Efficient infection of mature skeletal muscle with herpes simplex virus vectors by using dextran sulfate as a co-receptor

High-purity preparation of HSV-2 vaccine candidate ACAM529 is immunogenic and efficacious in vivo

Genital herpes is a sexually transmitted infection (STI) caused by herpes simplex virus 2 (HSV-2) and to a lesser extent herpes simplex virus 1 (HSV-1). Infection by HSV-2 is life-long and is associated with significant cost to healthcare systems and social stigma despite the highly prevalent nature of the disease. For instance, the proportion of HSV-2 seropositive to seronegative adults is approximately 1 in 5 in the US and greater than 4 in 5 in some areas of sub-Saharan Africa. The replication-defective vaccine strain virus dl5-29 was re-derived using cells appropriate for GMP manufacturing and renamed ACAM529. Immunization with dl5-29 was previously reported to be protective both in mice and in guinea pigs, however these studies were performed with vaccine that was purified using methods that cannot be scaled for manufacturing of clinical material. Here we describe methods which serve as a major step towards preparation of ACAM529 which may be suitable for testing in humans. ACAM529 can be harvested from infected cell culture of the trans-complementing cell line AV529 clone 19 (AV529-19) without mechanical cell disruption. ACAM529 may then be purified with respect to host cell DNA and proteins by a novel purification scheme, which includes a combination of endonuclease treatment, depth filtration, anion-exchange chromatography and ultrafiltration/diafiltration (UF/DF). The resultant virus retains infectivity and is ∼ 200-fold more pure with respect to host cell DNA and proteins than is ACAM529 purified by ultracentrifugation. Additionally, we describe a side-by-side comparison of chromatography-purified ACAM529 with sucrose cushion-purified ACAM529, which shows that both preparations are equally immunogenic and protective when tested in vivo.

Polymers for improving the in vivo transduction efficiency of AAV2 vectors

Background

Adeno-associated virus has attracted great attention as vehicle for body-wide gene delivery. However, for the successful treatment of a disease such as Duchenne muscular dystrophy infusion of very large amounts of vectors is required. This not only raises questions about the technical feasibility of the large scale production but also about the overall safety of the approach. One way to overcome these problems would be to find strategies able to increase the in vivo efficiency.

Methodology

Here, we investigated whether polymers can act as adjuvants to increase the in vivo efficiency of AAV2. Our strategy consisted in the pre-injection of polymers before intravenous administration of mice with AAV2 encoding a murine secreted alkaline phosphatase (mSeAP). The transgene expression, vector biodistribution and tissue transduction were studied by quantification of the mSeAP protein and real time PCR. The injection of polyinosinic acid and polylysine resulted in an increase of plasmatic mSeAP of 2- and 12-fold, respectively. Interestingly, polyinosinic acid pre-injection significantly reduced the neutralizing antibody titer raised against AAV2.

Conclusions

Our results show that the pre-injection of polymers can improve the overall transduction efficiency of systemically administered AAV2 and reduce the humoral response against the capsid proteins.

Therapeutic Strategies for Duchenne and Becker Dystrophies

Duchenne muscular dystrophy (DMD), a severe X-linked genetic disease affecting one in 3500 boys, is the most common myopathy in children. DMD is due to a lack of dystrophin, a submembrane protein of the cytoskeleton, which leads to the progressive degeneration of skeletal, cardiac, and smooth muscle tissue. A milder form of the disease, Becker muscular dystrophy (BMD), is characterized by the presence of a semifunctional truncated dystrophin, or reduced levels of full-length dystrophin. DMD is the focus of three different supportive or therapeutic approaches: gene therapy, cell therapy, and drug therapy. Here we consider these approaches in terms of three potential goals: improvement of dystrophic phenotype, expression of dystrophin, and overexpression of utrophin. Utrophin exhibits 80% homology with dystrophin and is able to perform similar functions. Pharmacological strategies designed to overexpress utrophin appear promising and may circumvent many obstacles to gene and cell-based therapies.

Gene transfer studies in animals: what do they really tell us about the prospects for gene therapy in DMD?

There is a pressing need to develop new therapeutic approaches to Duchenne muscular dystrophy, an X-linked fatal disease primarily affecting skeletal and cardiac muscle. Gene therapy is an approach that has attracted much interest since the description of the Duchenne muscular dystrophy gene and its mutations in 1987. Since 1990 numerous reporter and dystrophin gene transfer studies have been conducted on muscles of animals but mostly in mice. Experimental protocols have ranged from germ-line gene transfer (via the production of transgenics) to somatic gene transfer studies using viral or non-viral vectors. But what have we actually learned from such studies that can be applied to patients with Duchenne muscular dystrophy? Various dystrophin, utrophin and integrin recombinant cDNAs have been shown to prevent the development of muscular dystrophy in transgenic dystrophic (mdx) mice. Somatic gene transfer prior to the onset of pathology have been shown to prevent the development of the muscular dystrophy in the mdx mouse but the data is less convincing for the beneficial effects of somatic gene transfer following the establishment of pathology. The time of onset and the course of the disease differ substantially between mouse and man and raise concerns about the applicability of gene therapy in man where the disease manifests in utero and the progression is more severe. The other major concern relates to uncertainty over the efficiency of the different vectors in man, particularly as many patients are likely to have encountered the infectious forms of the viruses that are proposed as vectors.

Efficiency of protein transduction is cell type-dependent and is enhanced by dextran sulfate

Protein transduction domains (PTDs), both naturally occurring and synthetic, have been increasingly utilized to deliver biologically active agents to a variety of cell types in vitro and in vivo. We report that in addition to previously characterized arginine-rich PTDs, including TAT, lysine homopolymers were able to mediate transduction of a wide variety of cell types, as measured by flow cytometric and enzymatic assays. The efficiency of PTD-mediated transduction was influenced by the cell type tested, although polylysine homopolymers demonstrate levels of internalization that consistently exceeded those of TAT and arginine homopolymers. Transduction of arginine/lysine-rich PTDs occurred at 4 degrees C and following depletion of cellular ATP pools, albeit generally at reduced levels. Although transduction was reduced in Chinese hamster ovary mutant lines deficient in either heparan sulfate or glycosaminoglycan synthesis, uptake was restored to wild-type levels by incubating target cells with dextran sulfate. The enhancement of transduction by dextran sulfate suggests that electrostatic interactions play an important first step in the process by which PTDs and their cargo traverse the plasma membrane.

Herpes simplex virus type 1 amplicon vector-mediated gene transfer to muscle

Herpes simplex virus type 1 (HSV-1) amplicon vectors were evaluated for feasibility in gene therapy of Duchenne's muscular dystrophy (DMD). An amplicon vector expressing enhanced green fluorescent protein (eGFP) was examined for transduction efficiency and cytotoxicity in cultured muscle cells, and for transduction efficiency, duration of transgene expression, and immunogenicity in tibialis anterior (TA) muscles of neonatal mice. Transduction efficiencies in murine and human myoblasts were 60-90 and 50-60%, respectively, when myoblasts were transduced at multiplicities of infection (MOIs) of 1-5. Similar transduction efficiencies were observed in myotubes of both species. No cytotoxic effects were noticed at an MOI of 10, the highest MOI tested. An amplicon vector, HyMD, containing the full-length mouse dystrophin cDNA and its muscle creatine kinase (MCK) promoter-enhancer, with a total size of 26 kb, was constructed and used to transduce mdx mouse myotubes. The expression of dystrophin in these cells was demonstrated by immunocytochemistry. After injecting 4-6 x 10(5) transduction units (TU) of HSVGN amplicon vectors, 10-50% of myofibers in the injected TA muscles expressed GFP. Although transgene expression was attenuated over time, significant improvement in long-term transgene expression and persistence of vector DNA was achieved, when compared with the first generation of recombinant HSV-1 vectors. Immunohistochemistry showed a modest CD4(+) lymphocyte infiltration in the vicinity of the injection. A gradually developed CD8(+) lymphocyte infiltration was also seen, most likely related to the antigenicity of the transgene product, GFP. We conclude that the HSV-1 amplicon vector is a promising vehicle for gene delivery in DMD. However, new strategies need to be evaluated to increase the stability of transgene expression.

Utilization of sialic acid as a coreceptor enhances reovirus attachment by multistep adhesion strengthening

Many serotype 3 reoviruses bind to two different host cell molecules, sialic acid and an unidentified protein, using discrete receptor-binding domains in viral attachment protein, final sigma1. To determine mechanisms by which these receptor-binding events cooperate to mediate cell attachment, we generated isogenic reovirus strains that differ in the capacity to bind sialic acid. Strain SA+, but not SA-, bound specifically to sialic acid on a biosensor chip with nanomolar avidity. SA+ displayed 5-fold higher avidity for HeLa cells when compared with SA-, although both strains recognized the same proteinaceous receptor. Increased avidity of SA+ binding was mediated by increased k(on). Neuraminidase treatment to remove cell-surface sialic acid decreased the k(on) of SA+ to that of SA-. Increased k(on) of SA+ enhanced an infectious attachment process, since SA+ was 50-100-fold more efficient than SA- at infecting HeLa cells in a kinetic fluorescent focus assay. Sialic acid binding was operant early during SA+ attachment, since the capacity of soluble sialyllactose to inhibit infection decreased rapidly during the first 20 min of adsorption. These results indicate that reovirus binding to sialic acid enhances virus infection through adhesion of virus to the cell surface where access to a proteinaceous receptor is thermodynamically favored.

Gene therapy and molecular approaches to the treatment of hereditary muscular disorders

Gene therapy for inherited muscle disease is an active area of research and development. Initial emphasis has been on gene replacement but alternative approaches are increasingly being considered in order to overcome difficulties, such as the immune rejection of transduced cells, the need for appropriate and tissue-specific control of expression, and the requirement for systemic spread in some conditions. However, the most significant obstacles to the clinical success of gene therapy are still the lack of efficiency and accuracy of gene medicine delivery.

Herpes simplex viral and amplicon vector-mediated gene transfer into glia and neurons in organotypic spinal cord and dorsal root ganglion cultures

The progression of neurodegenerative diseases and secondary consequences of spinal cord injury may be diminished by introducing transgenes to glia, spinal neurons, and/or sensory neurons. Organotypic cultures of spinal cord slices and dorsal root ganglia proved to be an excellent system in which to compare the relative neurotropism of a replication-defective recombinant herpes simplex virus and herpes virus-derived amplicon vectors. Hundreds of beta-galactosidase-expressing cells, transduced by the viral vectors, were observed in spinal cord slices 3 and 8 days postinfection. Immunostaining to identify the infected cell type indicated that oligodendrocytes were permissive for viral vector transduction of beta-galactosidase in the spinal cord slice, whereas neurons were not. Heparan sulfate proteoglycan, the initial receptor for herpes contact with cells, was highly expressed in the white matter of the spinal cord slice, but was negligible in the gray matter. In contrast to the spinal cord, many fewer cells were infected in the dorsal root ganglia (DRG) by these vectors, but a majority of infected cells were identified as sensory neurons. Heparan sulfate proteoglycan expression was abundant in the sensory fibers emanating from the DRG and also surrounded each neuron within the ganglion. Our results demonstrate HSV-induced transgene expression that is amenable to ex vivo assessment of its physiological impact.