Imbalance of regulatory and cytotoxic SARS-CoV-2-reactive CD4+ T cells in COVID-19

The contribution of CD4+ T cells to protective or pathogenic immune responses to SARS-CoV-2 infection remains unknown. Here, we present a large-scale single-cell transcriptomic analysis of viral antigen-reactive CD4+ T cells from 40 COVID-19 patients. In hospitalized patients compared to non-hospitalized patients, we found increased proportions of cytotoxic follicular helper (TFH) cells and cytotoxic T helper cells (CD4-CTLs) responding to SARS-CoV-2, and reduced proportion of SARS-CoV-2-reactive regulatory T cells (TREG). Importantly, in hospitalized COVID-19 patients, a strong cytotoxic TFH response was observed early in the illness which correlated negatively with antibody levels to SARS-CoV-2 spike protein. Polyfunctional T helper (TH)1 and TH17 cell subsets were underrepresented in the repertoire of SARS-CoV-2-reactive CD4+ T cells compared to influenza-reactive CD4+ T cells. Together, our analyses provide so far unprecedented insights into the gene expression patterns of SARS-CoV-2-reactive CD4+ T cells in distinct disease severities. Single-cell RNA-seq were performed from pure populations of virus-reactive memory CD4+ T cells isolated ex vivo from SARS-CoV-2 infected individuals (n=40) and healthy controls (n=13).