, UKRI or the Department of Health.\n\n### Author Declarations\n\nI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.\n\nYes\n\nThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:\n\nHuman sera were obtained from the COVIDsortium Healthcare Workers bioresource which is approved by the ethical committee of UK National Research Ethics Service (20/SC/0149) and registered on [ClinicalTrials.gov][1] ([NCT04318314][2]). The study conformed to the principles of the Helsinki Declaration, and all subjects gave written informed consent.\n\nI confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.\n\nYes\n\nI 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).\n\nYes\n\nI 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.\n\nYes\n\nAll data produced in the present study are available upon reasonable request to the authors\n\n [1]: http://ClinicalTrials.gov\n [2]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04318314&atom=%2Fmedrxiv%2Fearly%2F2022%2F02%2F15%2F2022.02.14.22270845.atom