Systemic interleukin-6 responses following administration of adenovirus gene transfer vectors to humans by different routes

Cycloastragenol reduces inflammation in CLP-induced septic MICE by suppressing TLR4 signaling pathways

BACKGROUND

Aggressive systemic inflammation due to activation of macrophage-derived excessive immune responses is a critical cause of sepsis leading to clinical death. The effect of cycloastragenol (CAG) on cecal ligation and puncture (CLP)-induced systemic inflammation in mice with sepsis and the underlying mechanism are still unknown.

PURPOSE

Here, we firstly investigated the ameliorative functions of CAG in CLP-induced systemic inflammation in sepsis and LPS-mediated inflammatory response, and the impact of Toll-like receptor 4 (TLR4) pathway on the anti-inflammatory effects of CAG.

METHODS

The in vitro effect of CAG on RAW264.7 cells and THP-1-derived macrophages induced by LPS was detected with quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), and Western blotting (WB) assays. In addition, the association of TLR4-MD2 complex with CAG was measured through molecular docking, molecular dynamics (MD) simulation, surface plasmon resonance imaging (SPRi), cellular thermal shift assay (CETSA), immunofluorescence and WB. A specific inhibitor of TLR4 receptor TAK-242 and a TLR4-encoding adenovirus were adopted for verifying the functions of CAG. Meanwhile, the in vivo effects of CAG on cardiopulmonary structure, inflammatory factors and survival of CLP-induced septic mice were analyzed through hematoxylin and eosin staining, qPCR, ELISA, and survival analysis.

RESULTS

CAG hindered the LPS-induced production of inflammatory mediators like TNF-α, IL-6 and IL-1β within macrophages in vitro. It also inhibited MAPK and NF-κB pathway activation induced by binding of LPS to TLR4 receptor. As suggested by molecular docking results, the MD2-CAG binding energy was -9.53 kcal/mol. During the MD simulation, CAG could tightly bind to the binding pocket of MD2. SPRi revealed that the equilibrium dissociation constant (KD) value for CAG and TLR4 was 5.24× 10-9 M. Moreover, CAG enhanced the thermal stability of TLR4 by approximately 2.68 °C. It further inhibited the binding between LPS-488 and cell membrane receptors. These inhibitory effects of CAG could be partly reversed by TLR4 overexpression and could not increase by specifically blocking TLR4. In vivo, CAG attenuated cardiopulmonary injury and inflammation and improved survival in septic mice dose-dependently.

CONCLUSION

CAG exerts its anti-inflammatory activity through suppressing MAPK and NF-κB pathway activation caused by TLR4 activation and inhibiting inflammatory factor production dose-dependently.

Innate Immune Response to Viral Vectors in Gene Therapy

Viral vectors play a pivotal role in the field of gene therapy, with several related drugs having already gained clinical approval from the EMA and FDA. However, numerous viral gene therapy vectors are currently undergoing pre-clinical research or participating in clinical trials. Despite advancements, the innate response remains a significant barrier impeding the clinical development of viral gene therapy. The innate immune response to viral gene therapy vectors and transgenes is still an important reason hindering its clinical development. Extensive studies have demonstrated that different DNA and RNA sensors can detect adenoviruses, adeno-associated viruses, and lentiviruses, thereby activating various innate immune pathways such as Toll-like receptor (TLR), cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING), and retinoic acid-inducible gene I-mitochondrial antiviral signaling protein (RLR-MAVS). This review focuses on elucidating the mechanisms underlying the innate immune response induced by three widely utilized viral vectors: adenovirus, adeno-associated virus, and lentivirus, as well as the strategies employed to circumvent innate immunity.

Viral protein nanoparticles (Part 1): Pharmaceutical characteristics

Viral protein nanoparticles fill the gap between viruses and synthetic nanoparticles. Combining advantageous properties of both systems, they have revolutionized pharmaceutical research. Virus-like particles are characterized by a structure identical to viruses but lacking genetic material. Another type of viral protein nanoparticles, virosomes, are similar to liposomes but include viral spike proteins. Both systems are effective and safe vaccine candidates capable of overcoming the disadvantages of both traditional and subunit vaccines. Besides, their particulate structure, biocompatibility, and biodegradability make them good candidates as vectors for drug and gene delivery, and for diagnostic applications. In this review, we analyze viral protein nanoparticles from a pharmaceutical perspective and examine current research focused on their development process, from production to administration. Advances in synthesis, modification and formulation of viral protein nanoparticles are critical so that large-scale production of viral protein nanoparticle products becomes viable and affordable, which ultimately will increase their market penetration in the future. We will discuss their expression systems, modification strategies, formulation, biopharmaceutical properties, and biocompatibility.

Novel Therapeutic Approaches Targeting Post-Translational Modifications in Lung Cancer

Lung cancer is one of the most common cancers worldwide. It consists of two different subtypes: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Despite novel therapeutic options such as immunotherapy, only 20% of lung cancer patients survive the disease after five years. This low survival rate is due to acquired drug resistance and severe off-target effects caused by currently used therapies. Identification and development of novel and targeted therapeutic approaches are urgently required to improve the standard of care for lung cancer patients. Here, we describe the recent development of novel drug-delivery approaches, such as adenovirus, lipid nanoparticles, and PROTACs, that have been tested in clinical trials and experimentally in the context of fundamental research. These different options show that it is now possible to target protein kinases, phosphatases, ubiquitin ligases, or protein modifications directly in lung cancer to block disease progression. Furthermore, the recent acceptance of RNA vaccines using lipid nanoparticles has further revealed therapeutic options that could be combined with chemo-/immunotherapies to improve current lung cancer therapies. This review aims to compare recent advances in the pharmaceutical research field for the development of technologies targeting post-translational modifications or protein modifiers involved in the tumorigenesis of lung cancer.

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

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.

Cystic Fibrosis Gene Therapy: Looking Back, Looking Forward

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that encodes a cAMP-regulated anion channel. Although CF is a multi-organ system disease, most people with CF die of progressive lung disease that begins early in childhood and is characterized by chronic bacterial infection and inflammation. Nearly 90% of people with CF have at least one copy of the ΔF508 mutation, but there are hundreds of CFTR mutations that result in a range of disease severities. A CFTR gene replacement approach would be efficacious regardless of the disease-causing mutation. After the discovery of the CFTR gene in 1989, the in vitro proof-of-concept for gene therapy for CF was quickly established in 1990. In 1993, the first of many gene therapy clinical trials attempted to rescue the CF defect in airway epithelia. Despite the initial enthusiasm, there is still no FDA-approved gene therapy for CF. Here we discuss the history of CF gene therapy, from the discovery of the CFTR gene to current state-of-the-art gene delivery vector designs. While implementation of CF gene therapy has proven more challenging than initially envisioned; thanks to continued innovation, it may yet become a reality.

The analysis of innate immune response to adenovirus using antibody arrays

Even though natural infections with adenovirus (Ad) are largely harmless in humans, an intravenous Ad vector administration for gene delivery purposes, especially at high doses, stimulates strong innate and adaptive immune responses, and can be fatal to the host. In animal models, intravenous Ad administration has been shown to induce transcription and release in the serum of a great number of pro-inflammatory cytokines and chemokines. Macrophages, including tissue residential macrophages (e.g., Kupffer cells in the liver), and dendritic cells throughout the body are considered to be the primary source of these pro-inflammatory mediators following their transduction with Ads. Here, we provide an overview and methodology for the qualitative and quantitative analyses of pro-inflammatory cytokine and chemokine expression in the spleen and their release into the bloodstream after intravenous Ad delivery using antibody arrays.

A systematic comparison of the anti-tumoural activity and toxicity of the three Adv-TKs

Adenovirus 5 vectors, known respectively as, the first generation, second generation and oncolytic adenovirus, have been studied extensively in preclinical and clinical trials. However, hitherto few systemic evaluations of the efficacy and toxicity of these adenoviral vectors that have reflected the vertical history of adenovirus based cancer gene therapy strategies have been undertaken. This study has chosen Adv-TK, the well-established adjuvant treatment in cancer, and compared its efficacy and safety with those of the two newly synthesized oncolytic adenovirus vectors encoding the HSV-TK gene, namely M7 and M8. The results obtained showed that systemic administration of 1×10⁸ pfu M7 had an anti-tumour efficacy similar to that of 3×10¹⁰ pfu Adv-TK whilst M8 performed even better. Furthermore, compared to Adv-TK, M7 and M8 reduced the incidence of metastases and substantially prolonged the survival time of the mice xenografted with human orthotopic gastric carcinomas with disseminated metastasis. Even more exciting, however, were the similar toxic and immune safety results obtained from the administration of high doses of M7 or M8 in comparison with Adv-TK in immunocompetent and permissive syrian hamster. The data here exhibit a comprehensive display of the efficacy and safety of the three mutants and provide evidence for the future preclinical use of the M7 and M8 viruses.

Viral nanoparticles as platforms for next-generation therapeutics and imaging devices

Nanomaterials have been developed for potential applications in biomedicine, such as tissue-specific imaging and drug delivery. There are many different platforms under development, each with advantages and disadvantages, but viral nanoparticles (VNPs) are particularly attractive because they are naturally occurring nanomaterials, and as such they are both biocompatible and biodegradable. VNPs can be designed and engineered using both genetic and chemical protocols. The use of VNPs has evolved rapidly since their introduction 20 years ago, encompassing numerous chemistries and modification strategies that allow the functionalization of VNPs with imaging reagents, targeting ligands, and therapeutic molecules. This review discusses recent advances in the design of "smart" targeted VNPs for therapeutic and imaging applications.

FROM THE CLINICAL EDITOR

This review focuses on viral nanoparticles, which are considered attractive naturally occurring nanomaterials due to their inherent biocompatibility and biodegradability. These can be used as imaging reagents, targeting ligands and therapeutic molecules.

Recognition of virus infection and innate host responses to viral gene therapy vectors

The innate immune and inflammatory response represents one of the key stumbling blocks limiting the efficacy of viral-based therapies. Numerous human diseases could be corrected or ameliorated if viruses were harnessed to safely and effectively deliver therapeutic genes to diseased cells and tissues in vivo. Recent studies have shown that host cells recognize viruses using an elaborate network of sensor proteins localized at the plasma membrane, in endosomes, or in the cytosol. Three classes of sensors have been implicated in sensing viruses in mammalian cells-Toll-like receptors (TLRs), retinoid acid-inducible gene (RIG)-I-like receptors (RLRs), and nucleotide oligomerization domain (NOD)-like receptors (NLRs). The interaction of virus-associated nucleic acids with these sensor molecules triggers a signaling cascade that activates the principal host defense program aimed to limit or eliminate virus infection and restore tissue homeostasis. In addition, recent data strongly suggest that host cells can mount innate immune responses to viruses without prior recognition of their nucleic acids. To deliver therapeutic genes into the nuclei of diseased cells, viral gene therapy vectors must be efficient at penetrating either the plasma or endosomal membrane. The therapeutic use of high numbers of virus particles disturbs cellular homeostasis, triggering cell damage and stress pathways, or "sensing of modified self". Accumulating data indicate that the sensing of modified self might represent a powerful framework explaining the innate immune response activation by viral gene therapy vectors.

Virus infection recognition and early innate responses to non-enveloped viral vectors

Numerous human genetic and acquired diseases could be corrected or ameliorated if viruses are harnessed to safely and effectively deliver therapeutic genes to diseased cells and tissues in vivo. Innate immune and inflammatory response represents one of the key stumbling blocks during the development of viral-based therapies. In this review, current data on the early innate immune responses to viruses and to the most commonly used gene therapy vectors (using adenovirus and adeno-associated virus) will be discussed. Recent findings in the field may help develop new approaches to moderate these innate immune anti-viral responses and thus improve the safety of viral vectors for human gene therapy applications.

Intensive pharmacological immunosuppression allows for repetitive liver gene transfer with recombinant adenovirus in nonhuman primates

Repeated administration of gene therapies is hampered by host immunity toward vectors and transgenes. Attempts to circumvent antivector immunity include pharmacological immunosuppression or alternating different vectors and vector serotypes with the same transgene. Our studies show that B-cell depletion with anti-CD20 monoclonal antibody and concomitant T-cell inhibition with clinically available drugs permits repeated liver gene transfer to a limited number of nonhuman primates with recombinant adenovirus. Adenoviral vector-mediated transfer of the herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene was visualized in vivo with a semiquantitative transgene-specific positron emission tomography (PET) technique, liver immunohistochemistry, and immunoblot for the reporter transgene in needle biopsies. Neutralizing antibody and T cell-mediated responses toward the viral capsids were sequentially monitored and found to be repressed by the drug combinations tested. Repeated liver transfer of the HSV1-tk reporter gene with the same recombinant adenoviral vector was achieved in macaques undergoing a clinically feasible immunosuppressive treatment that ablated humoral and cellular immune responses. This strategy allows measurable gene retransfer to the liver as late as 15 months following the first adenoviral exposure in a macaque, which has undergone a total of four treatments with the same adenoviral vector.

A phase I trial of repeated intrapleural adenoviral-mediated interferon-beta gene transfer for mesothelioma and metastatic pleural effusions

We previously showed that a single intrapleural dose of an adenoviral vector expressing interferon-beta (Ad.IFN-beta) in patients with malignant pleural mesothelioma (MPM) or malignant pleural effusions (MPE) resulted in gene transfer, humoral antitumor immune responses, and anecdotal clinical responses manifested by modified Response Evaluation Criteria in Solid Tumors (RECIST) disease stability in 3 of 10 patients at 2 months and an additional patient with significant metabolic response on positron emission tomography (PET) imaging. This phase I trial was conducted to determine whether using two doses of Ad.IFN-beta vector would be superior. Ten patients with MPM and seven with MPE received two doses of Ad.IFN-beta through an indwelling pleural catheter. Repeated doses were generally well tolerated. High levels of IFN-beta were detected in pleural fluid after the first dose; however, only minimal levels were seen after the second dose of vector. Lack of expression correlated with the rapid induction of neutralizing Ad antibodies (Nabs). Antibody responses against tumor antigens were induced in most patients. At 2 months, modified RECIST responses were as follows: one partial response, two stable disease, nine progressive disease, and two nonmeasurable disease. One patient died after 1 month. By PET scanning, 2 patients had mixed responses and 11 had stable disease. There were seven patients with survival times longer than 18 months. This approach was safe, induced immune responses and disease stability. However, rapid development of Nabs prevented effective gene transfer after the second dose, even with a dose interval as short as 7 days.

Oncolytic adenoviral gene therapy in ovarian cancer: why we are not wasting our time

Preclinical gene-therapy studies in the past 15 years have repeatedly raised hopes that we were about to enter a brave new era. However, many clinical trials have disappointed. For tumor types with poor response rates to first-line conventional cytotoxic chemotherapy and/or high rates of chemorefractory disease, there remain very few treatment options. In this article we review gene therapy within the context of ovarian cancer. We examine why clinical data have been discouraging and discuss how the lessons learned from earlier trials are being applied to current research.

Tumor targeting using canine parvovirus nanoparticles

Advances in genetics, proteomics and cellular and molecular biology are being integrated and translated to develop effective methods for the prevention and control of cancer. One such combined effort is to create multifunctional nanodevices that will specifically recognize tumors and thus enable early diagnosis and provide targeted treatment of this disease. Viral particles are being considered for this purpose since they are inherently nanostructures with well-defined geometry and uniformity, ideal for displaying molecules in a precise spatial distribution at the nanoscale level and subject to greater structural control. Viruses are presumably the most efficient nanocontainer for cellular delivery as they have naturally evolved mechanisms for binding to and entering cells. Virus-based systems typically require genetic or chemical modification of their surfaces to achieve tumor-specific interactions. Interestingly, canine parvovirus (CPV) has a natural affinity for transferrin receptors (TfRs) (both of canine and human origin) and this property could be harnessed as TfRs are overexpressed by a variety of human tumor cells. Since TfR recognition relies on the CPV capsid protein, we envisioned the use of virus or its shells as tumor targeting agents. We observed that derivatization of CPV virus-like particles (VLPs) with dye molecules did not impair particle binding to TfRs or internalization into human tumor cells. Thus CPV-based VLPs with a natural tropism for TfRs hold great promise in the development of novel nanomaterial for delivery of a therapeutic and/or genetic cargo.

Influence of method of systemic administration of adenovirus on virus-mediated toxicity: focus on mortality, virus distribution, and drug metabolism

INTRODUCTION

Doses of 2 x 10(12) virus particles/kilogram (vp/kg) and higher of recombinant human adenovirus serotype 5 (HAdV-5) given via the tail vein induce significant toxicity and mortality in the rat. This was not observed when doses of 5.7 x 10(12) vp/kg were given through a surgically implanted jugular catheter. Here we assess how the manner by which HAdV-5 is introduced into the systemic circulation affects biodistribution, transgene expression, toxicity and mortality 0.25, 1, and 4 days after treatment in the rat. Animals were given 5.7 x 10(12) vp/kg of HAdV-5 expressing beta-galactosidase or saline through a jugular catheter or by direct tail vein injection.

RESULTS

All animals survived after jugular vein dosing. Tail vein injection of HAdV-5 increased the mortality rate to 42% (p< or =0.01). All deaths occurred within 4 h. Animals dosed through the jugular vein had significantly higher levels of transgene expression in the liver and spleen and significantly more viral genomes in these tissues and kidney and lung within the first 24 h of viral infection compared to those dosed by tail vein injection (p< or =0.01). There was no significant difference between the groups thereafter. Samples from animals that died contained even higher levels of viral genomes and serum transaminases were elevated on average by a factor of 4 at the time of death. There was no significant difference between the two dosing methods with respect to changes in hepatic cytochrome P450 expression and activity throughout the study.

CONCLUSION

These findings suggest that the method of systemic administration should be carefully considered when assessing toxicity data and other parameters at early time points after virus administration in the rat and possibly other animal models.

Adjuvant adenovirus-mediated delivery of herpes simplex virus thymidine kinase administration improves outcome of liver transplantation in patients with advanced hepatocellular carcinoma

PURPOSE

Previous poor results of liver transplantation (LT) have been confirmed in patients with advanced hepatocellular carcinoma (HCC). Adenovirus-mediated delivery of herpes simplex virus thymidine kinase (ADV-TK) therapy is an established adjuvant treatment in cancer, and we evaluated its potential as an adjuvant treatment for HCC patients who underwent LT.

EXPERIMENTAL DESIGN

Forty-five HCC patients with tumors >5 cm in diameter participated in the study over a follow-up period of 50 months. Among these patients, 22 received LT only, and 23 received LT combined with ADV-TK therapy. All HCC patients enrolled in this study had tumors >5 cm in diameter and no metastasis in lungs or bones was detected by computed tomography or magnetic resonance imaging scans.

RESULTS

The recurrence-free survival and the overall survival in the LT plus ADV-TK therapy group were 43.5% and 69.6%, respectively, at 3 years; both values were significantly higher than those in the LT-only group (9.1% and 19.9%, respectively). In the nonvascular invasion subgroup, overall survival was 100% and recurrence-free survival was 83.3% in the patients receiving LT plus ADV-TK, significantly higher than the patients receiving LT only.

CONCLUSIONS

HCC patients with no vascular invasion could be selected for LT followed by adjuvant ADV-TK therapy, regardless of intrahepatic huge or diffuse tumor. We propose that the current criteria for LT based on tumor size may be expanded if accompanied by ADV-TK therapy due to improved prognosis.

Polyethylene Glycol Modification of Adenovirus Reduces Platelet Activation, Endothelial Cell Activation, and Thrombocytopenia

Thrombocytopenia is one of the complications for in vivo administration of adenovirus serotype 5 (Ad5) vectors after intravenous injection. In this paper, we investigated the mechanism of Ad5-induced thrombocytopenia and how these effects are attenuated by polyethylene glycol (PEG) modification of Ad5 (Ad-PEG). After intravenous injection, accelerated platelet loss was observed in Ad-injected mice but not in their Ad-PEG-injected counterparts. This platelet loss induced by Ad5 corresponded with increases in coagulation D-dimer levels, splenomegaly, and, later, production of megakaryocytes in the bone marrow. In contrast, these responses were blunted or ablated after injection of Ad-PEG. Ad5 activated both platelets and endothelial cells directly in vitro as evidenced by induction of P-selectin and the formation of von Willebrand factor-platelet strings and in vivo as evidenced by the induction of E-selectin messenger RNA. PEGylation blunted these observed activations. These data suggest that Ad5 may induce thrombocytopenia by direct activation of endothelial cells in addition to its direct effects on platelets. This link provides an important clue for the understanding of the mechanisms of thrombocytopenia associated with Ad5. Given that PEGylation blunted interactions of Ad with platelets and endothelial cells, reduced D-dimer formation, reduced thrombocytopenia, and reduced splenomegaly, these data suggest that this simple vector modification may have utility to improve the safety of Ad vectors for human gene therapy.

A phase I clinical trial of single-dose intrapleural IFN-beta gene transfer for malignant pleural mesothelioma and metastatic pleural effusions: high rate of antitumor immune responses

PURPOSE

This phase 1 dose escalation study evaluated the safety and feasibility of single-dose intrapleural IFN-beta gene transfer using an adenoviral vector (Ad.IFN-beta) in patients with malignant pleural mesothelioma (MPM) and metastatic pleural effusions (MPE).

EXPERIMENTAL DESIGN

Ad.IFN-beta was administered through an indwelling pleural catheter in doses ranging from 9 x 10(11) to 3 x 10(12) viral particles (vp) in two cohorts of patients with MPM (7 patients) and MPE (3 patients). Subjects were evaluated for (a) toxicity, (b) gene transfer, (c) humoral, cellular, and cytokine-mediated immune responses, and (d) tumor responses via 18-fluorodeoxyglucose-positron emission tomography scans and chest computed tomography scans.

RESULTS

Intrapleural Ad.IFN-beta was generally well tolerated with transient lymphopenia as the most common side effect. The maximally tolerated dose achieved was 9 x 10(11) vp secondary to idiosyncratic dose-limiting toxicities (hypoxia and liver function abnormalities) in two patients treated at 3 x 10(12) vp. The presence of the vector did not elicit a marked cellular infiltrate in the pleural space. Intrapleural levels of cytokines were highly variable at baseline and after response to gene transfer. Gene transfer was documented in 7 of the 10 patients by demonstration of IFN-beta message or protein. Antitumor immune responses were elicited in 7 of the 10 patients and included the detection of cytotoxic T cells (1 patient), activation of circulating natural killer cells (2 patients), and humoral responses to known (Simian virus 40 large T antigen and mesothelin) and unknown tumor antigens (7 patients). Four of 10 patients showed meaningful clinical responses defined as disease stability and/or regression on 18-fluorodeoxyglucose-positron emission tomography and computed tomography scans at day 60 after vector infusion.

CONCLUSIONS

Intrapleural instillation of Ad.IFN-beta is a potentially useful approach for the generation of antitumor immune responses in MPM and MPE patients and should be investigated further for overall clinical efficacy.

Bio-distribution, toxicity and pathology of cowpea mosaic virus nanoparticles in vivo

Virus-based nanoparticles (VNPs) from a variety of sources are being developed for biomedical and nanotechnology applications that include tissue targeting and drug delivery. However, the fate of most of those particles in vivo has not been investigated. Cowpea mosaic virus (CPMV), a plant comovirus, has been found to be amenable to the attachment of a variety of molecules to its coat protein, as well as to modification of the coat protein sequence by genetic means. We report here the results of studies of the bio-distribution, toxicology, and pathology of CPMV in mice. Plasma clearance and tissue biodistribution were measured using CPMV particles derivatized with lanthanide metal complexes. CPMV particles were cleared rapidly from plasma, falling to undetectable levels within 20 min. By 30 min the majority of the injected VNPs were trapped in the liver and to a lesser extent the spleen with undetectable amounts in other tissues. At doses of 1 mg, 10 mg and 100 mg per kg body weight, no toxicity was noted and the mice appeared to be normal. Hematology was essentially normal, although with the highest dose examined, the mice were somewhat leukopenic with relative decreases in both neutrophils and lymphocytes. Histological examination of the spleen showed cellular infiltration, which upon flow cytometry analyses revealed elevated B lymphocytes on the first day following virus administration that subsequently subsided. Microscopic evaluation of various other tissues revealed a lack of apparent tissue degeneration or necrosis. Overall, CPMV appears to be a safe and non-toxic platform for in vivo biomedical applications.

Adenoviral p53 gene transfer and gemcitabine in three patients with liver metastases due to advanced pancreatic carcinoma

BACKGROUND

Current therapies for adenocarcinoma of the pancreas do not improve the life expectancy of patients.

METHODS

In a non-randomized pilot trail we tested whether a local therapy based upon an adenoviral gene transfer of wild type p53 in combination with gemcitabine administration would be safe in patients with liver metastases due to pancreatic carcinoma. We report on the clinical course of three patients with respect to safety, tolerability and tumor response.

RESULTS

Transient grade III toxicities occurred with fever, leucopenia, elevation of AP, ALT, AST, GGT, while grade IV toxicity occurred for bilirubin only. Laboratory tests suggested disseminated intravascular coagulation in all three patients, but fine needle biopsies of liver did not show any histological evidence of thrombus or clot formation. Progression of liver metastases was documented in one and stable disease in another patient two months after treatment. However, a major improvement with regression of the indexed lesion by 80% occurred in a third patient after a single administration of 7.5 x 10(12) viral particles, and time to progression was extended to six months.

CONCLUSION

The combination therapy of viral gene transfer and chemotherapy temporarily controls and diminishes tumor burden. Improvement of the toxicity profile is necessary. Further trials are warranted to improve treatment and life expectancy of patients suffering from fatal diseases such as pancreatic carcinoma.

Respective roles of TNF-alpha and IL-6 in the immune response-elicited by adenovirus-mediated gene transfer in mice

The immunogenicity of recombinant adenoviruses (Ad) constitutes a major concern for their use in gene therapy. Antibody- and cell-mediated immune responses triggered by adenoviral vectors hamper long-term transgene expression and efficient viral readministration. We previously reported that interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha play an essential role in both the acute phase and antibody response against Ad, respectively. As TNF-alpha controls the immune response and the development of the immune system, we examined here the consequence of blockade of TNF-alpha activity through Ad-mediated gene delivery of a dimeric mouse TNFR1-IgG fusion protein on transgene expression from a second Ad. Ad encoding TNFR1-IgG (AdTNFR1-Ig) was injected intravenously along with Ad encoding beta-galactosidase or alpha1-antitrypsin transgene in wild-type (IL-6(+/+)) but also in IL-6-deficient mice (IL-6(-/-)) to analyze how TNF-alpha and IL-6 diminish liver gene transfer efficacy. Blockade of TNF-alpha leads to increased transgene expression in both wild-type and IL-6(-/-) mice due to a reduced inflammatory response and to diminished recruitment of macrophages and NK cells towards the liver. Antibody responses against adenoviral particles and expressed transgenes were only delayed in AdTNFR1-Ig-treated wild-type mice, but were markedly reduced in AdTNFR1-Ig-treated IL-6(-/-) mice. Finally, treatment of mice with etanercept, a clinically approved anti-TNF-alpha drug, confirmed the importance of controlling proinflammatory cytokines during gene therapy by adenoviral vectors.

Increased hepatic transduction with reduced systemic dissemination and proinflammatory cytokines following hydrodynamic injection of helper-dependent adenoviral vectors

Hydrodynamic injection of helper-dependent adenoviral vectors (HDAd) in mice results in increased hepatic transduction, reduced splenic and pulmonary transduction, and reduced levels of the proinflammatory cytokines IL-6 and IL-12 compared to conventional injection. These results indicate that hepatic transduction by HDAd, at least alone, does not necessarily provoke a severe innate inflammatory response. Instead, they suggest that systemic vector dissemination may play a major role in the severity of the innate inflammatory response. These results further suggest that the safety and efficacy of HDAd-mediated, liver-directed gene therapy may be improved if the vector could be preferentially, if not exclusively, targeted to liver.

Isolation of neutrophils from mouse liver: A novel method to study effector leukocytes during inflammation

Neutrophils are phagocytic leukocytes that represent one of the first lines of defense during infection and injury. Neutrophils emigrate into tissues during inflammation and are phenotypically different compared to cells in the circulation. To further understand the biology of tissue-recruited neutrophils, we have developed a reliable method to isolate these cells from inflamed liver. Acute liver inflammation was induced in mice by systemic treatment with adenovirus vectors. Two hours following adenovirus treatment, livers were enzymatically digested and leukocytes isolated by Percoll density gradient centrifugation. Neutrophils were then purified by negative immunomagnetic separation. Neutrophils isolated in this manner were 95% pure as determined by flow cytometry and more than 97% viable by propidium iodide staining. In order to carry out molecular studies, we extracted high quality genomic DNA and RNA from isolated neutrophils. PCR was used to successfully amplify sample genes from isolated neutrophil DNA. Isolated neutrophil RNA was used in a ribonuclease protection assay to evaluate chemokine gene expression. Neutrophils were shown to express multiple chemokine mRNA transcripts including MIP-1 beta, MIP-2 and IP-10. This work describes a novel method to isolate highly pure, viable neutrophils from pathologically inflamed tissue for subsequent detailed cellular and molecular analysis.

Improved hepatic transduction, reduced systemic vector dissemination, and long-term transgene expression by delivering helper-dependent adenoviral vectors into the surgically isolated liver of nonhuman primates

Helper-dependent adenoviral vectors (HDAds) are attractive vectors for liver-directed gene therapy because they can mediate sustained, high-level transgene expression without chronic toxicity. However, high vector doses are required to achieve efficient hepatic transduction by systemic delivery because of a nonlinear dose response. Unfortunately, such high doses result in systemic vector dissemination and dose-dependent acute toxicity with potentially severe and lethal consequences. We hypothesize that the threshold to efficient hepatic transduction may be circumvented by delivering the vector into the surgically isolated liver via the portal vein. Total hepatic isolation was achieved by occluding hepatic inflow from the portal vein and hepatic artery and by occluding hepatic venous outflow at the inferior vena cava. We demonstrate in nonhuman primates that this approach resulted in significantly higher efficiency hepatic transduction with reduced systemic vector dissemination compared with systemic intravascular delivery. This method of delivery was associated with transient acute toxicity, the severity of which was variable. Importantly, stable, high levels of transgene expression were obtained for at least 665 days for one baboon and for at least 560 days for two baboons with no evidence of long-term toxicity.

Genetic Heterogeneity and Efficiency of Two Different Methods of Adenovirus-Mediated Gene Transfer in a Rat Liver Transplantation Model

PURPOSE

We used recombinant adenoviral vectors for gene therapy in liver transplantation, and investigated the efficacy of gene transfer and expression on the grafts and genetic heterogeneity, with two exogenous gene transfer methods in three different syngeneic rat strains.

METHODS

We transferred adenoviral vector encoding Escherichia coli beta-galactosidase via a donor tail vein 3 days before transplantation; via a recipient tail vein immediately after grafting; and ex vivo by perfusion and clamping during transplantation.

RESULTS

The high efficacy of beta-galactosidase gene transfer and expression was seen in both delivery systems, with 70% positivity for hepatocytes on day 3, which persisted for at least 3 weeks after transplantation. The efficacy of gene transfer and expression was similar in the three strains (DA, Lewis, and PVG).

CONCLUSIONS

These data suggest that adenovirus-mediated gene transfer delivers effective gene therapy by tail vein injection of a donor or a recipient, or by ex vivo graft perfusion in rat liver transplantation. It is not necessary to consider the differences in the strains. Furthermore, ex vivo graft perfusion is probably more suitable not only for rat liver transplantation but also possibly for future clinical application.

Oncolytic virotherapy for cancer treatment: challenges and solutions

Advances in gene modification and viral therapy have led to the development of a variety of vectors in several viral families that are capable of replication specifically in tumor cells. Because of the nature of viral delivery, infection, and replication, this technology, oncolytic virotherapy, may prove valuable for treating cancer patients, especially those with inoperable tumors. Current limitations exist, however, for oncolytic virotherapy. They include the body's B and T cell responses, innate inflammatory reactions, host range, safety risks involved in using modified viruses as treatments, and the requirement that most currently available oncolytic viruses require local administration. Another important constraint is that genetically enhanced vectors may or may not adhere to their replication restrictions in long-term applications. Several solutions and strategies already exist, however, to minimize or circumvent many of these limitations, supporting viral oncolytic therapy as a viable option and powerful tool in the fight against cancer.

The nude rat as an orthotopic model for cervical cancer

OBJECTIVE

The purposes of this study were to establish intracervical tumors of the nude rat as an orthotopic experimental model for human cervical cancer and to preliminary evaluate the effects of the adenoviral vector, Ad5CMV-p53, on orthotopic cervical tumor size.

METHODS

Human cervical cancer SiHa and ME-180 cells were injected into the cervix of the nude rat. Four days later, 1 x 10(9) plaque forming units (PFU) of Ad5CMV-p53 were injected into the cervix. The rats were later sacrificed to determine cervical tumor size.

RESULTS

Eight of ten nude rats developed SiHa cell tumors; all ten nude rats developed ME-180 cell tumors. Four of ten SiHa cell tumors metastasized to the pelvic cavity; no ME-180 cell tumors did. The growth of Ad5CMV-p53-infected cells was greatly suppressed. The ad5CMV-p53 treatment significantly reduced both cell tumor volumes in nude rat cervixes.

CONCLUSION

The nude rat cervix grows tumors similar to human cervical cancer tumors and makes an excellent experimental model. Transfection of cervical cancer cells with the wild-type p53 gene via Ad5CMV-p53 is a potential therapeutic approach to cervical cancer.

Interference with the IL-1-signaling pathway improves the toxicity profile of systemically applied adenovirus vectors

The safety of gene therapy vectors is a major concern when novel viral or nonviral therapeutics are proposed for applications in humans. Adenovirus (Ad) vectors have been extensively used as efficient gene delivery vehicles in vitro over the last two decades. However, upon i.v. application, they elicit robust innate and inflammatory responses that may be fatal for the host. To date, the primary cytokines and chemokines involved in the initiation of these host responses remain illusive. In this study, we demonstrate that IL-1 is a major mediator involved in the initiation of immediate host responses toward i.v. applied Ad vectors. Using mice in which IL-1 signaling was genetically eliminated (IL-1RI-KO), or wild-type animals for which signaling was blocked by anti-IL-1 Abs, we found that i.v. applied Ad vectors elicited dramatically reduced acute inflammatory responses when compared with control animals. Importantly, the efficiency of Ad gene transfer in vivo was not significantly affected by interfering with IL-1 signaling. Using an in situ hybridization technique, we found that hepatocytes and Kupffer cells trigger IL-1 transcription in liver tissue after i.v. Ad vector administration. We also found that expression of the MIP-2 chemokine gene (which is responsible for recruitment of neutrophils to the liver) depends on IL-1 activation. Our data indicate that immediate innate and inflammatory host responses toward i.v. applied Ad vectors can be pharmacologically controlled through interference with IL-1 signaling pathways.

Characterization of Hemodynamic Events Following Intravascular Infusion of Recombinant Adenovirus Reveals Possible Solutions for Mitigating Cardiovascular Responses

Intravascular administration of recombinant adenovirus (rAd) in cancer patients has been well tolerated. However, dose-limiting hemodynamic responses associated with suppression of cardiac output have been observed at doses of 7.5 x 10(13) particles. While analysis of hemodynamic responses induced by small-molecule pharmaceuticals is well established, little is known about the cardiovascular effects of rAd. Telemetric cardiovascular (CV) monitoring in mice was utilized to measure hemodynamic events following intravascular rAd administration. Electrocardiogram analysis revealed a block in the SA node 3-4 min postinfusion, resulting in secondary pacemaking initiated at the AV node. This was associated with acute bradycardia, reduced blood pressure, and hypothermia followed by gradual recovery. Adenovirus-primed murine sera with high neutralizing antibody (nAb) titers could inhibit CV responses, whereas human sera with equivalent nAb titers induced by natural infection were, surprisingly, not inhibitory. Interestingly, repeat dosing within 2-4 h of the primary injection resulted in desensitization, resembling tachyphylaxis, for subsequent CV responses. Last, depletion of Kupffer cells prior to rAd infusion precluded induction of CV responses. These inhibitory effects suggest that rAd interactions with certain cells of the reticular endothelial system are associated with induction of CV responses. Significantly, these studies may provide insight into management of acute adverse effects following rAd systemic delivery, enabling a broadening of therapeutic index.

Adenovirus binding to blood factors results in liver cell infection and hepatotoxicity

Adenoviruses (Ad) are efficient vehicles for gene delivery in vitro and in vivo. Therefore, they are a promising tool in gene therapy, particularly in the treatment of cancer and cardiovascular diseases. However, preclinical and clinical studies undertaken during the last decade have revealed a series of problems that limit both the safety and efficacy of Ad vectors, specifically after intravenous application. Major obstacles to clinical use include innate toxicity and Ad sequestration by nontarget tissues. The factors and mechanisms underlying these processes are poorly understood. The majority of intravenously injected Ad particles are sequestered by the liver, which in turn causes an inflammatory response characterized by acute transaminitis and vascular damage. Here, we describe a novel pathway that is used by Ad for infection of hepatocytes and Kupffer cells upon intravenous virus application in mice. We found that blood factors play a major role in targeting Ad vectors to hepatic cells. We demonstrated that coagulation factor IX and complement component C4-binding protein can bind the Ad fiber knob domain and provide a bridge for virus uptake through cell surface heparan sulfate proteoglycans and low-density lipoprotein receptor-related protein. An Ad vector, Ad5mut, which contained mutations in the fiber knob domain ablating blood factor binding, demonstrated significantly reduced infection of liver cells and liver toxicity in vivo. This study contributes to a better understanding of adenovirus-host interactions for intravenously applied vectors. It also provides a rationale for novel strategies to target adenovirus vector to specific tissues and to reduce virus-associated toxicity after systemic application.

Gene therapy for hepatocellular carcinoma using sonoporation enhanced by contrast agents

We examined whether sonoporation enhanced by a contrast agent (BR14) was effective in gene therapy for hepatocelluar carcinoma (HCC). Human hepatic cancer cells (SK-Hep1) and plasmid cDNAs expressing green fluorescent protein (GFP), interferonbeta (IFNbeta), and LacZ were used. In vitro, SK-Hep1 cell suspensions with DNA and BR14 were sonoporated. Expressions of every plasmid cDNA and the antitumor effect of IFNbeta were analyzed. In vivo, GFP and IFNbeta genes with BR14 were directly injected into subcutaneous tumors using SK-Hep1 in nude mice, and transcutaneous sonoporation of the tumors was performed. GFP gene transfections and tumor diameters after IFNbeta gene transfection were examined. In vitro, no SK-Hep1 cells were transfected without sonication, whereas transfections were successful after sonication with BR14. Antitumor effect of IFNbeta gene transfection by ultrasound (US) and with BR14 was revealed. In vivo, the SK-Hep1 cells expressed GFP, and the IFNbeta gene transfection by US with BR14 reduced tumor size significantly. In conclusion, gene therapy with sonoporation enhanced by a contrast agent may become a new treatment option for HCC.

Evaluation of polyethylene glycol modification of first-generation and helper-dependent adenoviral vectors to reduce innate immune responses

Adenoviruses are robust gene delivery vectors in vivo, but are limited by their propensity to provoke strong innate and adaptive responses. Previous work has demonstrated that polyethylene glycol (PEG) modification of adenovirus can protect the vectors from preexisting and adaptive immune responses by reducing protein-protein interactions. To test whether PEGylation can reduce innate immune responses to adenovirus by reducing their interactions with immune cells, first-generation (FG-Ad) and helper-dependent (HD-Ad) Ad5 vectors were PEGylated with SPA-PEG and tested in vitro and in vivo. We demonstrate that increasing PEGylation ablated in vitro transduction, but surprisingly had no negative effect on the level or distribution of in vivo gene delivery. This poor in vitro transduction could be rescued in part by physically forcing the PEGylated vectors onto cells, suggesting that physiological forces in vivo may enable transduction via heparin sulfate proteoglycan and integrin interactions. While transduction remained the same as for unmodified vectors, the PEGylated vectors reduced innate IL-6 responses by 70 and 50% in vivo for FG-Ad and HD-Ad. These reduced innate responses paralleled similar reductions in vector uptake by macrophages in vitro and Kupffer cells in vivo. These data suggest that PEGylation of Ad vectors can reduce innate immune responses without reducing transduction in vivo. These data also suggest that nonspecific vector uptake by macrophages and Kupffer cells may be critically involved in the initial activation of innate immune responses.

Antiangiogenic gene therapy of myeloproliferative disease developed in transgenic mice expressing P230 bcr/abl

Antiangiogenic gene therapy offers an attractive approach to the treatment of a variety of malignancies, including those of the hematological system. However, evaluation of this approach has been hampered by the lack of appropriate animal models. We have recently produced transgenic mice expressing P230 bcr/abl that develop myeloproliferative disease (MPD) closely resembling human chronic myelogenous leukemia. Using this MPD murine model, we examined the feasibility of systemic antiangiogenic gene therapy for hematological malignancy. An adenoviral vector containing the secretable endostatin gene was injected into the right quadriceps muscle of the MPD mice. The increased endostatin level was detected for at least 6 months. Hematological parameters including platelet counts, granulocyte counts, and the hemoglobin concentration were improved by this gene therapy. Infiltration of megakaryocytes was also significantly inhibited in treated MPD mice. Reduction of the microvessel density was confirmed by histological examination. These results demonstrated, for the first time, that antiangiogenic gene therapy is effective to inhibit leukemogenesis caused by expression of the chimeric bcr/abl gene.

Acute hepatotoxicity of oncolytic adenoviruses in mouse models is associated with expression of wild-type E1a and induction of TNF-alpha

Replication competent adenoviruses with various E1 modifications designed to restrict their replication to tumor cells are being evaluated as oncolytic agents in clinical trials. In mouse models, we observed that such oncolytic adenoviruses showed greater hepatotoxicity than E1-deleted adenovirus vectors following intravenous administration. Additional studies in congenic BALB/c, nude, and beige/Scid mice demonstrated dose-dependent hepatotoxicity and indicated that beige/Scid was the most sensitive strain. Comparison of E1-containing viruses showed that hepatotoxicity correlated with expression of wild-type E1a in the liver. Pharmacokinetic analysis showed rapid increases in viral DNA levels in the liver with a virus containing wild-type E1a. This was correlated with rapid induction of TNF-alpha to high levels and with rapid elevation of serum ALT. Hepatotoxicity was significantly reduced for an adenovirus with deletions in the region E1a (dl01/07) or a virus lacking E1a. The results suggest a mechanism for hepatotoxicity involving virus-induced production of local TNF-alpha release and E1a-mediated sensitization of hepatocyte killing.

Impact of Human Neutralizing Antibodies on Antitumor Efficacy of an Oncolytic Adenovirus in a Murine Model

PURPOSE

The purpose of this study was to assess the impact of anti-adenovirus neutralizing antibodies (AdNAbs) on the distribution, tolerability, and efficacy of intravenously administered oncolytic adenovirus. A translational model was developed to evaluate the impact of humoral immunity on intravenous administration of oncolytic adenovirus in humans.

EXPERIMENTAL DESIGN

Initially, severe combined immunodeficient (SCID)/beige mice were passively immunized with various amounts of human sera to establish a condition of preexisting humoral immunity similar to humans. A replication-deficient adenovirus encoding beta-galactosidase (rAd-betagal) was injected intravenously into these mice. An AdNAb titer that mitigated galactosidase transgene expression was determined. A xenograft tumor-bearing nude mouse model was developed to assess how a similar in vivo titer would impact the activity of 01/PEME, an oncolytic adenovirus, after intravenous administration.

RESULTS

In SCID/beige mice, there was a dose dependence between AdNAbs and galactosidase transgene expression; 90% of transgene expression was inhibited when the titer was 80. A similar titer reconstituted in the nude mice with human serum, as was done in the SCID/beige mice, did not abrogate the antitumor efficacy of the replicating adenovirus after intravenous administration. Viral DNA increased in tumors over time.

CONCLUSIONS

In intravenous administration, preexisting AdNAb titer of 80 significantly attenuated the activity of a 2.5 x 10(12) particles per kilogram dose of nonreplicating adenovirus; the same titer had no affect on the activity of an equivalent dose of replicating adenovirus. Our results suggest that a majority of patients with preexisting adenovirus immunity would be candidates for intravenous administration of oncolytic adenovirus.

Transbronchial administration of adenoviral-mediated interleukin-10 gene to the donor improves function in a pig lung transplant model

Interleukin-10 (IL-10) gene transfection of donor lungs prior to transplantation is an attractive strategy to reduce ischemia-reperfusion induced lung injury. However, experimental data with gene therapy in large animal models of lung transplantation are generally lacking. We have developed a simple clinically applicable technique for adenoviral-mediated gene delivery of human IL-10 to the lung of large animals that provides homogenous gene expression after 12-24 h of transfection. Using this technique of gene delivery, we have studied the dynamics of adenoviral gene delivery to the lung in the setting of lung transplantation. Although there is a persistent inflammatory response to the adenoviral vector, we achieved significant expression of human IL-10 in lung tissue before lung retrieval to obviate the deleterious impact of the adenoviral vector on the donor lung. The administration of adenoviral-mediated human IL-10 to the donor lung reduced ischemia-reperfusion injury and improved graft function after lung transplantation in this pig lung transplantation model. Transfection of adenoviral-mediated human IL-10 to the donor lung prevented the release of inflammatory cytokines such as IL-6 in lung tissue and plasma. We have demonstrated that IL-10 gene therapy has significant potential to prevent or treat the inflammatory response associated with ischemia-reperfusion injury in lung transplantation. In the future, IL-10 gene therapy could also be used for immunomodulation or tolerance induction.

CpG Methylation of a Plasmid Vector Results in Extended Transgene Product Expression by Circumventing Induction of Immune Responses

Gene therapy has the potential to cure inherited diseases if the delivered genes achieve long-term expression at therapeutic levels in the targeted tissues. Expression is commonly short-lived due to induction of cell-mediated immune responses to the gene therapy vehicle and/or the transgene product, which can be perceived as "foreign" by the host's immune system. Plasmid expression vectors have been used to deliver genes. Bacterial DNA carries immunostimulatory sequences in the form of unmethylated CpG motifs, which induce an inflammatory reaction that in turn promotes activation of transgene product-specific B and T cells. Elimination or methylation of immunostimulatory CpG sequences in plasmid expression vectors prevents the stimulation of transgene product-specific immune responses without necessarily reducing transgene expression. In this study, we tested if a CpG-methylated plasmid expression vector expressing the highly immunogenic glycoprotein of rabies virus can achieve prolonged transgene product expression by circumventing immune recognition. Our data show that mice inoculated with a CpG-methylated plasmid expression vector show delayed clearance of transfected cells and fail to mount a strong immune response to the transgene product. Gene transfer with a CpG-methylated plasmid results in a state of immunological low responsiveness to the transgene product, which may facilitate readministration of the transgene. Nevertheless, mice remain responsive to the transgene product delivered by a viral vector.

Gene therapy progress and prospects: adenoviral vectors

In September 1999, the perceptions of the use of adenoviral (Ad) vectors for gene therapy were altered when a patient exposed via the hepatic artery to a high dose of adenoviral vector succumbed to the toxicity related to vector administration. Appropriately, concerns were raised about continued use of the Ad vector system and, importantly, there were increased efforts to more fully understand the toxicity. Today it is recognized that there is no ideal vector system, and that while Ad vectors are not suitable for all applications, the significant advantages over other vector systems including efficient transduction of a variety of cell types, both quiescent and dividing, make it optimal for certain applications. These include protocols where high levels of short-term expression are sufficient to provide a therapeutic benefit. Potential target applications include therapeutic angiogenesis, administration into immune-privileged sites such as the CNS, or treatments where the adjuvant effect of adenovirus can be of benefit such as cancer vaccines. Broader applicability of Ad vectors will require resolution of toxicity issues. This review will therefore focus on studies conducted over the last 2 years that have advanced our understanding of the toxicity associated with Ad vectors, studies that have employed methods to reduce toxicity and improvements in Ad vectors themselves that will reduce toxicity by one of several mechanisms. These mechanisms include retargeting vector to the tissue of interest, minimizing or eliminating viral gene expression that is thought to result in loss of transduced cells, or by methods that seek to reduce the vector dose required for therapeutic benefit. An area where there remains significant room for improvement is when readministration of vector is required because transgene expression has decreased to background levels.

Immunity to adenovirus and adeno-associated viral vectors: implications for gene therapy

Viral vectors have provided effective methods for in vivo gene delivery for therapeutic purposes. The ability of viruses to infect a wide variety of cell types in vivo has been exploited for several applications, such as liver, lung, muscle, brain, eye and many others. Immune responses directed towards the viral capsids and the transgene products have severely affected the ability of these vectors to induce long-term gene expression. This paper reviews the influence of viral vectors on antigen-presenting cells (APC), which are central to the induction of innate as well as adaptive immune responses. In this respect, we have focused on adenovirus and adeno-associated viruses because of the polar responses these vector systems induce in vivo. While adenovirus vector can induce significant inflammatory responses, adeno-associated viral vectors are characterized by their inability to consistantly induce immune responses to the transgene product. Understanding the mechanism of infection, transduction and activation of APC by viral vectors will provide strategies to develop safe vectors and prevent immune responses in gene therapies.

Genetic heterogeneity in response to adenovirus gene therapy

BACKGROUND

After intravenous delivery of the adenoviral vector into rats or mice, 95-99% of the encoded protein is produced in the hepatocytes. We observed, as have others, that the early expression levels of the vector encoded protein vary, greatly, within a species, from one animal strain to another. This study was initiated to determine the molecular mechanism causing the difference: hepatic transfection, transcription or translation. For this purpose different doses of Ad5 luciferase and Ad5 LacZ were intravenously injected into Brown Norway rats and Wag/Rij rats, two strains that differ by a factor of 10 in encoded protein levels. The proportion of LacZ positive hepatocytes, the adenoviral DNA, specific transgenic RNA and luciferase protein were compared in the two strains.

RESULTS

The number of transduced hepatocytes and the amounts of Ad5 DNA in the livers was similar in both strains, whereas the Brown Norway rats produced 8 to 10 times more of both vector encoded proteins and of transgene mRNA than the Wag/Rij rats.

CONCLUSIONS

It is concluded that the difference between strains in vector encoded protein expression is due to different transcriptional events. No evidence was obtained to suggest that the differences are related to liver damage influenced by vector toxicity or immune reactions.