Introduction to Adenovirus and Recombinant Adenovirus

Biology of Wild Type Human Adenovirus (type 5)

Wild-type adenoviruses, including human adenovirus type 5, are associated with a number of mild disorders, such as respiratory infections in the elderly or children.  The entire adenovirus genome is a linear, double-stranded DNA of approximately 36Kb. There approximately two phases of adenovirus transcription, namely early and late phases, which occur before and after replication. The early-transcribed regions are E1, E2, E3 and E4.

The E1 gene products, including E1A and E1B, are involved in replication of the virus. The E2 proteins provide the machinery for viral DNA replication and transcription of late genes. Most of the E3 proteins are involved in modulating the immune response of infected cells. The E4 gene products are involved in the metabolism of virus messenger RNA and provide functions that promote virus DNA replication and shut-off of host protein synthesis.

The prime receptor for human adenoviruses is the Coxsackie/Adenovirus Receptor (CAR). Once inside the cell, the virus translocates to the nuclear pore complex, where the viral DNA is released into the nucleus. Transcription and replication take place in the nucleus of the infected cell.

Recombinant Adenovirus (DE1/E3)

To ensure replication deficiency of the virus, the E1 region is deleted allowing it to safely be used as a gene delivery tool. To accommodate larger recombinant genes (up to 8 Kb), 1st generation adenoviruses are both E1 and E3 deleted (E1/E3), since the E3 region is not essential for in vitro viral growth.
The adenovirus vector is able to deliver genes with 100% efficiency to a wide selection of cell types including dividing and non-dividing cells, primary cells, or cell lines. This ability far surpasses the gene delivery efficiency of lipid-based transfection approaches or other viral-based gene delivery systems.

Advantages of Using Recombinant Adenovirus

There are many advantages to using an adenovirus to introduce genetic material into host cells.
Recombinant adenovirus…

• has the ability to infect most mammalian cell types (both replicative and non-replicative).
• accommodates reasonably large transgenes (up to 8 kb).
• allows high expression of the recombinant protein.
• may be grown at high titer (10E10 VP/mL, which can be concentrated up to 10E13 VP/mL).
• is well tolerated, with post-infection viability of the host cells being almost 100%.
• remains epichromosomal (ie. does not integrate into the host chromosome) and does not inactivate genes or activate oncogenes.

All these have made recombinant adenoviruses the vector of choice for functional genomics research.