Recent progress in adenovirus vectors: focusing on VA-deleted AdV

Abstract

First-generation adenovirus vectors (FG-AdVs) are widely used because transduction efficiency of the vectors is very high. However, severe immune responses especially to the liver have been a serious problem of this vector. We succeeded to identify a viral protein that cause the immune responses and reported ''low-inflammatory AdVs'' that mostly solve this problem. However, to develop the ultimate form of this vector, it is necessary to remove virus-associated RNA (VA RNA) genes from the AdV vector genome. VA RNAs are transcribed by polymerase III; they are not essential for viral growth but have important roles to make appropriate circumstances for this virus. Large amount of VA RNAs are required in the late phase to support viral growth. Hence it is difficult to establish 293 cell lines that can support replication of AdVs lacking VA RNA genes (VA-deleted AdVs) supplying sufficient amount of VA RNA in trans. Recently we have developed a method for efficient production of VA-deleted AdVs and succeeded to obtain a high titer of VA-deleted AdVs. Then we construct VA-deleted AdVs expressing shRNA that knockdown the replication of hepatitis C virus (HCV). In fact, VA-deleted AdVs expressing these shRNAs suppressed HCV replication more effectively than conventional FG-AdV. Therefore, we showed that VA RNAs expressed from FG-AdVs probably compete with shRNA in the maturation pathway and reduce the effect of shRNAs. We think that VA-deleted AdV may substitute for current FG-AdVs and become a standard AdV.