Table 1

Viral delivery systems for the treatment of neurodegenerative diseases

CharacteristicsAdeno-associated virusAdenovirusRetrovirusLentivirusHerpes simplex virus
Wild-type virusSingle-stranded DNA (4.7 kb)Double-stranded linear DNA (36 kb)Diploid positive strand RNA (9.2 kb)Diploid positive strand RNA (9.2 kb)Double-stranded linear DNA (152 kb)
Maximum insert size4.5 kb7.5 kb8.0 kb8.0 kb20–40 kb
Achievable titre (per ml)High (>1012)High (>1011)Low (>108)Low (>108)High (>109)
InfectivityBroadBroadDividing cellsBroadBroad
Chromosomal integrationNo*NoYesYesNo
Transgene expressionLong (months to years)Short (days to weeks)Long (months to years)Long (months to years)Short (days to weeks)
Latency in host cellsNoYesNoNoYes
Pre-existing immunityYesYesUnlikelyUnlikely†Yes
Host immunological responseMinimalExtensiveMinimalNoneModerate
Potential in vivo risksInsertional mutagenesis*Inflammatory responseInsertional mutagenesisInsertional mutagenesisInflammatory response
  • *Some integration occurs, but at low frequency. The risk of insertional mutagenesis is minimal compared with other viral vectors.

  • †Except perhaps in patients with HIV infection.