Herpes simplex virus type 1 (HSV-1)-derived amplicon vectors for gene transfer and gene therapy

Amplicons are defective, helper -dependent, herpes simplex virus type 1 (HSV-1 )-derived vectors. The main interest of these vectors as gene transfer tools stems from the fact that the amplicon vector genomes do not carry protein-encoding viral sequences. Consequently, they are completely safe for the host and non-toxic for the infected cells. Moreover, the complete absence of virus genes provides space to accommodate very large foreign DNA sequences, up to almost 150-kbp, the size of the virus genome . This large transgene capacity can be used to deliver complete gene loci, including introns and exons, as well as long regulatory sequences, conferring tissue-specific expression, or stable maintenance of the transgene in proliferating cells. During many years the development of these vectors and their application in gene transfer experiments was hindered by the presence of contaminating toxic helper virus particles in the vector stocks. In recent years however, two different methodologies have been developed that allow generating amplicon stocks either completely free of helper particles or only faintly contaminated with fully defective helper particles. This chapter summarizes these two methodologies

Viral vector-mediated expression of K+ channels regulates electrical excitability in skeletal muscle

Modification of K+ currents by exogenous gene expression may lead to therapeutic interventions in skeletal muscle diseases characterized by alterations in electrical excitability. In order to study the specific effects of increasing outward K⁺ currents, we expressed a modified voltage-dependent K⁺ channel in primary cultured rat skeletal muscle cells. The rat Kv1.4 channel was expressed as an N-terminal fusion protein containing a bioluminescent marker (green fluorescent protein). Transgene expression was carried out using the helper-dependent herpes simplex 1 amplicon system. Transduced myoballs, identified using fluorescein optics and studied electrophysiologically with single-cell patch clamp, exhibited a greater than two-fold increase in K⁺ conductance by 2030 h after infection. This increase in K⁺ current led to a decrease in membrane resistance and a 10-fold increase in the current threshold for action potential generation. Electrical hyperexcitability induced by the Na⁺ channel toxin anemone toxin II (1 μM) was effectively counteracted by overexpression of Kv1.4 at 3032 h after transduction. Thus, virally induced overexpression of a voltage-gated K⁺ channel in skeletal muscle has a powerful effect in reducing electrical excitability