Induction of type I interferon by adenovirus-encoded small RNAs

Transduction with replication-incompetent recombinant adenovirus (Ad) vectors results in a rapid activation of innate immune responses, such as inflammatory cytokine production and subsequent tissue damage. The precise mechanisms of the innate immune responses induced by Ad vectors remain to be clarified. Possible components of Ad vectors that activate innate immune responses are the capsid protein, the viral genome (DNA), and viral transcripts. In the present study, we demonstrate that virus-associated RNAs (VA-RNAs), which are small RNAs transcribed by RNA polymerase III, induce the production of type I IFN (IFN-alpha and IFN-beta), but they do not induce the production of inflammatory cytokines (IL-6 and IL-12), in mouse embryonic fibroblasts (MEFs) and granulocyte-macrophage colony-stimulating factor-generated bone marrow-derived dendritic cells (GM-DCs). We also show that IFN-beta promoter stimulator-1 is involved in VA-RNA-dependent IFN-beta production in MEFs and is partially involved in type I IFN production in GM-DCs. This study provides important insight into the mechanisms of Ad vector-triggered innate immune responses, which may lead to more advanced and rational Ad vector designs for gene therapies and vaccine applications.