In addition to the desired gene, successful gene therapy requires an appropriate vehicle or vector for introduction of the transgene into the cell. For long term transformation of the host cell or organism, placing the transgene into a context in which it is replicated in synchrony with the cell genome is necessary. The human parvovirus, adeno-associated virus. (which requires adenovirus to multiply), has been used as a vector, because it has never been identified as a human pathogen, even though about 90% of adults have antibodies to the virus. Adeno-associated virus (AAV) integrates into the human genome at a specific site on chromosome 19 and can integrate its DNA even in non dividing cells (albeit at a lower frequency). Current AAV vectors have certain limitations: 1) they are difficult to produce in high concentration; 2) they have a limited capacity for the size of the transgene; 3) as currently made, they do not integrate in a site specific manner. Adenovirus (Ad) has also been used as a vector. Because Ad vectors do not integrate or replicate autonomously within the cell, they are able to transform only on a transient basis. However, it is relatively easy to produce large amounts of the Ad vector and the carrying capacity for the transgene is almost twice that of current AAV vectors. The goal of this project is to construct a hybrid virus vector between AAV and Ad which would have the desirable properties of both. Large amounts of the vector could be produced and the transgene could be integrated into a specific site in chromosome 19 for permanent expression. To create the hybrid vector the transgene, flanked by critical AAV terminal sequences, and the AAV rep gene required for site specific integration would be incorporated at separate sites into a backbone of Ad DNA. The vector virus will be tested both in cell culture in order to characterize its function at the molecular level and in animal models to assess host response, clearance and ability to transform in a long term manner.
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