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

Decreased Vector Gene Expression from E2b Gene-Deleted Adenovirus Serotype 5 Vaccines Intensifies Proinflammatory Immune Responses

Recombinant adenovirus serotype 5 (Ad5) vectors are promising vaccine candidates due to their intrinsic immunogenicity and potent transgene expression; however, widespread preexisting Ad5 immunity has been considered a developmental impediment to the use of traditional, or conventional, E1 and E3 gene-deleted Ad5 (Ad5[E1-]) vaccines. Even in the presence of anti-Ad5 immunity, recent murine and human studies have confirmed E2b gene-deleted Ad5 (Ad5[E1-,E2b-]) vaccines to be highly efficacious inducers of transgene-specific memory responses and significantly less toxic options than Ad5[E1-] vaccines. While these findings have been substantially confirmed, the molecular mechanisms underlying the different reactions to these vaccine platforms are unknown. Using cultures of human peripheral blood mononuclear cells (hPBMCs) derived from multiple human donors, we found that Ad5[E1-,E2b-] vaccines trigger higher levels of hPBMC proinflammatory cytokine secretion than Ad5[E1-] vaccines. Interestingly, these responses were generated regardless of the donors' preexisting anti-Ad5 humoral and cell-mediated immune response status. In vitro hPBMC infection with the Ad5[E1-,E2b-] vaccine also provoked greater Th1-dominant gene responses yet smaller amounts of Ad-derived gene expression than Ad5[E1-] vaccines. These results suggest that Ad5[E1-,E2b-] vaccines, in contrast to Ad5[E1-] vaccines, do not promote activities that suppress innate immune signaling, thereby allowing for improved vaccine efficacy and a superior safety profile independently of previous Ad5 immunity.

The generation and analyses of a novel combination of recombinant adenovirus vaccines targeting three tumor antigens as an immunotherapeutic

Phenotypic heterogeneity of human carcinoma lesions, including heterogeneity in expression of tumor-associated antigens (TAAs), is a well-established phenomenon. Carcinoembryonic antigen (CEA), MUC1, and brachyury are diverse TAAs, each of which is expressed on a wide range of human tumors. We have previously reported on a novel adenovirus serotype 5 (Ad5) vector gene delivery platform (Ad5 [E1-, E2b-]) in which regions of the early 1 (E1), early 2 (E2b), and early 3 (E3) genes have been deleted. The unique deletions in this platform result in a dramatic decrease in late gene expression, leading to a marked reduction in host immune response to the vector. Ad5 [E1-, E2b-]-CEA vaccine (ETBX-011) has been employed in clinical studies as an active vaccine to induce immune responses to CEA in metastatic colorectal cancer patients. We report here the development of novel recombinant Ad5 [E1-, E2b-]-brachyury and-MUC1 vaccine constructs, each capable of activating antigen-specific human T cells in vitro and inducing antigen-specific CD4⁺ and CD8⁺ T cells in vaccinated mice. We also describe the use of a combination of the three vaccines (designated Tri-Ad5) of Ad5 [E1-, E2b-]-CEA, Ad5 [E1-, E2b-]-brachyury and Ad5 [E1-, E2b-]-MUC1, and demonstrate that there is minimal to no “antigenic competition” in in vitro studies of human dendritic cells, or in murine vaccination studies. The studies reported herein support the rationale for the application of Tri-Ad5 as a therapeutic modality to induce immune responses to a diverse range of human TAAs for potential clinical studies.

Adenovirus-based vaccination against Clostridium difficile toxin A allows for rapid humoral immunity and complete protection from toxin A lethal challenge in mice

Clostridium difficile associated diarrhea (CDAD) is a critical public health problem worldwide with over 300,000 cases every year in the United States alone. Clearly, a potent vaccine preventing the morbidity and mortality caused by this detrimental pathogen is urgently required. However, vaccine efforts to combat C. difficile infections have been limited both in scope as well as to efficacy, as such there is not a vaccine approved for use against C. difficile to date. In this study, we have used a highly potent Adenovirus (Ad) based platform to create a vaccine against C. difficile. The Ad-based vaccine was able to generate rapid and robust humoral as well as cellular (T-cell) immune responses in mice that correlated with provision of 100% protection from lethal challenge with C. difficile toxin A. Most relevant to the clinical utility of this vaccine formulation was our result that toxin A specific IgGs were readily detected in plasma of Ad immunized mice as early as 3 days post vaccination. In addition, we found that several major immuno-dominant T cell epitopes were identified in toxin A, suggesting that the role of the cellular arm in protection from C. difficile infections may be more significant than previously appreciated. Therefore, our studies confirm that an Adenovirus based-C. difficile vaccine could be a promising candidate for prophylactic vaccination both for use in high risk patients and in high-risk environments.

Induction and comparison of SIV immunity in Ad5 naïve and Ad5 immune non-human primates using an Ad5 [E1-, E2b-] based vaccine

The effectiveness of recombinant Adenovirus serotype 5 (Ad5) vectors to induce immune responses against targeted antigens has been limited by the presence of pre-existing or Ad5 vaccine induced anti-vector immunity. The Ad5 [E1-, E2b-] platform, a recombinant Ad5 with additional deletions, has been previously reported by us to induce immune responses in the presence of Ad5 immunity. In an Ad5 immune non-human primate (NHP) model, an Ad5 [E1-, E2b-] construct expressing HIV-1 Gag induced immune responses in the presence of pre-existing Ad5 immunity. In the present study we expand on these prior observations by comparing the cell mediated immune (CMI) responses induced by Ad5 [E1-, E2b-]-SIV-gag/nef in Ad5 naïve and Ad5 immune NHP. Additionally, NHP were immunized with an Ad5 [E1-, E2b-]-HIV-pol construct following two homologous administrations of Ad5 [E1-, E2b-]-SIV-gag/nef to determine if an immune response could be induced against a third antigen in the presence of vaccine induced Ad5 immunity. Positive CMI responses, as assessed by interferon-gamma (IFN-γ) secreting lymphocytes, were induced against all three antigens. These CMI responses increased over a course of multiple immunizations and the response profiles observed in Ad5 naïve and Ad5 immune NHP were similar. No influence of the major histocompatibility complex on CMI responses was observed. These data indicate that the new Ad5 [E1-, E2b-] platform based vaccine could be used for homologous vaccination regimes to induce robust CMI responses in the presence of Ad5 vector immunity.

An Ad5[E1-, E2b-]-HER2/neu vector induces immune responses and inhibits HER2/neu expressing tumor progression in Ad5 immune mice

Immunotherapy is a promising approach for the treatment of cancers. Modified adenovirus 5 (Ad5) vectors have been used as a platform to deliver genes encoding tumor associated antigens (TAA). A major obstacle to Ad5 vector immunotherapy has been the induction of vector immunity following administration or the presence of pre-existing Ad5 immunity, which results in vector mitigation. It has been reported by us that the Ad5[E1-, E2b-] platform with unique deletions in the E1, E2b and E3 regions can induce potent cell mediated immunity (CMI) against delivered transgene products in the presence of pre-existing Ad5 immunity. Here we report the use of an Ad5[E1-, E2b-] vector platform expressing the TAA HER2/neu as a breast cancer immunotherapeutic agent. Ad5[E1-, E2b-]-HER2/neu induced potent CMI against HER2/neu in Ad5 naïve and Ad5 immune mice. Humoral responses were also induced and antibodies could lyse HER2/neu expressing tumor cells in the presence of complement in vitro. Ad5[E1-, E2b-]-HER2/neu prevented establishment of HER2/neu-expressing tumors and significantly inhibited progression of established tumors in Ad5 naïve and Ad5 immune murine models. These data demonstrate that in vivo delivery of Ad5[E1-, E2b-]-HER2/neu can induce anti-TAA immunity and inhibit progression of HER2/neu expressing cancers.

Generation of cell lines to complement adenovirus vectors using recombination-mediated cassette exchange

Background

Adenovirus serotype 5 (Ad5) has many favourable characteristics for development as a gene therapy vector. However, the utility of current Ad5 vectors is limited by transient transgene expression, toxicity and immunogenicity. The most promising form of vector is the high capacity type, which is deleted for all viral genes. However, these vectors can only be produced to relatively low titres and with the aid of helper virus. Therefore a continuing challenge is the generation of more effective Ad5 vectors that can still be grown to high titres. Our approach is to generate complementing cell lines to support the growth of Ad5 vectors with novel late gene deficiencies.

Results

We have used LoxP/Cre recombination mediated cassette exchange (RMCE) to generate cell lines expressing Ad5 proteins encoded by the L4 region of the genome, the products of which play a pivotal role in the expression of Ad5 structural proteins. A panel of LoxP parent 293 cell lines was generated, each containing a GFP expression cassette under the control of a tetracycline-regulated promoter inserted at a random genome location; the cassette also contained a LoxP site between the promoter and GFP sequence. Clones displayed a variety of patterns of regulation, stability and level of GFP expression. Clone A1 was identified as a suitable parent for creation of inducible cell lines because of the tight inducibility and stability of its GFP expression. Using LoxP-targeted, Cre recombinase-mediated insertion of an L4 cassette to displace GFP from the regulated promoter in this parent clone, cell line A1-L4 was generated. This cell line expressed L4 100K, 22K and 33K proteins at levels sufficient to complement L4-33K mutant and L4-deleted viruses.

Conclusions

RMCE provides a method for rapid generation of Ad5 complementing cell lines from a pre-selected parental cell line, chosen for its desirable transgene expression characteristics. Parent cell lines can be selected for high or low gene expression, and for tight regulation, allowing viral protein expression to mirror that found during infection. Cell lines derived from a single parent will allow the growth of different vectors to be assessed without the complication of varying complementing protein expression.

Overcoming pre-existing adenovirus immunity by genetic engineering of adenovirus-based vectors

Adenovirus (Ad)-based vectors offer several benefits showing their potential for use in a variety of vaccine applications. Recombinant Ad-based vaccines possess potent immunogenic potential, capable of generating humoral and cellular immune responses to a variety of pathogen-specific antigens expressed by the vectors. Ad5 vectors can be readily produced, allowing for usage in thousands of clinical trial subjects. This is now coupled with a history of safe clinical use in the vaccine setting. However, traditional Ad5-based vaccines may not be generating optimal antigen-specific immune responses, and generate diminished antigen-specific immune responses when pre-existing Ad5 immunity is present. These limitations have driven initiation of several approaches to improve the efficacy of Ad-based vaccines, and/or allow modified vaccines to overcome pre-existing Ad immunity. These include: generation of chemically modified Ad5 capsids; generation of chimeric Ads; complete replacement of Ad5-based vaccine platforms with alternative (human and non-human origin) Ad serotypes, and Ad5 genome modification approaches that attempt to retain the native Ad5 capsid, while simultaneously improving the efficacy of the platform as well as minimizing the effect of pre-existing Ad immunity. Here we discuss recent advances in- and limitations of each of these approaches, relative to their abilities to overcome pre-existing Ad immunity.

beta-Arrestins modulate Adenovirus-vector-induced innate immune responses: differential regulation by beta-arrestin-1 and beta-arrestin-2

Adenovirus (Ad)-based vectors have been utilized in human gene transfer clinical trials since 1993. Unfortunately, innate immune responses directed against the Ad capsid and/or its genetic cargo can significantly limit the usage of Ad vectors. Previous studies have demonstrated that several signaling pathways are triggered by Ads, inclusive of TLR-dependent pathways. The G-protein-coupled receptor adaptors beta-arrestin-1 (beta-Arr1) and beta-arrestin-2 (beta-Arr2) are known to have pivotal roles in regulating TLR4 triggered signaling and inflammatory responses. In this study, we examined the role of beta-arrestins in Ad5-vector-induced inflammatory responses. Our studies reveal that both beta-arrestins are capable of modulating Ad5-vector-induced inflammatory responses in vivo and in vitro. Importantly, our studies divulge another level of complexity to these responses, as our results demonstrate beta-Arr1 to be a positive regulator, and beta-Arr2 a negative regulator of Ad5 induced innate immune responses. These data may allow gene therapy biologists to more accurately study the mechanisms underlying Ad5-vector-induced immune responses, and may also direct future efforts to modulate these mechanisms to improve the safety and/or efficacy of this important gene transfer vector.

CR1/2 is an important suppressor of Adenovirus-induced innate immune responses and is required for induction of neutralizing antibodies

Human complement receptors 1 and 2 are well described as important regulators of innate and adaptive immune responses, having pivotal roles in regulating complement activation (CR1) and B cell maturation/survival. In contrast, the role of the murine homologues of CR1 and CR2 (mCR1/2) have been primarily defined as modulating activation of the adaptive immune system, with very little evidence available about the role of mCR1/2 in regulating the innate immune responses to pathogens. In this manuscript, we confirm that mCR1/2 plays an important role in regulating both the innate and adaptive immune responses noted after Adenovirus (Ad) mediated gene transfer. Our results uncovered a novel role of mCR1/2 in down-regulating several, complement dependent innate immune responses. We also unveiled the mechanism underlying the complement dependent induction of neutralizing antibodies to Ad capsids as a CR1/2 dependent phenomenon that correlates with B-cell activation. These results confirm that Ad interactions with the complement system are pivotal in understanding how to maximize the safety or potency of Ad mediated gene transfer for both gene therapy and vaccine applications.

Novel Adenovirus type 5 vaccine platform induces cellular immunity against HIV-1 Gag, Pol, Nef despite the presence of Ad5 immunity

Recombinant Adenovirus serotype 5 (Ad5) vectors have been used as vaccine platforms in numerous animal and human clinical studies. The immune response induced by Ad5 vaccines can be mitigated due to pre-existing Ad5 immunity. We previously reported the use of a novel Ad5 platform to induce cellular immune responses (CMI) against HIV-1 Gag in Ad5 hyper immune mice. Here, the effectiveness of the Ad5 [E1-, E2b-] vaccine platform was evaluated using a triad mixture of HIV-1 Gag, Pol, and Nef as antigenic transgenes. Broad CMI was induced following vaccination with the HIV-1 expressing vectors in Ad5 naïve and Ad5 immunized mice. A mixture of the three vaccines induced CMI against each transgene product even in the presence of hyper Ad5 immunity. These studies revealed that CMI responses to immunization with Ad5 [E1-, E2b-]-gag, Ad5 [E1-, E2b-]-pol or Ad5 [E1-, E2b-]-nef vectors were transgene specific and did not induce CMI responses against irrelevant antigens such as carcinoembryonic antigen (CEA), herpes simplex virus glycoprotein B (HSV), cytomegalovirus (CMV) or influenza virus antigens. We are evaluating this recombinant triad viral vector as an HIV-1 vaccine in a non-human primate model and the data indicate that the vaccine is worthy of clinical evaluation.

Transient pretreatment with glucocorticoid ablates innate toxicity of systemically delivered adenoviral vectors without reducing efficacy

More than 300 human clinical trials utilize recombinant adenoviruses (rAds) as a gene transfer vector, confirming that rAds continue to be of high clinical interest. A primary weakness of rAds is their known propensity to trigger an innate, proinflammatory immune response rapidly after high-dose, systemic administration. In this study, we investigated what affects that pre-emptive treatment with anti-inflammatory glucocorticoids might have upon Ad vector-triggered inflammatory immune responses. We found that a simple pretreatment regimen with Dexamethasone (DEX) can significantly reduce most Ad-induced innate immune responses. DEX prevented rAd induction of systemic cytokine/chemokine releases in a dose-dependent fashion, with higher dosages preventing rAd induction of acute thrombocytopenia, endothelial cell activation, proinflammatory gene induction, and leukocyte infiltration into transduced organs. Transient glucocorticoid pretreatment also significantly reduced rAd-induced adaptive immune responses, including a decreased induction of Ad-neutralizing antibodies (NAbs). Importantly, use of DEX did not reduce the efficacy of rAd-mediated gene transduction nor rAd-derived transgene expression. Our results demonstrate that a simple, pre-emptive and transient glucocorticoid pretreatment is a viable approach to reduce rAd-associated acute toxicities that currently limit the use of Ad vectors in systemic clinical applications.

A preliminary and comparative evaluation of a novel Ad5 [E1-, E2b-] recombinant-based vaccine used to induce cell mediated immune responses

Adenovirus vectors have been shown to be highly effective as vaccine platforms capable of inducing both humoral and cell mediated immune (CMI) responses. An Ad serotype 5 vector containing unique deletions in the E2b region (Ad5 [E1-, E2b-]) has been reported to have several advantages over conventional Adenovirus serotype 5 (Ad5) vectors deleted in only the E1 region (Ad5 [E1-]), including increased carrying capacity and diminished viral late gene expression. Here, we evaluated a novel Ad5 [E1-, E2b-] vector utilizing the E.C7 cell line for viral packaging. Its' effectiveness as a potential vaccine platform as compared to the currently utilized Ad5 [E1-]-based platform was assessed in both Ad5 naïve and Ad5 immune mice. We employed the HIV-1 Gag gene as the antigenic transgene expressed by the novel vector. Cellular expression of the Gag was confirmed by Western Blot analysis. Dose response studies using three intradermal immunizations of 10(7) to 10(10) virus particles (VP) of each construct revealed that immunization with 10(10)VP resulted in the maximum immunological response. Multiple immunizations of Ad naïve BALB/c mice with an Ad5 [E1-, E2b]-gag vaccine resulted in higher ELISpot CMI responses as compared to mice immunized with an Ad5 [E1-]-gag vaccine. More importantly, multiple immunizations of Ad5 immune BALB/c mice with an Ad5 [E1-, E2b]-gag vaccine resulted in significant increases in ELISpot CMI responses when compared to Ad5 immune mice vaccinated with an Ad5 [E1-]-gag vector. Preliminary studies in three Ad5 immune non-human primates (NHP) demonstrated that vaccination with Ad5 [E1-, E2b-]-gag-induced elevated levels of interferon-gamma and IL-2 secreting lymphocytes as assessed by ELISpot assays. These studies indicate that the novel Ad5 [E1-, E2b-] viral vector can be utilized as a potential vaccine platform to induce elevated CMI responses as compared to current generation Ad5 [E1-] viral vectors even in the presence of pre-existing Ad5 immunity.

Complex interactions with several arms of the complement system dictate innate and humoral immunity to adenoviral vectors

The complement system is known to play critical roles in pathogen identification, initiation of innate immune responses and facilitation of adaptive immune responses. Several studies have suggested that recombinant adenoviruses (rAds) interact with proteins of the complement system within minutes of administration. In this study, we assessed the roles of the alternative (Factor B), classical (C1q and C4) and common (C3) arms of the complement system in the innate and humoral response to systemic rAd administration using mice genetically deficient for each of these functions. Although most plasma cytokines and chemokines induced by Ads appeared to be elicited in a C3-dependent manner, we found that rAd-induced thrombocytopenia was dependent on Factor B and C3, implicating the alternative pathway as responsible for this response. Alteration of the complement-dependent transcriptome response after rAd-induced liver gene expression was also found to be Factor B- and C3-dependent. Ad interactions with the classical and alternative arms of the complement system can also be redundant, as many complement-dependent, Ad-induced innate immune responses appeared to be primarily C3-dependent. We also identified a C3 dependence of Ad-mediated induction of the nuclear factor-kappaB (NF-kappaB) activation pathway. Finally, we confirmed that humoral immune responses to the vector capsid, and the transgene it encodes, are also complement-dependent.

Regulatable gene expression systems for gene therapy

It is feasible to restrict transgene expression to a tissue or region in need of therapy by using promoters that respond to focusable physical stimuli. The most extensively investigated promoters of this type are radiation-inducible promoters and heat shock protein gene promoters that can be activated by directed, transient heat. Temporal regulation of transgenes can be achieved by various two- or three-component gene switches that are triggered by an appropriate small molecule inducer. The most commonly considered gene switches that are reviewed herein are based on small molecule-responsive transactivators derived from bacterial tetracycline repressor, insect or mammalian steroid receptors, or mammalian FKBP12/FRAP. A new generation of gene switches combines a heat shock protein gene promoter and a small molecule-responsive gene switch and can provide for both spatial and temporal regulation of transgene activity.

Multiple Innate Inflammatory Responses Induced after Systemic Adenovirus Vector Delivery Depend on a Functional Complement System

Excessive complement activation can result in extreme tissue damage and systemic inflammatory responses, similar to innate immune responses rapidly elicited after systemic adenovirus (Ad) injections. To determine if Ad interactions with the complement system impact upon Ad-induced innate immune responses, we injected Ad into complement-deficient, C3-knockout mice (C3-KO) or wild-type mice (WT) and quantitatively compared multiple anti-Ad innate immune responses in both strains of mice. In Ad-treated WT mice, we noted rapid increases in plasma KC levels (1 h post injection), followed by increases in IL-6, IFN-gamma, RANTES, IL-12(p40), IL-5, G-CSF, and GM-CSF and subsequently thrombocytopenia. Conversely, in Ad-treated C3-KO mice, many of these inflammatory responses were significantly blunted, including the avoidance of Ad-induced thrombocytopenia. Global liver transcriptome responses in Ad-treated WT mice were assessed by RT-PCR-validated gene array analysis and were found to be also significantly affected by the lack of complement activity in Ad-treated C3-KO mice. Finally, our results confirmed the ability of high dose Ads to transduce hepatocytes despite a lack of complement activity. In summary, Ad interactions with the mammalian complement system are significant and likely initiate and/or exacerbate many of the inflammatory responses noted after systemic Ad injections.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Fully deleted adenovirus persistently expressing GAA accomplishes long-term skeletal muscle glycogen correction in tolerant and nontolerant GSD-II mice

Glycogen storage disease type II (GSD-II) patients manifest symptoms of muscular dystrophy secondary to abnormal glycogen storage in cardiac and skeletal muscles. For GSD-II, we hypothesized that a fully deleted adenovirus (FDAd) vector expressing hGAA via nonviral regulatory elements (PEPCK promoter/ApoE enhancer) would facilitate long-term efficacy and decrease propensity to generate anti-hGAA antibody responses against hepatically secreted hGAA. Intravenous delivery of FDAdhGAA into GAA-tolerant or nontolerant GAA-KO mice resulted in long-term hepatic secretion of hGAA. Specifically, nontolerant mice achieved complete reversal of cardiac glycogen storage and near-complete skeletal glycogen correction for at least 180 days and tolerant mice for minimally 300 days coupled with the preservation of muscle strength. Anti-hGAA antibody levels in both mouse strains were significantly less relative to those previously generated by CMV-driven hGAA expression in nontolerant GAA-KO mice. However, plasma GAA levels decreased in nontolerant GAA-KO mice despite long-term intrahepatic GAA expression from the persistent vector. This intriguing result is discussed in light of other examples of "tolerance" induction by gene-transfer-based approaches.

Liver toxicities typically induced by first-generation adenoviral vectors can be reduced by use of E1, E2b-deleted adenoviral vectors

Adenoviral vectors from which the E1 region has been deleted ([E1(-)] Ad) are known to induce strong immune responses after systemic delivery. In this study we have evaluated liver toxicities in mice after intravenous injection with high doses of [E1(-)] or modified [E1(-), E2b(-)] Ad vectors (both expressing the bacterial beta-galactosidase [lacZ] marker gene) in C57BL/6, BALB/c, and SCID mice. Our data demonstrate a marked reduction in maximal liver toxicities and pathologies (typically noted at 21 days postinjection) with the use of the [E1(-), E2b(-)] modified vector in all strains of mice tested. Our data also demonstrated that despite the use of the [E1(-), E2b(-)] Ad vector, significant liver toxicities were still observed. To address this issue and the fact that the lacZ gene was perceived as a foreign antigen in the immune-competent C57BL/6 and BALB/c mice, we similarly injected mice tolerant of LacZ (lacZ-TG). In contrast to our studies in C57BL/6 and BALB/c mice, LacZ-TG mice exhibited virtually no evidence of hepatotoxicity after intravenous injection with the [E1(-), E2b(-)] vector, in contrast to use of the [E1(-)] Ad vector. Our results demonstrate that the [E1(-), E2b(-)] Ad vector class can reduce liver toxicities typically ascribed to Ad vector-mediated gene transfer after transfer of a highly immunogenic or foreign gene, whereas transfer of a transgene that is perceived as nonforeign by the host can be delivered with virtually no evidence of toxicity. On the basis of a careful review of the literature, these improvements in vector safety rival those noted with other, more significantly modified Ad vectors described to date.

Strain-specific rate of shutdown of CMV enhancer activity in murine liver confirmed by use of persistent [E1−, E2b−] adenoviral vectors

The systemic delivery of [E1(-)] adenoviral (Ad) vectors encoding a transgene results in efficient viral uptake and abundant transgene expression in the liver. However, [E1(-)]Ad vector persistence is transient due to cytotoxic T lymphocyte (CTL)-mediated loss of the Ad-infected cells. Our laboratory has previously demonstrated that additional modifications to the [E1(-)]Ad vector genome, by deletion of the Ad E2b genes, significantly decreased virus-genome-derived gene expression and simultaneously improved the long-term performance of the resultant [E1(-), E2b(-)]Ad vector. In this study, we confirmed that [E1(-), E2b(-)]Ad vector genomes could persist equally well in C57Bl/6 or Balb/c mouse hepatocytes. Despite vector genome persistence, we observed a strain-dependent variability in the duration of CMV enhancer/promoter-driven transgene expression in the liver. While Balb/c mice rapidly shut down [E1(-), E2b(-)]Ad-derived transgene expression, C57Bl/6 mice allowed for prolonged transgene expression. This occurred even when both strains were crossed into a severe combined immune-deficient background, demonstrating that host adaptive immune responses are not responsible for the phenomenon. Furthermore, differential methylation of the CMV enhancer/promoter was also not demonstrated in either strain of mouse, eliminating this mechanism as causative. Thus, alternative mechanisms for this phenomenon are discussed.

Correction/mutation of acid alpha-D-glucosidase gene by modified single-stranded oligonucleotides: in vitro and in vivo studies

Deficiency in acid alpha-D-glucosidase results in Pompe's disease. Modified single-stranded oligonucleotide (ODN) was designed to correct the acid alpha-D-glucosidase gene with a C1935 --> A (Asp --> Glu) point mutation which causes a complete loss of enzymatic activity for glycogen digestion in the lysosome. The ODN vectors contained a stretch of normal oligonucleotide flanked by phosphorothioated sequences. The 25mer and 35mer ODNs were homologous to the target sequence, except for a mismatched base in the middle. The ODNs caused permanent and inheritable restoration of acid alpha-D-glucosidase activity in skin fibroblast cells carrying this mutation derived from a Pompe's disease patient. Gene correction was confirmed by amplification refractory mutation system-PCR (ARMS-PCR), restriction fragment length polymorphism (RFLP) and direct DNA cloning and sequencing. The increased acid alpha-D-glucosidase activity was detected using 4-MUG as the artificial substrate. The correction efficiency, ranging from 0.5 to 4%, was dependent on the length and polarity of the MSSOV used, the optimal design being a sense-strand 35mer ODNs. Repeated treatment of the mutant fibroblast cells with the ODNs substantially increased correction. We also constructed ODN vectors to trigger specific and in vivo nonsense mutation in the mouse acid alpha-D-glucosidase gene. The ODNs were in complex with YEEE-K(18), an asialoglycoprotein-receptor ligand tagged with polylysine and targeted to hepatocytes and renal cells in vivo through intravenous injection. The mutated genotype was detected in the liver and the kidney by ARMS-PCR and glycogen accumulation in the lysosome of the liver cells. The studies demonstrate the utility of single-stranded ODN to direct targeted gene correction or mutation in a human hereditary disease and in an animal model. Our data open the possibility of developing ODN vector as a therapeutic approach for treatment of human hereditary diseases caused by point mutation.

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Gene therapy for pituitary tumors: from preclinical models to clinical implementation

Gene therapy, which entails the use of nucleic acids as drugs, is a new approach to treat disease. Gene therapy has been successfully implemented in several preclinical animal models, including several paradigms of experimental pituitary tumors. In spite of these successes, several critical issues need to be addressed before gene therapy can become a clinical reality for the treatment of pituitary tumors. These include the development of safer and more effective gene delivery vectors, the uncovering of novel therapeutic targets, the development of molecular switches which will allow turning therapeutic transgene expression "on" and "off" as and when it is needed, and the ability to scale up the vector preparations devoid of any putative contaminants. There are still many basic science developments that must take place in order to allow this new therapeutic technology to make its way successfully into the clinical arena to treat pituitary disease. We envisage these developments taking place within the next five years, gene therapy for pituitary tumors will then form part of the armamentarium available to better treat and manage pituitary tumors.

Genetically modified dendritic cells--a new, promising cancer treatment strategy?

Dendritic cells (DCs), the most potent antigen-presenting cells (APCs), were discovered almost 30 years ago. Due to the priming of antigen-specific immune responses mediated by CD4+ and CD8+ lymphocytes, DCs are crucial for the induction of adaptive immunity against cancer. Therefore, vaccination of cancer patients with DCs presenting tumour-associated antigens (TAAs) have been believed to be a promising anticancer strategy. Multiple clinical trials have been carried out in order to evaluate the safety and efficacy of cancer vaccines based on antigen-pulsed DCs. However, pulsing of DCs with particular peptides has several disadvantages: i) short-time duration of antigen-major histocompatability complex (MHC) complexes, ii) a requirement for matching defined peptides with MHC complexes and iii) exclusive presentation of single antigen epitopes. Application of gene transfer technologies in the field of DC-based vaccines made possible the development of novel, anticancer immunisation strategies. In several animal models, DCs modified with genes encoding TAA or immunostimulatory proteins have been shown to be effective in the induction of antitumour immune responses. Based on these encouraging results, a first clinical trial of prostate cancer patients vaccinated with gene modified DCs has recently been initiated. In this article, methods used for genetic modification of DCs and anticancer vaccination strategies based on genetically modified DCs are reviewed.

In vivo new bone formation by direct transfer of adenoviral-mediated bone morphogenetic protein-4 gene

Previous studies have demonstrated that bone morphogenetic protein-4 (BMP4) could participate in vivo endochondral ossification and is one of the main local contributing factors in the early stage of fracture healing. To investigate the effectiveness of BMP4 gene transfer, we constructed an adenoviral vector, Ad-BMP4, and evaluated its osteoinduction activity both in vitro and in vivo. In vitro study suggested that this vector could efficiently transduce mouse myoblast C2C12 cells and produce osteogenic BMP4 protein, as confirmed by immunofluorescence analysis and alkaline phosphatase activity assay. For in vivo study, Ad-BMP4 was directly injected into the hind limb muscles of male athymic nude rats. Visible new bone formation under X-ray films could be detected as early as three weeks post-injection. The bone tissue was further analyzed by histological staining and revealed a typical remodeled bone structure. In conclusion, this study is the first to establish the feasibility of adenovirus-based BMP4 gene therapy for bone regeneration.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Efficacy of gene therapy for a prototypical lysosomal storage disease (GSD-II) is critically dependent on vector dose, transgene promoter, and the tissues targeted for vector transduction

Lysosomal storage diseases are an intriguing target for gene therapy approaches, as transduction of a "depot" organ with a transgene encoding a lysosomal enzyme can be followed by secretion, systemic distribution, downstream uptake, and lysosomal targeting of the enzyme into non-transduced tissues. These benefits are of utmost importance when considering gene therapy approaches for glycogen storage disease type-II (GSD-II). GSD-II is a prototypical lysosomal storage disorder caused by lack of intralysosomal acid alpha-glucosidase (GAA) activity. Lack of GAA can result in a proximal limb myopathy and respiratory and cardiac failure, each due to abnormal glycogen accumulation in the skeletal muscles or cardiac tissues, respectively. After converting the liver into a "depot" organ, we found that intravenous injection of the [E1-,polymerase-]AdGAA vector allowed for hepatic secretion of GAA over an at least 20-fold dosage range. We noted that very low plasma GAA levels (derived from hepatic secretion of GAA) can allow for GAA uptake by muscle tissues (skeletal or cardiac), but significantly higher plasma GAA levels are required before glycogen "cross-correction" can occur in these same tissues. We also demonstrated that liver-specific enhancer/promoters prolonged GAA transgene expression from persistent [E1-,polymerase-] adenovirus based vector genomes for at least 180 days, and significantly diminished the amounts of neutralizing anti-GAA antibodies elicited in this animal model. Finally, we demonstrated that skeletal muscles can also serve as a "depot" organ for GAA secretion, allowing for secretion of GAA and its uptake by noninfected distal tissues, although glycogen reductions in non-injected muscles were not achieved by the latter approach.

Dystrophin expression in muscle following gene transfer with a fully deleted ("gutted") adenovirus is markedly improved by trans-acting adenoviral gene products

Helper-dependent adenoviruses (HDAd) are Ad vectors lacking all or most viral genes. They hold great promise for gene therapy of diseases such as Duchenne muscular dystrophy (DMD), because they are less immunogenic than E1/E3-deleted Ad (first-generation Ad or FGAd) and can carry the full-length (Fl) dystrophin (dys) cDNA (12 kb). We have compared the transgene expression of a HDAd (HDAdCMVDysFl) and a FGAd (FGAdCMV-dys) in cell culture (HeLa, C2C12 myotubes) and in the muscle of mdx mice (the mouse model for DMD). Both vectors encoded dystrophin regulated by the same cytomegalovirus (CMV) promoter. We demonstrate that the amount of dystrophin expressed was significantly higher after gene transfer with FGAdCMV-dys compared to HDAdCMVDysFl both in vitro and in vivo. However, gene transfer with HDAdCMVDysFl in the presence of a FGAd resulted in a significant increase of dystrophin expression indicating that gene products synthesized by the FGAd increase, in trans, the amount of dystrophin produced. This enhancement occurred in cell culture and after gene transfer in the muscle of mdx mice and dystrophic golden retriever (GRMD) dogs, another animal model for DMD. The E4 region of Ad is required for the enhancement, because no increase of dystrophin expression from HDAdCMVDysFl was observed in the presence of an E1/E4-deleted Ad in vitro and in vivo. The characterization of these enhancing gene products followed by their inclusion into an HDAd may be required to produce sufficient dystrophin to mitigate the pathology of DMD by HDAd-mediated gene transfer.

Adenovirus vectors with the 100K gene deleted and their potential for multiple gene therapy applications

The 100K protein has a number of critical roles vital for successful completion of the late phases of the adenovirus (Ad) life cycle. We hypothesized that the introduction of deletions within the 100K gene would allow for the production of a series of new classes of Ad vector, including one that is replication competent but blocked in the ability to carry out many late-phase Ad functions. Such a vector would have potential for several gene therapy applications, based upon its ability to increase the copy number of the transgene encoded by the vector (via genome replication) while decreasing the side effects associated with Ad late gene expression. To efficiently produce 100K-deleted Ad ([100K-]Ad) vectors, an E1- and 100K-complementing cell line (K-16) was successfully isolated. Transfection of an [E1-,100K-]Ad vector genome into the K-16 cells readily yielded high titers of the vector. After infection of noncomplementing cells, we demonstrated that [100K-]Ad vectors have a significantly decreased ability to express several Ad late genes. Additionally, if the E1 gene was present in the infected noncomplementing cells, [100K-]Ad vectors were capable of replicating their genomes to high copy number, but were significantly blocked in their ability to efficiently encapsidate the replicated genomes. Injection of an [E1-,100K-]Ad vector in vivo also correlated with significantly decreased hepatotoxicity, as well as prolonged vector persistence. In summary, the unique properties of [100K-]Ad vectors suggest that they may have utility in a variety of gene therapy applications.

Long-term efficacy after [E1-, polymerase-] adenovirus-mediated transfer of human acid-alpha-glucosidase gene into glycogen storage disease type II knockout mice

Glycogen storage disease type II (GSD-II) is a lethal, autosomal recessive metabolic myopathy caused by a lack of acid-alpha-glucosidase (GAA) activity in the cardiac and skeletal muscles. Absence of adequate intralysosomal GAA activity results in massive amounts of glycogen accumulation in multiple muscle groups, resulting in morbidity and mortality secondary to respiratory embarrassment and/or cardiomyopathy. In a mouse model of GSD-II, we demonstrate that infection of the murine liver with a modified adenovirus (Ad) vector encoding human GAA (hGAA) resulted in long-term persistence of the vector in liver tissues for at least 6 months. Despite both a rapid shutdown of hGAA mRNA expression from the vector, as well as the elicitation of anti-hGAA antibody responses (hGAA is a foreign antigen in this model), the hGAA secreted by the liver was taken up by all muscle groups analyzed and, remarkably, persisted in them for at least 6 months. The persistence of the protein also correlated with long-term correction of pathologic intramuscular glycogen accumulations in all muscle groups tested, but most notably the cardiac tissues, which demonstrated a significantly decreased glycogen content for at least 190 days after a single vector injection. The results suggest that gene therapy strategies may have the potential to significantly improve the clinical course for GSD-II patients.

A modified adenovirus can transfect cochlear hair cells in vivo without compromising cochlear function

The loss of cochlear hair cells, or the loss of their capacity to transduce acoustic signals, is believed to be the underlying mechanism in many forms of hearing loss. To develop viral vectors that allow for the introduction of genes directly into the cochleae of adult animals, replication-deficient (E1(-), E3(-)) and replication-defective (E1(-), E3(-), pol(-)) adenovirus vectors were used to transduce the bacterial beta-galactosidase gene into the hair cells of the guinea pig cochlea in vivo. Distortion product otoacoustic emissions, which monitor the functional status of outer hair cells, were measured throughout the viral infection periods to identify hair cell ototoxicity. The results demonstrated that the use of the (E1(-), E3(-)) adenovirus vectors containing CMV-driven LacZ, compromised cochlear function when gradually introduced into scala tympani via an osmotic pump. However, when (E1(-), E3(-), pol(-)) adenoviral vectors containing CMV-driven LacZ were used to transduce cochlear hair cells, there was no loss of cochlear function over the frequency regions tested, and beta-galactosidase (beta-gal) was detected in over 80% of all hair cells. Development of a viral vector that infects cochlear hair cells without virus-induced ototoxic effects is crucial for gene replacement strategies to treat certain forms of inherited deafness and for otoprotective strategies to prevent hair cell losses to treat progressive hearing disorders. Moreover, in vivo (E1(-), E3(-), pol(-)) adenovirus mediated gene-transfer techniques applied to adult guinea pig cochleae may be useful in testing several hypotheses concerning what roles specific genes play in normal cochlear function.

Adenoviral vector expressing ICP47 inhibits adenovirus-specific cytotoxic T lymphocytes in nonhuman primates

Studies from several laboratories have shown that administration of E1-deleted Ad vectors results only in transient transgene expression in the lungs of immunocompetent animals. This is due, at least in part, to destruction of vector-transduced cells by host cellular immune responses (predominantly CD8(+) CTLs) directed against viral proteins and/or immunogenic transgene products. We have previously demonstrated that E1-deleted Ad vectors can lead to persistent expression of human cystic fibrosis transmembrane conductance regulator (hCFTR) in the lungs of several strains of immunocompetent mice, despite the presence of Ad-specific CTLs. However, we found that these same vectors gave rise only to transient hCFTR expression in the lungs of rhesus monkeys. We have constructed new Ad vectors that coexpress both hCFTR and the ICP47 gene from herpes simplex virus. ICP47 has been shown to inhibit the transporter associated with antigen presentation, thus blocking major histocompatibility antigen I (MHC class I)-mediated antigen presentation to CD8(+) T cells. The Ad/hCFTR/ICP47 vector decreased levels of cell-surface MHC class I molecules on infected monkey and human cell lines. Similar results were obtained with primary human cells and primary monkey airway epithelial cells. In vitro studies showed that the Ad/hCFTR/ICP47 vector decreased cytolysis by both monkey and human CTLs. When Ad/hCFTR/ICP47 was administered to the lungs of rhesus monkeys, it inhibited the generation of Ad-specific CTLs. However, natural killer cell activity was enhanced in monkeys treated with the Ad/hCFTR/ICP47 vector.

Multiply deleted [E1, polymerase-, and pTP-] adenovirus vector persists despite deletion of the preterminal protein

BACKGROUND

The inherent limitations of [E1-]Ad vectors as gene therapy vehicles suggest that further modifications may improve their overall performance profiles. However, Ad vector modifications can have untoward effects on their basic biology, e.g., some helper-virus dependent Ad vectors have been found to be unstable without the presence of preterminal protein (pTP) activities. Despite this concern, we generated a new class of helper-virus independent Ad vector that was multiply deleted for the E1, polymerase, and pTP genes, and investigated the ramifications of these deletions upon several vector performance parameters.

METHODS

The construction and propagation of an [E1-, polymerase-, pTP-]Ad vector was achieved with the use of trans-complementing cells co-expressing the Ad E1, polymerase and pTP genes.

RESULTS

High titer production of the [E1-, polymerase-, pTP-]Ad vector was successfully accomplished via conventional Ad purification techniques. This unique class of Ad vector was capable of long-term gene transfer in vivo (despite lacking pTP functions) that was concomitant with a significantly decreased hepatic toxicity.

CONCLUSIONS

Previous studies had suggested that Ad genome persistence in vivo may be dependent upon the presence of low level vector genome replication and/or pTP functions. Our results suggest that [E1-, polymerase-, pTP-]Ad vectors can overcome these barriers. The further benefits afforded by the use of this class of Ad vector (increased cloning capacity, high level growth, decreased propensity to generate replication competent Ad (RCA), decreased toxicity) suggests that they will be highly beneficial for use in several aspects of human gene therapy.

Towards a molecular therapy for glycogen storage disease type II (Pompe disease)

Glycogen storage disease type II (GSD-II), also known as Pompe disease, is a fatal genetic muscle disorder caused by a deficiency of acid alpha-glucosidase, a glycogen-degrading lysosomal enzyme. Currently, there is no treatment for this fatal disorder. However, several lines of research suggest the possibility of future treatment. Enzyme replacement strategies hold the greatest hope for patients currently affected by GSD-II, but future strategies could include in vivo or ex vivo gene therapy approaches and/or mesenchymal stem cell or bone-marrow transplantation approaches. Each of the approaches might eventually be combined to further improve the overall clinical efficacy of any one treatment regimen. The lessons learned from GSD-II research will also benefit a great number of individuals affected by other genetic disorders.

Developments in gene therapy for muscular dystrophy

Gene therapy for muscular dystrophy (MD) presents significant challenges, including the large amount of muscle tissue in the body, the large size of many genes defective in different muscular dystrophies, and the possibility of a host immune response against the therapeutic gene. Overcoming these challenges requires the development and delivery of suitable gene transfer vectors. Encouraging progress has been made in modifying adenovirus (Ad) vectors to reduce immune response and increase capacity. Recently developed gutted Ad vectors can deliver full-length dystrophin cDNA expression vectors to muscle tissue. Using muscle-specific promoters to drive dystrophin expression, a strong immune response has not been observed in mdx mice. Adeno-associated virus (AAV) vectors can deliver small genes to muscle without provocation of a significant immune response, which should allow long-term expression of several MD genes. AAV vectors have also been used to deliver sarcoglycan genes to entire muscle groups. These advances and others reviewed here suggest that barriers to gene therapy for MD are surmountable.

Adenovirus vectors for gene delivery

Recent endeavors in the development of adenovirus as a gene vector have focused on the modification of virus tropism, the accommodation of larger genes, and the increase in stability and control of transgene expression. Whereas partial or total deletions of viral genes increase the cloning capacity and partly reduce the cellular immune response, control of the humoral response, which often precludes efficient readministration, remains a challenge.

Systemic correction of the muscle disorder glycogen storage disease type II after hepatic targeting of a modified adenovirus vector encoding human acid-alpha-glucosidase

This report demonstrates that a single intravenous administration of a gene therapy vector can potentially result in the correction of all affected muscles in a mouse model of a human genetic muscle disease. These results were achieved by capitalizing both on the positive attributes of modified adenovirus-based vectoring systems and receptor-mediated lysosomal targeting of enzymes. The muscle disease treated, glycogen storage disease type II, is a lysosomal storage disorder that manifests as a progressive myopathy, secondary to massive glycogen accumulations in the skeletal and/or cardiac muscles of affected individuals. We demonstrated that a single intravenous administration of a modified Ad vector encoding human acid alpha-glucosidase (GAA) resulted in efficient hepatic transduction and secretion of high levels of the precursor GAA proenzyme into the plasma of treated animals. Subsequently, systemic distribution and uptake of the proenzyme into the skeletal and cardiac muscles of the GAA-knockout mouse was confirmed. As a result, systemic decreases (and correction) of the glycogen accumulations in a variety of muscle tissues was demonstrated. This model can potentially be expanded to include the treatment of other lysosomal enzyme disorders. Lessons learned from systemic genetic therapy of muscle disorders also should have implications for other muscle diseases, such as the muscular dystrophies.