Inside this Month
Authors: Robert Frederickson
Journal: Molecular Therapy (2002)

The study of recombinant AAV vectors in animal models and clinical trials has been hampered by the difficulty in producing highly pure viral stocks in large quantities. Current procedures are difficult to scale up, often result in impurities, and tend to be isotype-specific, making vector comparison problematic. On page 678, Nicole Brument et al. present a new method of vector purification based on ion-exchange chromatography that is both scalable and applicable to AAV serotypes 2 and 5. An attractive alternative to repeated injections of therapeutic proteins for clinical applications in the use of muscle as an in vivo bioreactor. Such an approach requires a gene delivery system that permits long-term controlled expression of the therapeutic gene. On page 653, Roscilli et al. describe the creation of an artificial tamoxifen-inducible human transcription factor, HEA-3, that they use to drive expression of therapeutic reporter genes in cultured cells and mouse muscle. The dynamic range of the artificial expression cassette was quite high, showing a 100-fold induction in electroporated muscle in immunocompetent mice–with very low levels of basal expression. The use of adenoviruses as therapeutic agents to kill cancer cells in vivo has recently been tested in clinical trials with some success. More basic research is clearly necessary to understand the way these viruses lead to tumor cell death, however, necessitating the development of model systems in vivo that can mimic the biology of native tumors in humans. On page 609 of this issue, a multinational group led by M. Lamfers in Amsterdam examines the use of organotypic multicellular spheroids–small masses of tumor cells growing in suspension–for just this purpose. Genetic modification of hematopoietic stem cells (HSCs) is an attractive approach for the treatment of diverse blood disorders. Lentiviral vectors are promising tools for the stable genetic modification of HSCs, but there is much room for improvement. Polyclonal engraftment of genetically modified cells requires efficient transduction of the graft, particularly of primitive cells with self-renewal and multi-lineage repopulation capacity. In the first of three reports in this issue on the subject, Luigi Naldini and colleagues demonstrate on p. 615 that such primitive human HSCs are in fact efficiently transduced by a human immunodeficiency virus (HIV)-based lentiviral vector, leading to multi-copy gene transfer. They achieved polyclonal engraftment and long-term repopulation of the cells in both primary and secondary mouse recipients of the graft. On page 673, Anne Dubart-Kupperschmitt and co-workers present an improved protocol for HSC transduction, achieving > 90% transduction of cells from cord blood and > 80% transduction of cells from bone marrow. Although both of the previous studies used vectors based on HIV, some workers are developing vectors based on the feline immunodeficiency virus (FIV), because of safety concerns. Interestingly, on page 645, work from Gay Crooks’ lab demonstrates that expression of transgenes from FIV-based vectors appears to be impaired in HSCs relative to the expression seen with an HIV-based vector. As the transduction efficiency of the different vectors was similar, the results suggest the presence of an element in the FIV backbone that inhibits expression in human HSCs.