ELISpot
The T-cell mediated immune response against the SARS-CoV-2 RBD was assessed after the in vitro peptide stimulation of peripheral blood mononuclear cells (PBMC), followed by IFN-γ and IL-4 enzyme-linked immune absorbent spot (IFN-γ (BD Biosciences) and IL-4 (MabTech) ELISpot). A peptide pool of overlapping SARS-CoV-2 peptides, encompassing the SARS-CoV-2 spike RBD covering the Gamma variant was used in the assay (JPT Peptide Technologies GmbH, Germany). ElisPot Plates were scanned on an ImmunoSpot reader (Cellular Technology Ltd.). Specific spots were counted using the ImmunoSpot 5.0 software.