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

Viral protein nanoparticles (Part 1): Pharmaceutical characteristics

Viral protein nanoparticles fill the gap between viruses and synthetic nanoparticles. Combining advantageous properties of both systems, they have revolutionized pharmaceutical research. Virus-like particles are characterized by a structure identical to viruses but lacking genetic material. Another type of viral protein nanoparticles, virosomes, are similar to liposomes but include viral spike proteins. Both systems are effective and safe vaccine candidates capable of overcoming the disadvantages of both traditional and subunit vaccines. Besides, their particulate structure, biocompatibility, and biodegradability make them good candidates as vectors for drug and gene delivery, and for diagnostic applications. In this review, we analyze viral protein nanoparticles from a pharmaceutical perspective and examine current research focused on their development process, from production to administration. Advances in synthesis, modification and formulation of viral protein nanoparticles are critical so that large-scale production of viral protein nanoparticle products becomes viable and affordable, which ultimately will increase their market penetration in the future. We will discuss their expression systems, modification strategies, formulation, biopharmaceutical properties, and biocompatibility.

Affilin-based retargeting of adenoviral vectors to the epidermal growth factor receptor

INTRODUCTION

Treatment of head and neck squamous cell carcinomas (HNSCC) by oncolytic adenoviral vectors holds promise as an efficient anti-cancer therapy. The epidermal growth factor receptor (EGFR) represents an attractive target receptor since it is frequently overexpressed in many types of HNSCC.

METHODS

To achieve EGFR-specific targeting by human adenovirus type 5 (HAdV-5) based vectors, the EGFR affinity ligand Affilin was covalently attached in a position specific manner either to the fiber or the hexon protein of the vector capsid. In vitro and in vivo studies investigated EGFR-specific cancer cell transduction, susceptibility to natural sequestration mechanisms, pharmacokinetics and biodistribution profiles of Affilin-decorated vectors.

RESULTS

Affilin-decorated vectors showed strongly enhanced and EGFR-specific cancer cell transduction in vitro and less susceptibility to known sequestration mechanisms of HAdV-5 particles. However, in vivo neither systemic nor intratumoral vector administration resulted in an improved transduction of EGFR-positive tumors. Comprehensive analyses indicated hampered EGFR-targeting by Affilin-decorated vectors was caused by rapid vector particle consumption due to binding to the murine EGFR, insufficient tumor vascularization and poor target accessibility for Affilin in the solid tumor caused by a pronounced tumor stroma.

CONCLUSION

In vitro studies yielded proof-of-concept results demonstrating that covalent attachment of a receptor-specific Affilin to the adenoviral capsid provides an effective and versatile tool to address cancer-specific target receptors by adenoviral vectors. Regarding EGFR as the vector target, off-target tissue transduction and low receptor accessibility within the tumor tissue prevented efficient tumor transduction by Affilin-decorated vectors, rendering EGFR a difficult-to-target receptor for adenoviral vectors.

In Vivo Tracking for Oncolytic Adenovirus Interactions with Liver Cells

Hepatotoxicity remains an as yet unsolved problem for adenovirus (Ad) cancer therapy. The toxic effects originate both from rapid Kupffer cell (KCs) death (early phase) and hepatocyte transduction (late phase). Several host factors and capsid components are known to contribute to hepatotoxicity, however, the complex interplay between Ad and liver cells is not fully understood. Here, by using intravital microscopy, we aimed to follow the infection and immune response in mouse liver from the first minutes up to 72 h post intravenous injection of three Ads carrying delta-24 modification (Ad5-RGD, Ad5/3, and Ad5/35). At 15–30 min following the infusion of Ad5-RGD and Ad5/3 (but not Ad5/35), the virus-bound macrophages demonstrated signs of zeiosis: the formation of long-extended protrusions and dynamic membrane blebbing with the virus release into the blood in the membrane-associated vesicles. Although real-time imaging revealed interactions between the neutrophils and virus-bound KCs within minutes after treatment, and long-term contacts of CD8+ T cells with transduced hepatocytes at 24–72 h, depletion of neutrophils and CD8+ T cells affected neither rate nor dynamics of liver infection. Ad5-RGD failed to complete replicative cycle in hepatocytes, and transduced cells remained impermeable for propidium iodide, with a small fraction undergoing spontaneous apoptosis. In Ad5-RGD-immune mice, the virus neither killed KCs nor transduced hepatocytes, while in the setting of hepatic regeneration, Ad5-RGD enhanced liver transduction. The clinical and biochemical signs of hepatotoxicity correlated well with KC death, but not hepatocyte transduction. Real-time in vivo tracking for dynamic interactions between virus and host cells provides a better understanding of mechanisms underlying Ad-related hepatotoxicity.

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.

Kupffer cell release of platelet activating factor drives dose limiting toxicities of nucleic acid nanocarriers

This work establishes that Kupffer cell release of platelet activating factor (PAF), a lipidic molecule with pro-inflammatory and vasoactive signaling properties, dictates dose-limiting siRNA nanocarrier-associated toxicities. High-dose intravenous injection of siRNA-polymer nano-polyplexes (si-NPs) elicited acute, shock-like symptoms in mice, associated with increased plasma PAF and consequently reduced PAF acetylhydrolase (PAF-AH) activity. These symptoms were completely prevented by prophylactic PAF receptor inhibition or Kupffer cell depletion. Assessment of varied si-NP chemistries confirmed that toxicity level correlated to relative uptake of the carrier by liver Kupffer cells and that this toxicity mechanism is dependent on carrier endosome disruptive function. 4T1 tumor-bearing mice, which exhibit increased circulating leukocytes, displayed greater sensitivity to these toxicities. PAF-mediated toxicities were generalizable to commercial delivery reagent in vivo-jetPEI® and an MC3 lipid formulation matched to an FDA-approved nanomedicine. These collective results establish Kupffer cell release of PAF as a key mediator of siRNA nanocarrier toxicity and identify PAFR inhibition as an effective strategy to increase siRNA nanocarrier tolerated dose.

Adenovirus delivery of encoded monoclonal antibody protects against different types of influenza virus infection

Due to the high mutation and recombination rates of the influenza virus, current clinically licensed influenza vaccines and anti-influenza drugs provide limited protection against the emerging influenza virus epidemic. Therefore, universal influenza vaccines with high efficacy are urgently needed to ensure human safety and health. Passive immunization of influenza broadly neutralizing antibodies may become an ideal option for controlling influenza infection. CR9114 isolated from the peripheral blood mononuclear cells of healthy donors is a broadly neutralizing monoclonal antibody that targets different types of influenza viruses. As the adenovirus vector is one of the most promising delivery vehicles, we employed the chimpanzee adenoviral vector, AdC68, to express CR9114 as a universal anti-influenza vaccine, termed AdC68-CR9114, and evaluated its antibody expression and its broad spectrum of prophylactic and therapeutic effects in animal models. Based on our findings, AdC68-CR9114-infected cell expressed the broadly neutralizing antibody at a high level in vitro and in vivo, exhibited biological functions, and protected mice from different types of influenza virus infection at different time points. The findings from this study shed light on a new strategy for controlling and preventing influenza infection.

Adenovirus Biodistribution is Modified in Sensitive Animals Compared to Naïve Animals

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

Factors Which Contribute to the Immunogenicity of Non-replicating Adenoviral Vectored Vaccines

Adenoviral vectors are a safe and potently immunogenic vaccine delivery platform. Non-replicating Ad vectors possess several attributes which make them attractive vaccines for infectious disease, including their capacity for high titer growth, ease of manipulation, safety, and immunogenicity in clinical studies, as well as their compatibility with clinical manufacturing and thermo-stabilization procedures. In general, Ad vectors are immunogenic vaccines, which elicit robust transgene antigen-specific cellular (namely CD8+ T cells) and/or humoral immune responses. A large number of adenoviruses isolated from humans and non-human primates, which have low seroprevalence in humans, have been vectorized and tested as vaccines in animal models and humans. However, a distinct hierarchy of immunological potency has been identified between diverse Ad vectors, which unfortunately limits the potential use of many vectors which have otherwise desirable manufacturing characteristics. The precise mechanistic factors which underlie the profound disparities in immunogenicity are not clearly defined and are the subject of ongoing, detailed investigation. It has been suggested that a combination of factors contribute to the potent immunogenicity of particular Ad vectors, including the magnitude and duration of vaccine antigen expression following immunization. Furthermore, the excessive induction of Type I interferons by some Ad vectors has been suggested to impair transgene expression levels, dampening subsequent immune responses. Therefore, the induction of balanced, but not excessive stimulation of innate signaling is optimal. Entry factor binding or receptor usage of distinct Ad vectors can also affect their in vivo tropism following administration by different routes. The abundance and accessibility of innate immune cells and/or antigen-presenting cells at the site of injection contributes to early innate immune responses to Ad vaccination, affecting the outcome of the adaptive immune response. Although a significant amount of information exists regarding the tropism determinants of the common human adenovirus type-5 vector, very little is known about the receptor usage and tropism of rare species or non-human Ad vectors. Increased understanding of how different facets of the host response to Ad vectors contribute to their immunological potency will be essential for the development of optimized and customized Ad vaccine platforms for specific diseases.

Combined Genetic and Chemical Capsid Modifications of Adenovirus-Based Gene Transfer Vectors for Shielding and Targeting

Adenovirus vectors are potent tools for genetic vaccination and oncolytic virotherapy. However, they are prone to multiple undesired vector-host interactions, especially after in vivo delivery. It is a consensus that the limitations imposed by undesired vector-host interactions can only be overcome if defined modifications of the vector surface are performed. These modifications include shielding of the particles from unwanted interactions and targeting by the introduction of new ligands. The goal of the protocol presented here is to enable the reader to generate shielded and, if desired, retargeted human adenovirus gene transfer vectors or oncolytic viruses. The protocol will enable researchers to modify the surface of adenovirus vector capsids by specific chemical attachment of synthetic polymers, carbohydrates, lipids, or other biological or chemical moieties. It describes the cutting-edge technology of combined genetic and chemical capsid modifications, which have been shown to facilitate the understanding and overcoming of barriers for in vivo delivery of adenovirus vectors. A detailed and commented description of the crucial steps for performing specific chemical reactions with biologically active viruses or virus-derived vectors is provided. The technology described in the protocol is based on the genetic introduction of (naturally absent) cysteine residues into solvent-exposed loops of adenovirus-derived vectors. These cysteine residues provide a specific chemical reactivity that can, after production of the vectors to high titers, be exploited for highly specific and efficient covalent chemical coupling of molecules from a wide variety of substance classes to the vector particles. Importantly, this protocol can easily be adapted to perform a broad variety of different (non-thiol-based) chemical modifications of adenovirus vector capsids. Finally, it is likely that non-enveloped virus-based gene transfer vectors other than adenovirus can be modified from the basis of this protocol.

Gene-Therapeutic Strategies Targeting Angiogenesis in Peripheral Artery Disease

The World Health Organization announced that cardiovascular disease is the number one cause of death globally, representing 31% of all global deaths. Coronary artery disease (CAD) affects approximately 5% of the US population aged 40 years and older. With an age-adjusted prevalence of approximately 12%, peripheral artery disease (PAD) affects at least 8 to 12 million Americans. Both CAD and PAD are caused by mainly atherosclerosis, the hardening and narrowing of arteries over the years by lipid deposition in the vascular bed. Despite the significant advances in interventions for revascularization and intensive medical care, patients with CAD or PAD who undergo percutaneous transluminal angioplasty have a persistent high rate of myocardial infarction, amputation, and death. Therefore, new therapeutic strategies are urgently needed for these patients. To overcome this unmet need, therapeutic angiogenesis using angiogenic growth factors has evolved in an attempt to stimulate the growth of new vasculature to compensate for tissue ischemia. After nearly 20 years of investigation, there is growing evidence of successful or unsuccessful gene therapy for ischemic heart and limb disease. This review will discuss basic and clinical data of therapeutic angiogenesis studies employing angiogenic growth factors for PAD patients and will draw conclusions on the basis of our current understanding of the biological processes of new vascularization.

Barriers to systemic application of virus-based vectors in gene therapy: lessons from adenovirus type 5

Currently, virus-based vectors, namely derivatives of the adenovirus, are frequently used in a wide variety of ex vivo or local gene therapeutic applications. However, the efficacy of virus-based vectors in systemic applications is presently still extremely limited. Complex interactions of the various vector types with the patient's organism hinder successful vector deployment. Exemplary, here we summarize barriers to systemic application of Adenovirus-based vectors leading either to acute toxic effects or rapid vector neutralization and discuss strategies to overcome these barriers aiming to develop more efficient vector types.

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.

Systemic Vascular Transduction by Capsid Mutant Adeno-Associated Virus After Intravenous Injection

The ability to effectively deliver genetic material to vascular endothelial cells remains one of the greatest unmet challenges facing the development of gene therapies to prevent diseases with underlying vascular etiology, such as diabetes, atherosclerosis, and age-related macular degeneration. Herein, we assess the effectiveness of an rAAV2-based capsid mutant vector (Y272F, Y444F, Y500F, Y730F, T491V; termed QuadYF+TV) with strong endothelial cell tropism at transducing the vasculature after systemic administration. Intravenous injection of QuadYF+TV resulted in widespread transduction throughout the vasculature of several major organ systems, as assessed by in vivo bioluminescence imaging and postmortem histology. Robust transduction of lung tissue was observed in QuadYF+TV-injected mice, indicating a role for intravenous gene delivery in the treatment of chronic diseases presenting with pulmonary complications, such as α1-antitrypsin deficiency. The QuadYF+TV vector cross-reacted strongly with AAV2 neutralizing antibodies, however, indicating that a targeted delivery strategy may be required to maximize clinical translatability.

Ad5/48 hexon oncolytic virus expressing sTGFβRIIFc produces reduced hepatic and systemic toxicities and inhibits prostate cancer bone metastases

We are interested in developing oncolytic adenoviruses for the treatment of prostate cancer (PCa) bone metastases. A key limitation of Adenovirus 5 (Ad5) is that upon systemic administration, it produces major liver and systemic toxicities. To address this issue, a chimaeric Ad5/48 adenovirus mHAd.sTβRFc was created. Seven hypervariable regions of Ad5 hexon present in Ad5-based Ad.sTβRFc expressing soluble transforming growth factor beta receptor II-Fc fusion protein (sTGβRIIFc), were replaced by those of Ad48. mHAd.sTβRFc, like Ad.sTβRFc, was replication competent in the human PCa cells, and produced high levels of sTGβRIIFc expression. Compared to Ad.sTβRFc, the systemic delivery of mHAd.sTβRFc in nude mice resulted in much reduced systemic toxicity, and reduced liver sequestration. Ad.sTβRFc produced significant liver necrosis, and increases in alanine transaminase, aspartate transaminase, lactate dehydrogenase, tumor necrosis factor-α, and interleukin-6 levels, while mHAd.sTβRFc produced much reduced responses of these markers. Intravenous delivery of Ad.sTβRFc or mHAd.sTβRFc (5 × 10(10) viral particles/mouse) in nude mice bearing PC-3-luc PCa bone metastases produced inhibition of bone metastases. Moreover, a larger dose of the mHAd.sTβRFc (4 × 10(11) viral particles /mouse) was also effective in inhibiting bone metastases. Thus, mHAd.sTβRFc could be developed for the treatment of PCa bone metastases.

Innate immunity to adenovirus

Human adenoviruses are the most widely used vectors in gene medicine, with applications ranging from oncolytic therapies to vaccinations, but adenovirus vectors are not without side effects. In addition, natural adenoviruses pose severe risks for immunocompromised people, yet infections are usually mild and self-limiting in immunocompetent individuals. Here we describe how adenoviruses are recognized by the host innate defense system during entry and replication in immune and nonimmune cells. Innate defense protects the host and represents a major barrier to using adenoviruses as therapeutic interventions in humans. Innate response against adenoviruses involves intrinsic factors present at constant levels, and innate factors mounted by the host cell upon viral challenge. These factors exert antiviral effects by directly binding to viruses or viral components, or shield the virus, for example, soluble factors, such as blood clotting components, the complement system, preexisting immunoglobulins, or defensins. In addition, Toll-like receptors and lectins in the plasma membrane and endosomes are intrinsic factors against adenoviruses. Important innate factors restricting adenovirus in the cytosol are tripartite motif-containing proteins, nucleotide-binding oligomerization domain-like inflammatory receptors, and DNA sensors triggering interferon, such as DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 and cyclic guanosine monophosphate-adenosine monophosphate synthase. Adenovirus tunes the function of antiviral autophagy, and counters innate defense by virtue of its early proteins E1A, E1B, E3, and E4 and two virus-associated noncoding RNAs VA-I and VA-II. We conclude by discussing strategies to engineer adenovirus vectors with attenuated innate responses and enhanced delivery features.

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.

Integration profile and safety of an adenovirus hybrid-vector utilizing hyperactive sleeping beauty transposase for somatic integration

We recently developed adenovirus/transposase hybrid-vectors utilizing the previously described hyperactive Sleeping Beauty (SB) transposase HSB5 for somatic integration and we could show stabilized transgene expression in mice and a canine model for hemophilia B. However, the safety profile of these hybrid-vectors with respect to vector dose and genotoxicity remains to be investigated. Herein, we evaluated this hybrid-vector system in C57Bl/6 mice with escalating vector dose settings. We found that in all mice which received the hyperactive SB transposase, transgene expression levels were stabilized in a dose-dependent manner and that the highest vector dose was accompanied by fatalities in mice. To analyze potential genotoxic side-effects due to somatic integration into host chromosomes, we performed a genome-wide integration site analysis using linker-mediated PCR (LM-PCR) and linear amplification-mediated PCR (LAM-PCR). Analysis of genomic DNA samples obtained from HSB5 treated female and male mice revealed a total of 1327 unique transposition events. Overall the chromosomal distribution pattern was close-to-random and we observed a random integration profile with respect to integration into gene and non-gene areas. Notably, when using the LM-PCR protocol, 27 extra-chromosomal integration events were identified, most likely caused by transposon excision and subsequent transposition into the delivered adenoviral vector genome. In total, this study provides a careful evaluation of the safety profile of adenovirus/Sleeping Beauty transposase hybrid-vectors. The obtained information will be useful when designing future preclinical studies utilizing hybrid-vectors in small and large animal models.

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.

Intravenous injection of irradiated tumor cell vaccine carrying oncolytic adenovirus suppressed the growth of multiple lung tumors in a mouse squamous cell carcinoma model

BACKGROUND

Although cancer therapy using replication-selective oncolytic adenoviruses has been available for many years, its anti-tumor efficacy is suboptimal as a result of low and nonspecific infectivity that depends on coxsackie adenovirus receptor expression of the target cancer and normal cells, and generation of an anti-adenovirus neutralizing antibody. In addition, concerns of triggering a severe innate immune response against the adenovirus limit the systemic administration. We developed the carrier cell-based oncolytic virus system (CBOVS) using irradiated tumor cells as carrier cells and concealing the adenovirus (Ad-IAI.3B) inside to improve the specific infectivity. We investigated the anti-tumor effect of CBOVS in a multiple lung tumor mouse model.

METHODS

The ability of CBOVS to infect Ad-IAI.3B to the target cancer cells was examined in vitro in the presence of anti-adenovirus antibodies. To evaluate the systemic effect of CBOVS, we intravenously injected CBOVS into mice with lung tumors (KLN205 cell lines).

RESULTS

CBOVS enhanced the infectivity of Ad-IAI.3B to tumor cells in the presence of anti-adenovirus antibodies in vitro. Intravenous injections of CBOVS produced an accumulation of the adenovirus in the lung-bearing tumors and produced a strong anti-tumor effect in vivo. Furthermore, lymphocytes collected from the CBOVS-treated mice induced an increase in cytokines related to the Th1 response (interferon-γ, interleukin-12) by pulsing with KLN205.

CONCLUSIONS

These findings suggest that CBOVS could protect adenoviruses from neutralizing antibodies and systemically deliver them to lung tumors. Furthermore, CBOVS appears to have potential as a tumor cell vaccine that activates cytotoxic immunity against cancer cells.

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.

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.

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.

Improving adenovirus based gene transfer: strategies to accomplish immune evasion

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

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 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.

Adenovirus capsid-display of the retro-oriented human complement inhibitor DAF reduces Ad vector-triggered immune responses in vitro and in vivo

Adenovirus (Ad) vectors are widely used in human clinical trials. However, at higher dosages, Ad vector-triggered innate toxicities remain a major obstacle to many applications. Ad interactions with the complement system significantly contribute to innate immune responses in several models of Ad-mediated gene transfer. We constructed a novel class of Ad vectors, genetically engineered to "capsid-display" native and retro-oriented versions of the human complement inhibitor decay-accelerating factor (DAF), as a fusion protein from the C-terminus of the Ad capsid protein IX. In contrast to conventional Ad vectors, DAF-displaying Ads dramatically minimized complement activation in vitro and complement-dependent immune responses in vivo. DAF-displaying Ads did not trigger thrombocytopenia, minimized endothelial cell activation, and had diminished inductions of proinflammatory cytokine and chemokine responses. The retro-oriented display of DAF facilitated the greatest improvements in vivo, with diminished activation of innate immune cells, such as dendritic and natural killer cells. In conclusion, Ad vectors can capsid-display proteins in a manner that not only retains the functionality of the displayed proteins but also potentially can be harnessed to improve the efficacy of this important gene transfer platform for numerous gene transfer applications.

Lactoferrin protects against acetaminophen-induced liver injury in mice

Acetaminophen-induced liver injury (AILI) is a significant health problem and represents the most frequent cause of drug-induced liver failure in the United States. The development and implementation of successful therapeutic intervention strategies have been demanding, due to significant limitations associated with the current treatment for AILI. Lactoferrin (Lac), a glycoprotein present in milk, has been demonstrated to possess a multitude of biological functions. Our study demonstrated a profound protective effect of Lac in a murine model of AILI, which was not dependent on its iron-binding ability, inhibition of acetaminophen (APAP) metabolism, or a direct cytoprotective effect on hepatocytes. Instead, Lac treatment significantly attenuated APAP-induced liver sinusoidal endothelial cell dysfunction and ameliorated hepatic microcirculation disorder. This protective effect of Lac appeared to be dependent on hepatic resident macrophages (Kupffer cells [KCs]).

CONCLUSION

Collectively, our data indicate that Lac, through activation of KCs, inhibited APAP-induced liver sinusoidal endothelial cell damage and improved hepatic congestion, thereby protecting against AILI. These findings reveal the significant therapeutic potential of Lac during AILI and other types of liver diseases.

Induction of shock after intravenous injection of adenovirus vectors: a critical role for platelet-activating factor

Innate immune responses are a major barrier to safe systemic gene therapy with adenovirus (Ad) vectors. We show that intravenous (IV) injection of rats with Ad5 vectors causes a novel rapid shock reaction that involves hypotension, hemoconcentration, tissue edema, and vasocongestion, with notable pathology in the pancreas and the gastrointestinal system. We show for the first time that this reaction is dependent on platelet-activating factor (PAF), a lipid signaling molecule that is a known shock inducer. Ad upregulated PAF within 5 minutes in vivo, and antagonists of the PAF receptor were able to prevent Ad-induced shock. Ad upregulated PAF via the reticuloendothelial system (RES), because splenectomy or depletion of phagocytes blocked the ability of Ad to induce both PAF and shock. Rats were considerably more sensitive to Ad-induced shock than were mice, but PAF mediated shock in both species. Other Ad-induced innate immune responses such as cytokine induction and thrombocytopenia were not mediated by PAF. In summary, systemic IV injection of Ad stimulates the RES to upregulate PAF within a matter of minutes, which results in shock. The identification of this novel pathway suggests strategies to improve the safety of systemic gene therapy with Ad 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.

Liver tissue engineering in the evaluation of drug safety

Assessment of drug-liver interactions is an integral part of predicting the safety profile of new drugs. Existing model systems range from in vitro cell culture models to FDA-mandated animal tests. Data from these models often fail, however, to predict human liver toxicity, resulting in costly failures of clinical trials. In vitro screens based on cultured hepatocytes are now commonly used in early stages of development, but many toxic responses in vivo seem to be mediated by a complex interplay among several different cell types. We discuss some of the evolving trends in liver cell culture systems applied to drug safety assessment and describe an experimental model that captures complex liver physiology through incorporation of heterotypic cell-cell interactions, 3D architecture and perfused flow. We demonstrate how heterotypic interactions in this system can be manipulated to recreate an inflammatory environment and apply the model to test compounds that potentially exhibit idiosyncratic drug toxicity. Finally, we provide a perspective on how the range of existing and emerging in vitro liver culture approaches, from simple to complex, might serve needs across the range of stages in drug discovery and development, including applications in molecular therapeutics.

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.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.

Adenovirus activates complement by distinctly different mechanisms in vitro and in vivo: indirect complement activation by virions in vivo

Understanding innate immunity is key to improving the safety of adenovirus (Ad) vectors for systemic gene therapy. Ad has been shown to activate complement in vitro, but activation of complement after Ad injection in vivo has not been directly measured. Using complement protein C3a as a marker of complement activation, we show that types 2 and 5 human Ads cause rapid complement activation after intravenous injection in mice. Unexpectedly, the mechanisms in vivo were different than those in vitro. Antibodies were critical for the activation of complement by Ad in vitro, but antibodies were not required in vivo. The classical pathway was required in vitro, whereas complement activation in vivo involved both classical and nonclassical pathways as well as the reticuloendothelial system. Remarkably, the entry-deficient Ad mutant ts1 was completely unable to activate complement in vivo even though it was fully able to activate complement in vitro. This result demonstrates that the complement system senses intravenously injected Ad primarily by detecting the effects of Ad on cells rather than through direct interaction of complement with virions. Encouragingly, shielding Ad with polyethylene glycol was effective at reducing complement activation both in vitro and in vivo. In summary, intravenously injected Ad rapidly activates complement through multiple pathways, but these pathways are different than those identified by in vitro studies. In vitro studies are poorly predictive of in vivo mechanisms because Ad virions activate complement through indirect mechanisms in vivo.

Redundant and synergistic mechanisms control the sequestration of blood-born adenovirus in the liver

Human adenovirus (Ad) is a ubiquitous pathogen causing a wide range of diseases. Although the interactions of human Ad serotype 5 (Ad5) with susceptible cells in vitro are known in great detail, host factors controlling the tissue specificity of Ad5 infection in vivo remain poorly understood. Here, we analyzed the mechanisms of sequestration by the liver for blood-born human Ads and Ad5-based vectors. Our data suggest that several known mechanisms that lead to Ad5 sequestration by the liver become engaged in a redundant, sequential, and synergistic manner to ensure the rapid clearance of circulating virus particles from the blood. These mechanisms include (i) trapping of the virus by liver residential macrophages, Kupffer cells; (ii) Ad5 hepatocyte infection via blood factor-hexon interactions; and (iii) Ad5 penton RGD motif-mediated interactions with liver endothelial cells and hepatocytes, mediating virus retention in the space of Disse. More important, we show that when all of these mechanisms are simultaneously inactivated via mutations of Ad5 capsid proteins and pharmacological interventions, virus sequestration by the liver is markedly reduced. Therefore, our study is the first demonstration of the principal possibility of ablating the sequestration of blood-born Ad in the liver via specific inactivation of a defined set of mechanisms that control this process.

Cancer gene therapy with targeted adenoviruses

BACKGROUND

Clinical experience with adenovirus vectors has highlighted the need for improved delivery and targeting.

OBJECTIVE

This manuscript aims to provide an overview of the techniques currently under development for improving adenovirus delivery to malignant cells in vivo.

METHODS

Primary research articles reporting improvements in adenoviral gene delivery are described. Strategies include genetic modification of viral coat proteins, non-genetic modifications including polymer encapsulation approaches and pharmacological interventions.

RESULTS/CONCLUSION

Reprogramming adenovirus tropism in vitro has been convincingly demonstrated using a range of genetic and physical strategies. These studies have provided new insights into our understanding of virology and the field is progressing. However, there are still some limitations that need special consideration before adenovirus-targeted cancer gene therapy emerges as a routine treatment in the clinical setting.

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

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

Cancer-induced expansion and activation of CD11b+ Gr-1+ cells predispose mice to adenoviral-triggered anaphylactoid-type reactions

Intravascular delivery (1.5 x 10(9) particles and higher) of recombinant adenovirus (rAd) induces myeloid cell mediated, self-limiting hemodynamic responses in normal mice. However, we observed anaphylactoid-type reactions and exacerbated hemodynamic events following rAd injection in mice bearing malignant 4T1 mammary carcinoma. Because 4T1 tumors induce significant CD11b(+)Gr-1(+) myeloid cell expansion and activation, we set to determine whether this causes rAd-induced exaggerated responses. When treated with a single intravenous dose (1 x 10(10) particles) of rAd, mice implanted with 4T1 carcinoma succumbed due to the anaphylactoid-type reactions. In contrast, normal mice and mice implanted with a related mammary carcinoma (66cl4) that does not induce CD11b(+)Gr-1(+) cell expansion, showed minimal responses. Depletion of phagocytic CD11b(+)Gr-1(+) cells prior to rAd delivery protected 4T1 tumor-bearing animals, whereas passive transfer of CD11b(+)Gr-1(+) cells from 4T1 tumor-bearing animals was sufficient to convey susceptibility to anaphylactoid-type reactions in normal animals. We further show that there is upregulation of nitric oxide and leukotriene signaling pathways in the 4T1 tumor-induced CD11b(+)Gr-1(+) myeloid cells and that pretreating mice with inhibitors of nitric oxide synthetase and leukotrienes can attenuate the anaphylactoid-type reactions. These data show that malignant tumor growth can alter CD11b(+)Gr-1(+) myeloid cells, rendering hosts susceptible to anaphylactoid-type reactions upon intravascular treatment with rAd.

Clearance of adenovirus by Kupffer cells is mediated by scavenger receptors, natural antibodies, and complement

Kupffer cells (KCs) rapidly remove intravenously injected adenovirus (Ad) vectors from the circulation. A better understanding of the mechanisms involved could suggest strategies to improve Ad gene delivery by suppressing or evading KC uptake. We recently showed that clearance of Ad type 5 vectors by KCs does not involve the interaction of Ad with the well-established Ad receptors, namely, integrins or the coxsackievirus and Ad receptor (J. S. Smith, Z. Xu, J. Tian, S. C. Stevenson, and A. P. Byrnes, Hum. Gene Ther. 19:547-554, 2008). In the current study, we systematically quantified the contributions of various receptors and plasma proteins to the clearance of Ad by KCs. We found that scavenger receptors are a predominant mechanism for the clearance of Ad by KCs. In addition, we found that Ad is opsonized by natural immunoglobulin M antibodies and complement and that these opsonins play a contributory role in the clearance of Ad by KCs. We also examined additional mechanisms that have been postulated to be involved in the clearance of Ad, including the binding of Ad to platelets and vitamin K-dependent coagulation factors, but we found that neither of these were required for the clearance of Ad by KCs.

Retargeting polymer-coated adenovirus to the FGF receptor allows productive infection and mediates efficacy in a peritoneal model of human ovarian cancer

BACKGROUND

Transductional targeting of adenovirus following systemic or regional delivery remains one of the most difficult challenges for cancer gene medicine. The numerical excess and anatomical advantage of normal (non-cancer) cells in vivo demand far greater detargeting than is necessary for studies using single cell populations in vitro, and this must be coupled with efficient retargeting to cancer cells.

METHODS

Adenovirus (Ad5) particles were coated with reactive poly[N-(2-hydroxypropyl)methacrylamide] copolymers, to achieve detargeting, and retargeting ligands were attached to the coating. Receptor-mediated infection was characterised in vitro and anticancer efficacy was studied in vivo.

RESULTS

Polymer coating prevented the virus binding any cellular receptors and mediated complete detargeting in vitro and in vivo. These fully detargeted vectors were efficiently retargeted with the model ligand FGF2 to infect FGFR-positive cells. Specific transduction activity was the same as parental virus, and intracellular routing appeared unaffected. Levels of transduction were up to 100-fold greater than parental virus on CAR negative cells. This level of specificity permitted good efficacy in intraperitoneal cancer virotherapy, simultaneously decreasing peritoneal adhesions seen with parental virus. Following intravenous delivery FGF2 mediated unexpected binding to erythrocytes, improving circulation kinetics, but preventing the targeted virus from leaving the blood stream.

CONCLUSIONS

Polymer cloaking enables complete adenovirus detargeting, providing a versatile platform for receptor-specific retargeting. This approach can efficiently retarget cancer virotherapy in vivo. Ligands should be selected carefully, as non-specific interactions with non-target cells (e.g. blood cells) can deplete the pool of therapeutic virus available for targeting disseminated disease.

Polyinosinic acid enhances delivery of adenovirus vectors in vivo by preventing sequestration in liver macrophages

Adenovirus is among the preferred vectors for gene therapy because of its superior in vivo gene-transfer efficiency. However, upon systemic administration, adenovirus is preferentially sequestered by the liver, resulting in reduced adenovirus-mediated transgene expression in targeted tissues. In the liver, Kupffer cells are responsible for adenovirus degradation and contribute to the inflammatory response. As scavenger receptors present on Kupffer cells are responsible for the elimination of blood-borne pathogens, we investigated the possible implication of these receptors in the clearance of the adenovirus vector. Polyinosinic acid [poly(I)], a scavenger receptor A ligand, was analysed for its capability to inhibit adenovirus uptake specifically in macrophages. In in vitro studies, the addition of poly(I) before virus infection resulted in a specific inhibition of adenovirus-induced gene expression in a J774 macrophage cell line and in primary Kupffer cells. In in vivo experiments, pre-administration of poly(I) caused a 10-fold transient increase in the number of adenovirus particles circulating in the blood. As a consequence, transgene expression levels measured in different tissues were enhanced (by 5- to 15-fold) compared with those in animals that did not receive poly(I). Finally, necrosis of Kupffer cells, which normally occurs as a consequence of systemic adenovirus administration, was prevented by the use of poly(I). No toxicity, as measured by liver-enzyme levels, was observed after poly(I) treatment. From our data, we conclude that poly(I) can prevent adenovirus sequestration by liver macrophages. These results imply that, by inhibiting adenovirus uptake by Kupffer cells, it is possible to reduce the dose of the viral vector to diminish the liver-toxicity effect and to improve the level of transgene expression in target tissues. In systemic gene-therapy applications, this will have great impact on the development of targeted adenoviral vectors.

Amine-reactive pyridylhydrazone-based PEG reagents for pH-reversible PEI polyplex shielding

PEGylation which is reversed after the therapeutic agent reaches the target cell presents an attractive feature for drug, protein or nucleic acid delivery. Amine-reactive, endosomal pH cleavable polyethylene glycol aldehyde-carboxypyridylhydrazone, N-hydroxysuccinimide esters (PEG-HZN-NHS) were synthesized and applied for bioreversible surface shielding of DNA polyplexes. Monofunctional mPEG-HZN-NHS was synthesized by reacting succinimidyl hydraziniumnicotinate with mPEG-butyraldehyde (20 kDa). Bifunctional OPSS-PEG-HZN-NHS was synthesized analogously via a omega-2-pyridyldithio-PEG (10 kDa) propionaldehyde intermediate. Polyethylenimine (PEI) polyplexes were reacted with the pH-sensitive (mPEG-HZN-NHS) or the corresponding stable (mPEG-NHS) reagent. Both types of polyplexes remained shielded at pH 7.4 as demonstrated by particle size and zeta potential measurements after 4h of incubation at 37 degrees C. Polyplex deshielding at endosomal pH 5 was observed only with the mPEG-HZN-NHS shielded particles. This was confirmed by fluorescence correlation spectroscopy using the analogous Alexa-488 fluorescently labeled bifunctional PEGylation reagents. Luciferase gene transfections with epidermal growth factor (EGF) containing polyplexes using EGF-receptor overexpressing hepatoma HUH7 cells showed an up to 16-fold enhancement in gene expression with the reversibly shielded polyplexes as compared to stably shielded polyplexes. Consistently, the reversibly shielded polyplexes mediated also an enhanced tumor specific in vivo transgene expression after intravenous administration in a subcutaneous HUH7 tumor model in SCID mice.

Factors influencing retention of adenovirus within tumours following direct intratumoural injection

Direct intratumoural (IT) administration of adenovirus is widely used, however little is known about the resulting distribution of virus particles. Here we have evaluated the influence of tumour size, volume of injectate and occlusion of injection sites (to prevent retrograde seepage) on particle biodistribution and transgene expression. In subcutaneous MDA-231 xenografts, IT injection of relatively large volumes (4 x 20% (vol/vol) injections) resulted in just 40% of the administered dose being retained in tumour tissue after 30 min, with 15% in the liver thought to reflect systemic 'overflow'. Occlusion of the injection sites using surgical adhesive increased retention of the vector to 80% in the tumour with no increase in liver levels. Spread of expression was enhanced using multiple injection sites, but not by using larger injectate volumes. In ZR75.1 breast carcinoma xenografts virus distribution was different, with no evidence of systemic overflow leading to hepatic transduction following IT injection. Typically, clinical doses employ up to 30% vol/vol IT injections. Depending on the tumour, this may give considerable systemic overflow and might account for the high frequency of fevers observed. Virus performance might be improved by tailoring volumes and frequency of IT injection for tumour biology or histotype.

Wild-type adenoviruses from groups A-F evoke unique innate immune responses, of which HAd3 and SAd23 are partially complement dependent

Alternative human and non-human Ad serotype vectors are currently studied for gene therapy and/or vaccine applications to capitalize upon their likely ability to avoid pre-existing immunity to HAd5. However, relatively little attention has been given to the nature and scope of innate immune responses generated by alternative Ad serotypes. In this study, we characterized several innate immune responses after intravenous administration of wild-type Ad serotypes HAd31, HAd3, HAd5, HAd37, SAd23 and HAd41, representing groups A-F, respectively. Notably, biodistribution studies revealed significant differences between the serotypes, with high levels of HAd3 genomes found in the liver and lung, and HAd37 genomes found in the spleen after systemic administration. Relative to similar treatments with other Ad serotypes, HAd3 and SAd23 induced altered innate immune responses, illustrated by induction of higher levels of cellular gene transcription in several tissues, and higher plasma levels of cytokines and chemokines. We also investigated whether complement interactions have a role in HAd3- and SAd23-induced responses. We confirmed complement dependent gene transcription, plasma cytokine/chemokine responses, and liver toxicities incurred after administration of HAd3 and SAd23. This study highlights the potential benefits and/or limitations to the proposed use of alternative Ad serotypes for gene therapy or vaccine applications.

Role of MyD88 and TLR9 in the innate immune response elicited by serotype 5 adenoviral vectors

A replication-incompetent adenoviral (Ad) vector is generating interest for both gene therapy and immunotherapy. A major limitation of the use of Ad vectors is the innate immune response, which causes inflammatory cytokine production and tissue damage; however, the precise mechanism of the innate immune response remains to be clarified. Here, we show that serotype 5 human Ad vectors elicit innate immune responses through a myeloid differentiating factor 88 (MyD88)/Toll-like receptor (TLR)-9-dependent and/or -independent manner according to cell type. After stimulation with Ad vectors, the production of interleukin (IL)-6 and IL-12 was significantly decreased in MyD88- or TLR9-deficient dendritic cells (DCs), compared with wild-type DCs. In addition, the surface expression of maturation marker proteins, such as CD40, CD80, CD86, and MHC class II, in MyD88- or TLR9-deficient granulocyte-macrophage colony-stimulating factor (GM-CSF)-DCs was similar to that in wild-type DCs. On the other hand, MyD88- or TLR9-deficient peritoneal macrophages produced the same level of IL-6 as wild-type macrophages after infection with Ad vectors. We did not find any differences in the mRNA expression levels of the molecules involved in innate immunity, such as MyD88, TLR3, TLR7, and TLR9, between DCs and macrophages. The intravenous injection of luciferase-expressing Ad vectors into MyD88- or TLR9-deficient mice resulted in almost comparable levels of IL-6 and IL-12 production and luciferase expression with wild-type mice. These results suggest that Ad vectors can activate innate immunity via MyD88/TLR9-dependent and -independent mechanisms.