| HSV | Adenovirus | AAV | Retrovirus | Lentivirus | |
| Genomic Integration | Episomal,100% | Episomal,100% | Episomal >90%, | Integrated | Integrated |
| Cloning Capacity | 150 kb for amplicon; 40 kb for replication defective HSV | 8 kb for replication defective AdV; 30 kb for HC/gutless | 3.5–4.0 kb | 7–8 kb | 7–8 kb |
| Tropism | Broad host and cell type range, including dividing cells; preference for neurons | Strong for most tissues | Broad | Dividing cells only | Broad, including neurons |
| Duration of Expression In Vivo | Days (amplicon) to months (replication-defective) | First generation: 10 days to months; gutted: long | Long (2.5–6.0 months) | Days to months | Long (>12 months) |
| Advantages | Amplicon vectors easily amenable to genetic manipulation; high and broad transduction efficiency; helper virus-free stocks possible; concentrates to high titers | High and broad transduction efficiency; growth to high titers (1011) | Not pathogenic or immunogenic; helper virus-free stocks possible; growth to high titers (>1012) | Persistent gene transfer; useful for cell marking/lineage analysis | Stable, long-term expression; transduction of nondividing cells |
| Disadvantages | Occasional cytotoxicity; strong immune response possible | Severe inflammation and immune response; genetic manipulation unwieldy | Low cloning capacity | Insertional mutagenesis | Insertional mutagenesis; questionable safety; possible germ-line alterations |
HSV, herpes simplex virus; HC, high-capacity; AAV, adenoassociated virus; AdV, adenovirus.