A role for adeno-associated viral vectors in gene therapy

Abstract

Gene therapy constitutes a therapeutic intervention based on modification of the genetic material of living cells, by correcting genetic defects or overexpressing therapeutic proteins. The success of gene therapy protocols depends on the availability of therapeutically suitable genes, appropriate gene delivery systems and proof of safety and efficacy. Recent advances on the development of gene delivery systems, particularly on viral vectors engineering and improved gene regulatory systems, have led to marked progress in this field. Although the available vector systems can successfully transfer genes into cells, the ideal delivery vehicle has not been found. In this context, adeno-associated virus vectors (AAV) are arising as a promising tool for a wide range of applications, due to a combination of characteristics such as lack of pathogenicity and immunogenicity, wide range of cell tropism and long-term gene expression. Since its isolation, the biological properties of the adeno-associated virus have been increasingly understood, improving our ability to manipulate and use it as a safe and efficient gene therapy vector of wide spectrum. In this work, we review the bases of gene therapy, main types of gene transfer systems and basic properties and use of AAV vectors.

Viral Vectors in Neurobiology: Therapeutic and Research Applications

“…Three steps compose virus life cycle: infection of a host cell, replication of its genome within the host cell environment, and formation of new virions ( Figure 1B). This process is often but (1) viral binding to a membrane receptor/co-receptor; (2) endocytosis of the virus by the host cell; (3) virus intracellular trafficking through the endosomal compartment; (4) escape of the virus from the endosome; (5) virion uncoating; (6) entry into the nucleus; (7) viral genome conversion from a single-stranded to a double-stranded genome; and (8) integration into the host genome or permanence of an episomal form capable of expressing an encoded gene (from Coura and Nardi, 2008).…”

“…These vectors do offer some advantages over other vector systems which include the lack of initiating an immune response, their stability and ability to infect a variety of dividing and non-dividing cells. Unfortunately, they cannot incorporate genes larger than 5 kb and must be closely screened for adenoviral or HSV contamination (Berns, 1996;Grimm & Kay, 2003;Coura & Nardi, 2007;Coura & Nardi, 2008;Mezzina & Merten, 2011). …”

“…Depending on the duration planned for the treatment, type and location of target cells, and whether they undergo division or are quiescent, different vectors may be used, involving non-viral methods, non-integrating viral vectors or integrating viral vectors. Advances, especially, in viral vectors engineering and improved gene regulatory systems to facilitate and tightly control therapeutic gene expression have leading to GT progress (Coura & Nardi, 2008).…”

“…Since then, more than 5,000 patients have been treated in more than 1,000 clinical protocols all over the world (http://www.wiley.co.uk/genetherapy/ clinical). Despite the initial enthusiasm, however, the efficacy of gene therapy in clinical trials has not been as high as expected; a situation further complicated by ethical and safety concerns (Coura & Nardi, 2008). Further studies are being developed to solve these limitations.…”

“…(1); cotransfection of both plasmids in HEK 293 packaging cells, whose genome contains the Ad E1 gene, which together with the other Ad required genes, supplied by the helper plasmid, allows the establishment of a productive infection (2); empty capsid is formed by AAV structural proteins assembly into the nucleolus (3); the replicated ssDNA viral genome with the transgene flanked by ITRs (vector plasmid) are packaged into the empty capsid in the nucleoplasm (4), giving rise to a non-replicative recombinant AAV vector virion (5). The regulatory proteins act especially in the replication and packaging processes (from Coura and Nardi, 2008 …”