Canine adenovirus vectors for lung-directed gene transfer: efficacy, immune response, and duration of transgene expression using helper-dependent vectors

Deletion of the RGD motif from the penton base in oncolytic adenoviruses enhances antitumor efficacy of combined CAR T cell therapy

Oncolytic viruses often face challenges in achieving optimal antitumor immunity as standalone therapies. The penton base RGD-integrin interactions play a significant role in wild-type adenovirus-induced innate immune responses. To modify these responses, we present ISC301, a novel oncolytic adenovirus engineered by deleting the natural RGD motifs in the penton base while incorporating artificial RGD motifs in the fiber knobs. ISC301 demonstrated comparable in vitro infectivity, cytotoxic effects, and signaling profiles across various cell types to its parental ICOVIR-5, which retains the penton base RGD motif. In immunodeficient and immunocompetent mouse models, ISC301 exhibited similar in vivo antitumor efficacy to ICOVIR-5. However, ISC301 induced higher intratumoral inflammation through NF-κB activation, leading to increased levels of tumor-infiltrating leukocytes and higher proportion of cytotoxic CD8+ T cells. In addition, ISC301 elicits a heightened pro-inflammatory response in peripheral blood. Importantly, when combined with CAR T cell therapy, ISC301 exhibited superior antitumor efficacy, surpassing monotherapy outcomes. These findings emphasize the impact of adenoviral modifications on antitumor immune responses. The deletion of penton base RGD motifs enhances ISC301's pro-inflammatory profile and boosts CAR T cell therapy efficacy. This study enhances understanding of oncolytic virus engineering strategies, positioning ISC301 as a promising candidate for combined immunotherapeutic approaches in cancer treatment.

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.

Membrane Dynamics and Signaling of the Coxsackievirus and Adenovirus Receptor

The coxsackievirus and adenovirus receptor (CAR) belongs to the immunoglobulin superfamily and acts as a receptor for some adenovirus types and group B coxsackieviruses. Its role is best described in epithelia where CAR participates to tight junction integrity and maintenance. Recently, several studies aimed to characterize its potential interaction with intracellular signaling pathways and highlighted several features linking CAR to gene expression. In addition, the molecular mechanisms leading to CAR-specific membrane targeting via the secretory pathway in polarized cells and its internalization are starting to be unraveled. This chapter discusses the interaction between membrane dynamics, intracellular trafficking, and signaling of CAR.

CAV-2--why a canine virus is a neurobiologist's best friend

Canine adenovirus type 2 (CAV-2) vectors are powerful tools for fundamental and applied neurobiology due to their negligible immunogenicity, preferential transduction of neurons, widespread distribution via axonal transport, and duration of expression in the mammalian brain. CAV-2 vectors are internalized in neurons by the selective use of coxsackievirus and adenovirus receptor (CAR), which is located at the presynapse in neurons. Neuronal internalization and axonal transport is mediated by CAR, which potentiates vector biodistribution. The above characteristics, together with the ∼30kb cloning capacity of helper-dependent (HD) CAV-2 vectors, optimized CAV-2 vector creation, production and purification, is expanding the therapeutic and fundamental options for CNS gene transfer.

Evaluation of helper-dependent canine adenovirus vectors in a 3D human CNS model

Gene therapy is a promising approach with enormous potential for treatment of neurodegenerative disorders. Viral vectors derived from canine adenovirus type 2 (CAV-2) present attractive features for gene delivery strategies in the human brain, by preferentially transducing neurons, are capable of efficient axonal transport to afferent brain structures, have a 30-kb cloning capacity and have low innate and induced immunogenicity in preclinical tests. For clinical translation, in-depth preclinical evaluation of efficacy and safety in a human setting is primordial. Stem cell-derived human neural cells have a great potential as complementary tools by bridging the gap between animal models, which often diverge considerably from human phenotype, and clinical trials. Herein, we explore helper-dependent CAV-2 (hd-CAV-2) efficacy and safety for gene delivery in a human stem cell-derived 3D neural in vitro model. Assessment of hd-CAV-2 vector efficacy was performed at different multiplicities of infection, by evaluating transgene expression and impact on cell viability, ultrastructural cellular organization and neuronal gene expression. Under optimized conditions, hd-CAV-2 transduction led to stable long-term transgene expression with minimal toxicity. hd-CAV-2 preferentially transduced neurons, whereas human adenovirus type 5 (HAdV5) showed increased tropism toward glial cells. This work demonstrates, in a physiologically relevant 3D model, that hd-CAV-2 vectors are efficient tools for gene delivery to human neurons, with stable long-term transgene expression and minimal cytotoxicity.

Recent advances in gene therapy for lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a group of genetic diseases that result in metabolic derangements of the lysosome. Most LSDs are due to the genetic absence of a single catabolic enzyme, causing accumulation of the enzyme’s substrate within the lysosome. Over time, tissue-specific substrate accumulations result in a spectrum of symptoms and disabilities that vary by LSD. LSDs are promising targets for gene therapy because delivery of a single gene into a small percentage of the appropriate target cells may be sufficient to impact the clinical course of the disease. Recently, there have been several significant advancements in the potential for gene therapy of these disorders, including the first human trials. Future clinical trials will build upon these initial attempts, with an improved understanding of immune system responses to gene therapy, the obstacle that the blood–brain barrier poses for neuropathic LSDs, as well other biological barriers that, when overcome, may facilitate gene therapy for LSDs. In this manuscript, we will highlight the recent innovations in gene therapy for LSDs and discuss the clinical limitations that remain to be overcome, with the goal of fostering an understanding and further development of this important field.

Impact of adenovirus life cycle progression on the generation of canine helper-dependent vectors

Helper-dependent adenovirus vectors (HDVs) are safe and efficient tools for gene transfer with high cloning capacity. However, the multiple amplification steps needed to produce HDVs hamper a robust production process and in turn the availability of high-quality vectors. To understand the factors behind the low productivity, we analyzed the progression of HDV life cycle. Canine adenovirus (Ad) type 2 vectors, holding attractive features to overcome immunogenic concerns and treat neurobiological disorders, were the focus of this work. When compared with E1-deleted (ΔE1) vectors, we found a faster helper genome replication during HDV production. This was consistent with an upregulation of the Ad polymerase and pre-terminal protein and led to higher and earlier expression of structural proteins. Although genome packaging occurred similarly to ΔE1 vectors, more immature capsids were obtained during HDV production, which led to a ~4-fold increase in physical-to-infectious particles ratio. The higher viral protein content in HDV-producing cells was also consistent with an increased activation of autophagy and cell death, in which earlier cell death compromised volumetric productivity. The increased empty capsids and earlier cell death found in HDV production may partially contribute to the lower vector infectivity. However, an HDV-specific factor responsible for a defective maturation process should be also involved to fully explain the low infectious titers. This study showed how a deregulated Ad cycle progression affected cell line homeostasis and HDV propagation, highlighting the impact of vector genome design on virus-cell interaction.

Central nervous system delivery of helper-dependent canine adenovirus corrects neuropathology and behavior in mucopolysaccharidosis type VII mice

Canine adenovirus type 2 vectors (CAV-2) are promising tools to treat global central nervous system (CNS) disorders because of their preferential transduction of neurons and efficient retrograde axonal transport. Here we tested the potential of a helper-dependent CAV-2 vector expressing β-glucuronidase (HD-RIGIE) in a mouse model of mucopolysaccharidosis type VII (MPS VII), a lysosomal storage disease caused by deficiency in β-glucuronidase activity. MPS VII leads to glycosaminoglycan accumulation into enlarged vesicles in peripheral tissues and the CNS, resulting in peripheral and neuronal dysfunction. After intracranial administration of HD-RIGIE, we show long-term expression of β-glucuronidase that led to correction of neuropathology around the injection site and in distal areas. This phenotypic correction correlated with a decrease in secondary-elevated lysosomal enzyme activity and glycosaminoglycan levels, consistent with global biochemical correction. Moreover, HD-RIGIE-treated mice show significant cognitive improvement. Thus, injections of HD-CAV-2 vectors in the brain allow a global and sustained expression and may have implications for brain therapy in patients with lysosomal storage disease.

Methods for gene transfer to the central nervous system

Gene transfer is an increasingly utilized approach for research and clinical applications involving the central nervous system (CNS). Vectors for gene transfer can be as simple as an unmodified plasmid, but more commonly involve complex modifications to viruses to make them suitable gene delivery vehicles. This chapter will explain how tools for CNS gene transfer have been derived from naturally occurring viruses. The current capabilities of plasmid, retroviral, adeno-associated virus, adenovirus, and herpes simplex virus vectors for CNS gene delivery will be described. These include both focal and global CNS gene transfer strategies, with short- or long-term gene expression. As is described in this chapter, an important aspect of any vector is the cis-acting regulatory elements incorporated into the vector genome that control when, where, and how the transgene is expressed.

Impact of E1 and Cre on adenovirus vector amplification: developing MDCK CAV-2-E1 and E1-Cre transcomplementing cell lines

Adenovirus vectors have been extensively studied through the manipulation of viral genome. However, little attention is being paid to their producer cell-lines; cells are selected according to virus yields, neglecting the expression profile of transcomplementing gene products underlying cell performance. This work evaluates the impact of E1 (E1A and E1B) and Cre recombinase levels in the production of E1-deleted and helper-dependent canine adenovirus type 2 (CAV-2) vectors using MDCK cells. E1A and E1B gene expression and Cre activity were evaluated in different cell clones and compared with the corresponding cell productivity and susceptibility to oxidative stress injury. CAV-2 production was proportional to E1A expression (the highest levels of E1A corresponding to productivities of 3000–5000 I.P./cell), while E1B prolonged host cell viability after infection, conferring protection against apoptosis. Cre recombinase counteracted E1B anti-apoptotic properties, however viral production was maintained under high levels of Cre. Yet, Cre recombinase side effects can be reduced using cell lines with lower Cre-activities, without compromising the excision efficiency of helper vector packaging signal. These results highlight the influence of transcomplementing gene products on CAV-2 producer cell line performance, and the ability to express high levels of E1A and E1B as an important feature for cell line establishment and high adenovirus titers.

Canine recombinant adenovirus vector induces an immunogenicity-related gene expression profile in skin-migrated CD11b⁺ -type DCs

Gene expression profiling of the blood cell response induced early after vaccination has previously been demonstrated to predict the immunogenicity of vaccines. In this study, we evaluated whether the analysis of the gene expression profile of skin-migrated dendritic cells (DCs) could be informative for the in vitro prediction of immunogenicity of vaccine, using canine adenovirus serotype 2 (CAV2) as vaccine vector. CAV2 has been shown to induce immunity to transgenes in several species including sheep and is an interesting alternative to human adenovirus-based vectors, based on the safety records of the parental strain in dogs and the lack of pre-existing immunity in non-host species. Skin-migrated DCs were collected from pseudo-afferent lymph in sheep. Both the CD11b(+) -type and CD103(+) -type skin-migrated DCs were transduced by CAV2. An analysis of the global gene response to CAV2 in the two skin DC subsets showed that the gene response in CD11b(+) -type DCs was far higher and broader than in the CD103(+) -type DCs. A newly released integrative analytic tool from Ingenuity systems revealed that the CAV2-modulated genes in the CD11b(+) -type DCs clustered in several activated immunogenicity-related functions, such as immune response, immune cell trafficking and inflammation. Thus gene profiling in skin-migrated DC in vitro indicates that the CD11b(+) DC type is more responsive to CAV2 than the CD103(+) DC type, and provides valuable information to help in evaluating and possibly improving viral vector vaccine effectiveness.

An update on canine adenovirus type 2 and its vectors

Adenovirus vectors have significant potential for long- or short-term gene transfer. Preclinical and clinical studies using human derived adenoviruses (HAd) have demonstrated the feasibility of flexible hybrid vector designs, robust expression and induction of protective immunity. However, clinical use of HAd vectors can, under some conditions, be limited by pre-existing vector immunity. Pre-existing humoral and cellular anti-capsid immunity limits the efficacy and duration of transgene expression and is poorly circumvented by injections of larger doses and immuno-suppressing drugs. This review updates canine adenovirus serotype 2 (CAV-2, also known as CAdV-2) biology and gives an overview of the generation of early region 1 (E1)-deleted to helper-dependent (HD) CAV-2 vectors. We also summarize the essential characteristics concerning their interaction with the anti-HAd memory immune responses in humans, the preferential transduction of neurons, and its high level of retrograde axonal transport in the central and peripheral nervous system. CAV-2 vectors are particularly interesting tools to study the pathophysiology and potential treatment of neurodegenerative diseases, as anti-tumoral and anti-viral vaccines, tracer of synaptic junctions, oncolytic virus and as a platform to generate chimeric vectors.

Scavenger receptors and their potential as therapeutic targets in the treatment of cardiovascular disease

Scavenger receptors act as membrane-bound and soluble proteins that bind to macromolecular complexes and pathogens. This diverse supergroup of proteins mediates binding to modified lipoprotein particles which regulate the initiation and progression of atherosclerotic plaques. In vascular tissues, scavenger receptors are implicated in regulating intracellular signaling, lipid accumulation, foam cell development, and cellular apoptosis or necrosis linked to the pathophysiology of atherosclerosis. One approach is using gene therapy to modulate scavenger receptor function in atherosclerosis. Ectopic expression of membrane-bound scavenger receptors using viral vectors can modify lipid profiles and reduce the incidence of atherosclerosis. Alternatively, expression of soluble scavenger receptors can also block plaque initiation and progression. Inhibition of scavenger receptor expression using a combined gene therapy and RNA interference strategy also holds promise for long-term therapy. Here we review our current understanding of the gene delivery by viral vectors to cells and tissues in gene therapy strategies and its application to the modulation of scavenger receptor function in atherosclerosis.

SGSH gene transfer in mucopolysaccharidosis type IIIA mice using canine adenovirus vectors

Many viral backbones have been used as gene transfer vectors. However, the efficacy of therapy based on human-derived vectors may be limited by the high incidence of pre-existing humoral and cellular memory immunity. To circumvent some of the clinical disadvantages of vectors derived from common human pathogens, we have used an E1-deleted vector derived from a xenogenic adenovirus, canine adenovirus serotype 2 (CAV-2) to ameliorate neuropathological changes associated with the lysosomal storage disorder, mucopolysaccharidosis type IIIA (MPS IIIA). This presently untreatable condition is caused by N-sulfoglucosamine sulfohydrolase (SGSH) deficiency and is characterized by heparan sulfate accumulation and progressive neurodegeneration. Injection of CAV-SGSH-GFP into the thalamus of adult MPS IIIA mouse brain resulted in short-term gene expression. In contrast, intra-ventricular injection of newborn mice yielded dose-dependent transgene expression which persisted for at least 20-weeks and improved neuropathology. Together, these studies suggest that this E1-deleted CAV-2 vector is capable of mediating regional medium-term gene expression and facilitating improvements in neuropathology in MPS IIIA mice.

Construction and characterization of a recombinant canine adenovirus expressing GP5 and M proteins of porcine reproductive and respiratory syndrome virus

The causative agent of porcine reproductive and respiratory syndrome (PRRS) is PRRS virus (PRRSV), which belongs to the family Arteriviridae. GP5/M protein complex of PRRSV binds to sialoadhesion expressed on the cells to infect the cells. In this study, we developed a canine adenovirus type 2 (CAV-2) recombinant, termed rCAV2-GP5/M, expressing GP5 and M proteins. To evaluate the immunogenicity of the recombinant virus, mice were inoculated subcutaneously with rCAV2-GP5/M, and specific antibodies against PRRSV in the sera were measured by enzyme-linked immunosorbent assay and the viral neutralization test. Two weeks post-immunization (w.p.i.), anti-PRRSV antibodies were detected in the sera, slightly increased by booster immunization at four w.p.i., and then gradually decreased. The viral neutralizing test showed that neutralizing antibodies were present in the sera collected at two w.p.i., increased by booster immunization, and reached the maximum titer at six w.p.i. Lymphocyte proliferation responding to PRRSV antigens was also observed from two w.p.i. Although further studies are needed to evaluate the usefulness of the recombinant virus to protect pigs from PPRSV, we succeeded in developing a candidate vaccine against PPRSV infection by using CAV-2 vector.

A real-time PCR assay for quantification of canine adenoviral vectors

The pre-existing humoral and cellular immunity found in the great majority of the population raises concerns about the clinical efficacy and safety of vectors derived from ubiquitous human adenovirus serotypes. To alleviate these concerns, canine adenovirus type 2 vectors (CAV-2) were developed. Owing to their extraordinary neuronal tropism and efficient axonal retrograde transport, CAV-2 vectors hold great promise for the treatment of neurodegenerative diseases. The development and validation of a SYBR Green qPCR assay for determination of CAV-2 titers is reported in the present study. This method uses specific primers designed to amplify a small genomic fragment of CAV-2 structural genes (pVI-hexon). The method was accurate and reproducible as determined by the low intra- and inter-assay variability (<15% R.S.E.). It is sensitive and useful over a 5-log range (1 x 10(3) to 1 x 10(7)genome copies/reaction). The assay can be used to quantify purified vector samples as well as crude viral lysates. The titers obtained by qPCR correlated well with both, those obtained by OD(260) and TCID(50) as indicated by the high coefficients of determination obtained by regression analysis (r(2)>0.83). The development of this simple and rapid CAV-2 quantitation method should be helpful for process development and monitoring.

Functional organization of the major late transcriptional unit of canine adenovirus type 2

Vectors derived from canine adenovirus type 2 (CAV-2) are attractive candidates for gene therapy and live recombinant vaccines. CAV-2 vectors described thus far have been generated by modifying the virus genome, most notably early regions 1 and 3 or the fiber gene. Modification of these genes was underpinned by previous descriptions of their mRNA and protein-coding sequences. Similarly, the construction of new CAV-2 vectors bearing changes in other genomic regions, in particular many of those expressed late in the viral cycle, will require prior characterization of the corresponding transcriptional units. In this study, we provide a detailed description of the late transcriptional organization of the CAV-2 genome. We examined the major late transcription unit (MLTU) and determined its six families of mRNAs controlled by the putative major late promoter (MLP). All mRNAs expressed from the MLTU had a common non-coding tripartite leader (224 nt) at their 5' end. In transient transfection assays, the predicted MLP sequence was able to direct luciferase gene expression and the TPL sequence yielded a higher amount of transgene product. Identification of viral transcriptional products following in vitro infection confirmed most of the predicted protein-coding regions that were deduced from computer analysis of the CAV-2 genome. These findings contribute to a better understanding of gene expression in CAV-2 and lay the foundation required for genetic modifications aimed at vector optimization.

Adenovirus receptors and their implications in gene delivery

Adenoviruses (Ads) have gained popularity as gene delivery vectors for therapeutic and prophylactic applications. Ad entry into host cells involves specific interactions between cell surface receptors and viral capsid proteins. Several cell surface molecules have been identified as receptors for Ad attachment and entry. Tissue tropism of Ad vectors is greatly influenced by their receptor usage. A variety of strategies have been investigated to modify Ad vector tropism by manipulating the receptor-interacting moieties. Many such strategies are aimed at targeting and/or detargeting of Ad vectors. In this review, we discuss the various cell surface molecules that are implicated as receptors for virus attachment and internalization. Special emphasis is given to Ad types that are utilized as gene delivery vectors. Various strategies to modify Ad tropism using the knowledge of Ad receptors are also discussed.

First step in characterization of cis-acting sequences involved in fowl adenovirus 1 (CELO) packaging and its effect on the development of a helper-dependent vector strategy

Adenovirus-based vectors are widely developed for potential utilization as vectors in vaccine and gene therapy strategies. We focused on developing a helper-dependent adenoviral (HD-Ad) vector for the potential use of CELO, a member of the Aviadenovirus genus, in avian species vaccination. Our aim was to localize sequences which could play an essential role in CELO genome encapsidation and, when deleted, was unable to produce viruses to develop a helper CELO virus. A panel of 6 mutants with deletions between nt 80 and 350 of the CELO genome was constructed and characterized for its ability to produce viable virus. To develop a helper-dependent adenoviral vector derived from CELO, a helper virus was developed by inserting loxP sequences around the region containing the identified putative packaging sequences. A LMH (Leghorn Male Hepatocarcinoma) cell line expressing Cre recombinase was developed to allow the excision of this region. We demonstrated that the region from nt 200 to 250 was important and the region from nt 250 to 300 at the left end of the CELO genome was essential for virus encapsidation. We also showed that the loxP-flanked region was efficiently removed in a Cre expressing cell line to produce a candidate helper virus.

Lentivirus vector can be readministered to nasal epithelia without blocking immune responses

For many envisioned applications of lentivirus vectors as tools in respiratory biology and therapeutic gene delivery, the efficiency of gene transfer must be improved. We previously demonstrated stable, persistent (>11 months) in vivo expression following a single application of a feline immunodeficiency virus (FIV)-based lentivirus vector (GP64-FIV) to murine nasal epithelia. Here we investigate the efficacy of repeated administration of lentivirus vectors to the airways. Using quantitative bioluminescent imaging, we found that consecutive daily dosing achieved a linear increase in gene expression and greatly increased the number of epithelial cells targeted. Surprisingly, reporter gene expression also increased additively following each of seven doses of FIV delivered over consecutive weeks (1 dose/week), without the development of systemic or local neutralizing antibodies. This approach enhanced expression of both reporter and therapeutic transgenes. Transduction efficiency achieved following a single dose of FIV expressing mouse erythropoietin was insufficient to increase hematocrit, whereas seven consecutive daily doses significantly increased hematocrit. These unexpected results contrast strikingly with findings reported for adenovirus vectors. Prolonged gene expression has been observed in vivo following a single dose of virus vector; however, depending on the application, repeated administration of vector may be necessary to achieve stable, therapeutic gene expression.

A simple, lanthanide-based method to enhance the transduction efficiency of adenovirus vectors

Based upon the powerful bridging and charge-masking properties of lanthanide cations (Ln3+), we have investigated their use to improve the transduction efficiency of adenovirus vectors. Using a luciferase marker gene, it was possible to increase transgene expression by the murine mesenchymal stem cell line C3H10T(1/2) by up to four log orders when using very low multiplicities of infection in conjunction with Ln3+; La3+ was superior to Gd3+, Y3+ and Lu3+ in this regard. All Ln3+ were more effective than Ca2+. Flow cytometry, using a green fluorescent protein marker gene, confirmed that La3+ increased both the percentage of transduced cells and the level of transgene expression per cell. Transduction of primary cultures of a variety of different mesenchymal cells from human, rabbit, bovine and rat sources, as well as gene transfer to synovium and muscle in vivo, was also greatly enhanced. Our findings suggest that this lanthanide-based method holds much promise for expediting both experimental and clinical applications of gene transfer with adenoviral vectors.

Three-dimensional structure of canine adenovirus serotype 2 capsid

There are more than 100 known adenovirus (AdV) serotypes, including 50 human serotypes. Because AdV-induced disease is relatively species specific, vectors derived from nonhuman serotypes may have wider clinical potential based, in part, on the lack of ubiquitous memory immunity. Whereas a few of the human serotype capsids have been studied at the structural level, none of the nonhuman serotypes has been analyzed. The basis laid by the analysis of human AdV (hAdV) has allowed us to determine and compare the three-dimensional structure of the capsid of canine serotype 2 (CAV-2) to that of hAdV serotype 5 (hAdV-5). We show that CAV-2 capsid has a smoother structure than the human serotypes. Many of the external loops found in the hAdV-5 penton base and the hexon, against which the antibody response is directed, are shorter or absent in CAV-2. On the other hand, the CAV-2 fiber appears to be more complex, with two bends in the shaft. An interesting difference between the human and canine viruses is that the C-terminal part of protein IX is in a different position, making an antenna sticking out of the CAV-2 capsid. The comparison between the two viruses allows the identification of sites that should be easy to modify on the CAV-2 capsid for altering tissue tropism or other biological activities.

Helper-dependent adenovirus for the gene therapy of proliferative retinopathies: stable gene transfer, regulated gene expression and therapeutic efficacy

BACKGROUND

Ocular neovascular disorders, such as diabetic retinopathy and age-related macular degeneration, are the principal causes of blindness in developed countries. Current treatments are of limited efficacy, whereas a therapy based on intraocular gene transfer of angiostatic factors represents a promising alternative. For the first time we have explored the potential of helper-dependent adenovirus (HD-Ad), the last generation of Ad vectors, in the therapy of retinal neovascularization.

METHODS

We first analyzed efficiency and stability of intraretinal gene transfer following intravitreous injection in mice. A HD-Ad vector expressing green fluorescent protein (GFP) under the control of the cytomegalovirus (CMV) promoter (HD-Ad/GFP) was compared with a first-generation (E1/E3-deleted) Ad vector carrying an identical GFP expression cassette (FG-Ad/GFP). We also constructed HD-Ad vectors expressing a soluble form of the VEGF receptor (sFlt-1) in a constitutive (HD-Ad/sFlt-1) or doxycycline (dox)-inducible (HD-Ad/S-M2/sFlt-1) manner and tested their therapeutic efficacy upon intravitreous delivery in a rat model of oxygen-induced retinopathy (OIR).

RESULTS

HD-Ad/GFP promoted long-lasting (up to 1 year) transgene expression in retinal Müller cells, in marked contrast with the short-term expression observed with FG-Ad/GFP. Intravitreous injection of HD-Ad vectors expressing sFlt-1 resulted in detectable levels of sFlt-1 and inhibited retinal neovascularization by more than 60% in a rat model of OIR. Notably, the therapeutic efficacy of the inducible vector HD-Ad/S-M2/sFlt-1 was strictly dox-dependent.

CONCLUSIONS

HD-Ad vectors enable stable gene transfer and regulated expression of angiostatic factors following intravitreous injection and thus are attractive vehicles for the gene therapy of neovascular diseases of the retina.

Interactions between human plasma components and a xenogenic adenovirus vector: reduced immunogenicity during gene transfer

By the time we are adolescents most of us have been in contact with several of the >50 human adenovirus (HAd) serotypes. These common subclinical infections lead to an efficient anti-adenovirus cross-reacting adaptive immunity. During gene therapy, the ubiquitous anti-adenovirus humoral response and complement activation will modify and dictate vector biodistribution, as well as the response to the virion and transgene(s). In this study, we assayed the interactions of a xenogenic adenovirus derived from canine serotype 2 (CAV-2) with naturally occurring human antibodies (Abs) and the complement system. In our cohort, we found class G immunoglobulins (Igs) that recognized the intact CAV-2 virion and the external virion proteins. However, the majority of donors had low or no neutralizing Abs, class A, or class M Igs. Purified anti-HAd serotype 5 Abs also recognized CAV-2 virion proteins. In addition, in spite of the presence of anti-CAV-2 IgGs, CAV-2 poorly activated the classical and alternative complement cascades. This atypical response was due to a block upstream of the component 3 (C3) convertase and interplay between the component 1 (C1) inhibitor, the C1q-C1r2-C1s2 complex and CAV-2. Our data demonstrate that some xenogenic adenovirus vectors, like CAV-2, could lead to notably different outcomes following systemic delivery.

Contrasting effects of human, canine, and hybrid adenovirus vectors on the phenotypical and functional maturation of human dendritic cells: implications for clinical efficacy

Antipathogen immune responses create a balance between immunity, tolerance, and immune evasion. However, during gene therapy most viral vectors are delivered in substantial doses and are incapable of expressing gene products that reduce the host's ability to detect transduced cells. Gene transfer efficacy is also modified by the in vivo transduction of dendritic cells (DC), which notably increases the immunogenicity of virions and vector-encoded genes. In this study, we evaluated parameters that are relevant to the use of canine adenovirus serotype 2 (CAV-2) vectors in the clinical setting by assaying their effect on human monocyte-derived DC (hMoDC). We compared CAV-2 to human adenovirus (HAd) vectors containing the wild-type virion, functional deletions in the penton base RGD motif, and the CAV-2 fiber knob. In contrast to the HAd type 5 (HAd5)-based vectors, CAV-2 poorly transduced hMoDC, provoked minimal upregulation of major histocompatibility complex class I/II and costimulatory molecules (CD40, CD80, and CD86), and induced negligible morphological changes indicative of DC maturation. Functional maturation assay results (e.g., reduced antigen uptake; tumor necrosis factor alpha, interleukin-1beta [IL-1beta], gamma interferon [IFN-gamma], IL-10, IL-12, and IFN-alpha/beta secretion; and stimulation of heterologous T-cell proliferation) were also significantly lower for CAV-2. Our data suggested that this was due, in part, to the use of an alternative receptor and a block in vesicular escape. Additionally, HAd5 vector-induced hMoDC maturation was independent of the aforementioned cytokines. Paradoxically, an HAd5/CAV-2 hybrid vector induced the greatest phenotypical and functional maturation of hMoDC. Our data suggest that CAV-2 and the HAd5/CAV-2 vector may be the antithesis of Adenoviridae immunogenicity and that each may have specific clinical advantages.

Structural and Mutational Analysis of Human Ad37 and Canine Adenovirus 2 Fiber Heads in Complex with the D1 Domain of Coxsackie and Adenovirus Receptor

Adenovirus fibers from most serotypes bind the D1 domain of coxsackie and adenovirus receptor (CAR), although the binding residues are not strictly conserved. To understand this further, we determined the crystal structures of canine adenovirus serotype 2 (CAV-2) and the human adenovirus serotype 37 (HAd37) in complex with human CAR D1 at 2.3 and 1.5A resolution, respectively. Structure comparison with the HAd12 fiber head-CAR D1 complex showed that the overall topology of the interaction is conserved but that the interfaces differ in number and identity of interacting residues, shape complementarity, and degree of conformational adaptation. Using surface plasmon resonance, we characterized the binding affinity to CAR D1 of wild type and mutant CAV-2 and HAd37 fiber heads. We found that CAV-2 has the highest affinity but fewest direct interactions, with the reverse being true for HAd37. Moreover, we found that conserved interactions can have a minor contribution, whereas serotype-specific interactions can be essential. These results are discussed in the light of virus evolution and design of adenovirus vectors for gene transfer.