Fiber and penton base capsid modifications yield diminished adenovirus type 5 transduction and proinflammatory gene expression with retention of antigen-specific humoral immunity

Adenovirus-Derived Nano-Capsid Platforms for Targeted Delivery and Penetration of Macromolecules into Resistant and Metastatic Tumors

Macromolecular therapeutics such as nucleic acids, peptides, and proteins have the potential to overcome treatment barriers for cancer. For example, nucleic acid or peptide biologics may offer an alternative strategy for attacking otherwise undruggable therapeutic targets such as transcription factors and similar oncologic drivers. Delivery of biological therapeutics into tumor cells requires a robust system of cell penetration to access therapeutic targets within the cell interior. A highly effective means of accomplishing this may be borrowed from cell-penetrating pathogens such as viruses. In particular, the cell entry function of the adenovirus penton base capsid protein has been effective at penetrating tumor cells for the intracellular deposition of macromolecular therapies and membrane-impermeable drugs. Here, we provide an overview describing the evolution of tumor-targeted penton-base-derived nano-capsids as a framework for discussing the requirements for overcoming key barriers to macromolecular delivery. The development and pre-clinical testing of these proteins for therapeutic delivery has begun to also uncover the elusive mechanism underlying the membrane-penetrating function of the penton base. An understanding of this mechanism may unlock the potential for macromolecular therapeutics to be effectively delivered into cancer cells and to provide a treatment option for tumors resisting current clinical therapies.

E3 ubiquitin ligase Mindbomb 1 facilitates nuclear delivery of adenovirus genomes

The journey from plasma membrane to nuclear pore is a critical step in the lifecycle of DNA viruses, many of which must successfully deposit their genomes into the nucleus for replication. Viral capsids navigate this vast distance through the coordinated hijacking of a number of cellular host factors, many of which remain unknown. We performed a gene-trap screen in haploid cells to identify host factors for adenovirus (AdV), a DNA virus that can cause severe respiratory illness in immune-compromised individuals. This work identified Mindbomb 1 (MIB1), an E3 ubiquitin ligase involved in neurodevelopment, as critical for AdV infectivity. In the absence of MIB1, we observed that viral capsids successfully traffic to the proximity of the nucleus but ultimately fail to deposit their genomes within. The capacity of MIB1 to promote AdV infection was dependent on its ubiquitination activity, suggesting that MIB1 may mediate proteasomal degradation of one or more negative regulators of AdV infection. Employing complementary proteomic approaches to characterize proteins proximal to MIB1 upon AdV infection and differentially ubiquitinated in the presence or absence of MIB1, we observed an intersection between MIB1 and ribonucleoproteins (RNPs) largely unexplored in mammalian cells. This work uncovers yet another way that viruses utilize host cell machinery for their own replication, highlighting a potential target for therapeutic interventions that counter AdV infection.

Adenoviromics: Mining the Human Adenovirus Species D Genome

Human adenovirus (HAdV) infections cause disease world-wide. Whole genome sequencing has now distinguished 90 distinct genotypes in 7 species (A-G). Over half of these 90 HAdVs fall within species D, with essentially all of the HAdV-D whole genome sequences generated in the last decade. Herein, we describe recent new findings made possible by mining of this expanded genome database, and propose future directions to elucidate new functional elements and new functions for previously known viral components.

Going viral: a review of replication-selective oncolytic adenoviruses

Oncolytic viruses have had a tumultuous course, from the initial anecdotal reports of patients having antineoplastic effects after natural viral infections a century ago to the development of current cutting-edge therapies in clinical trials. Adenoviruses have long been the workhorse of virotherapy, and we review both the scientific and the not-so-scientific forces that have shaped the development of these therapeutics from wild-type viral pathogens, turning an old foe into a new friend. After a brief review of the mechanics of viral replication and how it has been modified to engineer tumor selectivity, we give particular attention to ONYX-015, the forerunner of virotherapy with extensive clinical testing that pioneered the field. The findings from those as well as other oncolytic trials have shaped how we now view these viruses, which our immune system has evolved to vigorously attack, as promising immunotherapy agents.

Diminished Innate Antiviral Response to Adenovirus Vectors in cGAS/STING-Deficient Mice Minimally Impacts Adaptive Immunity

Infection by adenovirus, a nonenveloped DNA virus, induces antiviral innate and adaptive immune responses. Studies of transformed human and murine cell lines using short hairpin RNA (shRNA) knockdown strategies identified cyclic guanine adenine synthase (cGAS) as a pattern recognition receptor (PRR) that contributes to the antiadenovirus response. Here we demonstrate how the cGAS/STING cascade influences the antiviral innate and adaptive immune responses in a murine knockout model. Using knockout bone marrow-derived dendritic cells (BMDCs) and bone marrow-derived macrophages (BMMOs), we determined that cGAS and STING are essential to the induction of the antiadenovirus response in these antigen-presenting cells (APCs) in vitro We next determined how the cGAS/STING cascade impacts the antiviral response following systemic administration of a recombinant adenovirus type 5 vector (rAd5V). Infection of cGAS(-/-) and STING(-/-) mice results in a compromised early antiviral innate response compared to that in wild-type (WT) controls: significantly lower levels of beta interferon (IFN-β) secretion, low levels of proinflammatory chemokine induction, and reduced levels of antiviral transcript induction in hepatic tissue. At 24 h postinfection, levels of viral DNA and reporter gene expression in the liver were similar in all strains. At 28 days postinfection, clearance of infected hepatocytes in cGAS or STING knockout mice was comparable to that in WT C57BL/6 mice. Levels of neutralizing anti-Ad5V antibody were modestly reduced in infected cGAS mice. These data support a dominant role for the cGAS/STING cascade in the early innate antiviral inflammatory response to adenovirus vectors. However, loss of the cGAS/STING pathway did not affect viral clearance, and cGAS deficiency had a modest influence on the magnitude of the antiviral humoral immune response to adenovirus infections.

IMPORTANCE

The detection of viral infection by host sentinel immune cells contributes to the activation of a complex and varied antiviral innate and adaptive immune response, which limits virus replication, spread, and susceptibility to infection. In this study, we have characterized how the cGAS/STING DNA-sensing cascade contributes to early detection of adenovirus infections. cGAS influences APC activation and early innate antiviral inflammatory immune responses, but adaptive immune pathways associated with virus clearance and anti-Ad antibody production were minimally influenced by the loss of the cGAS PRR signaling cascade.

Differential immunogenicity between HAdV-5 and chimpanzee adenovirus vector ChAdOx1 is independent of fiber and penton RGD loop sequences in mice

Replication defective adenoviruses are promising vectors for the delivery of vaccine antigens. However, the potential of a vector to elicit transgene-specific adaptive immune responses is largely dependent on the viral serotype used. HAdV-5 (Human adenovirus C) vectors are more immunogenic than chimpanzee adenovirus vectors from species Human adenovirus E (ChAdOx1 and AdC68) in mice, though the mechanisms responsible for these differences in immunogenicity remain poorly understood. In this study, superior immunogenicity was associated with markedly higher levels of transgene expression in vivo, particularly within draining lymph nodes. To investigate the viral factors contributing to these phenotypes, we generated recombinant ChAdOx1 vectors by exchanging components of the viral capsid reported to be principally involved in cell entry with the corresponding sequences from HAdV-5. Remarkably, pseudotyping with the HAdV-5 fiber and/or penton RGD loop had little to no effect on in vivo transgene expression or transgene-specific adaptive immune responses despite considerable species-specific sequence heterogeneity in these components. Our results suggest that mechanisms governing vector transduction after intramuscular administration in mice may be different from those described in vitro.

Dendritic cells transfected with adenoviral vectors as vaccines

Dendritic cells (DCs) are critical to the initiation of a T-cell response. They constitute the most potent antigen-presenting cell (APC) endowed with the unique capacity to stimulate an antigen-specific T-cell responses by naïve T cells. Adenoviruses (Ad) have high transduction efficiency for many cell types including cells of hematopoietic origin independent of their mitotic status, and replication-defective Ad have demonstrated a safety profile clinically. Further, Ad vectors provide a high level of transgene expression, and Ad-transduced DCs can effectively present antigenic proteins. In this chapter, we outline a functionally closed, good manufacturing protocol for the differentiation of monocytes into DCs and transduction by Ad vectors. Basic functional and phenotypic release assays are provided, as well as contrasting research approaches for Ad-transduced DC-based vaccines.

Unabated adenovirus replication following activation of the cGAS/STING-dependent antiviral response in human cells

The cGAS/STING DNA sensing complex has recently been established as a predominant pathogen recognition receptor (PRR) for DNA-directed type I interferon (IFN) innate immune activation. Using replication-defective adenovirus vectors and replication-competent wild-type adenovirus, we have modeled the influence of the cGAS/STING cascade in permissive human cell lines (A549, HeLa, ARPE19, and THP1). Wild-type adenovirus induced efficient early activation of the cGAS/STING cascade in a cell-specific manner. In all responsive cell lines, cGAS/STING short hairpin RNA (shRNA) knockdown resulted in a loss of TBK1 and interferon response factor 3 (IRF3) activation, a lack of beta interferon transcript induction, loss of interferon-dependent STAT1 activation, and diminished induction of interferon-stimulated genes (ISGs). Adenoviruses that infect through the coxsackievirus-adenovirus receptor (CAR) (Ad2 and Ad5) and the CD46 (Ad35) and desmoglein-2 (Ad7) viral receptors all induce the cGAS/STING/TBK1/IRF3 cascade. The magnitude of the IRF3/IFN/ISG antiviral response was strongly influenced by serotype, with Ad35>Ad7>Ad2. For each serotype, no enhancement of viral DNA replication or virus production occurred in cGAS or STING shRNA-targeted cell line pools. We found no replication advantage in permissive cell lines that do not trigger the cGAS/STING cascade following infection. The cGAS/STING/TBK1/IRF3 cascade was not a direct target of viral antihost strategies, and we found no evidence that Ad stimulation of the cGAS/STING DNA response had an impact on viral replication efficiency.

IMPORTANCE

This study shows for the first time that the cGAS DNA sensor directs a dominant IRF3/IFN/ISG antiviral response to adenovirus in human cell lines. Activation of cGAS occurs with viruses that infect through different high-affinity receptors (CAR, CD46, and desmoglein-2), and the magnitude of the cGAS/STING DNA response cascade is influenced by serotype-specific functions. Furthermore, activation of the cGAS cascade occurred in a cell-specific manner. Activation of the cGAS/STING response did not impact viral replication, and viral immune evasion strategies did not target the cGAS/STING/TBK1/IRF3 cascade. These studies provide novel insight into the early innate recognition response to adenovirus.

Progress in gene therapy for heart failure

Recent advances in our understanding of the pathophysiology of myocardial dysfunction in the setting of congestive heart failure have created a new opportunity in developing nonpharmacological approaches to treatment. Gene therapy has emerged as a powerful tool in targeting the molecular mechanisms of disease by preventing the ventricular remodeling and improving bioenergetics in heart failure. Refinements in vector technology, including the creation of recombinant adeno-associated viruses, have allowed for safe and efficient gene transfer. These advancements have been coupled with evolving delivery methods that include vascular, pericardial, and direct myocardial approaches. One of the most promising targets, SERCA2a, is currently being used in clinical trials. The recent success of the Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease phase 2 trials using adeno-associated virus 1-SERCA2a in improving outcomes highlights the importance of gene therapy as a future tool in treating congestive heart failure.

Adenovirus detection by the cGAS/STING/TBK1 DNA sensing cascade

Adenovirus (Ad) infection triggers a cell-specific antiviral response following exposure of viral DNA to the intracellular compartment. A variety of DNA sensors (DAI, AIM2, DDx41, RNA polymerase [Pol] III, and IFI16 [p204]) have been identified in recent years; however, the DNA sensor involved in detection of adenovirus has not been established. Cyclic GMP-AMP synthase (cGAS), a DNA sensor that produces a cyclic guanine-adenine dinucleotide (cGAMP) inducer of STING, has been examined to determine its role in generating an antiadenoviral response. Short hairpin RNA (shRNA) lentiviral vectors targeting TBK1, STING, and cGAS were established in murine MS1 endothelial and RAW 264.7 macrophage cell lines. Knockdown of TBK1, STING, and cGAS results in a dramatic reduction in the activation of the primary antiviral response marker phosphorylated interferon (IFN) response factor 3 (IRF3) following exposure to adenovirus. Furthermore, activation of secondary type I IFN signaling targets ((ptyr)STAT1 and (ptyr)STAT2 [(ptyr)STAT1/2]) was also compromised. Consistent with compromised activation of primary and secondary response markers, transcriptional activation of IRF3-responsive genes (beta IFN [IFN-β], ISG15, ISG54) and secondary response transcripts were diminished in cells knocked down in cGAS, STING, or TBK1. These data establish cGAS as the dominant cytosolic DNA sensor responsible for detection of internalized adenovirus leading to induction of the type I interferon antiviral cascade.

Gene therapy for cardiovascular disease: perspectives and potential

Cardiovascular disease is the most frequent cause of mortality in the western world, accounting for over 800,000 premature deaths per year in the EU alone. Cardiovascular disease is the second most common application for gene therapy clinical trials, which most frequently employ adenovirus serotype 5 (Ad5)-based vectors as delivery vehicles. Although interactions of Ad5 vectors with circulating proteins and cells can limit their efficacy after systemic administration, local gene delivery strategies show great potential in the cardiovascular setting, notably in the context of vascular delivery. Here we review the pathogenesis of bypass graft failure and in-stent restenosis, identifying potential therapeutic targets and discussing recent advances in the field of adenovirus biology and retargeting that, in concert, will potentially translate in coming years to more effective gene therapies for cardiovascular applications.

Cell-specific regulation of nucleic acid sensor cascades: a controlling interest in the antiviral response

In this study, we examined the capacities of non-antigen-presenting cell types to propagate antiviral signals following infection with recombinant adenovirus or by direct nucleic acid transfection. Three murine cell lines (RAW264.7 macrophages as a positive control, FL83B hepatocytes, and MS1 endothelial cells) were assessed following exposure to adenovirus, DNA, or RNA ligands. Based on primary (interferon response factor 3 [IRF3] phosphorylation) and secondary (STAT1/2 phosphorylation) response markers, we found each cell line presented a unique response profile: RAW cells were highly responsive, MS1 cells were modified in their response, and FL83B cells were essentially nonresponsive. Comparative reverse transcription-quantitative PCR (RT-qPCR) of nucleic acid sensing components revealed major differences between the three cell types. A prominent difference was at the level of adaptor molecules; TRIF, MyD88, MAVS, and STING. TRIF was absent in MS1 and FL83B cells, whereas MyD88 levels were diminished in FL83B hepatocytes. These differences resulted in compromised TLR-mediated activation. While the cytosolic adaptor MAVS was well represented in all cell lines, the DNA adaptor STING was deficient in FL83B hepatocytes (down by nearly 3 log units). The absence of STING provides an explanation for the lack of DNA responsiveness in these cells. This hypothesis was confirmed by acquisition of IRF3 activation in Flag-STING FL83B cells following DNA transfection. To consolidate the central role of adaptors in MS1 endothelial cells, short hairpin RNA (shRNA) knockdown of STING and MAVS resulted in a ligand-specific loss of IRF3 responsiveness. In contrast to the requirement for specific adaptor proteins, a requirement for a specific DNA sensor (AIM2, DDx41, or p204) in the IRF3 activation response was not detected by shRNA knockdown in MS1 cells. The data reveal that cell-specific regulation of nucleic acid sensing cascade components influences antiviral recognition responses, that controlling levels of adaptor molecules is a recurring strategy in regulating antiviral recognition response functions, and that comparative RT-qPCR has predictive value for antiviral/innate response functions in these cells.

Novel recombinant alphaviral and adenoviral vectors for cancer immunotherapy

Although cellular immunotherapy based on autolgous dendritic cells (DCs) targeting antigens expressed by metastatic cancer has demonstrated clinical efficacy, the logistical challenges in generating an individualized cell product create an imperative to develop alternatives to DC-based cancer vaccines. Particularly attractive alternatives include in situ delivery of antigen and activation signals to resident antigen-presenting cells (APCs), which can be achieved by novel fusion molecules targeting the mannose receptor and by recombinant viral vectors expressing the antigen of interest and capable of infecting DCs. A particular challenge in the use of viral vectors is the well-appreciated clinical obstacles to their efficacy, specifically vector-specific neutralizing immune responses. Because heterologous prime and boost strategies have been demonstrated to be particularly potent, we developed two novel recombinant vectors based on alphaviral replicon particles and a next-generation adenovirus encoding an antigen commonly overexpressed in many human cancers, carcinoembryonic antigen (CEA). The rationale for developing these vectors, their unique characteristics, the preclinical studies and early clinical experience with each, and opportunities to enhance their effectiveness will be reviewed. The potential of each of these potent recombinant vectors to efficiently generate clinically active anti-tumor immune response alone, or in combination, will be discussed.

Virus chimeras for gene therapy, vaccination, and oncolysis: adenoviruses and beyond

Several challenges need to be addressed when developing viruses for clinical applications in gene therapy, vaccination, or viral oncolysis, including specific and efficient target cell transduction, virus delivery via the blood stream, and evasion of pre-existing immunity. With rising frequency, these goals are tackled by generating chimeric viruses containing nucleic acid fragments or proteins from two or more different viruses, thus combining different beneficial features of the parental viruses. These chimeras have boosted the development of virus-based treatment regimens for major inherited and acquired diseases, including cancer. Using adenoviruses as the paradigm and prominent examples from other virus families, we review the technological and functional advances in therapeutic virus chimera development and recent successful applications that can pave the way for future therapies.

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.

Sensing adenovirus infection: activation of interferon regulatory factor 3 in RAW 264.7 cells

We have used the RAW 264.7 murine macrophage-like cell line as a platform to characterize the recognition and early signaling response to recombinant adenoviral vectors (rAdV). Infection of RAW 264.7 cells triggers an early response (2 to 6 h postinfection) that includes phosphorylation of the interferon (IFN) response factor 3 (IRF3) transcription factor, upregulation of IRF3 primary response genes (interferon-stimulated gene 56 [ISG56], beta IFN [IFN-β]), and subsequent type I IFN secondary signaling (STAT1/2 phosphorylation). Using short hairpin RNA (shRNA) lentiviral vectors, we show an essential role for Tank binding kinase 1 (TBK1) in this pathway. Data also support a role for STING (MITA) as an adaptor functioning in response to rAdV infection. Using UV/psoralen (Ps)-inactivated virus to block viral transcription, Ps-inactivated virus stimulated primary (IRF3) and secondary (STAT1/2) activation events to the same degree as untreated virus. IRF3 phosphorylation was not blocked in RAW 264.7 cells pretreated with the RNA polymerase III inhibitor ML60218. However, they were compromised in the type I IFN-dependent secondary response (phosphorylation of STAT1/STAT2). At 24 h postinfection, ML60218-treated cells were compromised in the overall antiviral response. Therefore, initial sensing of rAdV or viral DNA (vDNA) does not depend on viral template transcription, but ML60218 treatment influences cellular cascades required for an antiviral response to rAdV. Using overexpression or knockdown assays, we examined how four DNA sensors influence the antiviral response. Knockdown of DNA Activator of Interferon (DAI) and p204, the murine ortholog to IFI16, had minimal influence on IRF3 phosphorylation. However, knockdown of absent in melanoma 2 (AIM2) and the helicase DDX41 resulted in diminished levels of (pser388)IRF3 following rAdV infection. Based on these data, multiple DNA sensors contribute to an antiviral DNA recognition response, leading to TBK1-dependent IRF3 phosphorylation in RAW 264.7 cells.

Adenovirus: a blueprint for non-viral gene delivery

Although adenoviral vectors may not find a direct clinical role in gene therapy, an understanding of the mechanisms of DNA delivery that adenoviruses use is of vital importance to the design of next-generation non-viral gene delivery systems. Adenoviruses overcome a series of biological barriers, including endosomal escape, intracellular trafficking, capsid dissociation, and nuclear import of DNA, to deliver their genome to the host cell nucleus. The understanding of these processes at the molecular level is progressing and is set to inform the design of synthetic gene delivery systems.

The influence of innate and pre-existing immunity on adenovirus therapy

Recombinant adenovirus serotype 5 (Ad5) vectors have been studied extensively in preclinical gene therapy models and in a range of clinical trials. However, innate immune responses to adenovirus vectors limit effectiveness of Ad5 based therapies. Moreover, extensive pre-existing Ad5 immunity in human populations will likely limit the clinical utility of adenovirus vectors, unless methods to circumvent neutralizing antibodies that bind virus and block target cell transduction can be developed. Furthermore, memory T cell and humoral responses to Ad5 are associated with increased toxicity, raising safety concerns for therapeutic adenovirus vectors in immunized hosts. Most preclinical studies have been performed in naïve animals; although pre-existing immunity is among the greatest hurdles for adenovirus therapies, it is also one of the most neglected experimentally. Here we summarize findings using adenovirus vectors in naïve animals, in Ad-immunized animals and in clinical trials, and review strategies proposed to overcome innate immune responses and pre-existing immunity.

Evaluation of biodistribution and safety of adenovirus vector containing MDR1 in mice

Background

The aim of this study is to examine the safety and distribution of Ad-EGFP-MDR1, an adenovirus encoding human multidurg resistance gene (human MDR1), in the mice colon carcinoma model.

Methods

After bone marrow cells (BMCs) were infected with Ad-EGFP-MDR1, they were administered by intra bone marrow-bone marrow transplantation (IBM-BMT). Total adenovirus antibody and serum adenovirus neutralizing factor (SNF) were determined. Biodistribution of Ad-EGFP-MDR1 was detected by in situ hybridization and immunohistochemistry. The peripheral hematocyte white blood cell (WBC), haemoglobin (Hb), red blood cell (RBC) and platelet (Plt) counts were analyzed.

Results

Neither total adenovirus antibody nor SNF increased weeks after BMT. In situ hybridization and immunohistochemistry demonstrated concordant expression of human MDR1 and P-gp which were found in lung, intestine, kidney and BMCs after BMT, but not detected in liver, spleen, brain and tumor. No significant abnormality of the recovery hematocyte was observed on Day 30 after treatment.

Conclusion

The results indicate that IBM-BMT administration of a replication defective adenovirus is a feasible mode of delivery, allowing exogenous transference. The findings in this study are conducted for the future long-term studies of safety assessment of Ad-EGFP-MDR1.

Serotype 5 Adenovirus fiber (F7F41S) chimeric vectors incur packaging deficiencies when targeting peptides are inserted into Ad41 short fiber

Adenovirus is a well-established viral gene transfer model system that presents two major hurdles when being considered for cell-specific targeting applications. First is the need to detarget the vector from inherent host binding mechanisms, and second is the need to establish a productive and stable method to retarget the vector to a desired cell receptor. In previous studies we had generated an adenovirus vector platform that lacks the normal targeting attributes derived from the fiber and penton capsid proteins. In the current study we characterized our detargeted Ad5-based vectors (Ad5.F7F41S and Ad5.F7F41SDeltaRGD) as platforms for novel retargeted viruses. The experimental strategy relied on incorporating small peptide ligands into several sites of the Ad 41short fiber knob domain (AB, CD, HI, G and Cterm). Reengineering of Ad41 short fiber resulted either in a bypass to fiber 7 usage, or in a dominant negative packaging/production deficiency phenotype. Under specific growth conditions we could remedy some of the capsid deficiencies and generate high titer viruses. However when examined by Western blot analysis, the resulting viruses were still defective in capsid content. The tandem fiber F7F41S platform has revealed an unanticipated sensitivity of Adenovirus packaging to fiber 41short structural modifications. These studies indicate fiber assembly into an intact virion or fiber influenced capsid stability as a bottleneck to efficient particle production. We also demonstrate that virus particles characterized as mature virions following CsCl banding can vary significantly in capsid protein content. Considering the complexity of virus entry into a target cell, modified "mature virions" may be compromised at the level of transduction not only through the intended modification, but also by virtue of secondary structural packaging conflicts.

Virus binding to a plasma membrane receptor triggers interleukin-1 alpha-mediated proinflammatory macrophage response in vivo

The recognition of viral components by host pattern-recognition receptors triggers the induction of the antiviral innate immune response. Toll-like receptor 9 (TLR9) and NLRP3 inflammasome were shown to be the principal specific sensors of viral double-stranded DNA. Here we present evidence that macrophages in vivo activated an innate immune response to a double-stranded DNA virus, adenovirus (Ad), independently of TLR9 or NLRP3 inflammasome. In response to Ad, macrophage-derived IL-1 alpha triggered IL-1RI-dependent production of a defined set of proinflammatory cytokines and chemokines. The IL-1 alpha-mediated response required a selective interaction of virus arginine-glycine-aspartic acid (RGD) motifs with macrophage beta(3) integrins. Thus, these data identify IL-1 alpha-IL-1RI as a key pathway allowing for the activation of proinflammatory responses to the virus, independently of its genomic nucleic acid recognition.

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 induction of IRF3 occurs through a binary trigger targeting Jun N-terminal kinase and TBK1 kinase cascades and type I interferon autocrine signaling

Pathogen recognition is a critical function of immune sentinel cells. Naïve macrophages or dendritic cells (DCs) undergo pathogen-directed activation and maturation, and as mature antigen-presenting cells (APCs), they contribute essential functions to both innate and adaptive immunity. Using recombinant adenovirus (rAdV) as a model for murine APC activation by DNA viruses, we demonstrate a critical role for stress kinase activation in cell intrinsic and extrinsic antiviral signaling cascades. We propose two viral triggers, viral capsid and viral DNA, are required for APC activation. Endosomal escape and presentation of cytosolic rAdV DNA induces phosphorylation of TANK-binding kinase 1 (TBK1) at serine 172 but does not induce IkappaB kinase epsilon activity as determined by in vitro kinase assays. However, induction of TBK1 alone is not sufficient for interferon regulatory factor 3 (IRF3) phosphorylation. We show that capsid-dependent activation of Jun N-terminal kinase (JNK) stress kinase is a necessary step, licensing TBK1 phosphorylation of IRF3 at Ser 396. A second later phase of JNK activity is required to coordinate phosphorylation of JNK-dependent transcription factors (c-Jun/ATF2) with activated IRF3 in the induction of primary IRF3-responsive transcripts. Finally, we demonstrate that maximal JNK/TBK1/IRF3 stimulation by rAdV depends on an intact type I interferon (IFN) signaling cascade. By requiring multiple viral triggers and type I IFN autocrine regulation, APCs have an inherent fail-safe mechanism against inappropriate activation and maturation.

Sensing infection by adenovirus: Toll-like receptor-independent viral DNA recognition signals activation of the interferon regulatory factor 3 master regulator

Infection with adenovirus vectors (AdV) results in rapid activation of innate immunity, which serves the dual purpose of stimulating inflammatory antiviral host defenses and the adaptive immune system. Viral recognition by macrophages, dendritic cells, and other cell types requires an ability to sense the presence of a foreign molecular pattern by "pattern recognition receptors." The nature of the adenoviral sensor, the target ligand of the sensor, and the downstream antiviral signaling response triggered by virus infection have not been defined for this nonenveloped double-stranded DNA (dsDNA) virus. We have identified four critical links involved in AdV recognition by murine antigen-presenting cells (APC) and primary lung fibroblasts: (i) viral recognition occurs chiefly via a Toll-like receptor (TLR)-independent nucleic acid-sensing mechanism recognizing the viral dsDNA genome, (ii) the intact viral particle and capsid proteins are required for efficient intracellular delivery of the viral genome, (iii) delivery of the viral genome triggers interferon regulatory factor 3 (IRF3) phosphorylation, and (iv) IRF3 activation is the required dominant antiviral signaling pathway used by APC, whereas the "primary" involvement of NF-kappaB, mitogen-activated protein kinase, or Akt pathways is less prominent. In this study we provide the first direct evidence that infection by a dsDNA virus stimulates an IRF3-mediated interferon and proinflammatory response through a TLR-independent DNA-sensing mechanism.