|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.