Although such IFN-γ responses could theoretically be mediated by other cells (for example, natural killer or CD8 T cells)43, our previous observations with plant-derived influenza vaccine candidates29–32,45–47 and recent experience with an AS03-adjuvanted S protein vaccine in non-human primates48 suggest that this production is most likely attributable to CD4+ T cells. Here, CD4 is linked to influenza.