IL-2 and IFN-γ are biomarkers of SARS-CoV-2 specific cellular response in whole blood stimulation assays

Objectives: A proper description of the immune response to SARS-CoV-2 will be critical for the assessment of protection elicited after both infection and vaccination. Uncoupled T and B cell responses have been described in acute and convalescent patients and exposed individuals. We aimed to assess the potential usefulness of whole blood stimulation assays to identify functional cellular immune responses to SARS-CoV-2. Methods: Blood from COVID-19 recovered individuals (5 months after infection) and negative subjects was stimulated for 24 hours with HLA predicted peptide megapools of the Spike and Nucleoprotein, or the mixture of them. After stimulation, cytokines were quantified using a beads-based multiplex assay. Results: Interleukin-2 and IFN-γ were found to be specific biomarkers of SARS-CoV-2 cellular response. Using the Spike and Nucleoprotein mixture, 91.3% of COVID-19 recovered individuals presented an IL-2 stimulation index over the cut-off, while 82.6% showed IFN-γ. All the negative individuals presented an IL-2 response under the cut-off, while 5.3% of these subjects presented positive IFN-γ stimulation indexes. Moreover, IL-2 production correlated with IgG levels for Spike 1, RBD, and Nucleocapsid. Conclusion: We demonstrate the potential of whole blood stimulation assays and the quantification of IL-2 and IFN-γ for the analysis of SARS-CoV-2 functional cellular responses.