Coagulation factor X shields adenovirus type 5 from attack by natural antibodies and complement

Tropism and transduction of oncolytic adenovirus 5 vectors in cancer therapy: Focus on fiber chimerism and mosaicism, hexon and pIX

The cellular internalization (infection of cells) of adenovirus 5 (Ad5) is mediated by the initial attachment of the globular knob domain of the capsid fiber protein to the cell surface coxsackievirus and adenovirus receptor (CAR), then followed by the interaction of the virus penton base proteins with cellular integrins. In tumors, there is a substantial intra- and intertumoral variability in CAR expression. The CAR-negative cells generally exhibit very low infectability. Since the fiber knob is a primary mediator of Ad5 binding to the cell surface, improved infectivity of Ad5-based vectors as oncolytic agents may be achieved via genetic modifications of this domain. The strategies to modify or broaden tropism and increase transduction efficiency of Ad5-based vectors include: 1) an incorporation of a targeting peptide into the fiber knob domain (the HI loop and/or C-terminus); 2) fiber knob serotype switching, or pseudotyping, by constructing chimeric fibers consisting of the knob domain derived from an alternate serotype (e.g., Ad5/3 or Ad5/35 chimeras), which binds to receptor(s) other than CAR (e.g., desmoglein 2/DSG2 and/or CD46); 3) "fiber complex mosaicism", an approach of combining serotype chimerism with peptide ligand(s) incorporation (e.g., Ad5/3-RGD); 4) "dual fiber mosaicism" by expressing two separate fibers with distinct receptor-binding capabilities on the same viral particle (e.g., Ad5-5/3 or Ad5-5/σ1); 5) fiber xenotyping by replacing the knob and shaft domains of wild-type Ad5 fiber protein with fibritin trimerization domain of T4 bacteriophage or σ1 attachment protein of reovirus. Other genetic approaches to increase the CAR-independent transduction efficiency include insertion of a targeting peptide into the hypervariable region of the capsid protein hexon or fusion to the C-terminus of pIX. Finally, we consider a yet unsolved molecular mechanism of liver targeting by Ad5-based vectors (CAR-, integrin-, fiber shaft KKTK motif-, and hepatic heparan sulfate glycosaminoglycans-independent, but fiber-, hexon- and blood factor X-dependent).

Virotherapy Research in Germany: From Engineering to Translation

Virotherapy is a unique modality for the treatment of cancer with oncolytic viruses (OVs) that selectively infect and lyse tumor cells, spread within tumors, and activate anti-tumor immunity. Various viruses are being developed as OVs preclinically and clinically, several of them engineered to encode therapeutic proteins for tumor-targeted gene therapy. Scientists and clinicians in German academia have made significant contributions to OV research and development, which are highlighted in this review paper. Innovative strategies for "shielding," entry or postentry targeting, and "arming" of OVs have been established, focusing on adenovirus, measles virus, parvovirus, and vaccinia virus platforms. Thereby, new-generation virotherapeutics have been derived. Moreover, immunotherapeutic properties of OVs and combination therapies with pharmacotherapy, radiotherapy, and especially immunotherapy have been investigated and optimized. German investigators are increasingly assessing their OV innovations in investigator-initiated and sponsored clinical trials. As a prototype, parvovirus has been tested as an OV from preclinical proof-of-concept up to first-in-human clinical studies. The approval of the first OV in the Western world, T-VEC (Imlygic), has further spurred the involvement of investigators in Germany in international multicenter studies. With the encouraging developments in funding, commercialization, and regulatory procedures, more German engineering will be translated into OV clinical trials in the near future.

Capsid Engineering of Adenovirus Vectors: Overcoming Early Vector-Host Interactions for Therapy

Adenovirus-based vectors comprise the most frequently used vector type in clinical studies to date. Both intense lab research and insights from the clinical trials reveal the importance of a comprehensive understanding of vector-host interactions. Especially for systemic intravenous adenovirus vector delivery, it is paramount to develop safe and efficacious vectors. Very early vector-host interactions that take place in blood long before the first cell is being transduced are phenomena triggered by the surface, shape, and size of the adenovirus vector particles. Not surprisingly, a multitude of different technologies ranging from genetics to chemistry has been developed to alter the adenovirus vector surface. In this review, we discuss the most important technologies and evaluate them for their suitability to overcome hurdles imposed by early vector-host interactions.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Polysialic acid is a cellular receptor for human adenovirus 52

We present here that adenovirus type 52 (HAdV-52) attaches to target cells through a mechanism not previously observed in other human pathogenic viruses. The interaction involves unusual, transient, electrostatic interactions between the short fiber capsid protein and polysialic acid (polySia)-containing receptors on target cells. Knowledge about the binding interactions between polySia and its natural ligands is relatively limited, and our results therefore provide additional insight not only into adenovirus biology but also into the structural basis of polySia function. Since polySia can be found in high expression levels in brain and lung cancers where its presence is associated with poor prognosis, we suggest that this polySia-binding adenovirus could be useful for design of vectors for gene therapy of these cancers.

Human adenovirus 52 (HAdV-52) is one of only three known HAdVs equipped with both a long and a short fiber protein. While the long fiber binds to the coxsackie and adenovirus receptor, the function of the short fiber in the virus life cycle is poorly understood. Here, we show, by glycan microarray analysis and cellular studies, that the short fiber knob (SFK) of HAdV-52 recognizes long chains of α-2,8-linked polysialic acid (polySia), a large posttranslational modification of selected carrier proteins, and that HAdV-52 can use polySia as a receptor on target cells. X-ray crystallography, NMR, molecular dynamics simulation, and structure-guided mutagenesis of the SFK reveal that the nonreducing, terminal sialic acid of polySia engages the protein with direct contacts, and that specificity for polySia is achieved through subtle, transient electrostatic interactions with additional sialic acid residues. In this study, we present a previously unrecognized role for polySia as a cellular receptor for a human viral pathogen. Our detailed analysis of the determinants of specificity for this interaction has general implications for protein–carbohydrate interactions, particularly concerning highly charged glycan structures, and provides interesting dimensions on the biology and evolution of members of Human mastadenovirus G.

A novel capsid-modified oncolytic recombinant adenovirus type 5 for tumor-targeting gene therapy by intravenous route

Oncolytic adenovirus (Ad)-vectored gene therapy is a promising strategy for cancer treatment. However, the lack of cancer cell selectivity or tumor tissue specificity of Ads limits their clinical application by intravenous (IV) injection. In this paper, a novel recombinant Ad5 vector was constructed carrying the capsid protein IX modified by the tumor necrosis factor related apoptosis-inducing ligand (TRAIL), which targets tumor cells bearing high levels of its receptor far above those of normal cells. Specific association of the Ad virion with TRAIL was achieved using synthetic leucine zipper-like dimerization domains (zippers). Analysis of the chemical properties of the modified recombinant Ad (rAd5pz-zTRAIL-RFP) showed that the TRAIL protein was present on the surface of purified virus particles, and it could induce apoptosis of infected cancer cells prior to expression of foreign genes. We also constructed a novel modified recombinant oncolytic Ad (rAd5pz-zTRAIL-RFP-SΔ24E1a) which showed significantly enhanced anti-tumor effects both in vitro and in vivo by linkage of TRAIL to the viral capsid. Moreover, rAd5pz-zTRAIL-RFP-SΔ24E1a showed significantly improved tumor tissue targeting and reduced liver tropism when IV injected in vivo. Thus, we successfully obtained new oncolytic Ad5 gene therapy vectors with enhanced targeting and efficacy, providing a platform for further clinical application of Ad vectors for cancer treatment.

Hexons from adenovirus serotypes 5 and 48 differentially protect adenovirus vectors from neutralization by mouse and human serum

Adenovirus vectors are widely used in gene therapy clinical trials, and preclinical studies with these vectors are often conducted in mice. It is therefore critical to understand whether mouse studies adequately predict the behavior of adenovirus vectors in humans. The most commonly-used adenovirus vectors are derived from adenovirus serotype 5 (Ad5). The Ad5 hexon protein can bind coagulation factor X (FX), and binding of FX has a major impact on vector interactions with other blood proteins. In mouse serum, FX protects Ad5 vectors from neutralization by natural antibodies and complement. In the current study, we similarly find that human FX inhibits neutralization of Ad5 vectors by human serum, and this finding is consistent among individual human sera. We show that human IgM and human IgG can each induce complement-mediated neutralization when Ad5 vectors are not protected by FX. Although mouse and human serum had similar effects on Ad5 vectors, we found that this was not true for a chimeric Ad5 vector that incorporated hexon regions from adenovirus serotype 48. Interestingly, this hexon-chimeric vector was neutralized by human serum, but not by mouse serum. These findings indicate that studies in mouse serum accurately predict the behavior of Ad5 vectors in human serum, but mouse serum is not an accurate model system for all adenovirus vectors.

Adenoviral vector with shield and adapter increases tumor specificity and escapes liver and immune control

Most systemic viral gene therapies have been limited by sequestration and degradation of virions, innate and adaptive immunity, and silencing of therapeutic genes within the target cells. Here we engineer a high-affinity protein coat, shielding the most commonly used vector in clinical gene therapy, human adenovirus type 5. Using electron microscopy and crystallography we demonstrate a massive coverage of the virion surface through the hexon-shielding scFv fragment, trimerized to exploit the hexon symmetry and gain avidity. The shield reduces virion clearance in the liver. When the shielded particles are equipped with adaptor proteins, the virions deliver their payload genes into human cancer cells expressing HER2 or EGFR. The combination of shield and adapter also increases viral gene delivery to xenografted tumors in vivo, reduces liver off-targeting and immune neutralization. Our study highlights the power of protein engineering for viral vectors overcoming the challenges of local and systemic viral gene therapies.

Viral gene therapy can be limited by the efficacy of virion sequestration, immune responses and the silencing of genetic payloads. Here the authors engineer an advenovirus protein coat which shields the virion from the immune system while targeting cancer cells.

Blood Coagulation Factor X Exerts Differential Effects on Adenovirus Entry into Human Lymphocytes

It has been proposed that blood coagulation factors, principally factor X (FX), enhance the uptake of human adenovirus type 5 (Ad5) into cultured epithelial cells by bridging the viral hexon capsid protein and cell-surface heparan sulphate proteoglycans (HSPGs). We studied the effects of FX on Ad transduction of lymphoid cell lines (NK92MI, a natural killer cell line; Daudi, a B-cell line and Jurkat, a T-cell line) as well as primary peripheral blood lymphocytes (PBL) and HeLa epithelial cells using either replication-deficient Ad5, or a derivative in which the Ad5 fiber was replaced with that of another Ad type, Ad35, termed Ad5F35. PBL and NK92MI were resistant to Ad5 transduction. Transduction of Jurkat and Daudi cells by Ad5 was reduced by FX but without discernible effects on cell-surface Ad5 binding. FX reduced virus binding and transduction of all lymphoid cell lines by Ad5F35, as well as transduction of the T- and Natural Killer (NK)-cell populations of PBL. Flow cytometry analysis showed that all lymphoid cell lines were negative for HSPG components, in contrast to HeLa cells. FX reduced transduction of an HSPG-negative mutant Chinese hamster ovary cell line (CHOpgsA745) by Ad5 and Ad5F35, with Ad5F35 binding also being reduced by FX. These results point to fiber-dependent differences (Ad5 versus Ad35 fiber) in Ad binding to and transduction of human lymphoid and epithelial cells in the presence of FX.

Retargeted and detargeted adenovirus for gene delivery to the muscle

We previously selected muscle binding peptides 12.51 and 12.52 from "context-specific" phage display libraries for introduction into adenovirus (Ad) vectors. In this work, these peptides were inserted into the hypervariable region (HVR) 5 loop of the Ad5 hexon protein to display 720 peptides per virions. HVR-12.51 and 12.52 increased transduction of C2C12 cells up to 20-fold when compared to unmodified Ad5. 12.51 increased in vivo muscle transduction 2 to 7-fold over unmodified Ad after intramuscular injection in mice and hamsters. 12.52 did not increase muscle transduction. Notably, insertion of 12.51 into the hexon reduced liver transduction 80-fold when compared to unmodified Ad5 after intravenous injection. Increased muscle transduction in mice translated into increased immune responses after gene-based vaccination. These data suggest there are merits to retargeting and detargeting benefits to modifying the hexons of Ads with peptide ligands.

Comparison of Liver Detargeting Strategies for Systemic Therapy with Oncolytic Adenovirus Serotype 5

Oncolytic viruses would ideally be of use for systemic therapy to treat disseminated cancer. To do this safely, this may require multiple layers of cancer specificity. The pharmacology and specificity of oncolytic adenoviruses can be modified by (1) physical retargeting, (2) physical detargeting, (3) chemical shielding, or (4) by modifying the ability of viral early gene products to selectively activate in cancer versus normal cells. We explored the utility of these approaches with oncolytic adenovirus serotype 5 (Ad5) in immunocompetent Syrian hamsters bearing subcutaneous HaK tumors. After a single intravenous injection to reach the distant tumors, the physically hepatocyte-detargeted virus Ad5-hexon-BAP was more effective than conditionally replicating Ad5-dl1101/07 with mutations in its E1A protein. When these control or Ad5 treated animals were treated a second time by intratumoral injection, prior exposure to Ad5 did not affect tumor growth, suggesting that anti-Ad immunity neither prevented treatment nor amplified anti-tumor immune responses. Ad5-dl1101/07 was next chemically shielded with polyethylene glycol (PEG). While 5 kDa of PEG blunted pro-inflammatory IL-6 production induced by Ad5-dl1101/07, this shielding reduced Ad oncolytic activity.

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.

Advancing Public Health Using Regulatory Science to Enhance Development and Regulation of Medical Products: Food and Drug Administration Research at the Center for Biologics Evaluation and Research

Center for Biologics Evaluation and Research enhances and supports regulatory decision-making and policy development. This work contributes to our regulatory mission, advances medical product development, and supports Food and Drug Administration’s regulatory response to public health crises. This review presents some examples of our diverse scientific work undertaken in recent years to support our regulatory and public health mission.

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

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

Recent advances in genetic modification of adenovirus vectors for cancer treatment

Adenoviruses are widely used to deliver genes to a variety of cell types and have been used in a number of clinical trials for gene therapy and oncolytic virotherapy. However, several concerns must be addressed for the clinical use of adenovirus vectors. Selective delivery of a therapeutic gene by adenovirus vectors to target cancer is precluded by the widespread distribution of the primary cellular receptors. The systemic administration of adenoviruses results in hepatic tropism independent of the primary receptors. Adenoviruses induce strong innate and acquired immunity in vivo. Furthermore, several modifications to these vectors are necessary to enhance their oncolytic activity and ensure patient safety. As such, the adenovirus genome has been engineered to overcome these problems. The first part of the present review outlines recent progress in the genetic modification of adenovirus vectors for cancer treatment. In addition, several groups have recently developed cancer-targeting adenovirus vectors by using libraries that display random peptides on a fiber knob. Pancreatic cancer-targeting sequences have been isolated, and these oncolytic vectors have been shown by our group to be associated with a higher gene transduction efficiency and more potent oncolytic activity in cell lines, murine models, and surgical specimens of pancreatic cancer. In the second part of this review, we explain that combining cancer-targeting strategies can be a promising approach to increase the clinical usefulness of oncolytic adenovirus vectors.

Cryo-EM structure of human adenovirus D26 reveals the conservation of structural organization among human adenoviruses

Human adenoviruses (HAdVs) cause acute respiratory, ocular, and gastroenteric diseases and are also frequently used as gene and vaccine delivery vectors. Unlike the archetype human adenovirus C5 (HAdV-C5), human adenovirus D26 (HAdV-D26) belongs to species-D HAdVs, which target different cellular receptors, and is differentially recognized by immune surveillance mechanisms. HAdV-D26 is being championed as a lower seroprevalent vaccine and oncolytic vector in preclinical and human clinical studies. To understand the molecular basis for their distinct biological properties and independently validate the structures of minor proteins, we determined the first structure of species-D HAdV at 3.7 Å resolution by cryo-electron microscopy. All the hexon hypervariable regions (HVRs), including HVR1, have been identified and exhibit a distinct organization compared to those of HAdV-C5. Despite the differences in the arrangement of helices in the coiled-coil structures, protein IX molecules form a continuous hexagonal network on the capsid exterior. In addition to the structurally conserved region (3 to 300) of IIIa, we identified an extra helical domain comprising residues 314 to 390 that further stabilizes the vertex region. Multiple (two to three) copies of the cleaved amino-terminal fragment of protein VI (pVIn) are observed in each hexon cavity, suggesting that there could be ≥480 copies of VI present in HAdV-D26. In addition, a localized asymmetric reconstruction of the vertex region provides new details of the three-pronged "claw hold" of the trimeric fiber and its interactions with the penton base. These observations resolve the previous conflicting assignments of the minor proteins and suggest the likely conservation of their organization across different HAdVs.

Complex formation with pentraxin-2 regulates factor X plasma levels and macrophage interactions

We have identified PTX2 as a novel partner for FX in the circulation, and their plasma levels are interdependent. FX and PTX2 cooperate with SR-AI to prevent their uptake by macrophages.

A Special Connection between γδ T Cells and Natural Antibodies?

Natural antibodies (NAbs) play an important role in early host defense, autophagy and tissue remodeling, and in immune regulation. They arise spontaneously (without specific immunization), and are already present at birth. NAbs are produced by B1 B cells, MZ B cells and other B cell types. They include all major Ig subclasses but IgM antibodies are prevalent, especially early in development. NAbs may be poly-specific, recognize particular auto-antigens, or detect neo-determinants such as those exposed during apoptosis or generated by oxidation. NAbs do not require cognate T cell help but depend on soluble mediators produced by T cells. Our recent studies suggest that γδ T cells may have a special relationship with NAbs, and play a prominent role in their regulation, in part through the fine-tuning of IL-4 levels. The spontaneously activated state of these cells likely enables their cytokine production and other functions in the absence of external stimulation. Ontogenetically, the earlier arising γδ T cells are better positioned than αβ T cells to shape the developing repertoire of NAbs. Intriguingly, ligand specificities of NAbs and γδ T cell receptors appear to be overlapping, perhaps allowing γδ cognate help for certain NAb specificities. Via NAbs, γδ T cells could exert a regulatory influence on numerous processes in health and disease.

CXCL12 retargeting of an adenovirus vector to cancer cells using a bispecific adapter

Ad vectors are promising delivery vehicles for cancer therapeutic interventions. However, their application is limited by promiscuous tissue tropism and hepatotoxicity. This limitation can be avoided by altering the native tropism of Ads so that they can be redirected to the target cells through alternate cellular receptors. The CXCR4 chemokine receptor belongs to a large superfamily of G-protein-coupled receptors and is known to be upregulated in a wide variety of cancers, including breast cancer and melanoma. These receptors have been associated with cancer cell survival, progression, and metastasis. In the current study, an Ad to cancer cells overexpressing CXCR4 by using a bispecific adapter, sCAR-CXCL12, was retargeted. The sCAR-CXCL12 adapter contained the soluble ectodomain form of the native Ad5 receptor (sCAR), which was fused to a mature human chemokine ligand, CXCL12, through a short peptide linker. A dramatic increase in the infectivity of cancer cells using a targeted Ad vector compared with an untargeted vector was observed. Furthermore, sCAR-CXCL12 attenuated Ad infection of liver ex vivo and in vivo and enhanced Ad vector infection of xenograft tumors implanted in immunodeficient SCID-bg mice. Thus, the sCAR-CXCL12 adapter could be used to retarget Ad vectors to chemokine receptor-positive tumors.

Oncolytic adenovirus-mediated therapy for prostate cancer

Prostate cancer is a leading cause of cancer-related death and morbidity in men in the Western world. Tumor progression is dependent on functioning androgen receptor signaling, and initial administration of antiandrogens and hormone therapy (androgen-deprivation therapy) prevent growth and spread. Tumors frequently develop escape mechanisms to androgen-deprivation therapy and progress to castration-resistant late-stage metastatic disease that, in turn, inevitably leads to resistance to all current therapeutics, including chemotherapy. In spite of the recent development of more effective inhibitors of androgen–androgen receptor signaling such as enzalutamide and abiraterone, patient survival benefits are still limited. Oncolytic adenoviruses have proven efficacy in prostate cancer cells and cause regression of tumors in preclinical models of numerous drug-resistant cancers. Data from clinical trials demonstrate that adenoviral mutants have limited toxicity to normal tissues and are safe when administered to patients with various solid cancers, including prostate cancer. While efficacy in response to adenovirus administration alone is marginal, findings from early-phase trials targeting local-ized and metastatic prostate cancer suggest improved efficacy in combination with cytotoxic drugs and radiation therapy. Here, we review recent progress in the development of multimodal oncolytic adenoviruses as biological therapeutics to improve on tumor elimination in prostate cancer patients. These optimized mutants target cancer cells by several mechanisms including viral lysis and by expression of cytotoxic transgenes and immune-stimulatory factors that activate the host immune system to destroy both infected and noninfected prostate cancer cells. Additional modifications of the viral capsid proteins may support future systemic delivery of oncolytic adenoviruses.

Substitution of blood coagulation factor X-binding to Ad5 by position-specific PEGylation: Preventing vector clearance and preserving infectivity

The biodistribution of adenovirus type 5 (Ad5) vector particles is heavily influenced by interaction of the particles with plasma proteins, including coagulation factor X (FX), which binds specifically to the major Ad5 capsid protein hexon. FX mediates hepatocyte transduction by intravenously-injected Ad5 vectors and shields vector particles from neutralization by natural antibodies and complement. In mice, mutant Ad5 vectors that are ablated for FX-binding become detargeted from hepatocytes, which is desirable for certain applications, but unfortunately such FX-nonbinding vectors also become sensitive to neutralization by mouse plasma proteins. To improve the properties of Ad5 vectors for systemic delivery, we developed a strategy to replace the natural FX shield by a site-specific chemical polyethylene glycol shield. Coupling of polyethylene glycol to a specific site in hexon hypervariable region 1 yielded vector particles that were protected from neutralization by natural antibodies and complement although they were unable to bind FX. These vector particles evaded macrophages in vitro and showed significantly improved pharmacokinetics and hepatocyte transduction in vivo. Thus, site-specific shielding of Ad5 vectors with polyethylene glycol rendered vectors FX-independent and greatly improved their properties for systemic gene therapy.

Evaluation of CD46 re-targeted adenoviral vectors for clinical ovarian cancer intraperitoneal therapy

Ovarian cancer accounts for >140 000 deaths globally each year. Typically, disease is asymptomatic until an advanced, incurable stage. Although response to cytotoxic chemotherapy is frequently observed, resistance to conventional platinum-based therapies develop rapidly. Improved treatments are therefore urgently required. Virotherapy offers great potential for ovarian cancer, where the application of local, intraperitoneal delivery circumvents some of the limitations of intravenous strategies. To develop effective, adenovirus (Ad)-based platforms for ovarian cancer, we profiled the fluid and cellular components of patient ascites for factors known to influence adenoviral transduction. Levels of factor X (FX) and neutralizing antibodies (nAbs) in ascitic fluid were quantified and tumor cells were assessed for the expression of coxsackie virus and adenovirus receptor (CAR) and CD46. We show that clinical ascites contains significant levels of FX but consistently high CD46 expression. We therefore evaluated in vitro the relative transduction of epithelial ovarian cancers (EOCs) by Ad5 (via CAR) and Ad5 pseudotyped with the fiber of Ad35 (Ad5T*F35++) via CD46. Ad5T*F35++ achieved significantly increased transduction in comparison to Ad5 (P<0.001), independent of FX and nAb levels. We therefore propose selective transduction of CD46 over-expressing EOCs using re-targeted, Ad35-pseudotyped Ad vectors may represent a promising virotherapy for ovarian cancer.

Retargeting FX-binding-ablated HAdV-5 to vascular cells by inclusion of the RGD-4C peptide in hexon hypervariable region 7 and the HI loop

Recent studies have generated interest in the function of human adenovirus serotype 5 (HAdV-5) hexon:  factor X (FX) binding and subsequent hepatocyte transduction and interaction with the immune system. Here, we retargeted adenovirus serotype 5 vectors, ablated for FX interaction, by replacing amino acids in hexon HVR7 with RGD-4C or inserting the peptide into the fibre HI loop. These genetic modifications in the capsid were compatible with virus assembly, and could efficiently retarget transduction of the vector via the αvβ3/5 integrin-mediated pathway, but did not alter immune recognition by pre-existing human neutralizing anti-HAdV-5 antibodies or by natural antibodies in mouse serum. Thus, FX-binding-ablated HAdV-5 can be retargeted but remain sensitive to immune-mediated attack. These findings further refine HAdV-5-based vectors for human gene therapy and inform future vector development.

Advances in systemic delivery of anti-cancer agents for the treatment of metastatic cancer

INTRODUCTION

The successful treatment of metastatic cancer is refractory to strategies employed to treat confined, primary lesions, such as surgical resection and radiation therapy, and thus must be addressed by systemic delivery of anti-cancer agents. Conventional systemically administered chemotherapeutics are often ineffective and come with severe dose-limiting toxicities.

AREAS COVERED

This review focuses on the recent developments in systemic therapy for metastatic cancer. Firstly, the strategies employed to improve the efficacy of conventional chemotherapeutics by 'passively' and 'actively' targeting them to tumors are discussed. Secondly, recent advances in the use of biologics to better target cancer and to instigate anti-tumor immunity are reviewed. Under the label of 'biologics', antibody-therapies, T cell engaging therapies, oncolytic virotherapies and cell-based therapies are examined and evaluated.

EXPERT OPINION

Improving specificity of action, and engaging the immune system appear to be key goals in the development of novel or reformulated anti-cancer agents for the treatment of metastatic cancer. One of the largest areas of opportunity in this field will be the identification of robust predictive biomarkers for use in conjunction with these agents. Treatment regimens that combine an agent to elicit an immune response (such as an oncolytic virus), and an agent to potentiate/mediate that immune response (such as immune checkpoint inhibitors) are predicted to be more effective than treatment with either agent alone.

The relevance of coagulation factor X protection of adenoviruses in human sera

Intravenous delivery of adenoviruses is the optimal route for many gene therapy applications. Once in the blood, coagulation factor X (FX) binds to the adenovirus capsid and protects the virion from natural antibody and classical complement-mediated neutralisation in mice. However, to date, no studies have examined the relevance of this FX/viral immune protective mechanism in human samples. In this study, we assessed the effects of blocking FX on adenovirus type 5 (Ad5) activity in the presence of human serum. FX prevented human IgM binding directly to the virus. In individual human sera samples (n=25), approximately half of those screened inhibited adenovirus transduction only when the Ad5–FX interaction was blocked, demonstrating that FX protected the virus from neutralising components in a large proportion of human sera. In contrast, the remainder of sera tested had no inhibitory effects on Ad5 transduction and FX armament was not required for effective gene transfer. In human sera in which FX had a protective role, Ad5 induced lower levels of complement activation in the presence of FX. We therefore demonstrate for the first time the importance of Ad–FX protection in human samples and highlight subject variability and species-specific differences as key considerations for adenoviral gene therapy.

Late-phase miRNA-controlled oncolytic adenovirus for selective killing of cancer cells

Tissue-specific detargeting by miRNAs has been demonstrated to be a potent strategy to restrict adenoviral replication to cancer cells. These studies have generated adenoviruses with miRNA target sites placed in the 3′UTR of early gene products. In this work, we have studied the feasibility of providing tissue-specific selectivity to replication-competent adenoviruses through the regulation of the late structural protein fiber (L5 gene). We have engineered a 3′UTR containing eight miR-148a binding sites downstream the L5 coding sequence (Ad-L5-8miR148aT). We present in vitro and in vivo evidences of Ad-L5-8miR148aT miRNA-dependent regulation. In vitro data show that at 72 hours post-infection miR-148a-regulation impaired fiber expression leading to a 70% reduction of viral release. The application of seven consecutive rounds of infection in miR-148a cells resulted in 10.000-fold reduction of viral genomes released. In vivo, liver production of infective viral particles was highly impaired, similarly to that triggered by an adenovirus with miRNA target sites regulating the early E1A gene. Noticeably, mice treated with Ad-L5-8miR148aT showed an attenuation of adenoviral-induced hepatotoxicity but retained full lytic activity in cancer cells and exhibited robust antitumoral responses in patient-derived xenografts. Thus, miRNA-control of late proteins constitutes a novel strategy to provide selectivity to adenoviruses.

Oncolytic Adenovirus: Strategies and Insights for Vector Design and Immuno-Oncolytic Applications

Adenoviruses (Ad) are commonly used both experimentally and clinically, including oncolytic virotherapy applications. In the clinical area, efficacy is frequently hampered by the high rates of neutralizing immunity, estimated as high as 90% in some populations that promote vector clearance and limit bioavailability for tumor targeting following systemic delivery. Active tumor targeting is also hampered by the ubiquitous nature of the Ad5 receptor, hCAR, as well as the lack of highly tumor-selective targeting ligands and suitable targeting strategies. Furthermore, significant off-target interactions between the viral vector and cellular and proteinaceous components of the bloodstream have been documented that promote uptake into non-target cells and determine dose-limiting toxicities. Novel strategies are therefore needed to overcome the obstacles that prevent efficacious Ad deployment for wider clinical applications. The use of less seroprevalent Ad serotypes, non-human serotypes, capsid pseudotyping, chemical shielding and genetic masking by heterologous peptide incorporation are all potential strategies to achieve efficient vector escape from humoral immune recognition. Conversely, selective vector arming with immunostimulatory agents can be utilized to enhance their oncolytic potential by activation of cancer-specific immune responses against the malignant tissues. This review presents recent advantages and pitfalls occurring in the field of adenoviral oncolytic therapies.

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.

Hepatocyte Heparan Sulfate Is Required for Adeno-Associated Virus 2 but Dispensable for Adenovirus 5 Liver Transduction In Vivo

Adeno-associated virus 2 (AAV2) and adenovirus 5 (Ad5) are promising gene therapy vectors. Both display liver tropism and are currently thought to enter hepatocytes in vivo through cell surface heparan sulfate proteoglycans (HSPGs). To test directly this hypothesis, we created mice that lack Ext1, an enzyme required for heparan sulfate biosynthesis, in hepatocytes. Ext1(HEP) mutant mice exhibit an 8-fold reduction of heparan sulfate in primary hepatocytes and a 5-fold reduction of heparan sulfate in whole liver tissue. Conditional hepatocyte Ext1 gene deletion greatly reduced AAV2 liver transduction following intravenous injection. Ad5 transduction requires blood coagulation factor X (FX); FX binds to the Ad5 capsid hexon protein and bridges the virus to HSPGs on the cell surface. Ad5.FX transduction was abrogated in primary hepatocytes from Ext1(HEP) mice. However, in contrast to the case with AAV2, Ad5 transduction was not significantly reduced in the livers of Ext1(HEP) mice. FX remained essential for Ad5 transduction in vivo in Ext1(HEP) mice. We conclude that while AAV2 requires HSPGs for entry into mouse hepatocytes, HSPGs are dispensable for Ad5 hepatocyte transduction in vivo. This study reopens the question of how adenovirus enters cells in vivo.

IMPORTANCE

Our understanding of how viruses enter cells, and how they can be used as therapeutic vectors to manage disease, begins with identification of the cell surface receptors to which viruses bind and which mediate viral entry. Both adeno-associated virus 2 and adenovirus 5 are currently thought to enter hepatocytes in vivo through heparan sulfate proteoglycans (HSPGs). However, direct evidence for these conclusions is lacking. Experiments presented herein, in which hepatic heparan sulfate synthesis was genetically abolished, demonstrated that HSPGs are not likely to function as hepatocyte Ad5 receptors in vivo. The data also demonstrate that HSPGs are required for hepatocyte transduction by AAV2. These results reopen the question of the identity of the Ad5 receptor in vivo and emphasize the necessity of demonstrating the nature of the receptor by genetic means, both for understanding Ad5 entry into cells in vivo and for optimization of Ad5 vectors as therapeutic agents.

Development of Novel Adenoviral Vectors to Overcome Challenges Observed With HAdV-5-based Constructs

Recombinant vectors based on human adenovirus serotype 5 (HAdV-5) have been extensively studied in preclinical models and clinical trials over the past two decades. However, the thorough understanding of the HAdV-5 interaction with human subjects has uncovered major concerns about its product applicability. High vector-associated toxicity and widespread preexisting immunity have been shown to significantly impede the effectiveness of HAdV-5–mediated gene transfer. It is therefore that the in-depth knowledge attained working on HAdV-5 is currently being used to develop alternative vectors. Here, we provide a comprehensive overview of data obtained in recent years disqualifying the HAdV-5 vector for systemic gene delivery as well as novel strategies being pursued to overcome the limitations observed with particular emphasis on the ongoing vectorization efforts to obtain vectors based on alternative serotypes.

Dextrose-mediated aggregation of therapeutic monoclonal antibodies in human plasma: Implication of isoelectric precipitation of complement proteins

Many therapeutic monoclonal antibodies (mAbs) are clinically administered through intravenous infusion after mixing with a diluent, e.g., saline, 5% dextrose. Such a clinical setting increases the likelihood of interactions among mAb molecules, diluent, and plasma components, which may adversely affect product safety and efficacy. Avastin® (bevacizumab) and Herceptin® (trastuzumab), but not Remicade® (infliximab), were shown to undergo rapid aggregation upon dilution into 5% dextrose when mixed with human plasma in vitro; however, the biochemical pathways leading to the aggregation were not clearly defined. Here, we show that dextrose-mediated aggregation of Avastin or Herceptin in plasma involves isoelectric precipitation of complement proteins. Using mass spectrometry, we found that dextrose-induced insoluble aggregates were composed of mAb itself and multiple abundant plasma proteins, namely complement proteins C3, C4, factor H, fibronectin, and apolipoprotein. These plasma proteins, which are characterized by an isoelectronic point of 5.5–6.7, lost solubility at the resulting pH in the mixture with formulated Avastin (pH 6.2) and Herceptin (pH 6.0). Notably, switching formulation buffers for Avastin (pH 6.2) and Remicade (pH 7.2) reversed their aggregation profiles. Avastin formed little, if any, insoluble aggregates in dextrose-plasma upon raising the buffer pH to 7.2 or above. Furthermore, dextrose induced pH-dependent precipitation of plasma proteins, with massive insoluble aggregates being detected at pH 6.5–6.8. These data show that isoelectric precipitation of complement proteins is a prerequisite of dextrose-induced aggregation of mAb in human plasma. This finding highlights the importance of assessing the compatibility of a therapeutic mAb with diluent and human plasma during product development.

Transient depletion of specific immune cell populations to improve adenovirus-mediated transgene expression in the liver

BACKGROUND & AIMS

Adenoviral (Ad) vectors are currently one of the most efficient tools for in vivo gene transfer to the liver. However, anti-Ad immune responses limit the safety and efficacy of these vectors. The initial inflammatory reaction is a concern in terms of toxicity, and it favours the development of cellular and humoral responses leading to short transgene persistence and inefficient vector re-administrations. Therefore, safe and simple ways to interfere with these processes are needed. Study ways to deplete specific immune cell populations and their impact on liver-directed gene transfer.

METHODS

First-generation Ad vectors encoding reporter genes (luciferase or β-galactosidase) were injected intravenously into Balb/c mice. Kupffer cells and splenic macrophages were depleted by intravenous administration of clodronate liposomes. B lymphocytes, CD4(+) , CD8(+) T lymphocytes or NK cells were depleted by intraperitoneal injection of anti-M plus anti-D, anti-CD4, anti-CD8 or anti-asialo-GM1 antibodies respectively. Long-term evolution of luciferase expression in the liver was monitored by bioluminescence imaging.

RESULTS

The anti-CD4 monoclonal antibody impaired cellular and humoral immune responses, leading to efficient vector re-administration. Clodronate liposomes had no impact on humoral responses but caused a 100-1000 fold increase in liver transduction, stabilized transgene expression, reduced the concentration of inflammatory cytokines, and inhibited lymphocyte activation.

CONCLUSIONS

Transient CD4(+) T-cell depletion using antibodies is a clinically feasible procedure that allows efficient Ad redosing. Systemic administration of clodronate liposomes may further increase the safety and efficacy of vectors.

Adenovirus membrane penetration: Tickling the tail of a sleeping dragon

As is the case for nearly every viral pathogen, non-enveloped viruses (NEV) must maintain their integrity under potentially harsh environmental conditions while retaining the ability to undergo rapid disassembly at the right time and right place inside host cells. NEVs generally exist in this metastable state until they encounter key cellular stimuli such as membrane receptors, decreased intracellular pH, digestion by cellular proteases, or a combination of these factors. These stimuli trigger conformational changes in the viral capsid that exposes a sequestered membrane-perturbing protein. This protein subsequently modifies the cell membrane in such a way as to allow passage of the virion and accompanying nucleic acid payload into the cell cytoplasm. Different NEVs employ variations of this general pathway for cell entry (Moyer and Nemerow, 2011, Curr. Opin. Virol., 1, 44-49), however this review will focus on significant new knowledge obtained on cell entry by human adenovirus (HAdV).

Hexon modification to improve the activity of oncolytic adenovirus vectors against neoplastic and stromal cells in pancreatic cancer

Primary pancreatic carcinoma has an unfavourable prognosis and standard treatment strategies mostly fail in advanced cases. Virotherapy might overcome this resistance to current treatment modalities. However, data from clinical studies with oncolytic viruses, including replicating adenoviral (Ad) vectors, have shown only limited activity against pancreatic cancer and other carcinomas. Since pancreatic carcinomas have a complex tumor architecture and frequently a strong stromal compartment consisting of non-neoplastic cell types (mainly pancreatic stellate cells = hPSCs) and extracellular matrix, it is not surprising that Ad vectors replicating in neoplastic cells will likely fail to eradicate this aggressive tumor type. Because the TGFβ receptor (TGFBR) is expressed on both neoplastic cells and hPSCs we inserted the TGFBR targeting peptide CKS17 into the hypervariable region 5 (HVR5) of the capsid protein hexon with the aim to generate a replicating Ad vector with improved activity in complex tumors. We demonstrated increased transduction of both pancreatic cancer cell lines and of hPSCs and enhanced cytotoxicity in co-cultures of both cell types. Surface plasmon resonance analysis demonstrated decreased binding of coagulation factor X to CKS17-modified Ad particles and in vivo biodistribution studies performed in mice indicated decreased transduction of hepatocytes. Thus, to increase activity of replicating Ad vectors we propose to relax tumor cell selectivity by genetic hexon-mediated targeting to the TGFBR (or other receptors present on both neoplastic and non-neoplastic cells within the tumor) to enable replication also in the stromal cell compartment of tumors, while abolishing hepatocyte transduction, and thereby increasing safety.

Manipulating adenovirus hexon hypervariable loops dictates immune neutralisation and coagulation factor X-dependent cell interaction in vitro and in vivo

Adenoviruses are common pathogens, mostly targeting ocular, gastrointestinal and respiratory cells, but in some cases infection disseminates, presenting in severe clinical outcomes. Upon dissemination and contact with blood, coagulation factor X (FX) interacts directly with the adenovirus type 5 (Ad5) hexon. FX can act as a bridge to bind heparan sulphate proteoglycans, leading to substantial Ad5 hepatocyte uptake. FX “coating” also protects the virus from host IgM and complement-mediated neutralisation. However, the contribution of FX in determining Ad liver transduction whilst simultaneously shielding the virus from immune attack remains unclear. In this study, we demonstrate that the FX protection mechanism is not conserved amongst Ad types, and identify the hexon hypervariable regions (HVR) of Ad5 as the capsid proteins targeted by this host defense pathway. Using genetic and pharmacological approaches, we manipulate Ad5 HVR interactions to interrogate the interplay between viral cell transduction and immune neutralisation. We show that FX and inhibitory serum components can co-compete and virus neutralisation is influenced by both the location and extent of modifications to the Ad5 HVRs. We engineered Ad5-derived HVRs into the rare, native non FX-binding Ad26 to create Ad26.HVR5C. This enabled the virus to interact with FX at high affinity, as quantified by surface plasmon resonance, FX-mediated cell binding and transduction assays. Concomitantly, Ad26.HVR5C was also sensitised to immune attack in the absence of FX, a direct consequence of the engineered HVRs from Ad5. In both immune competent and deficient animals, Ad26.HVR5C hepatic gene transfer was mediated by FX following intravenous delivery. This study gives mechanistic insight into the pivotal role of the Ad5 HVRs in conferring sensitivity to virus neutralisation by IgM and classical complement-mediated attack. Furthermore, through this gain-of-function approach we demonstrate the dual functionality of FX in protecting Ad26.HVR5C against innate immune factors whilst determining liver targeting.

Adenoviruses are mostly considered self-limiting pathogens associated with respiratory, gastrointestinal and ocular infections; however, in immunocompromised subjects disseminated Ad infection can occur with life-threatening consequences. Many human Ads are capable of binding to coagulation factor X (FX). Following intravenous administration in animal models, FX binds directly to the major Ad capsid protein, the hexon, which subsequently results in virus accumulation in the liver. FX coating Ad5 also acts to shield against immune neutralisation via natural IgM antibodies and the classical complement system. Here we show that FX protection is not a conserved mechanism amongst Ads and identify the Ad5 hexon hypervariable regions (HVR) as the capsid proteins targeted by this host defense pathway. Furthermore, we show that genetic inclusion of Ad5 HVRs onto a native non-FX binder Ad26 to be sufficient to confer sensitivity to immune attack in vitro and in vivo. Using intravenous administration, we determine the significance of FX binding to the Ad5-derived HVRs with respect to defending the virus from neutralisation whilst mediating virus tropism. Our study gives new insight into the role of the viral HVRs and of FX at the interface between virus and host defense mechanisms.

Liposomal insulin promoter-thymidine kinase gene therapy followed by ganciclovir effectively ablates human pancreatic cancer in mice

PDX1 is overexpressed in pancreatic cancer, and activates the insulin promoter (IP). Adenoviral IP-thymidine kinase and ganciclovir (TK/GCV) suppresses human pancreatic ductal carcinoma (PDAC) in mice, but repeated doses carry significant toxicity. We hypothesized that multiple cycles of liposomal IP-TK/GCV ablate human PDAC in SCID mice with minimal toxicity compared to adenoviral IP-TK/GCV. SCID mice with intraperitoneal human pancreatic cancer PANC-1 tumor implants were given a single cycle of 35 µg iv L-IP-TK, or four cycles of 1, 10, 20, 30, or 35 µg iv L-IP-TK (n = 20 per group), followed by intraperitoneal GCV. Insulin and glucose levels were monitored in mice treated with four cycles of 35 µg iv L-IP-TK. We found that four cycles of 10-35 µg L-IP-TK/GCV ablated more PANC-1 tumor volume compared to a single cycle with 35 µg. Mice that received four cycles of 10 µg L-IP-TK demonstrated the longest survival (P < 0.05), with a median survival of 126 days. In comparison, mice that received a single cycle of 35 µg L-IP-TK/GCV or GCV alone survived a median of 92 days and 68.7 days, respectively. There were no significant changes in glucose or insulin levels following treatment. In conclusion, multiple cycles of liposomal IP-TK/GCV ablate human PDAC in SCID mice with minimal toxicity, suggesting non-viral vectors are superior to adenoviral vectors for IP-gene therapy.

Impact of natural IgM concentration on gene therapy with adenovirus type 5 vectors

Natural IgM inhibits gene transfer by adenovirus type 5 (Ad5) vectors. We show that polyreactive natural IgM antibodies bind to Ad5 and that inhibition of liver transduction by IgM depends on Kupffer cells. By manipulating IgM concentration in vivo, we demonstrate that IgM inhibits liver transduction in a concentration-dependent manner. We further show that differences in natural IgM between BALB/c and C57BL/6 mice contribute to lower efficiency of Ad5 gene transfer in BALB/c mice.

Human coagulation factor X-adenovirus type 5 complexes poorly stimulate an innate immune response in human mononuclear phagocytes

One of the first lines of host defense against many viruses in vertebrates is the innate immune system, which detects pathogen-associated molecular patterns (PAMPs) using pathogen recognition receptors (PRR). The dynamic interactions between pathogens and hosts create, in some cases, species-specific relationships. Recently, it was shown that murine factor X (mFX)-armored human adenovirus (HAd) stimulated a mFX-Toll-like receptor 4 (TLR4)-associated response in mouse macrophages in vitro and in vivo. Given the importance of studies using animals to better understand host-pathogen interactions, we asked if human FX (hFX)-armored HAd type 5 (HAd5) was capable of activating innate immune sensors in primary human mononuclear phagocytes. To this end, we assayed human mononuclear phagocytes for their ability to be stimulated by hFX-armored HAd5 via a TLR/NF-κB pathway, in particular, a TLR4 pathway. In our hands, we found no significant interaction, activation, or maturation of human mononuclear phagocytes caused by the presence of hFX-armored HAd5.

IMPORTANCE

Animals, and mice in particular, are often used as informative and powerful surrogates for how pathogens interact with natural host systems. When possible, extended and targeted studies in the natural host can then be performed. Our data will help us understand the differences in preclinical testing in mice and clinical use in humans in order to improve treatment for HAd diseases and Ad vector effectiveness.

Intracellular sensing of complement C3 activates cell autonomous immunity

Pathogens traverse multiple barriers during infection, including cell membranes. We found that during this transition, pathogens carried covalently attached complement C3 into the cell, triggering immediate signaling and effector responses. Sensing of C3 in the cytosol activated mitochondrial antiviral signaling (MAVS)-dependent signaling cascades and induced proinflammatory cytokine secretion. C3 also flagged viruses for rapid proteasomal degradation, preventing their replication. This system could detect both viral and bacterial pathogens but was antagonized by enteroviruses, such as rhinovirus and poliovirus, which cleave C3 using their 3C protease. The antiviral rupintrivir inhibited 3C protease and prevented C3 cleavage, rendering enteroviruses susceptible to intracellular complement sensing. Thus, complement C3 allows cells to detect and disable pathogens that have invaded the cytosol.

A targeting ligand enhances infectivity and cytotoxicity of an oncolytic adenovirus in human pancreatic cancer tissues

The addition of a targeting strategy is necessary to enhance oncolysis and secure safety of a conditionally replicative adenovirus (CRAd). We have constructed an adenovirus library displaying random peptides on the fiber, and have successfully identified a pancreatic cancer-targeting ligand (SYENFSA). Here, the usefulness of cancer-targeted CRAd for pancreatic cancer was examined as a preclinical study. First, we constructed a survivin promoter-regulated CRAd expressing enhanced green fluorescent protein gene (EGFP), which displayed the identified targeting ligand (AdSur-SYE). The AdSur-SYE resulted in higher gene transduction efficiency and oncolytic potency than the untargeted CRAd (AdSur) in several pancreatic cancer cell lines. An intratumoral injection of AdSur-SYE significantly suppressed the growth of subcutaneous tumors, in which AdSur-SYE effectively proliferated and spread. An ectopic infection in adjacent tissues and organs of intratumorally injected AdSur-SYE was decreased compared with AdSur. Then, to examine whether the targeting ligand actually enhanced the infectivity of CRAd in human pancreatic cancer tissues, tumor cells prepared from surgical specimens were infected with viruses. The AdSur-SYE increased gene transduction efficiency 6.4-fold higher than did AdSur in single cells derived from human pancreatic cancer, whereas the infectivity of both vectors was almost the same in the pancreas and other cancers. Immunostaining showed that most EGFP(+) cells were cytokeratin-positive in the sliced tissues, indicating that pancreatic cancer cells but not stromal cells were injected with AdSur-SYE. AdSur-SYE resulted in a stronger oncolysis in the primary pancreatic cancer cells co-cultured with mouse embryonic fibroblasts than AdSur did. CRAd in combination with a tumor-targeting ligand is promising as a next-generation of oncolytic virotherapy for pancreatic cancer.

The myeloid-binding peptide adenoviral vector enables multi-organ vascular endothelial gene targeting

Vascular endothelial cells (ECs) are ideal gene therapy targets as they provide widespread tissue access and are the first contact surfaces following intravenous vector administration. Human recombinant adenovirus serotype 5 (Ad5) is the most frequently used gene transfer system because of its appreciable transgene payload capacity and lack of somatic mutation risk. However, standard Ad5 vectors predominantly transduce liver but not the vasculature following intravenous administration. We recently developed an Ad5 vector with a myeloid cell-binding peptide (MBP) incorporated into the knob-deleted, T4 fibritin chimeric fiber (Ad.MBP). This vector was shown to transduce pulmonary ECs presumably via a vector handoff mechanism. Here we tested the body-wide tropism of the Ad.MBP vector, its myeloid cell necessity, and vector-EC expression dose response. Using comprehensive multi-organ co-immunofluorescence analysis, we discovered that Ad.MBP produced widespread EC transduction in the lung, heart, kidney, skeletal muscle, pancreas, small bowel, and brain. Surprisingly, Ad.MBP retained hepatocyte tropism albeit at a reduced frequency compared with the standard Ad5. While binding specifically to myeloid cells ex vivo, multi-organ Ad.MBP expression was not dependent on circulating monocytes or macrophages. Ad.MBP dose de-escalation maintained full lung-targeting capacity but drastically reduced transgene expression in other organs. Swapping the EC-specific ROBO4 for the CMV promoter/enhancer abrogated hepatocyte expression but also reduced gene expression in other organs. Collectively, our multilevel targeting strategy could enable therapeutic biological production in previously inaccessible organs that pertain to the most debilitating or lethal human diseases.

Experimental virotherapy of chemoresistant pancreatic carcinoma using infectivity-enhanced fiber-mosaic oncolytic adenovirus

Pancreatic cancer is a significant clinical problem and novel therapeutic approaches are desperately needed. Recent advances in conditionally replicative adenovirus-based (CRAd) oncolytic virus design allow the application of CRAd vectors as a therapeutic strategy to efficiently target and eradicate chemoresistant pancreatic cancer cells, thereby improving the efficacy of pancreatic cancer treatment. The goal of this study was to construct and validate the efficacy of an infectivity-enhanced, liver-untargeted, tumor-specific CRAd vector. A panel of CRAds has been derived that embodies the C-X-C chemokine receptor type 4 promoter for conditional replication, two-fiber complex mosaicism for targeting expansion and hexon hypervariable region 7 (HVR7) modification for liver untargeting. We evaluated CRAds for cancer virotherapy using a human pancreatic tumor xenograft model. Employment of the fiber mosaic approach improved CRAd replication in pancreatic tumor xenografts. Substitution of the HVR7 of the Ad5 hexon for Ad serotype 3 hexon resulted in decreased liver tropism of systemically administrated CRAd. Obtained data demonstrated that employment of complex mosaicism increased efficacy of the combination of oncolytic virotherapy with chemotherapy in a human pancreatic tumor xenograft model.

Deficiency of complement receptors CR2/CR1 in Cr2⁻/⁻ mice reduces the extent of secondary brain damage after closed head injury

Complement activation at the C3 convertase level has been associated with acute neuroinflammation and secondary brain injury after severe head trauma. The present study was designed to test the hypothesis that Cr2^-/- mice, which lack the receptors CR2/CD21 and CR1/CD35 for complement C3-derived activation fragments, are protected from adverse sequelae of experimental closed head injury. Adult wild-type mice and Cr2^-/- mice on a C57BL/6 genetic background were subjected to focal closed head injury using a standardized weight-drop device. Head-injured Cr2^-/- mice showed significantly improved neurological outcomes for up to 72 hours after trauma and a significantly decreased post-injury mortality when compared to wild-type mice. In addition, the Cr2^-/- genotype was associated with a decreased extent of neuronal cell death at seven days post-injury. Western blot analysis revealed that complement C3 levels were reduced in the injured brain hemispheres of Cr2^-/- mice, whereas plasma C3 levels remained unchanged, compared to wild-type mice. Finally, head-injured Cr2^-/- had an attenuated extent of post-injury C3 tissue deposition, decreased astrocytosis and microglial activation, and attenuated immunoglobulin M deposition in injured brains compared to wild-type mice. Targeting of these receptors for complement C3 fragments (CR2/CR1) may represent a promising future approach for therapeutic immunomodulation after traumatic brain injury.

Capsid modification strategies for detargeting adenoviral vectors

Adenoviral vectors hold immense potential for a wide variety of gene therapy based applications; however, their efficacy and toxicity is dictated by "off target" interactions that preclude cell specific targeting to sites of disease. A number of "off target" interactions have been described in the literature that occur between the three major capsid proteins (hexon, penton, and fiber) and components of the circulatory system, including cells such as erythrocytes, white blood cells, and platelets, as well as circulatory proteins including complement proteins, coagulation factors, von Willebrand Factor, p-selectin as well as neutralizing antibodies. Thus, to improve efficacious targeting to sites of disease and limit nonspecific uptake of virus to non-target tissues, specifically the liver and the spleen, it is necessary to develop suitable strategies for genetically modifying the capsid proteins to preclude these interactions. To this end we have developed versatile systems based on homologous recombination for modification of each of the major capsid proteins, which are described herein.

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.