Innate immune mechanisms dominate elimination of adenoviral vectors following in vivo administration

Pre-existent adenovirus antibody inhibits systemic toxicity and antitumor activity of CN706 in the nude mouse LNCaP xenograft model: implications and proposals for human therapy

Pre-existent humoral antibody to adenovirus potentially confounds human clinical trials involving intravascular administration of adenovirus. Using the LNCaP prostate cancer xenograft model in BALB/c nu/nu mice and the prostate-specific attenuated replication-competent adenovirus (ARCATM) CN706, we developed an animal model that systematically controls both the dose of intravascularly administered adenovirus and the titer of the pre-existent anti-Ad5 antibody, and then measures the virus-induced toxicity as well as antitumor activity. We prepared hyperimmune sera to adenovirus in rabbits, passively injected the purified rabbit anti-Ad5 antibody into tumor-bearing mice, and established measurable humoral anti-Ad5 antibody titers. CN706 was intravenously injected into the tail vein of animals 24 hr after passive anti-Ad5 antibody administration. In the absence of pre-existent antibody, the lethal dose (LD100) for BALB/c nu/nu mice was 2.5x10(11) CN706 particles, whereas 1x10(11) CN706 particles was not lethal. However, in the presence of a 1:80 pre-existent titer of Ad5 neutralizing antibody (NAb), intravenous injection of 5x10(11) CN706 particles was no longer lethal. In addition, pre-existent antibody also prevented antitumor activity in a dose-dependent manner: 1x 10(11) CN706 particles prevented LNCaP xenograft tumor progression, but antitumor activity was eliminated by a pre-existent 1:80 NAb titer. These results led us to propose transient removal of pre-existent adenovirus antibody by immunoapheresis. An affinity column of cloned virus capsid proteins was constructed that was able to specifically remove adenovirus antibody from human clinical serum samples. A 5-min disposable immunoassay was also developed to monitor the level of pre-existent antibody in sera before and after immunoapheresis. Clinically, this approach may enable controlled clinical studies of intravenously administered adenovirus in patients with pre-existent anti-adenovirus antibody.

Intravascular and endobronchial DNA delivery to murine lung tissue using a novel, nonviral vector

Gene transfer to the lung can be achieved via either the airway or the pulmonary vasculature. We evaluated gene transfer and expression by intravascular and endobronchial routes, using DNA complexed with G9 PAMAM dendrimer or naked plasmid DNA. Intravascular tail vein delivery of dendrimer-complexed pCF1CAT plasmid resulted in high levels of transgene expression in the lung at 12 and 24 hr, followed by a second peak of expression 3 to 5 days after administration. After intravenous administration of the complexes, CAT expression was never observed in organs other than the lung. There were only minimal levels of CAT protein expressed in the lung after intravenous administration of naked plasmid DNA. Repeated intravascular doses of the dendrimer-complexed plasmid, administered four times at 4-day intervals, maintained expression at 15-25% of peak concentrations achieved after the initial dose. Endobronchial delivery of naked pCF1CAT plasmid produced significant amounts of CAT protein in the lung. Comparison of intratracheal and intranasal routes resulted in similar expression levels of CAT in the lung and trachea. However, in juxtaposition to vascular delivery, intranasal delivery of dendrimer-complexed plasmid DNA gave lower levels of CAT expression than that observed with naked plasmid DNA. In situ localization of CAT enzymatic activity suggested that vascular administration seemed to achieve expression in the lung parenchyma, mainly within the alveoli, while endobronchial administration primarily targeted bronchial epithelium. Our results show that intravenously administered G9 dendrimer is an effective vector for pulmonary gene transfer and that transgene expression can be prolonged by repeated administration of dendrimer-complexed DNA.

Encapsulation of plasmid DNA in stabilized plasmid-lipid particles composed of different cationic lipid concentration for optimal transfection activity

In previous work (Wheeler et al. (1999) Gene Therapy 6, 271-281) we have shown that plasmid DNA can be entrapped in "stabilized plasmid lipid particles" (SPLP) using low levels (5-10 mol%) of cationic lipid, the fusogenic lipid dioleoylphosphatidylethanolamine (DOPE), and a polyethyleneglycol (PEG) coating for stabilization. The PEG moieties are attached to a ceramide anchor containing an arachidoyl acyl group (PEG-CerC20). However, these SPLP exhibit low transfection potencies in vitro as compared to plasmid/cationic lipid complexes formed with liposomes composed of cationic and neutral lipid at a 1:1 lipid ratio. The objective of this study was to construct SPLPs with increased cationic lipid contents that result in maximum transfection levels. A phosphate buffer detergent dialysis technique is described resulting in formation of SPLP containing 7-42.5 mol% DODAC with reproducible encapsulation efficiency of up to 80%. An octanoyl acyl group was used as anchor for the PEG moiety (PEG-CerC8) permitting a quick exchange out of the SPLP to further optimize the in vitro and in vivo transfection. We have demonstrated that this technique can be used to encapsulate either linearized DNA or supercoiled plasmids ranging from 3-20 kb. The SPLP formed could be isolated from empty vesicles by sucrose density gradient centrifugation, and exhibited a narrow size distribution of approximately 75 +/- 6 nm as determined by cryo-electron microscopy. The high plasmid-to-lipid ratio observed corresponded to one plasmid per particle. The SPLP consist of a lipid bilayer surrounding the plasmid DNA as visualized by cryo-electron microscopy. SPLP containing a range of DODAC concentrations were tested for in vitro and in vivo transfection. In vitro, in COS-7 cells transfection reached a maximum after 48 h. The transfection efficiency increased when the DODAC concentration in the SPLP was decreased from 42.5 to 24 mol% DODAC. Decreasing the cationic lipid concentration improved transfection in part due to decreased toxicity. In vivo studies using an intraperitoneal B16 tumor model and intraperitoneal administration of SPLP showed maximum transfection activity for SPLP containing 24 mol% DODAC. Gene expression observed in tumor cells was increased by approximately one magnitude as compared to cationic lipid/DNA complexes. The SPLP were stable and upon storage at 4 degrees C no significant change in the transfection activity was observed over a one-year period. Thus this phosphate buffer detergent dialysis technique can be used to generate SPLP formulations containing a wide range of cationic lipid concentrations to determine optimal SPLP composition for high transfection activity and low toxicity.

Stabilized plasmid-lipid particles: pharmacokinetics and plasmid delivery to distal tumors following intravenous injection

A previous study has shown that plasmid DNA can be encapsulated in lipid particles (SPLP, "stabilized plasmid lipid particles") of approximately 70 nm diameter composed of 1,2-dioleoyl-3-phosphatidyl-ethanolamine (DOPE), the cationic lipid N,N-dioleoyl-N,N-dimethylammonium chloride (DODAC) and poly(ethylene glycol) conjugated to ceramide (PEG-Cer) using a detergent dialysis process (Wheeler et al. (1999) Gene Therapy 6, 271-281). In this work we evaluated the potential of these SPLPs as systemic gene therapy vectors, determining their pharmacokinetics and the biodistribution of the plasmid and lipid components. It is shown that the blood clearance and the biodistribution of the SPLPs can be modulated by varying the acyl chain length of the ceramide group used as lipid anchor for the PEG polymer. Circulation lifetimes observed for SPLPs with PEG-CerC14 and PEG-CerC20 were t(1/2) = approximately 1 and approximately 10 h, respectively. The SPLPs are stable while circulating in the blood and the encapsulated DNA is fully protected from degradation by serum nucleases. The accelerated clearance of SPLPs with PEG-CerC14 is accompanied by increased accumulation in liver and spleen as compared to PEG-CerC20 SPLPs. Delivery of intact plasmid to liver and spleen was detected. Significant accumulation (approximately 10% of injected dose) of the long circulating SPLPs with PEG-CerC20 in a distal tumor (Lewis lung tumor in the mouse flank) was observed following i.v. application and delivery of intact plasmid to tumor tissue at approximately 6% injected dose/g tissue is demonstrated.

Second-generation adenoviral vectors do not prevent rapid loss of transgene expression and vector DNA from the arterial wall

The utility of adenoviral vectors for arterial gene transfer is limited by the brevity of their expression and by inflammatory host responses. As a step toward circumventing these difficulties, we used a rabbit model of in vivo arterial gene transfer to test 3 second-generation vectors: a vector containing a temperature-sensitive mutation in the E2A region, a vector deleted of E2A, and a vector that expresses the immunomodulatory 19-kDa glycoprotein (gp19k) from adenovirus 2. Compared with similar first-generation vectors, the second-generation vectors did not significantly prolong beta-galactosidase transgene expression or decrease inflammation in the artery wall. Although cyclophosphamide ablated the immune and inflammatory responses to adenovirus infusion, it only marginally prolonged transgene expression (94% drop in expression between 3 and 14 days). In experiments performed with "null" adenoviral vectors (no transgene), loss of vector DNA from the arterial wall was also rapid (>99% decrease between 1 hour and 14 days), unrelated to dose, and only marginally blunted by cyclophosphamide. Thus, the early loss of transgene expression after adenoviral arterial gene transfer is due primarily to loss of vector DNA, is not correlated with the presence of local vascular inflammation, and cannot be prevented by use of E2A-defective viruses, expression of gp19k, or cyclophosphamide-mediated immunosuppression. Adenovirus-induced vascular inflammation can be prevented by cyclophosphamide treatment or by lowering the dose of infused virus. However, stabilization of adenovirus-mediated transgene expression in the arterial wall is a more elusive goal and will require novel approaches that prevent the early loss of vector DNA.

In vivo targeted repair of a point mutation in the canine dystrophin gene by a chimeric RNA/DNA oligonucleotide

In the canine model of Duchenne muscular dystrophy in golden retrievers (GRMD), a point mutation within the splice acceptor site of intron 6 leads to deletion of exon 7 from the dystrophin mRNA, and the consequent frameshift causes early termination of translation. We have designed a DNA and RNA chimeric oligonucleotide to induce host cell mismatch repair mechanisms and correct the chromosomal mutation to wild type. Direct skeletal muscle injection of the chimeric oligonucleotide into the cranial tibialis compartment of a six-week-old affected male dog, and subsequent analysis of biopsy and necropsy samples, demonstrated in vivo repair of the GRMD mutation that was sustained for 48 weeks. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of exons 5-10 demonstrated increasing levels of exon 7 inclusion with time. An isolated exon 7-specific dystrophin antibody confirmed synthesis of normal-sized dystrophin product and positive localization to the sarcolemma. Chromosomal repair in muscle tissue was confirmed by restriction fragment length polymorphism (RFLP)-PCR and sequencing the PCR product. This work provides evidence for the long-term repair of a specific dystrophin point mutation in muscle of a live animal using a chimeric oligonucleotide.

Gene therapy for lung disease: hype or hope?

Gene therapy, the treatment of any disorder or pathophysiologic state on the basis of the transfer of genetic information, was a high-priority goal in the 1990s. The lung is a major target of gene therapy for genetic disorders, such as cystic fibrosis and alpha1-antitrypsin deficiency, and for other diseases, including lung cancer, malignant mesothelioma, pulmonary inflammation, surfactant deficiency, and pulmonary hypertension. This paper examines general concepts in gene therapy, summarizes the results of published clinical trials, and highlights areas of research aimed at overcoming challenges in the field. Although progress has been slower than anticipated, gene transfer has been safely achieved in patients with lung diseases. Recent advancements in understanding of the molecular basis of lung disease and the development of improved vector systems make it likely that gene therapy will be an important tool for the 21st-century clinician.

Immune responses against replication-deficient adenovirus inhibit ovalbumin-specific allergic reactions in mice

Replication-deficient adenovirus vector (Ad) is one of the most efficient gene transfer vehicles for human gene therapy. However, Ad is antigenic, known to evoke prominent inflammatory responses in vivo, and there are concerns that using Ad in patients with immune-mediated disorders (allergy and autoimmune diseases) may affect the status of the diseases. To evaluate this concept in a manner close to clinical scenarios, a mouse model of airway eosinophilic inflammation was developed by administering intraperitoneal injections and inhalations of chicken ovalbumin (OA), with Ad administered intranasally 5 days after the OA sensitization. The administration of Ad resulted in a significant suppression of eosinophil counts in peripheral blood as well as in the bronchoalveolar lavage fluid (BALF), and a decrease in OA-specific IgE. The decrease in the number of eosinophils in BALF was associated with a marked upregulation of interferon gamma (IFN-gamma) expression. In contrast, the Ad-specific, delayed-type hypersensitivity response and efficacy of reporter gene expression mediated by Ad were only marginally affected in animals sensitized with OA. Together, these data support the idea that Ad administration in patients with Th2-mediated immune disorders does not exacerbate the parameters of ongoing inflammations or gene transfer efficiency, and with its ability to induce prominent type 1 immune response to the antigen in vivo, Ad could potentially be used as an efficient adjuvant to control immune disorders where Th2 cell-mediated mechanisms are involved.

Prospects for gene-based immunopharmacology in salivary glands

The clinical potential of gene transfer is increasing. One likely major application of this emerging biotechnology will be for gene therapeutics, the use of a gene as a drug. Salivary glands provide an unusual but increasingly valuable target site for gene transfer. Studies in animal salivary glands from several laboratories, including our own, have provided proof of this concept. In this review, we provide a background and perspective on possible strategies for gene-based immunopharmacology in salivary glands. We use as a target disease model the autoimmune exocrinopathy Sjögren's syndrome.

Latest developments in gene transfer technology: achievements, perspectives, and controversies over therapeutic applications

Over the last decade, more than 300 phase I and phase II gene-based clinical trials have been conducted worldwide for the treatment of cancer and monogenic disorders. Lately, these trials have been extended to the treatment of AIDS and, to a lesser extent, cardiovascular diseases. There are 27 currently active gene therapy protocols for the treatment of HIV-1 infection in the USA. Preclinical studies are currently in progress to evaluate the possibility of increasing the number of gene therapy clinical trials for cardiopathies, and of beginning new gene therapy programs for neurologic illnesses, autoimmuno diseases, allergies, regeneration of tissues, and to implement procedures of allogeneic tissues or cell transplantation. In addition, gene transfer technology has allowed for the development of innovative vaccine design, known as genetic immunization. This technique has already been applied in the AIDS vaccine programs in the USA. These programs aim to confer protective immunity against HIV-1 transmission to individuals who are at risk of infection. Research programs have also been considered to develop therapeutic vaccines for patients with AIDS and generate either preventive or therapeutic vaccines against malaria, tuberculosis, hepatitis A, B and C viruses, influenza virus, La Crosse virus, and Ebola virus. The potential therapeutic applications of gene transfer technology are enormous. However, the effectiveness of gene therapy programs is still questioned. Furthermore, there is growing concern over the matter of safety of gene delivery and controversy has arisen over the proposal to begin in utero gene therapy clinical trials for the treatment of inherited genetic disorders. From this standpoint, despite the latest significant achievements reported in vector design, it is not possible to predict to what extent gene therapeutic interventions will be effective in patients, and in what time frame.

Fas- and tumor necrosis factor receptor 1-dependent but not perforin-dependent pathways cause injury in livers infected with an adenovirus construct in mice

Intravenous injection of type 5 adenovirus, deleted in the E1 and E3 regions, is shown to result in expression of viral antigens in the liver, initiating lymphocyte infiltration and liver injury. Following this infection, induction of Fas ligand (FasL), tumor necrosis factor alpha (TNF-alpha), and perforin mRNA are all demonstrable in the liver, pointing to a role of respective pathways in liver injury. Making use of mice in which the genes coding for Fas, FasL, TNF receptors (TNFRs), and perforin are inactivated, as well as recombinant proteins that inhibit Fas- and TNF-alpha-mediated apoptosis, it is shown that a functional perforin-mediated mechanism is not obligatory for cellular infiltration and progression of liver injury. In contrast functional Fas- and TNF-alpha-mediated mechanisms were found to be essential for liver injury to occur. Results are presented demonstrating that signaling through TNFR1, but not TNFR2, is involved in TNF-alpha-mediated liver damage. The conclusion is drawn that although perforin mRNA is induced in the virus-infected liver, Fas- and TNF-alpha-mediated mechanisms constitute the principal pathways by which the cell-mediated immune system causes acute liver injury.

Deletion of the adenoviral E1b-19kD gene enhances tumor cell killing of a replicating adenoviral vector

Replicating adenoviral vectors are a promising new modality for cancer treatment and clinical trials with such vectors are ongoing. Targeting these vectors to cancer cells has been the focus of research. However, even if perfect targeting were to be achieved, a vector still must effectively kill cancer cells and spread throughout the bulk of the tumor. The adenoviral E1b-19kD protein is a potent inhibitor of apoptosis and may therefore compromise the therapeutic efficacy of an adenoviral vector. In this study we have investigated if an E1b-19kD gene deletion could improve the ability of a replicating adenoviral vector to spread through and kill cancer cells. In several lung cancer cell lines an E1b-19kD-deleted virus (Ad337) induced substantially more apoptosis than did a wild-type virus (Ad309), and tumor cell survival was significantly reduced in three of four cell lines. In addition, the apoptotic effects of cisplatin or paclitaxel were augmented by Ad337, but inhibited by wild-type virus. The number of infectious virus particles in the supernatant of infected cells was increased with Ad337 compared with wild-type virus, indicating enhanced early viral release. Ad337, in contrast to Ad309, induced significantly larger plaques after infection of A549 cells. This well-described large plaque phenotype of an E1b-19kD mutant virus is likely the result of early viral release and enhanced cell-to-cell viral spread. Loss of E1b-19kD function caused only minor cell line-specific increase or decrease in viral yield. We conclude that deletion of the E1b-19kD gene may enhance the tumoricidal effects of a replicating adenoviral vector.

Adenoviral-mediated gene transfer to mouse salivary glands

Adenoviral vectors effectively transfer genes to rat salivary glands. However, potent immune responses limit their use in vivo. Mice offer more opportunities than rats for the study of these immune processes. We first established conditions for infection of mouse salivary glands, with an adenoviral vector. The effects of time, viral dose, viral diluent buffer volume, and dexamethasone on expression of a transgene, luciferase, were determined by means of the recombinant vector AdCMVluc. Optimal luciferase expression was observed when the vector was suspended in 50 microL of buffer. This volume completely filled the gland parenchyma and slightly distended the capsule. Dexamethasone increased immediate transgene expression and reduced the acute inflammation one day following viral administration, but did not alter subsequent mononuclear inflammation or transgene expression 14 or 28 days later. An adenoviral vector encoding either anti-inflammatory cytokine IL-4 or IL-10 was co-administered with AdCMVluc to increase transgene expression at 14 and 28 days. While this strategy did not extend the duration of luciferase expression, co-administration of AdCMVIL-10 with AdCMVluc almost completely eliminated the chronic inflammatory infiltrate in the glands after 28 days. This study demonstrates that adenoviral-mediated gene transfer to mouse submandibular glands is possible by intraductal cannulation and that reduction of either the acute or chronic inflammatory infiltrates was insufficient to increase long-term transgene expression in this tissue.

TNF-alpha receptor signaling and IL-10 gene therapy regulate the innate and humoral immune responses to recombinant adenovirus in the lung

Recombinant adenovirus-mediated gene therapy has demonstrated great promise for the delivery of genes to the pulmonary epithelium. However, dose-dependent inflammation and local immune responses abbreviate transgene expression. The purpose of these studies was to determine the role of TNF-alpha and individual TNF receptor signaling to adenovirus clearance and immune responses, and whether coexpression of human IL-10 could reduce inflammation and extend the duration of transgene expression in the lung. beta-Galactosidase expression in mice receiving intratracheal instillation of Adv/beta-gal (adenovirus construct expressing beta-galactosidase) was transient (less than 14 days), but a significant early increase of beta-galactosidase expression was seen in mice lacking either or both TNF-alpha receptors. Absence of TNF-alpha or the p55 receptor significantly attenuated the Ab response to both adenovirus and beta-galactosidase. Human IL-10 expression in the lung suppressed local TNF-alpha production following AdV/hIL-10 (adenovirus construct expressing human IL-10) delivery, but did not lead to increased or prolonged transgene expression when coexpressed with beta-galactosidase. Expression of human IL-10 following AdV/hIL-10 instillation extended at least 14 days, was nonimmunogenic, and suppressed the development of neutralizing Abs against adenoviral proteins as well as against human IL-10. We conclude that TNF-alpha signaling through both the p55 and p75 receptor plays important roles in the clearance of adenoviral vectors and the magnitude of the humoral immune response. Additionally, although coexpression of human IL-10 with beta-galactosidase had only modest effects on transgene expression, we demonstrate that AdV/hIL-10 is well tolerated, has extended expression compared with beta-galactosidase, and is nonimmunogenic in the lung.

Sustained expression of human apolipoprotein A-I after adenoviral gene transfer in C57BL/6 mice: role of apolipoprotein A-I promoter, apolipoprotein A-I introns, and human apolipoprotein E enhancer

Elevation of HDL cholesterol, after adenoviral apolipoprotein A-I (apo A-I) gene transfer, may delay or revert ischemic cardiovascular disease, provided transgene expression is persistent. Previously, we observed transient human apo A-I expression after adenoviral gene transfer with a cytomegalovirus (CMV)-driven construct containing the human apo A-I cDNA. Therefore, the effects of promoters (CMV or 256 base pairs of the human apo A-I promoter), introns of the human apo A-I gene, and the liver-specific human apolipoprotein E (apo E) enhancer on adenovirus-mediated human apo A-I expression were evaluated in C57BL/6 mice. In the presence of the CMV promoter, human apo A-I introns prolonged expression above 20 mg/dl from 14 to 35 days. Addition of one, two, or four copies of the human apo E enhancer in these constructs resulted in a copy-dependent but transient increase in expression for 14 days. The apo A-I promoter induced 3.2-fold lower peak levels of human apo A-I than did the CMV promoter, but insertion of four apo E enhancers in the apo A-I promoter-driven construct resulted in human apo A-I levels above 20 mg/dl for 6 months. The decline between day 6 and day 35 of human apo A-I expression driven by the CMV promoter was due to (1) a 2.5-fold decline in transgene DNA levels that is not observed with apo A-I promoter-driven constructs, and (2) CMV promoter attenuation as evidenced by a 7.6-fold decline in the human apo A-I mRNA/human apo A-I DNA copy number ratio between day 6 and day 35. Hepatotoxicity, as evidenced by up to 10-fold higher serum levels of transaminases on day 6 after gene transfer with CMV promoter-driven constructs than with apo A-I promoter-driven constructs, probably caused the accelerated decline of transgene DNA. In conclusion, gene transfer with an adenovirus comprising the 256-bp apo A-I promoter, the genomic apo A-I DNA, and four apo E enhancers, all of human origin, is associated with low hepatotoxicity and with the absence of promoter shutoff resulting in human apo A-I expression above 20 mg/dl for up to 6 months.

Fibroblast growth factor 2-retargeted adenoviral vectors exhibit a modified biolocalization pattern and display reduced toxicity relative to native adenoviral vectors

Targeted vectors provide a number of advantages for systemic and local gene delivery strategies. Several groups have investigated the utility of using various ligands to alter the tropism of adenovirus (Ad) vectors. We have previously demonstrated that fibroblast growth factor (FGF) ligands can specifically target DNA transfection and Ad transduction through high-affinity FGF receptors (FGFRs). FGFRs are overexpressed in abnormally proliferating tissues, such as malignancies. The present studies explore the effects of retargeting with FGF2 on the tissue localization pattern and the systemic toxicity of Ad in mice. Results of semiquantitative PCR analyses indicate that the distribution of FGF2-Ad vector genome sequences after intravenous administration in mice is altered. Markedly lower amounts (10- to 20-fold) of FGF2-Ad localize to the liver when compared with native Ad. This decrease in liver deposition translates into a significant reduction in subsequent toxicity as measured by serum transaminases and histopathology in mice injected with FGF2-AdHSV-thymidine kinase with and without ganciclovir administration. In an intraperitoneal model of ovarian cancer, FGF2-Ad generates increased transgene expression in tumor tissue when compared with Ad. Taken together, these results indicate that the retargeting of Ad with FGF2 results in a more efficient vector system for systemic and regional gene therapy applications, with concomitant lower levels of systemic toxicity.

Long-term reversal of hypercholesterolemia in low density lipoprotein receptor (LDLR)-deficient mice by adenovirus-mediated LDLR gene transfer combined with CD154 blockade

BACKGROUND

Deficiency of the low density lipoprotein receptor (LDLR) results in abnormal elevation of cholesterol within the intermediate and low density plasma lipoproteins (IDL/LDL), and predisposes to early onset atherosclerosis. Cholesterol reduction after adenovirus-mediated LDLR gene transfer to LDLR-deficient animals is transient, due to the elicitation of an immune response.

METHODS

The LDLR-deficient mouse was used as a model to investigate adenovirus-mediated LDLR gene transfer combined with short-term immunosuppression as a cholesterol lowering therapy. Mice were infused with replication-deficient recombinant adenovirus encoding LDLR under control of the cytomegalovirus promoter/enhancer (AdLDLR), and injected with a blocking antibody directed against CD154 (CD40 ligand) to suppress immune responses against the vector and foreign transgene product.

RESULTS

Mice given AdLDLR and treated with anti-CD154 expressed LDLR on hepatocytes and maintained cholesterol levels below or within normal range for at least 92 days. In contrast, without adjunct immunosuppression LDLR expression was transient, corresponding to temporary decline in cholesterol levels. Analysis of cholesterol concentrations in fractionated plasma showed remarkable reduction in all lipoprotein fractions at early time-points after gene transfer. At later time-points, non-immunosuppressed control mice regained the disease profile with elevated IDL/LDL cholesterol, while profiles of anti-CD154-treated mice were similar to normal. LDLR mRNA transcripts were present in livers of the anti-CD154-treated mice but not controls, 93 days after AdLDLR injection. However, vector DNA was detected in livers of both groups. These results suggest that loss of LDLR expression in the non anti-CD154-treated mice was in part due to immune-mediated promoter silencing, and that anti-CD154 prevented this effect.

CONCLUSION

Treatment with anti-CD154 antibody inhibits immune-mediated loss of transgene expression, enabling long-term reduction in cholesterol levels after AdLDLR gene transfer to LDLR-deficient mice.

Genetically modified CD34+ cells as cellular vehicles for gene delivery into areas of angiogenesis in a rhesus model

To develop a cellular vehicle able to reach systemically disseminated areas of angiogenesis, we sought to exploit the natural tropism of circulating endothelial progenitor cells (EPCs). Primate CD34+ EPCs were genetically modified with high efficiency and minimal toxicity using a non-replicative herpes virus vector. These EPCs localized in a skin autograft model of angiogenesis in rhesus monkeys, and sustained the expression of a reporter gene for several weeks while circulating in the blood. In animals infused with autologous CD34+ EPCs transduced with a thymidine kinase-encoding herpes virus, skin autografts and subcutaneous Matrigel pellets impregnated with vascular growth factors underwent necrosis or accelerated regression after administration of ganciclovir. Importantly, the whole intervention was perfectly well tolerated. The accessibility, easy manipulation, lack of immunogenicity of the autologous CD34+ cell vehicles, and tropism for areas of angiogenesis render autologous CD34+ circulating endothelial progenitors as ideal candidates for exploration of their use as cellular vehicles when systemic gene delivery to those areas is required. Gene Therapy (2000) 7, 43-52.

Cellular immune responses of healthy individuals to intradermal administration of an E1-E3- adenovirus gene transfer vector

In animals, Ad-mediated gene transfer initiates anti-Ad host immune responses that vary, depending on vector design, dose, host, and transgene. To begin to understand whether the anti-Ad vector responses in humans simulate those in animals, Ad(GV)CD.10, an E1-E3- Ad5 vector encoding the E. coli cytosine deaminase gene, was administered by the intradermal route to six normal individuals (8 x 10(7) to 8 x 10(9) particle units, each dose administered to two sites; n = 2 per group). No adverse events were observed. Polymerase chain reaction/Southern analysis demonstrated vector genome in the skin through 28 days in all individuals except one of two at the lowest dose. Local induration, independent of vector dose and baseline systemic anti-Ad5 neutralizing antibodies, developed in all subjects (6 to 17 mm, peak by day 3). Biopsies revealed a mild to moderate T cell (CD3+, CD4+, CD8+), B cell, and macrophage infiltrate at day 3, all decreased by day 28. Langerhans cells accumulated primarily in the papillary dermis. The day 3 cellular response was dose independent. On day 28, CD4+ and CD8+ T lymphocytes and macrophages showed dose dependency. There was minimal systemic Ad5-specific lymphocyte proliferation induced by Ad vector administration in three individuals studied, and no Ad5-specific cytotoxic T lymphocytes (evaluated in two subjects) could be detected. Thus, intradermal administration of an E1-E3- Ad vector to normal subjects induces mild/moderate local cellular responses, even in Ad-immunized individuals. These observations provide a baseline to determine if these human anti-Ad vector host responses can be circumvented by using "stealth" vectors and/or immunosuppression.

Enhanced Liver Uptake of Opsonized Red Blood Cells After In Vivo Transfer of FcγRIIA cDNA to the Liver

Fcγ receptors convey to phagocytic cells the ability to recognize, bind, and internalize IgG-coated cells and microorganisms. The present study demonstrates the use of adenovirus (Ad)-mediated gene transfer of human Fcγ receptor IIA cDNA to convert normally nonphagocytic cells (hepatocytes) into functional equivalents of phagocytic cells. Ad vector in vitro transfer and expression of FcγRIIA cDNA in primary rat hepatocytes was confirmed by flow cytometry anti-FcγRIIA immunodetection, and the function of the receptor was demonstrated by enhanced binding and phagocytosis of 51Cr-labeled IgG-opsonized erythrocytes. After in vivo gene transfer to rats, expression of FcγRIIA cDNA in hepatocytes was confirmed by Northern analysis and immunohistochemistry. Rats infected with the Ad vector carrying the FcγRIIA cDNA demonstrated enhanced clearance of opsonized erythrocytes, but not nonopsonized erythrocytes, from the circulation with increased sequestration within the liver. Together, these data demonstrate that Ad-mediated FcγRIIA gene transfer can convert normally IgG-nonphagocytic cells into phagocytic cells capable of recognizing, binding, and ingesting an opsonized particulate antigen, suggesting that gene transfer strategies might be used to transiently augment host defense by enhancing the clearance of immune complexes.

Replication-defective bovine adenovirus type 3 as an expression vector

Although recombinant human adenovirus (HAV)-based vectors offer several advantages for somatic gene therapy and vaccination over other viral vectors, it would be desirable to develop alternative vectors with prolonged expression and decreased toxicity. Toward this objective, a replication-defective bovine adenovirus type 3 (BAV-3) was developed as an expression vector. Bovine cell lines designated VIDO R2 (HAV-5 E1A/B-transformed fetal bovine retina cell [FBRC] line) and 6.93.9 (Madin-Darby bovine kidney [MDBK] cell line expressing E1 proteins) were developed and found to complement the E1A deletion in BAV-3. Replication-defective BAV-3 with a 1.7-kb deletion removing most of the E1A and E3 regions was constructed. This virus could be grown in VIDO R2 or 6.93.9 cells but not in FBRC or MDBK cells. The results demonstrated that the E1 region of HAV-5 has the capacity to transform bovine retina cells and that the E1A region of HAV-5 can complement that of BAV-3. A replication-defective BAV-3 vector expressing bovine herpesvirus type 1 glycoprotein D from the E1A region was made. A similar replication-defective vector expressing the hemagglutinin-esterase gene of bovine coronavirus from the E3 region was isolated. Although these viruses grew less efficiently than the replication-competent recombinant BAV-3 (E3 deleted), they are suitable for detailed studies with animals to evaluate the safety, duration of foreign gene expression, and ability to induce immune responses. In addition, a replication-competent recombinant BAV-3 expressing green fluorescent protein was constructed and used to evaluate the host range of BAV-3 under cell culture conditions. The development of bovine E1A-complementing cell lines and the generation of replication-defective BAV-3 vectors is a major technical advancement for defining the use of BAV-3 as vector for vaccination against diseases of cattle and somatic gene therapy in humans.

A Mouse Model of Arterial Gene Transfer

Abstract —We developed a murine model of arterial gene transfer and used it to test the role of antigen-specific immunity in the loss of adenovirus-mediated transgene expression. Adenoviral vectors encoding either β-galactosidase (β-gal) or green fluorescent protein were infused to the lumen of normal common carotids of CD-1 and C57BL/6 mice and atherosclerotic carotids of Apoe −/− mice. At 3 days after gene transfer, significant reporter gene expression was detected in all strains. Transgene expression was transient, with expression undetectable at 14 days. Next, a β-gal–expressing vector was infused into carotids of ROSA26 mice (transgenic for, and therefore tolerant of, β-gal) and RAG-2 −/− mice (deficient in recombinase-activating gene [RAG]-2 and therefore lacking in antigen-specific immunity). β-Gal expression was again high at 3 days but declined substantially (>90%) by 14 days. In vivo labeling with bromodeoxyuridine revealed that carotid endothelial proliferation was increased dramatically by the gene-transfer procedure alone, likely leading to the loss of episomal adenoviral DNA. Gene transfer to normal and atherosclerotic mouse carotids can be accomplished; however, elimination of antigen-specific immune responses does not prevent the early loss of adenovirus-mediated transgene expression. Efforts to prolong adenovirus-mediated transgene expression in the artery wall must be redirected. These efforts will likely include strategies to avoid the consequences of increased cell turnover. Nevertheless, despite the brevity of expression, this mouse model of gene transfer to normal and severely atherosclerotic arteries will likely be useful for investigating the genetic basis of vascular disease and for developing gene therapies. The full text of this article is available at http://www.circresaha.org.

Administration of helper-dependent adenoviral vectors and sequential delivery of different vector serotype for long-term liver-directed gene transfer in baboons

The efficiency of first-generation adenoviral vectors as gene delivery tools is often limited by the short duration of transgene expression, which can be related to immune responses and to toxic effects of viral proteins. In addition, readministration is usually ineffective unless the animals are immunocompromised or a different adenovirus serotype is used. Recently, adenoviral vectors devoid of all viral coding sequences (helper-dependent or gutless vectors) have been developed to avoid expression of viral proteins. In mice, liver-directed gene transfer with AdSTK109, a helper-dependent adenoviral (Ad) vector containing the human alpha(1)-antitrypsin (hAAT) gene, resulted in sustained expression for longer than 10 months with negligible toxicity to the liver. In the present report, we have examined the duration of expression of AdSTK109 in the liver of baboons and compared it to first-generation vectors expressing hAAT. Transgene expression was limited to approximately 3-5 months with the first-generation vectors. In contrast, administration of AdSTK109 resulted in transgene expression for longer than a year in two of three baboons. We have also investigated the feasibility of circumventing the humoral response to the virus by sequential administration of vectors of different serotypes. We found that the ineffectiveness of readministration due to the humoral response to an Ad5 first-generation vector was overcome by use of an Ad2-based vector expressing hAAT. These data suggest that long-term expression of transgenes should be possible by combining the reduced immunogenicity and toxicity of helper-dependent vectors with sequential delivery of vectors of different serotypes.

Effects of stuffer DNA on transgene expression from helper-dependent adenovirus vectors

We have analyzed transgene (lacZ) expression from a first-generation adenovirus (Ad) vector in comparison to helper-dependent (hd) Ads deleted for various portions of the viral coding sequences and generated by using the Cre/loxP helper-dependent system (R. J. Parks et al., Proc. Natl. Acad. Sci. USA 93:13565-13570, 1996). An hd vector deleted for approximately 70% of the Ad genome (AdRP1001) provided levels and durations of transgene expression similar to those of a control first generation Ad vector containing an identical expression cassette. Deletion of all Ad sequences from the hdAd and replacement with a approximately 22-kb fragment of lambda DNA resulted in a decrease in the level and duration of lacZ expression which could not be reversed by the inclusion of a matrix attachment region. However, substitution of the lambda stuffer in the fully deleted hdAd with sequences from the human hypoxanthine-guanine phosphoribosyltransferase gene resulted in significantly improved transgene expression. In vitro assays for cytotoxic T lymphocytes (CTL) directed against putative peptides encoded by the vector backbone showed that, although CTL were generated against the vector containing the lambda DNA, no such CTL were generated against the vector containing the hypoxanthine-guanine phosphoribosyltransferase (HPRT) sequences. Surprisingly, the rate of loss of the HPRT- and lambda-containing vectors from mouse liver was similar, despite the differences in expression kinetics, indicating that the lambda stuffer-directed CTL were inefficient at eliminating the transduced cells. Thus, the nature of the DNA backbone of hdAds can have important effects on the functioning of the vector. Since most fully deleted vectors require "stuffer" DNA as part of the vector backbone to maintain optimum vector size, these observations must be taken into account in the design of hdAd vectors.

Angiogenesis gene therapy: phase I assessment of direct intramyocardial administration of an adenovirus vector expressing VEGF121 cDNA to individuals with clinically significant severe coronary artery disease

BACKGROUND

Therapeutic angiogenesis, a new experimental strategy for the treatment of vascular insufficiency, uses the administration of mediators known to induce vascular development in embryogenesis to induce neovascularization of ischemic adult tissues. This report summarizes a phase I clinical experience with a gene-therapy strategy that used an E1(-)E3(-) adenovirus (Ad) gene-transfer vector expressing human vascular endothelial growth factor (VEGF) 121 cDNA (Ad(GV)VEGF121.10) to induce therapeutic angiogenesis in the myocardium of individuals with clinically significant coronary artery disease.

METHODS AND RESULTS

Ad(GV)VEGF121.10 was administered to 21 individuals by direct myocardial injection into an area of reversible ischemia either as an adjunct to conventional coronary artery bypass grafting (group A, n=15) or as sole therapy via a minithoracotomy (group B, n=6). There was no evidence of systemic or cardiac-related adverse events related to vector administration. In both groups, coronary angiography and stress sestamibi scan assessment of wall motion 30 days after therapy suggested improvement in the area of vector administration. All patients reported improvement in angina class after therapy. In group B, in which gene transfer was the only therapy, treadmill exercise assessment suggested improvement in most individuals.

CONCLUSIONS

The data are consistent with the concept that direct myocardial administration of Ad(GV)VEGF121.10 to individuals with clinically significant coronary artery disease appears to be well tolerated, and initiation of phase II evaluation of this therapy is warranted.

Retargeted delivery of adenoviral vectors through fibroblast growth factor receptors involves unique cellular pathways

A major goal of gene therapy is to improve target specificity by delivering vectors through alternative cellular receptors. We previously reported that adenoviral vector delivery through basic fibroblast growth factor (FGF2) receptors enhances both cellular transduction and in vivo efficacy. We now present studies addressing the cellular pathways and mechanisms underlying these events. Cellular receptors for adenoviruses are not required for transduction by FGF2-retargeted vectors. Moreover, alpha(V) integrins can antagonize FGF2 retargeting, in contrast to their obligatory role in non-retargeted vector delivery. By contrast, high-affinity FGF receptors, which are overexpressed on potential tumor targets, are required for FGF2-retargeted transduction. Low-affinity heparan sulfate proteoglycan interactions, however, are not a prerequisite, in marked contrast to their obligatory role in FGF2 mitogenic signaling. By comparing receptor expression and ligand binding with transgene expression, we also demonstrate that FGF2 retargeting enhances transduction by mechanisms other than increasing the number of targeted cells. Rather, the use of alternative targeting ligands supports the conclusion that specific receptor interactions and intracellular events serve to enhance transgene expression. Together, these studies highlight the unique delivery and transduction pathways used by FGF2-retargeted adenoviruses, and help define the basis for their enhanced in vivo efficacy.

Adenovirus-mediated gene expression in vivo is enhanced by the antiapoptotic bcl-2 gene

An adenovirus vector encoding the human Bcl-2 gene (hBcl-2) was derived. In vivo expression of hBcl-2 in murine livers enhanced and prolonged adenovirus-mediated gene expression. Furthermore, in the hBcl-2-treated group a significant reduction in the apoptosis induced by the adenovirus vector was observed. Thus, the cytoprotection of the vector-infected cells with antiapoptotic genes appears promising for successful in vivo gene therapy.

Strategy of liver-directed gene therapy: present status and future prospects

The liver is particularly amenable to gene therapy as it is the site of many metabolic diseases and malignancies. Thus, liver-directed gene therapy is being actively pursued and developed as a method of treatment for various liver diseases. Strategies of liver-directed gene therapy include drug delivery to the liver, compensation of the defective gene(s), anti-tumor activity, anti-viral therapy, and immunomodulation. The strategy chosen for liver-directed gene therapy depends on the genetic basis of the disease. Many aspects are key factors to the success of the chosen strategy: intervention of genes, efficient gene delivery system, stable transgene expression, transgene regulation, target cell transfection, and timing of transgene expression. Several tactics can be used to overcome problems in the above, and these include the use of a gene switch to exogenously regulate transgene expression, targeting at the transcriptional level, circumvention of the immune response (as in the use of adenovirus vector to achieve long-term correction of genetic diseases), and genetically engineered antibodies in gene transfer. At the present rate of research activity and development, gene therapies may soon be more efficient than current standard treatments for some liver diseases.

Use of a liver-specific promoter reduces immune response to the transgene in adenoviral vectors

Previous studies using adenoviral (Ad) vectors expressing human alpha1-antitrypsin (hAAT) under the control of ubiquitous promoters (RSV, mPGK) elicited the production of antibodies to hAAT in some mouse strains (C3H/HeJ and BALB/c) but not in others (C57BL/6J). In contrast, when a helper-dependent Ad vector (AdSTK109) with all viral coding sequences deleted and expressing hAAT from human genomic DNA with the endogenous promoter was used, C3H/HeJ mice failed to develop antibodies and demonstrated long-term expression. These results suggested that promoter choice and/or properties of the vector itself might influence the host immune response to the transgene product. Direct comparison of first-generation vectors expressing the hAAT cDNA from a ubiquitous mouse PGK promoter rather than from a liver-specific mouse albumin promoter demonstrated that an antibody response to hAAT occurred with the mPGK promoter but not with the albumin promoter in C3H/HeJ mice. As expected, neither vector elicits an antibody response in C57BL/6J mice. Coinjection of the two first-generation vectors containing the mPGK and albumin promoter in C3H/HeJ mice induced an antibody response with resulting loss of detectable hAAT from the sera of the injected mice in 3-4 weeks. From these data, we conclude that under certain conditions, the choice of promoter with its associated liver-specific expression can modulate the host immune response to the transgene independent of viral backbone.

Insertion of an RGD motif into the HI loop of adenovirus fiber protein alters the distribution of transgene expression of the systemically administered vector

Adenoviral vectors are attractive gene delivery vehicles, but their in vivo utility is reduced by lack of cell-specific infection. Tropism modification of the virion by genetic manipulation of capsid proteins is an attractive strategy to achieve targeted transduction. However, no genetic targeting strategies have yet been shown to modify the distribution of transgene expression following systemic administration of vector. This is an essential requirement if such approaches are to form a basis for further vector develop- ment. In this report we present data showing that insertion of a RGD motif into the HI loop of the adenoviral fiber knob results in a significant change in transgene expression profile following intravenous administration. The key finding that a motif in the HI loop is available for cellular interaction when administered systemically means that such modifications can be rationally considered as a foundation upon which further genetic modifications can be superimposed for targeted systemic gene therapy.

Implication of interfering antibody formation and apoptosis as two different mechanisms leading to variable duration of adenovirus-mediated transgene expression in immune-competent mice

This study explores the genetic and immunologic factors involved in the differences in duration of transgene expression following in vivo transduction with recombinant adenoviruses. Different strains of mice (C3H/HeJ [C3H], C57BL/6J [B6], BALB/cJ [Balb/c], C. B10-H2(b)/LiMcdJ [Balb.B], CB6F1/J [(Balb/c x B6)F1], B6C3F1/J [(B6 x C3H)F1], and BALB/cj SCID) received 5 x 10(9) PFU of the first-generation adenovirus, which expresses human alpha1-antitrypsin (Ad/RSVhAAT). While all strains studied showed similar patterns of anti-adenovirus antibody formation, only Balb/c and C3H mice developed significant levels of anti-hAAT antibodies by 8 weeks posttransduction. In addition, while all strains had quantitatively comparable amounts of adenovirus genomes and hAAT mRNA transcripts in the liver 9 days posttransduction, only Balb/c mice had undetectable adenovirus vector genomes and hAAT mRNA in the liver 40 days posttransduction. Terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling staining of liver sections from control and Ad/RSVhAAT-infected mice 5, 9, and 40 days posttransduction suggested that apoptosis was involved in the rapid elimination of transduced hepatocytes in Balb/c mice. Persistent expression of hAAT protein observed in BALB/cj SCID mice suggests that antigen-dependent immunity was essential for this apoptotic process in transduced Balb/c hepatocytes. In contrast to Balb/c mice, the loss of expression in C3H mice did not correlate with the loss of vector genomes or hAAT mRNA. Instead, the anti-hAAT antibodies in C3H but not Balb/c mice were found to interfere with detection of hAAT in the serum. In Balb. B and B6 mice, vector genome, hAAT mRNA transcripts, and hAAT protein levels persisted for at least 40 days posttransduction. This persistence correlated with poor anti-hAAT antibody formation and minimal hepatocyte toxicity. The expression of hAAT in (Balb/c x B6)F1 pups was found to be intermediate between the duration observed in the parental strains, while in (C3H x B6)F1 pups hAAT expression was similar to that seen in the B6 parents, which together support polygenic control of the immune responses in these mice. In summary, these findings suggest that there are three different profiles and at least two defined immune system-mediated mechanisms resulting in the loss of hAAT expression in mice and that different strains differ in the capacity to utilize these mechanisms.

Safety of direct myocardial administration of an adenovirus vector encoding vascular endothelial growth factor 121

A gene therapy strategy involving direct myocardial administration of an adenovirus (Ad) vector encoding the vascular endothelial growth factor 121 cDNA (Ad(GV)VEGF121.10) has been shown to be capable of "biological revascularization" of ischemic myocardium in an established porcine model [Mack, C.A. (1998). J. Thorac. Cardiovasc. Surg. 115, 168-177]. The present study evaluates the local and systemic safety of this therapy in this porcine ischemia model and in normal mice. Myocardial ischemia was induced in Yorkshire swine with an ameroid constrictor 21 days prior to vector administration. Ad(GV)VEGF121.10 (10(9) or 10(10) PFU), Ad5 wild type (10(9) PFU), AdNull (control vector with no transgene; 10(9) PFU), saline, or no injection (naive) was administered in 10 sites in the ischemic, circumflex distribution of the myocardium. Toxicity was assessed by survival, serial echocardiography, blood analyses, and myocardial and liver histology at 3 and 28 days after vector administration. All pigs survived to sacrifice, except for one animal in the Ad(GV)VEGF121.10 (10(10) PFU) group, which died as a result of oversedation. Echocardiograms of Ad(GV)VEGF121.10-treated pigs demonstrated no differences in pericardial effusion, mitral valve regurgitation, or regional wall motion compared with control pigs. Intramyocardial administration of Ad(GV)VEGF121.10 included only minimal myocardial inflammation and necrosis, and no hepatic inflammation or necrosis. Only a mild elevation of the white blood cell count was encountered on day 3, which was transient and self-limited in the Ad(GV)VEGF121.10 group as compared with the saline-treated animals. As a measure of inadvertent intravascular administration of vector, normal C57/BL6 mice received intravenous Ad(GV)VEGF121.10 (10(4), 10(6), 5 x 10(7), or 10(9) PFU), AdNull (5 x 10(7) or 10(9) PFU), or saline. Toxicity was assessed by survival, blood analyses, and organ histology at 3 and 7 days after vector administration. A separate group of C57/BL6 mice received intravenous AdmVEGF164 (Ad vector encoding the murine VEGF164 cDNA), Ad(GV)VEGF121.10, AdNull (10(8) PFU each group), or saline to assess duration of expression and safety of a homologous transgene. All mice survived to sacrifice except for 40% of the mice in the highest (10(9) PFU; a dose more than 10(3)-fold higher by body weight than the efficacious dose in pigs) Ad(GV)VEGF121.10 dose group, which died on days 5-6 after vector administration. The only differences seen in the blood analyses between treated and control mice were in the very high Ad(GV)VEGF121.10 dose group (10(9) PFU), which demonstrated an anemia as well as an increase in alkaline phosphatase when compared with all other treatment groups. Hepatic VEGF levels by ELISA in AdmVEGF164-treated mice did not persist beyond 14 days after vector administration, suggesting that persistent expression of a homologous VEGF gene transferred with an Ad vector is not a significant safety risk. Although this is not a chronic toxicity study, these data demonstrate the safety of direct myocardial administration of Ad(GV)VEGF121.10, and support the potential use of this strategy to treat human myocardial ischemia.

Recombinant adenovirus vectors for cytokine gene therapy in mice

BACKGROUND

Adenoviruses have several specific features useful for gene therapy. They infect various lineages of cells irrespective of cell cycle status. However, the exact mechanism of their infection and in vivo kinetics as a gene expression vector have not been elucidated.

OBJECTIVE

Using adenovirus vectors expressing marker genes, we examined the infectivity of these vectors (including cellular and tissue tropism), the duration and intensity of transgene expression, and the side effects.

METHODS

Various cells were infected with adenovirus expressing LacZ gene at various doses, and beta-galactosidase activity was measured and compared in relation with dose, time course, and cellular vitronectin receptor. Mice were injected with adenoviruses expressing LacZ, luciferase and GM-CSF, and in vivo gene expression was examined.

RESULTS

Adenovirus infection induced viral dose-dependent transgene expression that persisted for 2 weeks. Adherent cells were infected much more efficiently than nonadherent cells, probably because the former expressed much higher levels of the vitronectin receptor, one of the main receptors for adenovirus. Studies performed in mice with luciferase-expressing adenovirus revealed that the liver was the main target organ after intravenous injection and showed that the intravenous route was superior to other routes with regard to transgene expression. After intravenous injection of adenovirus expressing human GM-CSF, there was a transient and dose-dependent increase in the serum level of this cytokine. Administration of adenovirus expressing mouse GM-CSF enhanced hematopoiesis in the spleen and bone marrow.

CONCLUSION

These results indicated that adenoviruses can be used for in vivo cytokine gene therapy but suggested the necessity of taking into consideration the route of administration, the duration of transgene expression, the toxic dose, and host immune reactions.

Rapid clearance of syngeneic transplanted hepatocytes following transduction with E-1-deleted adenovirus indicates early host immune responses and offers novel ways for studying viral vector, target cell and host interactions

To distinguish between transduced cell clearance and transgene regulation following adenoviral gene transfer, we infected F344 rat hepatocytes with an E-1-deleted adenovirus (Ad beta gal) and studied cell survival in the liver of dipeptidyl peptidase IV-deficient (DPPIV-) F344 rats. Transplanted cells were localized with histochemical staining for DPPIV and transgene expression localized with staining for beta-galactosidase (lacZ). The transgene was expressed in 90-100% hepatocytes without impairment in cell viability in vitro, although transplanted cells were cleared mostly within 1 day by infiltrates containing activated macrophages, CD4+ or CD8+ lymphocytes, and phagocytes. When Ad beta gal-transduced hepatocytes were transplanted repeatedly at 14-day intervals, transplanted cells were cleared rapidly each time. LacZ expression following Ad beta gal administration to intact animals was associated with apoptosis and unscheduled DNA synthesis in the liver. To determine whether adenoviral antigen expression activated consequential MHC-restricted liver injury, we transplanted Ad beta gal-hepatocytes followed subsequently by transplantation of nontransduced hepatocytes. Transplanted cells expressing Ad beta gal were rapidly cleared as before, whereas nontransduced hepatocytes engrafted with progressive liver repopulation. The findings indicated that adenovirally transduced cells are cleared early in the host liver. Use of ex vivo strategies will facilitate analysis of modified adenoviral vectors in the context of immunoregulatory, cellular and viral mechanisms.

The extra- and intracellular barriers to lipid and adenovirus-mediated pulmonary gene transfer in native sheep airway epithelium

Gene transfer to the respiratory epithelium is currently suboptimal and may be helped by the identification of limiting biological barriers. We have, therefore, developed an ex vivo model which retains many of the characteristics of in vivo native airways including mucociliary clearance, mucus coverage and an intact cellular structure. Using this model we have demonstrated several barriers to gene transfer. Liposome-mediated gene transfer was inhibited by normal mucus, with removal of this layer increasing expression approximately 25-fold. In addition both liposome and adenovirus were inhibited by CF sputum. The apical membrane represented a significant barrier to both agents. Adenovirus-mediated expression could be significantly augmented by increasing contact time or by pre-treatment of tissues with a nominally calcium-free medium. The presence of these extracellular and plasma membrane barriers appeared to be the key parameters responsible for the approximately three log difference in gene expression found in vitro compared with our ex vivo model. Cytoskeletal elements and the cell cycle also influenced in vitro gene transfer, and represent further barriers which need to be overcome.

Systemic viral interleukin-10 gene delivery prevents cartilage invasion by human rheumatoid synovial tissue engrafted in SCID mice

OBJECTIVE

To assess the effects of viral interleukin-10 (vIL-10) gene delivery on human rheumatoid synovial tissue.

METHODS

SCID mice were engrafted subcutaneously with human rheumatoid synovial tissue and homologous cartilage before systemic injection of 10(9) plaque-forming units of type 5 E1a Elb-deficient non-replicative adenovirus vector containing the vIL-10 gene under control of the cytomegalovirus promoter (AdvIL-10; n = 10) or a control gene (AdvIL-10mut; n = 7). Three weeks later, the graft was removed for histologic analysis of cartilage invasion by synovial tissue. The number of CD3-positive mononuclear cells was assessed in the synovial tissue by immunohistology. Messenger RNA (mRNA) expression of matrix metalloproteinase 3 (MMP-3), tissue inhibitor of metalloproteinases 1 (TIMP-1), and proinflammatory cytokines was determined by polymerase chain reaction.

RESULTS

Systemic vIL-10 gene transfer resulted in high sustained production of vIL-10 protein in SCID mouse sera (mean +/- SD 25 +/- 5 ng/ml on day 40 post vector injection). Moreover, vIL-10 mRNA expression was detected in the synovial tissue 3 weeks after intravenous injection of AdvIL-10, reflecting the gene transfer in the human graft. In animals treated with AdvIL-10, cartilage invasion by rheumatoid synovial tissue was significantly inhibited compared with the control vector (mean +/- SD histologic score 2.5 +/- 0.52 versus 0.75 +/-0.8; P < 0.0001). The number of T cells infiltrating the synovium and perichondral resorption in the animals treated with AdvIL-10 gene were not significantly modified relative to the control vector. In animals treated with AdvIL-10, the MMP-3-TIMP-1 balance was partially restored, independent of the effect on mRNA expression of tumor necrosis factor a, IL-1, IL-6, or IL-8.

CONCLUSION

Systemic vIL-10 gene transfer prevented cartilage invasion by synovial tissue engrafted in SCID mice. This model offers the opportunity to study the biologic effects of gene transfer in vivo in rheumatoid synovium.

Effect of clodronate on macrophage depletion and adenoviral-mediated transgene expression in salivary glands

Expression of transgenes from adenoviral vectors is short-lived in salivary glands, in part because of immune responses to the virus and/or transgene product. Previous studies demonstrated that depletion of macrophages with multilamellar liposomes containing clodronate (Cl2MBP) increases adenoviral-mediated transgene expression in the liver. This technique was tested in salivary glands. Rats were treated with Cl2MBP-liposomes or control liposomes by femoral vein, intraperitoneal, or carotid artery injections. Thereafter, a recombinant adenovirus, AdCMVluciferase, was instilled intraductally in submandibular glands (SMGs), or delivered to the liver via femoral vein injection. Marked depletion (>94%) of liver macrophages and increased levels of luciferase activity in the liver (45-fold higher than controls) were present in animals receiving Cl2MBP-liposomes. In contrast, the same treatment never depleted more than 41% of SMG macrophages nor increased luciferase activity in SMGs, regardless of the route of administration. In conclusion, while macrophage depletion with Cl2MBP-liposomes is associated with markedly increased adenoviral-mediated transgene expression, this strategy was ineffective for salivary glands.

Inhibition of adenovirus-mediated gene transfer by bronchoalveolar lavage fluid

Human and animal trials with recombinant adenovirus have been discouraging, since the level of recombinant gene expression was low. Nonspecific and specific immune response mediated by, for example, macrophages, T cells and immunoglobulins may prevent infection or cause death of infected cells. We analyzed the effect of bronchoalveolar lavage fluid (BAL) on the efficiency of adenoviral infection in vitro. A total of 26 BAL samples of randomly selected patients was examined. Adenovirus-mediated gene transfer was quantified using AdCMV. Null, a recombinant adenovirus, in a modified titer assay based on immunocytochemical detection of infected 293 cells. In addition, the concentration of anti-adenovirus-type 5 IgA, IgG and IgM antibodies in BAL was determined by ELISA. 53.8% of the BAL samples (14 out of 26) reduced adenoviral infectivity by at least 50% (factor of inhibition > or = 2). All BAL samples effecting, a reduction in adenoviral infectivity contained detectable amounts of anti-adenovirus-type 5-IgA antibodies. However, the correlation between the concentration of IgA antibody and the strength of inhibition was weak (r = 0.336). Even high levels of anti-adenovirus-type 5-IgM, IgG or IgA antibodies did not influence adenoviral infectivity consistently. This observation indicates that BAL contains (a) anti-adenovirus-type 5 antibodies which are not directed against adenoviral epitopes responsible for the viral adherence and uptake process; and/or (b) inhibitors of viral infectivity different from antibodies.

Modification of the genetic program of human alveolar macrophages by adenovirus vectors in vitro is feasible but inefficient, limited in part by the low level of expression of the coxsackie/adenovirus receptor

Robust expression of genes transferred by adenovirus (Ad) vectors depends upon efficient entry of vectors into target cells. Cells deficient in the coxsackie/adenovirus receptor (CAR) are difficult targets for Ad-mediated gene transfer. We hypothesized that low levels of CAR expression may be responsible, in part, for the relative inefficiency of Ad-mediated gene transfer to human alveolar macrophages (AMs). CAR gene expression was detected in human AMs by reverse transcription-polymerase chain reaction and at low levels by Northern analysis. Indirect immunofluorescence showed specific, low-intensity surface staining for CAR, but at levels below those found on the positive-control A549 human lung epithelial cell line. Consistent with this, AMs expressed Ad vector transgenes 100 to 1,000-fold less efficiently than A549 cells, as assessed using the beta-galactosidase reporter (chemiluminescence assay) and green fluorescent protein (fluorescence microscopy and flow cytometry). At high multiplicity of infection, AMs from an HIV+ individual could be transduced with an AdIFNgamma vector to secrete detectable human interferon-gamma. Ad transgene expression by AMs was blocked by capsid fiber protein, suggesting that CAR is required in the pathway for productive Ad entry into alveolar macrophages. To confirm that Ad transgene expression by AMs is limited by low levels of CAR expression, cells were infected with an Ad vector containing the CAR complementary DNA (cDNA). Enhanced expression of CAR protein was demonstrated by indirect immunofluorescence, and the CAR cDNA-transduced cells showed 5-fold enhancement of subsequent Ad transgene expression. These observations demonstrate that human AMs can be targets for Ad-mediated gene transfer, but that efficiency of transgene expression is limited, at least in part, by low levels of CAR expression.

Interleukin-1 mediates a rapid inflammatory response after injection of adenoviral vectors into the brain

Adenovirus-mediated gene transfer into the brain is associated with significant inflammation and activation of anti-vector and anti-transgene immune responses that curtail the gene delivery of adenoviruses and therapeutic efficacy. Elucidating the molecular mediators of inflammatory and immune responses to adenoviruses injected into the brain should allow us to inhibit their inflammatory actions, thereby reducing vector clearance and enhance adenoviral-mediated gene transfer into the CNS. Cytokines are primary mediators of the immune response and are released during inflammation. Here we report for the first time that injection of replication-deficient adenovirus vectors into the cerebral ventricles of rats causes a rapid increase in body temperature. This fever response precedes any vector-encoded transgene expression and occurs with vectors encoding no transgene, as well as with vectors encoding a therapeutic transgene i.e., HSV1-thymidine kinase. No fever is detected after infection of the striatum, an important brain target in studies on neurodegeneration. After infection of the brain ventricles, CSF levels of immunoreactive tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta increase significantly (up to 300-fold). In the hypothalamus, the locus of thermoregulation in the brain, only IL-1beta and IL-6 are significantly elevated. A neutralizing TNF-alpha antibody has no effect on adenovirus-induced fever. However, pretreatment with either the IL-1 receptor antagonist or the cyclooxygenase inhibitor flurbiprofen completely abolishes adenovirus-induced fever, suggesting that IL-1 and prostaglandins are direct mediators of this response. These results are the first to demonstrate that IL-1, but not TNF-alpha, is the main mediator of a very early inflammatory response to adenovirus in the brain.

Persistence of an [E1-, polymerase-] adenovirus vector despite transduction of a neoantigen into immune-competent mice

The ability of a uniquely modified [E1-, polymerase-] adenovirus (Ad) vector to persist after the transduction of the bacterial beta-galactosidase gene into the livers of nontolerant, immune-competent adult mice was compared with an identical gene transfer attempt with an [E1-] Ad vector. After transduction, the E1-deleted vector was rapidly eliminated, but the modified vector persisted for at least 2 months (experiment duration). Modified vector persistence was also accompanied by prolonged transgene expression and decreased hepatotoxicity profiles. This result was in contrast to several reports suggesting that the transgene expressed by an Ad vector is the primary determinant of Ad vector elimination in vivo. Our results implied that the rapid immune clearance of Ad-transduced cells in vivo is codependent on the presence of two stimuli, or "hits." Hit 1 is due to Ad vector-derived gene expression while hit 2 is due to transgene immunogenicity. Attenuation of the first hit by the use of a significantly modified vector (such as the [E1-, polymerase-] Ad vector) allowed for extended persistence, despite the continued presence of the transgene-derived stimulus (hit 2). We discuss how the two-hit hypothesis is in fact congruent with a number of other reports that have analyzed Ad vector persistence in immune-competent animals. On the basis of our results, [E1-, polymerase-] Ad vectors should have broad benefits for use in human gene therapy situations in which the encoded transgene may be perceived as a neoantigen by the intact human immune system.

Selective Expansion of Alveolar Macrophages In Vivo by Adenovirus-Mediated Transfer of the Murine Granulocyte-Macrophage Colony-Stimulating Factor cDNA

Based on the hypothesis that genetic modification of freshly isolated alveolar macrophages (AM) with the granulocyte-macrophage colony-stimulating factor (GM-CSF) cDNA would induce AM to proliferate, this study focuses on the ability of adenoviral (Ad) vectors to transfer and efficiently express the murine (m) GM-CSF cDNA in murine AM with consequent expansion in the number of AM in vitro and in vivo. To demonstrate that an Ad vector can effectively transfer and express genes in AM, murine AM recovered by bronchoalveolar lavage from the lung of Balb/c mice were infected with an Ad vector coding for green fluorescent protein (GFP) in vitro and expressed GFP in a dose-dependent fashion. Infection of AM with an Ad vector containing an expression cassette coding for mGM-CSF led to GM-CSF expression and to AM proliferation in vitro. When AM infected with AdGFP were returned to the respiratory tract of syngeneic recipient mice, GFP-expressing cells could still be recovered by bronchoalveolar lavage 2 weeks later. In vitro infection of AM with AdmGM-CSF and subsequent transplantation of the genetically modified AM to the lungs of syngeneic recipients led to GM-CSF expression in vivo. Strikingly, the AM recovered by lavage 5 weeks after transplantation demonstrated an increased rate of proliferation, and the total number of alveolar macrophages was 1.9-fold greater than controls. Importantly, the increase in the numbers of AM was selective (ie, other inflammatory cell numbers were unchanged), and there was no modification to the lung architecture. Thus, it is feasible to genetically modify AM with Ad vectors and to use this strategy to modify the behavior of AM in vivo. Based on the importance of AM in the primary defense of the respiratory epithelial surface, this strategy may be useful in enhancing pulmonary defenses in immunodeficiency states.

Selective Expansion of Alveolar Macrophages In Vivo by Adenovirus-Mediated Transfer of the Murine Granulocyte-Macrophage Colony-Stimulating Factor cDNA

Based on the hypothesis that genetic modification of freshly isolated alveolar macrophages (AM) with the granulocyte-macrophage colony-stimulating factor (GM-CSF) cDNA would induce AM to proliferate, this study focuses on the ability of adenoviral (Ad) vectors to transfer and efficiently express the murine (m) GM-CSF cDNA in murine AM with consequent expansion in the number of AM in vitro and in vivo. To demonstrate that an Ad vector can effectively transfer and express genes in AM, murine AM recovered by bronchoalveolar lavage from the lung of Balb/c mice were infected with an Ad vector coding for green fluorescent protein (GFP) in vitro and expressed GFP in a dose-dependent fashion. Infection of AM with an Ad vector containing an expression cassette coding for mGM-CSF led to GM-CSF expression and to AM proliferation in vitro. When AM infected with AdGFP were returned to the respiratory tract of syngeneic recipient mice, GFP-expressing cells could still be recovered by bronchoalveolar lavage 2 weeks later. In vitro infection of AM with AdmGM-CSF and subsequent transplantation of the genetically modified AM to the lungs of syngeneic recipients led to GM-CSF expression in vivo. Strikingly, the AM recovered by lavage 5 weeks after transplantation demonstrated an increased rate of proliferation, and the total number of alveolar macrophages was 1.9-fold greater than controls. Importantly, the increase in the numbers of AM was selective (ie, other inflammatory cell numbers were unchanged), and there was no modification to the lung architecture. Thus, it is feasible to genetically modify AM with Ad vectors and to use this strategy to modify the behavior of AM in vivo. Based on the importance of AM in the primary defense of the respiratory epithelial surface, this strategy may be useful in enhancing pulmonary defenses in immunodeficiency states.