Design and application of HSV vectors for neuroprotection

An M2 Rather than a TH2 Response Contributes to Better Protection against Latency Reactivation following Ocular Infection of Naive Mice with a Recombinant Herpes Simplex Virus 1 Expressing Murine Interleukin-4

We found previously that altering macrophage polarization toward M2 responses by injection of colony-stimulating factor 1 (CSF-1) was more effective in reducing both primary and latent infections in mice ocularly infected with herpes simplex virus 1 (HSV-1) than M1 polarization by gamma interferon (IFN-γ) injection. Cytokines can coordinately regulate macrophage and T helper (T_H) responses, with interleukin-4 (IL-4) inducing type 2 T_H (T_H2) as well as M2 responses and IFN-γ inducing T_H1 as well as M1 responses. We have now differentiated the contributions of these immune compartments to protection against latency reactivation and corneal scarring by comparing the effects of infection with recombinant HSV-1 in which the latency-associated transcript (LAT) gene was replaced with either the IL-4 (HSV-IL-4) or IFN-γ (HSV-IFN-γ) gene using infection with the parental (LAT-negative) virus as a control. Analysis of peritoneal macrophages in vitro established that the replacement of LAT with the IL-4 or IFN-γ gene did not affect virus infectivity and promoted polarization appropriately. Protection against corneal scarring was significantly higher in mice ocularly infected with HSV-IL-4 than in those infected with HSV-IFN-γ or parental virus. Levels of primary virus replication in the eyes and trigeminal ganglia (TG) were similar in the three groups of mice, but the numbers of gC⁺ cells were lower on day 5 postinfection in the eyes of HSV-IL-4-infected mice than in those infected with HSV-IFN-γ or parental virus. Latency and explant reactivation were lower in both HSV-IL-4- and HSV-IFN-γ-infected mice than in those infected with parental virus, with the lowest level of latency being associated with HSV-IL-4 infection. Higher latency correlated with higher levels of CD8, PD-1, and IFN-γ mRNA, while reduced latency and T-cell exhaustion correlated with lower gC⁺ expression in the TG. Depletion of macrophages increased the levels of latency in all ocularly infected mice compared with their undepleted counterparts, with macrophage depletion increasing latency in the HSV-IL-4 group greater than 3,000-fold. Our results suggest that shifting the innate macrophage immune responses toward M2, rather than M1, responses in HSV-1 infection would improve protection against establishment of latency, reactivation, and eye disease.IMPORTANCE Ocular HSV-1 infections are among the most frequent serious viral eye infections in the United States and a major cause of virus-induced blindness. As establishment of a latent infection in the trigeminal ganglia results in recurrent infection and is associated with corneal scarring, prevention of latency reactivation is a major therapeutic goal. It is well established that absence of latency-associated transcripts (LATs) reduces latency reactivation. Here we demonstrate that recombinant HSV-1 expressing IL-4 (an inducer of T_H2/M2 responses) or IFN-γ (an inducer of T_H1/M1 responses) in place of LAT further reduced latency, with HSV-IL-4 showing the highest overall protective efficacy. In naive mice, this higher protective efficacy was mediated by innate rather than adaptive immune responses. Although both M1 and M2 macrophage responses were protective, shifting macrophages toward an M2 response through expression of IL-4 was more effective in curtailing ocular HSV-1 latency reactivation.

Regulable Transgene Expression in Dorsal Root Ganglia of a Replication-Defective Herpes Simplex Virus Type 1 Vector by Means of Sciatic Nerve Injection

BACKGROUND

Targeted and controllable gene delivery to neurons is essential to efforts to facilitate peripheral nerve regeneration. The authors investigated both the in vitro and in vivo expression profiles of a tetracycline-controlled, replication-defective, herpes simplex virus type 1-based vector.

METHODS

Mouse primary dorsal root ganglia cells were infected with QR9TO-LacZ in the absence or presence of tetracycline. LacZ gene expression was examined. It was also injected into sciatic nerves in CD-1 mice fed with and without tetracycline. LacZ expression in the upstream dorsal root ganglia was examined.

RESULTS

Following inoculation with QR9TO-LacZ, approximately 40 percent of the cultured primary dorsal root ganglia cells exhibited strong LacZ activity in the presence of tetracycline at 48 and 72 hours, whereas little was detected in those in the absence of tetracycline. Quantitative analysis revealed that the β-galactosidase activity within cells exposed to tetracycline increased 181-fold at 48 hours (p < 0.001) and 47-fold at 72 hours after infection (p < 0.05) compared with those without tetracycline. However, this LacZ transgene activity in the presence of tetracycline tapered off to less than sevenfold over baseline 168 hours after infection (p < 0.05). Furthermore, successful uptake of this replication-defective viral vector was evident in upstream dorsal root ganglia after sciatic nerve injection in mice. In addition, its expression profile was similar to that in vitro, as strong β-galactosidase activity was evident only in mice fed with a doxycycline-containing diet, and it tapered off by 168 hours.

CONCLUSION

The replication-defective herpes simplex virus type 1-based vector, which provides tightly regulated transgene expression in dorsal root ganglia by means of peripheral nerve injection, represents an appealing approach to improve peripheral nerve regeneration.

Alphaherpesvirus Latency: A Dynamic State of Transcription and Reactivation

Alphaherpesviruses infect a variety of species from sea turtles to man and can cause significant disease in mammals including humans and livestock. These viruses are characterized by a lytic and latent state in nerve ganglia, with the ability to establish a lifelong latent infection that is interrupted by periodic reactivation. Previously, it was accepted that latency was a dominant state and that only during relatively infrequent reactivation episodes did latent genomes within ganglia become transcriptionally active. Here, we review recent data, focusing mainly on Herpes Simplex Virus type 1 which indicate that the latent state is more dynamic than recently appreciated.

HSV-1 as a Model for Emerging Gene Delivery Vehicles

The majority of viral vectors currently used possess modest cargo capability (up to 40 kb) being based on retroviruses, lentiviruses, adenoviruses, and adenoassociated viruses. These vectors have made the most rapid transition from laboratory to clinic because their small genomes have simplified their characterization and modification. However, there is now an increasing need both in research and therapy to complement this repertoire with larger capacity vectors able to deliver multiple transgenes or to encode complex regulatory regions, constructs which can easily span more than 100 kb. Herpes Simplex Virus Type I (HSV-1) is a well-characterized human virus which is able to package about 150 kb of DNA, and several vector systems are currently in development for gene transfer applications, particularly in neurons where other systems have low efficiency. However, to reach the same level of versatility and ease of use as that of smaller genome viral vectors, simple systems for high-titer production must be developed. This paper reviews the major HSV-1 vector systems and analyses the common elements which may be most important to manipulate to achieve this goal.

Effects of herpes simplex virus vector-mediated enkephalin gene therapy on bladder overactivity and nociception

We previously reported the effects of herpes simplex virus (HSV) vector-mediated enkephalin on bladder overactivity and pain. In this study, we evaluated the effects of vHPPE (E1G6-ENK), a newly engineered replication-deficient HSV vector encoding human preproenkephalin (hPPE). vHPPE or control vector was injected into the bladder wall of female rats 2 weeks prior to the following studies. A reverse-transcription PCR study showed high hPPE transgene levels in L6 dorsal root ganglia innervating the bladder in the vHPPE group. The number of freezing behaviors, which is a nociceptive reaction associated with bladder pain, was also significantly lower in the vHPPE group compared with the control group. The number of L6 spinal cord c-fos-positive cells and the urinary interleukin (IL)-1β and IL-6 levels after resiniferatoxin (RTx) administration into the bladder of the vHPPE group were significantly lower compared with those of the control vector-injected group. In continuous cystometry, the vHPPE group showed a smaller reduction in intercontraction interval after RTx administration into the bladder. This antinociceptive effect was antagonized by naloxone hydrochloride. Thus, the HSV vector vHPPE encoding hPPE demonstrated physiological improvement in visceral pain induced by bladder irritation. Gene therapy may represent a potentially useful treatment modality for bladder hypersensitive disorders such as bladder pain syndrome/interstitial cystitis.

Targeted drug delivery to the peripheral nervous system using gene therapy

Gene transfer to target delivery of neurotrophic factors to the primary sensory afferent for treatment of polyneuropathy, or of inhibitory neurotransmitters for relief of chronic pain, offers the possibility of a highly selective targeted release of bioactive molecules within the nervous system. Preclinical studies with non-replicating herpes simplex virus (HSV)-based vectors injected into the skin to transduce neurons in the dorsal root ganglion have demonstrated efficacy in reducing-pain related behaviors in animal models of inflammatory pain, neuropathic pain, and pain caused by cancer, and in preventing progression of sensory neuropathy caused by toxins, chemotherapeutic drugs or resulting from diabetes. Successful completion of the first phase 1 clinical trial of HSV-mediated gene transfer in patients with intractable pain from cancer has set the stage for further clinical trials of this approach.

Gene therapy for bladder overactivity and nociception with herpes simplex virus vectors expressing preproenkephalin

Interstitial cystitis/painful bladder syndrome (IC/PBS) is a major challenge to treat. We studied the effect of targeted and localized expression of enkephalin in afferent nerves that innervate the bladder by gene transfer using replication-defective herpes simplex virus (HSV) vectors in a rat model of bladder hyperactivity and pain. Replication-deficient HSV vectors encoding preproenkephalin, which is a precursor for Met- and Leu-enkephalin, or control vector encoding the lacZ reporter gene, were injected into the bladder wall of female rats. After viral vector injection, quantitative polymerase chain reaction showed high preproenkephalin transgene levels in bladder and dorsal root ganglia innervating the bladder in enkephalin vector-treated animals. Functionally, enkephalin vector-treated animals showed reductions in bladder hyperactivity and nociceptive behavior induced by intravesical application of capsaicin; however, vector-mediated expression of enkephalin did not alter normal voiding. This antinociceptive effect of enkephalin gene therapy was antagonized by naloxone hydrochloride administration. Together, our results with HSV vectors encoding preproenkephalin demonstrated physiological improvement in visceral pain induced by bladder irritation. Thus, gene therapy may represent a potentially useful treatment modality for bladder hypersensitive disorders such as IC/PBS.

Gene therapy for the treatment of diabetic neuropathy

Neuropathy is a common, untreatable complication of type 1 and type 2 diabetes. In animal models peptide neurotrophic factors can be used to protect against the development of neuropathy, but the combination of short half-life and off-target effects of these potent pleiotropic peptides has limited translation to human therapy. Gene transfer is a promising strategy that may circumvent these limitations. In this article, we review the basic methods of gene transfer and the -preclinical data in rodent models that support the use of this approach in the treatment of diabetic neuropathy. The path to clinical applications and potential pitfalls in developing gene therapy for the treatment of diabetic neuropathy are considered.

Gene technology and tissue engineering

The interest in gene therapy to treat human diseases has increased with the advances in recombinant DNA technology and the improved physical, chemical and biological methods of delivering genes to mammalian cells. Areas of therapeutic interest for gene therapy relevant for tissue engineering are, for example, in the treatment of wounds, skin diseases, nerve, bone, and muscle diseases. The transfer of a gene into a cell can lead to the addition or modification of a function and may be an attractive alternative to the pharmacological use of proteins. The complementation of defective functions could also be an effective treatment for inherited skin diseases with a gene defect. The two major challenges facing gene technology in tissue engineering are the problem of identifying appropriate genes that are effective in tissue repair, and the reliable expression of the therapeutic gene at clinically beneficial levels. This review discusses principles and methods of delivering genes encoding growth factors into cells, together with their respective advantages and disadvantages.

Gene therapy for the treatment of sensory neuropathy

Sensory polyneuropathy can be a serious problem, but for the majority of clinically important neuropathies there are no available therapies. Neurotrophic and neuroprotective peptide factors have been identified that prevent or reverse neuropathy in rodent models of disease, but delivery of these highly pleiotropic peptides has posed an obstacle for translation into effective human therapies. Gene transfer into muscle using viral or non-viral vectors, or into neurons of the dorsal root ganglion using herpes simplex virus-based vectors, provides an alternative means to achieve this end. Studies in animal models have been promising, and the first human trial, using a plasmid to transfer the gene coding for vascular endothelial growth factor into muscle for the treatment of diabetic neuropathy, is now underway. Evidence supporting the trial and the challenges facing this therapy are reviewed.

Gene therapy in the treatment of lower extremity wounds

This article presents a brief overview of the etiology of chronic wounds of the lower extremities and their current medical and surgical treatment. Gene therapy as a potential tool for treating therapeutically challenging wounds is described in terms of the vectors employed in gene transfer, as well as the strategies used to promote wound healing. Results from animal model studies, as well as clinical trials, are presented.

Dual-gene, dual-cell type therapy against an excitotoxic insult by bolstering neuroenergetics

Increasing evidence suggests that glutamate activates the generation of lactate from glucose in astrocytes; this lactate is shuttled to neurons that use it as a preferential energy source. We explore this multicellular "lactate shuttle" with a novel dual-cell, dual-gene therapy approach and determine the neuroprotective potential of enhancing this shuttle. Viral vector-driven overexpression of a glucose transporter in glia enhanced glucose uptake, lactate efflux, and the glial capacity to protect neurons from excitotoxicity. In parallel, overexpression of a lactate transporter in neurons enhanced lactate uptake and neuronal resistance to excitotoxicity. Finally, overexpression of both transgenes in the respective cell types provided more protection than either therapy alone, demonstrating that a dual-cell, dual-gene therapy approach gives greater neuroprotection than the conventional single-cell, single-gene strategy.

HSV-1 virions engineered for specific binding to cell surface receptors

Expression of specific peptide epitopes on the surface of virions has significant potential for studying viral biology and designing vectors for targeted gene therapy. In this study, an HSV-1 amplicon plasmid expressing a modified glycoprotein C (gC), in which the heparan sulfate binding domain was replaced with a His-tag, was used in generating HSV-1 virions. Western blot analysis demonstrated the presence of modified gC in the purified virions. The amplicon vectors were packaged using a gC-, lacZ+ helper virus to generate a mixture of high-titer helper virus (lacZ+) and amplicon vectors (GFP+), which expressed modified gC in the virion envelope. His-tagged virions bound to 293 6H cells expressing a cell surface pseudo-His-tag receptor four-fold more efficiently than to parental 293 cells and also proved more effective than wild-type virus in binding to both cell types. Binding resulted in productive infection by the modified virions with expression of reporter genes and cytopathic effect comparable to those of wild-type virions. Thus, not only can HSV-1 tropism be manipulated to recognize a non-herpes simplex binding receptor, but it is also possible to increase the infective capacity of the vectors beyond that of the wild-type virus via specific ligand receptor combinations.

Gene therapy using replication-defective herpes simplex virus vectors expressing nerve growth factor in a rat model of diabetic cystopathy

Diabetic cystopathy is one of the common complications of diabetes and current therapy is limited. In the present study, the effects of gene therapy, using replication-defective herpes simplex virus type 1 (HSV-1) vectors to deliver and express the nerve growth factor (NGF) gene (HSV-NGF) on tissue NGF levels and bladder function, were evaluated in streptozotocin (STZ)-induced diabetic rats. Diabetic rats exhibited a significant decrease in NGF levels in the bladder and lumbosacral dorsal root ganglia (DRG) detected by enzyme-linked immunosorbent assay and displayed marked bladder dysfunction 12 weeks after STZ injection. In contrast, rats with bladder wall injection of the NGF expression vector 8 weeks after STZ treatment exhibited a significant increase of NGF levels in the bladder and L6 DRG 4 weeks after HSV-NGF injection. Along with the restoration of tissue NGF expression, in metabolic cage studies and cystometry, HSV-NGF-injected rats also showed significantly reduced bladder capacity and postvoid residual volume than diabetic rats injected with the control vector (HSV-lacZ), indicating that voiding function was improved after HSV vector-mediated NGF gene delivery. Thus, HSV vector-mediated NGF gene therapy may prove useful to restore decreased NGF expression in the bladder and bladder afferent pathways, thereby improving hypoactive bladder function in diabetes.

Exploiting the neurotherapeutic potential of peptides: targeted delivery using HSV vectors

Neurotrophic factors and peptide neurotransmitters represent two classes of potent macromolecules whose therapeutic use in the treatment of neurologic disease is limited by unwanted effects that result from the widespread distribution of cognate receptors within and beyond the neuraxis. Targeted gene delivery to sensory neurons of the dorsal root ganglion (DRG) by subcutaneous inoculation of herpes simplex virus (HSV)-based gene transfer vectors may be used to achieve local expression and release of these pleiotropic, short-lived molecules in a restricted area. Recent studies demonstrate that HSV-mediated transfer of genes coding for neurotrophic factors prevents the progression of disease in animal models of drug-induced or diabetic polyneuropathy and that HSV-mediated transfer of genes coding for inhibitory neurotransmitters provides a regional analgesic effect in animal models of chronic pain. The first human trial of HSV-mediated gene transfer to DRG is about to commence. HSV-mediated gene transfer may allow the therapeutic potential of these peptides for the treatment of neurologic disease to be realised.

The molecular biology of retinal ganglion cell death: caveats and controversies

Understanding the molecular pathways activated in dying retinal ganglion cells may lead to the development of therapies aimed at blocking the cell death process. As we learn more about ganglion cell death, it is becoming clear that several new hurdles must be overcome before preventing this process can be a realistic therapy. This review details three caveats about retinal ganglion cell death that should be considered. The first caveat centers on a critical step in the cell death pathway involving mitochondria. Blocking biochemical events after mitochondrial dysfunction, such as the caspase cascade, may provide only a transient effect on survival, since the cell has already sustained lethal damage. The second caveat is that blocking one cell death pathway may be ineffective because alternate pathways can become active. This caveat seems to be particularly relevant in neurons exposed to excitotoxic insults. The third caveat is that although it is possible to block cell death, this does not guarantee that the cell will be able to function normally. Consequently, it may be important to provide additional treatment to restore normal cell function in conjunction with therapies aimed at preventing their death.

Viral oncoapoptosis of human tumor cells

Many cancer cells refractory to radiation treatment and chemotherapy proliferate because of loss of intrinsic programmed cell death (apoptosis) regulation. Consequently, the resolution of these cancers are many times outside the management capabilities of conventional therapeutics. We now report that replication-defective delta27 herpes simplex virus (rd delta27) triggers apoptosis in three representative transformed human cell lines. Susceptibility to virus-induced cell death is dependent on the abundance and distribution of modified p53 protein in the tumor cells indicating specific targeting of the treatment. Primary human and mouse fibroblast cells that produce modified p53 are resistant to rd delta27 killing but not to apoptosis induced by nonviral environmental factors. These results suggest that induction of apoptosis by nonreplicating virus is a feasible genetic therapy approach for killing human cancer cells. Our findings may have important implications in designing novel virus-based anticancer strategies in appropriate animal model systems.

Altering behavior with gene transfer in the limbic system

There is now sufficient knowledge of the workings of the limbic system to allow experimental manipulation of behaviors anchored in limbic function. While such manipulations have traditionally involved lesions, stimulation or pharmacological approaches, it has become plausible to use gene transfer technology to alter patterns of gene expression in the nervous system. In this review, I consider ways in which gene transfer has been used to alter limbic function. These involve altering (a) cognition, (b) the rewarding properties of addictive substances, (c) patterns of social affiliation, and (d) responses to stress.

Immune responses to replication-defective HSV-1 type vectors within the CNS: implications for gene therapy

Herpes simplex virus (HSV) is a naturally occurring double-stranded DNA virus that has been adapted into an efficient vector for in vivo gene transfer. HSV-based vectors exhibit wide tropism, large transgene size capacity, and moderately prolonged transgene expression profiles. Clinical implementation of HSV vector-based gene therapy for prevention and/or amelioration of human diseases eventually will be realized, but inherently this goal presents a series of significant challenges, one of which relates to issues of immune system involvement. Few experimental reports have detailed HSV vector-engendered immune responses and subsequent resolution events primarily within the confines of the central nervous system. Herein, we describe the immunobiology of HSV and its derived vector platforms, thus providing an initiation point from where to propose requisite experimental investigation and potential approaches to prevent and/or counter adverse antivector immune responses.

Transgene-mediated enkephalin release enhances the effect of morphine and evades tolerance to produce a sustained antiallodynic effect in neuropathic pain

We examined the pharmacologic characteristics of herpes simplex virus (HSV) vector-mediated expression of proenkephalin in the dorsal root ganglion in a rodent model of neuropathic pain. We found that: (i). vector-mediated enkephalin produced an antiallodynic effect that was reversed by naloxone; (ii). vector-mediated enkephalin production in animals with spinal nerve ligation prevented the induction of c-fos expression in second order sensory neurons in the dorsal horn of spinal cord; (iii). the effect of vector-mediated enkephalin enhanced the effect of morphine, reducing the ED(50) of morphine 10-fold; (iv). animals did not develop tolerance to the continued production of vector-mediated enkephalin over a period of several weeks; and, (v). vector transduction continued to provide an analgesic effect despite the induction of tolerance to morphine. This is the first demonstration of gene transfer to provide an analgesic effect in neuropathic pain. The pharmacologic analysis demonstrates that transgene-mediated expression and local release of opioid peptides produce some effects that are distinct from peptide analogues delivered pharmacologically.

Regulated transgene delivery by ganciclovir in the brain without physiological alterations by a live attenuated herpes simplex virus vector

The distribution of a live attenuated herpes simplex virus (betaH1)-mediated gene delivery into the central nervous system (CNS) was regulated by growth inhibition with ganciclovir (GCV) and the effect of this transgene expression system on the physiologic response was characterized by the acoustic startle response and its prepulse inhibition. We inoculated betaH1 expressing beta-galactosidase (beta-gal) driven by the latency associated transcripts promoter into the right caudate putamen of rats. Histochemical analysis demonstrated that the inoculation of betaH1 in the right caudate putamen resulted in a high level of beta-gal expression in the neurons of the area projecting to the inoculation site. On 14 days after inoculation without GCV-treatment, beta-gal activity localized in the anterior olfactory nucleus, frontal, insular, orbital, parietal, perirhinal, piriform cortices and the temporal region including the amygdala. In contrast, the distribution of beta-gal activity was regulated by the interval between virus inoculation and GCV-treatment and maintained after its cessation without significant alteration. The whole process of transgene expression did not influence the emotional behavior, indicating that this vector system is a suitable model for analyzing the transgene function or applying the gene therapy for the CNS diseases.

Tetracycline-regulated gene expression in replication-incompetent herpes simplex virus vectors

Although herpes simplex virus (HSV) vectors appear to have great potential as gene delivery vectors both in vitro and in vivo, the expression of foreign genes in such vectors cannot be easily regulated. Of the known eukaryotic regulatory systems, the tetracycline-inducible gene expression system is perhaps the most widely used because of its induction characteristics and because of the well-known pharmacological properties of tetracycline (Tet) and analogs such as doxycycline. Here, we describe the adaptation of the Tet-inducible system for use in replication-incompetent HSV vectors. HSV vectors were constructed that contained several types of Tet-inducible promoters for foreign gene expression. These promoters contained a tetracycline response element (TRE) linked to either a minimal cytomegalovirus (CMV) immediate-early promoter, a minimal HSV ICP0 promoter, or a truncated HSV ICP0 promoter containing one copy of the HSV TAATGARAT cis-acting immediate-early regulatory element (where R represents a prime base). All three promoter constructs were regulated appropriately by doxycycline, as shown by the expression of the marker gene lacZ in cell lines engineered to express Tet transactivators. The ICP0 promoter constructs expressed the highest and most sustained levels of lacZ, but the CMV promoter construct had the highest relative level of induction, suggesting their use in different applications. To extend the utility of Tet-regulated HSV vectors, vectors were constructed that coexpressed an inducible Tet transactivator in addition to the inducible lacZ marker gene. This modification resulted in tetracycline-inducible gene expression that was not restricted to specific cell lines, and this vector was capable of inducible expression in irreversibly differentiated NT2 cells (NT-neurons) for several days. Finally, HSV vectors were constructed that expressed modified Tet transactivators, resulting in improved induction properties and indicating the flexibility of the Tet-regulated system for regulation of foreign gene expression in HSV vector-infected cells.

Retinal ganglion cell differentiation in cultured mouse retinal explants

The availability of genetically engineered mice harboring specific mutations in genes affecting one or more retinal cell types affords new opportunities for investigating the genetic regulatory mechanisms of vertebrate retina formation. When identifying critical regulatory genes involved in retina development it is often advantageous to complement in vivo analysis with in vitro characterization. In particular, by combining classical techniques of retinal explant culturing with gene transfer procedures relying on herpes simple virus (HSV) amplicon vectors, gain-of-function analysis with genes of interest can be performed quickly and efficiently. Here, details are provided for isolating and culturing explants containing retinal progenitor cells and for infecting the explants with HSV expression vectors that perturb or rescue retinal ganglion cells, the first cell type to differentiate in the retina. In addition, the availability of sensitive techniques to monitor gene expression, including detection of reporter gene expression using antibodies and detection of endogenous marker gene expression using quantitative RT-PCR, provides an effective means for comparing wild-type and mutant retinas from genetically engineered mice.

Viruses as gene delivery vectors: application to gene function, target validation, and assay development

A Biochemical Pharmacology Discussion Group Conference, was held at the headquarters of the New York Academy of Sciences on December 4, 2001 as part of an ongoing series designed to highlight and review areas important to modern drug development (Figure 1). Briefly introduced by Tom Kost (GlaxoSmithKline) and Michael Lotze (University of Pittsburgh), the focus was on the intersection of genomics, proteomics, and now "viromics." The latter term refers to the use of viruses and viral gene transfer to explore the complexity arising from the vast array of new targets available from the human and murine genomes. Indeed, access to large numbers of genes using viral vectors is a key tool for drug discovery and drug delivery. With 38,000 genes identified within the human genome, only 5000 are considered readily druggable. Generating tools such as these to validate targets represents a major part of the armamentarium of the postgenomic scientist. During the last 12 years alone, there have been over 26,000 publications on virus vectors. Many of them have been found useful in target validation, assay development, and evaluation in in vivo models and gene therapy. Thus, there is now an extensive knowledge base for several viral vectors, with unique attributes within each of them providing versatility, efficiency, and ease of use. The individual scientists presenting at the meeting illustrated many of the unique and useful characteristics of such vector systems including retrovirus, adenovirus, herpes virus, simbis virus, and baculovirus.

Gene transfer to salivary glands

This article provides a review of the application of gene transfer technology to studies of salivary glands. Salivary glands provide an uncommon target site for gene transfer but offer many experimental situations likely of interest to the cell biologist. The reader is provided with a concise overview of salivary biology, along with a general discussion of the strategies available for gene transfer to any tissue. In particular, adenoviral vectors have been useful for proof of concept studies with salivary glands. Several examples are given, using adenoviral-mediated gene transfer, for addressing both biological and clinical questions. Additionally, benefits and shortcomings affecting the utility of this technology are discussed.

Critical issues in gene therapy for neurologic disease

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

Delivery of novel macromolecular drugs against HIV-1

The development of new low molecular weight drugs against human immunodeficiency virus Type 1 (HIV-1) targets other than reverse transcriptase (RT) and protease, such as the integrase and the envelope glycoprotein, is likely to take many years. Macromolecular drugs, including antisense oligonucleotides, ribozymes, RNA decoys and transdominant mutant proteins, may be able to interfere with a relatively large number of viral targets, thereby decreasing the likelihood of the emergence of drug-resistant strains. It may also be relatively easy to alter the sequence of some of the macromolecular drugs to counter emerging drug-resistant viruses. The delivery of antisense oligonucleotides and ribozymes to HIV-1 infected or potentially infectable cells by antibody-targeted liposomes, certain cationic lipid formulations and pH-sensitive liposomes results in significant anti-HIV-1 activity. These carriers not only facilitate cytoplasmic delivery but also protect the drugs from nuclease digestion. Delivery of therapeutic genes (another form of macromolecular drug) to target cells is an important challenge of gene therapy. Following delivery by a viral vector, sufficient levels of gene expression must be maintained over an extended period of time to have therapeutic activity. Robust expression of therapeutically useful ribozymes, antisense, decoys and aptamers can be achieved by the use of Pol III expression systems. Moloney murine leukaemia virus- (MoMuLV), adeno-associated virus (AAV)-, or HIV-derived vectors expressing a variety of therapeutic genes have been used successfully to inhibit HIV-1 replication in cultured cells.

Gene therapy

With recent advances in molecular biology, the ability to transfer genes to patients is becoming a reality. Ongoing clinical trials using gene transfer techniques have illustrated the potential and pitfalls of this new therapeutic modality for the treatment of a wide variety of disorders. While these techniques are not currently a part of routine clinical practice, it is only a matter of time until some form of gene therapy is approved for general use in the clinic. This review highlights some of the basic methods used in current gene therapy protocols. The objective of this review is to familiarize practitioners with these concepts so they can more effectively follow the progress of this emerging technology and better inform their patients.

Plasmid DNA adsorbed onto cationic microparticles mediates target gene expression and antigen presentation by dendritic cells

Dendritic cells (DC) play a key role in antigen presentation and activation of specific immunity. Much current research focuses on harnessing the potency of DC for vaccines, gene therapy, and cancer immunotherapy applications. However, DC are not readily transfected in vitro by traditional nonviral techniques. A novel DNA vaccine formulation was used to determine if DC are transfected in vitro. The formulation consists of plasmid DNA adsorbed on to cationic microparticles composed of the biodegradable polymer polylactide-co-glycolide (PLG) and the cationic surfactant, cetyltrimethylammonium bromide (CTAB). Using preparations of fluorescent-labeled plasmid DNA formulated on PLG-CTAB microparticles to study internalization by macrophages and dendritic cells in vitro and in vivo, we found that most, but not all, of the fluorescence was concentrated in endosomal compartments. Furthermore, uptake of plasmid DNA encoding HIV p55 gag adsorbed to PLG-CTAB microparticles by murine bone marrow-derived dendritic cells resulted in target gene expression, as detected by RT-PCR. The antigen was subsequently processed and presented, resulting in stimulation of an H-2kd-restricted, gag-specific T cell hybridoma. Activation of the hybridoma, detected by IL-2 production, was dose-dependent in the range of 0.1-20 microg DNA (10-2000 microg PLG) and was sustained up to 5 days after transfection. Thus, adsorption of plasmid DNA on PLG-CTAB microparticles provides a potentially useful nonviral approach for in vitro transfection of dendritic cells. Gene Therapy (2000) 7, 2105-2112.

Hybrid vector designs to control the delivery, fate and expression of transgenes

One of the greatest challenges to gene therapy is the targetting of gene delivery selectively to the sites of disease and regulation of transgene expression without adverse effects. Ultimately, the successful realization of these goals is dependent upon improvements in vector design. Over the years, viral vector design has progressed from various types of replication-defective viral mutants to replication-conditioned viruses and, more recently, to 'gutted' and hybrid vectors, which have, respectively, eliminated expression of non-relevant or toxic viral genes and incorporated desired elements of different viruses so as to increase the efficacy of gene delivery in vivo. This review will focus on the different viral and cellular elements which have been incorporated into virus vectors to: improve transduction efficiencies; alter the entry specificity of virions; control the fate of transgenes in the host cells; and regulate transgene expression.

Gene therapy in wound repair and regeneration

The potential use of gene therapy to treat human disease increases with the development of various physical, chemical, and biological methods to deliver genes to mammalian cells, and with our rapidly expanding knowledge of the human genome. One area of therapeutic interest for gene therapy is the treatment of wound healing disorders. Most recently, recombinant human growth factor therapy has been examined as a means to treat problem wounds. However, this approach suffers from the difficulty in providing an accurate dose of growth factor and the expense of the recombinant proteins. Delivery of a gene that could be expressed within the wound is an attractive alternative to application of the protein. This review discusses several methods that have been used to deliver genes encoding growth factor proteins into wounds and the advantages/disadvantages of each approach. Novel methods to regulate the expression of the transgene are also presented, highlighting the ability of these unique vector systems to adjust gene dose as the wound heals. We expect that gene therapy will become a significant treatment modality for those wound healing pathologies refractory to other wound management approaches in the years ahead.