The Adeno-associated Virus - A Safe and Promising Vehicle for Liverspecific Gene Therapy of Inherited and Non-inherited Disorders

The first human adeno-associated virus (AAV) was originally discovered in 1960s as a contaminant of adenovirus stock preparation and thus it had not been of medical interest. Throughout the last three decades AAV has gained popularity to be used in gene therapy, mainly due to its replicative defectiveness and lack of pathogenicity in human. In addition, its ability to mediate stable and long-term expression in both non-dividing and dividing cells with specific tissue tropism makes AAV one of the most promising candidates for therapeutic gene transfer to treat many inherited as well as non-inherited disorders. Moreover, the use of AAV is not only restricted to overexpression of recombinant transgene, but also to over-express short hairpin RNA and microRNA to knockdown the expression of genes in targeted tissues.This review is organized into four parts. In the first part of the review, we discuss about the discovery and history of AAV, followed by detailed AAV biology such as virus genome, virus structure and its life cycle. In the second part of the review, the discussion is centred on the molecular mechanisms of AAV and tissue transduction, including receptor recognition and cell binding, endosomal entry, virus uncoating, nuclear entry and genome replication. Advantages and limitations of using AAV as a safe vehicle for gene delivery is also discussed. In the third part of the review, we discuss about the most commonly used AAV serotypes and variants isolated from human and non-human primates, focusing on their diverse tissue tropisms, transduction efficiency, immunological profiles and their applications in animal studies. Final part of the review focuses on the recent progress of in-vivo gene transfer using AAV for inherited and non-inherited diseases in both preclinical and clinical settings with a special emphasis on potential clinical applications of AAV in the field of liver disease.