A defective HSV-1 vector expresses Escherichia coli beta-galactosidase in cultured peripheral neurons

Introducing Genes into Mammalian Cells: Viral Vectors

Over the years, many different viral vector systems have been developed to take advantage of the specific biological properties and tropisms of a large number of mammalian viruses. As a result, researchers wanting to introduce and/or express genes in mammalian cells have many options, as discussed here.

Restriction of Replication of Oncolytic Herpes Simplex Virus with a Deletion of γ34.5 in Glioblastoma Stem-Like Cells

Oncolytic viruses, including herpes simplex viruses (HSVs), are a new class of cancer therapeutic engineered to infect and kill cancer cells while sparing normal tissue. To ensure that oncolytic HSV (oHSV) is safe in the brain, all oHSVs in clinical trial for glioma lack the γ34.5 genes responsible for neurovirulence. However, loss of γ34.5 attenuates growth in cancer cells. Glioblastoma (GBM) is a lethal brain tumor that is heterogeneous and contains a subpopulation of cancer stem cells, termed GBM stem-like cells (GSCs), that likely promote tumor progression and recurrence. GSCs and matched serum-cultured GBM cells (ScGCs), representative of bulk or differentiated tumor cells, were isolated from the same patient tumor specimens. ScGCs are permissive to replication and cell killing by oHSV with deletion of the γ34.5 genes (γ34.5- oHSV), while patient-matched GSCs were not, implying an underlying biological difference between stem and bulk cancer cells. GSCs specifically restrict the synthesis of HSV-1 true late (TL) proteins, without affecting viral DNA replication or transcription of TL genes. A global shutoff of cellular protein synthesis also occurs late after γ34.5- oHSV infection of GSCs but does not affect the synthesis of early and leaky late viral proteins. Levels of phosphorylated eIF2α and eIF4E do not correlate with cell permissivity. Expression of Us11 in GSCs rescues replication of γ34.5- oHSV. The difference in degrees of permissivity between GSCs and ScGCs to γ34.5- oHSV illustrates a selective translational regulatory pathway in GSCs that may be operative in other stem-like cells and has implications for creating oHSVs.IMPORTANCE Herpes simplex virus (HSV) can be genetically engineered to endow cancer-selective replication and oncolytic activity. γ34.5, a key neurovirulence gene, has been deleted in all oncolytic HSVs in clinical trial for glioma. Glioblastoma stem-like cells (GSCs) are a subpopulation of tumor cells thought to drive tumor heterogeneity and therapeutic resistance. GSCs are nonpermissive for γ34.5- HSV, while non-stem-like cancer cells from the same patient tumors are permissive. GSCs restrict true late protein synthesis, despite normal viral DNA replication and transcription of all kinetic classes. This is specific for true late translation as early and leaky late transcripts are translated late in infection, notwithstanding shutoff of cellular protein synthesis. Expression of Us11 in GSCs rescues the replication of γ34.5- HSV. We have identified a cell type-specific innate response to HSV-1 that limits oncolytic activity in glioblastoma.

Enhanced Vascularization and Survival of Neural Transplants with Ex Vivo Angiogenic Gene Transfer

Restoration of brain function by neural transplants is largely dependent upon the survival of donor neurons. Unfortunately, in both rodent models and human patients with Parkinson's disease the survival rate of transplanted neurons has been poor. We have employed a strategy to increase the availability of nutrients to the transplant by increasing the rate at which blood vessels are formed. Replication-deficient HSV-1 vectors containing the cDNA for human vascular endothelial growth factor (HSVhvegf) and the bacterial β-galacto-sidase gene (HSVlac) have been transduced in parallel into nonadherent neuronal aggregate cultures made of cells from embryonic day 15 rat mesencephalon. Gene expression from HSVlac was confirmed in fixed preparations by staining with X-gal. VEGF expression as determined by sandwich ELISA assay of culture supernatant was up to 322-fold higher in HSVhvegf-infected than HSVlac-infected sister cultures. This peptide was also biologically active, inducing endothelial cell proliferation in vitro. Adult Sprague-Dawley rats received bilateral transplants into the striatum, with HSVlac on one side and HSVhvegf on the other. At defined intervals up to 8 weeks, animals were sacrificed and vibratome sections of the striatum were assessed for various parameters of cell survival and vascularization. Results demonstrate dose-dependent increases in blood vessel density within transplants transduced with HSVhvegf. These transplants were vascularized at a faster rate up to 4 weeks after transplantation. After 8 weeks, the average size of the HSVhvegf-infected transplants was twice that of controls. In particular, the survival of transplanted dopaminergic neurons increased 3.9-fold. Taken together these experiments provide convincing evidence that the rate of vascularization may be a major determinant of neuronal survival that can be manipulated by VEGF gene transduction.

Neurobasal media facilitates increased specificity of siRNA-mediated knockdown in primary cerebellar cultures

BACKGROUND

Efficient and specific knockdown of proteins in post-mitotic cells such as differentiated neurons can be difficult to achieve. Further, special care must be taken to maintain the health of neurons in vitro. We wanted to achieve knockdown in primary cerebellar granule neurons, which can be effectively grown in Neurobasal™ media.

NEW METHOD

We tested the efficiency of siRNA from the Accell range from Dharmacon™ when delivered in Neurobasal™ media in contrast to the recommended Accell Delivery media provided by the manufacturer.

RESULTS

We observed a more specific knockdown of target in Neurobasal™ media, than in Accell Delivery media when using cerebellar granule neurons. Transfection efficiency and cell viability was comparable between the two media.

COMPARISON WITH EXISTING METHODS

Delivery of siRNA in Neurobasal™ media facilitates increased specificity of the knockdown compared to delivery in Accell Delivery media. The off-target effect observed in Accell Delivery media was not a secondary biological response to downregulation of target, but rather a mixture of specific and non-specific off-target effects.

CONCLUSIONS

Specific knockdown of target can be achieved in primary cerebellar granule cells using Accell siRNAs in Neurobasal™ media. This method ensures specific knockdown in post-mitotic neurons without the need for biosafety level 2 laboratories, additional reagents, or instruments needed by other transfection.

Gene regulation and genetics in neurochemistry, past to future

Ask any neuroscientist to name the most profound discoveries in the field in the past 60 years, and at or near the top of the list will be a phenomenon or technique related to genes and their expression. Indeed, our understanding of genetics and gene regulation has ushered in whole new systems of knowledge and new empirical approaches, many of which could not have even been imagined prior to the molecular biology boon of recent decades. Neurochemistry, in the classic sense, intersects with these concepts in the manifestation of neuropeptides, obviously dependent upon the central dogma (the established rules by which DNA sequence is eventually converted into protein primary structure) not only for their conformation but also for their levels and locales of expression. But, expanding these considerations to non-peptide neurotransmitters illustrates how gene regulatory events impact neurochemistry in a much broader sense, extending beyond the neurochemicals that translate electrical signals into chemical ones in the synapse, to also include every aspect of neural development, structure, function, and pathology. From the beginning, the mutability - yet relative stability - of genes and their expression patterns were recognized as potential substrates for some of the most intriguing phenomena in neurobiology - those instances of plasticity required for learning and memory. Near-heretical speculation was offered in the idea that perhaps the very sequence of the genome was altered to encode memories. A fascinating component of the intervening progress includes evidence that the central dogma is not nearly as rigid and consistent as we once thought. And this mutability extends to the potential to manipulate that code for both experimental and clinical purposes. Astonishing progress has been made in the molecular biology of neurochemistry during the 60 years since this journal debuted. Many of the gains in conceptual understanding have been driven by methodological progress, from automated high-throughput sequencing instruments to recombinant-DNA vectors that can convey color-coded genetic modifications in the chromosomes of live adult animals. This review covers the highlights of these advances, both theoretical and technological, along with a brief window into the promising science ahead. This article is part of the 60th Anniversary special issue.

Gene Transfer of Brain-derived Neurotrophic Factor (BDNF) Prevents Neurodegeneration Triggered by FXN Deficiency

Friedreich's ataxia is a predominantly neurodegenerative disease caused by recessive mutations that produce a deficiency of frataxin (FXN). Here, we have used a herpesviral amplicon vector carrying a gene encoding for brain-derived neurotrophic factor (BDNF) to drive its overexpression in neuronal cells and test for its effect on FXN-deficient neurons both in culture and in the mouse cerebellum in vivo. Gene transfer of BDNF to primary cultures of mouse neurons prevents the apoptosis which is triggered by the knockdown of FXN gene expression. This neuroprotective effect of BDNF is also observed in vivo in a viral vector-based knockdown mouse cerebellar model. The injection of a lentiviral vector carrying a minigene encoding for a FXN-specific short hairpin ribonucleic acid (shRNA) into the mouse cerebellar cortex triggers a FXN deficit which is accompanied by significant apoptosis of granule neurons as well as loss of calbindin in Purkinje cells. These pathological changes are accompanied by a loss of motor coordination of mice as assayed by the rota-rod test. Coinjection of a herpesviral vector encoding for BDNF efficiently prevents both the development of cerebellar neuropathology and the ataxic phenotype. These data demonstrate the potential therapeutic usefulness of neurotrophins like BDNF to protect FXN-deficient neurons from degeneration.

Neurons can be labeled with unique hues by helper virus-free HSV-1 vectors expressing Brainbow

BACKGROUND

A central problem in neuroscience is elucidating synaptic connections, the connectome. Because mammalian forebrains contain many neurons, labeling specific neurons with unique tags is desirable. A novel technology, Brainbow, creates hundreds of hues by combinatorial expression of multiple fluorescent proteins (FPs).

NEW METHOD

We labeled small numbers of neurons, and their axons, with unique hues, by expressing Brainbow from a helper virus-free Herpes Simplex Virus (HSV-1) vector.

RESULTS

The vector expresses a Brainbow cassette containing four FPs from a glutamatergic-specific promoter. Packaging HSV-Brainbow produced arrays of seven to eight Brainbow cassettes, and using Cre, each FP gene was in a position to be expressed, in different cassettes. Delivery into rat postrhinal (POR) cortex or hippocampus labeled small numbers of neurons with different, often unique, hues. An area innervated by POR cortex, perirhinal (PER) cortex, contained axons with different hues. Specific axons in PER cortex were matched to specific cell bodies in POR cortex, using hue.

COMPARISON WITH EXISTING METHODS

HSV-Brainbow is the only technology for labeling small numbers of neurons with unique hues. In Brainbow mice, many neurons contain the same hue. Brainbow-adeno-associated virus vectors require transduction of the same neuron with multiple vector particles, confounding neuroanatomical studies. Replication-competent Brainbow-pseudorabies virus vectors label multiple neurons with the same hue.

CONCLUSIONS

Attractive properties of HSV-Brainbow include each vector particle contains multiple cassettes, representing numerous hues, recombination products are stabile, and experimental control of the number of labeled neurons. Labeling neurons with unique hues will benefit mapping forebrain circuits.

Efficient gene delivery and selective transduction of astrocytes in the mammalian brain using viral vectors

Astrocytes are now considered as key players in brain information processing because of their newly discovered roles in synapse formation and plasticity, energy metabolism and blood flow regulation. However, our understanding of astrocyte function is still fragmented compared to other brain cell types. A better appreciation of the biology of astrocytes requires the development of tools to generate animal models in which astrocyte-specific proteins and pathways can be manipulated. In addition, it is becoming increasingly evident that astrocytes are also important players in many neurological disorders. Targeted modulation of protein expression in astrocytes would be critical for the development of new therapeutic strategies. Gene transfer is valuable to target a subpopulation of cells and explore their function in experimental models. In particular, viral-mediated gene transfer provides a rapid, highly flexible and cost-effective, in vivo paradigm to study the impact of genes of interest during central nervous system development or in adult animals. We will review the different strategies that led to the recent development of efficient viral vectors that can be successfully used to selectively transduce astrocytes in the mammalian brain.

Gene delivery using helper virus-free HSV-1 amplicon vectors

Herpes simplex virus type 1 (HSV-1)-based amplicon vectors contain only a very small percentage of the 152-kbp viral genome. Consequently, replication and packaging of amplicons depend on helper functions that are provided either by replication-defective mutants of HSV-1 or by replication-competent, but packaging-defective, HSV-1 genomes. Sets of cosmids that overlap and represent the entire HSV-1 genome can form, via homologous recombination, circular replication-competent viral genomes, which give rise to infectious virus progeny. However, if the DNA cleavage/packaging signals are deleted, reconstituted virus genomes are not packageable, but still provide all the helper functions required for the packaging of cotransfected amplicon DNA. The resulting stocks of packaged amplicon vectors are essentially free of contaminating helper virus. This unit describes the cotransfection of amplicon and cosmid or bacterial artificial chromosome (BAC) DNA into 2-2 cells by cationic liposome-mediated transfection and the harvesting of packaged vector particles. Support protocols provide methods for preparing cosmid and BAC DNA and determining the titers of amplicon stocks.

Overview of gene delivery into cells using HSV-1-based vectors

This overview describes the considerations involved in the preparation and use of a herpes simplex virus type 1 (HSV-1) amplicon as a vector for gene transfer into neurons. Strategies for gene delivery into neurons, either to study the molecular biology of brain function or for gene therapy, must utilize vectors that persist stably in postmitotic cells and that can be targeted both spatially and temporally in the nervous system in vivo. This unit describes the biology of HSV-1 along with a discussion covering development of amplicon and genomic HSV-1 vectors. Advantages and disadvantages of current HSV-1 vectors are presented, and HSV-1 vectors are compared with other vectors for gene transfer into neurons.

Overexpression of either lysine-specific demethylase-1 or CLOCK, but not Co-Rest, improves long-term expression from a modified neurofilament promoter, in a helper virus-free HSV-1 vector system

Long-term expression from helper virus-free Herpes Simplex Virus (HSV-1) vectors is required for many specific neural gene therapies and studies on neuronal physiology. We previously developed a promoter that supports long-term, neuron-specific expression by fusing the chicken ß-globin insulator (INS), followed by an upstream enhancer from the rat tyrosine hydroxylase (TH) promoter, to a neurofilament heavy gene (NFH) promoter. Here, we examined the capability of specific transcription factors to further improve long-term expression from this promoter. Following a HSV-1 virus infection, the virus genome is localized to promyelocytic leukemia protein (PML) nuclear bodies (NB). At these sites, specific cellular transcription factors interact with HSV-1 encoded transcription factors, and together regulate HSV-1 gene expression. Importantly, lysine-specific demethylase-1 (LSD1), CLOCK, and Co-Rest each activate HSV-1 gene expression. However, gene expression from HSV-1 vectors differs in a number of important aspects from the virus, including no HSV-1 genes are expressed. Nonetheless, these observations raise the possibility that specific transcription factors may improve long-term expression from specific promoters in HSV-1 vectors. Here, we show that overexpression of either LSD1 or CLOCK improves long-term expression from the INS-TH-NFH promoter, but overexpression of Co-Rest supports levels of long-term expression similar to those supported by a control vector. Further, overexpression of LSD1 is compatible with neuron-specific expression. Thus, overexpressing specific transcription factors can improve long-term expression from specific cellular promoters in HSV-1 vectors, and the chromatin structure of the vector has an important role in enabling expression.

A 16 bp upstream sequence from the rat tyrosine hydroxylase promoter supports long-term expression from a neurofilament promoter, in a helper virus-free HSV-1 vector system

Helper virus-free Herpes Simplex Virus vector-mediated gene transfer has supported studies on neuronal physiology, and may support specific gene therapies. Long-term, neuron-specific expression is required for many of these applications. A neurofilament heavy gene (NFH) promoter does not support long-term expression. We previously developed a promoter that supports long-term expression by fusing 6.3 kb of upstream sequences from the rat tyrosine hydroxylase (TH) promoter to a NFH promoter, and this promoter has supported physiological studies. The TH promoter fragment contains an enhancer, as it has activity in both orientations and at a distance from the basal promoter. Identifying this enhancer may support further improvements in long-term expression. A previous deletion analysis identified two ~100 bp fragments that each support long-term expression, and are contained within an ~320 bp fragment located ~3 kb from the TH promoter transcription start site. As this analysis used overlapping fragments, the two ~100 bp fragments contained 44 or 23 bp of unique sequence. Here, we used mutagenesis to identify a short sequence that supports long-term expression. We studied a 42 bp sequence, centered on the 23 bp unique sequence. Analysis of the wt sequence, and five mutations containing clustered changes that spanned the sequence, identified two adjacent mutations that do not support long-term expression, which together defined a 16 bp maximum essential sequence. This 16 bp sequence contains a putative E2F-1/DP-1 transcription factor binding site, and this transcription factor is expressed in many brain areas.

Antibody-mediated targeted gene transfer of helper virus-free HSV-1 vectors to rat neocortical neurons that contain either NMDA receptor 2B or 2A subunits

Because of the numerous types of neurons in the brain, and particularly the forebrain, neuron type-specific expression will benefit many potential applications of direct gene transfer. The two most promising approaches for achieving neuron type-specific expression are targeted gene transfer to a specific type of neuron and using a neuron type-specific promoter. We previously developed antibody-mediated targeted gene transfer with Herpes Simplex Virus (HSV-1) vectors by modifying glycoprotein C (gC) to replace the heparin binding domain, which mediates the initial binding of HSV-1 particles to many cell types, with the Staphylococcus A protein ZZ domain, which binds immunoglobulin (Ig) G. We showed that a chimeric gC-ZZ protein is incorporated into vector particles and binds IgG. As a proof-of-principle for antibody-mediated targeted gene transfer, we isolated complexes of these vector particles and an anti-NMDA NR1 subunit antibody, and demonstrated targeted gene transfer to neocortical cells that contain NR1 subunits. However, because most forebrain neurons contain NR1, we obtained only a modest increase in the specificity of gene transfer, and this targeting specificity is of limited utility for physiological experiments. Here, we report efficient antibody-mediated targeted gene transfer to NMDA NR2B- or NR2A-containing cells in rat postrhinal cortex, and a neuron-specific promoter further restricted recombinant expression to neurons. Of note, because NR2A-containing neurons are relatively rare, these results show that antibody-mediated targeted gene transfer with HSV-1 vectors containing neuron type-specific promoters can restrict recombinant expression to specific types of forebrain neurons of physiological significance.

Viral-mediated overexpression of mutant huntingtin to model HD in various species

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expansion of CAG repeats in the huntingtin (Htt) gene. Despite intensive efforts devoted to investigating the mechanisms of its pathogenesis, effective treatments for this devastating disease remain unavailable. The lack of suitable models recapitulating the entire spectrum of the degenerative process has severely hindered the identification and validation of therapeutic strategies. The discovery that the degeneration in HD is caused by a mutation in a single gene has offered new opportunities to develop experimental models of HD, ranging from in vitro models to transgenic primates. However, recent advances in viral-vector technology provide promising alternatives based on the direct transfer of genes to selected sub-regions of the brain. Rodent studies have shown that overexpression of mutant human Htt in the striatum using adeno-associated virus or lentivirus vectors induces progressive neurodegeneration, which resembles that seen in HD. This article highlights progress made in modeling HD using viral vector gene transfer. We describe data obtained with of this highly flexible approach for the targeted overexpression of a disease-causing gene. The ability to deliver mutant Htt to specific tissues has opened pathological processes to experimental analysis and allowed targeted therapeutic development in rodent and primate pre-clinical models.

Development of advanced therapies based on viral vector-mediated overexpression of therapeutic molecules and knockdown of disease-related genes for Parkinson’s disease

The last decade witnessed the translation of several gene-based therapeutic approaches from experimental studies to early clinical trials. Studies targeting the treatment of Parkinson’s disease (PD) were among the forefront of trials in the CNS. In this article, we overview three major strategies for the treatment of PD: the enzyme-replacement strategies are based on well-defined principles of functional restoration and are well suited for treatment of patients with advanced disease who would typically experience complications due to side effects of pharmacotherapy. Neurotrophic factor delivery, on the other hand, aims to delay the disability and eventually modifiy disease progression. Finally, we present an outlook to a completely new way of interfering with the disease process, which is taking advantage of recently discovered RNAi mechanisms in cells. Gene therapy is now becoming a reality in the clinics and developments in the next decade will help uncover the true potential of this approach for not only the treatment of PD patients, but also many other neurological disorders.

Genetic labeling of both the axons of transduced, glutamatergic neurons in rat postrhinal cortex and their postsynaptic neurons in other neocortical areas by herpes simplex virus vectors that coexpress an axon-targeted β-galactosidase and wheat germ agglutinin from a vesicular glutamate transporter-1 promoter

Neuronal circuits comprise the foundation for neuronal physiology and synaptic plasticity, and thus for consequent behaviors and learning, but our knowledge of neocortical circuits is incomplete. Mapping neocortical circuits is a challenging problem because these circuits contain large numbers of neurons, a high density of synapses, and numerous classes and subclasses of neurons that form many different types of synapses. Expression of specific genetic tracers in small numbers of specific subclasses of neocortical neurons has the potential to map neocortical circuits. Suitable genetic tracers have been established in neurons in subcortical areas, but application to neocortical circuits has been limited. Enabling this approach, Herpes Simplex Virus (HSV-1) plasmid (amplicon) vectors can transduce small numbers of neurons in a specific neocortical area. Further, expression of a particular genetic tracer can be restricted to specific subclasses of neurons; in particular, the vesicular glutamate transporter-1 (VGLUT1) promoter supports expression in VGLUT1-containing glutamatergic neurons in rat postrhinal (POR) cortex. Here, we show that expression of an axon-targeted β-galactosidase (β-gal) from such vectors supports mapping specific commissural and associative projections of the transduced neurons in POR cortex. Further, coexpression of wheat germ agglutinin (WGA) and an axon-targeted β-gal supports mapping both specific projections of the transduced neurons and identifying specific postsynaptic neurons for the transduced neurons. The neocortical circuit mapping capabilities developed here may support mapping specific neocortical circuits that have critical roles in cognitive learning.

Hexokinase II gene transfer protects against neurodegeneration in the rotenone and MPTP mouse models of Parkinson's disease

A typical feature of Parkinson's disease is the progressive loss of dopaminergic neurons in the substantia nigra, in which inhibition of mitochondrial complex I activity may play an important role. Rotenone or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) inhibit the mitochondrial complex I and they cause the death of substantia nigra dopaminergic neurons, thereby providing acute murine models of Parkinson's disease. We have found that increasing mitochondrial hexokinase II activity can prevent cell death in neuronal cultures treated with rotenone. As a result, we have studied the effects of hexokinase II gene transfer in vivo using a herpes simplex virus type 1 (HSV-1) amplicon vector. The placHK2 amplicon vector was injected into substantia nigra of mice that were subsequently administered rotenone or MPTP. Overexpression of hexokinase II prevented both rotenone and MPTP-induced dopaminergic neuronal cell death, as well as reducing the associated motor defects. Our results provide the first proof-of-principle that hexokinase II protects against dopaminergic neurodegeneration in vivo, emphasizing the role of this enzyme in promoting neuronal survival. Thus, the increase of hexokinase II expression by gene transfer or other means represents a promising approach to treat Parkinson's and other neurodegenerative diseases.

Antibody-mediated targeted gene transfer to NMDA NR1-containing neurons in rat neocortex by helper virus-free HSV-1 vector particles containing a chimeric HSV-1 glycoprotein C-staphylococcus A protein

Because of the heterogeneous cellular composition of the brain, and especially the forebrain, cell type-specific expression will benefit many potential applications of direct gene transfer. The two prevalent approaches for achieving cell type-specific expression are using a cell type-specific promoter or targeting gene transfer to a specific cell type. Targeted gene transfer with Herpes Simplex Virus (HSV-1) vectors modifies glycoprotein C (gC) to replace the heparin binding domain, which binds to many cell types, with a binding activity for a specific cell surface protein. We previously reported targeted gene transfer to nigrostriatal neurons using chimeric gC-glial cell line-derived neurotrophic factor or gC-brain-derived neurotrophic factor protein. Unfortunately, this approach is limited to cells that express the cognate receptor for either neurotrophic factor. Thus, a general strategy for targeting gene transfer to many different types of neurons is desirable. Antibody-mediated targeted gene transfer has been developed for targeting specific virus vectors to specific peripheral cell types; a specific vector particle protein is modified to contain the Staphylococcus A protein ZZ domain, which binds immunoglobulin (Ig) G. Here, we report antibody-mediated targeted gene transfer of HSV-1 vectors to a specific type of forebrain neuron. We constructed a chimeric gC-ZZ protein, and showed this protein is incorporated into vector particles and binds Ig G. Complexes of these vector particles and an antibody to the NMDA receptor NR1 subunit supported targeted gene transfer to NR1-containing neocortical neurons in the rat brain, with long-term (2 months) expression.

Thinking about repairing thinking

The work of Sinden et al. suggests that it may be possible to produce improvement in the “highest” areas of brain function by transplanting brain tissue. What appears to be the limiting factor is not the complexity of the mental process under consideration but the discreteness of the lesion which causes the impairment and the appropriateness and accuracy of placement of the grafted tissue.

Therapeutic uses for neural grafts: Progress slowed but not abandoned

In spite of Stein and Glasier's justifiable conclusion that initial optimism concerning the immediate clinical applicability of neural transplantation was premature, there exists much experimental evidence to support the potential for incorporating this procedure into a therapeutic arsenal in the future. To realize this potential will require continued evolution of our knowledge at multiple levels of the clinical and basic neurosciences.

The structure, operation, and functionality of intracerebral grafts

The concept of structure, operation, and functionality, as they may be understood by clinicians or researchers using neural transplantation techniques, are briefly defined. Following Stein & Glasier, we emphasize that the question of whether an intracerebral graft is really functional should be addressed not only in terms of what such a graft does in a given brain structure, but also in terms of what it does at the level of the organism.

The NGF superfamily of neurotrophins: Potential treatment for Alzheimer's and Parkinson's disease

Stein & Glasier suggest embryonic neural tissue grafts as a potential treatment strategy for Alzheimer's and Parkinson's disease. As an alternative, we suggest that the family of nerve growth factor-related neurotrophins and their trk (tyrosine kinase) receptors underlie cholinergic basal forebrain (CBF) and dopaminergic substantia nigra neuron degeneration in these diseases, respectively. Therefore, treatment approaches for these disorders could utilize neurotrophins.

Some practical and theoretical issues concerning fetal brain tissue grafts as therapy for brain dysfunctions

Grafts of embryonic neural tissue into the brains of adult patients are currently being used to treat Parkinson's disease and are under serious consideration as therapy for a variety of other degenerative and traumatic disorders. This target article evaluates the use of transplants to promote recovery from brain injury and highlights the kinds of questions and problems that must be addressed before this form of therapy is routinely applied. It has been argued that neural transplantation can promote functional recovery through the replacement of damaged nerve cells, the reestablishment of specific nerve pathways lost as a result of injury, the release of specific neurotransmitters, or the production of factors that promote neuronal growth. The latter two mechanisms, which need not rely on anatomical connections to the host brain, are open to examination for nonsurgical, less intrusive therapeutic use. Certain subjective judgments used to select patients who will receive grafts and in assessment of the outcome of graft therapy make it difficult to evaluate the procedure. In addition, little long-term assessment of transplant efficacy and effect has been done in nonhuman primates. Carefully controlled human studies, with multiple testing paradigms, are also needed to establish the efficacy of transplant therapy.

Models of neurological defects and defects in neurological models

The transition from research to patient following advances in transplantation research is likely to be disappointing unless it includes a better understanding of critically relevant characteristics of the neurological disorder and improvements in the animal models, particularly the behavioral features. The appropriateness of the model has less to do with the species than with how the species is used.

Pseudovirions as vehicles for the delivery of siRNA

Over the last two decades, small interfering RNA (siRNA)-mediated gene silencing has quickly become one of the most powerful techniques used to study gene function in vitro and a promising area for new therapeutics. Delivery remains a significant impediment to realizing the therapeutic potential of siRNA, a problem that is also tied to immunogenicity and toxicity. Numerous delivery vehicles have been developed, including some that can be categorized as pseudovirions: these are vectors that are directly derived from viruses but whose viral coding sequences have been eliminated, preventing their classification as viral vectors. Characteristics of the pseudovirions discussed in this review, namely phagemids, HSV amplicons, SV40 in vitro-packaged vectors, influenza virosomes, and HVJ-Envelope vectors, make them attractive for the delivery of siRNA-based therapeutics. Pseudovirions were shown to deliver siRNA effector molecules and bring about RNA interference (RNAi) in various cell types in vitro, and in vivo using immune-deficient and immune-competent mouse models. Levels of silencing were not always determined directly, but the duration of siRNA-induced knockdown lasted at least 3 days. We present examples of the use of pseudovirions for the delivery of synthetic siRNA as well as the delivery and expression of DNA-directed siRNA.

Versatile somatic gene transfer for modeling neurodegenerative diseases

A growing variety of technical approaches allow control over the expression of selected genes in living organisms. The ability to deliver functional exogenous genes involved in neurodegenerative diseases has opened pathological processes to experimental analysis and targeted therapeutic development in rodent and primate preclinical models. Biological adaptability, economic animal use, and reduced model development costs complement improved control over spatial and temporal gene expression compared with conventional transgenic models. A review of viral vector studies, typically adeno-associated virus or lentivirus, for expression of three proteins that are central to major neurodegenerative diseases, will illustrate how this approach has powered new advances and opportunities in CNS disease research.

Improved spatial learning in aged rats by genetic activation of protein kinase C in small groups of hippocampal neurons

Age-related decline in human cognition is well known, and there are correlative changes in the function of neocortical and hippocampal neurons. Similarly, age-related decline in learning has been observed in rodents, including deficits in a hippocampal-dependent learning paradigm, the Morris water maze. Furthermore, there are correlative deficits in specific signaling pathways, including protein kinase C (PKC) pathways, in cerebellar, hippocampal, or neocortical neurons. PKC pathways are strong candidates for mediating the molecular changes that underlie spatial learning, as they play critical roles in neurotransmitter release and synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), and deletion of specific PKC genes results in deficits in learning. Conversely, genetic activation of PKC pathways in small groups of hippocampal or cortical neurons enhances learning in specific paradigms. In this study, the authors delivered a constitutively active PKC into small groups of hippocampal dentate granule neurons in aged rats (using a herpes simplex virus-1 vector). Aged 2-year-old rats that received the constitutively active PKC displayed improved performance in the Morris water maze relative to controls in three different measures. These results indicate that PKC pathways play an important role in mediating spatial learning in aged rats. Additionally, these results represent a system for studying the neural mechanisms underlying aging-related learning deficits, and potentially developing gene therapies for cognitive and age-related deficits.

Bioluminescence imaging of calcium oscillations inside intracellular organelles

Ca(2+) oscillations inside intracellular organelles are important for regulation of functions such as gene expression at the nucleus, respiration at mitochondria or protein processing at the endoplasmic reticulum. Targeted aequorins are excellent calcium probes for subcellular analysis, but single-cell imaging has proven difficult because of low light yield. Here we describe a procedure that combines virus-based expression of targeted aequorins with photon-counting imaging. This methodology allows real-time resolution of changes of cytosolic, mitochondrial or nuclear Ca(2+) signals at the single-cell level.

Attenuation of seizure in P77PMC rats with an HSV-vector expressing IL-1ra in brain

Cloned human IL-1ra (IL-1 receptor antagonist, IL-1ra) cDNA is inserted into pHSVLac, resulting in recombinant named pHSV-IL-1ra. pHSVLac and pHSV-IL-lra were packaged into HSV-1 particles using HSV-1 ts K as helper virus. The results showed that: (i) vero cell infected by pHSV-IL-1ra particles showed IL-1ra expression; expression of beta-galactosidase is observed in meninges and some neurons closed to ventricular and maintained for 8 weeks in rats after intracerebroventricular injection of pHSV-IL-1ra particles; (ii) transgenic expression of IL-lra by pHSVIL-lra injection significantly inhibited seizure attacks of P77PMC rat. These studies indicate that HSV-1 vector expressing IL-1ra in brain attenuated seizure attacks of P77PMC rat.

Overview of gene delivery into cells using HSV-1-based vectors

This overview describes the considerations involved in the preparation and use of herpes simplex virus type 1 (HSV-1) as a vector for gene transfer into neurons. Strategies for gene delivery into neurons, either to study the molecular biology of brain function or for gene therapy, must utilize vectors that persist stably in postmitotic cells and that can be targeted both spatially and temporally in the nervous system in vivo. This unit describes the biology of HSV-1 along with a discussion covering development of amplicon and genomic HSV-1 vectors. Advantages and disadvantages of current HSV-1 vectors are presented, and HSV-1 vectors are compared with other vectors for gene transfer into neurons.

Generation of high-titer defective HSV-1 vectors

There are two types of replication-deficient herpes simplex virus type 1 (HSV-1) vectors: those in which the foreign DNA of interest is cloned into the viral genome itself, and those that are comprised of a plasmid (amplicon) carrying minimal HSV-1 sequences that allow it to be packaged into virus particles with the aid of a helper virus. This unit describes the generation of helper virus stocks. Preparation of recombinant amplicon vector particles by transfection of amplicon and superinfection of helper virus into cells, and harvesting of packaged particles, is also delineated. Thorough characterization of the viral vector stock involves measuring (1) the helper virus plaque-forming units per ml (pfu/ml) on 2-2 cells, (2) the wild-type HSV-1 pfu/ml on Vero cells, and (3) the amplicon stock infectious vector units per ml (ivu/ml) on PC12 cells. Support protocols detail methods for determining titers of helper virus and wild-type virus by plaque assay, and of amplicon stocks by vector assay.

Gene delivery using helper virus-free HSV-1 amplicon vectors

Herpes simplex virus type 1 (HSV-1)-based amplicon vectors contain only 1% of the viral genome. Consequently, replication and packaging of amplicons depend on helper functions provided either by replication-defective mutants of HSV-1 (helper viruses) or by replication-competent, but packaging-defective, HSV-1 genomes. Sets of cosmids that overlap and represent the entire HSV-1 genome can form, via homologous recombination, circular replication-competent viral genomes, which give rise to infectious virus progeny. If the DNA cleavage/packaging signals are deleted, reconstituted virus genomes are not packageable, but still provide all the helper functions required for the packaging of cotransfected amplicon DNA. Resulting stocks of packaged amplicon vectors are free of contaminating helper virus. The basic protocol describes the cotransfection of amplicon and cosmid DNA into 2-2 cells and the harvesting of packaged vector particles. Support protocols describe preparing cosmid DNA and methods for determining the titers of amplicon stocks.

Construction of replication-defective herpes simplex virus vectors

Advances in identification and characterization of gene products responsible for specific diseases of the nervous system have opened opportunities for novel therapies using gene transfer vectors for gene replacement. Herpes simplex virus (HSV)-based vectors are particularly well suited for gene delivery to neurons of the central and peripheral nervous systems. The authors have developed methods to delete HSV-1 IE gene functions and to subsequently introduce foreign genes into the HSV-1 genome using homologous recombination. This unit describes methods for generating cell lines that complement multiple essential gene deletion mutants as well for generating such replication-defective virus recombinants and inserting foreign DNA sequences into replication-defective viral genomes, the last step in preparing a vector. Three support protocols describe methods for preparing virus stocks, titering virus, and preparing viral DNA.

Enhanced nigrostriatal neuron-specific, long-term expression by using neural-specific promoters in combination with targeted gene transfer by modified helper virus-free HSV-1 vector particles

Background

Direct gene transfer into neurons has potential for developing gene therapy treatments for specific neurological conditions, and for elucidating neuronal physiology. Due to the complex cellular composition of specific brain areas, neuronal type-specific recombinant gene expression is required for many potential applications of neuronal gene transfer. One approach is to target gene transfer to a specific type of neuron. We developed modified Herpes Simplex Virus (HSV-1) particles that contain chimeric glycoprotein C (gC) – glial cell line-derived neurotrophic factor (GDNF) or brain-derived neurotrophic factor (BDNF) proteins. HSV-1 vector particles containing either gC – GDNF or gC – BDNF target gene transfer to nigrostriatal neurons, which contain specific receptors for GDNF or BDNF. A second approach to achieve neuronal type-specific expression is to use a cell type-specific promoter, and we have used the tyrosine hydroxylase (TH) promoter to restrict expression to catecholaminergic neurons or a modified neurofilament heavy gene promoter to restrict expression to neurons, and both of these promoters support long-term expression from HSV-1 vectors. To both improve nigrostriatal-neuron specific expression, and to establish that targeted gene transfer can be followed by long-term expression, we performed targeted gene transfer with vectors that support long-term, neuronal-specific expression.

Results

Helper virus-free HSV-1 vector packaging was performed using either gC – GDNF or gC – BDNF and vectors that contain either the TH promoter or the modified neurofilament heavy gene promoter. Vector stocks were injected into the midbrain proximal to the substantia nigra, and the rats were sacrificed at either 4 days or 1 month after gene transfer. Immunofluorescent costaining was performed to detect both recombinant gene products and nigrostriatal neurons. The combination of targeted gene transfer with neuronal-specific promoters improved nigrostriatal neuron-specific expression (83 to 93%) compared to either approach alone, and supported long-term (1 month) expression at levels similar to those observed using untargeted gene transfer.

Conclusion

Targeted gene transfer can be used in combination with neuronal-specific promoters to achieve a high level of nigrostriatal neuron-specific expression. Targeted gene transfer can be followed by long-term expression. Nigrostriatal neuron-specific expression may be useful for specific gene therapy approaches to Parkinson's disease or for genetic analyses of nigrostriatal neuron physiology.

Reduced pathology and improved behavioral performance in Alzheimer's disease mice vaccinated with HSV amplicons expressing amyloid-beta and interleukin-4

Immunotherapeutics designed to dissolve existing amyloid plaques or to interrupt amyloid-beta (Abeta) accumulation may be feasible for treatment and/or prevention of Alzheimer's disease (AD). "Shaping" the immune responses elicited against Abeta is requisite toward generating an efficacious and safe outcome; this can be achieved by minimizing the possibility of deleterious inflammatory reactions in the brain as observed in clinical testing of Abeta peptide/adjuvant-based modalities. Herpes simplex virus (HSV)-based amplicons can coexpress multiple antigens and/or immunomodulatory genes due to their large genetic size capacity, thereby facilitating antigen-specific immune response shaping. We have constructed an amplicon (HSV(IE)Abeta(CMV)IL-4) that co-delivers Abeta(1-42) with interleukin-4 (IL-4), a cytokine that promotes the generation of Th2-like T-cell responses, which are favored in the setting of AD immunotherapy. Triple-transgenic AD (3xTg-AD) mice, which progressively develop both amyloid and neurofibrillary tangle pathology, were vaccinated thrice with HSV(IE)Abeta(CMV)IL-4, or a set of control amplicon vectors. Increased Th2-related, Abeta-specific antibodies, improved learning and functioning of memory, and prevention of AD-related amyloid and tau pathological progression were observed significantly more in the HSV(IE)Abeta(CMV)IL-4 vaccinated mice as compared to the other experimental groups. Our study underscores the potential of Abeta immunotherapy for AD and highlights the potency of amplicons in facilitating the immune response modulation to a disease-relevant antigen.

Hexamethylene bisacetamide leads to reduced helper virus-free HSV-1 amplicon expression titers via suppression of ICP0

The herpes simplex virus (HSV)-derived amplicon vector has evolved into a promising gene transfer platform for widespread DNA delivery in gene replacement strategies and vaccine development given its ease of molecular manipulation, large transgene capacity, and transduction efficiencies of numerous cell types in vivo. The recent development of helper virus-free packaging methodologies bodes well for this vector system in its eventual implementation as a clinically viable therapeutic modality. For realization of clinical application, efforts have been made to enhance yields and quality of helper-free amplicon stocks. Hexamethylene bisacetamide (HMBA), a hybrid polar compound that exhibits stimulatory activity of HSV-1 immediate-early gene expression, has been employed as a standard reagent in helper virus-free packaging given its purported mode of action on virus gene expression kinetics. Unexpectedly, we have found that HMBA exhibits no titer-enhancing activity; in contrast, the compound enhances the proportion of amplicon virions that are non-expressive. Omission of HMBA during vector packaging led to a marked reduction in the ratios of vector genome-transducing to transgene-expressing virions. This effect was neither packaging-cell-specific nor amplicon-promoter-dependent. Analysis of resultant vector stocks indicated amplicon genome replication/concatenation was unaffected, but the level of particle-associated ICP0 was reduced in stocks packaged in the presence of HMBA. Inclusion of a co-transfected, ICP0-expressing plasmid into the packaging process led to significant rescue of amplicon expression titers, indicating that regulation of ICP0 concentrations is critical for maintenance of the amplicon genome expressive state.

Nerve-sparing therapy with oncolytic herpes virus for cancers with neural invasion

PURPOSE

The invasion of cancer cells along nerves is an ominous pathologic finding associated with poor outcomes for a variety of tumors, including pancreatic and head and neck carcinomas. Peripheral nerves may serve as a conduit for these cancers to track into the central nervous system. Cancer progression within nerves and surgical resection of infiltrated nerves result in a permanent loss of neural function, potentially causing cosmetic and functional morbidity. Herpes simplex viruses (HSV) have utility for gene transfer into nerves and as oncolytic agents. We studied the use of an attenuated HSV, NV1023, as treatment for cancers with neural invasion.

EXPERIMENTAL DESIGN AND RESULTS

NV1023 injection into the sciatic nerves of nude mice had no toxic effect on nerve function, whereas similar doses of wild-type HSV-1 (F' strain) caused complete nerve paralysis within 4 days and 100% mortality at day 6. NV1023 showed effective cytotoxicity in vitro on three neurotrophic human carcinoma cell lines, including pancreatic (MiaPaCa2), squamous cell (QLL2), and adenoid cystic (ACC3) carcinomas. A model of neural invasion was established by implanting human carcinoma cells in the sciatic nerves of nude mice. All control group mice developed left hind limb paralysis 5 to 7 weeks after tumor injection, whereas animals treated with NV1023 maintained intact nerve function and showed significant tumor regression (P < 0.0001).

CONCLUSIONS

These results show that NV1023 oncolytic therapy may effectively treat cancers with neural invasion and preserve neural function. These findings hold significant clinical implications for patients with cancer neural invasion.

HSV-1 amplicon vectors: a promising and versatile tool for gene delivery

Amplicons are defective and non-integrative vectors derived from herpes simplex virus type 1. They carry no virus genes in the vector genome and are, therefore, not toxic to the infected cells or pathogenic for the transduced organisms, making these vectors safe. In addition, the large transgenic capacity of amplicons, which allow delivery of < or = 150 Kbp of foreign DNA, make these vectors one of the most powerful, interesting and versatile gene delivery platforms. Here, the authors present recent technological developments that have significantly improved and extended the use of amplicons, both in cultured cells and in living organisms. In addition, this review illustrates the many possible applications that are presently being developed with amplicons and discuss the many difficulties still pending to be solved in order to achieve stable and physiologically regulated transgenic expression.

Neuronal specificity of HSV/sleeping beauty amplicon transduction in utero is driven primarily by tropism and cell type composition

A novel bipartite vector system consisting of the herpes simplex virus (HSV) amplicon and the Sleeping Beauty(SB) transposon was previously shown to efficiently deliver a "transgenon" (integrating transgene) in utero. This vector platform facilitated long-term transgenon expression specifically within neurons and neuronal precursor cells of the rodent brain. However, the mechanism underlying the neurospecificity of the HSV/SB amplicon in the setting of mouse embryogenesis is unknown. We find that embryonic cells expressing the Sox1 "neurocompetence" transcription factor represent the primary targets for HSV amplicon transduction in utero. These cells, which comprise the ependymal and subventricular zones (SVZs), express significant levels of high-mobility-group protein B1 (HMGB1), a co-factor shown to facilitate SB-mediated transposition. Using a conventional, non-integrating amplicon expressing Cre recombinase to "tag" transduced cells embryonically in ROSA26 Cre indicator mice in utero, we found transduced cells were exclusively of the neuronal lineage but that in comparison to HSV/SB-mediated in utero delivery, staining patterns were less widespread and "tagged" neuroprogenitor cells were absent. Our findings demonstrate that in utero HSV/SB amplicon gene transfer is primarily neurospecific owing to viral tropism and target cell populations present embryonically, where multi-potent cells of the developing embryo are supportive of SB-driven transposition.

Infectivity of herpes simplex virus type-1 (HSV-1) amplicon vectors in dendritic cells is determined by the helper virus strain used for packaging

Herpes simplex virus type-1 (HSV-1) amplicon vectors are being explored for a wide range of potential applications, including vaccine delivery and immunotherapy of cancer. While extensive effort has been directed towards the improvement of the amplicon "payload" in these vectors, relatively little attention has been paid to the effect of the packaging HSV-1 strains on the biological properties of co-packaged amplicon vectors. We therefore compared the biological properties of amplicon stocks prepared using a panel of primary HSV-1 isolates, a molecularly cloned strain used to package helper-free amplicons (designated here as F5), and two laboratory isolates (KOS and strain 17, which is the parent of the F5 clone). This analysis revealed considerable inter-strain variability in the ability of amplicon stocks packaged by different primary HSV-1 isolates to efficiently transduce established cell lines and primary human dendritic cells (DC). Amplicons packaged by both the F5 molecularly cloned virus and its laboratory-adapted parent (strain 17) were very inefficient at transducing DC, when compared to amplicons packaged by KOS or by several of the primary virus isolates. These finding have important implications for the future development of improved amplicon-based vaccine delivery systems and suggest that DC tropism may be an instrinsic property of some HSV-1 strains, independent of passage history or molecular cloning.

Nuclear calcium signaling by inositol trisphosphate in GH3 pituitary cells

It has been proposed that nuclear and cytosolic Ca(2+) ([Ca(2+)](N) and [Ca(2+)](C)) may be regulated independently. We address here the issue of whether inositol trisphosphate (IP(3)) can, bypassing changes of [Ca(2+)](C), produce direct release of Ca(2+) into the nucleoplasm. We have used targeted aequorins to selectively measure and compare the changes in [Ca(2+)](C) and [Ca(2+)](N) induced by IP(3) in GH(3) pituitary cells. Heparin, an IP(3) inhibitor that does not permeate the nuclear pores, abolished the [Ca(2+)](C) peaks but inhibited only partly the [Ca(2+)](N) peaks. The permeant inhibitor 2-aminoethoxy-diphenyl-borate (2-APB) blocked both responses. Removal of ATP also inhibited more strongly the [Ca(2+)](C) than [Ca(2+)](N) peak. The [Ca(2+)](N) and [Ca(2+)](C) responses differed also in their sensitivity to IP(3), the nuclear response showing higher affinity. Among IP(3) receptors, type 2 (IP(3)R2) has a higher affinity for IP(3) and is not inactivated by ATP removal. We find that IP(3)R2 immunoreactivity is present inside the nucleus whereas the other IP(3)R subtypes are detected only in the cytoplasm. The nuclear envelope (NE) of GH(3) cells showed deep invaginations into the nucleoplasm, with cytosol and cytoplasmic organella inside. These results indicate that GH(3) pituitary cells possess mechanisms able to produce selective increases of [Ca(2+)](N).

Functional recovery in a Friedreich's ataxia mouse model by frataxin gene transfer using an HSV-1 amplicon vector

There is currently no effective treatment for Friedreich's ataxia (FA), the most common of the hereditary ataxias. The disease is caused by mutations in FRDA that drastically reduce expression levels of the mitochondrial protein frataxin. In FA animal models, a key difficulty is obtaining the precise levels of frataxin expression in the appropriate tissues to provoke pathology without early lethality. To develop strategies to circumvent these problems, conditional frataxin transgenic mice have been generated. We now show that frataxin expression can be eliminated in neurons from these loxP[frda] mice by infection with CRE-expressing herpes simplex virus type 1 (HSV-1) amplicon vectors. We have also achieved in vivo delivery by stereotaxic injection of these CRE-expressing vectors into the brainstem of loxP[frda] mice to generate a localized gene knockout model. These mice develop a behavioral deficit in the rotarod assay detectable after 4 weeks, and when re-injected with HSV-1 amplicon vectors expressing human frataxin complementary DNA (cDNA) exhibit behavioral recovery as early as 4 weeks after the second injection. To the best of our knowledge, this is the first proof of principle of recovery of neurological function by a therapeutic agent aimed at correcting frataxin deficiency.

An HSV-1 amplicon system for prostate-specific expression of ICP4 to complement oncolytic viral replication for in vitro and in vivo treatment of prostate cancer cells

The aim of the present study was to determine whether a prostate-specific amplicon, containing a probasin-derived promoter (ARR(2)PB) upstream of an essential Herpes simplex virus-1 (HSV-1) viral gene, infected-cell polypeptide 4 (ICP4), could complement an HSV-1 helper virus with this gene deleted (ICP4-) and cause lytic replication specifically in prostate cancer cells. Two amplicon constructs, CMV-ICP4 and ARR(2)PB-ICP4, were packaged by a replication-deficient ICP4- helper virus. The amplicon viruses could complement ICP4- helper viruses to efficiently replicate and cause cell lysis in prostate cancer cells. Intratumoral injection of LNCaP human prostate cancer xenografts with either amplicon/helper virus resulted in >75% reduction in tumor volume and serum prostate specific antigen (PSA). Histological and Q-PCR (quantitative PCR) analyses indicated that the toxicity in nontumor tissues was much lower with ARR(2)PB-ICP4 than with CMV-ICP4 amplicon/helper virus. In conclusion, a replication-deficient HSV-1 virus could be complemented by an amplicon virus to restore its oncolytic activity in a tissue-specific and low toxicity fashion, illustrating that this approach could be a potentially useful strategy for developing an oncolytic viral therapy for prostate cancer.

Spatial and temporal expression of herpes simplex virus type 1 amplicon-encoded genes: implications for their use as immunization vectors

There is great interest in developing new immunization vectors. Helper virus-free herpes amplicons, plasmid-based vectors that encode no viral gene products and have an extremely large coding capacity, are attractive viral vaccine candidates for expressing recombinant proteins in vivo for immunization. Earlier studies in mice, using amplicons encoding the gp120 protein of human immunodeficiency virus (HIV), resulted in strikingly robust cellular immune responses as measured by cytotoxicity and interferon gamma enzyme-linked immunospot assays. To begin to understand how such vectors function in vivo to generate an immune response, we used amplicons encoding reporter constructs including green fluorescent protein (GFP) and luciferase to examine the duration of expression after administration to mice. Luciferase expression, measured with the IVIS system from Xenogen/Caliper Life Sciences (Hopkinton, MA) and by enzymatic assays of tissue extracts, revealed that expression after injection of the HSVluc amplicons peaked earlier than 24 hr after injection into mice. HSVegfp injection resulted in peak accumulation of GFP 24 hr after administration in vivo. Thus, both reporter genes revealed a rather rapid and robust expression pattern of short duration. The short period of expression appears in part to be due to gene silencing. Examination of the cells transduced by amplicons encoding GFP and human B7.1 suggested that the amplicons transduce a variety of cells, including professional antigen-presenting cells. From this and previous work, we conclude that amplicons may engender a potent immune response by directly transducing dendritic cells as well as by cross-priming of antigen produced by other transduced host cells.

Viral vectors: a wide range of choices and high levels of service

Viruses are intracellular parasites with simple DNA or RNA genomes. Virus life revolves around three steps: infection of a host cell, replication of its genome within the host cell environment, and formation of new virions; this process is often but not always associated with pathogenic effects against the host organism. Since the mid-1980s, the main goal of viral vectorology has been to develop recombinant viral vectors for long-term gene delivery to mammalian cells, with minimal associated toxicity. Today, several viral vector systems are close to achieving this aim, providing stable transgenic expression in many different cell types and tissues. Here we review application characteristics of four vector systems, derived from adeno-associated viruses, adenoviruses, retroviruses and herpes simplex virus-1, for in vivo gene delivery. We discuss the transfer capacity of the expression vectors, the stability of their transgenic expression, the tropism of the recombinant viruses, the likelihood of induction of immunotoxicity, and the ease (or difficulty) of the virus production. In the end, we discuss applications of these vectors for delivery of three molecular systems for conditional mutagenesis, two for inducible transcriptional control of transgenic expression (the tet and the dimerizer systems), and the third one for inducible control of endogenous gene expression based on RNA interference.

Isolation of an enhancer from the rat tyrosine hydroxylase promoter that supports long-term, neuronal-specific expression from a neurofilament promoter, in a helper virus-free HSV-1 vector system

Direct gene transfer into neurons, using a virus vector, has been used to study neuronal physiology and learning, and has potential for supporting gene therapy treatments for specific neurological diseases. Many of these applications require high-level, long-term recombinant gene expression, in forebrain neurons. We previously showed that addition of upstream sequences from the rat tyrosine hydroxylase (TH) promoter to a neurofilament heavy gene (NF-H) promoter supports long-term expression in forebrain neurons, from helper virus-free Herpes Simplex Virus (HSV-1) vectors. This element in the TH promoter satisfied the definition of an enhancer; it displayed activity at a distance from the basal promoter, and in both orientations. This enhancer supported physiological studies that required long-term expression; a modified neurofilament promoter, containing an insulator upstream of the TH-NFH promoter, supported expression in approximately 11,400 striatal neurons at 6 months after gene transfer, and expression for 7, 8, or 14 months, the longest times tested. In contrast, the NF-H promoter alone does not support long-term expression, indicating that the critical sequences are in the 6.3 kb fragment of the TH promoter. In this study, we performed a deletion analysis to identify the critical sequences in the TH promoter that support long-term expression. We localized these critical sequences to an approximately 320 bp fragment, and two subfragments of approximately 100 bp each. Vectors that contained each of these small fragments supported levels of long-term, neuronal-specific expression that were similar to the levels supported by a vector that contained the initial 6.3 kb fragment of the TH promoter. These small fragments of the TH promoter may benefit construction of vectors for physiological studies, and may support studies on the mechanism by which this enhancer supports long-term expression.