Adenovirus vectors for human gene therapy

Viral vector- and virus-like particle-based vaccines against infectious diseases: A minireview

To overcome the limitations of conventional vaccines, new platforms for vaccine design have emerged such as those based on viral vectors and virus-like particles (VLPs). Viral vector vaccines are highly efficient and the onset of protection is quick. Many recombinant vaccine candidates for humans are based on viruses belonging to different families such as Adenoviridae, Retroviridae, Paramyxoviridae, Rhabdoviridae, and Parvoviridae. Also, the first viral vector vaccine licensed for human vaccination was the Japanese encephalitis virus vaccine. Since then, several viral vectors have been approved for vaccination against the viruses of Lassa fever, Ebola, hepatitis B, hepatitis E, SARS-CoV-2, and malaria. VLPs are nanoparticles that mimic viral particles formed from the self-assembly of structural proteins and VLP-based vaccines against hepatitis B and E viruses, human papillomavirus, and malaria have been commercialized. As evidenced by the accelerated production of vaccines against COVID-19, these new approaches are important tools for vaccinology and for generating rapid responses against pathogens and emerging pandemic threats.

EPH/Ephrin-Targeting Treatment in Breast Cancer: A New Chapter in Breast Cancer Therapy

Breast cancer (BC) is the most common malignant tumor in women. Erythropoietin-producing hepatocellular receptors (EPHs), receptor tyrosine kinases binding the membrane-bound proteins ephrins, are differentially expressed in BC, and correlate with carcinogenesis and tumor progression. With a view to examining available therapeutics targeting the EPH/ephrin system in BC, a literature review was conducted, using the MEDLINE, LIVIVO, and Google Scholar databases. EPHA2 is the most studied EPH/ephrin target in BC treatment. The targeting of EPHA2, EPHA10, EPHB4, ephrin-A2, ephrin-A4, as well as ephrin-B2 in BC cells or xenograft models is associated with apoptosis induction, tumor regression, anticancer immune response activation, and impaired cell motility. In conclusion, EPHs/ephrins seem to represent promising future treatment targets in BC.

Adenovirus vector-based vaccines as forefront approaches in fighting the battle against flaviviruses

Flaviviruses are arthropod-borne viruses (arboviruses) that have been recently considered among the significant public health problems in defined geographical regions. In this line, there have been vaccines approved for some flaviviruses including dengue virus (DENV), Japanese encephalitis virus (JEV), yellow fever virus (YFV), and tick-borne encephalitis virus (TBEV), although the efficiency of such vaccines thought to be questionable. Surprisingly, there are no effective vaccine for many other hazardous flaviviruses, including West Nile and Zika viruses. Furthermore, in spite of approved vaccines for some flaviviruses, for example DENV, alternative prophylactic vaccines seem to be still needed for the protection of a broader population, and it originates from the unsatisfying safety, and the efficacy of vaccines that have been introduced. Thus, adenovirus vector-based vaccine candidates are suggested to be effective, safe, and reliable. Interestingly, recent widespread use of adenovirus vector-based vaccines for the COVID-19 pandemic have highlighted the importance and feasibility of their widespread application. In this review, the applicability of adenovirus vector-based vaccines, as promising approaches to harness the diseases caused by Flaviviruses, is discussed.

Introducing Genes into Mammalian Cells: Viral Vectors

Over the years, many different viral vector systems have been developed to take advantage of the specific biological properties and tropisms of a large number of mammalian viruses. As a result, researchers wanting to introduce and/or express genes in mammalian cells have many options, as discussed here.

Maternal immunization with a recombinant adenovirus-expressing fusion protein protects neonatal cotton rats from respiratory syncytia virus infection by transferring antibodies via breast milk and placenta

We evaluated the efficacy of a recombinant adenovirus that expresses a membrane-truncated respiratory syncytial virus (RSV) fusion protein (Ad-F0ΔTM) in newborns via maternal immunization (MI) of pregnant cotton rats. Intranasal Ad-F0ΔTM immunization was given to pregnant female rats, and MI-newborn rats were then challenged intranasally with RSV. Anti-RSV IgGs were observed in the serum of MI-newborn rats after birth. The pulmonary viral loads in Ad-F0ΔTM vs. control vector, Ad-LacZ, and MI-newborns on day 3 post-challenge were reduced by 4 log₁₀/g lung. The neutralizing antibody remained for up to 3 weeks in the serum of MI-newborns, which is when weaning began. Ad-F0ΔTM protected MI-newborns from RSV challenge for 1 week. Vertical-transferred protective antibodies were examined in the breast milk and placenta as well. Finally, anti-RSV immunity was not boosted but was only primed during the next RSV exposure in Ad-F0ΔTM-MI-newborns. Maternal Ad-F0ΔTM immunization provides acute protection against RSV infection in neonates.

Ebola virus vaccines - reality or fiction?

For 40 years ebolaviruses have been responsible for sporadic outbreaks of severe and often fatal hemorrhagic fever in humans and nonhuman primates. In December 2013 an unprecedented Zaire ebolavirus epidemic began in West Africa. Although "patient zero" has finally been reached after 2 years, the virus is again causing disease in the region. Currently there are no licensed vaccines or therapeutic countermeasures against ebolaviruses; however, the epidemic in West Africa has focused attention on the potential vaccine platforms developed over the past 15 years. There has been remarkable progress using a variety of platforms including DNA, subunit, and several viral vector approaches, replicating and non-replicating, which have shown varying degrees of protective efficacy in the "gold-standard" nonhuman primate models for Ebolavirus infections. A number of these vaccine platforms have moved into clinical trials over the past year with the hope of finding an efficacious vaccine to prevent future outbreaks/epidemics of Ebola hemorrhagic fever on the scale of the West African epidemic.

Treatment of melanoma with a serotype 5/3 chimeric oncolytic adenovirus coding for GM-CSF: Results in vitro, in rodents and in humans

Metastatic melanoma is refractory to irradiation and chemotherapy, but amenable to immunological approaches such as immune-checkpoint-inhibiting antibodies or adoptive cell therapies. Oncolytic virus replication is an immunogenic phenomenon, and viruses can be armed with immunostimulatory molecules. Therefore, oncolytic immuno-virotherapy of malignant melanoma is an appealing approach, which was recently validated by a positive phase 3 trial. We investigated the potency of oncolytic adenovirus Ad5/3-D24-GMCSF on a panel of melanoma cell lines and animal models, and summarized the melanoma-specific human data from the Advanced Therapy Access Program (ATAP). The virus effectively eradicated human melanoma cells in vitro and subcutaneous SK-MEL-28 melanoma xenografts in nude mice when combined with low-dose cyclophosphamide. Furthermore, virally-expressed granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulated the differentiation of human monocytes into macrophages. In contrast to human cells, RPMI 1846 hamster melanoma cells exhibited no response to oncolytic viruses and the chimeric 5/3 fiber failed to increase the efficacy of transduction, suggesting limited utility of the hamster model in the context of viruses with this capsid. In ATAP, treatments appeared safe and well-tolerated. Four out of nine melanoma patients treated were evaluable for possible therapy benefit with modified RECIST criteria: one patient had minor response, two had stable disease, and one had progressive disease. Two patients were alive at 559 and 2,149 days after treatment. Ad5/3-D24-GMCSF showed promising efficacy in preclinical studies and possible antitumor activity in melanoma patients refractory to other forms of therapy. This data supports continuing the clinical development of oncolytic adenoviruses for treatment of malignant melanoma.

Adenoviral vector-mediated gene therapy for gliomas: coming of age

INTRODUCTION

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and it carries a dismal prognosis. Adenoviral vector (Ad)-mediated gene transfer is being developed as a promising therapeutic strategy for GBM. Preclinical studies have demonstrated safety and efficacy of adenovirus administration into the brain and tumor mass in rodents and into the non-human primates' brain. Importantly, Ads have been safely administered within the tumor resection cavity in humans.

AREAS COVERED

This review gives background on GBM and Ads; we describe gene therapy strategies for GBM and discuss the value of combination approaches. Finally, we discuss the results of the human clinical trials for GBM that have used Ads.

EXPERT OPINION

The transduction characteristics of Ads, and their safety profile, added to their capacity to achieve high levels of transgene expression have made them powerful vectors for the treatment of GBM. Recent gene therapy successes in the treatment of retinal diseases and systemic brain metabolic diseases encourage the development of gene therapy for malignant glioma. Exciting clinical trials are currently recruiting patients; although, it is the large randomized Phase III controlled clinical trials that will provide the final decision on the success of gene therapy for the treatment of GBM.

Adenoviral vector-mediated gene therapy for gliomas: coming of age

INTRODUCTION

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and it carries a dismal prognosis. Adenoviral vector (Ad)-mediated gene transfer is being developed as a promising therapeutic strategy for GBM. Preclinical studies have demonstrated safety and efficacy of adenovirus administration into the brain and tumor mass in rodents and into the non-human primates' brain. Importantly, Ads have been safely administered within the tumor resection cavity in humans.

AREAS COVERED

This review gives background on GBM and Ads; we describe gene therapy strategies for GBM and discuss the value of combination approaches. Finally, we discuss the results of the human clinical trials for GBM that have used Ads.

EXPERT OPINION

The transduction characteristics of Ads, and their safety profile, added to their capacity to achieve high levels of transgene expression have made them powerful vectors for the treatment of GBM. Recent gene therapy successes in the treatment of retinal diseases and systemic brain metabolic diseases encourage the development of gene therapy for malignant glioma. Exciting clinical trials are currently recruiting patients; although, it is the large randomized Phase III controlled clinical trials that will provide the final decision on the success of gene therapy for the treatment of GBM.

HER3 targeting of adenovirus by fiber modification increases infection of breast cancer cells in vitro, but not following intratumoral injection in mice

Despite the tremendous potential of adenovirus (Ad) as a delivery vector for cancer gene therapy, its use in clinical settings has been limited, mainly as a result of the limited infectivity in many tumors and the wide tissue tropism associated with Ad. To modify the tropism of the virus, we have inserted the epidermal growth factor-like domain of the human heregulin-α (HRG) into the HI loop of Ad5 fiber. This insertion had no adverse effect on fiber trimerization nor did it affect incorporation of the modified fiber into infectious viral particles. Virions bearing modified fiber displayed growth characteristics and viral yields indistinguishable from those of wild-type (wt) virus. Most importantly, HRG-tagged virions showed enhanced infection of cells expressing the cognate receptors HER3/ErbB3 and HER4/ErbB4. This was significantly reduced in the presence of soluble HRG. Furthermore, HER3-expressing Chinese hamster ovary (CHO) cells were transduced by the HRG-modified virus, but not by wt virus. In contrast, CHO cells expressing the coxsackie-Ad receptor were transduced with both viruses. However, infection of an in vivo breast cancer xenograft model after intratumoral injection was similar with both viruses, suggesting that the tumor microenvironment and/or the route of delivery have important roles in infection of target cells with fiber-modified Ads.

Hypomorphic sialidase expression decreases serum cholesterol by downregulation of VLDL production in mice

Lipoprotein metabolism is an important contributing factor in the development and progression of atherosclerosis. Plasma lipoproteins and their receptors are heavily glycosylated and sialylated, and levels of sialic acids modulate their biological functions. Sialylation is controlled by the activities of sialyltranferases and sialidases. To address the impact of sialidase (neu1) activity on lipoprotein metabolism, we have generated a mouse model with a hypomorphic neu1 allele (B6.SM) that displays reduced sialidase expression and sialidase activity. The objectives of this study are to determine the impact of sialidase on the rate of hepatic lipoprotein secretion and lipoprotein uptake. Our results indicate that hepatic levels of cholesterol and triglycerides are significantly higher in B6.SM mice compared with C57Bl/6 mice; however, VLDL-triglyceride production rate is lower. In addition, B6.SM mice show significantly lower levels of hepatic microsomal triglyceride transfer protein (MTP) and active sterol-regulatory element binding protein (SREBP)-2 but higher levels of diglyceride acyltransferase (DGAT)2; these are all indicative of increased hepatic lipid storage. Rescue of sialidase activity in hypomorphic sialidase mice using helper-dependent adenovirus resulted in increased VLDL production and an increase in MTP levels. Furthermore, hypomorphic sialidase expression results in stabilization of hepatic LDL receptor (LDLR) protein expression, which enhances LDL uptake. These findings provide novel evidence for a central role of sialidase in the cross talk between the uptake and production of lipoproteins.

Calcium gluconate in phosphate buffered saline increases gene delivery with adenovirus type 5

Background

Adenoviruses are attractive vectors for gene therapy because of their stability in vivo and the possibility of production at high titers. Despite exciting preclinical data with various approaches, there are only a few examples of clear efficacy in clinical trials. Effective gene delivery to target cells remains the key variable determining efficacy and thus enhanced transduction methods are important.

Methods/Results

We found that heated serum could enhance adenovirus 5 mediated gene delivery up to twentyfold. A new protein-level interaction was found between fiber knob and serum transthyretin, but this was not responsible for the observed effect. Instead, we found that heating caused the calcium and phosphate present in the serum mix to precipitate, and this was responsible for enhanced gene delivery. This finding could have relevance for designing preclinical experiments with adenoviruses, since calcium and phosphate are present in many solutions. To translate this into an approach potentially testable in patients, we used calcium gluconate in phosphate buffered saline, both of which are clinically approved, to increase adenoviral gene transfer up to 300-fold in vitro. Gene transfer was increased with or without heating and in a manner independent from the coxsackie-adenovirus receptor. In vivo, in mouse studies, gene delivery was increased 2-, 110-, 12- and 13-fold to tumors, lungs, heart and liver and did not result in increased pro-inflammatory cytokine induction. Antitumor efficacy of a replication competent virus was also increased significantly.

Conclusion

In summary, adenoviral gene transfer and antitumor efficacy can be enhanced by calcium gluconate in phosphate buffered saline.

GammadeltaT cells initiate acute inflammation and injury in adenovirus-infected liver via cytokine-chemokine cross talk

Emerging studies suggest an important role for the innate immune response in replication-defective adenovirus (Ad)-mediated acute liver toxicity. Specifically, classical innate immune cells (including NK cells, neutrophils, and Kupffer cells) have all been implicated in the development of Ad-mediated acute liver toxicity. The nonclassical innate immune T cell, the gammadeltaT cell, has been implicated in the pathophysiology of several viral infections that predominantly affect the mucosa and brain, but the specific role in the pathology of AdLacZ-mediated acute liver inflammation and injury as well as accompanying vector clearance is largely unknown. In the present study, we demonstrated that a CXCL9-CXCR3-dependent mechanism governed the accumulation of gammadeltaT cells in the livers of mice infected with Ad expressing the Escherichia coli LacZ gene (AdLacZ). We also showed a critical role for gammadeltaT cells in initiating acute liver toxicity after AdLacZ administration, driven in part by the ability of gammadeltaT cells to promote the recruitment of the conventional T cell, the CD8(+) T cell, into the liver. Furthermore, reduced hepatic injury in AdLacZ-infected gammadeltaT-cell-deficient mice was associated with lower hepatic levels of gamma interferon (IFN-gamma) and CXCL9, an IFN-gamma-inducible chemokine. Finally, our study highlighted a key role for IFN-gamma and CXCL9 cross talk acting in a feedback loop to drive the proinflammatory effects of gammadeltaT cells during AdLacZ-mediated acute liver toxicity. Specifically, intracellular IFN-gamma produced by activated hepatic gammadeltaT cells interacts with hepatocytes to mediate hepatic CXCL9 production, with the consequent accumulation of CXCR3-bearing gammadeltaT cells in the liver to cause acute liver damage without vector clearance.

Development of lipid particles targeted via sugar-lipid conjugates as novel nuclear gene delivery system

Efficient nuclear gene delivery is essential for successful gene therapy. This study developed a novel system that mimics the mechanism of nuclear entry of adenovirus (Ad) by means of a Multifunctional Envelope-type Nano Device (MEND). In this system, plasmid DNA (pDNA) was condensed with polycation, followed by encapsulation in a lipid membrane. To target MEND to the nuclear pore complex (NPC), sugar served as a NPC-mediated nuclear targeting device was modified on the surface of the lipid envelope. This was accomplished via synthesis of a sugar-cholesterol conjugate. After binding of the MEND to the NPC, the pDNA core was transferred into the nucleus in conjunction with a breakdown of the lipid envelope. Sugar-modified MEND showed higher transfection efficiency compared with unmodified MEND, in non-dividing and dividing cells. Confocal microscopy confirmed that nuclear transfer of pDNA was improved by sugar modification of MEND. Furthermore, destabilization of the lipid envelope significantly enhanced transfection activity: therefore, nuclear-delivery efficiency was closely related to lipid envelope stability. Moreover, quantitative evaluation of cellular uptake and nuclear transfer processes by real-time PCR confirmed that the surface sugars affected nuclear transfer, but not cellular uptake. In summary, a novel system for the nuclear delivery of pDNA was successfully developed by using a sugar-modified MEND and by optimizing the lipid envelope stability.

Genetic modification of chondrocytes with insulin-like growth factor-1 enhances cartilage healing in an equine model

Gene therapy with insulin-like growth factor-1 (IGF-1) increases matrix production and enhances chondrocyte proliferation and survival in vitro. The purpose of this study was to determine whether arthroscopically-grafted chondrocytes genetically modified by an adenovirus vector encoding equine IGF-1 (AdIGF-1) would have a beneficial effect on cartilage healing in an equine femoropatellar joint model.

A total of 16 horses underwent arthroscopic repair of a single 15 mm cartilage defect in each femoropatellar joint. One joint received 2 × 107 AdIGF-1 modified chondrocytes and the contralateral joint received 2 × 107 naive (unmodified) chondrocytes. Repairs were analysed at four weeks, nine weeks and eight months after surgery. Morphological and histological appearance, IGF-1 and collagen type II gene expression (polymerase chain reaction, in situ hybridisation and immunohistochemistry), collagen type II content (cyanogen bromide and sodium dodecyl sulphate-polyacrylamide gel electrophoresis), proteoglycan content (dimethylmethylene blue assay), and gene expression for collagen type I, matrix metalloproteinase (MMP)-1, MMP-3, MMP-13, aggrecanase-1, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and TIMP-3 were evaluated.

Genetic modification of chondrocytes significantly increased IGF-1 mRNA and ligand production in repair tissue for up to nine weeks following transplantation. The gross and histological appearance of IGF-1 modified repair tissue was improved over control defects. Gross filling of defects was significantly improved at four weeks, and a more hyaline-like tissue covered the lesions at eight months. Histological outcome at four and nine weeks post-transplantation revealed greater tissue filling of defects transplanted with genetically modified chondrocytes, whereas repair tissue in control defects was thin and irregular and more fibrous. Collagen type II expression in IGF-1 gene-transduced defects was increased 100-fold at four weeks and correlated with increased collagen type II immunoreaction up to eight months.

Genetic modification of chondrocytes with AdIGF-1 prior to transplantation improved early (four to nine weeks), and to a lesser degree long-term, cartilage healing in the equine model.

The equine model of cartilage healing closely resembles human clinical cartilage repair. The results of this study suggest that cartilage healing can be enhanced through genetic modification of chondrocytes prior to transplantation.

Overcoming maternal antibody interference by vaccination with human adenovirus 5 recombinant viruses expressing the hemagglutinin and the nucleoprotein of swine influenza virus

Sows and gilts lack immunity to human adenovirus 5 (Ad-5) vectored vaccines so immunogens of swine pathogens can be expressed with these vaccines in order to immunize suckling piglets that have interfering, maternally derived antibodies. In this study 7-day-old piglets, that had suckled H3N2 infected gilts, were sham-inoculated with a non-expressing Ad-5 vector or given a primary vaccination with replication-defective Ad-5 viruses expressed the H3 hemagglutinin and the nucleoprotein of swine influenza virus (SIV) subtype H3N2. The hemagglutination inhibition (HI) titer of the sham-inoculated group (n = 12) showed continued antibody decay whereas piglets vaccinated with Ad-5 SIV (n = 23) developed an active immune response by the second week post-vaccination. At 4 weeks-of-age when the HI titer of the sham-inoculated group had decayed to 45, the sham-inoculated group and half of the Ad-5 SIV vaccinated pigs were boosted with a commercial inactivated SIV vaccine. The boosted pigs that had been primed in the presence of maternal interfering antibodies had a strong anamnestic response while sham-inoculated pigs did not respond to the commercial vaccine. Two weeks after the booster vaccination the pigs were challenged with a non-homologous H3N2 virulent SIV. The efficacy of the vaccination protocol was demonstrated by abrogation of clinical signs, by clearance of challenge virus from pulmonary lavage fluids, by markedly reduced virus shedding in nasal secretions, and by the absence of moderate or severe SIV-induced lung lesions. These recombinant Ad-5 SIV vaccines are useful for priming the immune system to override the effects of maternally derived antibodies which interfere with conventional SIV vaccines.

Expression of mutant cartilage oligomeric matrix protein in human chondrocytes induces the pseudoachondroplasia phenotype

Over 70 mutations in the cartilage oligomeric matrix protein (COMP), a large extracellular pentameric glycoprotein synthesized by chondrocytes, have been identified as causing two skeletal dysplasias: multiple epiphyseal dysplasia (MED/EDM1), and a dwarfing condition, pseudoachondroplasia (PSACH). These mutations induce misfolding of intracellular COMP, resulting in retention of the protein in the rough endoplasmic reticulum (rER) of chondrocytes. This accumulation of COMP in the rER creates the phenotypic enlarged rER cisternae in the cells, which is believed to compromise chondrocyte function and eventually cause cell death. To study the molecular mechanisms involved with the disease, we sought to develop an in vitro model that recapitulates the PSACH phenotype. Normal human chondrocytes were transfected with wildtype (wt-) COMP or with mutant COMP (D469del; mt-) recombinant adenoviruses and grown in a nonattachment redifferentiating culture system that provides an environment allowing formation of a differentiated chondrocyte nodule. Visualization of normal cells expressing COMP suggested the hallmarks of the PSACH phenotype. Mutant COMP expressed in normal cells was retained in enlarged rER cisternae, which also retained IX collagen (COL9) and matrilin-3 (MATN3). Although these proteins were secreted normally into the ECM of the wt-COMP nodules, reduced secretion of these proteins was observed in nodules composed of cells transfected with mt-COMP. The findings complement those found in chondrocytes from PSACH patient growth plates. This new model system allows for production of PSACH chondrocyte pathology in normal costochondral chondrocytes and can be used for future mechanistic and potential gene therapy studies.

An oncolytic adenovirus expressing soluble transforming growth factor-β type II receptor for targeting breast cancer: in vitro evaluation

In recent years, adenoviruses that selectively replicate in tumor cells have been developed. However, there is a tremendous need to improve their anticancer efficacy. We wish to investigate whether a strategy that combines the oncolytic effects of an adenoviral vector with simultaneous expression of soluble form of transforming growth factor-beta type II receptor (sTGFbetaRII) offers a therapeutic advantage. We chose to target TGF-betas because they play a pivotal role in late-stage tumorigenesis by enhancing tumor invasion and metastasis. A sTGFbetaRII cDNA was cloned in conditionally replicating adenoviral vector rAd-sTRII and in a replication-deficient adenovirus Ad-sTRII. Infection of MDA-MB-231 breast cancer cells with rAd-sTRII or Ad-sTRII followed by Western blot analysis indicated the expression of diffused glycosylated forms of sTGFbetaRII that were also secreted into the extracellular medium. The secreted proteins were shown to bind with TGF-beta and antagonize TGF-beta-induced p38 mitogen-activated protein kinase activity. However, marked differences in the replication potential of rAd-sTRII and Ad-sTRII were observed in breast tumor cells. Infection of MDA-MB-231 cells with rAd-sTRII resulted in cytotoxicity and significant increase in the adenoviral titers that were comparable with a wild-type adenovirus dl309. However, Ad-sTRII was much less toxic to the tumor cells, and the viral titers of Ad-sTRII remained relatively unchanged. These results suggest that the infection of breast tumor cells with conditionally replicating adenoviral vector rAd-sTRII produced sTGFbetaRII that can abrogate TGF-beta signaling while maintaining the replication potential of the virus, indicating that rAd-sTRII could be a potential anticancer agent.

Adenovirus Infection Dramatically Augments Lipopolysaccharide-Induced TNF Production and Sensitizes to Lethal Shock

We observed a remarkable synergism of adenoviruses and LPS in triggering the production of TNF in intact animals. We found that in mice pre-exposed to adenoviruses, LPS injections generated extremely high levels of TNF with altered kinetics. The elevated TNF synthesis stemmed mostly from posttranscriptional up-regulation of TNF production, although transcription of the TNF gene was also induced. Adenoviruses and LPS exhibited a significant but less dramatic synergism in the induction of IL-6, IFN-gamma, and NO. Only marginal changes were detected in the synthesis of a panel of other cytokines. Different serotypes of the virus showed practically identical effects. As deletion mutants lacking indispensable viral genes or UV inactivated virions exhibited similar activities as the infectious, wild-type virus, it seems unlikely that the viral genome plays any significant role in the phenomenon. Published data indicate that other viruses also show some kind of synergism with LPS, although by different cellular mechanisms. T cells and their IFN-gamma production--crucial in the synergism of influenza viruses and LPS--were dispensable in our experiments. We suggest that the phenomenon is probably a general one: an overlap between different molecular mechanisms detecting bacterial and viral pathogens and inducing mediators of nonspecific cell-mediated host defense. The synergism of viruses and LPS (bacteria) could be a concern in medical practice as well as in gene therapy experiments with high doses of recombinant adenoviruses.

Novel molecular approaches to cystic fibrosis gene therapy

Gene therapy holds promise for the treatment of a range of inherited diseases, such as cystic fibrosis. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of cystic fibrosis pulmonary disease has proved elusive. There are many reasons for this lack of progress, both macroscopically in terms of airway defence mechanisms and at the molecular level with regard to effective cDNA delivery. This review of approaches to cystic fibrosis gene therapy covers these areas in detail and highlights recent progress in the field. For gene therapy to be effective in patients with cystic fibrosis, the cDNA encoding the cystic fibrosis transmembrane conductance regulator protein must be delivered effectively to the nucleus of the epithelial cells lining the bronchial tree within the lungs. Expression of the transgene must be maintained at adequate levels for the lifetime of the patient, either by repeat dosage of the vector or by targeting airway stem cells. Clinical trials of gene therapy for cystic fibrosis have demonstrated proof of principle, but gene expression has been limited to 30 days at best. Results suggest that viral vectors such as adenovirus and adeno-associated virus are unsuited to repeat dosing, as the immune response reduces the effectiveness of each subsequent dose. Nonviral approaches, such as cationic liposomes, appear more suited to repeat dosing, but have been less effective. Current work regarding non-viral gene delivery is now focused on understanding the mechanisms involved in cell entry, endosomal escape and nuclear import of the transgene. There is now increasing evidence to suggest that additional ligands that facilitate endosomal escape or contain a nuclear localization signal may enhance liposome-mediated gene delivery. Much progress in this area has been informed by advances in our understanding of the mechanisms by which viruses deliver their genomes to the nuclei of host cells.

Evaluation of promoters for foreign gene expression in the E3 region of bovine adenovirus type-3

In order to optimize foreign gene expression in the E3 region of BAdV-3, we constructed full-length BAdV-3 genomic DNA clones containing a reporter gene (truncated glycoprotein gD of bovine herpesvirus 1, gDt), under the control of exogenous promoters inserted in either direction in the E3 region. Irrespective of exogenous transcriptional elements, viable recombinant BAdV-3 viruses could only be isolated when the gDt expression cassettes were inserted in the E3 region parallel to the direction of E3 transcription. Introduction of exogenous promoters altered the kinetics and amount of gDt expression in recombinant BAdV-3 infected cells. Interestingly, recombinant BAdV-3 containing gDt under the control of the mouse cytomegalovirus (MCMV) immediate early (IE) promoter expressed gDt more efficiently with noticeable differences in the amount and kinetics of expression. Moreover, animals immunized with recombinant BAdV-3 expressing gDt under the control of the MCMV IE promoter induced strong immune responses with reduced pathological lesions. These results suggest that BAdV vectors with the MCMV IE promoter may be useful for transgene expression and the development of vaccines.

Decreased tumorigenic potential of EphA2-overexpressing breast cancer cells following treatment with adenoviral vectors that express EphrinA1

The EphA2 receptor tyrosine kinase is frequently overexpressed in invasive breast cancer cells. Moreover, these malignant cells have unstable cell-cell contacts, which preclude EphA2 from interacting with its ligand, EphrinA1, which is anchored to the membrane of adjacent cells. This defect is important because ligand binding causes EphA2 to transmit signals that negatively regulate tumor cell growth and survival, whereas the absence of ligand binding favors these same behaviors. In our present study, human adenoviral type 5 (HAd) vectors were engineered to express secreted-forms of EphrinA1. These vectors were used to infect MDA-MB-231 human breast cancer cells, or MCF-10A human breast epithelial cells providing matched controls. Infection with HAd-EphrinA1-Fc (HAd vector expressing extracellular domain of human EphrinA1 attached to Fc portion of human IgG1 heavy chain) caused increased EphA2 activation and turnover and consequently decreased tumor cell viability in soft agar assays. Consistent with this observation, infection of MDA-MB-231 cells with HAd-EphrinA1-Fc prevented tumor formation in xenograft models. Furthermore, therapeutic modeling via intratumoral inoculation revealed that HAd-EphrinA1-Fc significantly inhibited subsequent tumor growth as compared to matched controls. These results suggest that targeting of EphA2 with adenoviral vectors may have therapeutic value.

Single mucosal, but not parenteral, immunization with recombinant adenoviral-based vaccine provides potent protection from pulmonary tuberculosis

Bacillus Calmette-Guerin (BCG) vaccine has failed to control the global tuberculosis (TB) epidemic, and there is a lack of safe and effective mucosal vaccines capable of potent protection against pulmonary TB. A recombinant replication-deficient adenoviral-based vaccine expressing an immunogenic Mycobacterium tuberculosis Ag Ag85A (AdAg85A) was engineered and evaluated for its potential to be used as a respiratory mucosal TB vaccine in a murine model of pulmonary TB. A single intranasal, but not i.m., immunization with AdAg85A provided potent protection against airway Mycobacterium tuberculosis challenge at an improved level over that by cutaneous BCG vaccination. Systemic priming with an Ag85A DNA vaccine and mucosal boosting with AdAg85A conferred a further enhanced immune protection which was remarkably better than BCG vaccination. Such superior protection triggered by AdAg85 mucosal immunization was correlated with much greater retention of Ag-specific T cells, particularly CD4 T cells, in the lung and was shown to be mediated by both CD4 and CD8 T cells. Thus, adenoviral TB vaccine represents a promising novel vaccine platform capable of potent mucosal immune protection against TB. Our study also lends strong evidence that respiratory mucosal vaccination is critically advantageous over systemic routes of vaccination against TB.

Protection of weaned pigs by vaccination with human adenovirus 5 recombinant viruses expressing the hemagglutinin and the nucleoprotein of H3N2 swine influenza virus

Swine influenza virus (SIV), subtype H3N2, is a recent reassortant virus that emerged in 1998 in North American swine causing severe respiratory and reproductive disease. In this study, two replication-defective adenovirus recombinants were developed as potential vaccines against H3N2 influenza viruses. Three groups of 3-week-old pigs (10 pigs per group) were vaccinated intramuscularly (IM) with the recombinants; one group was vaccinated with the recombinant adenovirus expressing the influenza virus H3 hemagglutinin (HA) protein, one group was vaccinated with the recombinant adenovirus expressing the nucleoprotein (NP), and one group was vaccinated with both recombinants in a mixture. Two additional control groups (10 pigs per group) were included in the animal trial. One control group was challenged with a virulent H3N2 field strain and one control group remained unchallenged. The results showed that pigs in the groups given the recombinant adenovirus expressing HA alone and HA plus NP developed high levels of virus-specific hemagglutination-inhibition (HI) antibody by 4 weeks post vaccination. Pigs in the group vaccinated with both recombinant viruses in a mixture were completely protected. Complete protection was shown by the lack of nasal shedding of virus following challenge and by the lack of lung lesions at 1 week following the challenge infection. Thus, replication-incompetent adenovirus vaccines given simultaneously to pigs are efficacious for SIV and have the additional advantage over commercial vaccines that suckling piglets have no pre-existing maternally-derived antibody to block early life vaccination.

Functional expression of thymidine kinase in human leukaemic and colorectal cells, delivered as EGFP fusion protein by herpesvirus saimiri-based vector

Herpesvirus saimiri (HVS) has the capacity to incorporate large amounts of heterologous DNA and can infect many different human cell types. To develop its potential as a gene therapy vector, we cloned herpes simplex virus thymidine kinase (TK) gene into the HVS genome in the form of an enhanced green fluorescent protein (EGFP) fusion protein, using a cosmid-based approach. At multiplicity of infection = 100 over 90% of human leukemic K562 and Jurkat cells were transduced with HVS/EGFP-TK. Conditions of no selective pressure expression were maintained at > 92% per cell division. Expression of the EGFP-TK fusion protein rendered transfected leukaemic cells sensitive to cytotoxic treatment with the prodrugs ganciclovir (GCV) and (E)-5-(2-bromovinyl)-2'deoxyuridine (BVDU) at concentrations as low as 10 ng/ml. The viral vector was also screened against a panel of colorectal and pancreatic carcinoma cell lines. All cell lines were transduced but showed a range of sensitivity to infection. Three of the most easily transduced cell lines: Mia PaCa, HCT116 and SW948 transduced with HVS/EGFP-TK were effectively ablated by subsequent treatment with GCV or BVDU. Our results show that in its current form HVS/EGFP-TK could be utilized as an antitumour agent, or it could be developed further by inclusion of a therapeutic gene, with TK presence ensuring a mechanism of controlled removal of modified cells when no longer necessary. These results suggest that HVS/EGFP-TK has a great potential for a number of gene therapy applications.

Intralesional Injection of Adenovirus Encoding CC Chemokine Ligand 16 Inhibits Mammary Tumor Growth and Prevents Metastatic-Induced Death after Surgical Removal of the Treated Primary Tumor

The CC chemokine ligand (CCL)16 exerts chemotactic activity on human monocytes and lymphocytes. Although no murine homologous has been defined, the TSA mouse adenocarcinoma cells engineered to express human CCL16 are rapidly rejected by syngenic mice. An adenovirus encoding CCL16 (AdCCL16) was generated using a Cre-Lox-based system and was used to determine whether this chemokine might also block pre-existing tumors. Both recombinant and viral CCL16 showed in vitro chemotactic activity for murine CD4(+) and CD8(+) lymphocytes and dendritic cells (DC). AdCCL16, but not the control empty vector, when injected in established nodules significantly delayed tumor growth. Immunohistochemistry revealed accumulation of CD4(+) and CD8(+) T cells and DC in the treated tumors as well as in draining lymph nodes. DC from such lymph nodes stimulated IFN-gamma by a T cell clone specific for the known TSA tumor-associated Ag (TAA), suggesting the tumor origin of these cells. Lymphocytes from the same nodes showed specific CTL activity against TSA tumor cells and their immunodominant TAA peptide. Antitumor activity required CD4, CD8, and IFN-gamma production, as shown using subset-depleted and knockout mice. Despite the robust and rapid immune response triggered by intratumoral injection of AdCCL16, the lesions were not completely rejected; however, the same treatment given before surgical excision of primary lesions prevented metastatic spread and cured 63% of mice bearing the 4T1 mammary adenocarcinoma, which is perhaps the most compelling model of spontaneous metastasis.

Five novel mutations in the lysosomal sialidase gene (NEU1) in type II sialidosis patients and assessment of their impact on enzyme activity and intracellular targeting using adenovirus-mediated expression

Sialidosis is an autosomal recessive disease resulting from a deficiency of lysosomal sialidase. Type II sialidosis is a rare disease characterized clinically by hydrops fetalis, hepatosplenomegaly, and severe psychomotor retardation. Genomic DNA from four unrelated sialidosis patients was screened for mutations within the sialidase gene NEU1. Five novel mutations were identified. Four are missense and one is nonsense: c.674G>C (p.R225P), c.893C>T (p.A298V), c.3G>A (p.M1?), c.941C>G (p.R341G), and c.69G>A (p.W23X). We have used our findings and diagnostic tools to confirm the presence of a homozygous null allele in a neonate sibling. Recombinant adenoviruses expressing the mutant sialidase alleles in primary cell cultures were utilized to assess the impact of each mutation on enzyme activity and intracellular localization. None of the mutant alleles expressed significant enzymatic activity. The p.R341G mutation exerts its pathological effect by perturbing substrate binding, while the p.A298V and p.R225P mutations appear to impair the folding of the sialidase enzyme. Our findings point to mutation-sensitive amino acids involved in catalytic function or structural stability and indicate the potential utility of these mutations for molecular diagnosis of this rare disease.

Replication-defective adenoviral vaccine vector for the induction of immune responses to dengue virus type 2

A recombinant replication-defective adenovirus vector that can overexpress the ectodomain of the envelope protein of dengue virus type 2 (NGC strain) has been constructed. This virus was immunogenic in mice and elicited dengue virus type 2 specific B- and T-cell responses. Sera from immunized mice contained neutralizing antibodies that could specifically recognize dengue virus type 2 and neutralize its infectivity in vitro, indicating that this approach has the potential to confer protective immunity. In vitro stimulation of splenocytes (from immunized mice) with dengue virus type 2 resulted in a significant proliferative response accompanied by the production of high levels of gamma interferon but did not show significant changes in interleukin-4 levels. This is suggestive of a Th1-like response (considered to be important in the maturation of cytotoxic T lymphocytes that are essential for the elimination of virus-infected cells). The data show that adenovirus vectors offer a promising alternative strategy for the development of dengue virus vaccines.

Evasion of the immune system by adenoviruses

Human adenoviruses (Ads) have the ability to transform primary cells, and certain Ads, the subgenus A adenoviruses such as Ad12, induce tumours in immunocompetent rodents. The oncogenic phenotype of the subgenus A adenoviruses is determined by the viral E1A oncogene. In order to generate tumours, Ad12-transformed cells must evade the cellular immune system of the host. Ad12 E1A gene products mediate transcriptional repression of several genes in the major histocompatibility complex (MHC) involved in antigen processing and presentation, resulting in evasion of cytotoxic T lymphocyte (CTL) killing of transformed cells. In this review, the molecular mechanisms of E1A-mediated transcriptional repression of MHC gene expression are described. In addition, evasion of natural killer (NK) cell killing by Ad-transformed cells is also considered.

Mechanisms of E3 Modulation of Immune and Inflammatory Responses

Adenoviruses contain genes that have evolved to control the host immune and inflammatory responses; however, it is not clear whether these genes function primarily to facilitate survival of the virus during acute infection or during its persistent phase. These issues have assumed greater importance as the use of adenoviruses as vectors for gene therapy has been expanded. This review will focus on the mechanism of immune evasion mediated by the proteins encoded within the early region 3 (E3) transcription region, which affect the functions of a number of cell surface receptors including Fas, intracellular cell signaling events involving NF-kappaB, and the secretion of pro-inflammatory molecules such as chemokines. The successful use of E3 genes in facilitating allogeneic transplantation and in preventing autoimmune diabetes in several transgenic mouse models will also be described.

Human cytomegalovirus US2 causes similar effects on both major histocompatibility complex class I and II proteins in epithelial and glial cells

The human cytomegalovirus (HCMV) glycoprotein US2 specifically binds to major histocompatibility complex (MHC) class I heavy chain (HC) and class II proteins DRalpha and DMalpha, triggering their degradation by proteasomes. Effects of US2 on class II proteins were originally characterized in HCMV- or adenovirus vector-infected U373 astroglioma cells. Here, we have extended characterization of US2-mediated degradation of class II DRalpha to two other cell lines, including biologically relevant epithelial cells. Comparison of the effects of US2 in cells expressing both class I and II proteins demonstrated only a slight preference for class I HC. Moreover, US2 caused degradation of DRalpha and DMalpha when these proteins were expressed by transfection without DRbeta, invariant chain (Ii), or DMbeta. Therefore, US2 binds to alpha chains of DR and DM and triggers endoplasmic reticulum degradation without formation of class II DR alphabeta/Ii or DM alphabeta complexes. Similar levels of degradation of class II alpha were observed in cells expressing vastly different amounts of class II, suggesting that cellular factors, other than class II, were limiting. We concluded that US2 has broad effects in a variety of cells that express both class I and II proteins and is relevant to HCMV infection in vivo.

Modified apoptotic molecule (BID) reduces hepatitis C virus infection in mice with chimeric human livers

Hepatitis C virus (HCV) encodes a polyprotein consisting of core, envelope (E1, E2, p7), and nonstructural polypeptides (NS2, NS3, NS4A, NS4B, NS5A, NS5B). The serine protease (NS3/NS4A), helicase (NS3), and polymerase (NS5B) constitute valid targets for antiviral therapy. We engineered BH3 interacting domain death agonist (BID), an apoptosis-inducing molecule, to contain a specific cleavage site recognized by the NS3/NS4A protease. Cleavage of the BID precursor molecule by the viral protease activated downstream apoptotic molecules of the mitochondrial pathway and triggered cell death. We extended this concept to cells transfected with an infectious HCV genome, hepatocytes containing HCV replicons, a Sindbis virus model for HCV, and finally HCV-infected mice with chimeric human livers. Infected mice injected with an adenovirus vector expressing modified BID exhibited HCV-dependent apoptosis in the human liver xenograft and considerable declines in serum HCV titers.

The role of capsid-endothelial interactions in the innate immune response to adenovirus vectors

Adenovirus (Ad) vectors can produce inflammatory responses at high doses. Intravenous administration of an Ad vector expressing green fluorescent protein (AdGFP) to naive mice induced a biphasic pattern of liver cytokine/chemokine gene expression over 7 days. Tumor necrosis factor alpha (TNF-alpha), macrophage inflammatory protein 2 (MIP-2), and interferon gamma-inducible protein 10 (IP-10) genes were upregulated, with two distinct peaks of mRNA expression occurring at 6 hr and 5 days. The administration of transcription-defective AdGFP particles induced the early but not the late peak of chemokine/cytokine gene expression, confirming that Ad vector-induced inflammation is capsid dependent in the early phase and transcription dependent in the late phase. To determine the role of adenoviral capsid motifs in the early phase, capsid-modified Ad vectors were employed. The intravenous administration of the RGD-deleted Ad vector AdL.PB*, the fiber mutant AdL.F*, or the double mutant AdL.F*PB* induced similar levels of cytokine/chemokine expression compared with the wild-type vector AdLuc. Kupffer cell blockade significantly reduced liver TNF-alpha, MIP-2, and IP-10 gene expression and liver inflammation after the administration of AdL.PB* or AdL.F*PB*. Fluorescence microscopy of AdLuc- and AdL.PB*-transduced liver at 1 hr revealed localization of Ad vectors to liver sinusoids in Kupffer cell-depleted mice. AdL.PB* induced less E-selectin and VCAM-1 gene expression in liver, confirming reduced endothelial activation in mice receiving RGD-deleted Ad vectors. In vitro studies of endothelial cells demonstrated reduced transduction and endothelial activation by AdL.PB* compared with AdLuc. These results demonstrate that adenovirus capsid RGD motifs are required for efficient transduction and endothelial cell activation. Altering vector tropism represents a feasible strategy to modulate the innate response to Ad vectors in nontargeted tissues.

Gene therapy for prostate cancer: toxicological profile of four HSV-tk transducing adenoviral vectors regulated by different promoters

Adenoviral vector delivery of the Herpes simplex virus thymidine kinase (HSV-tk) gene in combination with the prodrug ganciclovir (GCV) has been tested in phase I clinical trials for prostate cancer and found to exhibit a satisfactory toxicity profile. We have developed additional adenoviral vectors with differing promoters to optimize the expression profile and in the present study evaluate the potential systemic toxicity of these vectors. Four recombinant adenoviral vectors that express the HSV-tk gene were generated using three different promoters: CMV (leftward orientation); RSV (both rightward and leftward orientation); and the mouse caveolin-1 (cav-1) promoter (leftward orientation). Efficacy was determined in vitro by cytotoxicity assays in a mouse prostate cancer cell line, RM-9, and in vivo by treating orthotopic tumors. Potential toxicity was evaluated from liver histology and apoptotic cell counts and enzyme levels in the serum following intravenous adenoviral vector injection. Although there were differences in HSV-tk expression at the protein level among the four vectors there were no significant differences in in-vitro cytotoxicity studies with GCV or in vivo in tumor growth suppression of an orthotopic mouse prostate cancer model in GCV treated mice. Intravenous delivery of high doses of all adenoviral vectors lead to abnormalities in liver function as measured by specific serum markers and histological evaluation of liver tissue and increased levels of apoptosis in the liver. These abnormalities were most prevalent with the vector containing the CMV promoter and the rightward oriented RSV promoter. They were least prevalent in the vector regulated by the cav-1 promoter. Upregulation of specific chemokines, MIP-2 and MIP-1beta was correlated with apoptotic counts. Our results demonstrate that comprehensive toxicological analysis of adenoviral vectors provides internally consistent information that can differentiate vectors with comparable efficacy based on toxicity. In these studies vectors with the cav-1 promoter-driven and leftward RSV-driven HSV-tk gene demonstrated minimal toxicities with cytotoxic effectiveness comparable to more toxic vectors. Our studies further suggest that promoter selection can influence the toxic effects of an adenoviral gene therapy vector.

Gene Therapy for Pediatric Cancer: State of the Art and Future Perspectives

While modern treatments have led to a dramatic improvement in survival for pediatric malignancy, toxicities are high and a significant proportion of patients remain resistant. Gene transfer offers the prospect of highly specific therapies for childhood cancer. "Corrective" genes may be transferred to overcome the genetic abnormalities present in the precancerous cell. Alternatively, genes can be introduced to render the malignant cell sensitive to therapeutic drugs. The tumor can also be attacked by decreasing its blood supply with genes that inhibit vascular growth. Another possible approach is to modify normal tissues with genes that make them more resistant to conventional drugs and/or radiation, thereby increasing the therapeutic index. Finally, it may be possible to attack the tumor indirectly by using genes that modify the behavior of the immune system, either by making the tumor more immunogenic, or by rendering host effector cells more efficient. Several gene therapy applications have already been reported for pediatric cancer patients in preliminary Phase 1 studies. Although no major clinical success has yet been achieved, improvements in gene delivery technologies and a better understanding of mechanisms of tumor progression and immune escape have opened new perspectives for the cure of pediatric cancer by combining gene therapy with standard therapeutic available treatments.

Development of an Ad7 cosmid system and generation of an Ad7deltaE1deltaE3HIV(MN) env/rev recombinant virus

A strategy to circumvent immune responses to adenovirus (Ad) resulting from natural infection or repeated vector administrations involves sequential use of vectors from different Ad serotypes. To further develop an Ad-HIV recombinant AIDS vaccine approach, a replication-defective recombinant Ad from a non-subgroup C virus was required. Using a cosmid system, we generated an Ad7deltaE1deltaE3HIV(MN) env/rev recombinant virus and compared expression of the inserted HIV genes with a similarly constructed replication-competent Ad7deltaE3HIV(MN)env/rev recombinant. Ad7deltaE1deltaE3HIV(MN)env/rev expressed both HIV env and rev gene products. The envelope protein was correctly processed and functional, mediating syncytia formation of Ad7deltaE1deltaE3HIV(MN) env/rev-infected cells and CD4(+) T lymphocytes. Ad7deltaE1deltaE3HIV(MN)env/rev could be amplified on 293-ORF6 cells, containing the E4 ORF6 gene, shown earlier to support production of an Ad7 vector lacking the E1a gene. The utility of this cell line is now extended to the production of replication-defective Ad7 recombinants lacking E1a, E1b, and protein IX genes. Sequential immunizations with Ad-HIV recombinants based in different Ad serotypes have been shown to effectively elicit both humoral and cellular HIV-specific immune responses. The recombinant Ad7deltaE1deltaE3HIV(MN)env/rev will be useful in such AIDS vaccine strategies. Further, these studies have created new cosmid vectors that can be applied to generation of single- or double-deleted Ad7 recombinants with foreign genes inserted into the E1 and/or E3 regions.

Gutted adenoviral vector growth using E1/E2b/E3-deleted helper viruses

BACKGROUND

Helper-dependent, or gutted, adenoviruses (Ad) lack viral coding sequences, resulting in reduced immunotoxicity compared with conventional Ad vectors. Gutted Ad growth requires a conventional Ad to supply replication and packaging functions in trans. Methods that allow high-titer growth of gutted vectors while reducing helper contamination, and which use safer helper viruses, will facilitate the use of gutted Ad vectors in vivo.

METHODS

Replication-defective helper viruses were generated that are deleted for Ad E1, E2b and E3 genes, but which contain loxP sites flanking the packaging signal. Complementing Ad packaging cell lines (C7-cre cells) were also generated by transfecting 293 cells with the Ad E2b genes encoding DNA polymerase and pre-terminal protein, and with a cre-recombinase plasmid.

RESULTS

We show that C7-cre cells allow efficient production of gutted Ad using deltaE1 + deltaE2b + deltaE3 helper viruses whose growth can be limited by cre-loxP-mediated excision of the packaging signal. Gutted Ad vectors carrying approximately 28 kb cassettes expressing full-length dystrophin were prepared at high titers, similar to those obtained with E2b+ helpers, with a resulting helper contamination of <1%.

CONCLUSIONS

These new packaging cell lines and helper viruses offer several significant advantages for gutted Ad vector production. They allow gutted virus amplification using a reduced number of passages, which should reduce the chances of selecting rearranged products. Furthermore, the residual helper contamination in gutted vector preparations should be less able to elicit immunological reactions upon delivery to tissues, since E2b-deleted vectors display a profound reduction in viral gene expression.

Comparative sequence analysis of the largest E1A proteins of human and simian adenoviruses

The early region 1A (E1A) gene is the first gene expressed after infection with adenovirus and has been most extensively characterized in human adenovirus type 5 (hAd5). The E1A proteins interact with numerous cellular regulatory proteins, influencing a variety of transcriptional and cell cycle events. For this reason, these multifunctional proteins have been useful as tools for dissecting pathways regulating cell growth and gene expression. Despite the large number of studies using hAd5 E1A, relatively little is known about the function of the E1A proteins of other adenoviruses. In 1985, a comparison of E1A sequences from three human and one simian adenovirus identified three regions with higher overall levels of sequence conservation designated conserved regions (CR) 1, 2, and 3. As expected, these regions are critical for a variety of E1A functions. Since that time, the sequences of several other human and simian adenovirus E1A proteins have been determined. Using these, and two additional sequences that we determined, we report here a detailed comparison of the sequences of 15 E1A proteins representing each of the six hAd subgroups and several simian adenoviruses. These analyses refine the positioning of CR1, 2, and 3; define a fourth CR located near the carboxyl terminus of E1A; and suggest several new functions for E1A.

Recombinant adenovirus vectors for gene therapy and clinical trials

In the last decade adenovirus (AdV) vectors have emerged as promising technology in gene therapy. They have been used for genetic modification of a variety of somatic cells in vitro and in vivo. They have been widely used as gene delivery vectors in experiments both with curative and preventive purposes. AdV vectors have been used in the experimental and in some extent in the clinical gene therapy of a variety of cancers. The combination of recombinant AdV technology with chemotherapy (pro drug system) seems to be promising, too. AdV vectors offer several advantages over other vectors. Replication defective vectors can be produced in very high titers (10(11) pfu/ml) thus allowing a substantially greater efficiency of direct gene transfer; they have the capacity to infect both replicating and nonreplicating (quiescent) cells from a variety of tissues and species. Several important limitations of adenovirus mediated gene transfer are also known, such as the relatively short-term (transient) expression of foreign genes, induction of the host humoral and cellular immune response to viral proteins and viral infected cells, which may substantially inhibit the effect of repeated treatment with AdV vectors, the limited cloning capacity and the lack of target cell specificity. However, the well-understood structure, molecular biology and host cell interactions of AdV-s offer some potential solutions to these limitations.

Virus-based vectors for human vaccine applications

Vaccinology has experienced a dramatic resurgence recently, as traditional methodologies of using attenuated live pathogens or inactivated whole pathogens have been either ineffective or are not an acceptable risk for several disease targets, including HIV and Hepatitis C. Gene-based vaccines can stimulate potent humoral and cellular immune responses, and viral vectors might be an efficient strategy for both delivery of antigen-encoding genes, as well as facilitating and enhancing antigen presentation. Vectors derived from diverse viruses with distinct tropism and gene expression strategies have been developed, and are being evaluated in preclinical and clinical vaccine studies. Virus-based vaccines represent a promising approach for vaccines against infectious and malignant disease.

The nonapoptotic pathway mediating thymidine kinase/ganciclovir toxicity is reduced by signal from adenovirus type 5 early region 4

Suicide gene therapy using thymidine kinase/ganciclovir (Tk/GCV) yields highly variable results, in vitro and in vivo. To determine the reasons for such variations, we examined cellular mechanisms mediating its cytotoxicity in view of their interaction with adenoviral vectors (Ad) used for gene delivery. Here we report that the presence of adenovirus early region 4 (AdE4)-encoded viral proteins significantly decreases toxicity of Tk/GCV. The E4 region-encoded proteins exerted this effect when found on the adenoviral delivery vector and when provided in trans in Tk retrovirally transduced cells. The apoptotic response was assessed in GCV-treated cells. The decrease in toxicity caused by AdE4 proteins was not correlated with apoptotic response, as measured by internucleosomal DNA degradation and TUNEL assays. Our results indicate that apoptosis is not the only mechanism of Tk/GCV-induced cell death and that other mechanisms equally important in determining the success of such a gene therapy strategy should be considered when optimizing treatment conditions.

Review: conformation and folding of novel beta-structural elements in viral fiber proteins: the triple beta-spiral and triple beta-helix

Apart from alpha-helical coiled coils and the collagen triple helices, fibrous proteins can contain beta-structure in various conformations. Elongated enzymes such as pectate lyase and the bacteriophage P22 tailspike protein contain single-stranded beta-helices. Virus and bacteriophage fibers, which are often trimeric, have been shown to contain novel triple-stranded beta-structures such as the triple beta-spiral and the triple beta-helix. The conformation and folding of viral fibers containing beta-structure are discussed.

Analysis of early region 1 of porcine adenovirus type 3

To identify the proteins encoded by the porcine adenovirus 3 (PAV-3) E1 region, rabbit antisera were prepared using a bacterial fusion protein encoding E1A, E1B(small), or E1B(large) protein. Sera against E1A, E1B(small), and E1B(large) immunoprecipitated a protein of 35, 23, and 53 kDa, respectively, in in vitro translated and transcribed mRNA and PAV-3 infected cells. To determine the role of E1 proteins in PAV-3 replication, we constructed vectors with a deletion(s) in the E1 region. Mutant PAV211, containing deletions in E1A and E3, grew to titers similar to wild-type in VIDO R1 cells (E1A complementing) but not in swine testicular (ST) cells. No early protein (E1B(small), DNA binding protein) expression could be detected in PAV211 infected ST cells by Western blots. Mutant PAV212, containing deletions in E1B(small) and E3, grew to wild-type titers in VIDO R1 or ST cells. These deletions were successfully rescued, resulting in recombinant PAV214, containing deletions in E1A, E1B(small), and E3. However, mutant PAV-3, containing a triple stop codon inserted in the E1B(large) coding sequence, could not be isolated. Next, we constructed a recombinant PAV216 by inserting the green fluorescent protein gene flanked by a promoter and a poly(A) in the E1A region of the PAV214 genome. Both PAV214 and PAV216 replicate as efficiently as wild-type in VIDO R1 cells. These results suggested that (a) E1A is essential for virus replication and is required for the activation of other PAV-3 early genes, (b) E1B(small) is not essential for replication of PAV-3, and (c) E1B(large) is essential for virus replication. Moreover, the PAV216 vector can be used for the expression of a transgene.

In vivo episomal maintenance of a herpesvirus saimiri-based gene delivery vector

Herpesvirus saimiri (HVS) has several properties that make it amenable to development as a gene delivery vector. HVS offers the potential to incorporate large amounts of heterologous DNA and infect a broad range of human cell lines. Upon infection the viral genome can persist by virtue of episomal maintenance and stably maintains heterologous gene expression. Here we report an evaluation of the in vivo properties of HVS, with a view to its development as a gene delivery system. We demonstrate for the first time, the long-term persistence of the HVS genome in tumour xenografts generated from HVS-infected human carcinoma cell lines. The HVS-based vector remained latent in the xenograft without spreading to other organs. Moreover, the long-term in vivo maintenance of the HVS genome, as a nonintegrated circular episome, provided efficient sustained expression of a heterologous transgene. These in vivo results suggest that HVS-based vectors have potential for gene therapy applications.

Adenovirus vector designed for expression of toxic proteins

To construct recombinant adenoviruses expressing biologically active proteins may be impossible, or result in a significant reduction in virus yield, if the protein expressed has an inhibitory effect on virus replication or cellular growth. To overcome this problem, we previously designed adenovirus vectors expressing foreign proteins from inducible promoters. However, during our work with a replication-deficient virus expressing the ASF/SF2 splicing factor from a progesterone antagonist-inducible gene cassette, we discovered that ASF/SF2 was expressed at a significant level in the 293 producer cell line, even in the absence of inducer. 293 cells code for adenovirus E1A and E1B proteins and thus support the growth of E1-deficient adenoviruses. Here we show that this background ASF/SF2 expression results from a low level of E1A-mediated transactivation of the basal promoter driving transgene expression. To overcome the problem of leaky expression, we reconstructed a novel gene cassette that combines an inducible promoter and a Lac repressor protein-based block to reduce transcriptional elongation. We show that this novel vector system dramatically reduced background transgene expression and therefore should be useful for the rescue and propagation of high-titer stocks of recombinant adenoviruses expressing toxic proteins.

Gene therapy for paediatric leukaemia

Improvements in the chemotherapeutic and transplant regimens have had a significant impact in improving survival rates for paediatric leukaemia. However, there are still important problems to address including what options are available for patients with chemoresistant disease and what strategies are available to avoid the concerns regarding the toxicity associated with highly cytotoxic treatment regimens. Gene therapy and immunotherapy protocols hold great promise. Using gene transfer of a marker gene, a number of biological issues in the therapy of leukaemia have been addressed. For example, by gene marking autologous bone marrow grafts it has been possible to demonstrate that infused marrow contributes to relapse in acute and chronic myeloid leukaemias. In the allogeneic transplant setting, genetically modified T-cells have proven valuable for the prophylaxis and treatment of viral diseases and may have an important role in preventing or treating disease relapse. Gene transfer is also being used to modify tumour function, enhance immunogenicity, and confer drug-resistance to normal haematopoietic stem cells. With the continued scientific advancements in this field, gene therapy will almost certainly have a major impact on the treatment of paediatric leukaemia in the future.

Future of adenoviruses in the gene therapy of arthritis

Recombinant adenoviruses are straightforward to produce at high titres, have a promiscuous host-range, and, because of their ability to infect nondividing cells, lend themselves to in vivo gene delivery. Such advantages have led to their widespread and successful use in preclinical studies of arthritis gene therapy. While adenoviral vectors are well suited to 'proof of principle' experiments in laboratory animals, there are several barriers to their use in human studies at this time. Transient transgene expression limits their application to strategies, such as synovial ablation, which do not require extended periods of gene expression. Moreover, there are strong immunological barriers to repeat dosing. In addition, safety concerns predicate local, rather than systemic, delivery of the virus. Continued engineering of the adenoviral genome is producing vectors with improved properties, which may eventually overcome these issues. Promising avenues include the development of 'gutted' vectors encoding no endogenous viral genes and of adenovirus-AAV chimeras. Whether these will offer advantages over existing vectors, which may already provide safe, long-term gene expression following in vivo delivery, remains to be seen.