Studies in mice demonstrated that, similar to the live influenza vaccine, adenovirus-based vaccine and DNA immunization induced CTL cross-protective immune response against infection with multiple influenza A subtypes [94] [95] [96] [97] [98] . The variable rate of cross-reactive CTL response was achieved also by using adjuvants, or various formulations and delivery systems with experimental influenza vaccines in preclinical animal studies [reviewed in [99] ]. It was shown that application of virus-like particles or virosomal vaccines could be successfully used for efficient delivery of multiple CTL epitopes to the target cells resulting in induction of CTL response [100, 101] .