Spike is the most recognized antigen in the whole-blood platform in both acute and convalescent COVID-19 patients

Aiello, Alessandra; Fard, Saeid Najafi; Petruccioli, Elisa; Petrone, Linda; Vanini, Valentina; Farroni, Chiara; Cuzzi, Gilda; Navarra, Assunta; Gualano, Gina; Mosti, Silvia; Pierelli, Luca; Nicastri, Emanuele; Goletti, Delia

OBJECTIVES: To identify the best experimental approach to detect a SARS-CoV-2-specific T cell response using a whole-blood platform. METHODS: Whole-blood from 56 COVID-19 and 23 “NO-COVID-19” individuals were overnight stimulated with different concentrations (0.1 or 1 µg/mL) of SARS-CoV-2 PepTivator® Peptide Pools, including spike (pool S), nucleocapsid (pool N), membrane (pool M), and a MegaPool (MP) of these three peptide pools. ELISA was used to analyse IFN-γ levels. RESULTS: IFN-γ-response to every SARS-CoV-2 peptide pool was significantly increased in COVID-19 patients compared with “NO-COVID-19” individuals. Pool S and MegaPool were the most potent immunogenic stimuli (median: 0.51, IQR: 0.14-2.17; and median: 1.18, IQR: 0.27-4.72, respectively) compared to pools N and M (median: 0.22, IQR: 0.032-1.26; and median: 0.22, IQR: 0.01-0.71, respectively). Whole-blood test based on pool S and MegaPool showed a good sensitivity of 77% and a high specificity of 96%. IFN-γ-response was mediated by both CD4(+) and CD8(+) T cells, and detected independently of clinical parameters in both hospitalized and recovered patients. CONCLUSIONS: This easy-to-use assay for detecting SARS-CoV-2-specific T cell response may be implemented in clinical laboratories as a powerful diagnostic tool.