Table 1.

Salient properties of the main viral vectors used for human gene therapy

Parent virus	Key properties of wild-type virus	Advantages	Disadvantages	Comment
Adenovirus	Double stranded DNA genome, ~ 35Kb	Straightforward production of recombinant vectors at high titers	Inflammatory and antigenic	Various generations with increasingly deleted genomes “Gutted” vectors have no viral coding sequences and large carrying capacity but are difficult to produce.
	Non-enveloped	Transduces non-dividing cells		Tropism can be modified by altering coat proteins
	Over 50 serotypes	Wide choice of serotypes
	~ 100nm in size
	Genome remains episomal in infected cells
Herpes simplex virus	Double stranded DNA genome, ~ 150 Kb	Transduces non-dividing cells	Complex genome -Difficult to produce recombinant virus	HSV 1 and 2 most widely used as vectors. Herpes family includes Epstein Barr virus, CMV, etc
	Enveloped	Very efficient transduction of dividing and non-dividing cells	Cytotoxicity
	~ 200nm in size	Has a natural latency in neurons
	Genome remains episomal in infected cells	Very large carrying capacity
Adeno-associated virus	Single-stranded DNA genome, 4.8 Kb	Perceived to be safe (w.t. virus causes no known disease)	Difficult to produce	W.t. virus cannot replicate without helper virus
	Non-enveloped	Transduces non-dividing cells	Carrying capacity is insufficient for certain applications	W.t. virus integrates in a site-specific manner; recombinant virus remains as a stable, concatameric plasmid
	Growing number of serotypes identified	Thought to have low immunogenicity, but this is being re-evaluated	Transduction efficiency sometimes low	Limitations of single stranded genome now overcome by development of double copy (self complementary) DNA viruses
	~20 nm in size
Oncoretrovirus	RNA genome ~ 8–10 Kb	Straightforward production of recombinant vectors at moderate titers	Require host cell division	Usually used ex vivo
	Enveloped	Pseudotyped vectors have wide host range	Risk of insertional mutagenesis	2 genomes per virion, reverse transcribed into DNA
	~100nm in size
Lentivirus	RNA genome ~ 8–10 Kb	Straightforward production of recombinant vectors at moderate titers	Risk of insertional mutagenesis, but non-integrating vectors being developed	2 genomes per virion, reverse transcribed into DNA
	Enveloped	Pseudotyped vectors have wide host range and are often very efficient
	~100nm in size	Transduces non-dividing cells

Reproduced from reference [21] with permission