The human Ad is classified into six subgroups, ranging from A to F [2]. Most Ad serotypes belong to subgroups A, C, D, E, and F and use the coxsackievirus and adenovirus receptor (CAR) as a cellular receptor [3]. Ad serum type 5 (Ad5, subgroup C) has well-defined biological properties and has been widely used GDC-0199 ic50 as a vector in gene therapy and vaccine development. Results from human and non-human primate

studies suggest that deficient Ad vectors induce antigen-specific cell-mediated immune responses in vivo [4], [5] and [6]. The Ad5 vector is of particular interest since its safety has been proven in clinical trials; it is of high quality; and it can be produced easily [4], [5], [6], [7] and [8]. Unfortunately, a recent large-scale phase IIb clinical trial showed that subjects vaccinated 3 times with the Ad5 vector expressing HIV Gag, Pol, and Nef were not protected against HIV infection. Vaccination did not reduce the HIV viral load or improve the CD4

T cell count after HIV infection occurred in the trial participants [9]. Furthermore, a two-fold increase in HIV acquisition was observed among ALK inhibitor clinical trial vaccinated recipients, along with increased Ad5-neutralizing antibody titers, when compared with the increase in placebo recipients. This probably occurred because vaccination provides a more conducive environment for HIV replication via the activation of dendritic cells by the Ad5–antibody complex [10]. Another viral vector used in this study was the MVA virus. MVA is derived from

live vaccinia virus by more than 500 passages in chicken embryo fibroblast cells. It loses 15% of the genome compared to its parent Calpain vaccinia virus, leading to severe restriction in replication and virulence processes [11] and [12]. In humans, MVA is a replication-deficient virus. MVA has been safely administered to approximately 120,000 individuals as smallpox vaccine [13], and it has been clinically tested as a vaccine vector against other diseases such as HIV and cancer [14]. Since no single viral vector has been able to protect against HIV infection in clinical trials, the prime-boost regimen using different vaccines has been explored in animal models and has been found to elicit much higher immune response than a single vaccine [6], [15], [16], [17] and [18]. However, the effect of the two viral vectors when administered simultaneously is unclear because both the Ad virus and MVA virus are double-stranded, and their viral protein and genome DNA are capable of inducing innate immune responses [19], [20], [21], [22], [23] and [24], resulting in type I interferon (IFN) secretion following activation of adaptive immunity. On the other hand, type I interferon has innate antiviral activity against a variety of viruses. In this study, we co-administered Ad and MVA vectors encoding the HIV-1 gp160 Env gene or reporter genes to mice.