ABSTRACT
As of November 2021, the viral pathogen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing the coronavirus disease 2019 (COVID-19), has infected more than 250 million individuals worldwide and killed over 5 million people. In addition to known risk groups, also cancer patients are at increased risk for severe disease progression. Therefore, understanding the nature of the accompanying immune response is essential, especially the role of T cells for successful virus defense but also during immunopathology leading to severe disease outcomes. Furthermore, as neutralizing antibodies are reported to decay within months post infection or vaccination or are even absent due to cancer treatment, SARS-CoV-2-specific T cell persistence is discussed as an indicator of long-term protective immunity. Especially, in immunocompromised cancer patients, levels of SARS-CoV-2-specifc antibodies may not be efficiently detected. Therefore, we developed a rapid and easy flow cytometric assay for the analysis of SARS-CoV-2-reactive CD4+ and CD8+ T cells directly from whole blood.