Indeed, the relatively high numbers of CD8+ T cells specific for the influenza nucleoprotein immunodominant NP147 epitope measured in the vaccinated mice suggest that the WSN/TatΔ51–59 virus was able to replicate to some extent in vivo. Although no productive virus infection was detected with the inoculum dose used, WSN/Tat virus was nevertheless able to elicit Tat-specific antibodies after a single mucosal immunization of BALB/c mice. This evidence concerns the gene TAT and viral infectious disease.