Minicircle DNA vectors consisting of a circular expression cassette devoid of the bacterial plasmid DNA backbone provides several advantages including sustained transgene expression in quiescent cells/tissues. Their use has been limited by labor-intensive production. We report on a strategy for making multiple genetic modifications in E.coli to construct a producer strain that stably expresses a set of inducible minicircle-assembly enzymes, the øC31-integrase and I-SceI homing-endonuclease. This bacterial strain is capable of producing highly purified minicircle yields in the same time frame as routine plasmid DNA. It is now feasible for minicircle DNA vectors to replace routine plasmids in mammalian transgene expression studies.

The short duration of transgene expression remains a major obstacle for the implementation of nonviral DNA vectors in clinical gene therapy trials. Here, we demonstrate stable, long-term transgene expression in vivo by transfecting a linear DNA expression cassette (LDNA) into mouse liver. Interestingly, despite similar quantities and cellular distribution of injected DNAs in their livers, mice receiving LDNA encoding human alpha1-antitrypsin (hAAT) expressed approximately 10- to 100-fold more serum hAAT than mice injected with closed circular (cc) DNA for a period of 9 months (length of study). Furthermore, when a linear human factor IX expression cassette was delivered to factor IX-deficient mice, sustained serum concentrations of more than 4 microg/ml (80% of normal) of the human clotting factor and correction of the bleeding diathesis were obtained. Southern blot analyses indicate that, unlike ccDNA, LDNA rapidly formed large, unintegrated concatemers in vivo, suggesting that transgene persistence from plasmid-based vectors was influenced by the structure of the vector in transfected cells. No differences in transgene expression or DNA molecular structures were observed when AAV ITRs were included to flank the hAAT expression cassette in both ccDNA- and LDNA-treated animals. Linear DNA transfection provides an approach for achieving long-term expression of a transgene in vivo.

One of the major problems influencing the therapeutic efficacy of stem cell therapy is the poor cell survival following transplantation. This is partly attributed to insufficient resistance of transplanted stem cells to oxidative and inflammatory stresses at the injured sites. In the current study, we demonstrated the pivotal role of antioxidant levels in human umbilical cord mesenchymal stem cells (hUCMSCs) dynamic in vitro anti-stress abilities against lipopolysaccharide (LPS)/H2O2 intoxication and in vivo therapeutic efficacy in a murine acute liver failure model induced by D-galactosamine/LPS (Gal/LPS) by either reducing the antioxidant levels with diethyl maleate (DEM) or increasing antioxidant levels with edaravone. Both the anti- and pro-oxidant treatments dramatically influenced the survival, apoptosis, and reactive oxygen species (ROS) production of hUCMSCs through the MAPK-PKC-Nrf2 pathway in vitro. When compared with untreated and DEM-treated cells, edaravone-treated hUCMSCs rescued NOD/SCID mice from Gal/LPS-induced death, significantly improved hepatic functions and promoted host liver regeneration. These effects were probably from increased stem cell homing, promoted proliferation, decreased apoptosis and enhanced secretion of hepatocyte growth factor (HGF) under hepatic stress environment. In conclusion, elevating levels of antioxidants in hUCMSCs with edaravone can significantly influence their hepatic tissue repair capacity.