CD4 and infection: Conversely, it is also possible that the earlier and stronger Tat-specific CD4+ and CD8+ T-cell responses observed in IL-7-treated animals resulted from a more robust antigenic stimulation due to the higher amount of virus detected in these animals at day 4 post-infection; indeed, strong CD8+ T-cell responses were also detected in IL-15-treated animals, although they were incapable of controlling viral replication [33].