PT - JOURNAL ARTICLE AU - Elisa Rosati AU - Mikhail V. Pogorelyy AU - Anastasia A. Minervina AU - Alexander Scheffold AU - Andre Franke AU - Petra Bacher AU - Paul G. Thomas TI - Characterization of SARS-CoV-2 public CD4+ αβ T cell clonotypes through reverse epitope discovery AID - 10.1101/2021.11.19.469229 DP - 2021 Jan 01 TA - bioRxiv PG - 2021.11.19.469229 4099 - http://biorxiv.org/content/early/2021/11/22/2021.11.19.469229.short 4100 - http://biorxiv.org/content/early/2021/11/22/2021.11.19.469229.full AB - The amount of scientific data and level of public sharing produced as a consequence of the COVID-19 pandemic, as well as the speed at which these data were produced, far exceeds any previous effort against a specific disease condition. This unprecedented situation allows for development and application of new research approaches. One of the major technical hurdles in immunology is the characterization of HLA-antigen-T cell receptor (TCR) specificities. Most approaches aim to identify reactive T cells starting from known antigens using functional assays. However, the need for a reverse approach identifying the antigen specificity of orphan TCRs is increasing.Utilizing large public single-cell gene expression and TCR datasets, we identified highly public CD4+ T cell responses to SARS-CoV-2, covering >75% of the analysed population. We performed an integrative meta-analysis to deeply characterize these clonotypes by TCR sequence, gene expression, HLA-restriction, and antigen-specificity, identifying strong and public CD4+ immunodominant responses with confirmed specificity. CD4+ COVID-enriched clonotypes show T follicular helper functional features, while clonotypes depleted in SARS-CoV-2 individuals preferentially had a central memory phenotype. In total we identify more than 1200 highly public CD4+ T cell clonotypes reactive to SARS-CoV-2. TCR similarity analysis showed six prominent TCR clusters, for which we predicted both HLA-restriction and cognate SARS-CoV-2 immunodominant epitopes. To validate our predictions we used an independent cohort of TCR repertoires before and after vaccination with ChAdOx1, a replication-deficient simian adenovirus-vectored vaccine, encoding the SARS-CoV-2 spike protein. We find statistically significant enrichment of the predicted spike-reactive TCRs after vaccination with ChAdOx1, while the frequency of TCRs specific to other SARS-CoV-2 proteins remains stable. Thus, the CD4-associated TCR repertoire differentiates vaccination from natural infection.In conclusion, our study presents a novel reverse epitope discovery approach that can be used to infer HLA- and antigen-specificity of orphan TCRs in any context, such as viral infections, antitumor immune responses, or autoimmune disease.HighlightsIdentification of highly public CD4+ T cell responses to SARS-CoV-2Systematic prediction of exact immunogenic HLA class II epitopes for CD4+ T cell responseMethodological framework for reverse epitope discovery, which can be applied to other disease contexts and may provide essential insights for future studies and clinical applicationsCompeting Interest StatementP.B. and A.S. are consultants of Miltenyi Biotec, who own IP rights concerning parts of the ARTE technology. P.G.T has consulted and/or received honoraria and travel support from Illumina, Johnson and Johnson, and 10X Genomics. P.G.T. serves on the Scientific Advisory Board of Immunoscape and Cytoagents. The authors have applied for patents covering some aspects of these studies.