Improvements in HSV-1 Derived Amplicon Vectors for Gene Transfer

MELENDEZ MATÍAS; AGUIRRE ALEJANDRA; BAEZ M. VERÓNICA; BUENO CARLOS ; SALVETTI ANNA; JERUSALINSKY DIANA; EPSTEIN ALBERTO

Advances in Viral Genomes Research

Nova Science Publishers, Inc.

Lugar: New York; Año: 2013; p. 1 - 50

Viral vectors engineered to carry transgenic sequences can be delivered into discrete tissues or anatomical structures to express specific transgenes into the transduced cells. Therefore, they are useful tools to produce specific, transient and localized knockout, knockdown, ectopic expression or overexpression of a gene, leading to the possibility of analyzing both in vitro and in vivo molecular basis of relevant functions.  Replication-incompetent helper-dependent amplicon vectors, derived from herpes simplex virus type-1 (HSV-1) are devoid of viral genes. Thus, these vectors have great advantages among other vectors as potent tools to be used in vitro and in vivo: (i) minimal toxicity or adaptive immune induction, since they carry no viral genes; (ii) large transgene capacity, being able to carry up to 150 kbp of foreign DNA; (iii) widespread cellular tropism: amplicons can experimentally infect several cell types, either quiescent or not, though naturally HSV-1 infects mainly neurons and epithelial cells; (iv) absence of insertional mutagenesis, since the viral genome does not integrate into the host cell genome. These vectors have been used both on basic and applied research, and they have revealed as most suitable tools to study complex functions involving the nervous system, such as anxiety, sexual behavior, learning and memory. In addition, amplicon vectors are being used for the development of new experimental gene therapy approaches, both for inherited and acquired diseases affecting the nervous system, including neurodegenerative diseases. Although several technological improvements have been developed in the last decade, many difficulties regarding these appealing vectors remain still unresolved: i.e. the inability to generate large amounts of high-titre helper-free vectors and the fact that expression from the transgenic sequence delivered by the vectors is generally unstable, often leading to a complete silencing of expression after a few days. To overcome these obstacles and to improve these vectors, we modified (a) the amplicon genome, in order to fully delete bacterial sequences and (b) the nature of the complementing cell lines where the amplicons are produced, in order to enhance helper-free vector production. In this review article we summarize our efforts to improve these two aspects of amplicon methodology. In addition, we briefly review data supporting the potential of herpes simplex virus type 1-based amplicon vector model for gene delivery in primary cultures of neural cells and into the brain of living animals. We further discuss the conditions that would enable amplicon vectors to be used in experimental gene therapy approaches of medium and large animals, including human beings.