Herpes simplex viral vectors: late bloomers with big potential

An updated review of HSV-1 infection-associated diseases and treatment, vaccine development, and vector therapy application

Herpes simplex virus type 1 (HSV-1) is a globally widespread virus that causes and associates with a wide range of diseases, including herpes simplex encephalitis, herpes simplex keratitis, and herpes labialis. The interaction between HSV-1 and the host involves complex immune response mechanisms, including recognition of viral invasion, maintenance of latent infection, and triggering of reactivation. Antiviral therapy is the core treatment for HSV-1 infections. Meanwhile, vaccine development employs different strategies and methods, and several promising vaccine types have emerged, such as live attenuated, protein subunit, and nucleic acid vaccines, offering new possibilities for the prevention of HSV-1 infection. Moreover, HSV-1 can be modified into a therapeutic vector for gene therapy and tumour immunotherapy. This review provides an in-depth summary of HSV-1 infection-associated innate and adaptive immune responses, disease pathogenesis, current therapeutic approaches, recent advances in vaccine development, and vector therapy applications for cancer treatment. Through a systematic review of multiple aspects of HSV-1, this study aims to provide a comprehensive and detailed reference for the public on the prevention, control, and treatment of HSV-1.

Viral vector-mediated gene therapy for opioid use disorders

Chronic exposure to opioids typically results in adverse consequences. Opioid use disorder (OUD) is a disease of the CNS with behavioral, psychological, neurobiological, and medical manifestations. OUD induces a variety of changes of neurotransmitters/neuropeptides in the nervous system. Existing pharmacotherapy, such as opioid maintenance therapy (OMT) is the mainstay for the treatment of OUD, however, current opioid replacement therapy is far from effective for the majority of patients. Pharmacological therapy for OUD has been challenging for many reasons including debilitating side-effects. Therefore, developing an effective, non-pharmacological approach would be a critical advancement in improving and expanding treatment for OUD. Viral vector mediated gene therapy provides a potential new approach for treating opioid abused patients. Gene therapy can supply targeting gene products directly linked to the mechanisms of OUD to restore neurotransmitter and/or neuropeptides imbalance, and avoid the off-target effects of systemic administration of drugs. The most commonly used viral vectors in rodent studies of treatment of opioid-used disorder are based on recombinant adenovirus (AV), adeno-associated virus (AAV), lentiviral (LV) vectors, and herpes simplex virus (HSV) vectors. In this review, we will focus on the recent progress of viral vector mediated gene therapy in OUD, especially morphine tolerance and withdrawal.

Improvement of HSV-1 based amplicon vectors for a safe and long-lasting gene therapy in non-replicating cells

A key factor for developing gene therapy strategies for neurological disorders is the availability of suitable vectors. Currently, the most advanced are adeno-associated vectors that, while being safe and ensuring long-lasting transgene expression, have a very limited cargo capacity. In contrast, herpes simplex virus-based amplicon vectors can host huge amounts of foreign DNA, but concerns exist about their safety and ability to express transgenes long-term. We aimed at modulating and prolonging amplicon-induced transgene expression kinetics in vivo using different promoters and preventing transgene silencing. To pursue the latter, we deleted bacterial DNA sequences derived from vector construction and shielded the transgene cassette using AT-rich and insulator-like sequences (SAm technology). We employed luciferase and GFP as reporter genes. To determine transgene expression kinetics, we injected vectors in the hippocampus of mice that were longitudinally scanned for bioluminescence for 6 months. To evaluate safety, we analyzed multiple markers of damage and performed patch clamp electrophysiology experiments. All vectors proved safe, and we managed to modulate the duration of transgene expression, up to obtaining a stable, long-lasting expression using the SAm technology. Therefore, these amplicon vectors represent a flexible, efficient, and safe tool for gene delivery in the brain.

Oncolytic Viruses and Their Potential as a Therapeutic Opportunity in Osteosarcoma

Osteosarcoma remains an unmet medical need. Oncolytic viruses are gaining traction as novel cancer therapeutics. These viruses are either naturally nonpathogenic or engineered to be safe by specific genetic deletions yet retain the ability to infect and kill human cancer cells and elicit anticancer immunity. Some versions are being specifically designed and tested in patients with osteosarcoma, though due to their generalized mechanism of action most are being tested in patients across a broad range of cancer types. The activity of these viruses is impacted not only by the susceptibility of tumor cells to infection but also by the tumor microenvironment (TME) and by tumor immunogenicity. Here we review the field of oncolytic viruses with a particular emphasis on highlighting any available data in preclinical osteosarcoma models or in patients with osteosarcoma. While in general the viruses have been shown safe to administer to patients by a variety of routes, their therapeutic efficacy to date has been limited. Given the low rate of adverse events and the likely absence of long-term side effects, the utility of oncolytic viruses will most likely be realized when used in combination with other agents.

Current Trends in Viral Gene Therapy for Human Orthopaedic Regenerative Medicine

Background

Viral vector-based therapeutic gene therapy is a potent strategy to enhance the intrinsic reparative abilities of human orthopaedic tissues. However, clinical application of viral gene transfer remains hindered by detrimental responses in the host against such vectors (immunogenic responses, vector dissemination to nontarget locations). Combining viral gene therapy techniques with tissue engineering procedures may offer strong tools to improve the current systems for applications in vivo.

Methods

The goal of this work is to provide an overview of the most recent systems exploiting biomaterial technologies and therapeutic viral gene transfer in human orthopaedic regenerative medicine.

Results

Integration of tissue engineering platforms with viral gene vectors is an active area of research in orthopaedics as a means to overcome the obstacles precluding effective viral gene therapy.

Conclusions

In light of promising preclinical data that may rapidly expand in a close future, biomaterial-guided viral gene therapy has a strong potential for translation in the field of human orthopaedic regenerative medicine.

Sustained FXN expression in dorsal root ganglia from a nonreplicative genomic HSV-1 vector

BACKGROUND

Friedreich's ataxia (FA) is an autosomal recessive neurodegenerative disease caused by mutations in the frataxin gene (FXN), which lead to reduced levels of the essential mitochondrial protein frataxin. Currently, there is no effective cure.

METHODS

With the aim of developing a gene therapy for FA neuropathology, we describe the construction and preliminary characterization of a high-capacity nonreplicative genomic herpes simplex virus type 1 vector (H24B-FXNlac vector) carrying a reduced version of the human FXN genomic locus, comprising the 5-kb promoter and the FXN cDNA with the inclusion of intron 1.

RESULTS

We show that the transgene cassette contains the elements necessary to preserve physiological neuronal regulation of human FXN expression. Transduction of cultured fetal rat dorsal root ganglia neurons with the H24B-FXNlac vector results in sustained expression of human FXN transcripts and frataxin protein. Rat footpad inoculation with the H24B-FXNlac vector results in human FXN transgene delivery to the dorsal root ganglia, with expression persisting for at least 1 month.

CONCLUSIONS

The results of the present study support the feasibility of using this vector for sustained neuronal expression of human frataxin for FA gene therapy.

Viral Vector Biosafety in Laboratory Animal Research

Viral vector research presents unique occupational health and safety challenges to institutions due to the rapid development of both in vivo and in vitro gene-editing technologies. Risks to human and animal health make it incumbent on institutions to appropriately evaluate viral vector usage in research on the basis of available information and governmental regulations and guidelines. Here we review the factors related to risk assessment regarding viral vector usage in animals and the relevant regulatory documents associated with this research, and we highlight the most commonly used viral vectors in research today. This review is particularly focused on the background, use in research and associated health and environmental risks related to adenoviral, adeno-associated viral, lentiviral, and herpesviral vectors.

Virotherapy: cancer gene therapy at last?

For decades, effective cancer gene therapy has been a tantalising prospect; for a therapeutic modality potentially able to elicit highly effective and selective responses, definitive efficacy outcomes have often seemed out of reach. However, steady progress in vector development and accumulated experience from previous clinical studies has finally led the field to its first licensed therapy. Following a pivotal phase III trial, Imlygic (talimogene laherparepvec/T-Vec) received US approval as a treatment for cutaneous and subcutaneous melanoma in October 2015, followed several weeks later by its European authorisation. These represent the first approvals for an oncolytic virotherapy. Imlygic is an advanced-generation herpesvirus-based vector optimised for oncolytic and immunomodulatory activities. Many other oncolytic agents currently remain in development, providing hope that current success will be followed by other diverse vectors that may ultimately come to constitute a new class of clinical anti-cancer agents. In this review, we discuss some of the key oncolytic viral agents developed in the adenovirus and herpesvirus classes, and the prospects for further enhancing their efficacy by combining them with novel immunotherapeutic approaches.

Oncolytic virotherapy for pediatric malignancies: future prospects

Pediatric solid tumors remain a major health concern, with nearly 16,000 children diagnosed each year. Of those, ~2,000 succumb to their disease, and survivors often suffer from lifelong disability secondary to toxic effects of current treatments. Countless multimodality treatment regimens are being explored to make advances against this deadly disease. One targeted treatment approach is oncolytic virotherapy. Conditionally replicating viruses can infect tumor cells while leaving normal cells unharmed. Four viruses have been advanced to pediatric clinical trials, including herpes simplex virus-1, Seneca Valley virus, reovirus, and vaccinia virus. In this review, we discuss the mechanism of action of each virus, pediatric preclinical studies conducted to date, past and ongoing pediatric clinical trials, and potential future direction for these novel viral therapeutics.

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

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

Efficacy of Herpes Simplex Virus Vector Encoding the Human Preproenkephalin Gene for Treatment of Facial Pain in Mice

AIMS

To determine whether herpes simplex virus-based vectors can efficiently transduce mouse trigeminal ganglion (TG) neurons and attenuate preexisting nerve injury-induced whisker pad mechanical hypersensitivity in a trigeminal inflammatory compression (TIC) neuropathic pain model.

METHODS

Tissue transduction efficiencies of replication-conditional and replication-defective vectors to mouse whisker pads after topical administration and subcutaneous injection were assessed using quantitative real-time PCR (qPCR). Tissue tropism and transgene expression were assessed using qPCR and reverse-transcriptase qPCR following topical application of the vectors. Whisker pad mechanical sensitivities of TIC-injured mice were determined using graduated von Frey fibers before and after application of human preproenkephalin expressing replication-conditional vector (KHPE). Data were analyzed using one-way analysis of variance (ANOVA) and post hoc tests.

RESULTS

Transduction of target TGs was 8- to 50-fold greater after topical application than subcutaneous injection and ≥ 100-fold greater for replication-conditional than replication-defective vectors. Mean KHPE loads remained constant in TGs (4.5-9.8 × 10(4) copies/TG) over 3 weeks but were below quantifiable levels (10 copies/tissue) within 2 weeks of application in other nontarget cephalic tissues examined. Transgene expression in TGs was maximal during 2 weeks after topical application (100-200 cDNA copies/mL) and was below quantifiable levels (1 cDNA copy/mL) in all nontarget tissues. Topical KHPE administration reduced TIC-related mechanical hypersensitivity on whisker pads 4-fold (P < .05) for at least 1 week.

CONCLUSION

Topically administered KHPE produced a significant antinociceptive effect in the TIC mouse model of chronic facial neuropathic pain. This is the first report in which a gene therapeutic approach reduced trigeminal pain-related behaviors in an established pain state in mice.

Pediatric cancer gone viral. Part I: strategies for utilizing oncolytic herpes simplex virus-1 in children

Progress for improving outcomes in pediatric patients with solid tumors remains slow. In addition, currently available therapies are fraught with numerous side effects, often causing significant life-long morbidity for long-term survivors. The use of viruses to kill tumor cells based on their increased vulnerability to infection is gaining traction, with several viruses moving through early and advanced phase clinical testing. The prospect of increased efficacy and decreased toxicity with these agents is thus attractive for pediatric cancer. In part I of this two-part review, we focus on strategies for utilizing oncolytic engineered herpes simplex virus (HSV) to target pediatric malignancies. We discuss mechanisms of action, routes of delivery, and the role of preexisting immunity on antitumor efficacy. Challenges to maximizing oncolytic HSV in children are examined, and we highlight how these may be overcome through various arming strategies. We review the preclinical and clinical evidence demonstrating safety of a variety of oncolytic HSVs. In Part II, we focus on the antitumor efficacy of oncolytic HSV in pediatric tumor types, pediatric clinical advances made to date, and future prospects for utilizing HSV in pediatric patients with solid tumors.

DNA vaccination for prostate cancer: key concepts and considerations

While locally confined prostate cancer is associated with a low five year mortality rate, advanced or metastatic disease remains a major challenge for healthcare professionals to treat and is usually terminal. As such, there is a need for the development of new, efficacious therapies for prostate cancer. Immunotherapy represents a promising approach where the host's immune system is harnessed to mount an anti-tumour effect, and the licensing of the first prostate cancer specific immunotherapy in 2010 has opened the door for other immunotherapies to gain regulatory approval. Among these strategies DNA vaccines are an attractive option in terms of their ability to elicit a highly specific, potent and wide-sweeping immune response. Several DNA vaccines have been tested for prostate cancer and while they have demonstrated a good safety profile they have faced problems with low efficacy and immunogenicity compared to other immunotherapeutic approaches. This review focuses on the positive aspects of DNA vaccines for prostate cancer that have been assessed in preclinical and clinical trials thus far and examines the key considerations that must be employed to improve the efficacy and immunogenicity of these vaccines.