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Pre-existing anti-adenovirus (Ad) neutralizing antibodies (AdNAbs) are a major barrier in clinical gene therapy using Ad vectors and oncolytic Ads; however, it has not been fully elucidated which Ad capsid protein-specific antibodies are involved in AdNAb-mediated inhibition of Ad infection in vivo. In this study, mice possessing antibodies specific for each Ad capsid protein were prepared by intramuscular electroporation of each Ad capsid protein-expressing plasmid. Ad vector-mediated hepatic transduction was efficiently inhibited by more than 100-fold in mice immunized with a fiber protein-expressing plasmid or a penton base-expressing plasmid. An Ad vector pre-coated with FX before administration mediated more than 100-fold lower transduction efficiencies in the liver of warfarinized mice immunized with a fiber protein-expressing plasmid or a penton base-expressing plasmid, compared with those in the liver of warfarinized non-immunized mice. These data suggest that anti-fiber protein and anti-penton base antibodies bind to an Ad vector even though FX has already bound to the hexon, and inhibit Ad vector-mediated transduction. This study provides important clues for the development of a novel Ad vector that can circumvent inhibition with AdNAbs.

Adenovirus vectors (Adv) elicit innate immune responses via several pattern-recognition receptors. Although it has been suggested that various Adv-induced mechanisms play important roles in the induction of innate immunity in vitro , the impacts of these mechanisms in vivo remain unclear. Viral nucleic acids elicit innate immune responses through the recognition of cytosolic nucleic acid sensors and transduce intracellular signals to TANK-binding kinase (TBK) 1. In this study, to determine the impacts of viral nucleic acids on innate immune responses in vivo , we administered transgene-expressing Adv to Tbk1 -deficient mice. The systemic Adv administration failed to induce type I interferons (type I IFNs) in the spleen, but not the liver, of Tbk1 -deficient mice, resulting in the increase of transgene-expressing cells in the spleen, but not the liver. Moreover, Adv failed to induce type I IFNs in the bone-marrow-derived dendritic cells, but not the mouse embryonic fibroblasts, from Tbk1 -deficient mice in vitro . These results support the idea that Adv elicit innate immunity in immune cells and non-immune cells in a TBK1-dependent and TBK1-independent manner, respectively.

Few of the vaccines in current use can induce antigen- (Ag-) specific immunity in both mucosal and systemic compartments. Hence, the development of vaccines that realize both mucosal and systemic protection against various pathogens is a high priority in global health. Recently, it has been reported that intramuscular (i.m.) vaccination of an adenovirus vector (Adv) can induce Ag-specific cytotoxic T lymphocytes (CTLs) in both systemic and gut mucosal compartments. We previously revealed that type I IFN signaling is required for the induction of gut mucosal CTLs, not systemic CTLs. However, the molecular mechanism via type I IFN signaling is largely unknown. Here, we report that type I IFN signaling following i.m. Adv vaccination is required for the expression of type I IFN in the inguinal lymph nodes (iLNs), which are the draining lymph nodes of the administration site. We also showed that the type I IFN signaling is indispensable for the early activation of CTLs in iLNs. These data suggested that type I IFN signaling has an important role in the translation of systemic innate immune response into mucosal adaptive immunity by amplifying the innate immune signaling and activating CTLs in the iLN.

Various methods have been developed to facilitate the generation of recombinant adenovirus vectors. Two commercially available methods employing bacterial systems have been most widely used: the homologous recombination method in bacteria and an in vitro ligation method based on simple routine plasmid construction. These methods can insert foreign genes not only into the E1 deletion region but also into the E3 deletion region, thereby allowing the construction of a binary transgene expression system in which heterologous genes can be inserted into both E1 and E3 regions. By modifying these methods, capsid-mutant adenovirus vectors and small-interfering RNA-expressing adenovirus vectors can be also constructed in order to control vector tropism and to induce the knockdown of gene expression, respectively. In this paper, we focus on the advances made so far in the methods for generating recombinant adenovirus vectors.