Adenovirus serotype 5 (Ad5) is a human adenovirus that belongs to the family Adenoviridae and the genus Mastadenovirus. Adenoviruses are non-enveloped, double-stranded DNA viruses that can cause a wide range of infections in humans, including respiratory, gastrointestinal, and ocular diseases. Ad5 is a common serotype that has been extensively studied and is often used as a basis for adenoviral-based vectors in gene therapy and vaccine development.
The Ad5 genome is approximately 36 kilobases in length and contains over 30 genes, which are divided into two main categories: early genes (E1, E2, E3, and E4) and late genes (L1 to L5). Early genes are involved in viral replication and host immune response modulation, while late genes primarily encode the viral structural proteins required for virion assembly.
In the context of adenoviral-based vectors, the Ad5 DNA is often modified to remove certain viral genes responsible for replication and pathogenesis, while retaining essential elements for packaging the viral genome and infecting target cells. The modified Ad5 genome is then used to deliver a gene of interest to the target cells for research or therapeutic purposes. The resulting replication-deficient adenoviral vector can efficiently transduce a wide range of cell types, including dividing and non-dividing cells, leading to high levels of transgene expression.
However, the use of Ad5-based vectors has some limitations, including the risk of inducing strong immune responses against the viral components and the expressed transgene, as well as the potential for pre-existing immunity to Ad5 in the human population. To address these challenges, researchers are continuously working on developing strategies to reduce the immunogenicity of adenoviral vectors and exploring alternative serotypes or viral platforms for gene delivery.