MicroRNA-regulated viral vectors for gene therapy

Abstract

Safe and effective gene therapy approaches require targeted tissue-specific transfer of a therapeutic transgene. Besides traditional approaches, such as transcriptional and transductional targeting, microRNA-dependent post-transcriptional suppression of transgene expression has been emerging as powerful new technology to increase the specificity of vector-mediated transgene expression. MicroRNAs are small non-coding RNAs and often expressed in a tissue-, lineage-, activation- or differentiation-specific pattern. They typically regulate gene expression by binding to imperfectly complementary sequences in the 3’ untranslated region (UTR) of the mRNA. To control exogenous transgene expression, tandem repeats of artificial microRNA target sites are usually incorporated into the 3’ UTR of the transgene expression cassette, leading to subsequent degradation of transgene mRNA in cells expressing the corresponding microRNA. This targeting strategy, first shown for lentiviral vectors in antigen presenting cells, has now been used for tissue-specific expression of vector-encoded therapeutic transgenes, to reduce immune response against the transgene, to control virus tropism for oncolytic virotherapy, to increase safety of live attenuated virus vaccines and to identify and select cell subsets for pluripotent stem cell therapies, respectively. This review provides an introduction into the technical mechanism underlying microRNA-regulation, highlights new developments in this field and gives an overview of applications of microRNA-regulated viral vectors for cardiac, suicide gene cancer and hematopoietic stem cell therapy, as well as for treatment of neurological and eye diseases.

Keywords: MicroRNA; MicroRNA regulation; MicroRNA target sites; Viral vectors; Adeno-associated virus; RNA interference; Gene therapy; Vector targeting

Core tip: Post-transcriptional microRNA-induced suppression of gene expression is a simple new, highly efficient technology to restrict transgene expression to a specific tissue. It is based on the insertion of a target sequence for a cell-specifically expressed microRNA, typically into the 3’ untranslated region of a transgene expression cassette. MicroRNA-induced regulation can result in an up to 100-fold reduction of transgene expression in tissues where expression is not desired. This targeting strategy can be used in combination with other targeting strategies to further improve vector specificity for gene therapeutic approaches.