CD4 and infection: When we analyzed the immune response to our vaccination regimens one week before the FV challenge infection, we confirmed the strong induction of GagL85–93-specific CD8+ T cells by our Ad-based vaccine (Fig. 6a), and a slight induction of Env123–144-specific CD4+ T cells (Fig. 6b); interestingly, there were no significant levels of either GagL85–93-specific CD8+ or Env123–144-specific CD4+ T cell responses in F-MuLV-N immunized mice.