Influenza-induced IL-2+ TNF-α+ (IFN-γ−) CD4 T cells have been described as uncommitted Th1-primed precursor (Thpp) cells preferentially induced by newly encountered antigens, whereas common influenza epitope-specific CD4 T cells induced by multiple booster immunizations express IFN-γ after infections [46, 47]. This evidence concerns the gene CD4 and influenza.