Describe AAV vectors and their advantages for gene therapy.

Adeno-associated virus (AAV) vectors are derived from non-pathogenic parvovirus and are leading platforms for gene therapy. Different serotypes (AAV1-13+) have distinct tissue tropisms (AAV9 crosses blood-brain barrier, AAV8 targets liver). Recombinant AAV contains only ITRs flanking the therapeutic gene - no viral genes. Advantages include: low immunogenicity, long-term episomal expression in non-dividing cells, broad serotype selection, and established safety profile. Limitations include small packaging capacity (~4.7kb), potential neutralizing antibodies in patients, and high-dose manufacturing requirements. Production uses triple transfection or producer cell lines. FDA-approved examples include Luxturna and Zolgensma.