De Novo Design of Tissue-Specific Regulatory Elements Results in Robust Transduction in Heart and Liver: Implications for Cardiovascular Disease and Hemophilia

The therapeutic index of gene delivery vectors can be significantly improved by targeting gene delivery at the level of transduction or transcription. Transductional targeting can be achieved by modifying the vector capsid or envelope in order to deliver the therapeutic gene into the appropriate target cells. We have previously demonstrated that AAV9 vectors have an exquisite cardiac tropism that can be exploited to develop improved gene therapy approaches for cardiovascular disease. In addition, transductional targeting to the liver could be achieved using either AAV8 or AAV9 serotypes. To achieve transcriptional targeting we validated a novel data-mining algorithm, that allowed us to identify specific combinations of evolutionary conserved cardiac-specific or liver-specific transcription factor binding sites (TFBS). These TFBS combinations represent common denominators among highly expressed cardiac-specific or liver-specific genes, respectively. Consequently, unprecedented high levels of cardiac or liver-specific gene expression could be achieved using AAV vectors containing these de novo designed tissue-specific expression cassettes. In particular, a robust 100-fold robust enhancement in cardiac expression could be achieved following incorporation of these TFBS combinations into AAV9 vectors, while retaining high cardiac selectivity. Similarly, for liver-directed gene therapy, incorporation of these elements into an AAV vector resulted in physiologic or supra-physiologic clotting factor VIII (FVIII) or factor IX (FIX) expression levels, even at very low AAV vector doses. This was confirmed using non-viral PiggyBac transposon-based vectors. The superior performance of these liver-specific elements was subsequently validated following AAV transduction in non-human primates (NHP) resulting in FIX expression levels up to 40% of normal levels. The vectors were well tolerated in the recipient NHPs. This study underscores the potential of this novel bio-informatics algorithm for designing more efficacious and safer viral and non-viral gene therapy vectors for cardiac or hepatic gene delivery with important implications for gene therapy of cardiovascular disease, hemophilia and liver-borne disorder.

Publication year:2012