Adeno-associated virus 6 (AAV6) is a hybrid serotype of adeno associated virus that shares nearly identical capsid sequences with AAV1 and AAV2. It is a small non enveloped parvovirus with a single stranded DNA genome of about 4.7 kb. AAV6 uses terminal α2,3‑ and α2,6‑linked sialic acid and heparan sulfate as primary receptors and requires a helper virus for productive replication.
Explanation
AAV6 is considered a natural recombination between AAV1 and AAV2, and was first isolated from a human adenovirus stock. Sequence analyses reveal that its coding region shares ~99 % homology with AAV1 and contains several regions identical to AAV2, prompting debate about its classification. Like other dependoparvoviruses, the icosahedral capsid encloses inverted terminal repeats and two open reading frames encoding replication (Rep) proteins and capsid (Cap) proteins. Wild‑type AAV6 is non‑pathogenic and relies on co‑infection with adenovirus or herpesvirus for replication. Cell binding studies have shown that AAV6 attaches to sialylated proteoglycans—both α2,3‑ and α2,6‑linked sialic acids—and heparan sulfate; epidermal growth factor receptor acts as a co‑receptor facilitating endocytosis. These receptor interactions dictate its tissue tropism: in animal models the serotype transduces airway epithelial cells, liver parenchyma, skeletal muscle and cardiac muscle more efficiently than AAV2. Preclinical studies have also reported efficient transduction of cardiomyocytes in murine, porcine and canine models. Recombinant AAV6 vectors are purified by heparin or mucin chromatography due to their ability to bind both matrices.
Therapeutic potential and examples
Recombinant AAV6 vectors have been used to deliver therapeutic genes in a number of experimental models. Intratracheal administration of AAV6 expressing the human surfactant protein B gene restored surfactant levels in mouse models of lethal surfactant protein B deficiency, while intranasal delivery of AAV6 carrying alpha‑1 antitrypsin transduced airway epithelium in mice and dogs. Intramuscular injections of rAAV6 encoding micro‑dystrophin improved muscle function and extended survival in dystrophin‑deficient mice, and cardiac delivery of AAV6‑based vectors has been explored for heart failure and hemophilia. AAV6 is less neutralized by pre‑existing antibodies than AAV2, making it attractive for systemic administration. AAV6 occupies a unique position between AAV1 and AAV2 in terms of sequence and serology, yet its receptor usage and muscle‑ and airway‑tropic nature set it apart. Although no approved therapies currently use this serotype, rAAV6 vectors continue to be studied for respiratory, muscular and cardiac gene delivery. As with all AAVs, careful consideration of immunity and biodistribution is essential. Related Terms: Adeno Associated Virus 1, Adeno Associated Virus 2, Adeno Associated Virus 5, Adeno Associated Virus 7, Adeno Associated Virus 8