Further Reduction in Adenovirus Vector-Mediated Liver Transduction without Largely Affecting Transgene Expression in Target Organ by Exploiting MicroRNA-Mediated Regulation and the Cre-loxP Recombination System

In order to detarget undesirable transduction in the liver by an adenovirus (Ad) vector, we previously demonstrated that insertion of sequences perfectly complementary to liver-specific miR-122a into the 3′-untranslated region (UTR) of transgene specifically reduced the transgene expression in the liver by approximately 100-fold; however, a certain level of residual transgene expression was still found in the liver. In order to further suppress the hepatic transduction, we developed a two-Ad vector system that uses the microRNA (miRNA)-regulated transgene expression system and the Cre-loxP recombination system, i.e., insertion of miR-122a target sequences and loxP sites into the transgene expression cassette and coadministration of a Cre recombinase-expressing Ad vector. In addition, to maintain as much as possible the transgene expression in the spleen, which is the target organ of this study, spleen-specific miR-142-3p target sequences were inserted into the 3′-UTR of the Cre recombinase gene to suppres...