Gene transfer mediated by Herpes simplex virus (HSV-1) amplicon vectors
One of the greatest challenges to gene therapy is the targeting of gene delivery selectively to the sites of disease and regulation of transgene expression without adverse effects. Ultimately, the successful realization of these goals is dependent upon improvements in vector design. Over the years, viral vector design has progressed from various types of replication-defective viral mutants to replication-conditioned viruses and more recently to “gutted” and hybrid vectors, which have, respectively, eliminated expression of toxic viral genes and incorporated desired elements of different viruses so as to increase the efficacy of gene delivery in vivo. The major focus in the laboratory is to study both viral and cellular elements that may affect the level and regulation of transgene expression mediated by the HSV-1 amplicon viral vectors and the hybrid viruses (HSV/AAV amplicon viral vectors). A packaged amplicon is like a “gutless’ HSV, into which plasmid-like DNA rather than the actual viral genome is assembled into the viral particle. It has the following advantages over other vectors (i) they are easy to manipulate (ii) large transgene size up to 150 Kb (iii) one viral particle can deliver multiple copies of a transgene and (iv) the HSV-1 amplicon vectors are packaged using a helper-virus-free packaging system, thus, all the wild-type viral gene and their associated cytotoxicity are precluded. Viral elements that contribute to enhance short-term levels of transgene expression have been studied. Current work is focused on the incorporation of cell cycle-specific regulatory elements into the HSV-1 amplicon vectors. As hyperproliferation is a characteristic of malignant tumor cells, the strategy of transducing the resected region with these vectors that can be “switched on” once the residual dormant tumor cells start to proliferate, would represent potentially interesting tools for human cancer gene therapy. In addition, transcriptional promoters that are specifically functional in single tissues or are active in specific disease states, or are induced by tumor specific conditions are included to further enhance the level of selective targeting. We are also using genomic approaches to identify important genes and proteins involved in these cell-cycle dependent transcriptional regulations.
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