HSV-1 amplicon vectors--simplicity and versatility

Critical issues in gene therapy for neurologic disease

Gene therapy for the nervous system is a newly emerging field with special issues related to modes of delivery, potential toxicity, and realistic expectations for treatment of this vital and highly complex tissue. This review focuses on the potential for gene delivery to the brain, as well as possible risks and benefits of these procedures. This includes discussion of appropriate vectors, such as adeno-associated virus, lentivirus, gutless adenovirus, and herpes simplex virus hybrid amplicons, and cell vehicles, such as neuroprogenitor cells. Routes of delivery for focal and global diseases are enumerated, including use of migratory cells, facilitation of vascular delivery across the blood-brain barrier, cerebrospinal fluid delivery, and convection injection. Attention is given to examples of diseases falling into different etiologic types: metabolic deficiency states, including Canavan disease and lysosomal storage disorders; and degenerative conditions, including Parkinson's disease and other neurodegenerative conditions.

Expression of hepatitis C virus envelope glycoproteins by herpes simplex virus type 1-based amplicon vectors

Herpes simplex virus type 1 (HSV-1)-based amplicon vectors expressing hepatitis C virus (HCV) E1 and E2 glycoproteins were investigated. HSV-1 amplicon vectors carrying the E1E2p7- or E2p7-coding sequences of HCV type 1a under the control of the HSV-1 IE4 (alpha22/alpha47) promoter were constructed. Studies of infected HepG2, WRL 68 or Vero cells indicated that HSV-1-based amplicon vectors express high levels of HCV glycoproteins that are processed correctly. Immunofluorescence microscopy combined with immunoprecipitation and endoglycosidase treatment of cells infected with the HSV-1-based vectors expressing E1 and E2 showed that the two glycoproteins were retained in the endoplasmic reticulum and had the expected glycosylation patterns. Furthermore, although most of the E1 and E2 proteins formed disulfide-linked aggregates, significant amounts of monomeric forms of the two proteins were detected by SDS-PAGE under non-reducing conditions, suggesting the presence of non-covalently associated E1 and E2. Similar results were produced by a replication-competent recombinant HSV-1 vector expressing HCV E1 and E2. These results indicated that HSV-1-based amplicon vectors represent a useful expression system for the study of HCV glycoproteins.

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.

Interaction of large DNA viruses with dendritic cells

Dendritic cells (DC) with their unique capacity to prime naïve T cells are crucial in the induction of immunological responses, including anti-tumoral and anti-viral immunity. DC based immunotherapies are thus currently considered a particularly promising approach for cellular immunotherapy. The cloning of tumor associated antigens (TAAs) together with the possibility of manipulating viral genomes by biotechnological techniques has sparked the interest of using genetically modified viruses to transduce DC in order to achieve antigenic expression of TAA with the aim of inducing a protective immune response. An increasing number of modified viral vectors has been designed for gene therapy purposes and consecutively has been used for the ex vivo transduction of DC. It has been shown that viral vectors genetically engineered to express TAA or immune modifiers like cytokines or costimulatory molecules can lead to a high level of transgene expression. Furthermore, these studies have also revealed that viruses have developed several immune evasion mechanisms specifically targeting DC. Therefore, analysing the interactions of viruses with DC is crucial for the development of new viral vectors suitable for the transduction of DC. In this report we describe the interaction of two large DNA viruses, herpes simplex virus type 1 (HSV-1) and vaccinia virus (VV), with DC generated from peripheral blood mononuclear cells.

Gene therapy for prostate cancer: current status and future prospects

PURPOSE

Locally advanced, relapsed and metastatic prostate cancer has a dismal prognosis with conventional therapies offering no more than palliation. In recent years advances achieved in understanding the molecular biology of cancer have afforded clinicians and scientists the opportunity to develop a range of novel genetic therapies for this disease.

MATERIALS AND METHODS

We performed a detailed review of published reports of gene therapy for prostate cancer. Particular emphasis was placed on recent developments in the arena of nonviral (plasmid DNA, DNA coated gold particles, liposomes and polymer DNA complexes) and viral (adenovirus, retrovirus, adeno-associated virus, herpes virus and pox virus) vectors. Therapeutic strategies were categorized as corrective, cytoreductive and immunomodulatory gene therapy for the purpose of data analysis and comparison.

RESULTS

Locoregional administration of nonviral and viral vectors can yield impressive local gene expression and therapeutic effects but to our knowledge no efficient systemically delivered vector is available to date. Corrective gene therapy to restore normal patterns of tumor suppressor gene (p53, Rb, p21 and p16) expression or negate the effect of mutated tumor promoting oncogenes (ras, myc, erbB2 and bcl-2) have efficacy in animal models but this approach suffers from the fact that each cancer cell must be targeted. A wide variety of cytoreductive strategies are under development, including suicide, anti-angiogenic, radioisotopic and pro-apoptotic gene therapies. Each approach has strengths and weaknesses, and may best be suited for use in combination. Immunomodulatory gene therapy seeks to generate an effective local immune response that translates to systemic antitumor activity. Currently most studies involve immunostimulatory cytokine genes, such as granulocyte-macrophage colony-stimulating factor, or interleukin-2 or 12.

CONCLUSIONS

Various therapeutic genes have proved activity against prostate cancer in vitro and in vivo. However, the chief challenge facing clinical gene therapy strategies is the lack of efficient gene delivery by local and systemic routes. For the foreseeable future vector development may remain a major focus of ongoing research. Despite this caveat it is anticipated that gene therapy approaches may significantly contribute to the management of prostate cancer in the future.

Functional complementation of a genetic deficiency with human artificial chromosomes

We have shown functional complementation of a genetic deficiency in human cultured cells, using artificial chromosomes derived from cloned human genomic fragments. A 404-kb human-artificial-chromosome (HAC) vector, consisting of 220 kb of alphoid DNA from the centromere of chromosome 17, human telomeres, and the hypoxanthine guanine phosphoribosyltransferase (HPRT) genomic locus, was transferred to HPRT-deficient HT1080 fibrosarcoma cells. We generated several cell lines with low-copy-number, megabase-sized HACs containing a functional centromere and one or possibly several copies of the HPRT1 gene complementing the metabolic deficiency. The HACs consisted of alternating alphoid and nonalphoid DNA segments derived only from the input DNA (within the sensitivity limits of FISH detection), and the largest continuous alphoid segment was 158-250 kb. The study of both the structure and mitotic stability of these HACs offers insights into the mechanisms of centromere formation in synthetic chromosomes and will further the development of this human-gene-transfer technology.

Development of herpes simplex virus-1 amplicon-based immunotherapy for chronic lymphocytic leukemia

Herpes simplex virus (HSV)-based vectors have favorable biologic features for gene therapy of leukemia and lymphoma. These include high transduction efficiency, ability to infect postmitotic cells, and large packaging capacity. The usefulness of HSV amplicon vectors for the transduction of primary human B-cell chronic lymphocytic leukemia (CLL) was explored. Vectors were constructed encoding beta-galactosidase (LacZ), CD80 (B7.1), or CD154 (CD40L) and were packaged using either a standard helper virus (HSVlac, HSVB7.1, and HSVCD40L) or a helper virus-free method (hf-HSVlac, hf-HSVB7.1, and hf-HSVCD40L). Both helper-containing and helper-free vector stocks were studied for their ability to transduce CLL cells, up-regulate costimulatory molecules, stimulate allogeneic T-cell proliferation in a mixed lymphocyte tumor reaction, and generate autologous cytotoxic T lymphocytes (CTLs). Although helper-containing and helper-free amplicon stocks were equivalent in their ability to transduce CLL cells, a vigorous T-cell proliferative response was obtained using cells transduced with hf-HSVB7.1 but not with HSVB7.1. CLL cells transduced with either HSVCD40L or hf-HSVCD40L were compared for their ability to up-regulate resident B7.1 and to function as T-cell stimulators. Significantly enhanced B7.1 expression in response to CD40L was observed using hf-HSVCD40L but not with HSVCD40L. CLL cells transduced with hf-HSVCD40L were also more effective at stimulating T-cell proliferation than those transduced with HSVCD40L stocks and were successful in stimulating autologous CTL activity. It is concluded that HSV amplicons are efficient vectors for gene therapy of hematologic malignancies and that helper virus-free HSV amplicon preparations are better suited for immunotherapy.

HSV amplicon-mediated neurotrophin-3 expression protects murine spiral ganglion neurons from cisplatin-induced damage

Ototoxicity is a major dose-limiting side effect of cisplatin (DDP) administration due to its propensity to induce destruction of hair cells and neurons in the auditory system. Previous studies demonstrated that TrkC-expressing spiral ganglion neurons (SGN) are protected from the cytotoxic effects of DDP by localized delivery of the trophic factor neurotrophin-3 (NT-3). Successful in vivo implementation of such a therapy requires the development of an efficient gene delivery vehicle for expression of NT-3 within the cochlea. To this end, we constructed a herpes simplex virus (HSV) amplicon vector that expressed a c-Myc-tagged NT-3 chimera (HSVnt-3myc). Helper virus-free vector stocks were initially evaluated in vitro for their capacity to direct expression of NT-3 mRNA and protein. Transduction of cultured murine cochlear explants with HSVnt-3myc resulted in production of NT-3 mRNA and protein up to 3 ng/ml as measured over a 48-h period in culture supernatants. To determine whether NT-3 overexpression could abrogate DDP toxicity, cochlear explants were transduced with HSVnt-3myc or a murine intestinal alkaline phosphatase-expressing control vector, HSVmiap, and then exposed to cisplatin. HSVnt-3myc-transduced cochlear explants harbored significantly greater numbers of surviving SGNs than those infected with control virus. These data demonstrate that amplicon-mediated NT-3 transduction can attenuate the ototoxic action of DDP on organotypic culture. The potency of NT-3 in protecting spiral ganglion neurons from degeneration suggests that in vivo neurotrophin-based gene therapy may be useful for the prevention and/or treatment of hearing disorders.

FGF-2 regulation of neurogenesis in adult hippocampus after brain injury

Fibroblast growth factor-2 (FGF-2) promotes proliferation of neuroprogenitor cells in culture and is up-regulated within brain after injury. Using mice genetically deficient in FGF-2 (FGF-2(-/-) mice), we addressed the importance of endogenously generated FGF-2 on neurogenesis within the hippocampus, a structure involved in spatial, declarative, and contextual memory, after seizures or ischemic injury. BrdUrd incorporation was used to mark dividing neuroprogenitor cells and NeuN expression to monitor their differentiation into neurons. In the wild-type strain, hippocampal FGF-2 increased after either kainic acid injection or middle cerebral artery occlusion, and the numbers of BrdUrd/NeuN-positive cells significantly increased on days 9 and 16 as compared with the controls. In FGF-2(-/-) mice, BrdUrd labeling was attenuated after kainic acid or middle cerebral artery occlusion, as was the number of neural cells colabeled with both BrdUrd and NeuN. After FGF-2(-/-) mice were injected intraventricularly with a herpes simplex virus-1 amplicon vector carrying FGF-2 gene, the number of BrdUrd-labeled cells increased significantly to values equivalent to wild-type littermates after kainate seizures. These results indicate that endogenously synthesized FGF-2 is necessary and sufficient to stimulate proliferation and differentiation of neuroprogenitor cells in the adult hippocampus after brain insult.

Improved helper virus-free packaging system for HSV amplicon vectors using an ICP27-deleted, oversized HSV-1 DNA in a bacterial artificial chromosome

Herpes simplex virus type 1 (HSV-1) amplicons are prokaryotic plasmids containing one or more transcriptional units and two cis-acting HSV-1 sequences: a viral origin of DNA replication and a viral DNA cleavage/packaging signal. In the presence of HSV-1 "helper" functions, amplicons are replicated and packaged into HSV-1 virions. Despite recent improvements in packaging methods, stocks of amplicon vectors are still contaminated with replication-competent helper virus at a frequency of 10(-4)-10(-6). To overcome this problem, we report that: (i) genetic modifications of HSV-1 genomes can be routinely achieved in Escherichia coli, either by homologous or site-specific recombination, (ii) a novel HSV-1 bacterial artificial chromosome (fHSVDeltapacDelta27 0+), which has a deletion in the essential gene encoding ICP27 and an addition of ICP0 "stuffer" sequences to increase its size to 178 kb, supports the replication and packaging of cotransfected amplicon DNA without generating replication-competent helper virus (<1 helper virus per 10(8) TU amplicon vectors), and (iii) the resulting amplicon stocks have titers of up to 3-10 x 10(8) TU/ml after concentration. Elimination of replication-competent helper virus from HSV-1 amplicon vector stocks further improves safety in gene transfer applications.