Low-Avidity CD4<sup>+</sup> T Cell Responses to SARS-CoV-2 in Unexposed Individuals and Humans with Severe COVID-19.

Petra Bacher, Elisa Rosati, Daniela Esser, Gabriela Rios Martini, Carina Saggau, Esther Schiminsky, Justina Dargvainiene, Ina Schröder, Imke Wieters, Yascha Khodamoradi, Fabian Eberhardt, Maria J G T Vehreschild, Holger Neb, Michael Sonntagbauer, Claudio Conrad, Florian Tran, Philip Rosenstiel, Robert Markewitz, Klaus-Peter Wandinger, Max Augustin, Jan Rybniker, Matthias Kochanek, Frank Leypoldt, Oliver A Cornely, Philipp Koehler, Andre Franke, Alexander Scheffold
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Immunity (Cambridge, Mass.)
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CD4<sup>+</sup> T cells reactive against SARS-CoV-2 can be found in unexposed individuals, and these are suggested to arise in response to common cold coronavirus (CCCoV) infection. Here, we utilized SARS-CoV-2-reactive CD4<sup>+</sup> T cell enrichment to examine the antigen avidity and clonality of these cells, as well as the relative contribution of CCCoV cross-reactivity. SARS-CoV-2-reactive CD4<sup>+</sup> memory T cells were present in virtually all unexposed individuals examined, displaying low functional avidity and multiple, highly variable cross-reactivities that were not restricted to CCCoVs. SARS-CoV-2-reactive CD4<sup>+</sup> T cells from COVID-19 patients lacked cross-reactivity to CCCoVs, irrespective of strong memory T cell responses against CCCoV in all donors analyzed. In severe but not mild COVID-19, SARS-CoV-2-specific T cells displayed low functional avidity and clonality, despite increased frequencies. Our findings identify low-avidity CD4<sup>+</sup> T cell responses as a hallmark of severe COVID-19 and argue against a protective role for CCCoV-reactive T cells in SARS-CoV-2 infection.