Viral delivery systems for the treatment of neurodegenerative diseases
| Characteristics | Adeno-associated virus | Adenovirus | Retrovirus | Lentivirus | Herpes simplex virus |
|---|---|---|---|---|---|
| Wild-type virus | Single-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 size | 4.5 kb | 7.5 kb | 8.0 kb | 8.0 kb | 20–40 kb |
| Achievable titre (per ml) | High (>1012) | High (>1011) | Low (>108) | Low (>108) | High (>109) |
| Infectivity | Broad | Broad | Dividing cells | Broad | Broad |
| Chromosomal integration | No* | No | Yes | Yes | No |
| Transgene expression | Long (months to years) | Short (days to weeks) | Long (months to years) | Long (months to years) | Short (days to weeks) |
| Latency in host cells | No | Yes | No | No | Yes |
| Pre-existing immunity | Yes | Yes | Unlikely | Unlikely† | Yes |
| Host immunological response | Minimal | Extensive | Minimal | None | Moderate |
| Potential in vivo risks | Insertional mutagenesis* | Inflammatory response | Insertional mutagenesis | Insertional mutagenesis | Inflammatory 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.