A variety of different viral vectors are available for gene delivery into eukaryotic cell lines or live animals. Carefully choosing the correct vector with your experimental paradigm can maximize your chance for success! On this page you will find some of the most important viral vectors with their specific advantages and disadvantages.
Adenoviral plasmids the best option when the key concern is transient expression of proteins at a very high level. They are optimized for strong protein expression and adenoviral promoters prompt generation of copious amounts of mRNA.
Adenoviral vectors can also accommodate large inserts, up to approximately 8kB in size. In a properly transfected HEK cell line, up to 20% of expressed protein is likely to be from an adenoviral vector origin.
The adenovirus system is a strong option and has few weaknesses. The fairly large size of the wild-type adenovirus genome (nearly 40kB) can sometimes complicate transfection, and result in unstable protein expression.
Additionally, unlike retroviral vectors, adenoviral plasmids result in transient transgenic expression, i.e. plasmid DNA is not integrated into the host genome. Transient transfection is lost, most commonly through replication of host cells during passaging.
Adeno-Associated Viral (AAV) vectors have many of the same advantages as adenoviral vectors. High expression, very high viral titer, and a moderate quantity of mRNA and protein expression are all advantages associated with AAV vectors.
Like the adenoviral expression system, AAV gene delivery is most commonly transient. More recent work does permit genome integration from AAV vectors, but integration from these delivery systems is generally less targeted, and requires co-transfection with additional components requiring more effort, time, and overhead.
Retroviral plasmids represent a fairly narrow niche of use in transformation. The largest strength of a retroviral vector is in its ability to integrate plasmid DNA into the host genome to generate a cell line with stable expression, rather than transient expression.
Unlike transiently expressed genes, integrated, stable expression will persist over multiple generations.
The ability to generate stable expression does not come without a price. Retroviral vectors are less efficient than their counterparts (generally, fewer copies can be integrated). They can only infect actively dividing cell lines, and the titer of mRNA and protein produced by a retroviral vector is substantially lower than with other viral expression vectors.
Lentiviral vectors offer a slight improvement over retroviral vectors. Like retroviral vectors, many lentiviral expression vectors have the option integrate plasmid DNA is into the genome to generate a stably expressing cell line.
Unlike retroviral vectors, lentiviral vectors are able to infect both dividing and non-dividing cells, and produce higher titers of mRNA and more protein than retroviral vectors.
Like a retroviral vector, lentiviral vectors also produce a relatively low multiplicity of infection (only ~10 copies are integrated into the host genome). Expression characteristics are better than retroviral alternatives, but are still often several orders of magnitude below adenoviral or AAV vector options.