Helper-dependent adenovirus vectors elicit intact innate but attenuated adaptive host immune responses in vivo

The Immune System-A Double-Edged Sword for Adenovirus-Based Therapies

Pathogenic adenovirus (Ad) infections are widespread but typically mild and transient, except in the immunocompromised. As vectors for gene therapy, vaccine, and oncology applications, Ad-based platforms offer advantages, including ease of genetic manipulation, scale of production, and well-established safety profiles, making them attractive tools for therapeutic development. However, the immune system often poses a significant challenge that must be overcome for adenovirus-based therapies to be truly efficacious. Both pre-existing anti-Ad immunity in the population as well as the rapid development of an immune response against engineered adenoviral vectors can have detrimental effects on the downstream impact of an adenovirus-based therapeutic. This review focuses on the different challenges posed, including pre-existing natural immunity and anti-vector immunity induced by a therapeutic, in the context of innate and adaptive immune responses. We summarise different approaches developed with the aim of tackling these problems, as well as their outcomes and potential future applications.

CRISPR somatic genome engineering and cancer modeling in the mouse pancreas and liver

Genetically engineered mouse models (GEMMs) transformed the study of organismal disease phenotypes but are limited by their lengthy generation in embryonic stem cells. Here, we describe methods for rapid and scalable genome engineering in somatic cells of the liver and pancreas through delivery of CRISPR components into living mice. We introduce the spectrum of genetic tools, delineate viral and nonviral CRISPR delivery strategies and describe a series of applications, ranging from gene editing and cancer modeling to chromosome engineering or CRISPR multiplexing and its spatio-temporal control. Beyond experimental design and execution, the protocol describes quantification of genetic and functional editing outcomes, including sequencing approaches, data analysis and interpretation. Compared to traditional knockout mice, somatic GEMMs face an increased risk for mouse-to-mouse variability because of the higher experimental demands of the procedures. The robust protocols described here will help unleash the full potential of somatic genome manipulation. Depending on the delivery method and envisaged application, the protocol takes 3-5 weeks.

Viral Vector Vaccines Against ASF: Problems and Prospectives

African swine fever (ASF) is a highly contagious viral disease affecting pigs, with mortality rates a primary focus as they can reach up to 100%. The widespread and colossal economic losses from ASF have impacts on the development of animal husbandry practices in most countries within Africa, Asia, and Europe. Currently, a variety of approaches toward the development of vaccines against ASF are being employed. A promising new concept centered around more economical and time-consuming vaccine production is based on the use of viral vectors to deliver selected immunogens. This review discusses the results obtained from testing various viral vectors as carriers of targeted ASF virus genes. The safety and prospects of viral vectors, the possibilities around modulating cellular and humoral immune responses by choosing genes expressing immunodominant antigens, and the degree of protection in experimental animals from infection with a lethal dose of virulent ASF virus strains have been shown and discussed.

Genetic and Chemical Capsid Modifications of Adenovirus Vectors to Modulate Vector-Host Interactions

Adenovirus-based vectors are playing an important role as efficacious genetic vaccines to fight the current COVID-19 pandemic. Furthermore, they have an enormous potential as oncolytic vectors for virotherapy and as vectors for classic gene therapy. However, numerous vector-host interactions on a cellular and noncellular level, including specific components of the immune system, must be modulated in order to generate safe and efficacious vectors for virotherapy or classic gene therapy. Importantly, the current widespread use of Ad vectors as vaccines against COVID-19 will induce antivector immunity in many humans. This requires the development of strategies and techniques to enable Ad-based vectors to evade pre-existing immunity. In this review article, we discuss the current status of genetic and chemical capsid modifications as means to modulate the vector-host interactions of Ad-based vectors.

Oncolytic Adenoviruses for Cancer Therapy

Many immuno-therapeutic strategies are currently being developed to fight cancer. In this scenario, oncolytic adenoviruses (Onc.Ads) have an interesting role for their peculiar tumor selectivity, safety, and transgene-delivery capability. The major strength of the Onc.Ads is the extraordinary immunogenicity that leads to a strong T-cell response, which, together with the possibility of the delivery of a therapeutic transgene, could be more effective than current strategies. In this review, we travel in the adenovirus (Ads) and Onc.Ads world, focusing on a variety of strategies that can enhance Onc.Ads antitumoral efficacy, passing through tumor microenvironment modulation. Onc.Ads-based therapeutic strategies constitute additional weapons in the fight against cancer and appear to potentiate conventional and immune checkpoint inhibitors (ICIs)-based therapies leading to a promising scenario.

Capsid and Genome Modification Strategies to Reduce the Immunogenicity of Adenoviral Vectors

Adenovirus-based gene transfer vectors are the most frequently used vector type in gene therapy clinical trials to date, and they play an important role as genetic vaccine candidates during the ongoing SARS-CoV-2 pandemic. Immediately upon delivery, adenovirus-based vectors exhibit multiple complex vector-host interactions and induce innate and adaptive immune responses. This can severely limit their safety and efficacy, particularly after delivery through the blood stream. In this review article we summarize two strategies to modulate Ad vector-induced immune responses: extensive genomic and chemical capsid modifications. Both strategies have shown beneficial effects in a number of preclinical studies while potential synergistic effects warrant further investigations.

iMATCH: an integrated modular assembly system for therapeutic combination high-capacity adenovirus gene therapy

Adenovirus-mediated combination gene therapies have shown promising results in vaccination or treating malignant and genetic diseases. Nevertheless, an efficient system for the rapid assembly and incorporation of therapeutic genes into high-capacity adenoviral vectors (HCAdVs) is still missing. In this study, we developed the iMATCH (integrated modular assembly for therapeutic combination HCAdVs) platform, which enables the generation and production of HCAdVs encoding therapeutic combinations in high quantity and purity within 3 weeks. Our modular cloning system facilitates the efficient combination of up to four expression cassettes and the rapid integration into HCAdV genomes with defined sizes. Helper viruses (HVs) and purification protocols were optimized to produce HCAdVs with distinct capsid modifications and unprecedented purity (0.1 ppm HVs). The constitution of HCAdVs, with adapters for targeting and a shield of trimerized single-chain variable fragment (scFv) for reduced liver clearance, mediated cell- and organ-specific targeting of HCAdVs. As proof of concept, we show that a single HCAdV encoding an anti PD-1 antibody, interleukin (IL)-12, and IL-2 produced all proteins, and it led to tumor regression and prolonged survival in tumor models, comparable to a mixture of single payload HCAdVs in vitro and in vivo. Therefore, the iMATCH system provides a versatile platform for the generation of high-capacity gene therapy vectors with a high potential for clinical development.

Helper virus-free gutless adenovirus (HF-GLAd): a new platform for gene therapy

Gene therapy is emerging as a treatment option for inherited genetic diseases. The success of this treatment approach greatly depends upon gene delivery vectors. Researchers have attempted to harness the potential of viral vectors for gene therapy applications over many decades. Among the viral vectors available, gutless adenovirus (GLAd) has been recognized as one of the most promising vectors for in vivo gene delivery. GLAd is constructed by deleting all the viral genes from an adenovirus. Owing to this structural feature, the production of GLAd requires a helper that supplies viral proteins in trans. Conventionally, the helper is an adenovirus. Although the helper adenovirus efficiently provides helper functions, it remains as an unavoidable contaminant and also generates replication-competent adenovirus (RCA) during the production of GLAd. These two undesirable contaminants have raised safety concerns and hindered the clinical applications of GLAd. Recently, we developed helper virus-free gutless adenovirus (HF-GLAd), a new version of GLAd, which is produced by a helper plasmid instead of a helper adenovirus. Utilization of this helper plasmid eliminated the helper adenovirus and RCA contamination in the production of GLAd. HF-GLAd, devoid of helper adenovirus and RCA contaminants, will facilitate its clinical applications. In this review, we discuss the characteristics of adenoviruses, the evolution and production of adenoviral vectors, and the unique features of HF-GLAd as a new platform for gene therapy. Furthermore, we highlight the potential applications of HF-GLAd as a gene delivery vector for the treatment of various inherited genetic diseases.

Helper virus-free gutless adenovirus (HF-GLAd): a new platform for gene therapy

Gene therapy is emerging as a treatment option for inherited genetic diseases. The success of this treatment approach greatly depends upon gene delivery vectors. Researchers have attempted to harness the potential of viral vectors for gene therapy applications over many decades. Among the viral vectors available, gutless adenovirus (GLAd) has been recognized as one of the most promising vectors for in vivo gene delivery. GLAd is constructed by deleting all the viral genes from an adenovirus. Owing to this structural feature, the production of GLAd requires a helper that supplies viral proteins in trans. Conventionally, the helper is an adenovirus. Although the helper adenovirus efficiently provides helper functions, it remains as an unavoidable contaminant and also generates replicationcompetent adenovirus (RCA) during the production of GLAd. These two undesirable contaminants have raised safety concerns and hindered the clinical applications of GLAd. Recently, we developed helper virus-free gutless adenovirus (HF-GLAd), a new version of GLAd, which is produced by a helper plasmid instead of a helper adenovirus. Utilization of this helper plasmid eliminated the helper adenovirus and RCA contamination in the production of GLAd. HF-GLAd, devoid of helper adenovirus and RCA contaminants, will facilitate its clinical applications. In this review, we discuss the characteristics of adenoviruses, the evolution and production of adenoviral vectors, and the unique features of HF-GLAd as a new platform for gene therapy. Furthermore, we highlight the potential applications of HF-GLAd as a gene delivery vector for the treatment of various inherited genetic diseases. [BMB Reports 2020; 53(11): 565-575].

High-Capacity Adenoviral Vectors: Expanding the Scope of Gene Therapy

The adaptation of adenoviruses as gene delivery tools has resulted in the development of high-capacity adenoviral vectors (HC-AdVs), also known, helper-dependent or "gutless". Compared with earlier generations (E1/E3-deleted vectors), HC-AdVs retain relevant features such as genetic stability, remarkable efficacy of in vivo transduction, and production at high titers. More importantly, the lack of viral coding sequences in the genomes of HC-AdVs extends the cloning capacity up to 37 Kb, and allows long-term episomal persistence of transgenes in non-dividing cells. These properties open a wide repertoire of therapeutic opportunities in the fields of gene supplementation and gene correction, which have been explored at the preclinical level over the past two decades. During this time, production methods have been optimized to obtain the yield, purity, and reliability required for clinical implementation. Better understanding of inflammatory responses and the implementation of methods to control them have increased the safety of these vectors. We will review the most significant achievements that are turning an interesting research tool into a sound vector platform, which could contribute to overcome current limitations in the gene therapy field.

Helper-Dependent Adenovirus Transduces the Human and Rat Retina but Elicits an Inflammatory Reaction When Delivered Subretinally in Rats

The identification of >100 genes causing inherited retinal degeneration and the promising results of recent gene augmentation trials have led to an increase in the number of studies investigating the preclinical efficacy of viral-mediated gene transfer. Despite success using adeno-associated viruses, many disease-causing genes, such as ABCA4 or USH2A, are too large to fit into these vectors. One option for large gene delivery is the family of integration-deficient helper-dependent adenoviruses (HDAds), which efficiently transduce postmitotic neurons. However, HDAds have been shown in other organ systems to elicit an immune response, and the immunogenicity of HDAds in the retina has not been characterized. In this study, HDAd serotype 5 (HDAd5) was found to successfully transduce rod and cone photoreceptors in ex vivo human retinal organ cultures. The ocular inflammatory response to subretinal injection of the HDAd5 was evaluated using a rat model. Subretinal injection of HDAd5 carrying cytomegalovirus promoter-driven enhanced green fluorescent protein (HDAd5-CMVp-eGFP) elicited a robust inflammatory response by 3 days postinjection. This reaction included vitreous infiltration of ionized calcium-binding adapter molecule 1 (Iba1)-positive monocytes and increased expression of the proinflammatory protein, intercellular adhesion molecule 1 (ICAM-1). By 7 days postinjection, most Iba1-positive infiltrates migrated into the neural retina and ICAM-1 expression was significantly increased compared with buffer-injected control eyes. At 14 days postinjection, Iba1-positive cells persisted in the retinas of HDAd5-injected eyes, and there was thinning of the outer nuclear layer. Subretinal injection of an empty HDAd5 virus was used to confirm that the inflammatory response was in response to the HDAd5 vector and not due to eGFP-induced overexpression cytotoxicity. Subretinal injection of lower doses of HDAd5 dampened the inflammatory response, but also eGFP expression. Despite their larger carrying capacity, further work is needed to elucidate the inflammatory pathways involved and to identify an immunomodulation paradigm sufficient for safe and effective transfer of large genes to the retina using HDAd5.

Widespread airway distribution and short-term phenotypic correction of cystic fibrosis pigs following aerosol delivery of piggyBac/adenovirus

Cystic fibrosis (CF) is a common genetic disease caused by mutations in the gene coding for cystic fibrosis transmembrane conductance regulator (CFTR). Although CF affects multiple organ systems, chronic bacterial infections and inflammation in the lung are the leading causes of morbidity and mortality in people with CF. Complementation with a functional CFTR gene repairs this defect, regardless of the disease-causing mutation. In this study, we used a gene delivery system termed piggyBac/adenovirus (Ad), which combines the delivery efficiency of an adenoviral-based vector with the persistent expression of a DNA transposon-based vector. We aerosolized piggyBac/Ad to the airways of pigs and observed widespread pulmonary distribution of vector. We quantified the regional distribution in the airways and observed transduction of large and small airway epithelial cells of non-CF pigs, with ∼30–50% of surface epithelial cells positive for GFP. We transduced multiple cell types including ciliated, non-ciliated, basal, and submucosal gland cells. In addition, we phenotypically corrected CF pigs following delivery of piggyBac/Ad expressing CFTR as measured by anion channel activity, airway surface liquid pH, and bacterial killing ability. Combining an integrating DNA transposon with adenoviral vector delivery is an efficient method for achieving functional CFTR correction from a single vector administration.

In Vitro Validation of a CRISPR-Mediated CFTR Correction Strategy for Preclinical Translation in Pigs

Early efforts in cystic fibrosis (CF) gene therapy faced major challenges in delivery efficiency and sustained therapeutic gene expression. Recent advancements in engineered site-specific endonucleases such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 make permanent CF transmembrane conductance regulator (CFTR) gene correction possible. However, because of safety concerns of the CRISPR/Cas9 system and challenges in in vivo delivery to inflamed CF airway, CRISPR-based gene correction strategies need to be tested in proper animal models. In this study, we aimed at creating vectors for testing CFTR gene correction in pig models. We constructed helper-dependent adenoviral (HD-Ad) vectors to deliver CRISPR/Cas9 and a donor template (a 6 kb LacZ or 8.7 kb human CFTR expression cassette) into cultured pig cells. We demonstrated precise integration of each donor into the GGTA1 safe harbor through Cas9-induced homology directed repair with 3 kb homology arms. In addition, we showed that both LacZ and hCFTR were persistently expressed in transduced cells. Furthermore, we created a CFTR-deficient cell line for testing CFTR correction. We detected hCFTR mRNA and protein expression in cells transduced with the hCFTR vector. We also demonstrated CFTR function in the CF cells transduced with the HD-Ad delivering the CRISPR-Cas9 system and hCFTR donor at late cellular passages using the membrane potential sensitive dye-based assay (FLIPR^®). Combined with our previous report on gene delivery to pig airway basal cells, these data provide the feasibility of testing CRISPR/Cas9-mediated permanent human CFTR correction through HD-Ad vector delivery in pigs.

Viral Vector-Based Delivery of CRISPR/Cas9 and Donor DNA for Homology-Directed Repair in an In Vitro Model for Canine Hemophilia B

Gene therapy represents an attractive alternative to treat hemophilia B. Here we established three hepatocyte-derived cell lines based on Huh7, PLC/PRF/5, and Hep3B cells stably carrying a mutated canine FIX (cFIXmut) transgene containing a single point mutation in the catalytic domain. Based on these in vitro models resembling a commonly used canine large animal model, the tetracycline-controlled transcriptional activator (Tet-on)-inducible CRISPR/Cas9 system and an optimized donor were used to correct mutated cFIX gene through homology-directed repair (HDR). For efficient delivery of designer nuclease and donor DNA, we produced a high-capacity adenovirus vector type 5 (HCAdV5) containing the Tet-on-inducible cFIX-specific CRISPR/Cas9 system and a single-stranded adeno-associated virus type 2 vector (ssAAV2) containing the modified donor. Moreover, we designed a single HCAdV5 delivering all components for HDR. Our amplification-refractory mutation system based on qPCR analysis (ARMS-qPCR) revealed that the single vector application in Huh7-cFIXmut cells resulted in up to 5.52% HDR efficiencies, which was superior to the two-vector strategy. Furthermore the single vector also resulted in increased phenotypic correction efficiencies assayed by ELISA. We conclude that HDR in combination with viral vector delivery holds great promise for the correction of mutated FIX in disease models.

Biomaterials for Stem Cell Therapy for Cardiac Disease

Myocardial Infarction (MI) in cardiac disease is the result of heart muscle losses due to a wide range of factors. Cardiac muscle failure is a crucial condition that provokes life-threatening outcomes. Heretofore, regeneration therapies in MI have used stem-cell-based therapy instantly after a myocardial injury to prevent the disease process and tissue malfunction. Despite the therapeutic utility of stem-cell-based regenerative therapy, barriers to successful treatment have been addressed. In this chapter, we illustrate a variety of emerging biomaterial strategies for enhancing the function of therapeutic stem cells, such as cell surface modification to synthetically endowing stem cells with new characteristics and hydrogels with its biological and mechanical properties. These investments offer a potential accompaniment to traditional stem-cell-based therapies for enhancing the efficacy of stem cell therapy to design properly activating cardiac tissues.

Gene Therapy With Regulatory T Cells: A Beneficial Alliance

Gene therapy aims to replace a defective or a deficient protein at therapeutic or curative levels. Improved vector designs have enhanced safety, efficacy, and delivery, with potential for lasting treatment. However, innate and adaptive immune responses to the viral vector and transgene product remain obstacles to the establishment of therapeutic efficacy. It is widely accepted that endogenous regulatory T cells (Tregs) are critical for tolerance induction to the transgene product and in some cases the viral vector. There are two basic strategies to harness the suppressive ability of Tregs: in vivo induction of adaptive Tregs specific to the introduced gene product and concurrent administration of autologous, ex vivo expanded Tregs. The latter may be polyclonal or engineered to direct specificity to the therapeutic antigen. Recent clinical trials have advanced adoptive immunotherapy with Tregs for the treatment of autoimmune disease and in patients receiving cell transplants. Here, we highlight the potential benefit of combining gene therapy with Treg adoptive transfer to achieve a sustained transgene expression. Furthermore, techniques to engineer antigen-specific Treg cell populations, either through reprogramming conventional CD4⁺ T cells or transferring T cell receptors with known specificity into polyclonal Tregs, are promising in preclinical studies. Thus, based upon these observations and the successful use of chimeric (IgG-based) antigen receptors (CARs) in antigen-specific effector T cells, different types of CAR-Tregs could be added to the repertoire of inhibitory modalities to suppress immune responses to therapeutic cargos of gene therapy vectors. The diverse approaches to harness the ability of Tregs to suppress unwanted immune responses to gene therapy and their perspectives are reviewed in this article.

Gene therapy for monogenic liver diseases: clinical successes, current challenges and future prospects

Over the last decade, pioneering liver-directed gene therapy trials for haemophilia B have achieved sustained clinical improvement after a single systemic injection of adeno-associated virus (AAV) derived vectors encoding the human factor IX cDNA. These trials demonstrate the potential of AAV technology to provide long-lasting clinical benefit in the treatment of monogenic liver disorders. Indeed, with more than ten ongoing or planned clinical trials for haemophilia A and B and dozens of trials planned for other inherited genetic/metabolic liver diseases, clinical translation is expanding rapidly. Gene therapy is likely to become an option for routine care of a subset of severe inherited genetic/metabolic liver diseases in the relatively near term. In this review, we aim to summarise the milestones in the development of gene therapy, present the different vector tools and their clinical applications for liver-directed gene therapy. AAV-derived vectors are emerging as the leading candidates for clinical translation of gene delivery to the liver. Therefore, we focus on clinical applications of AAV vectors in providing the most recent update on clinical outcomes of completed and ongoing gene therapy trials and comment on the current challenges that the field is facing for large-scale clinical translation. There is clearly an urgent need for more efficient therapies in many severe monogenic liver disorders, which will require careful risk-benefit analysis for each indication, especially in paediatrics.

Gene Therapy for Metabolic Diseases

Gene therapy has recently shown great promise as an effective treatment for a number of metabolic diseases caused by genetic defects in both animal models and human clinical trials. Most of the current success has been achieved using a viral mediated gene addition approach, but gene-editing technology has progressed rapidly and gene modification is being actively pursued in clinical trials. This review focuses on viral mediated gene addition approaches, because most of the current clinical trials utilize this approach to treat metabolic diseases.

Methods and clinical development of adenovirus-vectored vaccines against mucosal pathogens

Adenoviruses represent the most widely used viral-vectored platform for vaccine design, showing a great potential in the fight against intracellular infectious diseases to which either there is a lack of effective vaccines or the traditional vaccination strategy is suboptimal. The extensive understanding of the molecular biology of adenoviruses has made the new technologies and reagents available to efficient generation of adenoviral-vectored vaccines for both preclinical and clinical evaluation. The novel adenoviral vectors including nonhuman adenoviral vectors have emerged to be the further improved vectors for vaccine design. In this review, we discuss the latest adenoviral technologies and their utilization in vaccine development. We particularly focus on the application of adenoviral-vectored vaccines in mucosal immunization strategies against mucosal pathogens including Mycobacterium tuberculosis, flu virus, and human immunodeficiency virus.

A Hybrid Adenoviral Vector System Achieves Efficient Long-Term Gene Expression in the Liver via piggyBac Transposition

Much research has gone into the development of hybrid gene delivery systems that combine the broad tropism and efficient transduction of adenoviral vectors with the ability to achieve stable expression of cargo genes. In addition to gene therapy applications, such a system has considerable advantages for studies of gene function in vivo, permitting fine-tuned genetic manipulation with higher throughput than can be achieved using standard transgenic and DNA targeting techniques. Existing strategies are limited, however, by low integration efficiencies, small cargo capacity, and/or a dependence on target cell division. The utility of this approach could be enhanced by a system that provides all of the following: (1) efficient delivery, (2) stable expression in a high percentage of target cells (whether mitotic or not), (3) large cargo capacity, (4) flexibility to use with a wide range of additional experimental conditions, and (5) simple experimental technique. Here we report the initial characterization of a hybrid system that meets these criteria by utilizing piggyBac (PB) transposition to achieve genomic integration from adenoviral vectors. We demonstrate stable expression of an adenovirus (Ad)-PB-delivered reporter gene in ∼20-40% of hepatocytes following standard tail vein injection. Its high efficiency and flexibility relative to existing hybrid adenoviral gene delivery approaches indicate a considerable potential utility of the Ad-PB system for therapeutic gene delivery and in vivo studies of gene function.

Cloning and Large-Scale Production of High-Capacity Adenoviral Vectors Based on the Human Adenovirus Type 5

High-capacity adenoviral vectors (HCAdV) devoid of all viral coding sequences represent one of the most advanced gene delivery vectors due to their high packaging capacity (up to 35 kb), low immunogenicity and low toxicity. However, for many laboratories the use of HCAdV is hampered by the complicated procedure for vector genome construction and virus production. Here, a detailed protocol for efficient cloning and production of HCAdV based on the plasmid pAdFTC containing the HCAdV genome is described. The construction of HCAdV genomes is based on a cloning vector system utilizing homing endonucleases (I-CeuI and PI-SceI). Any gene of interest of up to 14 kb can be subcloned into the shuttle vector pHM5, which contains a multiple cloning site flanked by I-CeuI and PI-SceI. After I-CeuI and PI-SceI-mediated release of the transgene from the shuttle vector the transgene can be inserted into the HCAdV cloning vector pAdFTC. Because of the large size of the pAdFTC plasmid and the long recognition sites of the used enzymes associated with strong DNA binding, careful handling of the cloning fragments is needed. For virus production, the HCAdV genome is released by NotI digest and transfected into a HEK293 based producer cell line stably expressing Cre recombinase. To provide all adenoviral genes for adenovirus amplification, co-infection with a helper virus containing a packing signal flanked by loxP sites is required. Pre-amplification of the vector is performed in producer cells grown on surfaces and large-scale amplification of the vector is conducted in spinner flasks with producer cells grown in suspension. For virus purification, two ultracentrifugation steps based on cesium chloride gradients are performed followed by dialysis. Here tips, tricks and shortcuts developed over the past years working with this HCAdV vector system are presented.

Helper-dependent adenoviral vectors for liver-directed gene therapy of primary hyperoxaluria type 1

Primary hyperoxaluria type 1 (PH1) is an inborn error of liver metabolism due to deficiency of the peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT) which catalyzes conversion of glyoxylate into glycine. AGT deficiency results in overproduction of oxalate which ultimately leads to end-stage renal disease and death. Organ transplantation as either preemptive liver transplantation or combined liver/kidney transplantation is the only available therapy to prevent disease progression. Gene therapy is an attractive option to provide an alternative treatment for PH1. Towards this goal, we investigated helper-dependent adenoviral (HDAd) vectors for liver-directed gene therapy of PH1. Compared to saline controls, AGT-deficient mice injected with an HDAd encoding the AGT under the control of a liver-specific promoter showed a significant reduction of hyperoxaluria and less increase of urinary oxalate following challenge with Ethylene Glycol (EG), a precursor of glyoxylate. These studies may thus pave the way to clinical application of HDAd for PH1 gene therapy.

Standard free droplet digital polymerase chain reaction as a new tool for the quality control of high-capacity adenoviral vectors in small-scale preparations

High-capacity adenoviral vectors (HCAdVs) are promising tools for gene therapy as well as for genetic engineering. However, one limitation of the HCAdV vector system is the complex, time-consuming, and labor-intensive production process and the following quality control procedure. Since HCAdVs are deleted for all viral coding sequences, a helper virus (HV) is needed in the production process to provide the sequences for all viral proteins in trans. For the purification procedure of HCAdV, cesium chloride density gradient centrifugation is usually performed followed by buffer exchange using dialysis or comparable methods. However, performing these steps is technically difficult, potentially error-prone, and not scalable. Here, we establish a new protocol for small-scale production of HCAdV based on commercially available adenovirus purification systems and a standard method for the quality control of final HCAdV preparations. For titration of final vector preparations, we established a droplet digital polymerase chain reaction (ddPCR) that uses a standard free-end-point PCR in small droplets of defined volume. By using different probes, this method is capable of detecting and quantifying HCAdV and HV in one reaction independent of reference material, rendering this method attractive for accurately comparing viral titers between different laboratories. In summary, we demonstrate that it is possible to produce HCAdV in a small scale of sufficient quality and quantity to perform experiments in cell culture, and we established a reliable protocol for vector titration based on ddPCR. Our method significantly reduces time and required equipment to perform HCAdV production. In the future the ddPCR technology could be advantageous for titration of other viral vectors commonly used in gene therapy.

TANK-binding kinase 1-dependent or -independent signaling elicits the cell-type-specific innate immune responses induced by the adenovirus vector

Adenovirus vectors (Adv) elicit innate immune responses via several pattern-recognition receptors. Although it has been suggested that various Adv-induced mechanisms play important roles in the induction of innate immunity in vitro, the impacts of these mechanisms in vivo remain unclear. Viral nucleic acids elicit innate immune responses through the recognition of cytosolic nucleic acid sensors and transduce intracellular signals to TANK-binding kinase (TBK) 1. In this study, to determine the impacts of viral nucleic acids on innate immune responses in vivo, we administered transgene-expressing Adv to Tbk1-deficient mice. The systemic Adv administration failed to induce type I interferons (type I IFNs) in the spleen, but not the liver, of Tbk1-deficient mice, resulting in the increase of transgene-expressing cells in the spleen, but not the liver. Moreover, Adv failed to induce type I IFNs in the bone-marrow-derived dendritic cells, but not the mouse embryonic fibroblasts, from Tbk1-deficient mice in vitro. These results support the idea that Adv elicit innate immunity in immune cells and non-immune cells in a TBK1-dependent and TBK1-independent manner, respectively.

Ad 2.0: a novel recombineering platform for high-throughput generation of tailored adenoviruses

Recombinant adenoviruses containing a double-stranded DNA genome of 26-45 kb were broadly explored in basic virology, for vaccination purposes, for treatment of tumors based on oncolytic virotherapy, or simply as a tool for efficient gene transfer. However, the majority of recombinant adenoviral vectors (AdVs) is based on a small fraction of adenovirus types and their genetic modification. Recombineering techniques provide powerful tools for arbitrary engineering of recombinant DNA. Here, we adopted a seamless recombineering technology for high-throughput and arbitrary genetic engineering of recombinant adenoviral DNA molecules. Our cloning platform which also includes a novel recombination pipeline is based on bacterial artificial chromosomes (BACs). It enables generation of novel recombinant adenoviruses from different sources and switching between commonly used early generation AdVs and the last generation high-capacity AdVs lacking all viral coding sequences making them attractive candidates for clinical use. In combination with a novel recombination pipeline allowing cloning of AdVs containing large and complex transgenes and the possibility to generate arbitrary chimeric capsid-modified adenoviruses, these techniques allow generation of tailored AdVs with distinct features. Our technologies will pave the way toward broader applications of AdVs in molecular medicine including gene therapy and vaccination studies.

Nanotherapeutics shielded with a pH responsive polymeric layer

Efficient intravenous delivery is the greatest single hurdle, with most nanotherapeutics frequently found to be unstable in the harsh conditions of the bloodstream. In the case of nanotherapeutics for gene delivery, viral vectors are often avidly recognized by both the innate and the adaptive immune systems. So, most modern delivery systems have benefited from being coated with hydrophilic polymers. Self-assembling delivery systems can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly, gene delivery viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Polymers that start degrading under acidic conditions are increasingly investigated as a pathway to trigger the release of drugs or genes once the carrier reaches a slightly acidic tumor environment or after the carrier has been taken up by cells, resulting in the localization of the polymer in acidic endosomes and lysosomes. Advances in the design of acid-degradable drug and gene delivery systems have been focused and discussed in this article with stress placed on HPMA-based copolymers. We designed a system that is able to "throw away" the polymer coat after successful transport of the vector into a target cell. Initial biological studies were performed and it was demonstrated that this principle is applicable for real adenoviral vectors. It was shown that the transfection ability of coated virus at pH 7.4 is 75 times lower then transfection at pH 5.4.

Sustained inhibition of hepatitis B virus replication in vivo using RNAi-activating lentiviruses

Chronic infection with hepatitis B virus (HBV) puts individuals at high risk for complicating cirrhosis and liver cancer, but available treatment to counter the virus rarely eliminates infection. Although harnessing RNA interference (RNAi) to silence HBV genes has shown the potential, achieving efficient and durable silencing of viral genes remains an important goal. Here we report on the propagation of lentiviral vectors (LVs) that successfully deliver HBV-targeting RNAi activators to liver cells. Mono- and tricistronic artificial primary microRNAs (pri-miRs) derived from pri-miR-31, placed under transcriptional control of the liver-specific modified murine transthyretin (mTTR) promoter, caused efficient inhibition of HBV replication markers. The tricistronic cassette was capable of silencing a mutant viral target and the effects were observed without disrupting the function of an endogenous miR (miR-16). The mTTR promoter stably expressed a reporter transgene in mouse livers over a study period of 1 year. Good silencing of HBV genes, without evidence of toxicity, was demonstrated following intravenous injection of LVs into neonatal HBV transgenic mice. Collectively, these data indicate that LVs may achieve sustained inhibition of HBV replication that is appealing for their therapeutic use.

Sheep lung segmental delivery strategy demonstrates adenovirus priming of local lung responses to bacterial LPS and the role of elafin as a response modulator

Viral lung infections increase susceptibility to subsequent bacterial infection. We questioned whether local lung administration of recombinant adenoviral vectors in the sheep would alter the susceptibility of the lung to subsequent challenge with bacterial lipopolysaccharide (LPS). We further questioned whether local lung expression of elafin, a locally produced alarm anti-LPS/anti-bacterial molecule, would modulate the challenge response. We established that adenoviral vector treatment primed the lung for an enhanced response to bacterial LPS. Whereas this local effect appeared to be independent of the transgene used (Ad-o-elafin or Ad-GFP), Ad-o-elafin treated sheep demonstrated a more profound lymphopenia in response to local lung administration of LPS. The local influence of elafin in modulating the response to LPS was restricted to maintaining neutrophil myeloperoxidase activity, and levels of alveolar macrophage and neutrophil phagocytosis at higher levels post-LPS. Adenoviral vector-bacterial synergism exists in the ovine lung and elafin expression modulates such synergism both locally and systemically.

Suppression of leaky expression of adenovirus genes by insertion of microRNA-targeted sequences in the replication-incompetent adenovirus vector genome

Leaky expression of adenovirus (Ad) genes occurs following transduction with a conventional replication-incompetent Ad vector, leading to an induction of cellular immunity against Ad proteins and Ad protein-induced toxicity, especially in the late phase following administration. To suppress the leaky expression of Ad genes, we developed novel Ad vectors by incorporating four tandem copies of sequences with perfect complementarity to miR-122a or miR-142-3p into the 3′-untranslated region (UTR) of the E2A, E4, or pIX gene, which were mainly expressed from the Ad vector genome after transduction. These Ad vectors easily grew to high titers comparable to those of a conventional Ad vector in conventional 293 cells. The leaky expression of these Ad genes in mouse organs was significantly suppressed by 2- to 100-fold, compared with a conventional Ad vector, by insertion of the miRNA-targeted sequences. Notably, the Ad vector carrying the miR-122a–targeted sequences into the 3′-UTR of the E4 gene expressed higher and longer-term transgene expression and more than 20-fold lower levels of all the Ad early and late genes examined in the liver than a conventional Ad vector. miR-122a–mediated suppression of the E4 gene expression in the liver significantly reduced the hepatotoxicity which an Ad vector causes via both adaptive and non-adaptive immune responses.

Inhibition of hepatitis B virus replication by helper dependent adenoviral vectors expressing artificial anti-HBV pri-miRs from a liver-specific promoter

Research on applying RNA interference (RNAi) to counter HBV replication has led to identification of potential therapeutic sequences. However, before clinical application liver-specific expression and efficient delivery of these sequences remain an important objective. We recently reported short-term inhibition of HBV replication in vivo by using helper dependent adenoviral vectors (HD Ads) expressing anti-HBV sequences from a constitutively active cytomegalovirus (CMV) promoter. To develop the use of liver-specific transcription regulatory elements we investigated the utility of the murine transthyretin (MTTR) promoter for expression of anti-HBV primary microRNAs (pri-miRs). HD Ads containing MTTR promoter effected superior expression of anti-HBV pri-miRs in mice compared to HD Ads containing the CMV promoter. MTTR-containing HD Ads resulted in HBV replication knockdown of up to 94% in mice. HD Ads expressing trimeric anti-HBV pri-miRs silenced HBV replication for 5 weeks. We previously showed that the product of the codelivered lacZ gene induces an immune response, and the duration of HBV silencing in vivo is likely to be attenuated by this effect. Nevertheless, expression of anti-HBV pri-miRs from MTTR promoter is well suited to countering HBV replication and development of HD Ads through attenuation of their immunostimulatory effects should advance their clinical utility.

Challenges and Prospects for Helper-Dependent Adenoviral Vector-Mediated Gene Therapy

Helper-dependent adenoviral (HDAd) vectors that are devoid of all viral coding sequences are promising non-integrating vectors for gene therapy because they efficiently transduce a variety of cell types in vivo, have a large cloning capacity, and drive long-term transgene expression without chronic toxicity. The main obstacle preventing clinical applications of HDAd vectors is the host innate inflammatory response against the vector capsid proteins that occurs shortly after intravascular vector administration and result in acute toxicity, the severity of which is dose dependent. Intense efforts have been focused on elucidating adenoviral vector-host interactions and the factors involved in the acute toxicity. This review focuses on the recent acquisition of data on such interactions and on strategies investigated to improve the therapeutic index of HDAd vectors.

Feasibility of Applying Helper-Dependent Adenoviral Vectors for Cancer Immunotherapy

Adenoviruses (Ads) infect a broad range of tissue types, and derived vectors have been extensively used for gene therapy. Helper-dependent Ad vectors (HDAds), devoid of viral coding sequences, allow for insertion of large or multiple transgenes in a single vector and have been preclinically used for the study of genetic disorders. However, the clinical application of Ad vectors including HDAds for genetic disorders has been hampered by an acute toxic response. This characteristic, while disadvantageous for gene replacement therapy, could be strategically advantageous for the activation of an immune response if HDAds were used as an adjunct treatment in cancer. Cancer treatments including immunotherapy are frequently limited by the inhibitory environment produced by both tumors and their stroma, each of which express numerous inhibitory molecules. Hence, multiple inhibitory mechanisms must be overcome for development of anti-tumor immunity. The large coding capacity of HDAds can accommodate multiple immune modulating transgenes that could produce a combined effect to overcome tumor-derived inhibition and ensure intratumoral effector T-cell proliferation and function. In this review, we discuss the potential advantages of HDAds to cancer immunotherapy based on potent host immune responses to Ads.

The evolution of adenoviral vectors through genetic and chemical surface modifications

A long time has passed since the first clinical trial with adenoviral (Ad) vectors. Despite being very promising, Ad vectors soon revealed their limitations in human clinical trials. The pre-existing immunity, the marked liver tropism and the high toxicity of first generation Ad (FG-Ad) vectors have been the main challenges for the development of new approaches. Significant effort toward the development of genetically and chemically modified adenoviral vectors has enabled researchers to create more sophisticated vectors for gene therapy, with an improved safety profile and a higher transduction ability of different tissues. In this review, we will describe the latest findings in the high-speed, evolving field of genetic and chemical modifications of adenoviral vectors, a field in which different disciplines, such as biomaterial research, virology and immunology, co-operate synergistically to create better gene therapy tools for modern challenges.

Innate functions of immunoglobulin M lessen liver gene transfer with helper-dependent adenovirus

The immune system poses obstacles to viral vectors, even in the first administration to preimmunized hosts. We have observed that the livers of B cell-deficient mice were more effectively transduced by a helper-dependent adenovirus serotype-5 (HDA) vector than those of WT mice. This effect was T-cell independent as shown in athymic mice. Passive transfer of the serum from adenovirus-naïve WT to Rag1KO mice resulted in a reduction in gene transfer that was traced to IgM purified from serum of adenovirus-naïve mice. To ascribe the gene transfer inhibition activity to either adenoviral antigen-specific or antigen-unspecific functions of IgM, we used a monoclonal IgM antibody of unrelated specificity. Both the polyclonal and the irrelevant monoclonal IgM inhibited gene transfer by the HDA vector to either cultured hepatocellular carcinoma cells or to the liver of mice in vivo. Adsorption of polyclonal or monoclonal IgMs to viral capsids was revealed by ELISAs on adenovirus-coated plates. These observations indicate the existence of an inborn IgM mechanism deployed against a prevalent virus to reduce early post-infection viremia. In conclusion, innate IgM binding to adenovirus serotype-5 capsids restrains gene-transfer and offers a mechanism to be targeted for optimization of vector dosage in gene therapy with HDA vectors.

Beyond Gene Delivery: Strategies to Engineer the Surfaces of Viral Vectors

Viral vectors have been extensively studied due to their great transduction efficiency compared to non-viral vectors. These vectors have been used extensively in gene therapy, enabling the comprehension of, not only the advantages of these vectors, but also the limitations, such as the activation of the immune system after vector administration. Moreover, the need to control the target of the vector has led to the development of chemical and non-chemical modifications of the vector surface, allowing researchers to modify the tropism and biodistribution profile of the vector, leading to the production of viral vectors able to target different tissues and organs. This review describes recent non-genetic modifications of the surfaces of viral vectors to decrease immune system activation and to control tissue targeting. The developments described herein provide opportunities for applications of gene therapy to treat acquired disorders and genetic diseases and to become useful tools in regenerative medicine.

Inhibition of HBV replication in vivo using helper-dependent adenovirus vectors to deliver antiviral RNA interference expression cassettes

BACKGROUND

HBV is hyperendemic to southern Africa and parts of Asia, but licensed antivirals have little effect on limiting life-threatening complications of the infection. Although RNA interference (RNAi)-based gene silencing has shown therapeutic potential, difficulties with delivery of anti-HBV RNAi effectors remain an obstacle to their clinical use. To address concerns about the transient nature of transgene expression and toxicity resulting from immunostimulation by recombinant adenovirus vectors (Ads), utility of RNAi-activating anti-HBV helper-dependent (HD) Ads were assessed in this study.

METHODS

Following intravenous administration of 5×10(9) unmodified or pegylated HD Ad infectious particles to HBV transgenic mice, HBV viral loads and serum HBV surface antigen levels were monitored for 12 weeks. Immunostimulation of HD Ads was assessed by measuring inflammatory cytokines, hepatic function and immune response to the co-delivered LacZ reporter gene.

RESULTS

Unmodified and pegylated HD Ads transduced 80-90% of hepatocytes and expressed short hairpin RNAs (shRNAs) were processed to generate intended HBV-targeting guides. Markers of HBV replication were decreased by approximately 95% and silencing was sustained for 8 weeks. Unmodified HD Ads induced release of proinflammatory cytokines and there was evidence of an adaptive immune response to β-galactosidase. However the HD Ad-induced innate immune response was minimal in preparations that were enriched with infectious particles.

CONCLUSIONS

HD Ads have potential utility for delivery of therapeutic HBV-silencing sequences and alterations of these vectors to attenuate their immune responses may further improve their efficacy.

Rapamycin enhances adenovirus-mediated cancer imaging and therapy in pre-immunized murine hosts

Tumor-specific adenoviral vectors comprise a fruitful gene-based diagnostic imaging and therapy research area for advanced stage of cancer, including metastatic disease. However, clinical translation of viral vectors has encountered considerable obstacles, largely due to host immune responses against the virus. Here, we explored the utilization of an immunosuppressant, rapamycin, to circumvent the anti-adenovirus immunity in immunocompetent murine prostate cancer models. Rapamycin diminished adenoviral-induced acute immune response by inhibiting NF-κB activation; it also reduced the scale and delayed the onset of inflammatory cytokine secretion. Further, we found that rapamycin abrogated anti-adenovirus antibody production and retarded the function of myeloid cells and lymphocytes that were activated upon viral administration in pre-immunized hosts. Thus, the co-administration of rapamycin prolonged and enhanced adenovirus-delivered transgene expression in vivo, and thereby augmented the imaging capability of adenoviral vectors in both bioluminescent and positron emission tomography modalities. Furthermore, we showed that despite an excellent response of cancer cells to a cytotoxic gene therapeutic vector in vitro, only minimal therapeutic effects were observed in vivo in pre-immunized mice. However, when we combined gene therapy with transient immunosuppression, complete tumor growth arrest was achieved. Overall, transient immunosuppression by rapamycin was able to boost the diagnostic utility and therapeutic potentials of adenoviral vectors.

A novel helper-dependent adenovirus-based cell culture model for Hepatitis C virus replication and production

Background

By using the hepatitis C virus (HCV) genotype 2a JFH-1 or its chimeric strains, a HCV infection system has been previously developed through several methods– such as in vitro-transcribed JFH1-RNA transfection or stable transfection of the JFH1 cDNA into human hepatoma Huh-7 cell line or its derivatives. However, other reliable methods for delivery of the HCV genome into cells are still worth trying. The helper-dependent adenovirus (HDAd) is devoid of all viral coding sequences and has a package capacity of 37 kb, which is suitably large for the delivery of the HCV genome. Here we report a new method for delivery of the HCV genome into Huh-7 and HepG2 cells by using the HDAd vector.

Results

Our results demonstrated that the infection of Huh-7 cells with the HDAdJFH1 virus led to efficient HCV replication and virion production. We found that the HCV viral RNA levels could reach 107 copies per milliliter (ml) in the culture medium. HDAdJFH1-infected Huh-7 cells could be cultured for 8 passages with the culture medium remaining infectious for naïve Huh-7 cells throughout this period. This infection system proved effective for evaluating the anti-HCV effects of IFN-α in Huh-7 cells. Co-infection of HepG2 cells with the HDAdJFH1 and HDAdmiR-122 virus also resulted in HCV expression and replication.

Conclusion

This is the first report of an HDAd-based strategy for HCV replication and production in vitro.

The role of chromatin in adenoviral vector function

Vectors based on adenovirus (Ad) are one of the most commonly utilized platforms for gene delivery to cells in molecular biology studies and in gene therapy applications. Ad is also the most popular vector system in human clinical gene therapy trials, largely due to its advantageous characteristics such as high cloning capacity (up to 36 kb), ability to infect a wide variety of cell types and tissues, and relative safety due to it remaining episomal in transduced cells. The latest generation of Ad vectors, helper‑dependent Ad (hdAd), which are devoid of all viral protein coding sequences, can mediate high-level expression of a transgene for years in a variety of species ranging from rodents to non-human primates. Given the importance of histones and chromatin in modulating gene expression within the host cell, it is not surprising that Ad, a nuclear virus, also utilizes these proteins to protect the genome and modulate virus- or vector‑encoded genes. In this review, we will discuss our current understanding of the contribution of chromatin to Ad vector function.

Adenoviral Vectors for Hemophilia Gene Therapy

Hemophilia is an inherited blood clotting disorder resulting from deficiency of blood coagulation factors. Current standard of care for hemophilia patients is frequent intravenous infusions of the missing coagulation factor. Gene therapy for hemophilia involves the introduction of a normal copy of the deficient coagulation factor gene thereby potentially offering a definitive cure for the bleeding disorder. A variety of approaches have been pursued for hemophilia gene therapy and this review article focuses on those that use adenoviral vectors.

Gene and cell-mediated therapies for muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating muscle disorder that affects 1 in 3,500 boys. Despite years of research and considerable progress in understanding the molecular mechanism of the disease and advancement of therapeutic approaches, there is no cure for DMD. The current treatment options are limited to physiotherapy and corticosteroids, and although they provide a substantial improvement in affected children, they only slow the course of the disorder. On a more optimistic note, more recent approaches either significantly alleviate or eliminate muscular dystrophy in murine and canine models of DMD and importantly, many of them are being tested in early phase human clinical trials. This review summarizes advancements that have been made in viral and nonviral gene therapy as well as stem cell therapy for DMD with a focus on the replacement and repair of the affected dystrophin gene.

Differential type I interferon-dependent transgene silencing of helper-dependent adenoviral vs. adeno-associated viral vectors in vivo

We previously dissected the components of the innate immune response to Helper-dependent adenoviral vectors (HDAds) using genetic models, and demonstrated that multiple pattern recognition receptor signaling pathways contribute to this host response to HDAds in vivo. Based on analysis of cytokine expression profiles, type I interferon (IFN) mRNA is induced in host mouse livers at 1 hour post-injection. This type I IFN signaling amplifies cytokine expression in liver independent of the nature of vector DNA sequences after 3 hours post-injection. This type I IFN signaling in response to HDAds administration contributes to transcriptional silencing of both HDAd prokaryotic and eukaryotic DNA in liver. This silencing occurs early and is mediated by epigenetic modification as shown by in vivo chromatin immunoprecipitation (ChIP) with anti-histone deacetylase (HDAC) and promyelocytic leukemia protein (PML). In contrast, self-complementary adeno-associated viral vectors (scAAVs) showed significantly lower induction of type I IFN mRNA in liver compared to HDAds at both early and late time points. These results show that the type I IFN signaling dependent transgene silencing differs between AAV and HDAd vectors after liver-directed gene transfer.

Combined cocaine hydrolase gene transfer and anti-cocaine vaccine synergistically block cocaine-induced locomotion

Mice and rats were tested for reduced sensitivity to cocaine-induced hyper-locomotion after pretreatment with anti-cocaine antibody or cocaine hydrolase (CocH) derived from human butyrylcholinesterase (BChE). In Balb/c mice, direct i.p. injection of CocH protein (1 mg/kg) had no effect on spontaneous locomotion, but it suppressed responses to i.p. cocaine up to 80 mg/kg. When CocH was injected i.p. along with a murine cocaine antiserum that also did not affect spontaneous locomotion, there was no response to any cocaine dose. This suppression of locomotor activity required active enzyme, as it was lost after pretreatment with iso-OMPA, a selective BChE inhibitor. Comparable results were obtained in rats that developed high levels of CocH by gene transfer with helper-dependent adenoviral vector, and/or high levels of anti-cocaine antibody by vaccination with norcocaine hapten conjugated to keyhole limpet hemocyanin (KLH). After these treatments, rats were subjected to a locomotor sensitization paradigm involving a “training phase" with an initial i.p. saline injection on day 1 followed by 8 days of repeated cocaine injections (10 mg/kg, i.p.). A 15-day rest period then ensued, followed by a final “challenge" cocaine injection. As in mice, the individual treatment interventions reduced cocaine-stimulated hyperactivity to a modest extent, while combined treatment produced a greater reduction during all phases of testing compared to control rats (with only saline pretreatment). Overall, the present results strongly support the view that anti-cocaine vaccine and cocaine hydrolase vector treatments together provide enhanced protection against the stimulatory actions of cocaine in rodents. A similar combination therapy in human cocaine users might provide a robust therapy to help maintain abstinence.

The human adenovirus type 5 E1B 55 kDa protein obstructs inhibition of viral replication by type I interferon in normal human cells

Vectors derived from human adenovirus type 5, which typically lack the E1A and E1B genes, induce robust innate immune responses that limit their therapeutic efficacy. We reported previously that the E1B 55 kDa protein inhibits expression of a set of cellular genes that is highly enriched for those associated with anti-viral defense and immune responses, and includes many interferon-sensitive genes. The sensitivity of replication of E1B 55 kDa null-mutants to exogenous interferon (IFN) was therefore examined in normal human fibroblasts and respiratory epithelial cells. Yields of the mutants were reduced at least 500-fold, compared to only 5-fold, for wild-type (WT) virus replication. To investigate the mechanistic basis of such inhibition, the accumulation of viral early proteins and genomes was compared by immunoblotting and qPCR, respectively, in WT- and mutant-infected cells in the absence or presence of exogenous IFN. Both the concentration of viral genomes detected during the late phase and the numbers of viral replication centers formed were strongly reduced in IFN-treated cells in the absence of the E1B protein, despite production of similar quantities of viral replication proteins. These defects could not be attributed to degradation of entering viral genomes, induction of apoptosis, or failure to reorganize components of PML nuclear bodies. Nor was assembly of the E1B- and E4 Orf6 protein- E3 ubiquitin ligase required to prevent inhibition of viral replication by IFN. However, by using RT-PCR, the E1B 55 kDa protein was demonstrated to be a potent repressor of expression of IFN-inducible genes in IFN-treated cells. We propose that a primary function of the previously described transcriptional repression activity of the E1B 55 kDa protein is to block expression of IFN- inducible genes, and hence to facilitate formation of viral replication centers and genome replication.

The most frequently used therapeutic vectors for gene transfer or cancer treatment are derived from human adenovirus type 5 (Ad5). We have observed previously that the E1B 55 kDa protein encoded by a gene routinely deleted from these vectors represses expression of numerous cellular genes regulated by interferon (IFN) α and β, which are important components of the innate immune response to viral infection. We therefore compared synthesis of pre-mRNA from IFN-inducible genes, viral yields and early reactions in the infectious cycle in normal human cells exposed to exogenous IFN and infected by wild-type or E1B 55 kDa null-mutant viruses. We report that the E1B 55 kDa protein is a potent repressor of expression of IFN-regulated genes, and protects viral replication against anti-viral actions of IFN by blocking inhibition of formation of viral replication centers and genome replication. These observations provide the first information about the function of the transcription repression activity of E1B during the infectious cycle. Importantly, they also suggest new design considerations for adenoviral vectors that can circumvent induction of innate immune responses, currently a major therapeutic limitation.

Biopump: Autologous skin-derived micro-organ genetically engineered to provide sustained continuous secretion of therapeutic proteins

A novel approach for sustained production of therapeutic proteins is described, using genetic modification of intact autologous micro-organ tissue explants from the subject's own skin. The skin-derived micro-organ can be maintained viable ex vivo for extended periods and is transduced with a transgene encoding a desired therapeutic protein, resulting in protein-secreting micro-organ (biopump (BP)). The daily protein production from each BP is quantified, enabling drug dosing by subcutaneous implantation of the requisite number of BPs into the patient to provide continuous production to the circulation of a known amount of the therapeutic protein. Each implanted BP remains localized and is accessible, to enable removal or ablation if needed. Examples from preclinical and clinical studies are presented, including use of associated virus vector 1 and helper-dependent adenoviral vectors producing BPs to provide long-term sustained secretion of recombinant interferon-α and erythropoietin.

Cocaine hydrolase gene therapy for cocaine abuse

Rapid progress in the past decade with re-engineering of human plasma butyrylcholinesterase has led to enzymes that destroy cocaine so efficiently that they prevent or interrupt drug actions in the CNS even though confined to the blood stream. Over the same time window, improved gene-transfer technology has made it possible to deliver such enzymes by endogenous gene transduction at high levels for periods of a year or longer after a single treatment. This article reviews recent advances in this field and considers prospects for development of a robust therapy aimed at aiding recovering drug users avoid addiction relapse.

Polymer coatings for delivery of nucleic acid therapeutics

Gene delivery remains the greatest challenge in applying nucleic acid therapeutic for a broad range of diseases. Combining stability during the delivery phase with activation and transgene expression following arrival at the target site requires sophisticated vectors that can discriminate between cell types and respond to target-associated conditions to trigger expression. Efficient intravenous delivery is the greatest single hurdle, with synthetic vectors frequently found to be unstable in the harsh conditions of the bloodstream, and viral vectors often recognized avidly by both the innate and the adaptive immune system. Both types of vectors benefit from coating with hydrophilic polymers. Self-assembling polyelectrolyte non-viral vectors can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Both types of vectors may also have their tropism changed following chemical linkage of novel ligands to the polymer coating. These families of vectors go some way towards realizing the goal of efficient systemic delivery of genes and should find a range of important uses in bringing this still-emerging field to fruition.