Writing in the journal Expert Review of Vaccines, David B. Weiner, Chair, Gene Therapy and Vaccine Program, CAMB University of Pennsylvania, and Abhishek Satishchandran review a book on Plasmids published by Caister Academic Press:

"Dr. George Lipps of the University of Bayreuth in Germany has assembled a clear and concise text which will be considered an important reference to plasmid researchers at the graduate level and beyond. The book has been fluently divided into 4 major topics of discussion, each further subdivided into increasing complex subcategories. The theme of cloning and expression vectors is maintained through the first three chapters. Appropriately, the basics plasmid biology are graciously provided in a series of lists and tables, easy enough for the most novice of graduate students ... This volume represents an important reference to bridge knowledge gaps and provide useful descriptions rooted in the fundamentals of plasmid biology. Dr. Lipps has done an excellent job in creating a useful, informative, and focused volume that should grace the shelf of many a molecular biologist well into the future."

Further reading: Plasmids: Current Research and Future Trends

Labels: plasmid, plasmids

Many attempts to construct different expression vector systems for mammalian cells have been made in recent years. These vector systems can be categorized in terms of vector administration, mechanisms of vector replication and mechanisms to achieve nuclear persistence of the vectors.

Episomal vectors, either based on viral plasmid replicons or on chromosomal elements, are invaluable tools for basic and applied science. The biochemistry and cell cycle dependent regulation of mammalian DNA replication has been extensively studied using SV40-based vectors and more recently, EBV-based vectors have been used to isolate putative mammalian origins of replication. The non-viral vectors whose functioning depends on the insertion of a chromosomal S/MAR sequence represent a minimal system to study the epigenetic regulation of mammalian DNA replication and the relevance of global functional nuclear architecture. The construction of mammalian artificial chromosomes has had a considerable impact on our understanding of the functional elements of the eukaryotic chromosome, telomeres, replication origins and centromeres. Similarly, the analysis of the biochemistry and regulation of transcription was greatly facilitated by the use of episomal vectors. These constructs will find even further applications for the analysis of basic biological phenomena, such as protein-protein interactions, signal transduction pathways, cell movements and many more.

Long term expression of transgenes in the absence of selection has been reported for EBV-based vectors, S/MAR-based vectors and mammalian artificial chromosomes, making these vectors attractive systems for the production of pharmaceutical relevant proteins in mammalian cells. Mammalian artificial chromosomes and S/MAR-based vectors have been successfully used for the genetic modification of mammalian organisms, such as mice and pigs, and have proven to be significantly more efficient than currently used integrating vectors.

Episomal vectors and especially vectors based on chromosomal elements may represent alternatives to the currently used viral vectors for genetic therapy. The major risks associated with virus-based vectors involve problems associated with insertional mutagenesis, imunogenicity and cytotoxicity. These problems were highlighted by the first therapy related fatality, in which death was caused by an inflammatory reaction that was attributed to the use of adenoviral vectors. Insertional mutagenesis events related to the use of integrating vectors have been reported for retroviral as well as AAV vectors. Since episomal vectors based exclusively on chromosomal elements do not need any virus-encoded protein for their function and furthermore do not integrate into the host cell genome, they should avoid the major safety risks that have been associated with virus-based vectors. Their use has been demonstrated in vitro and some have been propagated in animal systems. Their present main limitation is their low transfection efficiency compared to systems based on replication deficient viruses. However, recent success in the construction of non-viral episomal vectors and steady improvement of DNA transfection techniques makes it likely that these limitations can be overcome in the near future, so that optimized episomal vectors will be available for clinical trials.

fromBaiker et al in Chapter 3. Plasmids: Current Research and Future Trends

Further reading: Plasmids: Current Research and Future Trends

Labels: expression, plasmid, plasmids, vector