Adeno-associated virus

Adeno-Associated Viruses (AAV)

Adeno-Associated Viruses (AAV) are non-pathogenic viruses that infect humans and some other primate species. As members of the genus Dependoparvovirus within the family Parvoviridae, AAVs are distinguished by their small size, lack of a viral envelope, and a linear single-stranded DNA (ssDNA) genome of approximately 4.8 kilobases (kb). Measuring about 20 nanometers (nm) in diameter, these viruses are unique in their replication-defective nature, requiring co-infection with a helper virus, such as an adenovirus or herpesvirus, for productive infection.

Structural diagram of an Adeno-Associated Virus.

Characteristics

AAVs are characterized by:

• Small size (20 nm in diameter)
• Nonenveloped capsid
• Linear ssDNA genome (~4.8 kb)
• Replication-defective nature, requiring a helper virus for replication

Biology

The AAV genome encodes two primary genes:

• Rep (replication) genes involved in the replication, integration, and regulation of the viral genome.
• Cap (capsid) genes that encode viral capsid proteins, determining the virus's serotype and tropism.

Significance in Research and Therapy

Due to their non-pathogenicity and ability to infect both dividing and non-dividing cells, AAVs have become prominent vectors in gene therapy. They are used to deliver therapeutic genes to treat various genetic disorders, including:

• Hemophilia
• Leber's congenital amaurosis
• Spinal muscular atrophy

AAVs are preferred for their long-term expression of the therapeutic gene in targeted tissues and minimal immune response.

Gene Therapy Applications

Recent advancements in AAV vector design and delivery methods have expanded their use in treating a wide range of diseases. AAV vectors can be engineered to target specific tissues or cells, enhancing the efficiency and safety of gene therapy treatments.

Safety and Regulatory Approval

The safety profile of AAV vectors has led to the approval of several AAV-based therapies by regulatory agencies such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA). These approvals mark significant milestones in the field of gene therapy.

Future Directions

Research continues to focus on improving AAV vectors' targeting specificity, payload capacity, and reducing potential immune responses to enhance their therapeutic potential further.

See Also

• Gene therapy
• Viral vector
• Hemophilia treatment
• Ophthalmology in gene therapy

References

• Samulski, R.J., & Muzyczka, N. (2014). "AAV: An Overview of Unanswered Questions." Human Gene Therapy.
• Gao, G., Vandenberghe, L.H., & Wilson, J.M. (2020). "New AAV Serotypes for Improved Gene Therapy." Gene Therapy.

External Links

• National Institutes of Health: Adeno-Associated Virus for Cancer Gene Therapy
• FDA: Cellular & Gene Therapy Products.