Strong ubiquitous micro-promoters for recombinant adeno-associated viral vectors

Significant progress has been made in developing recombinant adeno-associated virus (rAAV) for clinical gene therapy. While rAAV is a versatile gene delivery platform, its packaging limit of 4.7 kb limits the diseases it can target. Here, we report two unusually small promoters that enable the expression of larger transgenes than standard promoters. These micro-promoters are only 84 (MP-84) and 135 bp (MP-135) in size but have activity in most cells and tissues comparable to the CAG promoter, the strongest ubiquitous promoter to date. MP-84- and MP-135-based rAAV constructs displayed robust activity in cultured cells from the three different germ-layer lineages. In addition, reporter gene expression was documented in human primary hepatocytes and pancreatic islets and in multiple mouse tissues in vivo, including brain and skeletal muscle. MP-84 and MP-135 will enable the therapeutic expression of transgenes currently too large for rAAV vectors.