Gene transfer into the central nervous system in vivo using a recombinanat lentivirus vector

The transformative potential of HSC gene therapy as a genetic medicine

Hematopoietic stem cells (HSCs) are precursor cells that give rise to blood, immune and tissue-resident progeny in humans. Their position at the starting point of hematopoiesis offers a unique therapeutic opportunity to treat certain hematologic diseases by implementing corrective changes that are subsequently directed through to multiple cell lineages. Attempts to exploit HSCs clinically have evolved over recent decades, from initial approaches that focused on transplantation of healthy donor allogeneic HSCs to treat rare inherited monogenic hematologic disorders, to more contemporary genetic modification of autologous HSCs offering the promise of benefits to a wider range of diseases. We are on the cusp of an exciting new era as the transformative potential of HSC gene therapy to offer durable delivery of gene-corrected cells to a range of tissues and organs, including the central nervous system, is beginning to be realized. This article reviews the rationale for targeting HSCs, the approaches that have been used to date for delivering therapeutic genes to these cells, and the latest technological breakthroughs in manufacturing and vector design. The challenges faced by the biotechnology cell and gene therapy sector in the commercialization of HSC gene therapy are also discussed.

Revisiting gene delivery to the brain: silencing and editing

Neurodegenerative disorders, ischemic brain diseases, and brain tumors are debilitating diseases that severely impact a person's life and could possibly lead to their demise if left untreated. Many of these diseases do not respond to small molecule therapeutics and have no effective long-term therapy. Gene therapy offers the promise of treatment or even a cure for both genetic and acquired brain diseases, mediated by either silencing or editing disease-specific genes. Indeed, in the last 5 years, significant progress has been made in the delivery of non-coding RNAs as well as gene-editing formulations to the brain. Unfortunately, the delivery is a major limiting factor for the success of gene therapies. Both viral and non-viral vectors have been used to deliver genetic information into a target cell, but they have limitations. Viral vectors provide excellent transduction efficiency but are associated with toxic effects and have limited packaging capacity; however, non-viral vectors are less toxic and show a high packaging capacity at the price of low transfection efficiency. Herein, we review the progress made in the field of brain gene therapy, particularly in the design of non-toxic and trackable non-viral vectors, capable of controlled release of genes in response to internal/external triggers, and in the delivery of formulations for gene editing. The application of these systems in the context of various brain diseases in pre-clinical and clinical tests will be discussed. Such promising approaches could potentially pave the way for clinical realization of brain gene therapies.

Preliminary study of microRNA-126 as a novel therapeutic target for primary hypertension

The present study aimed to explore microRNA-126 (miR-126) as a novel therapeutic target for primary hypertension. The lentiviral vector containing human immunodeficiency virus 1 (HIV-1), the miR-126 gene knockdown viral vector (lenti-miR-126-KD), and control lentiviral vector (lenti-scramble-miR) were constructed. Spontaneously hypertensive rats were randomly divided into 4 groups, which received a high dose of lenti-miR-126-KD (1×10⁸, n=5), low dose of lenti-miR-126-KD (1×10⁷, n=6), scramble-miR (5×10⁷, n=6), and PBS (n=6). Lentiviral vectors were injected into the tail vein. Data on the systolic blood pressure, diastolic pressure, mean arterial pressure, and heart rate were collected weekly. After 8 weeks of virus administration, the distribution of lentiviral vectors in different tissues was observed by fluorescence microscopy. Picric acid Sirius red and H&E staining were used to observe the target organ damage, and the ELISA kit was used to determine the serum nitric oxide (NO) content. The lentiviral vector was found to be constructed successfully. Eight weeks after the lentiviral vector injection, green fluorescent protein was observed in different tissues in each group. The blood pressure and heart rate were not significantly altered after lentiviral vector injection (P>0.05). No significant differences in the heart-to-body weight ratio among the four groups were observed (P=0.23). Picric acid Sirius red and H&E staining revealed that there was no significant difference in morphology among the four groups. No significant difference in the serum NO level among the four groups was noted (P=0.23). The miR-126 gene knockdown lentiviral vector was constructed successfully. No significant antihypertensive effect was observed by the knockdown of miR-126 for the treatment of primary hypertension. The target organs were not protected significantly after the treatment. The increased level of miR-126 expression in hypertensive patients may be due to a compensatory mechanism.

Endothelial cells maintain neural stem cells quiescent in their niche

Niches are specialized microenvironments that regulate stem cells' activity. The neural stem cell (NSC) niche defines a zone in which NSCs are retained and produce new cells of the nervous system throughout life. Understanding the signaling mechanisms by which the niche controls the NSC fate is crucial for the success of clinical applications. In a recent study, Sato and colleagues, by using state-of-the-art techniques, including sophisticated in vivo lineage-tracing technologies, provide evidence that endothelial amyloid precursor protein (APP) is an important component of the NSC niche. Strikingly, depletion of APP increased NSC proliferation in the subventricular zone, indicating that endothelial cells negatively regulate NSCs' growth. The emerging knowledge from this research will be important for the treatment of several neurological diseases.

Comparative study of the transfection efficiency of commonly used viral vectors in rhesus monkey (Macaca mulatta) brains

Viral vector transfection systems are among the simplest of biological agents with the ability to transfer genes into the central nervous system. In brain research, a series of powerful and novel gene editing technologies are based on these systems. Although many viral vectors are used in rodents, their full application has been limited in non-human primates. To identify viral vectors that can stably and effectively express exogenous genes within non-human primates, eleven commonly used recombinant adeno-associated viral and lentiviral vectors, each carrying a gene to express green or red fluorescence, were injected into the parietal cortex of four rhesus monkeys. The expression of fluorescent cells was used to quantify transfection efficiency. Histological results revealed that recombinant adeno-associated viral vectors, especially the serotype 2/9 coupled with the cytomegalovirus, human synapsin I, or Ca2+/calmodulin-dependent protein kinase II promoters, and lentiviral vector coupled with the human ubiquitin C promoter, induced higher expression of fluorescent cells, representing high transfection efficiency. This is the first comparison of transfection efficiencies of different viral vectors carrying different promoters and serotypes in non-human primates (NHPs). These results can be used as an aid to select optimal vectors to transfer exogenous genes into the central nervous system of non-human primates.

Destination Brain: the Past, Present, and Future of Therapeutic Gene Delivery

Neurological diseases and disorders (NDDs) present a significant societal burden and currently available drug- and biological-based therapeutic strategies have proven inadequate to alleviate it. Gene therapy is a suitable alternative to treat NDDs compared to conventional systems since it can be tailored to specifically alter select gene expression, reverse disease phenotype and restore normal function. The scope of gene therapy has broadened over the years with the advent of RNA interference and genome editing technologies. Consequently, encouraging results from central nervous system (CNS)-targeted gene delivery studies have led to their transition from preclinical to clinical trials. As we shift to an exciting gene therapy era, a retrospective of available literature on CNS-associated gene delivery is in order. This review is timely in this regard, since it analyzes key challenges and major findings from the last two decades and evaluates future prospects of brain gene delivery. We emphasize major areas consisting of physiological and pharmacological challenges in gene therapy, function-based selection of a ideal cellular target(s), available therapy modalities, and diversity of viral vectors and nanoparticles as vehicle systems. Further, we present plausible answers to key questions such as strategies to circumvent low blood-brain barrier permeability and most suitable CNS cell types for targeting. We compare and contrast pros and cons of the tested viral vectors in the context of delivery systems used in past and current clinical trials. Gene vector design challenges are also evaluated in the context of cell-specific promoters. Key challenges and findings reported for recent gene therapy clinical trials, assessing viral vectors and nanoparticles are discussed from the perspective of bench to bedside gene therapy translation. We conclude this review by tying together gene delivery challenges, available vehicle systems and comprehensive analyses of neuropathogenesis to outline future prospects of CNS-targeted gene therapies.

Genetic barcoding with fluorescent proteins for multiplexed applications

Fluorescent proteins, fluorescent dyes and fluorophores in general have revolutionized the field of molecular cell biology. In particular, the discovery of fluorescent proteins and their genes have enabled the engineering of protein fusions for localization, the analysis of transcriptional activation and translation of proteins of interest, or the general tracking of individual cells and cell populations. The use of fluorescent protein genes in combination with retroviral technology has further allowed the expression of these proteins in mammalian cells in a stable and reliable manner. Shown here is how one can utilize these genes to give cells within a population of cells their own biosignature. As the biosignature is achieved with retroviral technology, cells are barcoded 'indefinitely'. As such, they can be individually tracked within a mixture of barcoded cells and utilized in more complex biological applications. The tracking of distinct populations in a mixture of cells is ideal for multiplexed applications such as discovery of drugs against a multitude of targets or the activation profile of different promoters. The protocol describes how to elegantly develop and amplify barcoded mammalian cells with distinct genetic fluorescent markers, and how to use several markers at once or one marker at different intensities. Finally, the protocol describes how the cells can be further utilized in combination with cell-based assays to increase the power of analysis through multiplexing.

β-defensin 2 ameliorates lung injury caused by Pseudomonas infection and regulates proinflammatory and anti-inflammatory cytokines in rat

An important member of the defensin family, β-defensin 2, is believed to play an important role in defense against foreign pathogens. In the present study, we constructed lentiviral vectors to express and knockdown β-defensin 2 in rat lungs. The results showed that the infection of β-defensin 2 overexpression lentivirus and β-defensin 2 shRNA effectively increased and suppressed the expression of β-defensin 2 in rat lung, respectively. The overexpression of β-defensin 2 mediated by the lentiviral vector protected lung from infection of Pseudomonas aeruginosa, but shRNA targeting β-defensin 2 aggregated the damage of lung. In addition, we also found that β-defensin 2 overexpression increased basal expression of anti-inflammatory cytokine such as IL-4, IL-10 and IL-13 and decreased levels of proinflammatory cytokines which include IL-1α, IL-1β, IL-5, IL-6, IL-8, IL-18, and TNF-α. Moreover, in the process of cytokine regulation, NF-κB pathway may be involved. Taken together, these data suggest that β-defensin 2 has protective effects against infection of Pseudomonas aeruginosa in rat and plays a role in inflammatory regulation by adjusting cytokine levels.

Modulation of immune function by glutamatergic neurons in the cerebellar interposed nucleus via hypothalamic and sympathetic pathways

Our recent work has shown that the cerebellar interposed nucleus (IN) contains glutamatergic neurons that send axons directly to the hypothalamus. In the present study, we aimed to demonstrate modulation of cellular and humoral immunity by glutamatergic neurons in the cerebellar IN by means of gene interventions of glutaminase (GLS), an enzyme for glutamate synthesis, and to reveal pathways transmitting the immunomodulation. Injection of GLS-shRNA lentiviral vector into bilateral cerebellar IN downregulated GLS expression in the IN. The silencing of GLS gene in the cerebellar IN decreased interleukin (IL)-2 and interferon (IFN)-γ production, B-cell number, and IgM antibody level in response to antigen bovine serum albumin (BSA). On the contrary, injection of GLS lentiviral vector into bilateral cerebellar IN upregulated GLS expression in the IN. The GLS gene overexpression in the IN caused opposite immune effects to the GLS gene knockdown. Simultaneously, the GLS gene silencing in the cerebellar IN reduced and the GLS overexpression elevated glutamate content in the hypothalamus, but they both did not affect glycine and GABA contents in the hypothalamus. In addition, the immune changes caused by the GLS gene interventions in the IN were accompanied by alteration in norepinephrine content in the spleen and mesenteric lymph nodes but not by changes in adrenocortical and thyroid hormone levels in serum. These findings indicate that glutamatergic neurons in the cerebellar IN regulate cellular and humoral immune responses and suggest that such immunoregulation may be conveyed by cerebellar IN-hypothalamic glutamatergic projections and sympathetic nerves that innervate lymphoid tissues.

Methods for gene transfer to the central nervous system

Gene transfer is an increasingly utilized approach for research and clinical applications involving the central nervous system (CNS). Vectors for gene transfer can be as simple as an unmodified plasmid, but more commonly involve complex modifications to viruses to make them suitable gene delivery vehicles. This chapter will explain how tools for CNS gene transfer have been derived from naturally occurring viruses. The current capabilities of plasmid, retroviral, adeno-associated virus, adenovirus, and herpes simplex virus vectors for CNS gene delivery will be described. These include both focal and global CNS gene transfer strategies, with short- or long-term gene expression. As is described in this chapter, an important aspect of any vector is the cis-acting regulatory elements incorporated into the vector genome that control when, where, and how the transgene is expressed.

Lentivirus-mediated ERK2 siRNA reduces joint capsule fibrosis in a rat model of post-traumatic joint contracture

Extracellular signal-regulated kinase (ERK)-2 is presumed to play an important role in the development of post-traumatic joint contractures. Using a rat injury model, we investigated whether treatment with ERK2 small interfering RNA (siRNA) could reduce the extent of joint capsule fibrosis after an induced injury. Rats were separated into three groups (n = 32 each): non-operated control group, operated contracture group and contracture-treatment group. Stable post-traumatic joint contracture was created through surgical intra-articular joint injury followed by eight weeks of immobilization. In the contracture-treatment group, the rats were treated with lentivirus (LV)-mediated ERK2 siRNA at days 3 and 7 post-surgery. The posterior joint capsule was assessed by western blotting, immunohistochemistry and biochemical analysis for changes in ERK2, phosphorylated (p)-ERK2, myofibroblast, total collagen and relative collagen Type III expression level. Biomechanical testing was used to assess the development of flexion contractures. Statistical analysis was performed using an analysis of variance. In the operated contracture group, rats that developed flexion contractures also showed elevated phosphorylated p-ERK2 expression. In the contracture-treatment group, ERK2 siRNA significantly reduced p-ERK2 expression levels, as well as the severity of flexion contracture development (p < 0.01). Myofibroblast numbers and measurements of total collagen content were also significantly reduced following ERK2 siRNA (p < 0.01). Relative collagen type III expression as a proportion of total of Types I and III collagen, however, was significantly increased in response to ERK2 siRNA (p < 0.01). Our findings demonstrate a role for ERK2 in the induction of joint capsule fibrosis after injury. Furthermore, we show that development of flexion contractures and the resultant increase of joint capsule fibrosis can be reduced by LV-mediated ERK2 siRNA treatment.

Preferential lentiviral targeting of astrocytes in the central nervous system

The ability to visualize and genetically manipulate specific cell populations of the central nervous system (CNS) is fundamental to a better understanding of brain functions at the cellular and molecular levels. Tools to selectively target cells of the CNS include molecular genetics, imaging, and use of transgenic animals. However, these approaches are technically challenging, time consuming, and difficult to control. Viral-mediated targeting of cells in the CNS can be highly beneficial for studying and treating neurodegenerative diseases. Yet, despite specific marking of numerous cell types in the CNS, in vivo selective targeting of astrocytes has not been optimized. In this study, preferential targeting of astrocytes in the CNS was demonstrated using engineered lentiviruses that were pseudotyped with a modified Sindbis envelope and displayed anti-GLAST IgG on their surfaces as an attachment moiety. Viral tropism for astrocytes was initially verified in vitro in primary mixed glia cultures. When injected into the brains of mice, lentiviruses that displayed GLAST IgG on their surface, exhibited preferential astrocyte targeting, compared to pseudotyped lentiviruses that did not incorporate any IgG or that expressed a control isotype IgG. Overall, this approach is highly flexible and can be exploited to selectively target astrocytes or other cell types of the CNS. As such, it can open a window to visualize and genetically manipulate astrocytes or other cells of the CNS as means of research and treatment.

MiR-590-5P inhibits growth of HepG2 cells via decrease of S100A10 expression and Inhibition of the Wnt pathway

Hepatocellular carcinoma is one of the most common and lethal cancers worldwide, especially in developing countries. In the present study, we found that the expression of a microRNA, miR-590-5P, was down-regulated and S100A10 was up-regulated in six hepatocellular carcinoma cell lines. The reporter gene assay showed that overexpression of miR-590-5P effectively reduced the activity of luciferase expressed by a vector bearing the 3′ untranslated region of S100A10 mRNA. Ectopic miR-590-5P overexpression mediated by lentiviral infection decreased expression of S100A10. Infection of Lv-miR-590-5P inhibited cell growth and induced cell cycle G1 arrest in HepG2 cells. In addition, miR-590-5P expression suppressed the expression of Wnt5a, cMyc and cyclin D1, and increased the phosphorylation of β-catenin and expression of Caspase 3, which may contribute to the inhibitory effect of miR-590-5P on cell growth. Taken together, our data suggest that down-regulation of miR-590-5P is involved in hepatocellular carcinoma and the restoration of miR-590-5P can impair the growth of cancer cells, suggesting that miR-590-5P may be a potential target molecule for the therapy of hepatocellular carcinoma.

Prevention of Tendon Adhesions by ERK2 Small Interfering RNAs

Tendon adhesions are one of the most concerning complications after surgical repair of flexor tendon injury. Extracellular signal-regulated kinase (ERK) 2 plays crucial roles in fibroblast proliferation and collagen expression which contributes to the formation of tendon adhesions after flexor tendon surgery. Using a chicken model, we have examined the effects of a small interfering RNA (siRNA) targeting ERK2 delivered by a lentiviral system on tendon adhesion formation with an adhesion scoring system, histological assessment, and biomechanical evaluation. It was found that ERK2 siRNA effectively suppressed the increase of fibroblasts and the formation of tendon adhesions (p < 0.05 compared with the control group). Moreover, no statistically significant reduction in breaking force was detected between the ERK2 siRNA group and the control group. These results show that the lentiviral-mediated siRNA system is effective in preventing tendon adhesion formation but not to tendon healing, and may be used for tendon repair after confirmation and improvement by future detailed studies.

Silencing of amyloid precursor protein expression using a new engineered delta ribozyme

Alzheimer's disease (AD) etiological studies suggest that an elevation in amyloid-β peptides (Aβ) level contributes to aggregations of the peptide and subsequent development of the disease. The major constituent of these amyloid peptides is the 1 to 40–42 residue peptide (Aβ₄₀₋₄₂) derived from amyloid protein precursor (APP). Most likely, reducing Aβ levels in the brain may block both its aggregation and neurotoxicity and would be beneficial for patients with AD. Among the several possible ways to lower Aβ accumulation in the cells, we have selectively chosen to target the primary step in the Aβ cascade, namely, to reduce APP gene expression. Toward this end, we engineered specific SOFA-HDV ribozymes, a new generation of catalytic RNA tools, to decrease APP mRNA levels. Additionally, we demonstrated that APP-ribozymes are effective at decreasing APP mRNA and protein levels as well as Aβ levels in neuronal cells. Our results could lay the groundwork for a new protective treatment for AD.

Cell and Tissue Gene Targeting with Lentiviral Vectors

One of the main advantages of using lentivectors is their capacity to transduce a wide range of cell types, independently from the cell cycle stage. However, transgene expression in certain cell types is sometimes not desirable, either because of toxicity, cell transformation, or induction of transgene-specific immune responses. In other cases, specific targeting of only cancerous cells within a tumor is sought after for the delivery of suicide genes. Consequently, great effort has been invested in developing strategies to control transgene delivery/expression in a cell/tissue-specific manner. These strategies can broadly be divided in three; particle pseudotyping (surface targeting), which entails modification of the envelope glycoprotein (ENV); transcriptional targeting, which utilizes cell-specific promoters and/or inducible promoters; and posttranscriptional targeting, recently applied in lentivectors by introducing sequence targets for cell-specific microRNAs. In this chapter we describe each of these strategies providing some illustrative examples.

Spines, plasticity, and cognition in Alzheimer's model mice

The pathological hallmarks of Alzheimer's disease (AD)--widespread synaptic and neuronal loss and the pathological accumulation of amyloid-beta peptide (Aβ) in senile plaques, as well as hyperphosphorylated tau in neurofibrillary tangles--have been known for many decades, but the links between AD pathology and dementia and effective therapeutic strategies remain elusive. Transgenic mice have been developed based on rare familial forms of AD and frontotemporal dementia, allowing investigators to test in detail the structural, functional, and behavioral consequences of AD-associated pathology. Here, we review work on transgenic AD models that investigate the degeneration of dendritic spine structure, synaptic function, and cognition. Together, these data support a model of AD pathogenesis in which soluble Aβ initiates synaptic dysfunction and loss, as well as pathological changes in tau, which contribute to both synaptic and neuronal loss. These changes in synapse structure and function as well as frank synapse and neuronal loss contribute to the neural system dysfunction which causes cognitive deficits. Understanding the underpinnings of dementia in AD will be essential to develop and evaluate therapeutic approaches for this widespread and devastating disease.

Optimal promoter usage for lentiviral vector-mediated transduction of cultured central nervous system cells

Lentiviral vectors transduce both dividing and non-dividing cells and can support sustained expression of transgenes. These properties make them attractive for the transduction of neurons and other neural cell types in vitro and in vivo. Lentiviral vectors can be targeted to specific cell types by using different promoters in the lentiviral shuttle vector. Even with identical constructs, however, levels of expression can vary significantly in different types of neurons and different culture preparations; expression levels in the same neuronal subtypes can be very different in primary cell culture and in vivo. We systematically assessed the ability of different promoters to direct expression of foreign transgenes in primary murine neocortical neurons, cerebellar granule cells and in undifferentiated and differentiated neuroblastoma cells. In primary cortical neurons, constructs using the ubiquitin C promoter directed the highest level of transgene expression; the phosphoglycerate kinase (PGK) promoter also directed robust transgene expression, while the cytomegalovirus (CMV) and MND (a synthetic promoter that contains the U3 region of a modified MoMuLV LTR with myeloproliferative sarcoma virus enhancer) promoters resulted in the expression of the transgenes in only limited number of neurons. In contrast, in cerebellar granule cells and in differentiated SH-SY5Y neuroblastoma cultures, the CMV promoter directed the most robust transgene expression. There was similar variability in transgene expression directed by these promoters in primary cultures of oligodendrocytes and astrocytes. These findings may prove useful in the design of lentiviral vectors for use in cell culture models of the nervous system.

Lentiviral vectors in gene therapy: their current status and future potential

The concept of gene therapy originated in the mid twentieth century and was perceived as a revolutionary technology with the promise to cure almost any disease of which the molecular basis was understood. Since then, several gene vectors have been developed and the feasibility of gene therapy has been shown in many animal models of human disease. However, clinical efficacy could not be demonstrated until the beginning of the new century in a small-scale clinical trial curing an otherwise fatal immunodeficiency disorder in children. This first success, achieved after retroviral therapy, was later overshadowed by the occurrence of vector-related leukemia in a significant number of the treated children, demonstrating that the future success of gene therapy depends on our understanding of vector biology. This has led to the development of later-generation vectors with improved efficiency, specificity, and safety. Amongst these are HIV-1 lentivirus-based vectors (lentivectors), which are being increasingly used in basic and applied research. Human gene therapy clinical trials are currently underway using lentivectors in a wide range of human diseases. The intention of this review is to describe the main scientific steps leading to the engineering of HIV-1 lentiviral vectors and place them in the context of current human gene therapy.

Efficient inhibition of the formation of joint adhesions by ERK2 small interfering RNAs

Transforming growth factor-beta1 and fibroblast growth factor-2 play very important roles in fibroblast proliferation and collagen expression. These processes lead to the formation of joint adhesions through the SMAD and MAPK pathways, in which extracellular signal-regulated kinase (ERK)2 is considered to be crucial. Based on these theories, we examined the effects of a lentivirus-mediated small interfering RNA (siRNA) targeting ERK2 on the suppression of joint adhesion formation in vivo. The effects were assessed in vivo from different aspects including the adhesion score, histology and joint contracture angle. We found that the adhesions in the ERK2 siRNA group became soft and weak, and were easily stretched. Accordingly, the flexion contracture angles in the ERK2 siRNA group were also reduced (P<0.05 compared with the control group). The animals appeared healthy, with no signs of impaired wound healing. In conclusion, local delivery of a lentivirus-mediated siRNA targeting ERK2 can ameliorate joint adhesion formation effectively and safely.

The Use of Lentiviral Vectors and Cre/loxP to Investigate the Function of Genes in Complex Behaviors

The use of conventional knockout technologies has proved valuable for understanding the role of key genes and proteins in development, disease states, and complex behaviors. However, these strategies are limited in that they produce broad changes in gene function throughout the neuroaxis and do little to identify the effects of such changes on neural circuits thought to be involved in distinct functions. Because the molecular functions of genes often depend on the specific neuronal circuit in which they are expressed, restricting gene manipulation to specific brain regions and times may be more useful for understanding gene functions. Conditional gene manipulation strategies offer a powerful alternative. In this report we briefly describe two conditional gene strategies that are increasingly being used to investigate the role of genes in behavior – the Cre/loxP recombination system and lentiviral vectors. Next, we summarize a number of recent experiments which have used these techniques to investigate behavior after spatial and/or temporal and gene manipulation. These conditional gene targeting strategies provide useful tools to study the endogenous mechanisms underlying complex behaviors and to model disease states resulting from aberrant gene expression.

Efficient inhibition of fibroblast proliferation and collagen expression by ERK2 siRNAs

Transforming growth factor-beta1 and fibroblast growth factor-2 play very important roles in fibroblast proliferation and collagen expression. These processes lead to the formation of joint adhesions through the SMAD and MAPK pathways, in which ERK2 is supposed to be crucial. Based on these assumptions, lentivirus (LV)-mediated small interfering RNAs (siRNAs) targeting ERK2 were used to suppress the proliferation and collagen expression of rat joint adhesion tissue fibroblasts (RJATFs). Among four siRNAs examined, siRNA1 caused an 84% reduction in ERK2 expression (p<0.01) and was selected as the most efficient siRNA for use in this study. In subsequent experiments, significant downregulation of types I and III collagen were observed by quantitative RT-PCR and Western blot analyses. MTT assays and flow cytometry revealed marked inhibition of RJATF proliferation, but no apoptosis. In conclusion, LV-mediated ERK2 siRNAs may represent novel therapies or drug targets for preventing joint adhesion formation.

Continuous expression of corticotropin-releasing factor in the central nucleus of the amygdala emulates the dysregulation of the stress and reproductive axes

An increase in corticotropin-releasing factor (CRF) is a putative factor in the pathophysiology of stress-related disorders. As CRF expression in the central nucleus of the amygdala (CeA) is important in adaptation to chronic stress, we hypothesized that unrestrained synthesis of CRF in CeA would mimic the consequences of chronic stress exposure and cause dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, increase emotionality and disrupt reproduction. To test this hypothesis, we used a lentiviral vector to increase CRF-expression site specifically in CeA of female rats. Increased synthesis of CRF in CeA amplified CRF and arginine vasopressin peptide concentration in the paraventricular nucleus of the hypothalamus, and decreased glucocorticoid negative feedback, both markers associated with the pathophysiology of depression. In addition, continuous expression of CRF in CeA also increased the acoustic startle response and depressive-like behavior in the forced swim test. Protein levels of gonadotropin-releasing hormone in the medial preoptic area were significantly reduced by continuous expression of CRF in CeA and this was associated with a lengthening of estrous cycles. Finally, sexual motivation but not sexual receptivity was significantly attenuated by continuous CRF synthesis in ovariectomized estradiol-progesterone-primed females. These data indicate that unrestrained CRF synthesis in CeA produces a dysregulation of the HPA axis, as well as many of the behavioral, physiological and reproductive consequences associated with stress-related disorders.Molecular Psychiatry (2009) 14, 37-50; doi:10.1038/mp.2008.91; published online 12 August 2008.

Alzheimer's, atherosclerosis, and aggregates: a role for bacterial degradation

Several of the most prevalent and severe age-related diseases, notably Alzheimer's disease and atherosclerosis, feature the accumulation of non-degradable aggregates within the lysosomes of disease-affected cells. At an early point in disease progression, the breakdown of lysosomal contents by the resident catabolic enzymes stops working properly. A return of lysosomal enzymatic activity to pre-disease levels may restore aggregate elimination. In this review, a method of bioremediation-derived lysosomal enzyme enhancement is proposed, featuring the cellular introduction of microbial-isolated enzymes, or xenoenzymes. The benefits and challenges of using xenoenzymes to break down aggregates are discussed. As the size of our elderly population grows, the incidence of age-related diseases will increase, necessitating the exploration of radical, but potentially powerful, therapeutic strategies.

Simian immunodeficiency virus vector pseudotypes differ in transduction efficiency and target cell specificity in brain

Lentiviral vectors have proven to be promising tools for transduction of brain cells in vivo and in vitro. In this study, we have examined the central nervous system (CNS) transduction efficiencies and patterns of a self-inactivating simian immunodeficiency virus (SIVmac)-derived lentiviral vector pseudotyped with glycoproteins from the vesicular stomatitis virus (VSV-G), the amphotropic murine leukemia virus (MLV4070Aenv), the lymphocytic choriomeningitis virus (LCMV-GP), the Ross River virus (RRV-GP) and the rabies virus (RV-G). All glycoproteins were efficiently incorporated into SIV virions, allowing efficient transduction of neuronal cell lines as well as of primary dissociated mouse brain cell cultures. After injection of highly concentrated vector stocks into the striatum of adult mice, quantitative analyses revealed high transduction efficiency with VSV-G pseudotypes, while LCMV-GP and RV-G pseudotypes exhibited moderate transduction efficiencies. MLV4070Aenv and RRV-GP pseudotypes, however, showed only weak levels of transduction after stereotactic injection into the brain. Regarding cell tropism in vivo, VSV-G-pseudotyped SIV vectors transduced neuronal as well as glial cells, whereas all other pseudotypes preferentially transduced neuroglial cells. In addition, we analyzed the influence of the central polypurine tract (cPPT) in context of the VSV-G-pseudotyped SIV transfer vector for infection of brain cells. Deletion of the cPPT sequence from the transfer vector decreased the in vivo transduction efficiency by fourfold, and, more importantly, this modification changed the transduction pattern, since these vectors were no longer able to infect neuronal cells in vivo. Vector injection into the brain did elicit a humoral immune response in the injected hemisphere; however, no gross signs of inflammation could be detected. Analysis of the biodistribution of the vector revealed that, besides the injected brain region, no vector-specific sequences could be detected in any of the organs evaluated. These data indicate SIV vectors as efficient gene delivery vehicles for the treatment of neurodegenerative diseases.

Evidence for intercellular trafficking of VP22 in living cells

The intercellular trafficking property of the herpes simplex virus type 1 tegument protein VP22 makes it a promising tool for overcoming low transduction efficiencies in gene therapy. However, recent reports suggest not only that VP22 cannot facilitate intercellular spreading and that trafficking of VP22 fusion proteins results from artifacts of cell fixation only. To provide direct evidence for the presence or absence of VP22-mediated intercellular trafficking, we generated an adenoviral vector with a dual expression cassette for VP22 fused to green fluorescent protein (VP22 GFP) and DsRed under the control of distinct human cytomegalovirus immediate-early enhancer/promoter regions. Using this vector, we were able to distinguish clearly between primary transduced cells and cells taking up VP22GFP by intercellular trafficking. To our knowledge, for the first time, we could demonstrate by live-cell confocal fluorescence microscopy that VP22GFP can be found intracellularly in unfixed recipient cells. The extent of VP22 spread was similar in paraformaldehyde-fixed cells and unfixed cells as demonstrated by fluorescence-activated cell sorting analysis. We thus confirmed the ability of VP22-mediated intercellular trafficking in live unfixed cells.

Lentiviral vectors for cancer immunotherapy: transforming infectious particles into therapeutics

Lentiviral vectors have emerged as promising tools for both gene therapy and immunotherapy purposes. They exhibit several advantages over other viral systems in that they are less immunogenic and are capable of transducing a wide range of different cell types, including dendritic cells (DC). DC transduced ex vivo with a whole range of different (tumor) antigens were capable of inducing strong antigen-specific T-cell responses, both in vitro and in vivo. Recently, the administration of lentiviral vectors in vivo has gained substantial interest as an alternative method for antigen-specific immunization. This method offers a number of advantages over DC vaccines as the same lentivirus can in principle be used for all patients resulting in a significantly reduced cost and requirement for considerably less expertise for the generation and administration of lentiviral vaccines. By selectively targeting lentiviral vectors to, or restricting transgene expression in certain cell types, selectivity, safety and efficacy can be further improved. This review will focus on the use of direct administration of lentiviral vectors encoding tumor-associated antigens (TAA) for the induction of tumor-specific immune responses in vivo, with a special focus on problems related to the generation of large amounts of highly purified virus and specific targeting of antigen-presenting cells (APC).

Differential characteristics of HIV-based versus SIV-based lentiviral vector systems: Gene delivery to neurons and axonal transport of expressed gene

The differential characteristics of lentiviral vectors based on human and simian immunodeficiency viruses (HIV and SIV) were investigated in rats and monkeys. Each vector was injected into the striatum, and the expression patterns of the marker gene green fluorescent protein (GFP) were analyzed in the basal ganglia. With respect to the capability of gene delivery to neural cells, the HIV-based vector exhibited a higher tropism to neurons than to astroglias in the striatum, and vice versa for the SIV-based vector. The preferential direction of axonal transport of striatally expressed GFP was also examined in the present study. The HIV-based vector allowed for both anterograde transport via the striatopallidal and striatonigral pathways and retrograde transport via the nigrostriatal pathway. The GFP labeling of axon terminals through anterograde transport was apparent regardless of the animal species, while that of neuronal cell bodies through retrograde transport was much more prominent in monkeys than in rats. As for the SIV-based vector, on the other hand, evidence for anterograde transport was obtained much more markedly in monkeys than in rats, and only weak or no retrograde transport occurred in either monkeys or rats. Our results indicate that HIV-based, but not SIV-based, lentiviral vectors possess the high tropism to neurons and permit retrograde transport of an expressed gene, especially in primates. The latter property might carry a potential benefit in gene therapy for Parkinson's disease, as stereotaxic injections of the vectors could be performed into the striatum, spatially larger than the substantia nigra, with greater certainty.

Axons mediate the distribution of arylsulfatase A within the mouse hippocampus upon gene delivery

Axonal transport of the lysosomal enzyme arylsulfatase A (ARSA) may be an additional mechanism of enzyme distribution after in vivo brain gene transfer in an animal model of metachromatic leukodystrophy (MLD). Direct molecular demonstration of the movement of this lysosomal enzyme within axonal networks was missing. We generated lentiviral vectors carrying the ARSA cDNA tagged with hemagglutinin or the green fluorescent protein and examined the subcellular localization and anatomical distribution of the tagged enzymes within the MLD hippocampus after in vivo lentiviral gene transfer. The use of tagged ARSA allowed direct real-time observation and tracking of axon-dendritic transport of the enzyme after lentiviral gene therapy. Tagged ARSA was expressed in transduced pyramidal, granule, and hilar neurons within the lentiviral-injected side and was robustly contained in vesicles within ipsilateral axon-dendritic processes as well as in vesicles associated with contralateral axons and commissural axons of the ventral hippocampal commissure. Axonal transport of tagged ARSA led to the correction of hippocampal defects in long-term treated MLD mice, which was accompanied by enzyme uptake in nontransduced contralateral neurons, enzyme accumulation within the lysosomal compartment, and clearance of sulfatide storage deposits in this region of the MLD brain. These results contribute to the understanding of the mechanisms of distribution of lysosomal enzymes within the mammalian brain after direct gene therapy, demonstrating the use of neural processes for enzyme transport.

Appropriating microbial catabolism: A proposal to treat and prevent neurodegeneration

Intraneuronal, largely proteinaceous aggregates accumulate in all major neurodegenerative disorders. Lysosomal degradation of proteinaceous and other material declines early in such diseases. This suggests that intraneuronal aggregates consist of material which is normally broken down in the lysosome and thus accumulates when lysosomal degradation fails. This is plausible even though those aggregates are generally non-lysosomal, because lysosomal uptake may be affected. Thus, restoring lysosomal function might eliminate them--and without increasing the concentration of the soluble monomers or oligomers of which they are formed. This approach is therefore unlikely to be harmful and may well be beneficial. How might lysosomes be rejuvenated? Since lysosomal dysfunction is likely to be caused by intralysosomal material that is resistant to lysosomal degradation, normal function might be recovered by augmenting that function to cause the toxin to be degraded. Here, I describe how such augmentation might be achieved with microbial enzymes. Soil microbes display astonishing catabolic diversity, something exploited for decades in the bioremediation industry. Environments enriched in human remains impose selective pressure on the microbial population to evolve the ability to degrade any recalcitrant, energy-rich human material. Thus, microbes may exist that can degrade these lysosomal toxins. If so, it should be possible to isolate the genes responsible and modify them for therapeutic activity in the mammalian lysosome.

Lentiviral Vectors for Use in the Central Nervous System

Lentiviral vectors have been used extensively as gene transfer tools for the central nervous system throughout the past decade since they transduce most cell types in the brain, resulting in high-level and long-term transgene expression. This review discusses some of the recent progress in this field, including preclinical gene therapy experiments in disease models, development of regulated vectors, and the application of siRNA's using lentiviral vectors. We also describe some of the features that make lentiviral vectors a likely candidate for human gene therapy in the brain.

Reversion of the biochemical defects in murine embryonic Sandhoff neurons using a bicistronic lentiviral vector encoding hexosaminidase alpha and beta

Sandhoff disease, a neurodegenerative disorder characterized by the intracellular accumulation of GM2 ganglioside, is caused by mutations in the hexosaminidase beta-chain gene resulting in a hexosaminidase A (alphabeta) and B (betabeta) deficiency. A bicistronic lentiviral vector encoding both the hexosaminidase alpha and beta chains (SIV.ASB) has previously been shown to correct the beta-hexosaminidase deficiency and to reduce GM2 levels both in transduced and cross-corrected human Sandhoff fibroblasts. Recent advances in determining the neuropathophysiological mechanisms in Sandhoff disease have shown a mechanistic link between GM2 accumulation, neuronal cell death, reduction of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) activity, and axonal outgrowth. To examine the ability of the SIV.ASB vector to reverse these pathophysiological events, hippocampal neurons from embryonic Sandhoff mice were transduced with the lentivector. Normal axonal growth rates were restored, as was the rate of Ca(2+) uptake via the SERCA and the sensitivity of the neurons to thapsigargin-induced cell death, concomitant with a decrease in GM2 and GA2 levels. Thus, we have demonstrated that the bicistronic vector can reverse the biochemical defects and down-stream consequences in Sandhoff neurons, reinforcing its potential for Sandhoff disease in vivo gene therapy.

Gene therapy progress and prospects: development of improved lentiviral and retroviral vectors--design, biosafety, and production

Replication defective vectors derived from simple retroviruses or the more complex genomes of lentiviruses continue to offer the advantages of long-term expression, cell and tissue specific tropism, and large packaging capacity for the delivery of therapeutic genes. The occurrence of adverse events caused by insertional mutagenesis in three patients in a gene therapy trial for X-linked SCID emphasizes the potential for problems in translating this approach to the clinic. Several genome-wide studies of retroviral integration are now providing novel insights into the integration site preferences of different vector classes. We review recent developments in vector design, integration, biosafety, and production.

Long-term expression of the human glucocerebrosidase gene in vivo after transplantation of bone-marrow-derived cells transformed with a lentivirus vector

BACKGROUND

Gaucher disease is a lysosomal storage disorder resulting from a deficiency of glucocerebrosidase (GC). Recently, lentivirus vectors have been developed for efficient gene transfer into hematopoietic stem cells (HSCs). A recombinant lentivirus vector was used to evaluate the transduction of the human GC gene into murine bone-marrow-derived HSCs and its expression in their progeny.

METHODS

Murine HSCs were transduced with lentivirus vector (lenti-EF-GC; MOI = 10-100). We transplanted female wild-type C57BL/6J mice with genetically modified male HSCs via the tail vein.

RESULTS

We show that intravenous transplantation of transduced HSCs has therapeutic potential. Enzyme activity was increased two- to three-fold in various tissues, especially in the hematopoietic system. Numerous transplanted HSCs survived for 6 months and were shown by PCR to contain the provirus genes; the Y chromosome was identified by FISH analysis in the cells of female mouse recipients.

CONCLUSIONS

The recombinant lentiviral vector transduces HSCs that are capable of long-term gene expression in vivo. This approach is potentially useful for the treatment of patents with Gaucher disease and other lysosomal storage disorders.

Medical bioremediation: prospects for the application of microbial catabolic diversity to aging and several major age-related diseases

Several major diseases of old age, including atherosclerosis, macular degeneration and neurodegenerative diseases are associated with the intracellular accumulation of substances that impair cellular function and viability. Moreover, the accumulation of lipofuscin, a substance that may have similarly deleterious effects, is one of the most universal markers of aging in postmitotic cells. Reversing this accumulation may thus be valuable, but has proven challenging, doubtless because substances resistant to cellular catabolism are inherently hard to degrade. We suggest a radically new approach: augmenting humans' natural catabolic machinery with microbial enzymes. Many recalcitrant organic molecules are naturally degraded in the soil. Since the soil in certain environments - graveyards, for example - is enriched in human remains but does not accumulate these substances, it presumably harbours microbes that degrade them. The enzymes responsible could be identified and engineered to metabolise these substances in vivo. Here, we survey a range of such substances, their putative roles in age-related diseases and the possible benefits of their removal. We discuss how microbes capable of degrading them can be isolated, characterised and their relevant enzymes engineered for this purpose and ways to avoid potential side-effects.

Protein transduction of Rab9 in Niemann-Pick C cells reduces cholesterol storage

Niemann-Pick disease type C (NPC) is a genetic disorder in which patient cells exhibit lysosomal accumulation of cholesterol and sphingolipids (SLs) caused by defects in either NPC1 or NPC2 proteins. We previously demonstrated that NPC1 human skin fibroblasts overexpressing endosomal Rab proteins (Rab7 or Rab9) showed a correction in the storage disease phenotype. In the current study, we used protein transduction to further investigate Rab9-mediated reduction of stored lipids in NPC cells. Recombinant human Rab9 fused with the herpes simplex virus VP22 protein fragment was overexpressed, purified, and added to culture medium to induce protein transduction. When VP22-Rab9 was transduced into NPC1 fibroblasts, nearly all cells showed significant reduction in cellular free cholesterol levels, with no cytotoxicity up to 5 microM. A fraction of the VP22-Rab9 that was transduced into the cells was shown to bind to rab GDP dissociation inhibitor, suggesting that this pool of VP22-Rab9 had become prenylated. The reduction in cellular free cholesterol was associated with correction of abnormal intracellular trafficking of BODIPY-lactosylceramide and an increase of sterols in the culture media. The clearance of lysosomal free cholesterol was also associated with a decrease in LDL-receptor levels. In addition, we demonstrated reduction of intracellular cholesterol by VP22-Rab9 transduction in NPC2 fibroblasts and in cultured mouse NPC1 neurons. These observations provide important new information about the correction of membrane traffic in NPC cells by Rab9 overexpression and may lead to new therapeutic approaches for treatment of this disease.

Bicistronic lentiviral vector corrects beta-hexosaminidase deficiency in transduced and cross-corrected human Sandhoff fibroblasts

Sandhoff disease is an autosomal recessive neurodegenerative disease characterized by a GM2 ganglioside intralysosomal accumulation. It is due to mutations in the beta-hexosaminidases beta-chain gene, resulting in a beta-hexosaminidases A (alphabeta) and B (betabeta) deficiency. Mono and bicistronic lentiviral vectors containing the HEXA or/and HEXB cDNAs were constructed and tested on human Sandhoff fibroblasts. The bicistronic SIV.ASB vector enabled a massive restoration of beta-hexosaminidases activity on synthetic substrates and a 20% correction on the GM2 natural substrate. Metabolic labeling experiments showed a large reduction of ganglioside accumulation in SIV.ASB transduced cells, demonstrating a correct recombinant enzyme targeting to the lysosomes. Moreover, enzymes secreted by transduced Sandhoff fibroblasts were endocytosed in deficient cells via the mannose 6-phosphate pathway, allowing GM2 metabolism restoration in cross-corrected cells. Therefore, our bicistronic lentivector supplying both alpha- and beta-subunits of beta-hexosaminidases may provide a potential therapeutic tool for the treatment of Sandhoff disease.

VP22 enhances antibody responses from DNA vaccines but not by intercellular spread

In some species DNA vaccines elicit potent humoral and cellular immune responses. However, their performance in humans and non-human primates is less impressive. There are suggestions in the literature that an increase in the intercellular distribution of protein expressed from a DNA vaccine may enhance immunogenicity. We incorporated the Herpes Simplex Virus type 1 (HSV) VP22 gene, which encodes a protein that has been described as promoting intercellular spread, into a DNA vector in which it was fused to enhanced green fluorescent protein (EGFP). Following transfection of the plasmid DNA into mammalian cells, distribution of the fusion protein VP22-EGFP was not increased compared to EGFP alone. Furthermore, we found no evidence to suggest that VP22 was capable of mediating intercellular spread. However, when these constructs were used as DNA vaccines to immunise mice, antibody levels specific to EGFP were significantly enhanced when EGFP was fused to VP22. These data suggest that amplification of the immune response may occur via mechanisms other than VP22-mediated intercellular spread of antigen.

Lentivirus-based genetic manipulations of cortical neurons and their optical and electrophysiological monitoring in vivo

It is becoming increasingly clear that single cortical neurons encode complex and behaviorally relevant signals, but efficient means to study gene functions in small networks and single neurons in vivo are still lacking. Here, we establish a method for genetic manipulation and subsequent phenotypic analysis of individual cortical neurons in vivo. First, lentiviral vectors are used for neuron-specific gene delivery from alpha-calcium/calmodulin-dependent protein kinase II or Synapsin I promoters, optionally in combination with gene knockdown by means of U6 promoter-driven expression of short-interfering RNAs. Second, the phenotypic analysis at the level of single cortical cells is carried out by using two-photon microscopy-based techniques: high-resolution two-photon time-lapse imaging is used to monitor structural dynamics of dendritic spines and axonal projections, whereas cellular response properties are analyzed electrophysiologically by two-photon microscopy directed whole-cell recordings. This approach is ideally suited for analysis of gene functions in individual neurons in the intact brain.

Lentiviral vectors

Vectors based on lentiviruses have reached a state of development such that clinical studies using these agents as gene delivery vehicles have now begun. They have particular advantages for certain in vitro and in vivo applications especially the unique capability of integrating genetic material into the genome of non-dividing cells. Their rapid progress into clinical use reflects in part the huge body of knowledge which has accumulated about HIV in the last 20 years. Despite this, many aspects of viral assembly on which the success of these vectors depends are rather poorly understood. Sufficient is known however to be able to produce a safe and reproducible high titre vector preparation for effective transduction of growth-arrested tissues such as neural tissue, muscle and liver.

Expression and secretion of human glucocerebrosidase mediated by recombinant lentivirus vectors in vitro and in vivo: implications for gene therapy of Gaucher disease

Gaucher disease is a lysosomal storage disorder resulting from a deficiency of glucocerebrosidase (GC). In this study, we showed that vascular and hepatic delivery of a HIV-1-based lentivirus vector encoding human GC cDNA produced therapeutic levels of GC protein. A high level of expression of GC was produced in cultured fibroblasts derived from patients with Gaucher disease by transducing the cells with recombinant lentivirus vectors. GC secreted by transduced fibroblasts was taken up by adjacent GC-deficient cells by endocytosis. Intraportal administration of lenti-EF-GC viral vector resulted in efficient transduction and expression of the GC. Vascular delivery of vector resulted in high levels of GC expression in mice that persisted in most organs over the four months. No significant abnormalities were found attributable to recombinant lentivirus vectors in any of the tissues examined. This study represents an initial step toward gene transfer using recombinant lentivirus vectors for treatment of Gaucher disease.

Gaucher and Fabry diseases: from understanding pathophysiology to rational therapies

Over the past 40 years there has been remarkable development in our understanding of the pathophysiology of lysosomal storage disorders. This review describes the research carried out on the sphingolipid storage disorders from the first demonstration of the underlying metabolic abnormality in Gaucher disease to the development of enzyme replacement therapy for Gaucher and Fabry diseases. Initial developments in gene therapy are also described.

CONCLUSION

The introduction of enzyme replacement therapy has provided a lifeline for patients with Gaucher or Fabry disease. It is anticipated that future developments, including gene therapy, will provide additional therapeutic options.

Effect of intranasal administration of semliki forest virus recombinant particles expressing reporter and cytokine genes on the progression of experimental autoimmune encephalomyelitis

We have initiated studies to determine the feasibility of employing the Semliki Forest virus (SFV) expression system as a central nervous system (CNS) vector. We investigated the effects of infecting Balb/c mice intranasally (i.n.) with recombinant SFV particles expressing the enhanced green fluorescent protein (EGFP) reporter gene. EGFP expression was detected by fluorescence microscopy in the olfactory bulb as early as 1 day postinfection. No pathological changes were associated with infection. Viral RNA could be detected in the olfactory mucosa only, whereas fluorescence was detected in axons in the olfactory bulb, indicating that only the expressed protein was present. A vector expressing interleukin 10 (IL-10) was constructed and shown to induce good cytokine expression in cultured cells. IL-10 expression in the nasal passage and olfactory bulb of infected mice was enhanced following i.n. administration of such particles. Mice induced for experimental autoimmune encephalomyelitis (EAE) were treated i.n. with vectors expressing EGFP and IL-10 and with empty vector. The EGFP-expressing and empty vectors were found to exacerbate EAE, whereas that expressing IL-10 ameliorated EAE. It is concluded that the mice showed a significant biological response when treated i.n. with recombinant SFV particles and that such particles administered by the i.n. route have potential as a noninvasive vector for protein delivery to the CNS.