Construction of a Multi-Functional Helper-Dependent Adenovirus Based System for Cancer Gene Therapy

Adenovirus holds great promise as a gene delivery system; it can hold large amounts of exogenous DNA andcan be chemically and genetically modified to improve targeting to specific cells and tissues. A recombinantadenovirus construct expressing p53 is currently in clinical use as a cancer therapy in China. However, the useof adenovirus constructs in therapy is limited due to patients' strong immune response against these viruses andtheir gene products. To overcome this problem helper-dependent adenoviruses which do not express any viralgene products have been developed. Because the helper-dependent viruses do not express any viral gene products,a helper virus is required for their replication and encapsidation into infectious particles. This manuscriptdescribes the construction of a prototype helper-dependent adenovirus system built such that it can be easilymodified. The helper-dependent virus described here is built of a series of four cassettes, each with its ownfunction. Furthermore, each individual cassette can be removed and replaced with a cassette with a differentfunction. In this way, different helper-dependent viruses can be readily created. This type of system could bevery useful in cancer therapy: For example, libraries of different cassettes could be maintained, allowing rapidassembly of constructs able to provide therapy for individual tumor types.