The CEF peptide pool stimulates CD8+ T cells to produce preferentially IFN-γ and is recommended as a positive control in IFN-γ ELISpot and FluoroSpot assays using human PBMC. The CEF peptide pool consists of 23 MHC class I-restricted viral peptides from human CMV, EBV and influenza virus. It has been shown to induce IFN-γ responses in almost 90% of all Caucasians.