SARS-CoV-2 specific T-cell responses and correlations with COVID-19 patient predisposition.

COVID-19 has emerged as a global pandemic caused by SARS-CoV-2. So far, viral targets of cellular immunity and factors determining successful mounting of T-cell responses are poorly defined. We therefore analyzed cellular responses to membrane, nucleocapsid and spike protein in individuals suffering from moderate or severe infection and after recovery from mild disease. We demonstrate that the CoV-2 specific CD4+ T-helper cell response is directed against all three proteins with comparable magnitude, ex vivo proliferation and portions of responding patients. However, deceased individuals were more frequently amongst non-responders. Higher patient age and comorbidity index correlated with increased frequencies of CoV-2 specific CD4+ T-cells, harboring higher portions of IL-2-, but lower portions of IFNI³ secreting cells. Diminished frequencies of membrane protein reactive IFNI³+ T cells were particularly associated with higher Acute Physiology And Chronic Health Evaluation II scores in patients admitted to intensive care. CoV-2 specific T cells exhibited elevated PD-1 expression in active patients as compared to recovered individuals with previous mild disease. In summary, our data suggest a link between individual patient predisposition with respect to age and comorbidity and impairment of CoV-2 specific Th1-type cellular immunity, thereby supporting a concept of altered T-cell function in patients at risk.