Lethal toxicity, severe endothelial injury, and a threshold effect with high doses of an adenoviral vector in baboons

Adenovirus vector-attributed hepatotoxicity blocks clinical application in gene therapy

Adenoviruses (Ads), common self-limiting pathogens in humans and animals, usually cause conjunctivitis, mild upper respiratory tract infection or gastroenteritis in humans and hepatotoxicity syndrome in chickens and dogs, posing great threats to public health and livestock husbandry. Artificially modified Ads, which wipe out virulence-determining genes, are the most frequently used viral vectors in gene therapy, and some Ad vector (AdV)-related medicines and vaccines have been licensed and applied. Inherent liver tropism enables AdVs to specifically deliver drugs/genes to the liver; however, AdVs are closely associated with acute hepatotoxicity in immunocompromised individuals, and the side effects of AdVs, which stimulate a strong inflammatory reaction in the liver and cause acute hepatotoxicity, have largely limited clinical application. Therefore, this review systematically elucidates the intimate relationship between AdVs and hepatotoxicity in terms of virus and host and precisely illustrates the accumulated understanding in this field over the past decades. This review demonstrates the liver tropism of AdVs and molecular mechanism of AdV-induced hepatotoxicity and looks at the studies on AdV-mediated animal hepatotoxicity, which will undoubtedly deepen the understanding of AdV-caused liver injury and be of benefit in the further safe development of AdVs.

Systemic cancer therapy with engineered adenovirus that evades innate immunity

Oncolytic virus therapy is a cancer treatment modality that has the potential to improve outcomes for patients with currently incurable malignancies. Although intravascular delivery of therapeutic viruses provides access to disseminated tumors, this delivery route exposes the virus to opsonizing and inactivating factors in the blood, which limit the effective therapeutic virus dose and contribute to activation of systemic toxicities. When human species C adenovirus HAdv-C5 is delivered intravenously, natural immunoglobulin M (IgM) antibodies and coagulation factor X rapidly opsonize HAdv-C5, leading to virus sequestration in tissue macrophages and promoting infection of liver cells, triggering hepatotoxicity. Here, we showed that natural IgM antibody binds to the hypervariable region 1 (HVR1) of the main HAdv-C5 capsid protein hexon. Using compound targeted mutagenesis of hexon HVR1 loop and other functional sites that mediate virus-host interactions, we engineered and obtained a high-resolution cryo-electron microscopy structure of an adenovirus vector, Ad5-3M, which resisted inactivation by blood factors, avoided sequestration in liver macrophages, and failed to trigger hepatotoxicity after intravenous delivery. Systemic delivery of Ad5-3M to mice with localized or disseminated lung cancer led to viral replication in tumor cells, suppression of tumor growth, and prolonged survival. Thus, compound targeted mutagenesis of functional sites in the virus capsid represents a generalizable approach to tailor virus interactions with the humoral and cellular arms of the immune system, enabling generation of "designer" viruses with improved therapeutic properties.

Untangling the Intricacies of Infection, Thrombosis, Vaccination, and Antiphospholipid Antibodies for COVID-19

Advanced SARS-CoV-2 infections not uncommonly associate with the occurrence of silent or manifest thrombotic events which may be found as focal or systemic disease. Given the potential complexity of COVID-19 illnesses, a multifactorial causation is likely, but several studies have focused on infection-induced coagulopathy. Procoagulant states are commonly found in association with the finding of antiphospholipid antibodies. The correlation of the latter with thrombosis and/or clinical severity remains controversial. Although measures of antiphospholipid antibodies most commonly include assessments for lupus anticoagulant, anticardiolipin, and anti-ß2-glycoprotein-I antibodies, lesser common antibodies have been detected, and there remains speculation that other yet undiscovered autoimmune thrombotic events may yet be found. The recent discovery of post-vaccination thromboses associated with platelet factor 4 antibody has created another level of concern. The pathogenesis of antiphospholipid antibodies and their role in COVID-19-related thrombosis deserves further attention. The multifactorial nature of thrombosis associated with both infection and vaccination should continue to be studied as new events unfold. Even if a cause-and-effect relationship is variable at best, such dedicated research is likely to generate other valuable insights that are applicable to medicine generally.

Human Adenovirus Serotype 5 Is Sensitive to IgM-Independent Neutralization In Vitro and In Vivo

Human adenovirus 5 (HAdV-5) is used as a vector in gene therapy clinical trials, hence its interactions with the host immune system have been widely studied. Previous studies have demonstrated that HAdV-5 binds specifically to murine coagulation factor X (mFX), inhibiting IgM and complement-mediated neutralization. Here, we examined the physical binding of immune components to HAdV-5 by nanoparticle tracking analysis, neutralization assays, mass spectrometry analysis and in vivo experiments. We observed that purified mouse Immunoglobulin M (IgM) antibodies bound to HAdV-5 only in the presence of complement components. Active serum components were demonstrated to bind to HAdV-5 in the presence or absence of mFX, indicating that immune molecules and mFX might bind to different sites. Since binding of mFX to HAdV-5 blocks the neutralization cascade, these findings suggested that not all complement-binding sites may be involved in virion neutralization. Furthermore, the data obtained from serum neutralization experiments suggested that immune molecules other than IgM and IgG may trigger activation of the complement cascade in vitro. In vivo experiments were conducted in immunocompetent C57BL/6 or immuno-deficient Rag2^-/- mice. HAdV-5T* (a mutant HAdV-5 unable to bind to human or mFX) was neutralized to some extent in both mouse models, suggesting that murine immunoglobulins were not required for neutralization of HAdV-5 in vivo. Liquid Chromatography-Mass Spectrometry (LC-MS/MS) analysis of HAdV-5 and HAdV-5T* after exposure to murine sera showed stable binding of C3 and C4b in the absence of mFX. In summary, these results suggest that HAdV-5 neutralization can be mediated by both the classical and alternative pathways and that, in the absence of immunoglobulins, the complement cascade can be activated by direct binding of C3 to the virion.

Gene therapy for monogenic liver diseases: clinical successes, current challenges and future prospects

Over the last decade, pioneering liver-directed gene therapy trials for haemophilia B have achieved sustained clinical improvement after a single systemic injection of adeno-associated virus (AAV) derived vectors encoding the human factor IX cDNA. These trials demonstrate the potential of AAV technology to provide long-lasting clinical benefit in the treatment of monogenic liver disorders. Indeed, with more than ten ongoing or planned clinical trials for haemophilia A and B and dozens of trials planned for other inherited genetic/metabolic liver diseases, clinical translation is expanding rapidly. Gene therapy is likely to become an option for routine care of a subset of severe inherited genetic/metabolic liver diseases in the relatively near term. In this review, we aim to summarise the milestones in the development of gene therapy, present the different vector tools and their clinical applications for liver-directed gene therapy. AAV-derived vectors are emerging as the leading candidates for clinical translation of gene delivery to the liver. Therefore, we focus on clinical applications of AAV vectors in providing the most recent update on clinical outcomes of completed and ongoing gene therapy trials and comment on the current challenges that the field is facing for large-scale clinical translation. There is clearly an urgent need for more efficient therapies in many severe monogenic liver disorders, which will require careful risk-benefit analysis for each indication, especially in paediatrics.

Defining a Novel Role for the Coxsackievirus and Adenovirus Receptor in Human Adenovirus Serotype 5 Transduction In Vitro in the Presence of Mouse Serum

Human adenoviral serotype 5 (HAdV-5) vectors have predominantly hepatic tropism when delivered intravascularly, resulting in immune activation and toxicity. Coagulation factor X (FX) binding to HAdV-5 mediates liver transduction and provides protection from virion neutralization in mice. FX is dispensable for liver transduction in mice lacking IgM antibodies or complement, suggesting that alternative transduction pathways exist. To identify novel factor(s) mediating HAdV-5 FX-independent entry, we investigated HAdV-5 transduction in vitro in the presence of serum from immunocompetent C57BL/6 or immunocompromised mice lacking IgM antibodies (Rag 2^-/- and NOD-scid-gamma [NSG]). Sera from all three mouse strains enhanced HAdV-5 transduction of A549 cells. While inhibition of HAdV-5-FX interaction with FX-binding protein (X-bp) inhibited transduction in the presence of C57BL/6 serum, it had negligible effect on the enhanced transduction observed in the presence of Rag 2^-/- or NSG serum. Rag 2^-/- serum also enhanced transduction of the FX binding-deficient HAdV-5HVR5*HVR7*E451Q (AdT*). Interestingly, Rag 2^-/- serum enhanced HAdV-5 transduction in a FX-independent manner in CHO-CAR and SKOV3-CAR cells (CHO or SKOV3 cells transfected to stably express human coxsackievirus and adenovirus receptor [CAR]). Additionally, blockade of CAR with soluble HAdV-5 fiber knob inhibited mouse serum-enhanced transduction in A549 cells, suggesting a potential role for CAR. Transduction of HAdV-5 KO1 and HAdV-5/F35 (CAR binding deficient) in the presence of Rag 2^-/- serum was equivalent to that of HAdV-5, indicating that direct interaction between HAdV-5 and CAR is not required. These data suggest that FX may protect HAdV-5 from neutralization but has minimal contribution to HAdV-5 transduction in the presence of immunocompromised mouse serum. Alternatively, transduction occurs via an unidentified mouse serum protein capable of bridging HAdV-5 to CAR.IMPORTANCE The intravascular administration of HAdV-5 vectors can result in acute liver toxicity, transaminitis, thrombocytopenia, and injury to the vascular endothelium, illustrating challenges yet to overcome for HAdV-5-mediated systemic gene therapy. The finding that CAR and potentially an unidentified factor present in mouse serum might be important mediators of HAdV-5 transduction highlights that a better understanding of the complex biology defining the interplay between adenovirus immune recognition and cellular uptake mechanisms is still required. These findings are important to inform future optimization and development of HAdV-5-based adenoviral vectors for gene therapy.

Pseudotyping Serotype 5 Adenovirus with the Fiber from Other Serotypes Uncovers a Key Role of the Fiber Protein in Adenovirus 5-Induced Thrombocytopenia

Adenovirus (Ad) infection in humans is associated with inflammatory responses and thrombocytopenia. Although several studies were conducted in mice models to understand molecular and cellular mechanisms of Ad-induced inflammatory responses, only few of them turned their interest toward the mechanisms of Ad-induced thrombocytopenia. Using different depletion methods, the present study ruled out any significant role of spleen, macrophages, and vitamin K-dependent factor in Ad-induced thrombocytopenia. Interestingly, mice displaying thrombocytopenia expressed high levels of cytokines/chemokines after Ad administration. Most importantly, pseudotyping adenovirus with the fiber protein from other serotypes was associated with reduction of both cytokine/chemokine production and thrombocytopenia. Altogether, our results suggest that capsid fiber protein (and more precisely its shaft) of Ad serotype 5 triggers the cytokine production that leads to Ad-induced thrombocytopenia.

Long-term, high-level hepatic secretion of acid α-glucosidase for Pompe disease achieved in non-human primates using helper-dependent adenovirus

Pompe disease (glycogen storage disease type II (GSD-II)) is a myopathy caused by a genetic deficiency of acid α-glucosidase (GAA) leading to lysosomal glycogen accumulation causing muscle weakness, respiratory insufficiency and death. We previously demonstrated in GSD-II mice that a single injection of a helper-dependent adenovirus (HD-Ad) expressing GAA resulted in at least 300 days of liver secretion of GAA, correction of the glycogen storage in cardiac and skeletal muscles and improved muscle strength. Recent reports suggest that gene therapy modeling for lysososomal storage diseases in mice fails to predict outcomes in larger animal models. We therefore evaluated an HD-Ad expressing GAA in non-human primates. The baboons not only tolerated the procedure well, but the results also confirmed that a single dose of the HD-Ad allowed the livers of the treated animals to express and secrete large amounts of GAA for at least 6 months, at levels similar to those achieved in mice. Moreover, we detected liver-derived GAA in the heart, diaphragm and skeletal muscles of the treated animals for the duration of the study at levels that corrected glycogen accumulation in mice. This work validates our proof-of-concept studies in mice, and justifies future efforts using Ad-based vectors in Pompe disease patients.

Helper-dependent adenoviral vectors for liver-directed gene therapy of primary hyperoxaluria type 1

Primary hyperoxaluria type 1 (PH1) is an inborn error of liver metabolism due to deficiency of the peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT) which catalyzes conversion of glyoxylate into glycine. AGT deficiency results in overproduction of oxalate which ultimately leads to end-stage renal disease and death. Organ transplantation as either preemptive liver transplantation or combined liver/kidney transplantation is the only available therapy to prevent disease progression. Gene therapy is an attractive option to provide an alternative treatment for PH1. Towards this goal, we investigated helper-dependent adenoviral (HDAd) vectors for liver-directed gene therapy of PH1. Compared to saline controls, AGT-deficient mice injected with an HDAd encoding the AGT under the control of a liver-specific promoter showed a significant reduction of hyperoxaluria and less increase of urinary oxalate following challenge with Ethylene Glycol (EG), a precursor of glyoxylate. These studies may thus pave the way to clinical application of HDAd for PH1 gene therapy.

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.

Ethics of Cancer Gene Transfer Clinical Research

Translation of cancer gene transfer confronts many familiar-and some distinctive-ethical challenges. In what follows, I survey three major ethical dimensions of cancer gene transfer development. Subheading 1 centers on the ethics of planning, designing, and reporting animal studies. Subheading 2 describes basic elements of human subjects protection as pertaining to cancer gene transfer. In Subheading 3, I describe how cancer gene transfer researchers have obligations to downstream consumers of the evidence they produce.

A reduction in the human adenovirus virion size through use of a shortened fibre protein does not enhance muscle transduction following systemic or localised delivery in mice

We have investigated whether reducing the overall size of adenovirus (Ad), through use of a vector containing a shortened fibre, leads to enhanced distribution and dissemination of the vector. Intravenous or intraperitoneal injection of Ad5SlacZ (12 nm fibre versus the normal Ad5 37 nm fibre) or Ad5SpKlacZ (shortened fibre with polylysine motif in the H-I loop of fibre knob domain) led to similar levels of lacZ expression compared to Ad5LlacZ (native Ad5 fibre) in the liver of treated animals, but did not enhance extravasation into the tibialis anterior muscle. Direct injection of the short-fibre vectors into the tibialis anterior muscle did not result in enhanced spread of the vector through muscle tissue, and led to only sporadic transgene expression in the spinal cord, suggesting that modifying the fibre length or redirecting viral infection to a more common cell surface receptor does not enhance motor neuron uptake or retrograde transport.

Selective suppression of autocatalytic caspase-3 driven by two-step transcriptional amplified human telomerase reverse transcriptase promoter on ovarian carcinoma growth in vitro and in mice

The objective of our study was to construct recombinant adenovirus (rAd) AdHTVP2G5-rev-casp3, which expresses autocatalytic caspase-3 driven by human telomerase reverse transcriptase promoter (hTERTp) with a two-step transcription amplification (TSTA) system and investigate its antitumor effects on ovarian cancer in vitro and in vivo. Fluorescent detection was used to detect EGFP expression in various cells. Cell viabilities were determined using the Cell Counting Kit-8 and flow cytometry. RT-PCR and immunoblotting assays were used to detect cellular apoptotic activities. Tumor growth and survival of tumor-bearing mice were studied. The hTERTp-TSTA system showed the strongest activity in hTERT-positive cancer cells when compared with hTERTp and cytomeglovirus promoter (CMVp). In contrast, it showed no activity in hTERT‑negative HUVECs. AdHTVP2G5‑rev-casp3 markedly suppressed the survival of AO cells in a dose-dependent modality with a viability rate of 17.8 ± 3.5% at an MOI of 70, which was significantly lower than that by AdHT-rev-casp3 and Ad-rev-casp3 (rAds which express rev-caspase-3 driven by hTERTp and CMVp, respectively). In contrast, AdHTVP2G5‑rev-casp3 induced little HUVEC death with a viability rate of 92.7 ± 5.2% at the same MOI. Additionally, AdHTVP2G5-rev-casp3 (MOI=70) caused significant apoptosis in AO cells with an apoptotic rate of 42%. The tumor growth suppression rate of AdHTVP2G5-rev-casp3 was 81.52%, significantly higher than that of AdHT-rev-casp3 (54.94%) or Ad-rev-casp3 (21.35%). AdHTVP2G5-rev-casp3 significantly improved the survival of tumor-bearing mice with little liver damage, with a mean survival of 258 ± 28 days. These results showed that AdHTVP2G5-rev-casp3 caused effective apoptosis with significant tumor selectivity, strongly suppressed tumor growth and improved mouse survival with little liver toxicity. It can be a potent therapeutic agent for tumor targeted treatment of ovarian cancer.

Challenges and Prospects for Helper-Dependent Adenoviral Vector-Mediated Gene Therapy

Helper-dependent adenoviral (HDAd) vectors that are devoid of all viral coding sequences are promising non-integrating vectors for gene therapy because they efficiently transduce a variety of cell types in vivo, have a large cloning capacity, and drive long-term transgene expression without chronic toxicity. The main obstacle preventing clinical applications of HDAd vectors is the host innate inflammatory response against the vector capsid proteins that occurs shortly after intravascular vector administration and result in acute toxicity, the severity of which is dose dependent. Intense efforts have been focused on elucidating adenoviral vector-host interactions and the factors involved in the acute toxicity. This review focuses on the recent acquisition of data on such interactions and on strategies investigated to improve the therapeutic index of HDAd vectors.

Peptide-based technologies to alter adenoviral vector tropism: ways and means for systemic treatment of cancer

Due to the fundamental progress in elucidating the molecular mechanisms of human diseases and the arrival of the post-genomic era, increasing numbers of therapeutic genes and cellular targets are available for gene therapy. Meanwhile, the most important challenge is to develop gene delivery vectors with high efficiency through target cell selectivity, in particular under in situ conditions. The most widely used vector system to transduce cells is based on adenovirus (Ad). Recent endeavors in the development of selective Ad vectors that target cells or tissues of interest and spare the alteration of all others have focused on the modification of the virus broad natural tropism. A popular way of Ad targeting is achieved by directing the vector towards distinct cellular receptors. Redirecting can be accomplished by linking custom-made peptides with specific affinity to cellular surface proteins via genetic integration, chemical coupling or bridging with dual-specific adapter molecules. Ideally, targeted vectors are incapable of entering cells via their native receptors. Such altered vectors offer new opportunities to delineate functional genomics in a natural environment and may enable efficient systemic therapeutic approaches. This review provides a summary of current state-of-the-art techniques to specifically target adenovirus-based gene delivery vectors.

IL-1α and complement cooperate in triggering local neutrophilic inflammation in response to adenovirus and eliminating virus-containing cells

Inflammation is a highly coordinated host response to infection, injury, or cell stress. In most instances, the inflammatory response is pro-survival and is aimed at restoring physiological tissue homeostasis and eliminating invading pathogens, although exuberant inflammation can lead to tissue damage and death. Intravascular injection of adenovirus (Ad) results in virus accumulation in resident tissue macrophages that trigger activation of CXCL1 and CXCL2 chemokines via the IL-1α-IL-1RI signaling pathway. However, the mechanistic role and functional significance of this pathway in orchestrating cellular inflammatory responses to the virus in vivo remain unclear. Resident metallophilic macrophages expressing macrophage receptor with collagenous structure (MARCO⁺) in the splenic marginal zone (MZ) play the principal role in trapping Ad from the blood. Here we show that intravascular Ad administration leads to the rapid recruitment of Ly-6G⁺7/4⁺ polymorphonuclear leukocytes (PMNs) in the splenic MZ, the anatomical compartment that remains free of PMNs when these cells are purged from the bone marrow via a non-inflammatory stimulus. Furthermore, PMN recruitment in the splenic MZ resulted in elimination of virus-containing cells. IL-1α-IL-1RI signaling is only partially responsible for PMN recruitment in the MZ and requires CXCR2, but not CXCR1 signaling. We further found reduced recruitment of PMNs in the splenic MZ in complement C3-deficient mice, and that pre-treatment of IL-1α-deficient, but not wild-type mice, with complement inhibitor CR2-Crry (inhibits all complement pathways at C3 activation) or CR2-fH (inhibits only the alternative complement activation pathway) prior to Ad infection, abrogates PMN recruitment to the MZ and prevents elimination of MARCO⁺ macrophages from the spleen. Collectively, our study reveals a non-redundant role of the molecular factors of innate immunity – the chemokine-activating IL-1α-IL-1RI-CXCR2 axis and complement – in orchestrating local inflammation and functional cooperation of PMNs and resident macrophages in the splenic MZ, which collectively contribute to limiting disseminated pathogen spread via elimination of virus-containing cells.

Adenovirus (Ad) induces a potent activation of pro-inflammatory cytokines and chemokines upon interaction with tissue macrophages in vivo. However, critical factors affecting cellular inflammatory responses to Ad and their functional significance remain unclear. Here we show that in the model of disseminated infection, intravenous Ad administration leads to a rapid release of pro-inflammatory Ly-6G⁺7/4⁺ leukocytes (PMNs) from the bone marrow into the blood. PMNs enter into peripheral tissues and, in the case of spleen, are accumulated in proximity to the virus-containing MARCO⁺ macrophages within the splenic marginal zone (MZ). Mechanistic dissection of molecular queues that guide PMN migration reveals that CXCL1 and CXCL2 chemokines are only partially responsible for CXCR2-dependent PMN recruitment into the splenic MZ. We further found that complement cooperates with IL-1α-IL-1RI-CXCR2 signaling pathways in recruitment of PMNs to the splenic MZ, which results in elimination of virus-containing MARCO⁺ macrophages from the spleen. Administration of complement-blocking CR2-Crry or CR2-fH proteins into IL-1α-deficient, but not wild-type, mice prevents PMN accumulation in the splenic MZ and elimination of virus-containing macrophages from the spleen. Our study defines the functional significance of molecular and cellular host defense mechanisms that cooperate in eliminating virus-containing cells in the model of acute disseminated Ad infection.

The evolution of adenoviral vectors through genetic and chemical surface modifications

A long time has passed since the first clinical trial with adenoviral (Ad) vectors. Despite being very promising, Ad vectors soon revealed their limitations in human clinical trials. The pre-existing immunity, the marked liver tropism and the high toxicity of first generation Ad (FG-Ad) vectors have been the main challenges for the development of new approaches. Significant effort toward the development of genetically and chemically modified adenoviral vectors has enabled researchers to create more sophisticated vectors for gene therapy, with an improved safety profile and a higher transduction ability of different tissues. In this review, we will describe the latest findings in the high-speed, evolving field of genetic and chemical modifications of adenoviral vectors, a field in which different disciplines, such as biomaterial research, virology and immunology, co-operate synergistically to create better gene therapy tools for modern challenges.

Autocatalytic caspase-3 driven by human telomerase reverse transcriptase promoter suppresses human ovarian carcinoma growth in vitro and in mice

OBJECTIVES

To construct recombinant adenoviruses AdHT-rev-casp3 and Ad-rev-casp3, which express autocatalysis caspase-3 driven by human telomerase reverse transcriptase promoter and cytomegalovirus promoter, respectively; and to investigate their antitumor effects on ovarian cancer in vitro and in vivo.

METHODS

Cell viabilities were determined using the cell counting kit 8 and flow cytometry. Reverse transcriptase polymerase chain reaction and immunoblotting assays were used to detect cellular apoptotic activities after treatments. Tumor growth and survival of mice bearing AO cells were studied.

RESULTS

AdHT-rev-casp3 significantly suppressed the survival of AO cells in a dose-dependent modality with a viability rate of 60.45% ± 7.8% at an multiplicity of infection (MOI) of 70 and 42.18 ± 5.3% at an MOI of 100, which was somewhat lower than that of the AO cells treated with Ad-rev-casp3 (32.28% ± 5.3% and 21.84% ± 3.4%, respectively). In contrast, AdHT-rev-casp3 induced little human umbilical vein epithelial cell (HUVEC) death with a viability rate of 98.52% ± 6.9% at an MOI of 70, whereas Ad-rev-casp3 induced significant cell death in HUVEC with a viability rate of 27.14% ± 5.4%. Additionally, AdHT-rev-casp3 (MOI = 70) caused significant apoptosis in AO cells with an apoptotic rate of 25.97%, whereas it caused undetectable apoptosis in HUVECs with the rate of only 1.75%. Ad-rev-casp3 (MOI = 70) caused strong apoptosis in both AO and HUVECs, with the rate of 35.82% and 38.12%, respectively. AdHT-rev-casp3 caused markedly higher levels of active caspase-3, causing no detectable active caspase-3 expression in HUVECs. The tumor growth suppression rate of AdHT-rev-casp3 was 54.94%, significantly higher than that of phosphate-buffered saline at the end point of the study. AdHT-rev-casp3 significantly improved the survival of mice receiving intraperitoneal inoculation of AO cells with little liver damage, with the mean survival of 177 ± 12 days.

CONCLUSIONS

AdHT-rev-casp3 causes effective apoptosis with significant tumor selectivity, suppresses tumor growth, and improves the mouse survival with little liver toxicity. It can be a potent therapeutic agent for the tumor-targeting treatment of ovarian cancer.

Enhanced adenovirus transduction of hMSCs using 3D hydrogel cell carriers

Hydrogels are increasingly being investigated as a means to implant cells for tissue engineering. One way to further enhance the repair response would be to combine the hydrogel cell carrier with gene transfer. Gene therapy, using adenoviral vectors, is an effective way to provide transient delivery of bioactive factors. However, current protocols require further optimization, especially if they are to be transferred into the clinic. This study opted to compare the efficiency of protocols for standard two-dimensional (2D) versus three-dimensional (3D), adenoviral-mediated, transduction of human mesenchymal stem cells. Two different multiplicities of infection were tested. After encapsulation in fibrin, alginate or agarose, cells were cultured for 28 days. Transduction in 3D showed a much higher efficiency, compared to standard 2D transduction protocols. In 3D, the amount of transgene produced was significantly higher, for every condition investigated. Furthermore, transduction in 3D does not require a cell culture step and can be conducted within the operating theatre. In conclusion, it was demonstrated that 3D transduction, using adenoviral vectors, is superior to standard transduction protocols in 2D. It therefore, might help increasing its administration in tissue engineering and clinical applications.

The transcription factor IRF3 triggers "defensive suicide" necrosis in response to viral and bacterial pathogens

Although molecular components that execute noninflammatory apoptotic cell death are well defined, molecular pathways that trigger necrotic cell death remain poorly characterized. Here, we show that in response to infection with adenovirus or Listeria monocytogenes, macrophages in vivo undergo rapid proinflammatory necrotic death that is controlled by interferon-regulatory factor 3 (IRF3). The transcriptional activity of IRF3 is, surprisingly, not required for the induction of necrosis, and it proceeds normally in mice deficient in all known regulators of necrotic death or IRF3 activation, including RIPK3, caspases 1, 8, or 11, STING, and IPS1/MAVS. Although L. monocytogenes triggers necrosis to promote the infection, IRF3-dependent necrosis is required for reducing pathogen burden in the models of disseminated infection with adenovirus. Therefore, our studies implicate IRF3 as a principal and nonredundant component of a physiologically regulated necrotic cell-death pathway that operates as an effective innate immune mechanism of host protection against disseminated virus infection.

The transcription factor IRF3 triggers "defensive suicide" necrosis in response to viral and bacterial pathogens

Although molecular components that execute noninflammatory apoptotic cell death are well defined, molecular pathways that trigger necrotic cell death remain poorly characterized. Here, we show that in response to infection with adenovirus or Listeria monocytogenes, macrophages in vivo undergo rapid proinflammatory necrotic death that is controlled by interferon-regulatory factor 3 (IRF3). The transcriptional activity of IRF3 is, surprisingly, not required for the induction of necrosis, and it proceeds normally in mice deficient in all known regulators of necrotic death or IRF3 activation, including RIPK3, caspases 1, 8, or 11, STING, and IPS1/MAVS. Although L. monocytogenes triggers necrosis to promote the infection, IRF3-dependent necrosis is required for reducing pathogen burden in the models of disseminated infection with adenovirus. Therefore, our studies implicate IRF3 as a principal and nonredundant component of a physiologically regulated necrotic cell-death pathway that operates as an effective innate immune mechanism of host protection against disseminated virus infection.

Systemically administered liposome-encapsulated Ad-PEDF potentiates the anti-cancer effects in mouse lung metastasis melanoma

BACKGROUND

The use of adenoviral vector for gene therapy is still an important strategy for advanced cancers, however, the lack of the requisite coxsackie-adenovirus receptor in cancer cells and host immune response to adenovirus limit the application of adenoviral vector in vivo.

METHOD

We designed the antiangiogenic gene therapy with recombinant PEDF adenovirus (Ad-PEDF) encapsulated in cationic liposome (Ad-PEDF/Liposome), and investigated the anti-tumor efficacy of Ad-PEDF/Liposome complex on inhibition of tumor metastasis.

RESULTS

We found that systemic administration of Ad-PEDF/liposome was well tolerated and resulted in marked suppression of tumor growth, and was more potent than uncoated Ad-PEDF to induce apoptosis in B16-F10 melanoma cells and inhibit murine pulmonary metastases in vivo. After Ad-luciferase was encapsulated with liposome, its distribution decreased in liver and increased in lung. The anti-Ad IgG level of Ad-PEDF/Liposome was significantly lower than Ad-PEDF used alone.

CONCLUSION

The present findings provide evidences of systematic administration of cationic liposome-encapsulated Ad-PEDF in pulmonary metastatic melanoma mice model, and show an encouraging therapeutic effect for further exploration and application of more complexes based on liposome-encapsulated adenovirus for more cancers.

SR-A and SREC-I are Kupffer and endothelial cell receptors for helper-dependent adenoviral vectors

Helper-dependent adenoviral (HDAd) vectors can mediate long-term, high-level transgene expression from transduced hepatocytes with no chronic toxicity. However, a toxic acute response with potentially lethal consequences has hindered their clinical applications. Liver sinusoidal endothelial cells (LSECs) and Kupffer cells are major barriers to efficient hepatocyte transduction. Understanding the mechanisms of adenoviral vector uptake by non-parenchymal cells may allow the development of strategies aimed at overcoming these important barriers and to achieve preferential hepatocyte gene transfer with reduced toxicity. Scavenger receptors on Kupffer cells bind adenoviral particles and remove them from the circulation, thus preventing hepatocyte transduction. In the present study, we show that HDAd particles interact in vitro and in vivo with scavenger receptor-A (SR-A) and with scavenger receptor expressed on endothelial cells-I (SREC-I) and we exploited this knowledge to increase the efficiency of hepatocyte transduction by HDAd vectors in vivo through blocking of SR-A and SREC-I with specific fragments antigen-binding (Fabs).

Coagulation factor X activates innate immunity to human species C adenovirus

Although coagulation factors play a role in host defense for "living fossils" such as horseshoe crabs, the role of the coagulation system in immunity in higher organisms remains unclear. We modeled the interface of human species C adenovirus (HAdv) interaction with coagulation factor X (FX) and introduced a mutation that abrogated formation of the HAdv-FX complex. In vivo genome-wide transcriptional profiling revealed that FX-binding-ablated virus failed to activate a distinct network of nuclear factor κB-dependent early-response genes that are activated by HAdv-FX complex downstream of TLR4/MyD88/TRIF/TRAF6 signaling. Our study implicates host factor "decoration" of the virus as a mechanism to trigger an innate immune sensor that responds to a misplacement of coagulation FX from the blood into intracellular macrophage compartments upon virus entry into the cell.

Immune safety of a novel oncolytic mutant M1 after administration in vivo

The aim of this study was to evaluate the safety and efficiency of a novel, oncolytic adenovirus mutant M1 administered in conjunction with immunosuppressive agents. Animal models were established by administering purified M1 either intravenously or retroperitoneally. At different time points, blood samples were taken from the mice for testing of liver and renal function. Microscopic examination of the liver was performed to observe pathological changes. Immunohistochemical analyses were used to evaluate the expression of the adenovirus in the liver. Lymphocyte recruitment to the liver and the activation of adenovirus specific T cells were also analyzed. No signs of general toxicity were observed, but transient increases in ALT and Scr were observed following the administration of M1. Microscopic examination revealed a mild inflammatory response in the liver. Compared to intravenous injection, higher expression levels of adenoviral proteins were observed after retroperitoneal injection. Combined treatment with cyclosporine A resolved the liver and kidney dysfunction and increased the concentration of the adenovirus in the liver. The use of the novel oncolytic adenovirus mutant M1 in vivo is safe, and the combined administration of M1 with immunosuppressive agents was able to enhance the effectiveness and safety profile of M1.

Ad3-hTERT-E1A, a fully serotype 3 oncolytic adenovirus, in patients with chemotherapy refractory cancer

Twenty-five patients with chemotherapy refractory cancer were treated with a fully serotype 3-based oncolytic adenovirus Ad3-hTERT-E1A. In mice, Ad3 induced higher amounts of cytokines but less liver damage than Ad5 or Ad5/3. In humans, the only grade 3 adverse reactions were self-limiting cytopenias and generally the safety profile resembled Ad5-based oncolytic viruses. Patients that had been previously treated with Ad5 viruses presented longer lasting lymphocytopenia but no median increase in Ad3-specific T-cells in blood, suggesting immunological activity against antigens other than Ad3 hexon. Frequent alterations in antitumor T-cells in blood were seen regardless of previous virus exposure. Neutralizing antibodies against Ad3 increased in all patients, whereas Ad5 neutralizing antibodies remained stable. Treatment with Ad3-hTERT-E1A resulted in re-emergence of Ad5 viruses from previous treatments into blood and vice versa. Signs of possible efficacy were seen in 11/15 (73%) patients evaluable for tumor markers, four of which were treated only intravenously. Particularly promising results were seen in breast cancer patients and especially those receiving concomitant trastuzumab. Taken together, Ad3-hTERT-E1A seems safe for further clinical testing or development of armed versions. It offers an immunologically attractive alternative, with possible pharmacodynamic differences and a different receptor compared to Ad5.

Balloon catheter delivery of helper-dependent adenoviral vector results in sustained, therapeutic hFIX expression in rhesus macaques

Hemophilia B is an excellent candidate for gene therapy because low levels of factor IX (FIX) (≥1%) result in clinically significant improvement of the bleeding diathesis. Helper-dependent adenoviral (HDAd) vectors can mediate long-term transgene expression without chronic toxicity. To determine the potential for HDAd-mediated liver-directed hemophilia B gene therapy, we administered an HDAd expressing hFIX into rhesus macaques through a novel and minimally invasive balloon occlusion catheter-based method that permits preferential, high-efficiency hepatocyte transduction with low, subtoxic vector doses. Animals given 1 × 10(12) and 1 × 10(11) virus particle (vp)/kg achieved therapeutic hFIX levels for the entire observation period (up to 1,029 days). At 3 × 10(10) and 1 × 10(10) vp/kg, only subtherapeutic hFIX levels were achieved which were not sustained long-term. Balloon occlusion administration of HDAd was well tolerated with negligible toxicity. Five of six animals developed inhibitors to hFIX. These results provide important information in assessing the clinical utility of HDAd for hemophilia B gene therapy.

shRNA-induced interferon-stimulated gene analysis

RNA interference (RNAi) is a cellular mechanism to inhibit the expression of gene products in a highly specific manner. In recent years, RNAi has become the cornerstone of gene function studies, shortening the otherwise long process of target identification and validation. In addition, small interfering RNA (siRNA) and short-hairpin RNA (shRNA) therapies are being developed for the treatment of a variety of human diseases. Despite its huge potential for gene silencing, a hurdle to safe and effective RNAi is the activation of innate immune responses. Induction of innate immunity is dose- and sequence-dependent, and is also influenced by target tissue and delivery vehicle. Research on the molecular mechanisms mediating this response is helping to improve the design of the RNAi molecules. Nevertheless, appropriate testing for the presence of this undesired effect is needed prior to making conclusions on the outcome of the silencing treatment.

Protection of adenovirus from neutralizing antibody by cationic PEG derivative ionically linked to adenovirus

Background

The generation of anti-adenovirus neutralizing antibody (NAb) in humans severely restricts the utilization of recombinant adenovirus serotype 5 (Ad5) vectors in gene therapy for a wide range of clinical trials. To overcome this limitation, we ionically complexed Ad5 with a newly synthesized copolymer, which we called APC, making an adenovirus shielded from NAb.

Methods

APC, a cationic polyethylene glycol derivative, was synthesized via two steps of ring-opening copolymerization of ethylene oxide and allyl glycidyl ether, followed by the addition of 2-mercaptoethylamine. The copolymer or the control PEI-2k was ionically complexed to anionic Ad5 in 5% glucose, and in vitro transduction assays were carried out in coxsackievirus and adenovirus receptor-positive cells (A549) and coxsackievirus and adenovirus receptor-negative cells (B16 and SKOV3). The physical properties and morphology of adenovirus alone or the complexes were investigated respectively by zeta potential, size distribution, and transmission electron microscopy image. Then cytotoxicity of APC was examined using 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide assays. Finally, the ability of APC to protect adenovirus from NAb was evaluated by transfection assays after a neutralizing effect.

Results

APC was successfully synthesized and showed a low cytotoxicity. Positively charged Ad5/APC exhibited slightly increased diameter (130.2 ± 0.60 nm) than naked Ad5 (115.6 ± 5.46 nm) while Ad5/PEI-2k showed severe aggregation (1382 ± 79.9 nm). Ad5/APC achieved a gene transfection level as high as Ad5/PEI-2k in A549 or B16 cells, and significantly higher than Ad5/PEI-2k in SKOV3 cells. Most importantly, after the exposure to the neutralizing antibody, naked Ad5 and Ad5/PEI-2k exhibited poor gene expression while Ad5/APC still showed significantly efficient gene expression.

Conclusion

Our results demonstrated that Ad5/APC complex offered good protection for Ad5 against NAb in vitro and suggested a potential strategy of resistance to NAb in vivo.

Gene therapy: light is finally in the tunnel

After two decades of ups and downs, gene therapy has recently achieved a milestone in treating patients with Leber's congenital amaurosis (LCA). LCA is a group of inherited blinding diseases with retinal degeneration and severe vision loss in early infancy. Mutations in several genes, including RPE65, cause the disease. Using adeno-associated virus as a vector, three independent teams of investigators have recently shown that RPE65 can be delivered to retinal pigment epithelial cells of LCA patients by subretinal injections resulting in clinical benefits without side effects. However, considering the whole field of gene therapy, there are still major obstacles to clinical applications for other diseases. These obstacles include innate and immune barriers to vector delivery, toxicity of vectors and the lack of sustained therapeutic gene expression. Therefore, new strategies are needed to overcome these hurdles for achieving safe and effective gene therapy. In this article, we shall review the major advancements over the past two decades and, using lung gene therapy as an example, discuss the current obstacles and possible solutions to provide a roadmap for future gene therapy research.

Immune recognition of gene transfer vectors: focus on adenovirus as a paradigm

Recombinant Adenovirus (Ad) based vectors have been utilized extensively as a gene transfer platform in multiple pre-clinical and clinical applications. These applications are numerous, and inclusive of both gene therapy and vaccine based approaches to human or animal diseases. The widespread utilization of these vectors in both animal models, as well as numerous human clinical trials (Ad-based vectors surpass all other gene transfer vectors relative to numbers of patients treated, as well as number of clinical trials overall), has shed light on how this virus vector interacts with both the innate and adaptive immune systems. The ability to generate and administer large amounts of this vector likely contributes not only to their ability to allow for highly efficient gene transfer, but also their elicitation of host immune responses to the vector and/or the transgene the vector expresses in vivo. These facts, coupled with utilization of several models that allow for full detection of these responses has predicted several observations made in human trials, an important point as lack of similar capabilities by other vector systems may prevent detection of such responses until only after human trials are initiated. Finally, induction of innate or adaptive immune responses by Ad vectors may be detrimental in one setting (i.e., gene therapy) and be entirely beneficial in another (i.e., prophylactic or therapeutic vaccine based applications). Herein, we review the current understanding of innate and adaptive immune responses to Ad vectors, as well some recent advances that attempt to capitalize on this understanding so as to further broaden the safe and efficient use of Ad-based gene transfer therapies in general.

Intracellular efficacy of tumor-targeting group I intron-based trans-splicing ribozyme

BACKGROUND

Group I intron-based trans-splicing ribozyme, which can specifically reprogram human telomerase reverse transcriptase (hTERT) RNA, could be a useful tool for tumor-targeted gene therapy. In the present study, the therapeutic feasibility of this ribozyme was investigated by analyzing trans-splicing efficacy in vivo as well as in cells.

METHODS

We assessed transgene activation, degree of ribozyme expression, targeted hTERT mRNA level, or the level of trans-splicing products in hTERT(+) cells or in human tumor nodules xenografted in animals after ribozyme administration.

RESULTS

The activity and efficacy of the trans-splicing ribozyme in cells was dependent on the amount of endogenous hTERT mRNA and/or the accumulation of ribozyme RNA in cells. Intracellular activity of the ribozyme reached a plateau when no more targetable substrate mRNA was available or the ribozyme RNA level was fully saturated. In addition, the efficacy of ribozyme in xenografted tumor tissues was dependent on the dose of the delivered ribozyme-encoding adenoviral vector, indicating the potential of the ribozyme expression level as a determining factor for the in vivo efficacy of the trans-splicing ribozyme. On the basis of these results, we enhanced the intracellular ribozyme activity by increasing the ribozyme expression level transcriptionally and/or post-transcriptionally.

CONCLUSIONS

We analyzed ribozyme efficacy and determined the most influential factors of its trans-splicing reaction in mammalian cell lines as well as in vivo. The present study could provide insights into the optimization of the trans-splicing ribozyme-based RNA replacement approach to cancer treatment.

Coagulation factor X mediates adenovirus type 5 liver gene transfer in non-human primates (Microcebus murinus)

Coagulation factor X (FX)-binding ablated adenovirus type 5 (Ad5) vectors have been genetically engineered to ablate the interaction with FX, resulting in substantially reduced hepatocyte transduction following intravenous administration in rodents. Here, we quantify viral genomes and gene transfer mediated by Ad5 and FX-binding-ablated Ad5 vectors in non-human primates. Ad5 vectors accumulated in and mediated gene transfer predominantly to the liver, whereas FX-binding-ablated vectors primarily targeted the spleen but showed negligible liver gene transfer. In addition, we show that Ad5 binding to hepatocytes may be due to the presence of heparan sulfate proteoglycans (HSPGs) on the cell membrane. Therefore, the Ad5-FX-HSPG pathway mediating liver gene transfer in rodents is also the mechanism underlying Ad5 hepatocyte transduction in Microcebus murinus.

Helper-dependent adenoviral vectors for liver-directed gene therapy

Helper-dependent adenoviral (HDAd) vectors devoid of all viral-coding sequences are promising non-integrating vectors for liver-directed gene therapy because they have a large cloning capacity, can efficiently transduce a wide variety of cell types from various species independent of the cell cycle and can result in long-term transgene expression without chronic toxicity. The main obstacle preventing clinical applications of HDAd for liver-directed gene therapy is the host innate inflammatory response against the vector capsid proteins that occurs shortly after intravascular vector administration resulting in acute toxicity, the severity of which is dependent on vector dose. Intense efforts have been focused on elucidating the factors involved in this acute response and various strategies have been investigated to improve the therapeutic index of HDAd vectors. These strategies have yielded encouraging results with the potential for clinical translation.

Exploiting the therapeutic potential of microRNAs in viral diseases: expectations and limitations

New therapeutic approaches are urgently needed for serious diseases, including cancer, cardiovascular diseases, viral infections, and others. A recent direction in drug development is the utilization of nucleic acidbased therapeutic molecules, such as antisense oligonucleotides, ribozymes, short interfering RNA (siRNA), and microRNA (miRNA). miRNAs are endogenous, short, non-coding RNA molecules. Some viruses encode their own miRNAs, which play pivotal roles in viral replication and immune evasion strategies. Conversely, viruses that do not encode miRNAs may manipulate host cell miRNAs for the benefits of their replication. miRNAs have therefore become attractive tools for the study of viral pathogenesis. Lately, novel therapeutic strategies based on miRNA technology for the treatment of viral diseases have been progressing rapidly. Although this new generation of molecular therapy is promising, there are still several challenges to face, such as targeting delivery to specific tissues, avoiding off-target effects of miRNAs, reducing the toxicity of the drugs, and overcoming mutations and drug resistance. In this article, we review the current knowledge of the role and therapeutic potential of miRNAs in viral diseases, and discuss the limitations of these therapies, as well as strategies to overcome them to provide safe and effective clinical applications of these new therapeutics.

Correction of hyperbilirubinemia in gunn rats using clinically relevant low doses of helper-dependent adenoviral vectors

Crigler-Najjar syndrome type I is a severe inborn error of bilirubin metabolism caused by a complete deficiency of uridine diphospho-glucuronosyl transferase 1A1 (UGT1A1) and results in life-threatening unconjugated hyperbilirubinemia. Lifelong correction of hyperbilirubinemia by liver-directed gene therapy using a helper-dependent adenoviral (HDAd) vector has been previously reported in the Gunn rat, a model of Crigler-Najjar syndrome, but was only achieved using high doses (≥ 3 × 10(12) viral particles [vp]/kg), which are likely to elicit a severe toxic response in humans. Therefore, in this study, we investigate strategies to achieve correction of hyperbilirubinemia in the Gunn rat using clinically relevant low HDAd doses. We have found that correction of hyperbilirubinemia in the Gunn rat can be achieved with a low dose of 5 × 10(11) vp/kg by using an HDAd vector bearing a more potent UGT1A1 expression cassette. Furthermore, by using hydrodynamic injection of the improved HDAd vector, correction of hyperbilirubinemia in the Gunn rat can be achieved using an even lower dose of 5 × 10(10) vp/kg. Although hydrodynamic injection as performed in rats is not acceptable in humans, clinically attractive, minimally invasive methods have been successfully developed to mimic hydrodynamic injection of HDAd vector in non-human primates. Therefore, using an improved expression cassette combined with a more efficient method of vector delivery permits correction of hyperbilirubinemia in the Gunn rat using clinically relevant low HDAd doses and may thus pave the way to clinical application of HDAd vectors for Crigler-Najjar syndrome gene therapy.

Helper-Dependent Adenoviral Vectors

Helper-dependent adenoviral vectors are devoid of all viral coding sequences, possess a large cloning capacity, and can efficiently transduce a wide variety of cell types from various species independent of the cell cycle to mediate long-term transgene expression without chronic toxicity. These non-integrating vectors hold tremendous potential for a variety of gene transfer and gene therapy applications. Here, we review the production technologies, applications, obstacles to clinical translation and their potential resolutions, and the future challenges and unanswered questions regarding this promising gene transfer technology.

Species differences in the pharmacology and toxicology of PEGylated helper-dependent adenovirus

Clinically relevant doses of helper-dependent adenoviruses (HDAds) provoke the host response against capsid proteins in primates and rodents. To determine if PEGylation truly affects this, baboons and mice were given either HDAd or PEG-HDAd expressing beta-galactosidase at 5 × 10¹¹ or 3 × 10¹² virus particles per kilogram (vp/kg) by iv infusion. Serum cytokines and blood chemistries were assessed for 96 h. PEG-HDAd reduced IL-6 6-fold in mice and 3-fold in the primate. This vector reduced IL-12 by 50% in both animal models. PEGylation reduced serum transaminases by approximately 50% at each dose in the primate and the mouse. PEGylation did not alter hepatic transduction efficiency in the mouse but did reduce transduction efficiency in the liver and the spleen of primates. Unmodified and PEGylated virus suppressed hepatic CYP3A activity in both animal models. PEGylation doubled the half-life (t(½)) of the virus in the mouse and cut plasma clearance (CL) in half without affecting the half-life in primates. These results suggest that there are notable species-specific differences in the biodistribution of and response to PEG-modified vectors which may be linked to differences in binding properties to coagulation factors, receptor density and tissue architecture in the liver.

Gene therapy with helper-dependent adenoviral vectors: current advances and future perspectives

Recombinant Adenoviral vectors represent one of the best gene transfer platforms due to their ability to efficiently transduce a wide range of quiescent and proliferating cell types from various tissues and species. The activation of an adaptive immune response against the transduced cells is one of the major drawbacks of first generation Adenovirus vectors and has been overcome by the latest generation of recombinant Adenovirus, the Helper-Dependent Adenoviral (HDAd) vectors. HDAds have innovative features including the complete absence of viral coding sequences and the ability to mediate high level transgene expression with negligible chronic toxicity. This review summarizes the many aspects of HDAd biology and structure with a major focus on in vivo gene therapy application and with an emphasis on the unsolved issues that these vectors still presents toward clinical application.

Vasoactive intestinal peptide increases hepatic transduction and reduces innate immune response following administration of helper-dependent Ad

Helper-dependent adenoviral vectors (HDAd) are effective tools for liver-directed gene therapy because they can mediate long-term transgene expression in the absence of chronic toxicity. However, high vector doses required for efficient hepatocyte transduction by intravascular delivery result in systemic vector dissemination and dose-dependent activation of the innate immunity. Therefore, strategies to achieve high-efficiency hepatocyte transduction using low vector doses and/or to reduce the acute elevations of proinflammatory cytokines and chemokines may have significant clinical potential. Vasoactive intestinal peptide (VIP) is an endogenous neuropeptide involved in the regulation of hepatic blood flow and plays an important role as modulator of immune functions. Here, we show that VIP pretreatment in mice is able to increase hepatocyte transduction by HDAd, decrease vector uptake by the spleen, reduce elevation of proinflammatory serum cytokines interleukin (IL)-6 and IL-12, and reduce serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) following intravenous HDAd injection. VIP pretreatment also resulted in a reduction in the expression of the chemokines macrophage-inflammatory protein 2 (MIP-2), monocyte chemotactic protein 1 (MCP-1), and regulated on activation normal T-cell expressed and secreted (RANTES) in the livers of mice injected with HDAd. These results suggest that VIP can improve the therapeutic index of HDAd by increasing hepatocyte transduction efficiency while reducing cytokine and chemokine expression following intravascular delivery of HDAd.

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

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

MyD88-dependent silencing of transgene expression during the innate and adaptive immune response to helper-dependent adenovirus

Activation of the host innate immune response after systemic administration of adenoviral vectors constitutes a principal impediment to successful clinical gene replacement therapies. Although helper-dependent adenoviruses (HDAds) lack all viral functional genes, systemic administration of a high dose of HDAd still elicits a potent innate immune response in host animals. Toll-like receptors (TLRs) are innate receptors that sense microbial products and trigger the maturation of antigen-presenting cells and cytokine production via MyD88-dependent signaling (except TLR3). Here we show that mice lacking MyD88 exhibit a dramatic reduction in proinflammatory cytokines after intravenous injection of a high dose of HDAd, and show significantly reduced induction of the adaptive immune response when compared with wild-type and TLR2-deficient mice. Importantly, MyD88(-/-) mice also show significantly higher and longer sustained transgene expression than do wild-type mice. Chromatin immunoprecipitation studies using wild-type and MyD88-deficient primary mouse embryonic fibroblasts showed significant MyD88-dependent transcriptional silencing of the HDAd-encoded transgenes. Our results demonstrate that MyD88 signaling, activated by systemic delivery of HDAd, initiates an innate immune response that suppresses transgene expression at the transcriptional level before initiation of the adaptive immune response.

Influence of chimeric human-bovine fibers on adenoviral uptake by liver cells and the antiviral immune response

Human adenoviruses (HAdV) are widely used for in vitro and in vivo gene transfer. Viral hepatotropism, inflammatory responses and neutralization by pre-existing antibodies (NAbs) are obstacles for clinical applications of HAdV vectors. Although the multifactorial events leading to innate HAdV toxicity are far from being elucidated, there is a consensus that the majority of intravenously injected-HAdV vectors is sequestered by Kuppfer cells, probably independently of coagulation factors. In this study, we show that the adenoviral-associated humoral and innate cytokine immune responses are significantly reduced when HAdV-5 vector carrying human bovine chimeric fibers (HAdV-5-F2/BAdV-4) is intravenously injected into mice. Fiber pseudotyping modified its interaction with blood coagulation factors, as FIX and FX no longer mediate the infection of liver cells by HAdV-5-F2/BAdV-4. As a consequence, at early time points post-infection, several cytokines and chemokines (IFN-gamma, IL-6, IP-10, MCP-1, RANTES and MP1beta) were found to be present at lower levels in the plasma of mice that had been intravenously injected with HAdV-5-F2/BAdV-4 compared with mice injected with the parental vector HAdV-5. Moreover, genetic modification of the fiber allowed HAdV-5-F2/BAdV-4 to partially escape neutralization by NAbs.

Systemic adenoviral gene delivery to orthotopic murine breast tumors with ablation of coagulation factors, thrombocytes and Kupffer cells

BACKGROUND

Rapid clearance of adenoviruses from blood by macrophage lineage cells of the liver and spleen, and binding to platelets, hinder their successful systemic use for cancer gene therapy. Vitamin K dependent coagulation factors are important mediators for the adenovirus liver tropism. Here we aim to determine the effects of coagulation factor, thrombocyte and liver macrophage (Kupffer cell) ablation on biodistribution of serotype 5 adenoviruses in mice with orthotopic breast tumors.

METHODS

Prior to intravenous injection of adenoviruses, mice bearing orthotopic breast tumors were pretreated with warfarin to inhibit vitamin K dependent coagulation factor synthesis, an anti-platelet antibody causing thrombocytopenia or an inhibitor of the Kupffer cell scavenger receptor or their combination. Virus availability in blood after injection was determined from blood samples and transgene expression in tissues analyzed 72 hours afterwards with In Vivo Imaging and luciferase assays.

RESULTS

Warfarin pretreatment reduced gene delivery to liver, spleen and lung. Kupffer cell ablation increased persistence of adenoviruses in blood but didn't affect biodistribution significantly. Depletion of Kupffer cells combined with thrombocytopenia doubled the systemic gene delivery of 5/3 chimeric adenovirus to tumors (p < 0.05). Triple ablation of platelets, Kupffer cells and coagulation factors increased the tumor to liver ratio of systemic adenovirus gene delivery by 81% (p < 0.05).

CONCLUSIONS

Depletion of coagulation factors can reduce transduction of liver, spleen and lung. Kupffer cell depletion is the most feasible method of increasing amount adenovirus in systemic blood flow and in combination with ablation of thrombocytes can increase the transduction of adenovirus to tumors.

PEGylated Adenoviruses: From Mice to Monkeys

Covalent modification with polyethylene glycol (PEG), a non-toxic polymer used in food, cosmetic and pharmaceutical preparations for over 60 years, can profoundly influence the pharmacokinetic, pharmacologic and toxciologic profile of protein and peptide-based therapeutics. This review summarizes the history of PEGylation and PEG chemistry and highlights the value of this technology in the context of the design and development of recombinant viruses for gene transfer, vaccination and diagnostic purposes. Specific emphasis is placed on the application of this technology to the adenovirus, the most potent viral vector with the most highly characterized toxicity profile to date, in several animal models.

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

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