Viral vectors for gene transfer: current status of gene therapeutics

Gene modification therapies for hereditary diseases in the fetus

Proof-of-principle disease models have demonstrated the feasibility of an intrauterine gene modification therapy (in utero gene therapy (IUGT)) approach to hereditary diseases as diverse as coagulation disorders, haemoglobinopathies, neurogenetic disorders, congenital metabolic, and pulmonary diseases. Gene addition, which requires the delivery of an integrating or episomal transgene to the target cell nucleus to be transcribed, and gene editing, where the mutation is corrected within the gene of origin, have both been used successfully to increase normal protein production in a bid to reverse or arrest pathology in utero. While most experimental models have employed lentiviral, adenoviral, and adeno-associated viral vectors engineered to efficiently enter target cells, newer models have also demonstrated the applicability of non-viral lipid nanoparticles. Amelioration of pathology is dependent primarily on achieving sustained therapeutic transgene expression, silencing of transgene expression, production of neutralising antibodies, the dilutional effect of the recipient's growth on the mass of transduced cells, and the degree of pre-existing cellular damage. Safety assessment of any IUGT strategy will require long-term postnatal surveillance of both the fetal recipient and the maternal bystander for cell and genome toxicity, oncogenic potential, immune-responsiveness, and germline mutation. In this review, we discuss advances in the field and the push toward clinical translation of IUGT.

Adeno-associated virus-based malaria booster vaccine following attenuated replication-competent vaccinia virus LC16m8Δ priming

We previously demonstrated that boosting with adeno-associated virus (AAV) type 1 (AAV1) can induce highly effective and long-lasting protective immune responses against malaria parasites when combined with replication-deficient adenovirus priming in a rodent model. In the present study, we compared the efficacy of two different AAV serotypes, AAV1 and AAV5, as malaria booster vaccines following priming with the attenuated replication-competent vaccinia virus strain LC16m8Δ (m8Δ), which harbors the fusion gene encoding both the pre-erythrocytic stage protein, Plasmodium falciparum circumsporozoite (PfCSP) and the sexual stage protein (Pfs25) in a two-dose heterologous prime-boost immunization regimen. Both regimens, m8Δ/AAV1 and m8Δ/AAV5, induced robust anti-PfCSP and anti-Pfs25 antibodies. To evaluate the protective efficacy, the mice were challenged with sporozoites twice after immunization. At the first sporozoite challenge, m8Δ/AAV5 achieved 100% sterile protection whereas m8Δ/AAV1 achieved 70% protection. However, at the second challenge, 100% of the surviving mice from the first challenge were protected in the m8Δ/AAV1 group whereas only 55.6% of those in the m8Δ/AAV5 group were protected. Regarding the transmission-blocking efficacy, we found that both immunization regimens induced high levels of transmission-reducing activity (>99%) and transmission-blocking activity (>95%). Our data indicate that the AAV5-based multistage malaria vaccine is as effective as the AAV1-based vaccine when administered following an m8Δ-based vaccine. These results suggest that AAV5 could be a viable alternate vaccine vector as a malaria booster vaccine.

Adeno-associated virus-mediated IL-12 gene expression alleviates lung inflammation and Th2-responses in OVA-sensitized asthmatic mice

High levels of allergen exposure increase the prevalence of asthma in development countries. The asthmatic Th2 response is characterized with high eosinophil infiltration, elevated Th2 cytokines and IgE secretion resulting in local or systemic inflammation. However, the treatment with palliative Th2 inhibitor drugs can't completely control asthma and that is why the development of novel approaches is still important. Based on Th1 and Th2 immune homeostasis, the enhanced Th1 immune response has high potential to alleviate Th2 immune response. Thus, we aimed to overexpress single chain IL-12 (scIL-12) via recombinant adeno-associated virus (rAAV) vector (as rAAV-IL-12) and test the efficacy in an ovalbumin (OVA)-induced asthmatic murine model. We firstly demonstrated the bioactivity of exogenous scIL-12. The expression of exogenous scIL-12 was also detected in the lungs of rAAV-IL-12 transduced mice. The data demonstrated that overexpression of exogenous scIL-12 significantly suppressed total cell numbers and eosinophil infiltration, as well as the mucus secretion in rAAV-IL-12-treated mice. The decreased OVA-specific IgE in bronchoalveolar lavage fluid (BALF) and gene expression of Th2-cytokines or CCL11 in lung were observed. In addition, the production of cytokines in the supernatants of OVA-stimulated splenocytes was suppressed with rAAV-IL-12 treatment. Thus, scIL-12 expression by rAAV vector was able to modulate Th2 activity and has the potential to be developed as a feasible strategy in modulating allergic diseases.

Comparative analysis of adeno-associated virus serotypes for gene transfer in organotypic heart slices

Background

Vectors derived from adeno-associated viruses (AAVs) are widely used for gene transfer both in vitro and in vivo and have gained increasing interest as shuttle systems to deliver therapeutic genes to the heart. However, there is little information on their tissue penetration and cytotoxicity, as well as the optimal AAV serotype for transferring genes to diseased hearts. Therefore, we aimed to establish an organotypic heart slice culture system for mouse left ventricular (LV) myocardium and use this platform to analyze gene transfer efficiency, cell tropism, and toxicity of different AAV serotypes.

Methods

LV tissue slices, 300 µm thick, were prepared from 15- to 17-day-old transgenic alpha-myosin heavy-chain-mCherry mice using a vibrating microtome. Tissue slice viability in air-liquid culture was evaluated by calcein-acetoxymethyl ester staining, mCherry fluorescence intensity, and the tetrazolium assay. Four recombinant AAV serotypes (1, 2, 6, 8) expressing green fluorescent protein (GFP) under the CAG promoter were added to the slice surface. Gene transfer efficiency was quantified as the number of GFP-positive cells per slice. AAV cell tropism was examined by comparing the number of GFP-positive cardiomyocytes (CMs) and fibroblasts within heart slices.

Results

Slices retained viability in in vitro culture for at least 5 days. After adding AAV particles, AAV6-infected slices showed the highest number of GFP-expressing cells, almost exclusively CMs. Slice incubation with AAV1, 2, and 8 resulted in fewer GFP-positive cells, with AAV2 having the lowest gene transfer efficiency. None of the AAV serotypes tested caused significant cytotoxicity when compared to non-infected control slices.

Conclusions

We have established a readily available mouse organotypic heart slice culture model and provided evidence that AAV6 may be a promising gene therapy vector for heart failure and other cardiac diseases.

Dynorphin-based "release on demand" gene therapy for drug-resistant temporal lobe epilepsy

Focal epilepsy represents one of the most common chronic CNS diseases. The high incidence of drug resistance, devastating comorbidities, and insufficient responsiveness to surgery pose unmet medical challenges. In the quest of novel, disease-modifying treatment strategies of neuropeptides represent promising candidates. Here, we provide the "proof of concept" that gene therapy by adeno-associated virus (AAV) vector transduction of preprodynorphin into the epileptogenic focus of well-accepted mouse and rat models for temporal lobe epilepsy leads to suppression of seizures over months. The debilitating long-term decline of spatial learning and memory is prevented. In human hippocampal slices obtained from epilepsy surgery, dynorphins suppressed seizure-like activity, suggestive of a high potential for clinical translation. AAV-delivered preprodynorphin expression is focally and neuronally restricted and release is dependent on high-frequency stimulation, as it occurs at the onset of seizures. The novel format of "release on demand" dynorphin delivery is viewed as a key to prevent habituation and to minimize the risk of adverse effects, leading to long-term suppression of seizures and of their devastating sequel.

Outlook and future of inner ear therapy

Drug delivery to the inner ear is an ideal method to treat a wide variety of otologic conditions. A broad range of potential applications is just beginning to be explored. New approaches combine principles of inner ear pharmacokinetics with emerging technologies of drug delivery including novel delivery systems, drug-device combinations, and new categories of drugs. Strategies include cell-specific targeting, manipulation of gene expression, local activation following systemic delivery, and use of stem cells, viral vectors, and gene editing systems. Translation of these therapies to the clinic remains challenging given the potential risks of intracochlear and intralabyrinthine trauma, our limited understanding of the etiologies of particular inner ear disorders, and paucity of accurate diagnostic tools at the cellular level. This review provides an overview of future methods, delivery systems, disease targets, and clinical considerations required for translation to clinical medicine.

Direct reprogramming of mouse fibroblasts into neural cells via Porphyra yezoensis polysaccharide based high efficient gene co-delivery

BACKGROUND

The cell source for transplantation therapy is always a prerequisite question to be solved in clinical applications. Neural cells are considered non-regenerable, which highly restrict their application in the treatment for nerve injury. Therefore, neural trans-differentiation based on gene transfection provides a new solution to this issue. Compared to viral strategy, non-viral gene delivery systems are considered as a more promising way to achieve this aim. This study centers on a novel application of Porphyra yezoensis polysaccharide as a non-viral gene carrier for the neural trans-differentiation of mouse fibroblasts.

RESULTS

Ethanediamine modified P. yezoensis polysaccharide (Ed-PYP) served as a gene carrier and a group of plasmids that encode Ascl1, Brn4, and Tcf3 (pABT) self-assembled into nanoparticles. Results demonstrated that Ed-PYP-pABT nanoparticles at Ed-PYP: pABT weight ratio of 40:1 was the optimal candidate for gene delivery. ELISA assay revealed the highest expression levels of NGF, BDNF and SHH at 14 days after last transfection. Immunofluorescence and western blot assays also showed robust expression of neural markers including Nestin, GFAP, β-3tubulin, NF200, GAP43 and MAP2, in induced 3T6 cells at this time point.

CONCLUSION

Overall, these findings indicated that the P. yezoensis polysaccharide-based non-viral gene co-delivery system is a promising strategy for the generation of neural cells, which might facilitate the developments in the recovery of neural injuries.

Neurotrophin Gene Therapy in Deafened Ears with Cochlear Implants: Long-term Effects on Nerve Survival and Functional Measures

Because cochlear implants function by stimulating the auditory nerve, it is assumed that the condition of the nerve plays an important role in the efficacy of the prosthesis. Thus, considerable research has been devoted to methods of preserving the nerve following deafness. Neurotrophins have been identified as a potential contributor to neural health, but most of the research to date has been done in young animals and for short periods (less than 3 to 6 months) after the onset of treatment. The first objective of the current experiment was to examine the effects of a neurotrophin gene therapy delivery method on spiral ganglion neuron (SGN) preservation and function in the long term (5 to 14 months) in mature guinea pigs with cochlear implants. The second objective was to examine several potential non-invasive monitors of auditory nerve health following the neurotrophin gene therapy procedure. Eighteen mature adult male guinea pigs were deafened by cochlear perfusion of neomycin and then one ear was inoculated with an adeno-associated viral vector with an Nft3-gene insert (AAV.Ntf3) and implanted with a cochlear implant electrode array. Five control animals were deafened and inoculated with an empty AAV and implanted. Data from 43 other guinea pig ears from this and previous experiments were used for comparison: 24 animals implanted in a hearing ear, nine animals deafened and implanted with no inoculation, and ten normal-hearing non-implanted ears. After 4 to 21 months of psychophysical and electrophysiological testing, the animals were prepared for histological examination of SGN densities and inner hair cell (IHC) survival. Seventy-eight percent of the ears deafened and inoculated with AAV.Ntf3 showed better SGN survival than the 14 deafened-control ears. The degree of SGN preservation following the gene therapy procedure was variable across animals and across cochlear turns. Slopes of psychophysical multipulse integration (MPI) functions were predictive of SGN density, but only in animals with preserved IHCs. MPI was not affected by the AAV.Ntf3 treatment, but there was a minor improvement in temporal integration (TI). AAV.Ntf3 treatment had significant effects on ECAP and EABR amplitude growth func-tion (AGF) slopes; the reduction in slope in deafened ears was ameliorated by the AAV.Ntf3 treatment. Slopes of the ECAP and EABR AGFs were predictive of SGN density in a broad area near and just apical to the implant. The highest ensemble spontaneous activity (ESA) values were seen in animals with surviving IHCs, but AAV.Ntf3 treatment in deafened ears resulted in slightly higher ESA values compared to deafened untreated ears. Overall, a combination of the psychophysical and electrophysiological measures can be useful for monitoring the health of the implanted cochlea in guinea pigs. These measures should be applicable for assessing cochlear health in human subjects.

Construction and expression of a lentivirus expression vector carrying the VEGF165-EGFP fusion gene in breast cancer MCF-7 cells

Vascular endothelial growth factor (VEGF)165 is one of the most abundant and potent angiogenic factors in both physiological and pathological conditions. However, the function and mechanism of VEGF165 in tumors and their environment remain to be elucidated. In the present study, a lentivirus vector (LV) that contained the VEGF165-enhanced green fluorescent protein (EGFP) fusion gene was constructed and transfected into the human breast cancer cell line MCF-7. Following transfection, the expression of VEGF165 in MCF-7 cells was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting. Further cellular localization of VEGF165 was observed through fluorescence microscopy. The titer of the recombinant lentivirus was 5.44×10⁷ TU/ml in the LV-VEGF165-EGFP group and 5.00×10⁸ TU/ml in the LV-EGFP negative control group. RT-qPCR and western blotting demonstrated that the expression of VEGF165 was significantly increased in the LV-VEGF165-EGFP group compared with the control group. The present study lays the foundation for in vitro and in vivo studies on tumor cell derived-VEGF165. Furthermore, the present fusion gene expression vector may provide a potential approach for gene therapy treatment of cancer and other diseases that require regulation of angiogenesis.

Development of Novel Vaccines Against Infectious Diseases Based on Chimpanzee Adenoviral Vector

Vaccination is considered to be the most effective method of preventing infectious or other diseases. Adenovirus (Ad) is one the most promising vectors in vaccine research and development. It can induce not only potent humoral but also cellular immune responses, and has therefore been widely applied in basic and translational studies. Chimpanzee Ad is a rare serotype circulating in humans. This circumvents the problem of preexisting immunity to human Ad serotypes, enhancing Chimpanzee Ad prospects in vaccine development. Here we describe experimental procedures used to generate a new generation of rabies vaccine based on a chimpanzee Ad vector, which can be extended in the development of novel vaccines against other infectious diseases.

Viral-mediated Ntf3 overexpression disrupts innervation and hearing in nondeafened guinea pig cochleae

Synaptopathy in the cochlea occurs when the connection between inner hair cells and the auditory nerve is disrupted, leading to impaired hearing and nerve degeneration. Experiments using transgenic mice have shown that overexpression of NT3 by supporting cells repairs synaptopathy caused by overstimulation. To accomplish such therapy in the clinical setting, it would be necessary to activate the neurotrophin receptor on auditory neurons by other means. Here we test the outcome of NT3 overexpression using viral-mediated gene transfer into the perilymph versus the endolymph of the normal guinea pig cochlea. We inoculated two different Ntf3 viral vectors, adenovirus (Adv) or adeno-associated virus (AAV) into the perilymph, to facilitate transgene expression in the mesothelial cells and cochlear duct epithelium, respectively. We assessed outcomes by comparing Auditory brainstem response (ABR) thresholds prior to that at baseline to thresholds at 1 and 3 weeks after inoculation, and then performed histologic evaluation of hair cells, nerve endings, and synaptic ribbons. We observed hearing threshold shifts as well as disorganization of peripheral nerve endings and disruption of synaptic connections between inner hair cells and peripheral nerve endings with both vectors. The data suggest that elevation of NT3 levels in the cochlear fluids can disrupt innervation and degrade hearing.

Development of Recombinant Adeno-Associated Virus Serotype 2/8 Carrying Kringle Domains of Human Plasminogen for Sustained Expression and Cancer Therapy

Angiostatin and other plasminogen derivatives exhibit antitumor activities directly or indirectly, have demonstrated promising anticancer effects in preclinical studies, but have mostly failed in clinical trials partly due to their short serum half-lives. Our previous studies demonstrated that recombinant human plasminogen kringle 1-5 (K1-5) has superior antitumor activity compared with angiostatin. In addition, optimization of recombinant K1-5 with three amino acid substitutions enhances its antitumor effect. The current study was thus undertaken to evaluate prolonged expression of optimized K1-5 as cancer gene therapy. The recombinant adeno-associated virus (AAV) vector was used to express a secreted form of the optimized K1-5 (AAV-sK15tm) to improve its pharmacokinetic profile, which was considered to be the hurdle in angiostatin treatment of cancer. We successfully generated high-titer recombinant AAV vectors and observed sustained transgene expression for 567 days after a single injection of virus. The treated animals did not display any visible signs of abnormalities and showed normal serum biochemistry. The therapeutic potential of this treatment modality was demonstrated by both a strong inhibition of lung metastasis in the mouse B16F10 melanoma model and significant growth retardation of Lewis lung carcinoma xenografts in C57BL/6N mice as well as human A2058 melanoma xenografts in NOD/SCID (nonobese diabetic/severe combined immunodeficient) mice. Taken together, our results suggested that AAV-sK15tm produced long-term suppressive effects on cancer growth in vivo and should warrant serious consideration for clinical development.

Rapid, Efficient, and Modular Generation of Adenoviral Vectors via Isothermal Assembly

Adenoviral vectors have yielded promising results as carriers for gene transfer and vaccines in basic research and clinical applications. However, most common procedures to construct adenoviral vectors and manipulate adenovirus (Ad) genomes are complex and labor-intensive. An easy and detailed protocol for the rapid, efficient, and modular generation of chimpanzee Ad serotype 68 (AdC68) as a molecular clone via isothermal assembly, which directionally assembles multiple DNA fragments in a single isothermal reaction without restriction enzymes or ligases, is presented. Any serotype of adenovirus with the sequence of genome known can be constructed as a molecular clone by this method. Recombinant adenoviral vectors can be created via one-step isothermal assembly in <3 days, and recombinant Ads can be rescued within 8 days. This protocol is practical for manipulations of Ad genomes, because an entire Ad genome can be divided into specific fragments within modular plasmids. © 2016 by John Wiley & Sons, Inc.

Glucocorticoid Cell Priming Enhances Transfection Outcomes in Adult Human Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSCs) are one of the most widely researched stem cell types with broad applications from basic research to therapeutics, the majority of which require introduction of exogenous DNA. However, safety and scalability issues hinder viral delivery, while poor efficiency hinders nonviral gene delivery, particularly to hMSCs. Here, we present the use of a pharmacologic agent (glucocorticoid) to overcome barriers to hMSC DNA transfer to enhance transfection using three common nonviral vectors. Glucocorticoid priming significantly enhances transfection in hMSCs, demonstrated by a 3-fold increase in efficiency, 4-15-fold increase in transgene expression, and prolonged transgene expression when compared to transfection without glucocorticoids. These effects are dependent on glucocorticoid receptor binding and caused in part by maintenance of normal metabolic function and increased cellular (5-fold) and nuclear (6-10-fold) DNA uptake over hMSCs transfected without glucocorticoids. Results were consistent across five human donors and in cells up to passage five. Glucocorticoid cell priming is a simple and effective technique to significantly enhance nonviral transfection of hMSCs that should enhance their clinical use, accelerate new research, and decrease reliance on early passage cells.

Adenovirus-Vectored Broadly Neutralizing Antibodies Directed Against gp120 Prevent Human Immunodeficiency Virus Type 1 Acquisition in Humanized Mice

Despite nearly three decades of research, a safe and effective vaccine against human immunodeficiency virus type 1 (HIV-1) has yet to be achieved. More recently, the discovery of highly potent anti-gp160 broadly neutralizing antibodies (bNAbs) has garnered renewed interest in using antibody-based prophylactic and therapeutic approaches. Here, we encoded bNAbs in first-generation adenoviral (ADV) vectors, which have the distinctive features of a large coding capacity and ease of propagation. A single intramuscular injection of ADV-vectorized bNAbs in humanized mice generated high serum levels of bNAbs that provided protection against multiple repeated challenges with a high dose of HIV-1, prevented depletion of peripheral CD4(+) T cells, and reduced plasma viral loads to below detection limits. Our results suggest that ADV vectors may be a viable option for the prophylactic and perhaps therapeutic use of bNAbs in humans.

Bioethical conflicts of gene therapy: a brief critical review

Methods and techniques employed in gene therapy are reviewed in parallel with pertinent ethical conflicts. Clinical interventions based on gene therapy techniques preferentially use vectors for the transportation of therapeutic genes, however little is known about the potential risks and damages to the patient. Thus, attending carefully to the clinical complications arising as well as to security is essential. Despite the scientific and technological advances, there are still many uncertainties about the side effects of gene therapy. Moreover, there is a need, above all, to understand the principles of bioethics as both science and ethics, in accordance with its socioecological responsibility, in order to prioritize the health and welfare of man and nature, using properly natural resources and technology. Therefore, it is hard to determine objective results and to which extent the insertion of genes can affect the organism, as well as the ethical implication.

Advances, nuances, and potential pitfalls when exploiting the therapeutic potential of RNA interference

The discovery of RNA interference (RNAi) holds the potential to alter the paradigm of medical therapeutics. With the ability to selectively silence the function of a gene, RNAi not only provides an indispensable research tool for determining the function of a gene, but also offers potential for the development of novel therapeutics that will inhibit specific genes involved in disease. New concepts in therapeutics have been uncovered through the study of RNAi. Nuances have emerged. For instance, global RNAi pathways can be affected by somatic mutations in cancer and cellular stress, such as hypoxia. Also, viral gene therapy can have unexpected effects on endogenous short noncoding RNA pathways. Therefore, it is important to understand where RNAi therapeutics enter the processing pathways. We highlight the evolving use of RNAi as a new class of therapeutics, such as for amyloidosis, and address some of the anticipated challenges associated with its clinical application.

Transcription factor decoy: a pre-transcriptional approach for gene downregulation purpose in cancer

Gene therapy as a therapeutic approach has been the dream for many scientists around the globe. Many strategies have been proposed and applied for this purpose, yet the void for a functional safe method is still apparent. Since most of the diseases are caused by undesirable upregulation (oncogenes) or downregulation (tumor suppressor genes) of genes, major gene therapy's techniques affect gene expression. Most of the methods are used in post-transcriptional level such as RNA inhibitory (RNAi) and splice-switching oligonucleotides (SSOs). RNAi blocks messenger RNA (mRNA) translation by mRNA degradation or interruption between attachments of mRNA with ribosomes' subunits. However, one of the novel methods is the usage of transcription factor targeted decoys. DNA decoys are the new generation of functional gene downregulatory oligonucleotides which compete with specific binding sites of transcription factors. Considering the exponential growth of this technique in both in vitro and in vivo studies, in this paper, we aim to line out the description, design, and application of decoys in research and therapy.

Nanoparticle-mediated p53 gene therapy for tumor inhibition

The p53 tumor suppressor gene is mutated in 50% of human cancers, resulting in more aggressive disease with greater resistance to chemotherapy and radiation therapy. Advances in gene therapy technologies offer a promising approach to restoring p53 function. We have developed polymeric nanoparticles (NPs), based on poly (lactic-co-glycolic acid), that provide sustained intracellular delivery of plasmid DNA, resulting in sustained gene expression without vector-associated toxicity. Our previous studies with p53 gene-loaded NPs (p53NPs) demonstrated sustained antiproliferative effects in cancer cells in vitro. The objective of this study was to evaluate the efficacy of p53NPs in vivo. Tumor xenografts in mice were established with human p53-null prostate cancer cells. Animals were treated with p53NPs by either local (intratumoral injection) or systemic (intravenous) administration. Controls included saline, p53 DNA alone, and control NPs. Mice treated with local injections of p53NPs demonstrated significant tumor inhibition and improved animal survival compared with controls. Tumor inhibition corresponded to sustained and greater p53 gene and protein expression in tumors treated with p53NPs than with p53 DNA alone. A single intravenous dose of p53NPs was successful in reducing tumor growth and improving animal survival, although not to the same extent as with local injections. Imaging studies showed that NPs accumulate in tumor tissue after intravenous injection; however, further improvement in tumor targeting efficiency of p53NPs may be needed for better outcome. In conclusion, the NP-mediated p53 gene therapy is effective in tumor growth inhibition. NPs may be developed as nonviral vectors for cancer and other genetic diseases.

Identifying Intracellular pDNA Losses From a Model of Nonviral Gene Delivery

Nonviral gene delivery systems are a type of nanocommunication system that transmit plasmid packets (i.e., pDNA packets) that are programmed at the nanoscale to biological systems at the microscopic cellular level. This engineered nanocommunication system suffers large pDNA losses during transmission of the genetically encoded information, preventing its use in biotechnological and medical applications. The pDNA losses largely remain uncharacterized, and the ramifications of reducing pDNA loss from newly designed gene delivery systems remain difficult to predict. Here, the pDNA losses during primary and secondary transmission chains were identified utilizing a MATLAB model employing queuing theory simulating delivery of pEGFPLuc transgene to HeLa cells carried by Lipofectamine 2000 nonviral DNA carrier. Minimizing pDNA loss during endosomal escape of the primary transmission process results in increased number of pDNA in the nucleus with increased transfection, but with increased probability of cell death. The number of pDNA copies in the nucleus and the amount of time the pDNAs are in the nucleus directly correlates to improved transfection efficiency. During secondary transmission, pDNAs are degraded during distribution to daughter cells. Reducing pDNA losses improves transfection, but a balance in quantity of nuclear pDNA, mitosis, and toxicity must be considered in order to achieve therapeutically relevant transfection levels.

Scalable downstream strategies for purification of recombinant adeno- associated virus vectors in light of the properties

Recombinant adeno-associated virus (rAAV) vector is one of the promising delivery tools for gene therapy. Currently, hundreds of clinical trials are performed but the major barrier for clinical application is the absence of any ideal large scale production technique to obtain sufficient and highly pure rAAV vector. The large scale production technique includes upstream and downstream processing. The upstream processing is a vector package step and the downstream processing is a vector purification step. For large scale downstream processing, the scientists need to recover rAAV from dozens of liters of cell lysate or medium, and a variety of purification strategies have been developed but not comprehensively compared till now. Consequently, this review will evaluate the scalable downstream purification strategies systematically, especially those based on the physicochemical properties of AAV virus, and attempt to find better scalable downstream strategies for rAAV vectors.

Caged protein nanoparticles for drug delivery

Caged protein nanoparticles possess many desirable features for drug delivery, such as ideal sizes for endocytosis, non-toxic biodegradability, and the ability to functionalize at three distinct interfaces (external, internal, and inter-subunit) using the tools of protein engineering. Researchers have harnessed these attributes by covalently and non-covalently loading therapeutic molecules through mechanisms that facilitate release within specific microenvironments. Effective delivery depends on several factors, including specific targeting, cell uptake, release kinetics, and systemic clearance. The innate ability of the immune system to recognize and respond to proteins has recently been exploited to deliver therapeutic compounds with these platforms for immunomodulation. The diversity of drugs, loading/release mechanisms, therapeutic targets, and therapeutic efficacy are discussed in this review.

Intravitreal drug delivery in retinal disease: are we out of our depth?

INTRODUCTION

With the ever-increasing global burden of retinal disease, there is an urgent need to vastly improve formulation strategies that enhance posterior eye delivery of therapeutics. Despite intravitreal administration having demonstrated notable superiority over other routes in enhancing retinal drug availability, there still exist various significant physical/biochemical barriers preventing optimal drug delivery into the retina. A further complication lies with an inability to reliably translate laboratory-based retinal models into a clinical setting. Several formulation approaches have recently been evaluated to improve intravitreal therapeutic outcomes, and our aim in this review is to highlight strategies that hold the most promise.

AREAS COVERED

We discuss the complex barriers faced by the intravitreal route and examine how formulation strategies including implants, nanoparticulate carriers, viral vectors and sonotherapy have been utilized to attain both sustained delivery and enhanced penetration through to the retina. We conclude by highlighting the advances and limitations of current in vitro, ex vivo and in vivo retinal models in use by researchers globally.

EXPERT OPINION

Various nanoparticle compositions have demonstrated the ability to overcome the retinal barriers successfully; however, their utility is limited to the laboratory setting. Optimization of these formulations and the development of more robust experimental retinal models are necessary to translate success in the laboratory into clinically efficacious outcomes.

Thrombomodulin domain 1 ameliorates diabetic nephropathy in mice via anti-NF-κB/NLRP3 inflammasome-mediated inflammation, enhancement of NRF2 antioxidant activity and inhibition of apoptosis

AIMS/HYPOTHESIS

Chronic inflammatory processes have been increasingly shown to be involved in the pathogenesis of diabetes and diabetic nephropathy. Recently, we demonstrated that a lectin-like domain of thrombomodulin (THBD), which is known as THBD domain 1 (THBDD1) and which acts independently of protein C activation, neutralised an inflammatory response in a mouse model of sepsis. Here, therapeutic effects of gene therapy with adeno-associated virus (AAV)-carried THBDD1 (AAV-THBDD1) were tested in a mouse model of type 2 diabetic nephropathy.

METHODS

To assess the therapeutic potential of THBDD1 and the mechanisms involved, we delivered AAV-THBDD1 (10(11) genome copies) into db/db mice and tested the effects of recombinant THBDD1 on conditionally immortalised podocytes.

RESULTS

A single dose of AAV-THBDD1 improved albuminuria, renal interstitial inflammation and glomerular sclerosis, as well as renal function in db/db mice. These effects were closely associated with: (1) inhibited activation of the nuclear factor κB (NF-κB) pathway and the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome; (2) promotion of nuclear factor (erythroid-derived 2)-like 2 (NRF2) nuclear translocation; and (3) suppression of mitochondria-derived apoptosis in the kidney of treated mice.

CONCLUSIONS/INTERPRETATION

AAV-THBDD1 gene therapy resulted in improvements in a model of diabetic nephropathy by suppressing the NF-κB-NLRP3 inflammasome-mediated inflammatory process, enhancing the NRF2 antioxidant pathway and inhibiting apoptosis in the kidney.

Angelica sinensis polysaccharide nanoparticles as novel non-viral carriers for gene delivery to mesenchymal stem cells

This study centers on the use of a nanoparticle based on the polysaccharide from Angelica sinensis (ASP) as an efficient and safe non-viral gene vector. After modification with branched low molecular weight polyethylenimine (1200 Da), the cationized ASP (cASP) was combined with the plasmid encoding transforming growth factor-beta 1 (TGF-β1) to form a spherical nano-scaled particle (i.e., cASP-pTGF-β1 nanoparticle). This nanoparticle was applied to transfect rat bone marrow mesenchymal stem cells and human umbilical cord mesenchymal stem cells. As a result, nanoparticles (cASP/pDNA weight ratio 10:1) had the greatest transfection efficiency in both cells, which was significantly higher than those of Lipofectamine2000 and PEI (25 kDa). This was in agreement with the findings of the semi-quantitative RT-PCR and live cell imaging. These nanoparticles were also less toxic than Lipofectamine2000 and PEI (25 kDa). Therefore, cASP could be a potential candidate for a novel non-viral gene vector.

FROM THE CLINICAL EDITOR

These authors demonstrate the use of a nanoparticle-based efficient and safe non-viral gene vector delivery system via a spherical nanoparticle based on a polysaccharide from Angelica sinensis, with parameters superior to Lipofectamine2000.

Phase I dose-escalation study of VB-111, an antiangiogenic virotherapy, in patients with advanced solid tumors

PURPOSE

VB-111 is an antiangiogenic agent consisting of a nonreplicating adenovirus vector (Ad-5) with a modified murine pre-proendothelin promoter leading to apoptosis of tumor vasculature by expressing a Fas-chimera transgene in angiogenic endothelial cells. In a phase I dose-escalation study, pharmacokinetics, pharmacodynamics, safety, and efficacy of a single dose of VB-111 in patients with advanced solid tumors were evaluated.

EXPERIMENTAL DESIGN

VB-111 was administered as a single i.v. infusion at escalating doses from 1 × 10(10) (cohort 1) to 1 × 10(13) (cohort 7) viral particles (VP) in successive cohorts. Assessments included pharmacokinetic and pharmacodynamic profiles, tumor response, and overall survival.

RESULTS

Thirty-three patients were enrolled. VB-111 was safe and well-tolerated; self-limited fever and chills were seen at doses above 3 × 10(11) VPs. Transgene expression was not detected in blood but was detected in an aspirate from a subcutaneous metastasis after treatment. One patient with papillary thyroid carcinoma had a partial response.

CONCLUSIONS

VB-111 was safe and well tolerated in patients with advanced metastatic cancer at a single administration of up to 1 × 10(13) VPs. Evidence of transgene expression in tumor tissue and tumor response was observed.

Nonviral gene transfer strategies to promote bone regeneration

Despite the inherent ability of bone to regenerate itself, there are a number of clinical situations in which complete bone regeneration fails to occur. In view of shortcomings of conventional treatment, gene therapy may have a place in cases of critical-size bone loss that cannot be properly treated with current medical or surgical treatment. The purpose of this review is to provide an overview of gene therapy in general, nonviral techniques of gene transfer including physical and chemical methods, RNA-based therapy, therapeutic genes to be transferred for bone regeneration, route of application including ex vivo application, and direct gene therapy approaches to regenerate bone.

Selective biophysical interactions of surface modified nanoparticles with cancer cell lipids improve tumor targeting and gene therapy

Targeting gene- or drug-loaded nanoparticles (NPs) to tumors and ensuring their intratumoral retention after systemic administration remain key challenges to improving the efficacy of NP-based therapeutics. Here, we investigate a novel targeting approach that exploits changes in lipid metabolism and cell membrane biophysics that occur during malignancy. We hypothesized that modifications to the surface of NPs that preferentially increase their biophysical interaction with the membrane lipids of cancer cells will improve intratumoral retention and in vivo efficacy upon delivery of NPs loaded with a therapeutic gene. We have demonstrated that different surfactants, incorporated onto the NPs' surface, affect the biophysical interactions of NPs with the lipids of cancer cells and normal endothelial cells. NPs surface modified with didodecyldimethylammoniumbromide (DMAB) demonstrated greater interaction with cancer cell lipids, which was 6.7-fold greater than with unmodified NPs and 5.5-fold greater than with endothelial cell lipids. This correlated with increased uptake of DMAB-modified NPs with incubation time by cancer cells compared to other formulations of NPs and to uptake by endothelial cells. Upon systemic injection, DMAB-NPs demonstrated a 4.6-fold increase in tumor accumulation compared to unmodified NPs which also correlated to improved efficacy of p53 gene therapy. Characterization of the biophysical interactions between NPs and lipid membranes of tumors or other diseased tissues/organs may hold promise for engineering targeted delivery of therapeutics.

RNA interference--a silent but an efficient therapeutic tool

RNA interference (RNAi) is an evolutionary conserved gene regulation pathway that has emerged as an important discovery in the field of molecular biology. One of the important advantages of RNAi in therapy is that it brings about efficient downregulation of gene expression by targeting complementary transcripts in comparison with other antisense-based techniques. RNAi can be can be achieved by introducing chemically synthesized small interfering RNAs (siRNAs) into a cell system. A more stable knockdown effect can be brought about by the use of plasmid or viral vectors encoding the siRNA. RNAi has been used in reverse genetics to understand the function of specific genes and also as a therapeutic tool in treating human diseases. This review provides a brief insight into the therapeutic applications of RNAi against debilitating diseases.

Long-term expression of rAAV2-hIL15 enhances immunoglobulin production and lymphokine-activated killer cell-mediated human glioblastoma cell death

Glioblastoma is the most aggressive primary brain tumor and its prognosis remains poor despite different treatment modalities including surgery, radiotherapy and chemotherapy. Therefore, more useful treatments for glioblastoma patients are required. Human interleukin 15 (hIL15) is an immunomodulator that has antitumor activities. hIL15 combined with gene therapy method is also currently under cosideration as a treatment option. Since recombinant adeno-associated virus serotype 2 (rAAV2) with low immunogenicity and long-term gene expression in human clinical trials has been demonstrated, rAAV2 encoding hIL15 (rAAV2-hIL15) were used to inhibit human glioblastoma growth in the present study. rAAV2-hIL15, which is able to express IL15 protein with bioactivity, was successfully produced and purified. Data of this study demonstrated that the long-term expression of rAAV2-hIL15 enhances immunoglobulin (Ig) production and the cytotoxic activity of lymphokine-activated killer (LAK) cells. In addition, results of the present study showed that rAAV2-hIL15 delays tumor growth on a xenografted human glioblastoma mice model. Taken together, these results indicated that rAAV2-hIL15 constitutes a powerful and potent gene immunotherapy method for human glioblastoma treatment.

Genetic manipulation of myoblasts and a novel primary myosatellite cell culture system: comparing and optimizing approaches

The genetic manipulation of skeletal muscle cells in vitro is notoriously difficult, especially when using undifferentiated muscle cell lines (myoblasts) or primary muscle stem cells (myosatellites). We therefore optimized methods of gene transfer by overexpressing green fluorescent protein (GFP) in mouse C2C12 cells and in a novel system, primary rainbow trout myosatellite cells. A common lipid-based transfection reagent was used (Lipofectamine 2000) along with three different viral vectors: adeno-associated virus serotype 2 (AAV2), baculovirus (BAC) and lentivirus. Maximal transfection efficiencies of 49% were obtained in C2C12 cells after optimizing cell density and reagent : DNA ratio, although the GFP signal rapidly dissipated with proliferation and was not maintained with differentiation. The transduction efficiency of AAV2 was optimized to 65% by extending incubation time and decreasing cell density, although only 30% of cells retained expression after passing. A viral comparison revealed that lentivirus was most efficient at transducing C2C12 myoblasts as 97% of cells were transduced with only 10(6) viral genomes (vg) compared to 54% with 10(8) vg AAV2 and 23% with 10(9) vg BAC. Lentivirus also transduced 90% of primary trout myosatellites compared to 1-10% with AAV2 and BAC. The phosphoglycerate kinase 1 (pgk) promoter was 10-fold more active than the cytomegalovirus immediate-early promoter in C2C12 cells and both were effective in trout myosatellites. Maximal transduction of C2C12 myotubes was achieved by differentiating myoblasts previously transduced with lentivirus and the pgk promoter. Thus, our optimized protocol proved highly effective in diverse muscle cell systems and could therefore help overcome a common technological barrier.

Pseudotyped adeno-associated virus 2/9-delivered CCL11 shRNA alleviates lung inflammation in an allergen-sensitized mouse model

Airway infiltration by eosinophils is a major characteristic of chronic asthma. CCL11 (eotaxin-1) is secreted by lung epithelial cells and functions as the major chemokine for eosinophil recruitment. Pseudotyped adeno-associated virus (AAV) 2/9, composed by the AAV2 rep and AAV9 cap genes, can efficiently target lung epithelial cells and might carry gene sequences with therapeutic potential for asthma. This study aimed to determine whether pseudotyped AAV2/9 virus carrying the small hairpin RNA targeting CCL11 and expressed by CMV/U6 promoter could reduce eosinophilia and asthmatic responses in mite allergen-sensitized mice. Mice were sensitized by intraperitoneal and challenged by intratracheal injection with recombinant Dermatophagoides pteronyssinus group 2 allergen (rDp2). AAV2/9 viral vectors were intratracheally injected three days before the first challenge. AAV2/9 sh47 virus significantly reduced airway hyperresponsiveness, airway resistance, CCL11 levels, and eosinophilia in the lungs of sensitized mice. Th2 cytokines, including interleukins (IL)-4, IL-5, and IL-10, were also significantly reduced in the bronchoalveolar lavage fluid of AAV2/9 sh47 virus-treated mice. Th2 cytokine levels were also reduced in rDp2-stimulated mediastinal lymphocytes in treated mice. However, serum levels of rDp2-specific IgG1 and IgE, as well as Th2 cytokine levels in rDp2-stimulated splenocyte culture supernatants, were comparable to the sensitized control group. The results suggest that AAV2/9 sh47 virus relieved local instead of systemic inflammatory responses. Therefore, the CMV/U6 promoter with AAV2/9 viral vector, which is preferable to target lung epithelia cells, might be applied as a novel therapeutic approach for asthma.

Conditionally replicating adenovirus SG500-expressed mutant Dm-dNK gene for breast cancer therapy

The purpose of this analysis was to investigate the enzyme activity and specificity of using adenovirus-mediated Drosophila melanogaster deoxyribonucleoside kinase (Dm-dNK) mutants in combination with gemcitabine. Compared with herpes simplex type 1 thymidine kinase (HSV-TK) and other known dNKs, this Dm-dNK enzyme has a broader substrate specificity and a higher catalytic rate. We created the Dm-dNK mutants (dNKmu) by site-directed mutagenesis at the sites of 244E, 245S, 251S and 252R, with the last 10 amino acids in the amino acid sequence randomly mutated. We evaluated the enzyme activity and substrate specificity. The engineered enzymes showed a relative increase in phosphorylation in the nucleoside analogs of BVDU ((E)-5‑(2-Bromovinyl)-2'-deoxyuridine) or gemcitabine (DFDC, 2',2'-difluoro-deoxycytidine) compared with the wild-type enzyme. The dNKmu enzymes were expressed in the breast cancer cell lines MDA-MB-231 (ER-) and MCF7 (ER+). In studying the sensitivity of the cell lines to DFDC, conditionally replicative adenovirus (CRAd) SG500-dNKmu showed higher expression and enzymatic activity than the replication-defective adenovirus SG500 in cancer cells, but with less cytotoxicity to cancer cells than that of SG500. Our data suggest that the triple phosphorylated DFDC catalyzed by dNKmu inhibited the replication of adenovirus with a simultaneous positive therapeutic effect to cancer cells. Therefore, concomitant use of the SG500‑dNKmu and DFDC could be a novel targeted strategy in suicide gene therapy with safe control of excessive virus replication.

Vector systems for prenatal gene therapy: principles of adeno-associated virus vector design and production

Vectors based on adeno-associated virus (AAV) show great promise for safe, efficacious therapeutic gene transfer in extensive pre-clinical data and, recently, in clinical trials. Careful vector design and choice from a range of natural or synthetic pseudotypes allow targeted, efficient, and sustained expression of therapeutic genes. The efficiency of gene delivery can be further enhanced through the use of drug pre-treatment or co-infection with a suitable helper virus. This chapter describes current best practice for AAV production, including complete methods for: (1) efficient generation of vector without the use of helper viruses, simplifying the transition to GMP-grade production for clinical applications; (2) efficient and easily scalable purification of the virus by affinity chromatography, allowing rapid production of highly concentrated, high titre stocks; (3) reliable quantification and assaying of viral stocks, along with short- and long-term storage considerations.

Gene delivery to bone

Gene delivery to bone is useful both as an experimental tool and as a potential therapeutic strategy. Among its advantages over protein delivery are the potential for directed, sustained and regulated expression of authentically processed, nascent proteins. Although no clinical trials have been initiated, there is a substantial pre-clinical literature documenting the successful transfer of genes to bone, and their intraosseous expression. Recombinant vectors derived from adenovirus, retrovirus and lentivirus, as well as non-viral vectors, have been used for this purpose. Both ex vivo and in vivo strategies, including gene-activated matrices, have been explored. Ex vivo delivery has often employed mesenchymal stem cells (MSCs), partly because of their ability to differentiate into osteoblasts. MSCs also have the potential to home to bone after systemic administration, which could serve as a useful way to deliver transgenes in a disseminated fashion for the treatment of diseases affecting the whole skeleton, such as osteoporosis or osteogenesis imperfecta. Local delivery of osteogenic transgenes, particularly those encoding bone morphogenetic proteins, has shown great promise in a number of applications where it is necessary to regenerate bone. These include healing large segmental defects in long bones and the cranium, as well as spinal fusion and treating avascular necrosis.

Poly(amidoamine) polymers: soluble linear amphiphilic drug-delivery systems for genes, proteins and oligonucleotides

Polymer-drug and polymer-protein conjugates are emerging as a robust and well-characterized class of therapeutic entity. Although there are no low-molecular-weight soluble polymer conjugates in routine clinical use, there are many examples of routinely used high-molecular-weight drugs conjugated to soluble polymers (e.g., Oncospar). Advances in synthetic polymer chemistry have fostered the development of linear poly(amidoamine)s (PAA)s that impart both biodegradability, 'smart' (pH responsive) biological activity and biocompatibility. In their linear form, such as hyper-branched poly(amidoamine) (PAMAM) dendrimers, linear PAAs can be used to deliver large therapeutic entities such as peptides, proteins and genes to either the cytosol or nucleus. Furthermore, these polymers offer great potential in vivo due to their ability to either target the liver or be directed away from the liver and enter tumor mass via the enhanced permeability and retention (EPR) effect. PAAs also exhibit minimal toxicity (dependent upon backbone chemistry), relative to well-characterized polymers used for gene delivery. The propensity of PAAs to modulate intracellular trafficking resulting in their cytosolic translocation has also recently been quantified in vivo and is the primary focus of this article.

Impact of capsid modifications by selected peptide ligands on recombinant adeno-associated virus serotype 2-mediated gene transduction

Vectors based on adeno-associated virus serotype 2 (AAV2) belong to today's most promising and most frequently used viral vectors in human gene therapy. Like in many other vector systems, the broad but non-specific tropism limits their use for certain cell types or tissues. One approach to screen for transduction-improved vectors is the selection of random peptide libraries displayed directly on the AAV2 capsid. Although the AAV2 library system has been widely applied for the successful selection of improved gene therapy vectors, it remains unknown which steps of the transduction process are most affected and therefore critical for the selection of targeting peptides. Attachment to the cell surface is the first essential step of AAV-mediated gene transduction; however, our experiments challenge the conventional belief that enhanced gene transfer is equivalent to more efficient cell binding of recombinant AAV2 vectors. A comparison of the various steps of gene transfer by vectors carrying a wild-type AAV2 capsid or displaying two exemplary peptide ligands selected from AAV2 random libraries on different human tumour cell lines demonstrated strong alterations in cell binding, cellular uptake, as well as intracellular processing of these vectors. Combined, our results suggest that entry and post-entry events are decisive for the selection of the peptides NDVRSAN and GPQGKNS rather than their cell binding efficiency.

Genetically modified pigs for biomedical research

During the last two decades, pigs have been used to develop some of the most important large animal models for biomedical research. Advances in pig genome research, genetic modification (GM) of primary pig cells and pig cloning by nuclear transfer, have facilitated the generation of GM pigs for xenotransplantation and various human diseases. This review summarizes the key technologies used for generating GM pigs, including pronuclear microinjection, sperm-mediated gene transfer, somatic cell nuclear transfer by traditional cloning, and somatic cell nuclear transfer by handmade cloning. Broadly used genetic engineering tools for porcine cells are also discussed. We also summarize the GM pig models that have been generated for xenotransplantation and human disease processes, including neurodegenerative diseases, cardiovascular diseases, eye diseases, bone diseases, cancers and epidermal skin diseases, diabetes mellitus, cystic fibrosis, and inherited metabolic diseases. Thus, this review provides an overview of the progress in GM pig research over the last two decades and perspectives for future development.

Gene therapy for the treatment of Parkinson's disease: the nature of the biologics expands the future indications

The pharmaceutical industry's development of therapeutic medications for the treatment of Parkinson's disease (PD) endures, as a result of the continuing need for better agents, and the increased clinical demand due to the aging population. Each new drug offers advantages and disadvantages to patients when compared to other medical offerings or surgical options. Deep brain stimulation (DBS) has become a standard surgical remedy for the effective treatment of select patients with PD, for whom most drug regimens have failed or become refractory. Similar to DBS as a surgical option, gene therapy for the treatment of PD is evolving as a future option. In the four different PD gene therapy approaches that have reached clinical trials investigators have documented an excellent safety profile associated with the stereotactic delivery, viral vectors and doses utilized, and transgenes expressed. In this article, we review the clinically relevant gene therapy strategies for the treatment of PD, concentrating on the published preclinical and clinical results, and the likely mechanisms involved. Based on these presentations, we advance an analysis of how the nature of the gene therapy used may eventually expand the scope and utility for the management of PD.