First of all, adenoviruses are relatively susceptible for genetic modifications and can be easily produced in high titers. After transduction of the cells, adenoviral genome is not integrated into the host DNA and stays in the episomal form. As a result, the risk of the possible activation of the cellular oncogenes is minimal. Adenovirusbased vaccines proved to elicit a vigorous and sustained humoral and T cell responses to the incorporated antigen that is considered to be crucial in clearance of persistent viral diseases [127, [139] [140] [141] . The benefit of adenoviral vectors as a vaccine carrier is not only limited to stable delivery of proteins of interest. Several findings on additional immunostimulatory effects, for example, induction of the innate immune response, that originate from the nature of adenoviruses itself, may enhance the vaccine efficacy. Capsid of adenoviruses demonstrates immunostimulatory properties, that is why the coadministration of the adjuvant is usually unnecessary. Those vectors can directly transduce DCs causing their maturation and upregulation of MHC and costimulatory molecules on their surface, thus lead to enhanced antigen presentation. Moreover, it was shown that AdV-transduced DCs are secreting antiviral cytokines, such as IFNα, TNFα, and IL-6 [142] . Interleukin-6 is one of the most important factors that suppress the function of the regulatory T cells [143, 144] . Nevertheless, modified adenoviruses apart from the abovementioned advantages have one serious limitation. Thus far, vectors that were comprehensively examined as the vaccines have been based on the human adenovirus serotype 5 (Ad5) [127] . This serotype is the most common in the human population. Anti-Ad5 neutralizing antibodies are detectable in 45%-90% of adults [145] . The preexisting immunity directed against Ad5 is considered as a main reason of failure in the phase I clinical trial of a protective HIV-1 vaccine. STEP study guided by Merck pharmaceutical concern, based on 3-dose regimen of a trivalent Ad5 vaccine, suggested that the immunization might increase the risk of HIV-1 infection in the subjects with high neutralizing anti-Ad5 titers [146] [147] [148] . Moreover, even single immunization may induce immunity to the vector in seronegative individuals.