Second generation adenoviral Vectors

These vectors have been developed to overcome these difficulties. Here of E1/E2 or E3/E4 expression cassettes are called deleted and replaced. The E1/E2 or E3/E4 proteins are required for viral DNA replication. Similar to first generation viral vector, cell lines which can complement both E1and E2 or E3 and E4 are needed. It can carry DNA insert upto 10.5kb

Advantages:

• It has improved safety and increased transgene expression.

Disadvantages:

• These viral vectors are associated with immunological problems.
• Construction of these vectors is difficult.

Third generation adenoviral Vectors

These vectors are otherwise called as gutless adenovirus. These are also known as helper dependent adenovirus as they lack all the coding sequences and require helper virus which carries all the coding sequences. Helper virus for example AAV, or artificially disabled viruses provide the viral functions needed for successful infection like viral DNA replication, viral assembly and infection of new cells etc. The size of insert DNA can be 36kb and hence called as high capacity adenoviruses. They carry only 5' inverted terminal repeats (ITR) and 3' packaging signals (ψ).

Advantages:

• These are non-integrative and high-capacity vectors.
• It can be produced in high titer and the construction of these vector is easy.
• It shows longer stability and reduced immune response.

Disadvantages:

• Helper virus contamination can cause diseases like conjunctivitis, pharyngitis, cold and respiratory disease.