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

Chimeric oncolytic adenovirus evades neutralizing antibodies from human patients and exhibits enhanced anti-glioma efficacy in immunized mice

Oncolytic viruses are a promising treatment for patients with high-grade gliomas, but neutralizing antibodies can limit their efficacy in patients with prior virus exposure or upon repeated virus injections. Data from a previous clinical trial using the oncolytic adenovirus Delta-24-RGD showed that generation of anti-viral neutralizing antibodies may affect the long-term survival of glioma patients. Past studies have examined the effects of neutralizing antibodies during systemic virus injections, but largely overlooked their impact during local virus injections into the brain. We found that immunoglobulins colocalized with viral proteins upon local oncolytic virotherapy of brain tumors, warranting a strategy to prevent virus neutralization and maximize oncolysis. Thus, we generated a chimeric virus, Delta-24-RGD-H43m, by replacing the capsid protein HVRs from the serotype 5-based Delta-24-RGD with those from the rare serotype 43. Delta-24-RGD-H43m evaded neutralizing anti-Ad5 antibodies and conferred a higher rate of long-term survival than Delta-24-RGD in glioma-bearing mice. Importantly, Delta-24-RGD-H43m activity was significantly more resistant to neutralizing antibodies present in sera of glioma patients treated with Delta-24-RGD during a phase 1 clinical trial. These findings provide a framework for a novel treatment of glioma patients that have developed immunity against Delta-24-RGD.

Targeted, safe, and efficient gene delivery to human hematopoietic stem and progenitor cells in vivo using the engineered AVID adenovirus vector platform

Targeted delivery and cell-type-specific expression of gene-editing proteins in various cell types in vivo represent major challenges for all viral and non-viral delivery platforms developed to date. Here, we describe the development and analysis of artificial vectors for intravascular delivery (AVIDs), an engineered adenovirus-based gene delivery platform that allows for highly targeted, safe, and efficient gene delivery to human hematopoietic stem and progenitor cells (HSPCs) in vivo after intravenous vector administration. Due to a set of refined structural modifications, intravenous administration of AVIDs did not trigger cytokine storm, hepatotoxicity, or thrombocytopenia. Single intravenous administration of AVIDs to humanized mice, grafted with human CD34+ cells, led to up to 20% transduction of CD34+CD38-CD45RA- HSPC subsets in the bone marrow. Importantly, targeted in vivo transduction of CD34+CD38-CD45RA-CD90-CD49f+ subsets, highly enriched for human hematopoietic stem cells (HSCs), reached up to 19%, which represented a 1,900-fold selectivity in gene delivery to HSC-enriched over lineage-committed CD34-negative cell populations. Because the AVID platform allows for regulated, cell-type-specific expression of gene-editing technologies as well as expression of immunomodulatory proteins to ensure persistence of corrected HSCs in vivo, the HSC-targeted AVID platform may enable development of curative therapies through in vivo gene correction in human HSCs after a single intravenous administration.

Structural Model for Factor X Inhibition of IgM and Complement-Mediated Neutralization of Adenovirus

Adenovirus has strong therapeutic potential as an oncolytic virus and gene therapy vector. However, injecting human species C serotype 5 adenovirus, HAdv-C5, into the bloodstream leads to numerous interactions with plasma proteins that affect viral tropism and biodistribution, and can lead to potent immune responses and viral neutralization. The HAdv/factor X (FX) interaction facilitates highly efficient liver transduction and protects virus particles from complement-mediated neutralization after intravenous delivery. Ablating the FX interaction site on the HAdv-C5 capsid leaves the virus susceptible to neutralization by natural IgM followed by activation of the complement cascade and covalent binding of complement components C4b and C3b to the viral capsid. Here we present structural models for IgM and complement components C1, C4b, and C3b in complex with HAdv-C5. Molecular dynamics simulations indicate that when C3b binds near the vertex, multiple stabilizing interactions can be formed between C3b, penton base, and fiber. These interactions may stabilize the vertex region of the capsid and prevent release of the virally encoded membrane lytic factor, protein VI, which is packaged inside of the viral capsid, thus effectively neutralizing the virus. In a situation where FX and IgM are competing for binding to the capsid, IgM may not be able to form a bent conformation in which most of its Fab arms interact with the capsid. Our structural modeling of the competitive interaction of FX and IgM with HAdv-C5 allows us to propose a mechanistic model for FX inhibition of IgM-mediated virus neutralization. According to this model, although IgM may bind to the capsid, in the presence of FX it will likely retain a planar conformation and thus be unable to promote activation of the complement cascade at the virus surface.

HDAd6/35++ - A new helper-dependent adenovirus vector platform for in vivo transduction of hematopoietic stem cells

In previous studies, we achieved safe and efficient in vivo hematopoietic stem cell (HSC) transduction in mobilized mice and macaques with intravenously injected helper-dependent adenovirus HDAd5/35++ vectors. These vectors are derivatives of serotype Ad5-containing CD46-affinity enhanced Ad35 fiber knob domains. Considering the impact of anti-Ad5/HDAd5/35++ neutralizing serum antibodies present in the human population, we generated HSC-retargeted HDAd6/35++ vectors derived from serotype 6. We found a lower prevalence and titers of serum anti-HDAd6/35++ in human samples compared with HDAd5/35++. HDAd6/35++ vectors efficiently transduced human and rhesus CD34+ cells in vitro. Intravenous injection of HDAd5/35++-GFP or HDAd6/35++-GFP vectors after G-CSF/AMD3100 mobilization of mice with established human hematopoiesis or human CD46 transgenic mice resulted in comparable GFP marking rates in HSCs in the bone marrow and spleen. In long-term in vivo HSC transduction and selection studies with integrating vectors, stable GFP expression in >75% of PBMCs was show for both vectors. In contrast with HDAd5/35++, undesired transduction of hepatocytes was minimal with HDAd6/35++. Furthermore, HDAd6/35++ allowed for efficient in vivo HSC transduction in Ad5-pre-immune mice. These features, together with the straightforward production of HDAd6/35++ vectors at high yield, make this new HDAd vector platform attractive for clinical translation of the in vivo approach.

Evaluation of Human Mesenchymal Stromal Cells as Carriers for the Delivery of Oncolytic HAdV-5 to Head and Neck Squamous Cell Carcinomas

Human multipotent mesenchymal stromal cells (hMSCs) are of significant therapeutic interest due to their ability to deliver oncolytic adenoviruses to tumors. This approach is also investigated for targeting head and neck squamous cell carcinomas (HNSCCs). HAdV-5-HexPos3, a recently reported capsid-modified vector based on human adenovirus type 5 (HAdV-5), showed strongly improved infection of both hMSCs and the HNSCC cell line UM-SCC-11B. Given that, we generated life cycle-unmodified and -modified replication-competent HAdV-5-HexPos3 vector variants and analyzed their replication within bone marrow- and adipose tissue-derived hMSCs. Efficient replication was detected for both life cycle-unmodified and -modified vectors. Moreover, we analyzed the migration of vector-carrying hMSCs toward different HNSCCs. Although migration of hMSCs to HNSCC cell lines was confirmed in vitro, no homing of hMSCs to HNSCC xenografts was observed in vivo in mice and in ovo in a chorioallantoic membrane model. Taken together, our data suggest that HAdV-5-HexPos3 is a potent candidate for hMSC-based oncolytic therapy of HNSCCs. However, it also emphasizes the importance of generating optimized in vivo models for the evaluation of hMSC as carrier cells.

The Adenovirus Vector Platform: Novel Insights into Rational Vector Design and Lessons Learned from the COVID-19 Vaccine

The adenovirus vector platform remains one of the most efficient toolboxes for generation of transfer vehicles used in gene therapy and virotherapy to treat tumors, as well as vaccines to protect from infectious diseases. The adenovirus genome and capsids can be modified using highly efficient techniques, and vectors can be produced at high titers, which facilitates their rapid adaptation to current needs and disease applications. Over recent years, the adenovirus vector platform has been in the center of attention for vaccine development against the ongoing coronavirus SARS-CoV-2/COVID-19 pandemic. The worldwide deployment of these vaccines has greatly deepened the knowledge on virus-host interactions and highlighted the need to further improve the effectiveness and safety not only of adenovirus-based vaccines but also of gene therapy and oncolytic virotherapy vectors. Based on the current evidence, we discuss here how adenoviral vectors can be further improved by intelligent molecular design. This review covers the full spectrum of state-of-the-art strategies to avoid vector-induced side effects ranging from the vectorization of non-canonical adenovirus types to novel genome engineering techniques.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Influence of Heparan Sulfate Proteoglycans and Factor X on species D Human Adenovirus Uptake and Transduction

More than 100 human adenovirus (Ad) types were identified, of which species D comprises the largest group. Heparan sulfate proteoglycans (HSPGs) were shown to function as cell surface receptors for cell binding and uptake of some Ads, but a systematic analysis of species D Ads is lacking. Previous research focused on Ad5 and blood coagulation factor X (FX) complexes, which revealed that Ad5 can transduce cells with low expression levels of its main coxsackievirus-adenovirus receptor in the presence of high HSPG expression levels in a FX dependent manner. Based on our reporter gene-tagged Ad-library, we explored for the first time a broad spectrum of species D Ads to study the role of HSPG on their cellular uptake. This study was performed on three Chinese Hamster Ovary (CHO) cell lines with different forms of HSPG (only proteoglycan (745), non-sulfated HSPG (606) or sulfated HSPG (K1)). The effect of Ad:FX complexes on Ad uptake was explored in the presence of physiological levels of FX in blood (6-10 µg/mL). We found that sulfation of HSPG plays an important role in cellular uptake and transduction of FX-bound Ad5 but neither HSPG nor FX influenced uptake of all tested species D Ads. Because FX has no influence on transduction efficiencies of species D Ads and therefore may not bind to them, these Ads may not be protected from attack by neutralizing IgM antibodies or the complement pathway, which may have implications for species D Ads used as vaccine and gene therapy vectors.

Effects of pre-existing anti-adenovirus antibodies on transgene expression levels and therapeutic efficacies of arming oncolytic adenovirus

Oncolytic adenoviruses (OAds), most of which are based on species C human adenovirus serotype 5 (Ad5) (OAd5), have recently received much attention as potential anticancer agents. High seroprevalence of anti-Ad5 neutralizing antibodies is a major hurdle for Ad5-based gene therapy. However, the impacts of anti-Ad5 neutralizing antibodies on OAd5-mediated transgene expression in the tumor and antitumor effects remain to be fully elucidated. In this study, we examined the impact of anti-Ad5 neutralizing antibodies on the OAd5-mediated antitumor effects and OAd5-mediated transgene expression. The luciferase expression of OAd-tAIB-Luc, which contains the cytomegalovirus promoter-driven luciferase gene, was inhibited in human cultured cells in the presence of human serum. Although the inhibitory effects of human serum possessing the low anti-Ad5 neutralizing antibody titers were overcome by long-term infection, the in vitro tumor cell lysis activities of OAd-tAIB-Luc were entirely attenuated by human serum containing the high titers of anti-Ad5 neutralizing antibodies. OAd-tAIB-Luc-mediated luciferase expression in the subcutaneous tumors 3 days after administration and tumor growth suppression levels following intratumoral administration were significantly lower in mice possessing the high titers of anti-Ad5 neutralizing antibodies, compared to those in control mice. These results suggested that pre-existing anti-Ad5 antibodies attenuated both transgene expression and potential antitumor effects of OAd5 following intratumoral administration.

Adenovirus vector system: construction, history and therapeutic applications

Since the isolation of adenovirus (AdV) in 1953, AdVs have been used as vectors for various therapeutic purposes, such as gene therapy in cancers and other malignancies, vaccine development and delivery of CRISPR-Cas9 machinery. Over the years, several AdV vector modifications have been introduced, including fiber switching, incorporation of ligands in the viral capsid and hexon modification of the fiber, to improve the efficiency of AdV as a vector. CRISPR-Cas9 has recently been used for these modifications and is also used in other adeno-associated viruses. These modifications further allow the production of AdV libraries that display random peptides for the production of cancer-targeting AdV vectors. This review focuses on the common methods of AdV construction, changes in AdV tropism for the improvement of therapeutic efficiency and the role of AdV vectors in gene therapy, vaccine development and CRISPR-Cas9 delivery.

Binding of adenovirus species C hexon to prothrombin and the influence of hexon on vector properties in vitro and in vivo

The majority of adenovirus (Ad) vectors are based on human Ad type 5, which is a member of Ad species C. Species C also includes the closely-related types 1, 2, 6, 57 and 89. It is known that coagulation factors bind to Ad5 hexon and play a key role in the liver tropism of Ad5 vectors, but it is unclear how coagulation factors affect vectors derived from other species C Ads. We evaluated species C Ad vectors both in vitro and following intravenous injection in mice. To assess the impact of hexon differences, we constructed chimeric Ad5 vectors that contain the hexon hypervariable regions from other species C types, including vectors with hexon mutations that decreased coagulation factor binding. After intravenous injection into mice, vectors with Ad5 or Ad6 hexon had strong liver tropism, while vectors with chimeric hexon from other Ad types had weaker liver tropism due to inhibition by natural antibodies and complement. In addition, we discovered a novel ability of hexon to bind prothrombin, which is the most abundant coagulation factor in blood, and we found striking differences in the affinity of Ads for human, mouse and bovine coagulation factors. When compared to Ad5, vectors with non-Ad5 species C hexons had considerably higher affinity for both human and mouse prothrombin. Most of the vectors tested were strongly dependent on coagulation factors for liver transduction, but vectors with chimeric Ad6 hexon showed much less dependence on coagulation factors than other vectors. We found that in vitro neutralization experiments with mouse serum predicted in vivo behavior of Ad5 vectors, but in vitro experiments did not predict the in vivo behavior of vectors based on other Ad types. In sum, hexons from different human Ad species C viruses confer diverse properties on vectors, including differing abilities to target the liver.

C1q as a target molecule to treat human disease: What do mouse studies teach us?

The complement system is a field of growing interest for pharmacological intervention. Complement protein C1q, the pattern recognition molecule at the start of the classical pathway of the complement cascade, is a versatile molecule with additional non-canonical actions affecting numerous cellular processes. Based on observations made in patients with hereditary C1q deficiency, C1q is protective against systemic autoimmunity and bacterial infections. Accordingly, C1q deficient mice reproduce this phenotype with susceptibility to autoimmunity and infections. At the same time, beneficial effects of C1q deficiency on disease entities such as neurodegenerative diseases have also been described in murine disease models. This systematic review provides an overview of all currently available literature on the C1q knockout mouse in disease models to identify potential target diseases for treatment strategies focusing on C1q, and discusses potential side-effects when depleting and/or inhibiting C1q.

Hexon modification of human adenovirus type 5 vectors enables efficient transduction of human multipotent mesenchymal stromal cells

In adenovirus type 5 (HAdV-5)-derived viral vectors, the fiber protein has been the preferred locale for modifications to alter the natural viral tropism. Hexon, the most abundant capsid protein, has rarely been used for retargeting purposes, likely because the insertion of larger targeting peptides into Hexon often interferes with the assembly of the viral capsid. We previously observed that positively charged molecules enhance the transduction of human multipotent mesenchymal stromal cells (hMSCs)—a cell type of significant interest for clinical development but inefficiently transduced by unmodified HAdV-5-based vectors. As efficient HAdV-5-mediated gene transfer would greatly increase the therapeutic potential of hMSCs, we tested the hypothesis that introducing positively charged amino acids into Hexon might enhance the transduction of hMSCs, enabling efficient expression of selected transgenes. From the constructs that could be rescued as functional virions, one (HAdV-5-HexPos3) showed striking transduction of hMSCs with up to 500-fold increased efficiency. Evaluation of the underlying mechanism identified heparan sulfate proteoglycans (HSPGs) to be essential for virus uptake by the cells. The ease and efficiency of transduction of hMSCs with this vector will facilitate the development of genetically modified hMSCs as therapeutic vehicles in different disciplines, including oncology or regenerative medicine.

Innate immune surveillance of the circulation: A review on the removal of circulating virions from the bloodstream

Many viruses utilize the lymphohematogenous route for dissemination; however, they may not freely use this highway unchecked. The reticuloendothelial system (RES) is an innate defense system that surveys circulating blood, recognizing and capturing viral particles. Examination of the literature shows that the bulk of viral clearance is mediated by the liver; however, the precise mechanism(s) mediating viral vascular clearance vary between viruses and, in many cases, remains poorly defined. Herein, we summarize what is known regarding the recognition and capture of virions from the circulation prior to the generation of a specific antibody response. We also discuss the consequences of viral capture on viral pathogenesis and the fate of the captor cell. Finally, this understudied topic has implications beyond viral pathogenesis, including effects on arbovirus ecology and the application of virus-vectored gene therapies.

Cytokine Responses to Adenovirus and Adenovirus Vectors

The expression of cytokines and chemokines in response to adenovirus infection is tightly regulated by the innate immune system. Cytokine-mediated toxicity and cytokine storm are known clinical phenomena observed following naturally disseminated adenovirus infection in immunocompromised hosts as well as when extremely high doses of adenovirus vectors are injected intravenously. This dose-dependent, cytokine-mediated toxicity compromises the safety of adenovirus-based vectors and represents a critical problem, limiting their utility for gene therapy applications and the therapy of disseminated cancer, where intravenous injection of adenovirus vectors may provide therapeutic benefits. The mechanisms triggering severe cytokine response are not sufficiently understood, prompting efforts to further investigate this phenomenon, especially in clinically relevant settings. In this review, we summarize the current knowledge on cytokine and chemokine activation in response to adenovirus- and adenovirus-based vectors and discuss the underlying mechanisms that may trigger acute cytokine storm syndrome. First, we review profiles of cytokines and chemokines that are activated in response to adenovirus infection initiated via different routes. Second, we discuss the molecular mechanisms that lead to cytokine and chemokine transcriptional activation. We further highlight how immune cell types in different organs contribute to synthesis and systemic release of cytokines and chemokines in response to adenovirus sensing. Finally, we review host factors that can limit cytokine and chemokine expression and discuss currently available and potential future interventional approaches that allow for the mitigation of the severity of the cytokine storm syndrome. Effective cytokine-targeted interventional approaches may improve the safety of systemic adenovirus delivery and thus broaden the potential clinical utility of adenovirus-based therapeutic vectors.

Infection of non-cancer cells: A barrier or support for oncolytic virotherapy?

Oncolytic viruses are designed to specifically target cancer cells, sparing normal cells. Although numerous studies demonstrate the ability of oncolytic viruses to infect a wide range of non-tumor cells, the significance of this phenomenon for cancer virotherapy is poorly understood. To fill the gap, we summarize the data on infection of non-cancer targets by oncolytic viruses with a special focus on tumor microenvironment and secondary lymphoid tissues. The review aims to address two major questions: how do attenuated viruses manage to infect normal cells, and whether it is of importance for oncolytic virotherapy.

Refined Capsid Structure of Human Adenovirus D26 at 3.4 Å Resolution

Various adenoviruses are being used as viral vectors for the generation of vaccines against chronic and emerging diseases (e.g., AIDS, COVID-19). Here, we report the improved capsid structure for one of these vectors, human adenovirus D26 (HAdV-D26), at 3.4 Å resolution, by reprocessing the previous cryo-electron microscopy dataset and obtaining a refined model. In addition to overall improvements in the model, the highlights of the structure include (1) locating a segment of the processed peptide of VIII that was previously believed to be released from the mature virions, (2) reorientation of the helical appendage domain (APD) of IIIa situated underneath the vertex region relative to its counterpart observed in the cleavage defective (ts1) mutant of HAdV-C5 that resulted in the loss of interactions between the APD and hexon bases, and (3) the revised conformation of the cleaved N-terminal segments of pre-protein VI (pVIn), located in the hexon cavities, is highly conserved, with notable stacking interactions between the conserved His13 and Phe18 residues. Taken together, the improved model of HAdV-D26 capsid provides a better understanding of protein–protein interactions in HAdV capsids and facilitates the efforts to modify and/or design adenoviral vectors with altered properties. Last but not least, we provide some insights into clotting factors (e.g., FX and PF4) binding to AdV vectors.

Proposed mechanism for rare thrombotic events after use of some Covid-19 vaccines

Administration of AstraZeneca/Oxford and Johnson & Johnson/Janssen Covid-19 vaccines which use an adenovirus vector for DNA delivery has been associated with very rare thromboembolic complications coupled with an immune response to platelet factor 4 protein. The cause of this has not yet been identified. It is known that binding of coagulation factor proteins to the surface of some adenoviruses can protect their function. Here I propose that the thromboembolic events are caused by impairment of coagulation factor X binding to the virus capsid. The unprotected capsid then stimulates an immune response leading to platelet activation, increased thrombogenicity and formation of an antibody complex with platelet factor 4. Impaired binding of factor X may be due to an undiagnosed mutation in affected individuals. Options to test this mechanism experimentally and potential remedial actions to resolve the hazard are described. This mechanism offers a remedial route to address concerns about the safety of these vaccines, which are otherwise well-positioned to deliver global Covid-19 immunity across diverse healthcare economies.

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

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

Adenovirus vector-attributed hepatotoxicity blocks clinical application in gene therapy

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

A Single Amino Acid at Residue 188 of the Hexon Protein Is Responsible for the Pathogenicity of the Emerging Novel Virus Fowl Adenovirus 4

Since 2015, severe hydropericardium-hepatitis syndrome (HHS) associated with a novel fowl adenovirus 4 (FAdV-4) has emerged in China, representing a new challenge for the poultry industry. Although various highly pathogenic FAdV-4 strains have been isolated, the virulence factor and the pathogenesis of novel FAdV-4 are unclear. In our previous studies, we reported that a large genomic deletion (1,966 bp) is not related to increased virulence. Here, two recombinant chimeric viruses, rHN20 strain and rFB2 strain, were generated from a highly pathogenic FAdV-4 strain by replacing the hexon or fiber-2 gene of a nonpathogenic FAdV-4, respectively. Both chimeric strains showed similar titers to the wild-type strain in vitro. Notably, rFB2 and the wild-type strain induced 100% mortality, while no mortality or clinical signs appeared in chickens inoculated with rHN20, indicating that hexon, but not fiber-2, determines the novel FAdV-4 virulence. Furthermore, an R188I mutation in the hexon protein identified residue 188 as the key amino acid for the reduced pathogenicity. The rR188I mutant strain was significantly neutralized by chicken serum in vitro and in vivo, whereas the wild-type strain was able to replicate efficiently. Finally, the immunogenicity of the rescued rR188I was investigated. Nonpathogenic rR188I provided full protection against lethal FAdV-4 challenge. Collectively, these findings provide an in-depth understanding of the molecular basis of novel FAdV-4 pathogenicity and present rR188I as a potential live attenuated vaccine candidate or a novel vaccine vector for HHS vaccines. IMPORTANCE HHS associated with a novel FAdV-4 infection in chickens has caused huge economic losses to the poultry industry in China since 2015. The molecular basis for the increased virulence remains largely unknown. Here, we demonstrate that the hexon gene is vital for FAdV-4 pathogenicity. Furthermore, we show that the amino acid residue at position 188 of the hexon protein is responsible for pathogenicity. Importantly, the rR188I mutant strain was neutralized by chicken serum in vitro and in vivo, whereas the wild-type strain was not. Further, the rR188I mutant strain provided complete protection against FAdV-4 challenge. Our results provide a molecular basis of the increased virulence of novel FAdV-4. We propose that the rR188I mutant is a potential live attenuated vaccine against HHS and a new vaccine vector for HHS-combined vaccines.

Genetic and Chemical Capsid Modifications of Adenovirus Vectors to Modulate Vector-Host Interactions

Adenovirus-based vectors are playing an important role as efficacious genetic vaccines to fight the current COVID-19 pandemic. Furthermore, they have an enormous potential as oncolytic vectors for virotherapy and as vectors for classic gene therapy. However, numerous vector-host interactions on a cellular and noncellular level, including specific components of the immune system, must be modulated in order to generate safe and efficacious vectors for virotherapy or classic gene therapy. Importantly, the current widespread use of Ad vectors as vaccines against COVID-19 will induce antivector immunity in many humans. This requires the development of strategies and techniques to enable Ad-based vectors to evade pre-existing immunity. In this review article, we discuss the current status of genetic and chemical capsid modifications as means to modulate the vector-host interactions of Ad-based vectors.

Systemic cancer therapy with engineered adenovirus that evades innate immunity

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

Nonreplicating Adenoviral Vectors: Improving Tropism and Delivery of Cancer Gene Therapy

Recent preclinical and clinical studies have used viral vectors in gene therapy research, especially nonreplicating adenovirus encoding strategic therapeutic genes for cancer treatment. Adenoviruses were the first DNA viruses to go into therapeutic development, mainly due to well-known biological features: stability in vivo, ease of manufacture, and efficient gene delivery to dividing and nondividing cells. However, there are some limitations for gene therapy using adenoviral vectors, such as nonspecific transduction of normal cells and liver sequestration and neutralization by antibodies, especially when administered systemically. On the other hand, adenoviral vectors are amenable to strategies for the modification of their biological structures, including genetic manipulation of viral proteins, pseudotyping, and conjugation with polymers or biological membranes. Such modifications provide greater specificity to the target cell and better safety in systemic administration; thus, a reduction of antiviral host responses would favor the use of adenoviral vectors in cancer immunotherapy. In this review, we describe the structural and molecular features of nonreplicating adenoviral vectors, the current limitations to their use, and strategies to modify adenoviral tropism, highlighting the approaches that may allow for the systemic administration of gene therapy.

Capsid and Genome Modification Strategies to Reduce the Immunogenicity of Adenoviral Vectors

Adenovirus-based gene transfer vectors are the most frequently used vector type in gene therapy clinical trials to date, and they play an important role as genetic vaccine candidates during the ongoing SARS-CoV-2 pandemic. Immediately upon delivery, adenovirus-based vectors exhibit multiple complex vector-host interactions and induce innate and adaptive immune responses. This can severely limit their safety and efficacy, particularly after delivery through the blood stream. In this review article we summarize two strategies to modulate Ad vector-induced immune responses: extensive genomic and chemical capsid modifications. Both strategies have shown beneficial effects in a number of preclinical studies while potential synergistic effects warrant further investigations.

iMATCH: an integrated modular assembly system for therapeutic combination high-capacity adenovirus gene therapy

Adenovirus-mediated combination gene therapies have shown promising results in vaccination or treating malignant and genetic diseases. Nevertheless, an efficient system for the rapid assembly and incorporation of therapeutic genes into high-capacity adenoviral vectors (HCAdVs) is still missing. In this study, we developed the iMATCH (integrated modular assembly for therapeutic combination HCAdVs) platform, which enables the generation and production of HCAdVs encoding therapeutic combinations in high quantity and purity within 3 weeks. Our modular cloning system facilitates the efficient combination of up to four expression cassettes and the rapid integration into HCAdV genomes with defined sizes. Helper viruses (HVs) and purification protocols were optimized to produce HCAdVs with distinct capsid modifications and unprecedented purity (0.1 ppm HVs). The constitution of HCAdVs, with adapters for targeting and a shield of trimerized single-chain variable fragment (scFv) for reduced liver clearance, mediated cell- and organ-specific targeting of HCAdVs. As proof of concept, we show that a single HCAdV encoding an anti PD-1 antibody, interleukin (IL)-12, and IL-2 produced all proteins, and it led to tumor regression and prolonged survival in tumor models, comparable to a mixture of single payload HCAdVs in vitro and in vivo. Therefore, the iMATCH system provides a versatile platform for the generation of high-capacity gene therapy vectors with a high potential for clinical development.

Structure-Based Modeling of Complement C4 Mediated Neutralization of Adenovirus

Adenovirus (AdV) infection elicits a strong immune response with the production of neutralizing antibodies and opsonization by complement and coagulation factors. One anti-hexon neutralizing antibody, called 9C12, is known to activate the complement cascade, resulting in the deposition of complement component C4b on the capsid, and the neutralization of the virus. The mechanism of AdV neutralization by C4b is independent of downstream complement proteins and involves the blockage of the release of protein VI, which is required for viral escape from the endosome. To investigate the structural basis underlying how C4b blocks the uncoating of AdV, we built a model for the complex of human adenovirus type-5 (HAdV5) with 9C12, together with complement components C1 and C4b. This model positions C4b near the Arg-Gly-Asp (RGD) loops of the penton base. There are multiple amino acids in the RGD loop that might serve as covalent binding sites for the reactive thioester of C4b. Molecular dynamics simulations with a multimeric penton base and C4b indicated that stabilizing interactions may form between C4b and multiple RGD loops. We propose that C4b deposition on one RGD loop leads to the entanglement of C4b with additional RGD loops on the same penton base multimer and that this entanglement blocks AdV uncoating.

Adenovirus-Extracellular Protein Interactions and Their Impact on Innate Immune Responses by Human Mononuclear Phagocytes

The aim of this review is to highlight how, in a syngeneic system, human mononuclear phagocytes respond to environments containing human adenovirus (HAdV) and soluble extracellular proteins that influence their innate immune response. Soluble extracellular proteins, including immunoglobulins, blood clotting factors, proteins of the complement system, and/or antimicrobial peptides (AMPs) can exert direct effects by binding to a virus capsid that modifies interactions with pattern recognition receptors and downstream signaling. In addition, the presence, generation, or secretion of extracellular proteins can indirectly influence the response to HAdVs via the activation and recruitment of cells at the site of infection.

Chorioallantoic Membrane Tumor Model for Evaluating Oncolytic Viruses

Oncolytic viruses are promising anticancer agents; however, regarding their clinical efficacy, there is still significant scope for improvement. Preclinical in vivo evaluation of oncolytic viruses is mainly based on syngeneic or xenograft tumor models in mice, which is labor-intensive and time-consuming. Currently, a large proportion of developmental work in the research field of oncolytic viruses is directed toward overcoming cellular and noncellular barriers to achieve improved virus delivery to primary tumors and metastases. To evaluate the large number of genetically or chemically modified viruses regarding tumor delivery and biodistribution patterns, it would be valuable to have an in vivo model available that would allow easy screening experiments, that is of higher complexity than monoclonal cell lines, and that could be used as a platform method before confirmatory studies in small and large animals. Based on our data, we believe that the chicken chorioallantoic membrane (CAM) assay is a quick and low-cost high-throughput tumor model system for the in vivo analysis of oncolytic viruses. Here we describe the establishment, careful characterization, and optimization of the CAM model as an in vivo model for the evaluation of oncolytic viruses. We have used human adenovirus type 5 (HAdV-5) as an example for validation but are confident that the model can be used as a test system for replicating viruses of many different virus families. We show that the CAM tumor model enables intratumoral and intravenous virus administration and is a feasible and conclusive model for the analysis of relevant virus-host interactions, biodistribution patterns, and tumor-targeting profiles.

The superior role of coagulation factor FX over FVII in adenoviral-mediated innate immune induction of the hepatocyte: an in vitro experiment

Aim of the study

To better understanding the contribution of coagulation factors to the extent of adenovirus-mediated innate toxicity on the hepatocyte.

Material and methods

Adenovirus-36 (AD) and adenovector type 5-GFP (Ad5-GFP) were propagated and titered; then, they were loaded with coagulation factors VII or X. The complex of adenovirus with coagulation factor VII and X were for size and charge parameters. After adding AD-VII and AD-X complexes, the expression levels of innate inflammatory genes including protein kinase R (PKR), interleukin (IL)-1β, IL-8 and IL-18 were measured by Real-time PCR on a hepatocellular carcinoma cell line, HepG2.

Results

The loading of coagulation factors VII and X on Ad5-GFP enhanced the transduction rate up to 50% and 60% (p < 0.05), respectively, compared to the adenovector alone (30%) (p < 0.05). The formation of the coagulation factor-virus complex leads to multimodal size distribution with an increase in average hydrodynamic size and absolute zeta potential. The qPCR results showed that PKR expression increased significantly after treatment with all adenoviruses. These findings also showed that AD had a significant (p = 0.0152) inflammatory impact on Hep-G2. However, AD which was loaded with FX (AD-X) exhibited the most inflammatory effect (p = 0.0164). Significantly, the expression of IL-1β (p = 0.0041), IL-8 (p = 0.0107) and IL-18 (p = 0.0193) were also enhanced following FX loading. On the other hand, the AD-VII complex showed the least effect of innate immune induction when compared to the negative control (p < 0.05).

Conclusions

The loading of coagulation factors, particularly FX, could enhance the transduction efficiency of Ad5-GFP. Furthermore, adenovirus loaded with FX exhibited more innate toxicity on the hepatocytes, while it was not the case for FVII.

Lactoferrin-Hexon Interactions Mediate CAR-Independent Adenovirus Infection of Human Respiratory Cells

Many viruses enter target cells using cell adhesion molecules as receptors. Paradoxically, these molecules are abundant on the lateral and basolateral side of intact, polarized, epithelial target cells, but absent on the apical side that must be penetrated by incoming viruses to initiate infection. Our study provides a model whereby viruses use different mechanisms to infect polarized epithelial cells depending on which side of the cell—apical or lateral/basolateral—is attacked. This study may also be useful to understand the biology of other viruses that use cell adhesion molecules as receptors.

Virus entry into host cells is a complex process that is largely regulated by access to specific cellular receptors. Human adenoviruses (HAdVs) and many other viruses use cell adhesion molecules such as the coxsackievirus and adenovirus receptor (CAR) for attachment to and entry into target cells. These molecules are rarely expressed on the apical side of polarized epithelial cells, which raises the question of how adenoviruses—and other viruses that engage cell adhesion molecules—enter polarized cells from the apical side to initiate infection. We have previously shown that species C HAdVs utilize lactoferrin—a common innate immune component secreted to respiratory mucosa—for infection via unknown mechanisms. Using a series of biochemical, cellular, and molecular biology approaches, we mapped this effect to the proteolytically cleavable, positively charged, N-terminal 49 residues of human lactoferrin (hLF) known as human lactoferricin (hLfcin). Lactoferricin (Lfcin) binds to the hexon protein on the viral capsid and anchors the virus to an unknown receptor structure of target cells, resulting in infection. These findings suggest that HAdVs use distinct cell entry mechanisms at different stages of infection. To initiate infection, entry is likely to occur at the apical side of polarized epithelial cells, largely by means of hLF and hLfcin bridging HAdV capsids via hexons to as-yet-unknown receptors; when infection is established, progeny virions released from the basolateral side enter neighboring cells by means of hLF/hLfcin and CAR in parallel.

IMPORTANCE Many viruses enter target cells using cell adhesion molecules as receptors. Paradoxically, these molecules are abundant on the lateral and basolateral side of intact, polarized, epithelial target cells, but absent on the apical side that must be penetrated by incoming viruses to initiate infection. Our study provides a model whereby viruses use different mechanisms to infect polarized epithelial cells depending on which side of the cell—apical or lateral/basolateral—is attacked. This study may also be useful to understand the biology of other viruses that use cell adhesion molecules as receptors.

Adenoviruses - Infection, pathogenesis and therapy

Both well-known and emerging viruses increasingly affect humans and cause disease, sometimes with devastating impact on society. The viruses present in the biosphere are the top predators in the life chain, virtually without enemies, except perhaps the immune system, and harsh environmental physicochemical conditions restricting their dissemination. We know a lot about viruses, but do we know enough? This series of reviews is dedicated to adenoviruses (AdVs), a family of nonenveloped DNA viruses occurring in vertebrates, including humans. AdVs have been the focus of intense research for more than 67 years. Besides causing disease, they have immensely contributed to the advance of life sciences and medicine over the past decades. Recently, AdVs have been widely used as vehicles in gene therapy and vaccination. They continue to provide fundamental insights into virus-host interactions in cells, tissues and organisms, as well as systems and metabolic networks. This special issue of FEBS Letters presents a unique collection of 23 state-of-the-art review articles by leading adenovirologists. In this prelude, I present the chapters, which provide a solid basis for further exploring the rich heritage in adenovirus molecular cell biology, structural biology, genetics, immunology, gene therapy and epidemiology. I conclude with an essential discussion of six blind spots in adenovirology.

Retargeting adenoviruses for therapeutic applications and vaccines

Adenoviruses (Ads) are robust vectors for therapeutic applications and vaccines, but their use can be limited by differences in their in vitro and in vivo pharmacologies. This review emphasizes that there is not just one Ad, but a whole virome of diverse viruses that can be used as therapeutics. It discusses that true vector targeting involves not only retargeting viruses, but importantly also detargeting the viruses from off-target cells.

High-Capacity Adenoviral Vectors: Expanding the Scope of Gene Therapy

The adaptation of adenoviruses as gene delivery tools has resulted in the development of high-capacity adenoviral vectors (HC-AdVs), also known, helper-dependent or “gutless”. Compared with earlier generations (E1/E3-deleted vectors), HC-AdVs retain relevant features such as genetic stability, remarkable efficacy of in vivo transduction, and production at high titers. More importantly, the lack of viral coding sequences in the genomes of HC-AdVs extends the cloning capacity up to 37 Kb, and allows long-term episomal persistence of transgenes in non-dividing cells. These properties open a wide repertoire of therapeutic opportunities in the fields of gene supplementation and gene correction, which have been explored at the preclinical level over the past two decades. During this time, production methods have been optimized to obtain the yield, purity, and reliability required for clinical implementation. Better understanding of inflammatory responses and the implementation of methods to control them have increased the safety of these vectors. We will review the most significant achievements that are turning an interesting research tool into a sound vector platform, which could contribute to overcome current limitations in the gene therapy field.

Expanding the Spectrum of Adenoviral Vectors for Cancer Therapy

Adenoviral vectors (AdVs) have attracted much attention in the fields of vaccine development and treatment for diseases such as genetic disorders and cancer. In this review, we discuss the utility of AdVs in cancer therapies. In recent years, AdVs were modified as oncolytic AdVs (OAs) that possess the characteristics of cancer cell-specific replication and killing. Different carriers such as diverse cells and extracellular vesicles are being explored for delivering OAs into cancer sites after systemic administration. In addition, there are also various strategies to improve cancer-specific replication of OAs, mainly through modifying the early region 1 (E1) of the virus genome. It has been documented that oncolytic viruses (OVs) function through stimulating the immune system, resulting in the inhibition of cancer progression and, in combination with classical immune modulators, the anti-cancer effect of OAs can be even further enforced. To enhance the cancer treatment efficacy, OAs are also combined with other standard treatments, including surgery, chemotherapy and radiotherapy. Adenovirus type 5 (Ad5) has mainly been explored to develop vectors for cancer treatment with different modulations. Only a limited number of the more than 100 identified AdV types were converted into OAs and, therefore, the construction of an adenovirus library for the screening of potential novel OA candidates is essential. Here, we provide a state-of-the-art overview of currently performed and completed clinic trials with OAs and an adenovirus library, providing novel possibilities for developing innovative adenoviral vectors for cancer treatment.

Enhancing the antitumor activity of an engineered TRAIL-coated oncolytic adenovirus for treating acute myeloid leukemia

The use of oncolytic viruses has emerged as a promising therapeutic approach due to the features of these viruses, which selectively replicate and destroy tumor cells while sparing normal cells. Although numerous oncolytic viruses have been developed for testing in solid tumors, only a few have been reported to target acute myeloid leukemia (AML) and overall patient survival has remained low. We previously developed the oncolytic adenovirus rAd5pz-zTRAIL-RFP-SΔ24E1a (A4), which carries the viral capsid protein IX linked to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and results in increased infection of cancer cells and improved tumor targeting. To further improve the therapeutic potential of A4 by enhancing the engagement of virus and leukemia cells, we generated a new version of A4, zA4, by coating A4 with additional soluble TRAIL that is fused with a leucine zipper-like dimerization domain (zipper). ZA4 resulted in enhanced infectivity and significant inhibition of the proliferation of AML cells from cell lines and primary patient samples that expressed moderate levels of TRAIL-related receptors. ZA4 also elicited enhanced anti-AML activity in vivo compared with A4 and an unmodified oncolytic adenoviral vector. In addition, we found that the ginsenoside Rh2 upregulated the expression of TRAIL receptors and consequently enhanced the antitumor activity of zA4. Our results indicate that the oncolytic virus zA4 might be a promising new agent for treating hematopoietic malignancies such as AML.

Interactions of viruses and the humoral innate immune response

The innate immune response is crucial for defense against virus infections where the complement system, coagulation cascade and natural antibodies play key roles. These immune components are interconnected in an intricate network and are tightly regulated to maintain homeostasis and avoid uncontrolled immune responses. Many viruses in turn have evolved to modulate these interactions through various strategies to evade innate immune activation. This review summarizes the current understanding on viral strategies to inhibit the activation of complement and coagulation cascades, evade natural antibody-mediated clearance and utilize complement regulatory mechanisms to their advantage.

Immune Responses to Viral Gene Therapy Vectors

Several viral vector-based gene therapy drugs have now received marketing approval. A much larger number of additional viral vectors are in various stages of clinical trials for the treatment of genetic and acquired diseases, with many more in pre-clinical testing. Efficiency of gene transfer and ability to provide long-term therapy make these vector systems very attractive. In fact, viral vector gene therapy has been able to treat or even cure diseases for which there had been no or only suboptimal treatments. However, innate and adaptive immune responses to these vectors and their transgene products constitute substantial hurdles to clinical development and wider use in patients. This review provides an overview of the type of immune responses that have been documented in animal models and in humans who received gene transfer with one of three widely tested vector systems, namely adenoviral, lentiviral, or adeno-associated viral vectors. Particular emphasis is given to mechanisms leading to immune responses, efforts to reduce vector immunogenicity, and potential solutions to the problems. At the same time, we point out gaps in our knowledge that should to be filled and problems that need to be addressed going forward.

Innate immunity to adenovirus: lessons from mice

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

Interaction of adenovirus with antibodies, complement, and coagulation factors

Adenovirus (AdV) is one of the most widely used vectors for gene therapy and vaccine studies due to its excellent transduction efficiency, capacity for large transgenes, and high levels of gene expression. When administered intravascularly, the fate of AdV vectors is heavily influenced by interactions with host plasma proteins. Some plasma proteins can neutralize AdV, but AdV can also specifically bind plasma proteins that protect against neutralization and preserve activity. This review summarizes the plasma proteins that interact with AdV, including antibodies, complement, and vitamin K-dependent coagulation factors. We will also review the complex interactions of these plasma proteins with each other and with cellular proteins, as well as strategies for developing better AdV vectors that evade or manipulate plasma proteins.

Patchy Amphiphilic Dendrimers Bind Adenovirus and Control Its Host Interactions and in Vivo Distribution

The surface of proteins is heterogeneous with sophisticated but precise hydrophobic and hydrophilic patches, which is essential for their diverse biological functions. To emulate such distinct surface patterns on macromolecules, we used rigid spherical synthetic dendrimers (polyphenylene dendrimers) to provide controlled amphiphilic surface patches with molecular precision. We identified an optimal spatial arrangement of these patches on certain dendrimers that enabled their interaction with human adenovirus 5 (Ad5). Patchy dendrimers bound to the surface of Ad5 formed a synthetic polymer corona that greatly altered various host interactions of Ad5 as well as in vivo distribution. The dendrimer corona (1) improved the ability of Ad5-derived gene transfer vectors to transduce cells deficient for the primary Ad5 cell membrane receptor and (2) modulated the binding of Ad5 to blood coagulation factor X, one of the most critical virus-host interactions in the bloodstream. It significantly enhanced the transduction efficiency of Ad5 while also protecting it from neutralization by natural antibodies and the complement system in human whole blood. Ad5 with a synthetic dendrimer corona revealed profoundly altered in vivo distribution, improved transduction of heart, and dampened vector sequestration by liver and spleen. We propose the design of bioactive polymers that bind protein surfaces solely based on their amphiphilic surface patches and protect against a naturally occurring protein corona, which is highly attractive to improve Ad5-based in vivo gene therapy applications.

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

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

Genetic strategy to decrease complement activation with adenoviral therapies

Background

A major obstacle to using recombinant adenoviral vectors in gene therapy is the natural ability of human adenovirus to activate the classical and alternate complement pathways. These innate immune responses contribute to hepatic adenoviral uptake following systemic delivery and enhance the humoral immune responses associated with adenoviral infection.

Methods

A recombinant Ad5 vector was genetically modified to display a peptide sequence (“rH17d’”), a known inhibitor of the classical complement pathway. The replication-defective vectors Ad5.HVR2-rH17d’ and Ad5.HVR5-rH17d’ were constructed by engineering the rH17d’ peptide into the hypervariable region (HVR)-2 or HVR5 of their major capsid protein hexon. Control Ad5 vectors were created by incorporation of a 6-histidine (His₆)-insert in either HVR2 or HVR5 (Ad5.HVR2-His₆ and Ad5.HVR5-His₆, respectively). All vectors encoded CMV promoter-controlled firefly luciferase (Luc). The four vectors were evaluated in TIB76 mouse liver cells and immunocompetent mice to compare infectivity and liver sequestration, respectively.

Results

In vitro studies demonstrated that preincubation of all the Ad5 vectors with fresh serum significantly increased their gene transfer relative to preincubation with PBS except Ad5.HVR5-rH17d’, whose infectivity of liver cells showed no serum-mediated enhancement. In line with that, mice injected with Ad5.HVR2-rH17d’ or Ad5.HVR5-rH17d’ showed significantly lower luciferase expression levels in the liver as compared to the respective control vectors, whereas efficiency of tumor transduction by rH17d’ and His₆ vectors following their intratumoral injection was similar.

Conclusions

Displaying a complement-inhibiting peptide on the Ad5 capsid surface by genetic modification of the hexon protein could be a suitable strategy for reducing Ad5 liver tropism (Ad5 sequestration by liver), which may be applicable to other gene therapy vectors with natural liver tropism.

Complement C4 Prevents Viral Infection through Capsid Inactivation

The complement system is vital for anti-microbial defense. In the classical pathway, pathogen-bound antibody recruits the C1 complex (C1qC1r₂C1s₂) that initiates a cleavage cascade involving C2, C3, C4, and C5 and triggering microbial clearance. We demonstrate a C4-dependent antiviral mechanism that is independent of downstream complement components. C4 inhibits human adenovirus infection by directly inactivating the virus capsid. Rapid C4 activation and capsid deposition of cleaved C4b are catalyzed by antibodies via the classical pathway. Capsid-deposited C4b neutralizes infection independent of C2 and C3 but requires C1q antibody engagement. C4b inhibits capsid disassembly, preventing endosomal escape and cytosolic access. C4-deficient mice exhibit heightened viral burdens. Additionally, complement synergizes with the Fc receptor TRIM21 to block transduction by an adenovirus gene therapy vector but is partially restored by Fab virus shielding. These results suggest that the complement system could be altered to prevent virus infection and enhance virus gene therapy efficacy.

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Complement components C1 and C4 mediate potent neutralization of adenovirus

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Deposition of C4b on the viral capsid inactivates capsid disassembly

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C4 exerts direct antiviral functions independent from its role as a C3-convertase

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C4 antiviral functions synergize with TRIM21-mediated virus neutralization

Microbubble-mediated delivery of human adenoviruses does not elicit innate and adaptive immunity response in an immunocompetent mouse model of prostate cancer

Background

Gene transfer to malignant sites using human adenoviruses (hAds) has been limited because of their immunogenic nature and host specificity. Murine cells often lack some of the receptors needed for hAds attachment, thus murine cells are generally non-permissive for human adenoviral infection and replication, which limits translational studies.

Methods

We have developed a gene transfer method that uses a combination of lipid-encapsulated perfluorocarbon microbubbles and ultrasound to protect and deliver hAds to a target tissue, bypassing the requirement of specific receptors.

Results

In an in vitro model, we showed that murine TRAMP-C2 and human DU145 prostate cancer cells display a comparable expression pattern of receptors involved in hAds adhesion and internalization. We also demonstrated that murine and human cells showed a dose-dependent increase in the percentage of cells transduced by hAd-GFP (green fluorescent protein) after 24 h and that GFP transgene was efficiently expressed at 48 and 72 h post-transduction. To assess if our image-guided delivery system could effectively protect the hAds from the immune system in vivo, we injected healthy immunocompetent mice (C57BL/6) or mice bearing a syngeneic prostate tumor (TRAMP-C2) with hAd-GFP/MB complexes. Notably, we did not observe activation of innate (TNF-α and IL-6 cytokines), or adaptive immune response (neutralizing antibodies, INF-γ+ CD8⁺ T cells).

Conclusions

This study brings us a step closer to demonstrating the feasibility of murine cancer models to investigate the clinical translation of image guided site-specific adenoviral gene therapy mediated by ultrasound-targeted microbubble destruction.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1771-0) contains supplementary material, which is available to authorized users.

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

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

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.