Editing Viral Vector Engineering (section)

== 4. Adeno-Associated Viral (AAV) Vectors: Safe and Transient ==

AAVs are small, non-enveloped viruses that carry single-stranded DNA. They are naturally non-pathogenic (they do not cause human disease).
* '''Mechanism:''' Unlike lentiviruses, AAV vectors generally do not integrate their payload into the host genome. Instead, the therapeutic DNA remains in the nucleus as an episome (a separate, circular piece of DNA).
* '''Application:''' Because they don't integrate, AAVs have a much lower risk of causing cancer. They are the preferred vector for ''in vivo'' gene therapies targeting post-mitotic (non-dividing) cells, such as neurons or retinal cells (e.g., Luxturna for inherited blindness). Because the cells don't divide, the episomal DNA is not diluted out and can provide long-term therapeutic expression.
* '''Drawback:''' AAVs have a very small cargo capacity (around 4.7 kilobases), limiting the size of the therapeutic gene they can carry. Additionally, because many people have been naturally exposed to wild-type AAVs, pre-existing immunity can neutralize the vector before it reaches its target.