Readministration of adenovirus vector in nonhuman primate lungs by blockade of CD40-CD40 ligand interactions

Oncolytic Virotherapy: An Advanced Microbial Approach for the Management of Cancer

Destruction of the tumor (cancerous) cells may be caused by live viruses, which have replicative ability and replicate selectively in tumor cells, known as oncolytic virotherapy. In comparison of conservative cancer therapy, tumor-selective replicating viruses have more advantages. These viruses have introduced new methodologies for the human cancer treatment. Numerous strategies are used in development of virotherapeutics. Virotherapy is not unusual concept, but modern advances in technology of genetic modification of oncolytic viruses have improved the ability of targeting tumor cells more specifically, it triggered the development of novel ammunition to fight cancer. An effective virotherapeutic approach with oncolytic viruses exhibits the feasibility and safety under clinical approach. New strategies are being explored to overcome basic obstacles and challenges in virotherapy. Administration of oncolytic viruses, logically, will successfully augment new treatments against many kinds of tumors. Some encouraging antitumor responses shown by combination therapy are provoking strong immunity against established cancer. Chief developments in oncolytic virotherapy have seen in past several years. Significant understandings have been provided by findings on the interface among immune comebacks and viruses, whereas potential results have shown in clinical trials.

Delivery of Anti-IFNAR1 shRNA to Hepatic Cells Decreases IFNAR1 Gene Expression and Improves Adenoviral Transduction and Transgene Expression

Chronic liver injury leads to advanced fibrosis, cirrhosis, and hepatocellular carcinoma. Genetical cell treatment related to the use of adenovirus (Ads) has proven to be beneficial and efficient in the recovery of hepatic diseases. Nevertheless, they are highly immunogenic and trigger an immune response where interferons type 1 (IFN-I) play a very important role. Three shRNAs against the Interferon-1 receptor (IFNAR1) were designed and cloned in pENTR/U6 plasmid and amplified in DH5α cells. Huh7 cells were transfected with these plasmids in the presence or absence of 1 × 10⁹ viral particles/ml of adenovirus containing the green fluorescent protein gene used as a reporter. Transfection with the shRNA plasmids partially inhibited the IFNAR1 expression. This inhibition substantially decreased antiviral response, demonstrated by the decrease of IFNAR1, IFN-α, and TNF-α gene expression, and the decrease at protein levels of IFNAR1, Protein kinase RNA-activated (PKR), and phosphorylated STAT1, allowing higher adenoviral transduction and transgene expression. Interestingly it was seen shRNA inhibited macrophage activation. These results suggest that the inhibition of the IFN-I pathway could be a strategy to minimize the immune response against Adenoviral vectors allowing higher Adenovirus transduction extending the transgene expression.

Repeated systemic dosing of AAV vectors in immunocompetent mice after blockade of T-cell costimulatory pathways

Neutralizing antibodies (NAbs) strongly limit adeno-associated virus (AAV) vector transduction and repeated administration. Previous studies have shown that NAbs induced by AAVs are associated with T and B cell activation and that the B7/CD28 and CD40/CD40L costimulation signaling pathways are involved. CTLA4 and CD40 are vital molecules that participate in the costimulatory pathway. In this study, we evaluated CTLA4-Ig and CD40-Ig immunosuppressive efficacies through AAV and investigated their effects on the feasibility for multiple systemic administrations of AAV vectors. The results showed that a single administration of AAV vector carrying either CTLA4-Ig alone or with CD40-Ig could greatly reduce the level of NAbs. An AAV serotype-specific immune tolerance could be successfully established, which enabled repeated, i.e., second and third, systemic administration of AAV vectors in the same mice. A combination of CTLA4-Ig and CD40-Ig delivered via AAV vectors significantly inhibited T and B cell activations without affecting immune response to the total immunoglobulin G (IgG) production and cytokines. Interestingly, exogenous gene expression significantly improved after multiple administrations of AAV vector in vivo. Our study generates a reliable and effective method for repeated dosing of AAV vectors that is needed on gene therapy.

Adenovirus Biodistribution is Modified in Sensitive Animals Compared to Naïve Animals

Pre-existing immune response against adenovirus could diminish transgene expression efficiency when Ad is employed in humans as gene therapy vector. We previously used Ad-hΔuPA (Recombinant adenovirus expressing human urokinase-type plasminogen activator) as antifibrotic gene therapy in cirrhosis models and demonstrated its effectiveness. As a further clinical approach, transient Cyclosporine A (CsA) immunosuppression was induced in cirrhotic animals to determine whether Ad-hΔuPA administration retained efficacy. Adenovirus sensitization was achieved by systemic administration of non-therapeutic Ad-βGal (Recombinant adenovirus expressing beta-galactosidase) after 4 weeks of intraperitoneal carbon tetrachloride (CCl₄) regimen. Cirrhosis induction continued up to 8 weeks. At the end of CCl₄ intoxication, immunosuppression was achieved with three CsA doses (40 mg/kg) as follows: 24 h before administration of Ad-hΔuPA, at the moment of Ad-hΔuPA injection and finally, 24 h after Ad-hΔuPA inoculation. At 2 and 72 h after Ad-hΔuPA injection, animals were sacrificed. Liver, spleen, lung, kidney, heart, brain, and testis were analyzed for Ad-biodistribution and transgene expression. In naïve animals, Ad-hΔuPA genomes prevailed in liver and spleen, while Ad-sensitized rats showed Ad genomes also in their kidney and heart. Cirrhosis and Ad preimmunization status notably diminished transgene liver expression compared to healthy livers. CsA immunosuppression in cirrhotic animals has no effect on Ad-hΔuPA biodistribution, but increments survival.

Long-Term Expression of the Human CFTR Gene in Mouse Airway via Helper-Dependent Adenoviral Vector Delivery and Transient Immunosuppression

Sustained expression of the CFTR gene is a major challenge to gene therapy with either viral or nonviral vectors with immune response to vector and transgene products. One strategy to achieve sustained CFTR expression is to modulate the host immune system through transient immunosuppression. In this study, we examined cyclophosphamide (cytoxan), dexamethasone (Dex), and a combination of cyclosporin, methylprednisolone, and azathioprine (combination) for their effects on long-term expression of the human CFTR delivered with helper-dependent adenoviral vectors in mouse airways. We found that cyclophosphamide significantly enhanced long-term expression of the transgenic human CFTR and the reporter gene LacZ by reducing host immune responses. Dex administration greatly reduced neutralizing antibody production but had no effect on transgene expression. Treatment with a combination of cyclosporin A, azathioprine, and methylprednisolone affected neither CFTR gene expression nor inflammation. Our data suggest that transient immunosuppression might be a strategy to improve sustained expression in gene therapy.

Xenogenic Adenoviral Vectors

Many nonhuman adenoviruses (AdVs) of simian, bovine, porcine, canine, ovine, murine, and fowl origin are being developed as gene delivery systems for recombinant vaccines and gene therapy applications. In addition to circumventing preexisting human AdV (HAdV) immunity, nonhuman AdV vectors utilize coxsackievirus-adenovirus receptor or other receptors for vector internalization, thereby expanding the range of cell types that can be targeted. Nonhuman AdV vectors also provide excellent platforms for veterinary vaccines. A specific nonhuman AdV vector when used in its species of origin could provide an excellent animal model for evaluating the vector efficacy and pathogenesis. These vectors are useful in prime–boost approaches with other AdV vectors or with other gene delivery systems including DNA immunization and viral or bacterial vectors. When multiple vector inoculations are required, nonhuman AdV vectors could supplement HAdV or other viral vectors.

Vaccines within vaccines: the use of adenovirus types 4 and 7 as influenza vaccine vectors

Adenovirus Types 4 and 7 (Ad4 and Ad7) are associated with acute respiratory distress (ARD). In order to prevent widespread Ad-associated ARD (Ad-ARD) the United States military immunizes new recruits using a safe and effective lyophilized wildtype Ad4 and Ad7 delivered orally in an enteric-coated capsule. We cloned Ad4 and Ad7 and modified them to express either a GFP-Luciferase (GFPLuc) fusion gene or a centralized influenza H1 hemagglutinin (HA1-con). BALB/c mice were injected with GFPLuc expressing viruses intramuscularly (i.m.) and intranasally (i.n.). Ad4 induced significantly higher luciferase expression levels as compared with Ad7 by both routes. Ad7 transduction was restored using a human CD46+ transgenic mouse model. Mice immunized with serial dilutions of viruses expressing the HA1-con influenza vaccine gene were challenged with 100 MLD 50 of influenza virus. Ad4 protected BALB/c mice at a lower dose by i.m. immunization as compared with Ad7. Unexpectedly, there was no difference in protection by i.n. immunization. Although Ad7 i.m. transduction was restored in CD46+ transgenic mice, protection against influenza challenge required even higher doses as compared with the BALB/c mice. However, Ad7 i.n. immunized CD46+ transgenic mice were better protected as compared with Ad4. Interestingly, the restoration of Ad7 transduction in CD46+ mice did not increase vaccine efficacy and indicates that Ad7 may transduce a different subset of cells through alternative receptors in the absence of CD46. These data indicate that both Ad4 and Ad7 can effectively induce anti-H1N1 immunity against a heterologous challenge using a centralized H1 gene. Future studies in non-human primates or human clinical trials will determine the overall effectiveness of Ad4 and Ad7 as vaccines for influenza.

Unlinked memory helper responses promote long-lasting humoral alloimmunity

Essential help for long-lived alloantibody responses is theoretically provided only by CD4 T cells that recognize target alloantigen, processed and presented by the allospecific B cell. We demonstrate that in an alloresponse to multiple MHC disparities, cognate help for class-switched alloantibody may also be provided by CD4 T cells specific for a second "helper" alloantigen. This response was much shorter-lived than when help was provided conventionally, by Th cell recognition of target alloantigen. Nevertheless, long-lasting humoral alloimmunity developed when T cell memory against the helper alloantigen was first generated. Costimulatory blockade abrogated alloantibody produced through naive Th cell recognition of target alloantigen but, crucially, blockade was ineffective when help was provided by memory responses to the accessory helper alloantigen. These results suggest that memory Th cell responses against previously encountered graft alloantigen may be the dominant mechanism for providing help to generate new specificities of alloantibody in transplant patients receiving immunosuppression.

Improving adenovirus based gene transfer: strategies to accomplish immune evasion

Adenovirus (Ad) based gene transfer vectors continue to be the platform of choice for an increasing number of clinical trials worldwide. In fact, within the last five years, the number of clinical trials that utilize Ad based vectors has doubled, indicating growing enthusiasm for the numerous positive characteristics of this gene transfer platform. For example, Ad vectors can be easily and relatively inexpensively produced to high titers in a cGMP compliant manner, can be stably stored and transported, and have a broad applicability for a wide range of clinical conditions, including both gene therapy and vaccine applications. Ad vector based gene transfer will become more useful as strategies to counteract innate and/or pre-existing adaptive immune responses to Ads are developed and confirmed to be efficacious. The approaches attempting to overcome these limitations can be divided into two broad categories: pre-emptive immune modulation of the host, and selective modification of the Ad vector itself. The first category of methods includes the use of immunosuppressive drugs or specific compounds to block important immune pathways, which are known to be induced by Ads. The second category comprises several innovative strategies inclusive of: (1) Ad-capsid-display of specific inhibitors or ligands; (2) covalent modifications of the entire Ad vector capsid moiety; (3) the use of tissue specific promoters and local administration routes; (4) the use of genome modified Ads; and (5) the development of chimeric or alternative serotype Ads. This review article will focus on both the promise and the limitations of each of these immune evasion strategies, and in the process delineate future directions in developing safer and more efficacious Ad-based gene transfer strategies.

Efficient, specific and targeted delivery of genes to the lung

Many inherited and acquired pulmonary disorders without satisfactory therapies may be amenable to gene therapy. Despite numerous advances, efficient delivery and expression of the therapeutic transgene at physiological levels for phenotypic correction of disease has proved elusive. This article focuses on various strategies aimed at achieving targeted delivery to the lungs. Both physical methods and biological targeting have been successfully applied in various gene delivery systems. Targeting of different cell types has been achieved by pseudotyping of viral vectors with capsids from different serotypes and modification of nonviral vectors with targeting ligands. Both classes of vectors are discussed with respect to their gene delivery and expression efficiencies, longevity of expression and immunogenicity. Moreover, gene therapy clinical trials for different lung diseases are discussed.

Gene transfer to the lung: lessons learned from more than 2 decades of CF gene therapy

Gene therapy is currently being developed for a wide range of acute and chronic lung diseases. The target cells, and to a degree the extra and intra-cellular barriers, are disease-specific and over the past decade the gene therapy community has recognized that no one vector is good for all applications, but that the gene transfer agent (GTA) has to be carefully matched to the specific disease target. Gene therapy is particularly attractive for diseases that currently do not have satisfactory treatment options and probably easier for monogenic disorders than for complex diseases. Cystic fibrosis (CF) fulfils these criteria and is, therefore, a good candidate for gene therapy-based treatment. This review will focus on CF as an example for lung gene therapy, but lessons learned may be applicable to other target diseases.

Co-expression of sCD40LIg and CTLA4Ig mediated by adenovirus prolonged mouse skin allograft survival

OBJECTIVE

To investigate the role of simultaneous blockade of CD40/CD40L and B7/CD28 pathways in the immune tolerance via co-expression of sCD40LIg and CTLA4Ig mediated by replication-defective adenovirus.

METHODS

Ad-sCD40LIg-IRES(2)-CTLA4Ig, replication-defective adenovirus co-expressing sCD40LIg and CTLA4Ig, was constructed and identified. The co-expression of sCD40LIg and CTLA4Ig was evaluated with confocal laser scanning microscope and Western blotting. Skin transplantations of C57BL/6 to BALB/c mice were performed. PBS, Ad-Shuttle-CMV and Ad-sCD40LIg-IRES(2)-CTLA4Ig were administered. Skin graft survival was monitored and the mRNA expression of both genes was evaluated in the skin allografts.

RESULTS

Ad-sCD40LIg-IRES(2)-CTLA4Ig was constructed successfully and identified. The co-expression of sCD40LIg and CTLA4Ig was identified with confocal laser scanning microscopy and Western blotting. Compared to the skin graft mean survival time (MST) of non-treated group ((5.75+/-0.71) d) or Ad-Shuttle-CMV-treated group ((5.50+/-0.53) d), the skin graft MST was dramatically prolonged in the Ad-sCD40LIg-IRES(2)-CTLA4Ig-treated group ((16.38+/-1.19) d, P<0.001). The mRNA expression of both genes was detected.

CONCLUSION

Ad-sCD40LIg-IRES(2)-CTLA4Ig, a replication-defective adenovirus carrying genes encoding sCD40LIg and CTLA4Ig, was constructed. Simultaneous blockade of CD40/CD40L and B7/CD28 costimulatory pathway mediated by replication-defective adenovirus significantly prolonged skin allograft survival in mice.

Readministration of helper-dependent adenovirus to mouse lung

Adenovirus vectors (Ad) are widely used in gene therapy studies, including those aimed at treating cystic fibrosis lung disease. Various approaches have been investigated to blunt the host immune response to Ad, including development of helper-dependent (HD) Ad. The host cytotoxic T-cell response to HD-Ad is generally lower than to earlier-generation Ad. However, antibodies are formed which could inhibit the efficacy of HD-Ad readministration. In this first study of HD-Ad readministration to the lung, we found that a second administration of HD-Ad to mice was possible with minimal loss of transgene expression. In contrast, when first-generation (FG) Ad was administered initially, followed by HD-Ad or FG-Ad, transgene expression was reduced. Significantly lower concentrations of antibodies against Ad were found in lung lavage fluid and serum from mice that received two doses of HD-Ad (when the initial HD-Ad lacked a transgene), compared to mice that received FG-Ad followed by HD-Ad. These data suggest that readministration of HD-Ad for lung gene therapy may be feasible.

Intrapulmonary IFN-beta gene therapy using an adenoviral vector is highly effective in a murine orthotopic model of bronchogenic adenocarcinoma of the lung

Given previous work showing that an adenoviral vector expressing IFN-beta (Ad.IFNbeta) was highly effective in eradicating i.p. mesothelioma tumors, the antitumor efficacy of this agent was evaluated in an orthotopic model of bronchogenic adenocarcinoma of the lung. These transgenic mice have a conditionally expressed, oncogenic K-rasG12D allele that can be activated by intratracheal administration of an adenovirus expressing Cre recombinase (Ad.Cre). K-rasG12D mutant mice were given Ad.Cre intranasally to activate the oncogene. Mice were then given 10(9) plaque-forming units of a control vector (Ad.LacZ) or Ad.IFNbeta intranasally 3 and 4 weeks later, a time when lung tumors had been established. Cells derived from K-ras-mutated lung tumors were also grown in the flanks of mice to study mechanisms of therapeutic responses. In two separate experiments, untreated tumor-bearing mice all died by day 57 (median survival, 49 days). Ad.LacZ-treated mice all died by day 71 (median survival, 65 days). In contrast, 90% to 100% of mice treated with Ad.IFNbeta were long-term survivors (>120 days; P < 0.001). In addition, immunity to re-challenge with tumor cells was induced. In vitro and flank tumor studies showed that Ad.IFNbeta induced direct tumor cell killing and that depleting natural killer or CD8+ T cells, but not CD4+ T cells, with antibodies attenuated the effect of Ad.IFNbeta. These studies, showing remarkable antitumor activity in this orthotopic lung cancer model, provide strong preclinical support for a trial of Ad.IFNbeta to treat human non-small cell lung cancer.

Development of nonhuman adenoviruses as vaccine vectors

Human adenoviral (HAd) vectors have demonstrated great potential as vaccine vectors. Preclinical and clinical studies have demonstrated the feasibility of vector design, robust antigen expression and protective immunity using this system. However, clinical use of adenoviral vectors for vaccine purposes is anticipated to be limited by vector immunity that is either preexisting or develops rapidly following the first inoculation with adenoviral vectors. Vector immunity inactivates the vector particles and rapidly removes the transduced cells, thereby limiting the duration of transgene expression. Due to strong vector immunity, subsequent use of the same vector is usually less efficient. In order to circumvent this limitation, nonhuman adenoviral vectors have been proposed as alternative vectors. In addition to eluding HAd immunity, these vectors possess most of the attractive features of HAd vectors. Several replication-competent or replication-defective nonhuman adenoviral vectors have been developed and investigated for their potential as vaccine-delivery vectors. Here, we review recent advances in the design and characterization of various nonhuman adenoviral vectors, and discuss their potential applications for human and animal vaccination.

Challenges and strategies: the immune responses in gene therapy

The host immune responses, including T lymphocytes mediated immune response and humoral immune responses are the important parts of the challenges in gene therapy. There are some potential immunostimulants in gene delivery systems, such as viral and non-viral vectors. Viral gene products, transgene products, viral proteins derived from viral particles required by dead-end infection, and CpG DNA in plasmid may play important roles in inducing the host immune responses when foreign genes are transferred into the targeted tissues. The immune responses should lead to many problems in gene therapy: transient expression of therapeutic gene, non-efficient re-administration of the same vectors, and severe side-effects in clinical trials. Although RNAi may act as gene therapeutic agent for suppression of specific gene expression, little attention has been given to the potential non-specific effects that might be induced. It was reported that small interfering RNAs (siRNAs) can induce the host interferon response following transfected to mammalian cells. Facing these challenges, a number of studies have been focused on taking measures to solve them, such as immunosuppression, selection of different administration routes and dose of the vectors, using the tissue-specific promoters and modifying the vectors.

Immune responses against adenoviral vectors and their transgene products: a review of strategies for evasion

Human adenoviruses have been adopted as attractive vectors for in vivo gene therapy since they have a well-characterized genomic organization, can be grown to high titres and efficiently transduce a wide spectrum of dividing and non-dividing cells. However, the first-generation of adenoviral (Ad) vectors yielded only transient expression of the transgene in most immunocompetent mice. This constituted a major limitation of this early vector type. In contrast, persistent transgene expression can be established in immunodeficient mice. This suggests that the immunogenicity of adenoviral vectors limits the effective period of adenovirus-based gene therapy. Much effort has been put in devising strategies to circumvent the limitations imposed onto gene therapy by the immune system. Improvements in vector design have significantly improved the performance of the adenovirus vectors. Based on these results it is reasonable to anticipate that new modifications of the vectors will overcome some of the immunological barriers and will further expand the applicability of adenovirus-derived vectors.

Aerosol delivery of an enhanced helper-dependent adenovirus formulation to rabbit lung using an intratracheal catheter

BACKGROUND

Poor transduction of the ciliated airway epithelium and inefficient airway delivery of viral vectors are common difficulties encountered in lung gene therapy trials with large animals and humans.

METHODS

We delivered a helper-dependent adenovirus vector, incorporating a human epithelial cell-specific expression cassette, to rabbit lung. An intratracheal device was used to aerosolize a moderate dose of virus (5 x 10(11) particles), mixed with the enhancing agent LPC (L-alpha-lysophosphatidylcholine), directly into the airways. Lung mechanics, body weight and temperature, transgene expression and histopathology were studied at day 5.

RESULTS

Transgene expression was seen in the epithelium of large and small airways, from trachea to terminal bronchioles, with a strong tendency toward the right lung. All cell types of the surface epithelium were transduced. Extensive transduction of the epithelium (66% of cells in trachea) was obtained using virus formulated in isotonic 0.1% LPC, while virus formulated in 0.01% LPC transduced fewer cells (24% in trachea). A transient decrease in dynamic lung compliance was observed immediately following aerosol delivery. Fever and mild-to-moderate patchy pneumonia without edema were also observed.

CONCLUSION

These data demonstrate a strategy for efficient and effective transduction of airway epithelium in a large animal.

Porcine adenoviral vectors evade preexisting humoral immunity to adenoviruses and efficiently infect both human and murine cells in culture

Preexisting immunity against human adenoviruses (HAd) limits the efficiency of transduction of HAd vectors in humans. In addition, development of a vector-specific immune response after the first inoculation with a HAd vector further lowers vector uptake following readministration. We investigated the usefulness of porcine adenovirus serotype 3 (PAd3)-based vectors as a supplement to HAd vectors. Here we demonstrate that preexisting HAd-specific neutralizing antibodies in humans do not cross-neutralize PAd3. In order to generate E1A-deleted PAd3 vectors, an E1-complementing cell line of porcine origin was produced. E1A-deleted PAd3 vector expressing green fluorescent protein; GFP (PAd-GFP) and E1-deleted HAd5 vector expressing GFP (HAd-GFP) transduced human cell lines with comparable efficiencies. Both of these vectors efficiently transduced murine MT1A2 breast cancer cell line, while PAd-GFP transduced murine NIH 3T3 fibroblast cell line significantly better (P < 0.05) than HAd-GFP. These results suggest that PAd3 vectors would be promising supplement to HAd vectors as a delivery vehicle for recombinant vaccines and gene therapy applications.

A hemodynamic response to intravenous adenovirus vector particles is caused by systemic Kupffer cell-mediated activation of endothelial cells

Intravascular injection of adenoviral vectors may result in a toxic and potentially lethal reaction, the mechanism of which is poorly understood. We noted that mice demonstrated a transient change in behavior that was characterized by inactivity and lethargy within minutes after intravenous injection of relatively low doses of adenoviral vectors (including high-capacity gutless vectors). Moreover, immediately after vector injection a significant drop in blood pressure was measured that most probably was caused by the systemic activation of endothelial cells as monitored by detection of phosphorylated Akt/PKB kinase, activated endothelial nitric oxide synthase (eNOS), and nitrotyrosine. The activation of the endothelium was the result of the interaction of viral particles with Kupffer cells, which are resident macrophages of the liver representing the first line of defense of the innate immune system. Surprisingly, the uptake of vector particles by Kupffer cells not only resulted in their strong activation, but also in their nearly complete disappearance from the liver. Our results suggest that the toxicity of intravenously injected adenoviral vectors may be directly linked to the activation and destruction of Kupffer cells.

Inhibition of costimulation allows for repeated systemic administration of adenoviral vector in rhesus monkeys

Immunogenicity of recombinant adenoviral (Ad) vectors severely hampers the clinical development of gene therapy protocols using repeated vector administrations. Inhibition of costimulation by APCs was explored as a strategy to circumvent the immune response against Ad particles. This strategy was tested in rhesus monkeys, treated transiently with chimeric anti-human CD40 and anti-human CD86 antagonist monoclonal antibodies (MAbs) at the time of systemic administration of a recombinant Ad vector. After Ad vector administration in the absence of immunosuppressive treatment, transgene expression in the serum lasted about 3-4 weeks. All control animals developed a strong neutralizing antibody (NAb) response to the Ad particles, which totally prevented efficient administration of a second vector, as shown by the lack of transgene expression. Treatment with anti-CD40 and anti-CD86 chimeric MAbs delayed or blocked the development of a humoral response against Ad and the infiltration of CD8(+) lymphocytes into the liver. This resulted in (i) increased persistence of Ad-transduced cells after injection of a first vector encoding a nonimmunogenic transgene, and (ii) the possibility of readministering a second Ad vector with significant efficacy. In both respects, the combined blockade of CD40 and CD86 was more efficient than treatment with anti-CD40 alone. This study shows for the first time in non-human primates that blocking CD40 and CD86 costimulatory molecules represents a promising strategy to inhibit immune responses against an Ad vector injected systemically.

Protection of Cftr knockout mice from acute lung infection by a helper-dependent adenoviral vector expressing Cftr in airway epithelia

We developed a helper-dependent adenoviral vector for cystic fibrosis lung gene therapy. The vector expresses cystic fibrosis transmembrane conductance regulator (Cftr) using control elements from cytokeratin 18. The vector expressed properly localized CFTR in cultured cells and in the airway epithelia of mice. Cftr RNA and protein were present in whole lung and bronchioles, respectively, for 28 days after a vector dose. Acute inflammation was minimal to moderate. To test the therapeutic potential of the vector, we challenged mice with a clinical strain of Burkholderia cepacia complex (Bcc). Cftr knockout mice (but not Cftr+/+ littermates) challenged with Bcc developed severe lung histopathology and had high lung bacteria counts. Cftr knockout mice receiving gene therapy 7 days before Bcc challenge had less severe histopathology, and the number of lung bacteria was reduced to the level seen in Cftr+/+ littermates. These data suggest that gene therapy could benefit cystic fibrosis patients by reducing susceptibility to opportunistic pathogens.

Immunological hurdles to lung gene therapy

Gene delivery has the potential to offer effective treatment to patients with life-threatening lung diseases such as cystic fibrosis, alpha1-antitrypsin deficiency and lung cancer. Phase I/II clinical trials have shown that, in principle, gene transfer to the lung is feasible and safe. However, gene expression from both viral and non-viral gene delivery systems has been inefficient. In addition to extra- and intracellular barriers, the host innate and acquired immune system represents a major barrier to successful gene transfer to the lung. Results from studies in experimental animals and clinical trials have shown that inflammatory, antibody and T cell responses can limit transgene expression duration and readministration of the gene transfer vector. We will review here how the development of pharmacological and/or immunological agents can modulate the host immune system and the limitations of these strategies. A better understanding of the immunological barriers which exist in the lung might allow for a more sustained expression of the transgene and importantly help overcome the problem of readministration of viral vectors.

Selective depletion or blockade of Kupffer cells leads to enhanced and prolonged hepatic transgene expression using high-capacity adenoviral vectors

Tissue macrophages, in particular hepatic Kupffer cells (KCs), contribute to early inflammatory responses following adenoviral vector administration. This study evaluates the effect of selective and transient (3 days) depletion of KCs by a single injection of clodronate liposomes on the in vivo performance of high-capacity adenoviral (HC-Ad) vectors. In KC-depleted C57BL/6 and C3H mice increased and stabilized hAAT levels were observed following intravenous injection of HC-Ad vectors expressing human alpha-1 anti-trypsin (hAAT) either from the hAAT promoter or from the human cytomegalovirus promoter. Comparable increases in hAAT levels were obtained in mice preinjected with a transcriptionally silent HC-Ad vector. Interestingly, in the majority of animals of both strains depletion of KCs was sufficient to prevent the generation of anti-hAAT antibodies, resulting in prolonged transgene expression. Thus, short-term and selective depletion of hepatic macrophages at the same time significantly increased hepatic transgene expression and reduced the humoral immune response to the transgenic protein.

Barriers to and new approaches for gene therapy and gene delivery in cystic fibrosis

Clinical trials of gene therapy for cystic fibrosis suggest that current levels of gene transfer efficiency are probably too low to result in clinical benefit, largely as a result of the barriers faced by gene transfer vectors within the airways. The respiratory epithelium has evolved a complex series of extracellular barriers (mucus, lack of receptors, immune surveillance, etc.) aimed at preventing penetration of lumenally delivered materials, including gene therapy vectors. In addition, once in the cell, further hurdles have to be overcome, including DNA degradation, nuclear import and the ability to maintain long-term transgene expression. Strategies to overcome these barriers will be addressed in this review and include the use of: (i) clinically relevant adjuncts to overcome the extra- and intracellular barriers; (ii) less-conventional delivery routes, such as intravenous or in utero administration; (iii) more efficient non-viral vectors and 'stealth' viruses which can be re-administered; and (iv) new approaches to prolong transgene expression by means of alternative promoters or integrating vectors. These advances have the potential to improve the efficiency of gene delivery to the airway epithelium, thus making gene therapy a more realistic option for cystic fibrosis.

Gene therapy progress and prospects: cystic fibrosis

Since the cloning of the cystic fibrosis gene (CFTR) in 1989, 18 clinical trials have been carried out, including five in the 2 years reviewed here. Most trials demonstrated proof-of-principle for gene transfer to the airway. However, gene transfer efficiency with each of the three gene transfer agents (adenovirus (Ad), adeno-associated virus 2 (AAV2) and cationic liposomes) was low, and most likely insufficient to achieve clinical benefit. Here, we will review the clinical and pre-clinical progress for the last 2 years (2000-2001) and briefly speculate on future prospects for the next 2 in CF gene therapy.

Cells as vehicles for cancer gene therapy: the missing link between targeted vectors and systemic delivery?

Systemic administration of currently manufactured viral stocks has not so far achieved sufficient circulating titers to allow therapeutic targeting of metastatic disease. This is due to low initial viral titers, immune inactivation, nonspecific adhesion, and loss of particles. One way to exploit the elegant molecular manipulations that have been made to increase vector targeting is to protect these vectors until they reach the local sites of tumor growth. Various cell types home preferentially to tumors and can be loaded with the constructs required to produce targeted vectors. Here we discuss the potential of using such cell carriers to chaperone precious vectors directly to the tumors. The vectors can incorporate mechanisms to achieve tumor site-inducible expression, along with tumor cell-specific expression of the therapeutic gene and/or replicating viral genomes that would be released at the tumor. In this way, the great advances that have so far been made with the engineering of vector tropisms might be genuinely exploited and converted into clinical benefit.

Transient blocking of both B7.1 (CD80) and B7.2 (CD86) in addition to CD40-CD40L interaction fully abrogates the immune response following systemic injection of adenovirus vector

Blockade of the CD40-CD40L and CD80/CD86-CD28 costimulatory pathways represents a strategy to inhibit the immune response against Ad vectors designed for gene therapy applications. Since most previous studies have used a CTLA4-Ig fusion molecule binding to both CD80 and CD86, the respective roles of these B7 molecules remained undefined. We have studied the effect of blocking monoclonal Abs (mAbs) directed against the costimulatory molecules CD40L, CD80 and CD86, alone or in different combinations, on the humoral and cellular immune responses against Ad. Groups of mice were transiently treated with each combination of blocking mAbs upon systemic injection of a first Ad vector. Combinations of anti-CD80 + anti-CD86 or anti-CD40L + anti-CD86 mAbs resulted in strong inhibition of the immune response against Ad. Using either of these mAb pairs, a second vector could be administered 1 month after the first injection but with lower efficiency than in naive animals. Thus, CD86 stands as the pivotal B7 molecule involved in the development of the immune response against Ad. However, only the blockade of both CD80 and CD86 in addition to CD40L fully inhibited the humoral and cellular responses against the Ad vector, such that readministration after 1 month was as efficient as in naive animals. At the time of readministration, treated animals had regained their ability to mount a normal immune response to the second Ad vector, showing that tolerance was not induced.

Tumor antigen-specific induction of transcriptionally targeted retroviral vectors from chimeric immune receptor-modified T cells

High-level systemic delivery of viral vectors to tumors has proved problematic as a result of immune neutralization, nonspecific adhesion, and clearance of circulating viral particles. Some cell types localize to tumors in response to particular biological properties associated with tumor growth. Their use to deliver viral vectors to tumors would allow precious viral stocks to be protected until they can be released at high local concentrations. Here, we describe a mechanism by which retroviral vector production by T cells can be regulated by a tumor-specific trigger through engagement of a chimeric immune receptor (CIR) with its target antigen. The virus that is released from the T cells can also be transcriptionally targeted. Finally, we show that it is possible to use vector-loaded, antigen-triggered human T cells as therapeutic, tumor-specific vector delivery cells in models of both local intratumoral and systemic delivery to both lung and liver metastases. This strategy incorporates multiple levels of targeting into the delivery system at the stages of surface targeting, viral production, and gene expression.

Prolonged blockade of CD40-CD40 ligand interactions by gene transfer of CD40Ig results in long-term heart allograft survival and donor-specific hyporesponsiveness, but does not prevent chronic rejection

Previous work on blockade of CD40-CD40 ligand interaction in mice and primates with anti-CD40 ligand mAbs has resulted in a moderate prolongation of allograft survival without the development of true allograft tolerance. In this study, we show in rats that adenovirus-mediated gene transfer of CD40Ig sequences into the graft resulted in prolonged (>200 days) expression of CD40Ig and in long-term (>300 days) survival. Recipients expressing CD40Ig displayed strongly (>90%) inhibited mixed leukocyte reactions and alloantibody production at early (days 5 and 17) and late time points (>100 day) after transplantation, but showed limited inhibition of leukocyte infiltration and cytokine production as evaluated by immunohistology at early time points (day 5). Recipients of long-surviving hearts showed donor-specific hyporesponsiveness since acceptance of second cardiac allografts was donor specific. Nevertheless, long-term allografts (>100 days) displayed signs of chronic rejection vasculopathy. Occluded vessels showed leukocyte infiltration, mainly composed of CD4(+) and CD8(+) cells, macrophages, and mast cells. These recipients also showed antidonor CTL activity. Recipients expressing CD40Ig did not show nonspecific immunosuppression, as they were able to mount anticognate immune responses that were partially inhibited at early time points and were normal thereafter. We conclude that gene transfer-mediated expression of CD40Ig resulted in a highly efficient inhibition of acute heart allograft rejection in rats. This treatment induced donor-specific inhibition of certain alloreactive mechanisms in the short-, but not the long-term, which resulted in long-term survival of allografts concomitant with the development of chronic rejection.

Toxicity of a first-generation adenoviral vector in rhesus macaques

We constructed a first-generation adenovirus vector (AVC3FIX5) that we used to assess the rhesus macaque as a nonhuman primate model for preclinical testing of hemophilia B gene therapy vectors. Although we succeeded in our primary objective of demonstrating expression of human factor IX we encountered numerous toxic side effects that proved to be dose limiting. Following intravenous administration of AVC3FIX5 at doses of 3.4 x 10(11) vector particles/kg to 3.8 x 10(12) vector particles/kg, the animals in our study developed antibodies against human factor IX, and dose-dependent elevations of enzymes specific for liver, muscle, and lung injury. In addition, these animals showed dose-dependent prolongation of clotting times as well as acute, dose-dependent decreases in platelet counts and concomitant elevation of fibrinogen and von Willebrand factor. These abnormalities may be caused by the direct toxic effects of the adenovirus vector itself, or may result indirectly from the accompanying acute inflammatory response marked by elevations in IL-6, a key regulator of the acute inflammatory response. The rhesus macaque may be a useful animal model in which to evaluate mechanisms of adenovirus toxicities that have been encountered during clinical gene therapy trials.

Budesonide enhances repeated gene transfer and expression in the lung with adenoviral vectors

The immune response with generation of neutralizing antiviral antibodies is an obstacle to effective repeated adenoviral gene transfer. Different immunosuppressive drugs facilitate repeat administration of adenovectors, but the clinical utility is uncertain because of systemic side effects. We investigated the use of topical corticosteroid in improving gene expression after repeated injection of adenovectors into mouse lungs. Using a vector expressing murine interleukin-6 (mIL-6) as a marker cytokine for gene expression, we show that budesonide given around exposure to adenovirus to the lung significantly maintained high levels of expressed transgene protein in bronchoalveolar lavage fluid (BALF) after as many as four consecutive injections of virus at two weekly intervals (p = 0.02 versus saline). Differences between treatment groups were most obvious 4 and 6 wk after the initial exposure to adenovirus (equivalent to three and four total exposures). In Week 4, transgene mIL-6 concentration was 2,327 +/- 955 pg/ml in budesonide compared with 336 +/- 246 pg/ml in saline-treated mice (p = 0.001). However, budesonide did not significantly protect transgene expression beyond Week 8 (four prior exposures). The improved transgene expression in budesonide-treated compared with saline-treated animals was associated with a reduction, but not prevention of neutralizing antiviral antibodies (BALF p < 0.001, serum p = 0.04). We conclude that budesonide can be valuable in gene therapy of the lung where repeated transient gene transfer is necessary.

Local high-capacity adenovirus-mediated mCTLA4Ig and mCD40Ig expression prolongs recombinant gene expression in skeletal muscle

Multiple forms of muscular dystrophy are due to the absence of cytoskeletal muscle proteins that normally protect the integrity of muscle cells. The lack of any adequate treatments for these devastating diseases propels research toward the development of strategies for gene delivery to skeletal muscle. High-capacity adenoviral vectors (HC-AdV) devoid of all viral coding sequences have been developed to avoid expression of viral proteins by the gene therapy vector. However, the capsid proteins that are an essential component of the input viral vector and any residual helper virus in the vector preparation could induce an immune response. Furthermore, the therapeutic protein provided by a gene transfer vector presents the potential to induce an immune response in a patient who does not express a normal cellular protein due to genetic mutation. Therefore, we hypothesize that some immune suppression will be required with therapeutic gene delivery designed for the treatment of patients with inherited muscle diseases. In this study, we constructed and rescued three HC-AdVs expressing murine CTLA4Ig, murine CD40Ig, or both. The backbone vector without a gene insert was rescued as a negative control vector. The production of relevant proteins from each vector was determined in vitro. In vivo function of each of the immunosuppressant vectors was assayed by co-injection with an enhanced green fluorescent protein (EGFP)-expressing first-generation adenoviral vector (AdEGFP) into the tibialis anterior muscle of C57BL/10 mice. Higher levels of muscle EGFP expression were observed in animals receiving an immunosuppressant vector. Furthermore, the production of total anti-AdV and anti-EGFP antibodies was reduced in mice treated with each of the three immunosuppressant vectors. A second intramuscular administration of AdEGFP alone 4 weeks after the initial co-injection was successful in all immunosuppressant vector-treated groups, but not in the negative control vector-treated group. All groups had a high antibody response to adenoviral proteins after the second injection of AdEGFP alone, indicating that the initial co-injection did not tolerize against vector capsid antigens.

Improved Adenoviral Vector for Vascular Gene Therapy

Abstract —First-generation, E1-deleted adenoviral vectors (ΔE1-AV) can transduce the vascular endothelium with high efficiency, but their use is limited by the resulting acute endothelial injury and the long-term development of intimal hyperplasia. To reduce the impact of viral proteins on the gene-modified cells, a second-generation adenoviral vector with an additional pair of deletions in the E4 region was developed. To determine whether this ΔE1/ΔE4-AV vector would be useful for vascular gene transfer, we directly compared the efficiency of gene transfer to uninjured rabbit carotid arteries using either an ΔE1/ΔE4-AV or an ΔE1-AV vector encoding β-galactosidase. Both vectors efficiently transduced vascular endothelium; however, the ΔE1/ΔE4-AV vector gene–modified vessels showed higher β-galactosidase expression 10 days after gene transfer. Importantly, the ΔE1/ΔE4-AV vector produced substantially less endothelial cell activation, less inflammation, and reduced neointimal hyperplasia compared with the ΔE1-AV vector–treated vessels. The ΔE1-AV vector–transduced vessels also demonstrated significantly impaired endothelium-dependent relaxation whereas the ΔE1/ΔE4-AV vector did not impact vasomotor function, even at doses of virus in 5-fold excess of the amount required for >90% transduction of the endothelium. We conclude that the ΔE1/ΔE4-AV vector is superior to the ΔE1-AV vector for vascular gene therapy because of the prolonged transgene expression, reduced vascular inflammation, reduced intimal hyperplasia, and maintenance of normal vasomotor function.

Factors affecting long-term expression of a secreted transgene product after intravenous administration of a retroviral vector

We have studied parameters affecting in vivo expression of human growth hormone (hGH) in mice after intravenous administration of a retroviral vector encoding the protein as a model system for clotting factor VIII gene therapy. Such treatment results in a brief burst of high-level expression followed by lower level sustained expression of the hGH in the circulation. The major targets for transduction in the mouse are liver and spleen. Such direct transduction (i.e., without surgical or chemical induction of cell division) requires vector at high titer (>/=10(8) cfu/ml) and is dose dependent. Transduction efficiency decreases with increasing age of the recipient. Nevertheless, long-term expression in adults is observed after administration of vector as a split dose on 2 consecutive days. We also show that anti-vector immune responses may enhance long-term expression and that both anti-vector and anti-transgene immunity can be modulated. This work provides a framework for the rational development of means to enhance the efficiency of retroviral vectors for use in clinical gene replacement therapy.

An immunomodulatory procedure that stabilizes transgene expression and permits readministration of E1-deleted adenovirus vectors

Immune responses against E1-deleted adenovirus vectors and/or their transgene products result in the rapid elimination of vector-transduced cells and the generation of neutralizing antibodies. Different strategies of immunomodulation to stabilize transgene expression at therapeutic levels and to permit productive vector readministration have been examined. Our previous studies have shown that depletion of macrophages from spleen and liver decreases hepatic inflammation, significantly prolongs transgene expression, and delays the onset of humoral immune responses after systemic administration of an E1-deleted adenovirus vector. In the present study, we have examined the effects of macrophage depletion in combination with temporary blockade of CD40 ligation on E1-deleted adenovirus vector-mediated gene transfer. Alone, each of these treatments significantly inhibited the humoral immune response against the transgene product and prolonged its expression. Together, these treatments completely stabilized transgene expression and inhibited the production of neutralizing anti-adenovirus antibodies, permitting successful vector readministration. Animals rendered immunologically unresponsive to vector and transgene antigens regained their ability to mount productive immune responses against the vector after recovery of immune function, but remained unresponsive to the transgene product. These experiments demonstrate that this treatment is transient and antigen-specific.