The role of capsid-endothelial interactions in the innate immune response to adenovirus vectors

Recombinant Adeno-Associated Viral Vector-Mediated Gene Transfer of hTBX18 Generates Pacemaker Cells from Ventricular Cardiomyocytes

Sinoatrial node dysfunction can manifest as bradycardia, leading to symptoms of syncope and sudden cardiac death. Electronic pacemakers are the current standard of care but are limited due to a lack of biological chronotropic control, cost of revision surgeries, and risk of lead- and device-related complications. We therefore aimed to develop a biological alternative to electronic devices by using a clinically relevant gene therapy vector to demonstrate conversion of cardiomyocytes into sinoatrial node-like cells in an in vitro context. Neonatal rat ventricular myocytes were transduced with recombinant adeno-associated virus vector 6 encoding either hTBX18 or green fluorescent protein and maintained for 3 weeks. At the endpoint, qPCR, Western blot analysis and immunocytochemistry were used to assess for reprogramming into pacemaker cells. Cell morphology and Arclight action potentials were imaged via confocal microscopy. Compared to GFP, hTBX18-transduced cells showed that hTBX18, HCN4 and Cx45 were upregulated. Cx43 was significantly downregulated, while sarcomeric α-actinin remained unchanged. Cardiomyocytes transduced with hTBX18 acquired the tapering morphology of native pacemaker cells, as compared to the block-like, striated appearance of ventricular cardiomyocytes. Analysis of the action potentials showed phase 4 depolarization and a significant decrease in the APD50 of the hTBX18-transduced cells. We have demonstrated that rAAV-hTBX18 gene transfer to ventricular myocytes results in morphological, molecular, physiological, and functional changes, recapitulating the pacemaker phenotype in an in vitro setting. The generation of these induced pacemaker-like cells using a clinically relevant vector opens new prospects for biological pacemaker development.

Adenovirus Type 6: Subtle Structural Distinctions from Adenovirus Type 5 Result in Essential Differences in Properties and Perspectives for Gene Therapy

Adenovirus vectors are the most frequently used agents for gene therapy, including oncolytic therapy and vaccine development. It’s hard to overestimate the value of adenoviruses during the COVID-19 pandemic as to date four out of four approved viral vector-based SARS-CoV-2 vaccines are developed on adenovirus platform. The vast majority of adenoviral vectors are based on the most studied human adenovirus type 5 (HAdV-C5), however, its immunogenicity often hampers the clinical translation of HAdV-C5 vectors. The search of less seroprevalent adenovirus types led to another species C adenovirus, Adenovirus type 6 (HAdV-C6). HAdV-C6 possesses high oncolytic efficacy against multiple cancer types and remarkable ability to induce the immune response towards carrying antigens. Being genetically very close to HAdV-C5, HAdV-C6 differs from HAdV-C5 in structure of the most abundant capsid protein, hexon. This leads to the ability of HAdV-C6 to evade the uptake by Kupffer cells as well as to distinct opsonization by immunoglobulins and other blood proteins, influencing the overall biodistribution of HAdV-C6 after systemic administration. This review describes the structural features of HAdV-C6, its interaction with liver cells and blood factors, summarizes the previous experiences using HAdV-C6, and provides the rationale behind the use of HAdV-C6 for vaccine and anticancer drugs developments.

A "Prime and Deploy" Strategy for Universal Influenza Vaccine Targeting Nucleoprotein Induces Lung-Resident Memory CD8 T cells

Lung-resident memory T cells (TRM) play an essential role in protecting against pulmonary virus infection. Parenteral administration of DNA vaccine is generally not sufficient to induce lung CD8 TRM cells. This study investigates whether intramuscularly administered DNA vaccine expressing the nucleoprotein (NP) induces lung TRM cells and protects against the influenza B virus. The results show that DNA vaccination poorly generates lung TRM cells and massive secondary effector CD8 T cells entering the lungs after challenge infection do not offer sufficient protection. Nonetheless, intranasal administration of non-replicating adenovirus vector expressing no Ag following priming DNA vaccination deploys NP-specific CD8 TRM cells in the lungs, which subsequently offers complete protection. This novel 'prime and deploy' strategy could be a promising regimen for a universal influenza vaccine targeting the conserved NP Ag.

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.

Repairing the heart: State-of the art delivery strategies for biological therapeutics

Myocardial infarction (MI) is one of the leading causes of mortality worldwide. It is caused by an acute imbalance between oxygen supply and demand in the myocardium, usually caused by an obstruction in the coronary arteries. The conventional therapy is based on the application of (a combination of) anti-thrombotics, reperfusion strategies to open the occluded artery, stents and bypass surgery. However, numerous patients cannot fully recover after these interventions. In this context, new therapeutic methods are explored. Three decades ago, the first biologicals were tested to improve cardiac regeneration. Angiogenic proteins gained popularity as potential therapeutics. This is not straightforward as proteins are delicate molecules that in order to have a reasonably long time of activity need to be stabilized and released in a controlled fashion requiring advanced delivery systems. To ensure long-term expression, DNA vectors-encoding for therapeutic proteins have been developed. Here, the nuclear membrane proved to be a formidable barrier for efficient expression. Moreover, the development of delivery systems that can ensure entry in the target cell, and also correct intracellular trafficking towards the nucleus are essential. The recent introduction of mRNA as a therapeutic entity has provided an attractive intermediate: prolonged but transient expression from a cytoplasmic site of action. However, protection of the sensitive mRNA and correct delivery within the cell remains a challenge. This review focuses on the application of synthetic delivery systems that target the myocardium to stimulate cardiac repair using proteins, DNA or RNA.

Innate immunity to adenovirus: lessons from mice

Adenovirus is a highly evolutionary successful pathogen, as it is widely prevalent across the animal kingdom, infecting hosts ranging from lizards and frogs to dolphins, birds, and humans. Although natural adenovirus infections in humans rarely cause severe pathology, intravenous injection of high doses of adenovirus-based vectors triggers rapid activation of the innate immune system, leading to cytokine storm syndrome, disseminated intravascular coagulation, thrombocytopenia, and hepatotoxicity, which individually or in combination may cause morbidity and mortality. Much of the information on exactly how adenovirus activates the innate immune system has been gathered from mouse experimental systems. Intravenous administration of adenovirus to mice revealed mechanistic insights into cellular and molecular components of the innate immunity that detect adenovirus particles, activate pro-inflammatory signaling pathways and cytokine production, sequester adenovirus particles from the bloodstream, and eliminate adenovirus-infected cells. Collectively, this information greatly improved our understanding of mechanisms of activation of innate immunity to adenovirus and may pave the way for designing safer adenovirus-based vectors for therapy of genetic and acquired human diseases.

Cardiomyocyte Progenitor Cells as a Functional Gene Delivery Vehicle for Long-Term Biological Pacing

Sustained pacemaker function is a challenge in biological pacemaker engineering. Human cardiomyocyte progenitor cells (CMPCs) have exhibited extended survival in the heart after transplantation. We studied whether lentivirally transduced CMPCs that express the pacemaker current I_f (encoded by HCN4) can be used as functional gene delivery vehicle in biological pacing. Human CMPCs were isolated from fetal hearts using magnetic beads coated with Sca-1 antibody, cultured in nondifferentiating conditions, and transduced with a green fluorescent protein (GFP)- or HCN4-GFP-expressing lentivirus. A patch-clamp analysis showed a large hyperpolarization-activated, time-dependent inward current (−20 pA/pF at −140 mV, n = 14) with properties typical of I_f in HCN4-GFP-expressing CMPCs. Gap-junctional coupling between CMPCs and neonatal rat ventricular myocytes (NRVMs) was demonstrated by efficient dye transfer and changes in spontaneous beating activity. In organ explant cultures, the number of preparations showing spontaneous beating activity increased from 6.3% in CMPC/GFP-injected preparations to 68.2% in CMPC/HCN4-GFP-injected preparations (P < 0.05). Furthermore, in CMPC/HCN4-GFP-injected preparations, isoproterenol induced a significant reduction in cycle lengths from 648 ± 169 to 392 ± 71 ms (P < 0.05). In sum, CMPCs expressing HCN4-GFP functionally couple to NRVMs and induce physiologically controlled pacemaker activity and may therefore provide an attractive delivery platform for sustained pacemaker function.

Gene Therapy Approaches to Biological Pacemakers

Bradycardia arising from pacemaker dysfunction can be debilitating and life threatening. Electronic pacemakers serve as effective treatment options for pacemaker dysfunction. They however present their own limitations and complications. This has motivated research into discovering more effective and innovative ways to treat pacemaker dysfunction. Gene therapy is being explored for its potential to treat various cardiac conditions including cardiac arrhythmias. Gene transfer vectors with increasing transduction efficiency and biosafety have been developed and trialed for cardiovascular disease treatment. With an improved understanding of the molecular mechanisms driving pacemaker development, several gene therapy targets have been identified to generate the phenotypic changes required to correct pacemaker dysfunction. This review will discuss the gene therapy vectors in use today along with methods for their delivery. Furthermore, it will evaluate several gene therapy strategies attempting to restore biological pacing, having the potential to emerge as viable therapies for pacemaker dysfunction.

Next-generation pacemakers: from small devices to biological pacemakers

Electrogenesis in the heart begins in the sinoatrial node and proceeds down the conduction system to originate the heartbeat. Conduction system disorders lead to slow heart rates that are insufficient to support the circulation, necessitating implantation of electronic pacemakers. The typical electronic pacemaker consists of a subcutaneous generator and battery module attached to one or more endocardial leads. New leadless pacemakers can be implanted directly into the right ventricular apex, providing single-chamber pacing without a subcutaneous generator. Modern pacemakers are generally reliable, and their programmability provides options for different pacing modes tailored to specific clinical needs. Advances in device technology will probably include alternative energy sources and dual-chamber leadless pacing in the not-too-distant future. Although effective, current electronic devices have limitations related to lead or generator malfunction, lack of autonomic responsiveness, undesirable interactions with strong magnetic fields, and device-related infections. Biological pacemakers, generated by somatic gene transfer, cell fusion, or cell transplantation, provide an alternative to electronic devices. Somatic reprogramming strategies, which involve transfer of genes encoding transcription factors to transform working myocardium into a surrogate sinoatrial node, are furthest along in the translational pipeline. Even as electronic pacemakers become smaller and less invasive, biological pacemakers might expand the therapeutic armamentarium for conduction system disorders.

Biodistribution and residence time of adenovector serotype 5 in normal and immunodeficient mice and rats detected with bioluminescent imaging

As concerns increase about adenovirus type 5 (Ad5) being a safe gene transfer vector, it is important to evaluate its distribution, residence time, and possible toxicity in immunodeficient populations. To characterize the potential risk associated with different Ad5 vector delivery modes, we used immunocompetent and immunodeficient Rag2^−/− animals to establish mouse and rat models that could be monitored with bioluminescent imaging following intramuscular or intravascular infection with an engineered replication-incompetent Ad5 virus carrying the firefly luciferase gene (Ad5-Fluc). The Ad5 vector was less well-tolerated by Rag2^−/− animals than by wildtype ones, with delayed residence time, wider virus dissemination, less weight gain, and relatively severe pathological changes. In intravascularly Ad5-Fluc-infected Rag2^−/− mice, systemic virus dissemination extended from the abdomen to the limbs and head on day 9 post-infection. Additionally, significant increases in plasma TNF-α and IFN-γ, which may be important factors in the heightened immunopathology in the liver and brain, were detected in the Rag2^−/− mice 30 days after intravascular delivery. The Ad5 vector was better tolerated after intramuscular delivery than after intravascular delivery. Ad5-Fluc/Rag2^−/− mice and rats can be used as reliable models of an immunodeficient population in which to evaluate the safety of Ad5-vectored vaccines or gene therapy products.

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

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

Mesenchymal Stromal Cells for Linked Delivery of Oncolytic and Apoptotic Adenoviruses to Non-small-cell Lung Cancers

Oncolytic adenoviruses (OAdV) represent a promising strategy for cancer therapy. Despite their activity in preclinical models, to date the clinical efficacy remains confined to minor responses after intratumor injection. To overcome these limitations, we developed an alternative approach using the combination of the OAdv ICOVIR15 with a replication incompetent adenoviral vector carrying the suicide gene of inducible Caspase 9 (Ad.iC9), both of which are delivered by mesenchymal stromal cells (MSCs). We hypothesized that coinfection with ICOVIR15 and Ad.iC9 would allow MSCs to replicate both vectors and deliver two distinct types of antitumor therapy to the tumor, amplifying the cytotoxic effects of the two viruses, in a non-small-cell lung cancer (NSCLC) model. We showed that MSCs can replicate and release both vectors, enabling significant transduction of the iC9 gene in tumor cells. In the in vivo model using human NSCLC xenografts, MSCs homed to lung tumors where they released both viruses. The activation of iC9 by the chemical inducer of dimerization (CID) significantly enhanced the antitumor activity of the ICOVIR15, increasing the tumor control and translating into improved overall survival of tumor-bearing mice. These data support the use of this innovative approach for the treatment of NSCLC.

Long-term toxicity study of rAd5-hTERTC27 in SD rats and Cynomolgus monkeys by intravenous injection

rAd5-hTERTC27, a replication-defective adenovirus vector carrying hTERTC27, has been proposed for possible use against hepatocellular carcinoma (HCC). In this study, we investigated the long-term toxicity of rAd5-hTERTC27 in SD rats and Cynomolgus monkeys. rAd5-hTERTC27 was administered intravenously once a week for 13 weeks followed by a one-month recovery period. As of 4 months, all animals displayed overall good health. Anti-adenoviral antibodies emerged in a dose-independent manner. The levels of complement components, C3 and C4, in the rAd5-hTERTC27 middle-dose and high-dose groups and C4 in the rAd5-EGFP group increased significantly after the 2nd treatment in monkeys. Slight-mild pathological changes of the liver occurred only in the rAd5-hTERTC27 high-dose group (2/16) in rats and not in any other group in either rats or monkeys. With the increase of the dose, the incidence of lymphocyte depletion in the spleen of rats and reactive hyperplasia of the splenic corpuscle in monkeys increased. However, the changes in the liver and spleen were reversible. Given the above data, intravenous administration of rAd5-hTERTC27 (up to 4×10(10)VP/kg in rats and 0.9×10(10)VP/kg in monkeys) appears to be well-tolerated, providing support for its potentially safe use in clinical trials for the treatment of HCC.

Efficient lung orthotopic tumor-growth suppression of oncolytic adenovirus complexed with RGD-targeted bioreducible polymer

Oncolytic adenoviruses (Ad) have been developed for the eradication of tumors. Although they hold much promise as a cancer therapy, they have a short blood circulation time and high liver toxicity. An effective strategy to overcome these problems has been complexing Ad with shielding materials. However, the therapeutic efficacy of the Ad complexes has also been an issue because passive accumulation does not allow for sufficient delivery of Ad to the cancer cells. To enhance the therapeutic efficacy of the polymer-coated Ads, the attachment of a targeting moiety to polymer-coated Ad vectors is inescapable. Our lab has previously reported the potential use of Arg-Gly-Asp (RGD)-targeted bioreducible polymers with a polyethylene glycol (PEG) linker for delivering oncolytic Ads. We have shown the enhanced in vitro transduction efficiency and increased cancer-killing effect with producing progeny oncolytic Ad particles. In addition, we have shown significant tumor-growth inhibition of the polymer-shielded Ad in an in vivo lung orthotopic tumor model. The shielding effect of the Ad surface with the polymers allowed evasion of host immune responses and reduction of liver toxicity. This data demonstrates that the RGD-conjugated bioreducible polymer for delivering the oncolytic Ad vectors could be utilized for cancer therapy via systemic administration.

Kupffer Cells in Health and Disease

Kupffer cells (KC), the resident macrophages of the liver, represent the largest population of mononuclear phagocytes in the body. Phenotypic, developmental, and functional aspects of these cells in steady state and in different diseases are the focus of this review. Recently it has become evident that KC precursors seed the liver already early in fetal development, and the population can be maintained independently from circulating monocytes. However, inflammatory conditions allow rapid differentiation of monocytes into mature cells that are indistinguishable from genuine KC. KC are located in the lumen of sinusoids that receive blood both from the portal vein, carrying nutrients and microbial products from the gut, and from the hepatic artery. This positions KC ideally for their prime function, namely surveillance and clearance of the circulation. As such, they are important in iron recycling by phagocytosing effete erythrocytes, for instance. The immunophenotype of KC, characterized by a wide variety of endocytic receptors, is indicative of this scavenger function. In maintaining homeostasis, KC have an ambivalent response to exogenous triggers. On the one hand, their surveillance function requires alert responses to potentially hazardous substances. On the other hand, continuous exposure of the cells to the trigger-rich content of blood originating from the gut dampens their responsiveness to further stimuli. This ambivalence is also reflected in their diverse roles in disease pathogenesis. For the latter, we sketch the contribution of KC by giving examples of their role in metabolic disease, infections, and liver injury.

Inhibition of HBV replication in vivo using helper-dependent adenovirus vectors to deliver antiviral RNA interference expression cassettes

BACKGROUND

HBV is hyperendemic to southern Africa and parts of Asia, but licensed antivirals have little effect on limiting life-threatening complications of the infection. Although RNA interference (RNAi)-based gene silencing has shown therapeutic potential, difficulties with delivery of anti-HBV RNAi effectors remain an obstacle to their clinical use. To address concerns about the transient nature of transgene expression and toxicity resulting from immunostimulation by recombinant adenovirus vectors (Ads), utility of RNAi-activating anti-HBV helper-dependent (HD) Ads were assessed in this study.

METHODS

Following intravenous administration of 5×10(9) unmodified or pegylated HD Ad infectious particles to HBV transgenic mice, HBV viral loads and serum HBV surface antigen levels were monitored for 12 weeks. Immunostimulation of HD Ads was assessed by measuring inflammatory cytokines, hepatic function and immune response to the co-delivered LacZ reporter gene.

RESULTS

Unmodified and pegylated HD Ads transduced 80-90% of hepatocytes and expressed short hairpin RNAs (shRNAs) were processed to generate intended HBV-targeting guides. Markers of HBV replication were decreased by approximately 95% and silencing was sustained for 8 weeks. Unmodified HD Ads induced release of proinflammatory cytokines and there was evidence of an adaptive immune response to β-galactosidase. However the HD Ad-induced innate immune response was minimal in preparations that were enriched with infectious particles.

CONCLUSIONS

HD Ads have potential utility for delivery of therapeutic HBV-silencing sequences and alterations of these vectors to attenuate their immune responses may further improve their efficacy.

Rapamycin enhances adenovirus-mediated cancer imaging and therapy in pre-immunized murine hosts

Tumor-specific adenoviral vectors comprise a fruitful gene-based diagnostic imaging and therapy research area for advanced stage of cancer, including metastatic disease. However, clinical translation of viral vectors has encountered considerable obstacles, largely due to host immune responses against the virus. Here, we explored the utilization of an immunosuppressant, rapamycin, to circumvent the anti-adenovirus immunity in immunocompetent murine prostate cancer models. Rapamycin diminished adenoviral-induced acute immune response by inhibiting NF-κB activation; it also reduced the scale and delayed the onset of inflammatory cytokine secretion. Further, we found that rapamycin abrogated anti-adenovirus antibody production and retarded the function of myeloid cells and lymphocytes that were activated upon viral administration in pre-immunized hosts. Thus, the co-administration of rapamycin prolonged and enhanced adenovirus-delivered transgene expression in vivo, and thereby augmented the imaging capability of adenoviral vectors in both bioluminescent and positron emission tomography modalities. Furthermore, we showed that despite an excellent response of cancer cells to a cytotoxic gene therapeutic vector in vitro, only minimal therapeutic effects were observed in vivo in pre-immunized mice. However, when we combined gene therapy with transient immunosuppression, complete tumor growth arrest was achieved. Overall, transient immunosuppression by rapamycin was able to boost the diagnostic utility and therapeutic potentials of adenoviral vectors.

Immunocompetent nontransgenic mouse models for studying hepatitis B virus immune responses

Although the chronicity of hepatitis B virus (HBV) infection is the result of impaired HBV-specific immune responses that cannot eliminate or clear the infected hepatocytes efficiently, many issues remained unsettled. It is thus crucial to have a suitable laboratory animal to study the immunopathogenesis of HBV infection and the mechanisms of HBV persistence. To meet the requirement of a mouse model resembling natural chronic HBV infection in human, there are several approaches in the development of mouse animal model by using hydrodynamic-based transfection of HBV DNA, delivery of adenovirus or adeno-associated viral vectors containing HBV DNA for studying HBV immune responses. These immunocompetent nontransgenic mouse animal models will provide new approaches to investigate the mechanisms of immune pathogenesis in HBV infection.

Preclinical safety evaluation of rAd5-hTERTC27 by intravenous injection

The safety of rAd5-hTERTC27, a replication defective adenovirus vector carrying hTERTC27 for possible use against hepatocellular carcinoma (HCC) was assessed. In single-dose evaluations, intravenous dose levels of up to 2×10(11)VP/kg in rats and 9×10(10)VP/kg in monkeys were well tolerated with no abnormal changes in general signs, body weight and food consumption, and no significant differences in biochemical parameters, urinalysis, ECG, and systemic necropsy observations between the rAd5 groups and solvent control group except that slight hematological change was observed. No hemolytic effect using rabbit blood, local perivasculitis following intravenous injection in rabbits or systemic anaphylaxis in guinea pigs following intravenous dosing was seen. No effects on the central nervous system of mice occurred following intravenous dosing with the exception of an increase in sleep duration at the dose of 1.2×10(11)VP/kg (p<0.05) but not at lower doses of 2×10(10) and 6×10(10)VP/kg in the hypnotic synergism test. These results demonstrate that administration of rAd5-hTERTC27 was well tolerated in an initial set of safety studies as part of an evaluation to allow human trials for the treatment of HCC.

Therapeutic efficacy of a systemically delivered oncolytic adenovirus - biodegradable polymer complex

Despite great efforts to develop a more effective oncolytic adenovirus (Ad) for eradicating tumors, in vivo application via systemic administration is strictly limited to local injection due to host immune responses by Ad surface proteins and liver accumulation by the inherent nature of the Ad. In the last decade, numerous techniques using synthetic polymers have widely emerged to shield the exterior of therapeutic Ad vectors for systemic delivery. We developed a cationic polymer linked with polyethylene glycol for systemically delivering oncolytic Ad. The increased transduction efficiency and oncolytic effect of the Ad vectors physically coated with the polymer were evaluated, showing the optimal size (130 nm) of the Ad/polymer complex for systemic administration and prolonged stability of the Ad/polymer complex. Marked tumor growth suppression of the oncolytic Ad delivered by the polymer through systemic injection was observed in HT1080 and A549 xenograft models. The masking effect of the Ad surface by the polymer elicited evasion of innate adaptive immune responses and the tumor-to-liver ratio of the complex was significantly elevated 1229-fold greater than that of a naked Ad. These results demonstrate that the potential system of oncolytic Ad complexed with the biodegradable polymer may be useful for developing therapeutic vector systems via systemic delivery.

Chapter eight--Oncolytic adenoviruses for cancer immunotherapy: data from mice, hamsters, and humans

Adenovirus is one of the most commonly used vectors for gene therapy and two products have already been approved for treatment of cancer in China (Gendicine(R) and Oncorine(R)). An intriguing aspect of oncolytic adenoviruses is that by their very nature they potently stimulate multiple arms of the immune system. Thus, combined tumor killing via oncolysis and inherent immunostimulatory properties in fact make these viruses in situ tumor vaccines. When further engineered to express cytokines, chemokines, tumor-associated antigens, or other immunomodulatory elements, they have been shown in various preclinical models to induce antigen-specific effector and memory responses, resulting both in full therapeutic cures and even induction of life-long tumor immunity. Here, we review the state of the art of oncolytic adenovirus, in the context of their capability to stimulate innate and adaptive arms of the immune system and finally how we can modify these viruses to direct the immune response toward cancer.

Multiphasic triacylglycerol dynamics in the intact heart during acute in vivo overexpression of CD36

Cardiac triacylglycerol (TAG) stores buffer the intracellular availability of long chain fatty acid (LCFA) that act as nuclear receptor ligands, substrate for lipotoxic derivatives, and high energy-yield fuel. The kinetic characteristics of TAG turnover and homeostatic mechanisms linking uptake and storage dynamics in hearts have until now remained elusive. This work examines TAG pool dynamics in the intact beating heart, under normal conditions and in response to acute gene expression-induced changes in CD36. Dynamic mode (13)C NMR elucidated multiple kinetic processes in (13)C-palmitate incorporation into TAG: an initial, saturable exponential component and a slower linear rate. Although previous work indicates the linear component to reflect TAG turnover, we hypothesized the saturable exponential to reflect transport of LCFA across the sarcolemma. Thus, we overexpressed the LCFA transporter CD36 through cardiac-specific adenoviral infection in vivo. Within 72 h, CD36 expression was increased 40% in intact hearts, accelerating the exponential phase relative to PBS-infused hearts. TAG turnover also increased with elevations in adipose triglyceride lipase (ATGL) and a modest increase in diacylglycerol acyltransferase 1 (DGAT1), without a significant expansion of the intracellular lipid pools. The results demonstrate a dynamic system of reciprocal gene regulation that couples saturable LCFA uptake across the sarcolemma to TAG synthesis/lipolysis rates.

Targeting of liposomes via PSGL1 for enhanced tumor accumulation

Purpose

To improve the delivery of liposomes to tumors using P-selectin glycoprotein ligand 1 (PSGL1) mediated binding to selectin molecules, which are upregulated on tumorassociated endothelium.

Methods

PSGL1 was orientated and presented on the surface of liposomes to achieve optimal selectin binding using a novel streptavidin-protein G linker molecule. Loading of PSGL1 liposomes with luciferin allowed their binding to e-selectin and activated HUVEC to be quantified in vitro and their stability, pharmacokinetics and tumor accumulation to be tested in vivo using murine models.

Results

PSGL1 liposomes showed 5-fold (p < 0.05) greater selectin binding than identically formulated control liposomes modified with ligand that did not contain the selectin binding domain. When added to HUVEC, PSGL1 liposomes showed >7-fold (p < 0.001) greater attachment than control liposomes. In in vivo studies PSGL1 liposomes showed similar stability and circulation to control liposomes but demonstrated a >3-fold enhancement in the level of delivery to tumors (p < 0.05).

Conclusions

The technologies and strategies described here may contribute to clinical improvements in the selectivity and efficacy of liposomal drug delivery agents.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-012-0875-5) contains supplementary material, which is available to authorized users.

Ad5:Ad48 hexon hypervariable region substitutions lead to toxicity and increased inflammatory responses following intravenous delivery

The development of adenoviral vectors for intravascular (i.v.) delivery will require improvements to their in vivo safety and efficacy. The hypervariable regions (HVRs) of the Ad5 hexon are a target for neutralizing antibodies, but also interact with factor X (FX), facilitating hepatocyte transduction. Ad48, a species D adenovirus, does not bind FX and has low seroprevalence. Therefore, it has been suggested that Ad5HVR48(1-7), a hexon-chimeric vector featuring the seven HVRs from Ad48, should display advantageous properties for gene therapy, by evading pre-existing Ad5 immunity and blocking FX interactions. We investigated the in vivo biodistribution of Ad5, Ad5HVR48(1-7), and Ad48 following i.v. delivery. Ad5HVR48(1-7) displayed reduced hepatocyte transduction and accumulation in Kupffer cells (KCs), but triggered a robust proinflammatory response, even at relatively low doses of vector. We detected elevated serum transaminases (48 hours) and increased numbers of periportal CD11b(+)/Gr-1(+) cells in the livers of Ad5HVR48(1-7)-treated animals following i.v., but not intramuscular (i.m.), delivery. In contrast, Ad48 did not elevate transaminases or result in the accumulation of CD11b(+)/Gr-1(+) cells. Collectively, these findings suggest that substantial hexon modifications can lead to unexpected properties which cannot be predicted from parental viruses. Therefore, refined mutations may be preferential for the successful development of targeted vector systems which require i.v. administration.

Biodistribution and inflammatory profiles of novel penton and hexon double-mutant serotype 5 adenoviruses

The use of adenovirus serotype 5 (Ad5) vectors in the clinical setting is severely hampered by the profound liver tropism observed after intravascular delivery coupled with the pronounced inflammatory and innate immune response elicited by these vectors. Liver transduction by circulating Ad5 virions is mediated by a high-affinity interaction between the capsid hexon protein and blood coagulation factor X (FX), whilst penton–α_vintegrin interactions are thought to contribute to the induction of anti-Ad5 inflammatory and innate immune responses. To overcome these limitations, we sought to develop and characterise for the first time novel Ad5 vectors possessing mutations ablating both hexon:FX and penton:integrin interactions. As expected, intravascular administration of the FX binding-ablated Ad5HVR5*HVR7*E451Q vector (AdT*) resulted in significantly reduced liver transduction in vivo compared to Ad5. In macrophage-depleted mice, increased spleen uptake of AdT* was accompanied by an elevation in the levels of several inflammatory mediators. However ablation of the penton RGD motif in the AdT* vector background (AdT*RGE) resulted in a significant 5-fold reduction in spleen uptake and attenuated the antiviral inflammatory response. A reduction in spleen uptake and inflammatory activation was also observed in animals after intravascular administration of Ad5RGE compared to the parental Ad5 vector, with reduced co-localisation of the viral beta-galactosidase transgene with MAdCAM-1 + sinus-lining endothelial cells. Our detailed assessment of these novel adenoviruses indicates that penton base RGE mutation in combination with FX binding-ablation may be a viable strategy to attenuate the undesired liver uptake and pro-inflammatory responses to Ad5 vectors after intravascular delivery.

Linearized oncolytic adenoviral plasmid DNA delivered by bioreducible polymers

As an effort to overcome limits of adenovirus (Ad) as a systemic delivery vector for cancer therapy, we developed a novel system using oncolytic Ad plasmid DNA with two bioreducible polymers: arginine-grafted bioreducible poly(disulfide amine)polymer (ABP) and PEG5k-conjugated ABP (ABP5k) in expectation of oncolytic effect caused by progeny viral production followed by replication. The linearized Ad DNAs for active viral replication polyplexed with each polymer were able to replicate only in human cancer cells and produce progeny viruses. The non-immunogenic polymers delivering the DNAs markedly elicited to evade the innate and adaptive immune response. The biodistribution ratio of the polyplexes administered systemically was approximately 99% decreased in liver when compared with naked Ad. Moreover, tumor-to-liver ratio of the Ad DNA delivered by ABP or ABP5k was significantly elevated at 229- or 419-fold greater than that of naked Ad, respectively. The ABP5k improved the chance of the DNA to localize within tumor versus liver with 1.8-fold increased ratio. In conclusion, the innovative and simple system for delivering oncolytic Ad plasmid DNA with the bioreducible polymers, skipping time-consuming steps such as generation and characterization of oncolytic Ad vectors, can be utilized as an alternative approach for cancer therapy.

Enhancing the therapeutic efficacy of adenovirus in combination with biomaterials

With the reason that systemically administered adenovirus (Ad) is rapidly extinguished by innate/adaptive immune responses and accumulation in liver, in vivo application of the Ad vector is strictly restricted. For achieving to develop successful Ad vector systems for cancer therapy, the chemical or physical modification of Ad vectors with polymers has been generally used as a promising strategy to overcome the obstacles. With polyethylene glycol (PEG) first in order, a variety of polymers have been developed to shield the surface of therapeutic Ad vectors and well accomplished to extend circulation time in blood and reduce liver toxicity. However, although polymer-coated Ads can successfully evacuate from a series of guarding systems in vivo and locate within tumors by enhanced permeability and retention (EPR) effect, the possibility to entering into the target cell is few and far between. To endow targeting moiety to polymer-coated Ad vectors, a diversity of ligands such as tumor-homing peptides, growth factors or antibodies, have been introduced with avoiding unwanted transduction and enhancing therapeutic efficacy. Here, we will describe and classify the characteristics of the published polymers with respect to Ad vectors. Furthermore, we will also compare the properties of variable targeting ligands, which are being utilized for addressing polymer-coated Ad vectors actively.

Adenovirus virus-associated RNAs induce type I interferon expression through a RIG-I-mediated pathway

The current study demonstrates that adenovirus virus-associated RNA (VA) is recognized by retinoic acid-inducible gene I (RIG-I), a cytosolic pattern recognition receptor, and activates RIG-I downstream signaling, leading to the induction of type I interferons (IFNs), similarly to Epstein-Barr virus-encoded small RNA. Further analysis revealed that adenovirus infection leads to biphasic type I IFN induction at 12 to 24 h and 48 to 60 h postinfection. The later induction coincided with VA expression and was reduced by virus UV inactivation or RIG-I silencing. These results suggest that VA-mediated RIG-I activation is involved in activating innate immune responses during adenovirus infection.

Inhibition of the inflammatory cytokine TNF-α increases adenovirus activity in ovarian cancer via modulation of cIAP1/2 expression

Oncolytic adenoviruses show promise as a cancer treatment. However, they generate acute inflammatory responses with production of cytokines, including tumor necrosis factor-α (TNF-α). We investigated whether inhibition of TNF-α augments efficacy of the E1A CR2-deleted adenovirus dl922-947 in ovarian cancer. dl922-947 induced transcription of TNF-α and its downstream signaling targets interleukin-6 and -8 (IL-6 and IL-8) in ovarian cancer cells. In vitro, RNAi-mediated knockdown of TNF-α reduced production of multiple inflammatory cytokines after infection and increased ovarian cancer cell sensitivity to virus cytotoxicity, as did treatment with the anti-TNF-α antibody infliximab. In vivo, stable knockdown of TNF-α in IGROV-1 xenografts increased the anticancer activity of dl922-947. In addition, inhibition of TNF-α using monoclonal antibodies also improved dl922-947 efficacy. This increased efficacy resulted from suppression of cellular inhibitor of apoptosis-1 and -2 (cIAP1 and cIAP2) transcription in malignant cells and a consequent increase in caspase-mediated apoptosis. These findings suggest that TNF-α acts as a survival factor in adenovirus-infected cells. Combining TNF-α inhibition with oncolytic adenoviruses could improve antitumor activity in clinical trials.

Pharmacological interventions for improving adenovirus usage in gene therapy

Gene therapy may be an innovative and promising new treatment strategy for cancer but is limited due to a low efficiency and specificity of gene delivery to the target cells. Adenovirus is the preferred gene therapy vector for systemic delivery because of its unparalleled in vivo transduction efficiency. Intravenous administration of low doses of adenovirus results in adenovirus sequestration in the liver due to binding to the scavenger receptor present on Kupffer cells. When the amount of adenovirus surpasses the binding capacity of Kupffer cells, hepatocytes absorb adenovirus particles in a blood factor-dependent manner. Increasing the Ad dose even more will saturate both the Kupffer cells and hepatocytes. Then sinusoid endothelial cells bind adenovirus particles in an RGD motif-dependent manner. Strategies to eradicate the binding to liver cells include drugs to interfere or eliminate binding to specific cell types, adenovirus capsid protein mutations and chemical modifications of adenovirus to shield the capsid proteins from cellular receptors. The combined use of these approaches should ultimately lead to successful systemic application of adenovirus in humans.

Innate immunity of the liver microcirculation

The liver is a complex organ with a unique microcirculation and both synthetic and immune functions. Innate immune responses have been studied in response to single inflammatory mediators and several clinically relevant models of infection and injury. While standard histological techniques have been used in many models, the liver microcirculation is also amenable to in vivo examination using epifluorescent, confocal and transillumination intravital microscopy. These techniques have begun to clarify not only the molecular mechanisms but also the specific cell populations involved in the liver inflammation. In this review, we discuss the cells and mediators involved in hepatic innate immunity in simple and complex models of injury and infection, and present the view that the liver microcirculation utilizes non-classical pathways for leukocyte recruitment.

Tropism-modification strategies for targeted gene delivery using adenoviral vectors

Achieving high efficiency, targeted gene delivery with adenoviral vectors is a long-standing goal in the field of clinical gene therapy. To achieve this, platform vectors must combine efficient retargeting strategies with detargeting modifications to ablate native receptor binding (i.e. CAR/integrins/heparan sulfate proteoglycans) and “bridging” interactions. “Bridging” interactions refer to coagulation factor binding, namely coagulation factor X (FX), which bridges hepatocyte transduction in vivo through engagement with surface expressed heparan sulfate proteoglycans (HSPGs). These interactions can contribute to the off-target sequestration of Ad5 in the liver and its characteristic dose-limiting hepatotoxicity, thereby significantly limiting the in vivo targeting efficiency and clinical potential of Ad5-based therapeutics. To date, various approaches to retargeting adenoviruses (Ad) have been described. These include genetic modification strategies to incorporate peptide ligands (within fiber knob domain, fiber shaft, penton base, pIX or hexon), pseudotyping of capsid proteins to include whole fiber substitutions or fiber knob chimeras, pseudotyping with non-human Ad species or with capsid proteins derived from other viral families, hexon hypervariable region (HVR) substitutions and adapter-based conjugation/crosslinking of scFv, growth factors or monoclonal antibodies directed against surface-expressed target antigens. In order to maximize retargeting, strategies which permit detargeting from undesirable interactions between the Ad capsid and components of the circulatory system (e.g. coagulation factors, erythrocytes, pre-existing neutralizing antibodies), can be employed simultaneously. Detargeting can be achieved by genetic ablation of native receptor-binding determinants, ablation of “bridging interactions” such as those which occur between the hexon of Ad5 and coagulation factor X (FX), or alternatively, through the use of polymer-coated “stealth” vectors which avoid these interactions. Simultaneous retargeting and detargeting can be achieved by combining multiple genetic and/or chemical modifications.

Minimal RB-responsive E1A promoter modification to attain potency, selectivity, and transgene-arming capacity in oncolytic adenoviruses

Oncolytic adenoviruses are promising anticancer agents due to their ability to self-amplify at the tumor mass. However, tumor stroma imposes barriers difficult to overcome by these agents. Transgene expression is a valuable strategy to counteract these limitations and to enhance antitumor activity. For this purpose, the genetic backbone in which the transgene is inserted should be optimized to render transgene expression compatible with the adenovirus replication cycle and to keep genome size within the encapsidation size limit. In order to design a potent and selective oncolytic adenovirus that keeps intact all the viral functions with minimal increase in genome size, we inserted palindromic E2F-binding sites into the endogenous E1A promoter. The insertion of these sites controlling E1A-Δ24 results in a low systemic toxicity profile in mice. Importantly, the E2F-binding sites also increased the cytotoxicity and the systemic antitumor activity relative to wild-type adenovirus in all cancer models tested. The low toxicity and the increased potency results in improved antitumor efficacy after systemic injection and increased survival of mice carrying tumors. Furthermore, the constrained genome size of this backbone allows an efficient and potent expression of transgenes, indicating that this virus holds promise for overcoming the limitations of oncolytic adenoviral therapy.

Evaluation of innate immunity and vector toxicity following inoculation of bovine, porcine or human adenoviral vectors in a mouse model

Nonhuman adenovirus (Ad) vectors derived from bovine Ad serotype 3 (BAd3) or porcine Ad serotype 3 (PAd3) can circumvent pre-existing immunity against human Ad (HAd). We have previously reported differential transduction of human and nonhuman cells by these Ad vectors, and their distinct receptor usage and biodistribution. To compare the induction of innate immunity, vector toxicity and vector uptake by Kupffer cells (KCs) following intravenous administration of PAd3, BAd3, or HAd5 vectors in mice, we determined mRNA expression levels of proinflammatory chemokines and cytokines, and Toll-like receptors (TLRs) in the liver and spleen. Tissue toxicity of these vectors was assessed by comparing serum levels of liver-specific enzymes, histopathology and Kupffer cell (KC) depletion. Compared to the HAd5 vector, PAd3 and BAd3 vectors were more potent stimulators of innate immune responses as indicated by enhanced mRNA expression of TLRs and proinflammatory chemokines and cytokine genes. Histopathological changes in the liver were most pronounced in HAd5-inoculated mice while BAd3- or PAd3-inoculated mice revealed mild histologic changes that were confined to early time points. Inoculation with HAd5 or PAd3 vectors resulted in a significant (P<0.05) decline of the number of KCs in the liver. Together, these results extend our previous observations regarding distinct in vivo biology of nonhuman and human Ad vectors.

Adenovirus 5-fiber 35 chimeric vector mediates efficient apical correction of the cystic fibrosis transmembrane conductance regulator defect in cystic fibrosis primary airway epithelia

In vivo gene transfer to the human respiratory tract by adenovirus serotype 5 (Ad5) vectors has revealed their limitations related to inefficient gene transfer, host antiviral response, and innate adenoviral toxicity. In the present work, we compared the cytotoxicity and efficiency of Ad5 and a chimeric Ad5F35 vector with respect to CFTR gene transfer to cystic fibrosis (CF) and non-CF human airway epithelial cells. We found that high doses of Ad5 vector had an adverse effect on the function of exogenous and endogenous CFTR. Results obtained with Ad5 capsid mutants suggested that the RGD motifs on the penton base capsomers were responsible for the negative effect on CFTR function. This negative interference did not result from a lower level of biosynthesis and/or altered cellular trafficking of the CFTR protein, but rather from an indirect mechanism of functional blockage of CFTR, related to the RGD integrin-mediated endocytic pathway of Ad5. No negative interference with CFTR was observed for Ad5F35, an Ad5-based vector pseudotyped with fibers from Ad35, a serotype that uses another cell entry pathway. In vitro, Ad5F35 vector expressing the GFP-tagged CFTR (Ad5F35-GFP-CFTR) showed a 30-fold higher efficiency of transduction and chloride channel correction in CFTR-deficient cells, compared with Ad5GFP-CFTR. Ex vivo, Ad5F35-GFP-CFTR had the capacity to transduce efficiently reconstituted airway epithelia from patients with CF (CF-HAE) via the apical surface, restored chloride channel function at relatively low vector doses, and showed relatively stable expression of GFP-CFTR for several weeks.

Adenovirus infection results in alterations of insulin signaling and glucose homeostasis

Recombinant adenovirus (Ad) vectors can initiate an inflammatory response, limiting its use in gene therapy and basic research. Despite increased efforts to better understand Ad infection, little is known about how it affects cellular metabolic responses. In the current studies, we explored the effects of Ad vectors on insulin signaling molecules and glucose homeostasis. Nonreplicative Ad vectors were injected into rats through the tail vein, and at 4-13 days postinjection insulin signaling and glucose tolerance were examined. Ad vector infection significantly reduced total levels of the insulin receptor (IR), and insulin receptor substrates 1 and 2 (IRS-1, IRS-2) in the liver of rats, resulting in decreased insulin-induced tyrosine phosphorylation of IR, IRS-1, and IRS-2, and decreased interaction of IRS-1 and IRS-2 with phosphoinositide 3-kinase (PI3K). In addition, Ad infection resulted in impaired systemic glucose homeostasis, which recovered by 13 days, after the protein levels of IR, IRS-1, and IRS-2 had started to normalize. Expression of a TNF inhibitor or Kupffer cell depletion attenuated the Ad vector-induced decreases of insulin signaling molecules, indicating a potential role of Kupffer cell activation in this process. These studies provide evidence that systemic administration of Ad vectors can impair insulin signaling in liver, resulting in altered systemic glucose metabolism. Thus, effects of Ad vector infection on insulin action and glucose metabolism need to be considered when Ad vectors are used in research or gene therapy and may be more broadly applicable to other viral agents.

Engineered adenovirus serotypes for overcoming anti-vector immunity

Adenovirus (Ad)-based gene transfer has been successfully utilised in gene therapy and vaccine applications. To date, an increasing number of human clinical trials utilise recombinant Ad-based vectors as a gene transfer platform. In particular, progress has been made recently in utilising Ad-based vectors as a vaccine platform in HIV, cancer immunotherapy approaches and in vaccination for other infections. Despite these successes, the scientific and bio-industrial communities have recently recognised that innate and pre-existing immunity against Ad vectors can constitute a serious obstacle to the development and application of this technology. It is essential to overcome vector-mediated immune responses, such as production of inflammatory cytokines and pre-existing immunity to Ad, because the induction of these responses not only shortens the period of gene expression but also leads to serious side effects. This review focuses on the biology of Ad infection and the approaches that are being adopted to overcome immunity against the Ad-based vectors.

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

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

Scavenger receptor A: a new route for adenovirus 5

Adenoviruses are common pathogens associated with respiratory diseases, gastrointestinal illnesses and/or conjunctivitis. Currently, this virus is used as a vector in gene therapy trials. The promise of viral gene therapy applications is substantially reduced because the virus is cleared by liver macrophages upon systemic administration. The mechanism underlying adenoviral tropism to and degradation in macrophages is poorly understood. We identified a new adenoviral receptor, the scavenger receptor A (SR-A), responsible for uptake of the virus in macrophages. CHO cells expressing SR-A showed increased viral transgene expression when compared with wild type cells. Preincubation of J774 macrophage cells with SR-A ligands decreased significantly adenoviral uptake. Electron-microscopy analysis of infected J774 cells showed activation of a viral degradation pathway. Infection of mice with adenovirus resulted in a substantial decrease of the virus in liver macrophages when SR-A was blocked. Our data provide a basis for understanding of the adenoviral uptake and degradation mechanism in macrophages in vitro and in vivo. Inhibition of adenoviral SR-A uptake can be utilized in gene therapy applications to increase its efficiency and efficacy.

Expanded anticancer therapeutic window of hexon-modified oncolytic adenovirus

One of the significant hurdles toward safe and efficacious systemic treatment of cancer with oncolytic adenoviruses (Ads) is dose-limiting hepatotoxicity that prevents the increase of a therapeutic dose. In this study, we expanded the therapeutic window of oncolytic serotype 5 Ad (Ad5) by a genetic modification of hypervariable loop 5 (HVR5) in the capsid protein hexon that prevented infection of hepatocytes due to ablation of binding to blood factors. This oncolytic virus, Ad-GL-HB, had significantly reduced levels of hepatocyte transduction in immunocompetent and immunodeficient mice as compared to parental virus Ad-GL. The hepatocyte detargeting decreased liver damage and increased the maximum tolerated dose of Ad-GL-HB tenfold relative to that of Ad-GL. Intravenous (i.v.) injection of Ad-GL or Ad-GL-HB into tumor-bearing mice produced equally increased survival rates demonstrating that while Ad-GL-HB detargeted hepatocytes, it sustained tumor cell infection after systemic administration. The significantly improved safety of the virus allowed it to be used at increased doses for improved systemic antitumor efficacy. Our results suggest that hexon modifications provide valuable strategies for systemic oncolytic Ad therapy.

Chemical modification with high molecular weight polyethylene glycol reduces transduction of hepatocytes and increases efficacy of intravenously delivered oncolytic adenovirus

Oncolytic adenoviruses are anticancer agents that replicate within tumors and spread to uninfected tumor cells, amplifying the anticancer effect of initial transduction. We tested whether coating the viral particle with polyethylene glycol (PEG) could reduce transduction of hepatocytes and hepatotoxicity after systemic (intravenous) administration of oncolytic adenovirus serotype 5 (Ad5). Conjugating Ad5 with high molecular weight 20-kDa PEG but not with 5-kDa PEG reduced hepatocyte transduction and hepatotoxicity after intravenous injection. PEGylation with 20-kDa PEG was as efficient at detargeting adenovirus from Kupffer cells and hepatocytes as virus predosing and warfarin. Bioluminescence imaging of virus distribution in two xenograft tumor models in nude mice demonstrated that PEGylation with 20-kDa PEG reduced liver infection 19- to 90-fold. Tumor transduction levels were similar for vectors PEGylated with 20-kDa PEG and unPEGylated vectors. Anticancer efficacy after a single intravenous injection was retained at the level of unmodified vector in large established prostate carcinoma xenografts, resulting in complete elimination of tumors in all animals and long-term tumor-free survival. Anticancer efficacy after a single intravenous injection was increased in large established hepatocellular carcinoma xenografts, resulting in significant prolongation of survival as compared with unmodified vector. The increase in efficacy was comparable to that obtained with predosing and warfarin pretreatment, significantly extending the median of survival. Shielding adenovirus with 20-kDa PEG may be a useful approach to improve the therapeutic window of oncolytic adenovirus after systemic delivery to primary and metastatic tumor sites.

Hepatic gene transfer as a means of tolerance induction to transgene products

The liver is a preferred target organ for gene therapy not only for liver-specific diseases but also for disorders that require systemic delivery of a protein. Diseases that could benefit from hepatic gene transfer include hemophilia, metabolic disorders, lysosomal storage disorders, and others. For a successful delivery of the transgene and sustained expression, the protocol must avoid immune responses in order to be efficacious. A growing number of studies have demonstrated that liver-directed transfer can induce transgene product-specific immune tolerance. Tolerance obtained via this route requires optimal engineering of the vector to eliminate transgene expression in antigen presenting cells while restricting high levels of therapeutic expression to hepatocytes. Innate immune responses may prevent tolerance induction, cause toxicity, and have to be minimized. Discussed in our review is the crucial role of CD4(+)CD25(+) regulatory T cells in tolerance to the hepatocyte-derived gene product, the immunobiology of the liver and our current understanding of its tolerogenic properties, current and proposed research as to the mechanisms behind the liver's unique cellular environment, as well as development of the tools for tolerance induction such as advanced vector systems.

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

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