Functions and mechanisms of action of the adenovirus E3 proteins

Adenoviral Vector System: A Comprehensive Overview of Constructions, Therapeutic Applications and Host Responses

Adenoviral vectors are crucial for gene therapy and vaccine development, offering a platform for gene delivery into host cells. Since the discovery of adenoviruses, first-generation vectors with limited capacity have evolved to third-generation vectors flacking viral coding sequences, balancing safety and gene-carrying capacity. The applications of adenoviral vectors for gene therapy and anti-viral treatments have expanded through the use of in vitro ligation and homologous recombination, along with gene editing advancements such as CRISPR-Cas9. Current research aims to maintain the efficacy and safety of adenoviral vectors by addressing challenges such as pre-existing immunity against adenoviral vectors and developing new adenoviral vectors from rare adenovirus types and non-human species. In summary, adenoviral vectors have great potential in gene therapy and vaccine development. Through continuous research and technological advancements, these vectors are expected to lead to the development of safer and more effective treatments.

The Immune System-A Double-Edged Sword for Adenovirus-Based Therapies

Pathogenic adenovirus (Ad) infections are widespread but typically mild and transient, except in the immunocompromised. As vectors for gene therapy, vaccine, and oncology applications, Ad-based platforms offer advantages, including ease of genetic manipulation, scale of production, and well-established safety profiles, making them attractive tools for therapeutic development. However, the immune system often poses a significant challenge that must be overcome for adenovirus-based therapies to be truly efficacious. Both pre-existing anti-Ad immunity in the population as well as the rapid development of an immune response against engineered adenoviral vectors can have detrimental effects on the downstream impact of an adenovirus-based therapeutic. This review focuses on the different challenges posed, including pre-existing natural immunity and anti-vector immunity induced by a therapeutic, in the context of innate and adaptive immune responses. We summarise different approaches developed with the aim of tackling these problems, as well as their outcomes and potential future applications.

Advances of Recombinant Adenoviral Vectors in Preclinical and Clinical Applications

Adenoviruses (Ad) have the potential to induce severe infections in vulnerable patient groups. Therefore, understanding Ad biology and antiviral processes is important to comprehend the signaling cascades during an infection and to initiate appropriate diagnostic and therapeutic interventions. In addition, Ad vector-based vaccines have revealed significant potential in generating robust immune protection and recombinant Ad vectors facilitate efficient gene transfer to treat genetic diseases and are used as oncolytic viruses to treat cancer. Continuous improvements in gene delivery capacity, coupled with advancements in production methods, have enabled widespread application in cancer therapy, vaccine development, and gene therapy on a large scale. This review provides a comprehensive overview of the virus biology, and several aspects of recombinant Ad vectors, as well as the development of Ad vector, are discussed. Moreover, we focus on those Ads that were used in preclinical and clinical applications including regenerative medicine, vaccine development, genome engineering, treatment of genetic diseases, and virotherapy in tumor treatment.

The Development and Characterization of a Next-Generation Oncolytic Virus Armed with an Anti-PD-1 sdAb for Osteosarcoma Treatment In Vitro

Osteosarcoma (OS) is a primary bone malignancy characterized by an aggressive nature, limited treatment options, low survival rate, and poor patient prognosis. Conditionally replicative adenoviruses (CRAds) armed with immune checkpoint inhibitors hold great potential for enhanced therapeutic efficacy. The present study aims to investigate the anti-tumor efficacy of CAV2-AU-M2, a CAV2-based CRAd armed with an anti-PD-1 single-domain antibody (sdAb), against OS cell lines in vitro. The infection, conditional replication, cytopathic effects, and cytotoxicity of CAV2-AU-M2 were tested in four different OS cell lines in two-dimensional (2D) and three-dimensional (3D) cell cultures. CAV2-AU-M2 showed selective replication in the OS cells and induced efficient tumor cell lysis and death. Moreover, CAV2-AU-M2 produced an anti-PD-1 sdAb that demonstrated effective binding to the PD-1 receptors. This study demonstrated the first CRAd armed with an anti-PD-1 sdAb. This combined approach of two distinct immunotherapies is intended to enhance the anti-tumor immune response in the tumor microenvironment.

Development of oncolytic and gene therapy vectors based on adenovirus serotype 4 as an alternative to adenovirus serotype 5

BACKGROUND

Adenoviral vectors are among the most frequently used vectors for gene therapy and cancer treatment. Most vectors are derived from human adenovirus (Ad) serotype 5 despite limited applicability caused by pre-existing immunity and unfavorable liver tropism, whereas the other more than 100 known human serotypes remain largely unused. Here, we screened a library of human Ad types and identified Ad4 as a promising candidate vector.

METHODS

Reporter-gene-expressing viruses representative of the natural human Ad diversity were used to transduce an array of muscle cell lines and two- or three-dimensional tumor cultures. The time-course of transgene expression was monitored by fluorescence or luminescence measurements. To generate replication-deficient Ad4 vector genomes, successive homologous recombination was applied.

RESULTS

Ad4, 17 and 50 transduced human cardiomyocytes more efficiently than Ad5, whereas Ad37 was found to be superior in rhabdomyocytes. Despite its moderate transduction efficiency, Ad4 showed efficient and long-lasting gene expression in papillomavirus (HPV) positive tumor organoids. Therefore, we aimed to harness the potential of Ad4 for improved muscle transduction or oncolytic virotherapy of HPV-positive tumors. We deleted the E1 and E3 transcription units to produce first generation Ad vectors for gene therapy. The E1- and E1/E3-deleted vectors were replication-competent in HEK293 cells stably expressing E1 but not in the other cell lines tested. Furthermore, we show that the Ad5 E1 transcription unit can complement the replication of E1-deleted Ad4 vectors.

CONCLUSIONS

Our Ad4-based gene therapy vector platform contributes to the development of improved Ad vectors based on non-canonical serotypes for a broad range of applications.

Construction and application of adenoviral vectors

Adenoviral vectors have been widely used as vaccine candidates or potential vaccine candidates against infectious diseases due to the convenience of genome manipulation, their ability to accommodate large exogenous gene fragments, easy access of obtaining high-titer of virus, and high efficiency of transduction. At the same time, adenoviral vectors have also been used extensively in clinical research for cancer gene therapy and treatment of diseases caused by a single gene defect. However, application of adenovirus also faces a series of challenges such as poor targeting, strong immune response against the vector itself, and they cannot be used repeatedly. It is believed that these problems will be solved gradually with further research and technological development in related fields. Here, we review the construction methods of adenoviral vectors, including "gutless" adenovirus and discuss application of adenoviral vectors as prophylactic vaccines for infectious pathogens and their application prospects as therapeutic vaccines for cancer and other kinds of chronic infectious disease such as human papillomavirus, hepatitis B virus, and hepatitis C virus.

Pathogenicity and virulence of human adenovirus F41: Possible links to severe hepatitis in children

Over 100 human adenoviruses (HAdVs) have been isolated and allocated to seven species, A-G. Species F comprises two members-HAdV-F40 and HAdV-F41. As their primary site of infection is the gastrointestinal tract they have been termed, with species A, enteric adenoviruses. HAdV-F40 and HAdV-F41 are a common cause of gastroenteritis and diarrhoea in children. Partly because of difficulties in propagating the viruses in the laboratory, due to their restrictions on growth in many cell lines, our knowledge of the properties of individual viral proteins is limited. However, the structure of HAdV-F41 has recently been determined by cryo-electron microscopy. The overall structure is similar to those of HAdV-C5 and HAdV-D26 although with some differences. The sequence and arrangement of the hexon hypervariable region 1 (HVR1) and the arrangement of the C-terminal region of protein IX differ. Variations in the penton base and hexon HVR1 may play a role in facilitating infection of intestinal cells by HAdV-F41. A unique feature of HAdV-F40 and F41, among human adenoviruses, is the presence and expression of two fibre genes, giving long and short fibre proteins. This may also contribute to the tropism of these viruses. HAdV-F41 has been linked to a recent outbreak of severe acute hepatitis "of unknown origin" in young children. Further investigation has shown a very high prevalence of adeno-associated virus-2 in the liver and/or plasma of some cohorts of patients. These observations have proved controversial as HAdV-F41 had not been reported to infect the liver and AAV-2 has generally been considered harmless.

Adenoviral Gene Therapy Vectors in Clinical Use-Basic Aspects with a Special Reference to Replication-Competent Adenovirus Formation and Its Impact on Clinical Safety

Adenoviral vectors are commonly used in clinical gene therapy. Apart from oncolytic adenoviruses, vector replication is highly undesired as it may pose a safety risk for the treated patient. Thus, careful monitoring for the formation of replication-competent adenoviruses (RCA) during vector manufacturing is required. To render adenoviruses replication deficient, their genomic E1 region is deleted. However, it has been known for a long time that during their propagation, some viruses will regain their replication capability by recombination in production cells, most commonly HEK293. Recently developed RCA assays have revealed that many clinical batches contain more RCA than previously assumed and allowed by regulatory authorities. The clinical significance of the higher RCA content has yet to be thoroughly evaluated. In this review, we summarize the biology of adenovirus vectors, their manufacturing methods, and the origins of RCA formed during HEK293-based vector production. Lastly, we share our experience using minimally RCA-positive serotype 5 adenoviral vectors based on observations from our clinical cardiovascular gene therapy studies.

The pathologic spectrum of adenovirus nephritis in the kidney allograft

Adenovirus nephritis (ADVN) is a rare and understudied complication of kidney transplantation. Unlike BK virus nephropathy (BKVN), our knowledge of clinicopathologic manifestations of ADVN remains rudimentary and essentially limited to case reports. To expand on this, we retrospectively studied 11 kidney transplant recipients with ADVN and compared their allograft biopsies to 33 kidney transplant recipients with BKVN using conventional microscopy and the 770 gene Nanostring Banff Human Organ Transplant Profiling Panel. Patients with ADVN had a median age of 44 years, were predominantly male, and developed ADVN at a median of 31 months post-transplantation. Eight patients presented with fever and ten had hematuria. The most common histologic manifestations included granulomas (82%), tubulocentric inflammation (73%), and tubular degenerative changes consistent with acute tubular necrosis (73%). During a median follow-up of 55 months after biopsy, three patients developed allograft failure from subsequent acute rejection. All seven patients with available follow-up PCR showed resolution of viremia at a median of 30 days after diagnosis. Compared to BKVN, ADVN demonstrated more granulomas and less tubulointerstitial scarring. On follow-up, patients with ADVN had more rapid clearance of viral DNA from plasma. Transcriptomic analyses showed that ADVN had increased expression of several pro-inflammatory transcriptomes, mainly related to innate immunity, was associated with increased expression of transcripts with inhibitory effects on inflammatory response and showed higher enrichment with neutrophils, which can cause aggressive but short-lasting damage. Thus, we demonstrate that, despite its association with aggressive neutrophil-rich inflammation, ADVN does not often lead to allograft failure. Hence, preventing subsequent acute rejection following resolution of ADVN may improve allograft survival.

A Renaissance for Oncolytic Adenoviruses?

In the 1990s, adenovirus became one of the first virus types to be genetically engineered to selectively destroy cancer cells. In the intervening years, the field of "oncolytic viruses" has slowly progressed and culminated in 2015 with the FDA approval of Talimogene laherparepvec, a genetically engineered herpesvirus, for the treatment of metastatic melanoma. Despite the slower progress in translating oncolytic adenovirus to the clinic, interest in the virus remains strong. Among all the clinical trials currently using viral oncolytic agents, the largest proportion of these are using recombinant adenovirus. Many trials are currently underway to use oncolytic virus in combination with immune checkpoint inhibitors (ICIs), and early results using oncolytic adenovirus in this manner are starting to show promise. Many of the existing strategies to engineer adenoviruses were designed to enhance selective tumor cell replication without much regard to interactions with the immune system. Adenovirus possesses a wide range of viral factors to attenuate both innate anti-viral pathways and immune cell killing. In this review, we summarize the strategies of oncolytic adenoviruses currently in clinical trials, and speculate how the mutational backgrounds of these viruses may impact upon the efficacy of these agents in oncolytic and immunotherapy. Despite decades of research on human adenoviruses, the interactions that these viruses have with the immune system remains one of the most understudied aspects of the virus and needs to be improved to rationally design the next generation of engineered viruses.

An Old Acquaintance: Could Adenoviruses Be Our Next Pandemic Threat?

Human adenoviruses (HAdV) are one of the most important pathogens detected in acute respiratory diseases in pediatrics and immunocompromised patients. In 1953, Wallace Rowe described it for the first time in oropharyngeal lymphatic tissue. To date, more than 110 types of HAdV have been described, with different cellular tropisms. They can cause respiratory and gastrointestinal symptoms, even urinary tract inflammation, although most infections are asymptomatic. However, there is a population at risk that can develop serious and even lethal conditions. These viruses have a double-stranded DNA genome, 25-48 kbp, 90 nm in diameter, without a mantle, are stable in the environment, and resistant to fat-soluble detergents. Currently the diagnosis is made with lateral flow immunochromatography or molecular biology through a polymerase chain reaction. This review aimed to highlight the HAdV variability and the pandemic potential that a HAdV3 and 7 recombinant could have considering the aggressive outbreaks produced in health facilities. Herein, we described the characteristics of HAdV, from the infection to treatment, vaccine development, and the evaluation of the social determinants of health associated with HAdV, suggesting the necessary measures for future sanitary control to prevent disasters such as the SARS-CoV-2 pandemic, with an emphasis on the use of recombinant AdV vaccines to control other potential pandemics.

High genetic stability of co-circulating human adenovirus type 31 lineages over 59 years

Type 31 of human adenovirus species A (HAdV-A31) is a significant pathogen primarily associated with diarrhoea in children but also with life-threatening disseminated disease in allogeneic haematopoietic stem cell transplant (HSCT) recipients. Nosocomial outbreaks of HAdV-A31 have been frequently described. However, the evolution of HAdV-A31 has not been studied in detail. The evolution of other HAdV types is driven either by intertypic recombination, where different types exchange genome regions, or by immune escape selection of neutralisation determinants. Complete genomic HAdV-A31 sequences from sixty diagnostic specimens of the past 18 years (2003-21) were generated, including fourteen specimens of a presumed outbreak on two HSCT wards. Additionally, twenty-three complete genomes from GenBank were added to our phylogenetic analysis as well as in silico generated and previously published restriction fragment polymorphism (RFLP) data. Phylogenetic analysis of eighty-three genomes indicated that HAdV-A31 evolved slowly with six lineages co-circulating. The two major lineages were lineage 1, which included the prototype from 1962 and nine recent isolates, and lineage 2, which split into four sublineages and included most isolates from 2003 to 2021. The average nucleotide identity within lineages was high (99.8 per cent) and identity between lineages was 98.7 and 99.2 per cent. RFLP data allowed the construction of a lower-resolution phylogeny with two additional putative lineages. Surprisingly, regions of higher diversity separating lineages were found in gene regions coding for non-structural and minor capsid proteins. Intertypic recombinations were not observed, but the phylogeny of lineage 3 was compatible with an interlineage recombination event in the fibre gene. Applying the phylogenetic analysis to the presumed nosocomial outbreak excluded two suspected transmission events and separated it into two different, simultaneous outbreaks caused by different sublineages of lineage 2. However, due to the high nucleotide identity within HAdV-A31 lineages, the proof of infection chains remains debatable. This in-depth study on the molecular phylogeny of HAdV-A31 highlights the high genetic stability of co-circulating HAdV-A31 lineages over almost six decades. It also supports the epidemiological hypothesis that HAdV-A31 circulates as an etiological agent of a childhood disease infecting immunologically naive patients without strong positive selection of immune escape variants and recombinants.

Nonhuman Primate Adenoviruses of the Human Adenovirus B Species Are Potent and Broadly Acting Oncolytic Vector Candidates

The use of human adenoviruses (hAds) as oncolytic agents has demonstrated considerable potential. However, their efficacy in clinical studies is generally moderate and often varies between patients. This may, in part, be attributable to variable pre-existing neutralizing immunity in patients, which can impact the antitumor efficacy and lead to response heterogeneity. Our aim was to isolate new Ads for the development of oncolytic vectors with low prevalence of neutralizing immunity in the human population. To this end, we isolated a collection of new nonhuman primate (nhp) Ads from stool samples of four great ape species held captive. We elected 12 isolates comprising the broadest genetic variability for further characterization. For three new nhpAds, all classified as the human adenovirus B (HAdV-B) species, no neutralizing activity could be detected when exposed to a preparation of immunoglobulins isolated from a pool of >1,000 donors as a surrogate of population immunity. In addition, the nhpAds of the HAdV-B species showed enhanced oncolytic potency compared to nhpAds of the HAdV-C species as well as to human adenovirus type 5 (HAdV-C5) in vitro when tested in a panel of 29 human cancer cell lines. Next-generation sequencing of the viral genomes revealed higher sequence similarity between hAds and nhpAds of HAdV-B compared to HAdV-C, which might underlie the differences in oncolytic ability. As a proof-of-concept, the Rb-binding domain of the E1A protein of the gorilla-derived HAdV-B nhpAd-lumc007 was deleted, thereby creating a new oncolytic derivative, which demonstrated increased oncolytic potential compared to HAdV-C5. Collectively, our data demonstrate that nhpAds of the HAdV-B species can serve as an alternative for the development of potent oncolytic Ad vectors with limited pre-existing neutralizing immunity in humans.

Mouse Adenovirus Type 1 Persistence Exacerbates Inflammation Induced by Allogeneic Bone Marrow Transplantation

Bone marrow transplantation (BMT) recipients are at risk for substantial morbidity and mortality from human adenovirus infections, often in the setting of reactivation of persistent virus. Human adenovirus persistence in mucosal lymphocytes has been described, but specific cellular reservoirs of persistence and effects of persistence on host responses to unrelated stimuli are not completely understood. We used mouse adenovirus type 1 (MAV-1) to characterize persistence of an adenovirus in its natural host and test the hypothesis that persistence increases complications of bone marrow transplantation (BMT). Following intranasal infection of C57BL/6J mice, MAV-1 DNA was detected in lung, mediastinal lymph nodes, and liver during acute infection at 7 days post infection (dpi), and at lower levels at 28 dpi that remained stable through 150 dpi. Expression of early and late viral transcripts was detected in those organs at 7 dpi but not at later time points. MAV-1 persistence was not affected by deficiency of IFN-γ. We detected no evidence of MAV-1 reactivation in vivo following allogeneic BMT of persistently infected mice. Persistent infection did not substantially affect mortality, weight loss, or pulmonary inflammation following BMT. However, T cell infiltration and increased expression of pro-inflammatory cytokines consistent with graft-versus-host disease (GVHD) were more pronounced in livers of persistently infected BMT mice than in uninfected BMT mice. These results suggest that MAV-1 persists in multiple sites without detectable evidence of ongoing replication. Our results indicate that MAV-1 persistence alters host responses to an unrelated challenge, even in the absence of detectable reactivation. Importance Long-term persistence in an infected host is an essential step in the life cycle of DNA viruses. Adenoviruses persist in their host following acute infection, but the nature of adenovirus persistence remains incompletely understood. Following intranasal infection of mice, we found that MAV-1 persists for a prolonged period in multiple organs, although we did not detect evidence of ongoing replication. Because BMT recipients are at risk for substantial morbidity and mortality from human adenovirus infections, often in the setting of reactivation of persistent virus in the recipient, we extended our findings using MAV-1 infection in a mouse model of BMT. MAV-1 persistence exacerbated GVHD-like inflammation following allogeneic BMT, even in the absence of virus reactivation. This novel finding suggests that adenovirus persistence has consequences, and it highlights the potential for a persistent adenovirus to influence host responses to unrelated challenges.

Genomic analyses of human adenoviruses unravel novel recombinant genotypes associated with severe infections in pediatric patients

Human adenoviruses (HAdVs) are highly contagious pathogens of clinical importance, especially among the pediatric population. Studies on comparative viral genomic analysis of cases associated with severe and mild infections due to HAdV are limited. Using whole-genome sequencing (WGS), we investigated whether there were any differences between circulating HAdV strains associated with severe infections (meningitis, sepsis, convulsion, sudden infant death syndrome, death, and hospitalization) and mild clinical presentations in pediatric patients hospitalized between the years 1998 and 2017 in a tertiary care hospital group in Bern, Switzerland covering a population base of approx. 2 million inhabitants. The HAdV species implicated in causing severe infections in this study included HAdV species C genotypes (HAdV1, HAdV2, and HAdV5). Clustering of the HAdV whole-genome sequences of the severe and mild cases did not show any differences except for one sample (isolated from a patient presenting with sepsis, meningitis, and hospitalization) that formed its own cluster with HAdV species C genotypes. This isolate showed intertypic recombination events involving four genotypes, had the highest homology to HAdV89 at complete genome level, but possessed the fiber gene of HAdV1, thereby representing a novel genotype of HAdV species C. The incidence of potential recombination events was higher in severe cases than in mild cases. Our findings confirm that recombination among HAdVs is important for molecular evolution and emergence of new strains. Therefore, further research on HAdVs, particularly among susceptible groups, is needed and continuous surveillance is required for public health preparedness including outbreak investigations.

The endoplasmic reticulum unfolded protein response - homeostasis, cell death and evolution in virus infections

Viruses elicit cell and organismic stress, and offset homeostasis. They trigger intrinsic, innate and adaptive immune responses, which limit infection. Viruses restore homeostasis by harnessing evolutionary conserved stress responses, such as the endoplasmic reticulum (ER) unfolded protein response (UPRER). The canonical UPRER restores homeostasis based on a cell-autonomous signalling network modulating transcriptional and translational output. The UPRER remedies cell damage, but upon severe and chronic stress leads to cell death. Signals from the UPRER flow along three branches with distinct stress sensors, the inositol requiring enzyme (Ire) 1, protein kinase R (PKR)-like ER kinase (PERK), and the activating transcription factor 6 (ATF6). This review shows how both enveloped and non-enveloped viruses use the UPRER to control cell stress and metabolic pathways, and thereby enhance infection and progeny formation, or undergo cell death. We highlight how the Ire1 axis bypasses apoptosis, boosts viral transcription and maintains dormant viral genomes during latency and persistence periods concurrent with long term survival of infected cells. These considerations open new options for oncolytic virus therapies against cancer cells where the UPRER is frequently upregulated. We conclude with a discussion of the evolutionary impact that viruses, in particular retroviruses, and anti-viral defense has on the UPRER.

HUMAN ADENOVIRUS TYPE 4 COMPRISES TWO MAJOR PHYLOGROUPS WITH DISTINCT REPLICATIVE FITNESS AND VIRULENCE PHENOTYPES

Human adenovirus type 4 (HAdV-E4) is the only type (and serotype) classified within species Human mastadenovirus E that has been isolated from a human host to the present. Recent phylogenetic analysis of whole genome sequences of strains representing the spectrum of intratypic genetic diversity described to date identified two major evolutionary lineages designated phylogroups (PG) I, and II, and validated the early clustering of HAdV-E4 genomic variants into two major groups by low resolution restriction fragment length polymorphism analysis. In this study we expanded our original analysis of intra- and inter-PG genetic variability, and used a panel of viruses representative of the spectrum of genetic diversity described for HAdV-E4 to examine the magnitude of inter- and intra-PG phenotypic diversity using an array of cell-based assays and a cotton rat model of HAdV respiratory infection. Our proteotyping of HAdV-E strains using concatenated protein sequences in selected coding regions including E1A, E1B-19K and -55K, DNA polymerase, L4-100K, various E3 proteins, and E4-34K confirmed that the two clades encode distinct variants/proteotypes at most of these loci. Our in vitro and in vivo studies demonstrated that PG I and PG II differ in their growth, spread, and cell killing phenotypes in cell culture and in their pulmonary pathogenic phenotypes. Surprisingly, the differences in replicative fitness documented in vitro between PGs did not correlate with the differences in virulence observed in the cotton rat model. This body of work is the first reporting phenotypic correlates of naturally occurring intratypic genetic variability for HAdV-E4. IMPORTANCE Human adenovirus type 4 (HAdV-E4) is a prevalent causative agent of acute respiratory illness of variable severity and of conjunctivitis and comprises two major phylogroups that carry distinct coding variations in proteins involved in viral replication and modulation of host responses to infection. Our data show that PG I and PG II are intrinsically different regarding their ability to grow and spread in culture and to cause pulmonary disease in cotton rats. This is the first report of phenotypic divergence among naturally occurring known genetic variants of a HAdV type of medical importance. This research reveals readily detectable phenotypic differences between strains representing phylogroups I and II, and it introduces a unique experimental system for the elucidation of the genetic basis of adenovirus fitness and virulence and thus for increasing our understanding of the implications of intratypic genetic diversity in the presentation and course of HAdV-E4-associated disease.

The genome position of a therapeutic transgene strongly influences the level of expression in an armed oncolytic human adenovirus vector

Efficacy of oncolytic, conditionally-replicating adenovirus (CRAd) vectors can be enhanced by "arming" the vector with therapeutic transgenes. We examined whether inclusion of an intact early region 3 (E3) and the reptilian reovirus fusogenic p14 fusion-associated small transmembrane (FAST) protein enhanced vector efficacy. The p14 FAST transgene was cloned between the fiber gene and E4 region, with an upstream splice acceptor for replication-dependent expression from the major late promoter. In A549 cells, this vector expressed p14 FAST protein at very low levels, and showed a poor ability to mediate cell-cell fusion, relative to a similar vector encoding p14 FAST within the E3 deletion. Although expression of E3 proteins from the CRAd increased plaque size, poor expression of p14 FAST protein compromised the fusogenic capacity of the vector. Thus, location of a therapeutic transgene within a CRAd can significantly impact expression of the transgene and is an important consideration in vector design.

Vaccines based on replication incompetent Ad26 viral vectors: Standardized template with key considerations for a risk/benefit assessment

Replication-incompetent adenoviral vectors have been under investigation as a platform to carry a variety of transgenes, and express them as a basis for vaccine development. A replication-incompetent adenoviral vector based on human adenovirus type 26 (Ad26) has been evaluated in several clinical trials. The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to evaluate the safety and features of recombinant viral vector vaccines. This paper reviews features of the Ad26 vectors, including tabulation of safety and risk assessment characteristics of Ad26-based vaccines. In the Ad26 vector, deletion of E1 gene rendering the vector replication incompetent is combined with additional genetic engineering for vaccine manufacturability and transgene expression optimization. These vaccines can be manufactured in mammalian cell lines at scale providing an effective, flexible system for high-yield manufacturing. Ad26 vector vaccines have favorable thermostability profiles, compatible with vaccine supply chains. Safety data are compiled in the Ad26 vaccine safety database version 4.0, with unblinded data from 23 ongoing and completed clinical studies for 3912 participants in five different Ad26-based vaccine programs. Overall, Ad26-based vaccines have been well tolerated, with no significant safety issues identified. Evaluation of Ad26-based vaccines is continuing, with >114,000 participants vaccinated as of 4th September 2020. Extensive evaluation of immunogenicity in humans shows strong, durable humoral and cellular immune responses. Clinical trials have not revealed impact of pre-existing immunity to Ad26 on vaccine immunogenicity, even in the presence of Ad26 neutralizing antibody titers or Ad26-targeting T cell responses at baseline. The first Ad26-based vaccine, against Ebola virus, received marketing authorization from EC on 1st July 2020, as part of the Ad26.ZEBOV, MVA-BN-Filo vaccine regimen. New developments based on Ad26 vectors are underway, including a COVID-19 vaccine, which is currently in phase 3 of clinical evaluation.

Viral Interactions with Adaptor-Protein Complexes: A Ubiquitous Trait among Viral Species

Numerous viruses hijack cellular protein trafficking pathways to mediate cell entry or to rearrange membrane structures thereby promoting viral replication and antagonizing the immune response. Adaptor protein complexes (AP), which mediate protein sorting in endocytic and secretory transport pathways, are one of the conserved viral targets with many viruses possessing AP-interacting motifs. We present here different mechanisms of viral interference with AP complexes and the functional consequences that allow for efficient viral propagation and evasion of host immune defense. The ubiquity of this phenomenon is evidenced by the fact that there are representatives for AP interference in all major viral families, covered in this review. The best described examples are interactions of human immunodeficiency virus and human herpesviruses with AP complexes. Several other viruses, like Ebola, Nipah, and SARS-CoV-2, are pointed out as high priority disease-causative agents supporting the need for deeper understanding of virus-AP interplay which can be exploited in the design of novel antiviral therapies.

Microscopy deep learning predicts virus infections and reveals mechanics of lytic-infected cells

Imaging across scales reveals disease mechanisms in organisms, tissues, and cells. Yet, particular infection phenotypes, such as virus-induced cell lysis, have remained difficult to study. Here, we developed imaging modalities and deep learning procedures to identify herpesvirus and adenovirus (AdV) infected cells without virus-specific stainings. Fluorescence microscopy of vital DNA-dyes and live-cell imaging revealed learnable virus-specific nuclear patterns transferable to related viruses of the same family. Deep learning predicted two major AdV infection outcomes, non-lytic (nonspreading) and lytic (spreading) infections, up to about 20 hr prior to cell lysis. Using these predictive algorithms, lytic and non-lytic nuclei had the same levels of green fluorescent protein (GFP)-tagged virion proteins but lytic nuclei enriched the virion proteins faster, and collapsed more extensively upon laser-rupture than non-lytic nuclei, revealing impaired mechanical properties of lytic nuclei. Our algorithms may be used to infer infection phenotypes of emerging viruses, enhance single cell biology, and facilitate differential diagnosis of non-lytic and lytic infections.

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Artificial intelligence identifies HSV- and AdV-infected cells without specific probes.

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Imaging lytic-infected cells reveals nuclear envelope rupture and AdV dissemination.

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Live cell imaging and neural networks presciently pinpoint lytic-infected cells.

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Lytic-infected cell nuclei have mechanical properties distinct from non-lytic nuclei.

Molecular characterization of canine adenovirus type 2 in dogs from India

A total of 26 nasal swab samples were collected from dogs with gastroenteritis and respiratory tract infections in and around Chennai, India during 2019–20. All the samples were subjected to PCR using common primers for rapid diagnosis and differentiation of CAV1 and CAV2. Only one sample produced an amplicon of 1030 bp indicating the presence of CAV2 which was confirmed by further sequencing. The analysis of the sequence revealed 100 per cent identity with other CAV type 2 isolates from Brazilian, Canadian and USA strains and 95.9 per cent identity with other Indian CAV2 strains. The phylogenetic analysis of E3 gene reveal two distinct clusters (Asian and America-Europe subgroup) in which our strain (ABT/MVC/CAV2/001) grouped with CAV2 of America-Europe subgroup instead of Asian continent subgroup.This study confirms a novel CAV2 strain using molecular techniques which are genetically distinct in nature from other Indian CAV2 strains that is currently circulating in India.

A replication-competent adenovirus-vectored influenza vaccine induces durable systemic and mucosal immunity

BACKGROUNDTo understand the features of a replicating vaccine that might drive potent and durable immune responses to transgene-encoded antigens, we tested a replication-competent adenovirus type 4 encoding influenza virus H5 HA (Ad4-H5-Vtn) administered as an oral capsule or via tonsillar swab or nasal spray.METHODSViral shedding from the nose, mouth, and rectum was measured by PCR and culturing. H5-specific IgG and IgA antibodies were measured by bead array binding assays. Serum antibodies were measured by a pseudovirus entry inhibition, microneutralization, and HA inhibition assays.RESULTSAd4-H5-Vtn DNA was shed from most upper respiratory tract-immunized (URT-immunized) volunteers for 2 to 4 weeks, but cultured from only 60% of participants, with a median duration of 1 day. Ad4-H5-Vtn vaccination induced increases in H5-specific CD4+ and CD8+ T cells in the peripheral blood as well as increases in IgG and IgA in nasal, cervical, and rectal secretions. URT immunizations induced high levels of serum neutralizing antibodies (NAbs) against H5 that remained stable out to week 26. The duration of viral shedding correlated with the magnitude of the NAb response at week 26. Adverse events (AEs) were mild, and peak NAb titers were associated with overall AE frequency and duration. Serum NAb titers could be boosted to very high levels 2 to 5 years after Ad4-H5-Vtn vaccination with recombinant H5 or inactivated split H5N1 vaccine.CONCLUSIONReplicating Ad4 delivered to the URT caused prolonged exposure to antigen, drove durable systemic and mucosal immunity, and proved to be a promising platform for the induction of immunity against viral surface glycoprotein targets.TRIAL REGISTRATIONClinicalTrials.gov NCT01443936 and NCT01806909.FUNDINGIntramural and Extramural Research Programs of the NIAID, NIH (U19 AI109946) and the Centers of Excellence for Influenza Research and Surveillance (CEIRS), NIAID, NIH (contract HHSN272201400008C).

Heat Shock Protein 90 Chaperones E1A Early Protein of Adenovirus 5 and Is Essential for Replication of the Virus

Adenovirus infections tend to be mild, but they may pose a serious threat for young and immunocompromised individuals. The treatment is complicated because there are no approved safe and specific drugs for adenovirus infections. Here, we present evidence that 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG), an inhibitor of Hsp90 chaperone, decreases the rate of human adenovirus 5 (HAdV-5) replication in cell cultures by 95%. 17-AAG inhibited the transcription of early and late genes of HAdV-5, replication of viral DNA, and expression of viral proteins. 6 h after infection, Hsp90 inhibition results in a 6.3-fold reduction of the newly synthesized E1A protein level without a decrease in the E1A mRNA level. However, the Hsp90 inhibition does not increase the decay rate of the E1A protein that was constitutively expressed in the cell before exposure to the inhibitor. The co-immunoprecipitation proved that E1A protein interacted with Hsp90. Altogether, the presented results show, for the first time. that Hsp90 chaperones newly synthesized, but not mature, E1A protein. Because E1A serves as a transcriptional co-activator of adenovirus early genes, the anti-adenoviral activity of the Hsp90 inhibitor might be explained by the decreased E1A level.

Emerging antiviral therapeutics for human adenovirus infection: Recent developments and novel strategies

Human adenoviruses (HAdV) are ubiquitous human pathogens that cause a significant burden of respiratory, ocular, and gastrointestinal illnesses. Although HAdV infections are generally self-limiting, pediatric and immunocompromised individuals are at particular risk for developing severe disease. Currently, no approved antiviral therapies specific to HAdV exist. Recent outbreaks underscore the need for effective antiviral agents to treat life-threatening infections. In this review we will focus on recent developments in search of potential therapeutic agents for controlling HAdV infections, with a focus on those targeting post-entry stages of the virus replicative cycle.

Helper virus-free gutless adenovirus (HF-GLAd): a new platform for gene therapy

Gene therapy is emerging as a treatment option for inherited genetic diseases. The success of this treatment approach greatly depends upon gene delivery vectors. Researchers have attempted to harness the potential of viral vectors for gene therapy applications over many decades. Among the viral vectors available, gutless adenovirus (GLAd) has been recognized as one of the most promising vectors for in vivo gene delivery. GLAd is constructed by deleting all the viral genes from an adenovirus. Owing to this structural feature, the production of GLAd requires a helper that supplies viral proteins in trans. Conventionally, the helper is an adenovirus. Although the helper adenovirus efficiently provides helper functions, it remains as an unavoidable contaminant and also generates replication-competent adenovirus (RCA) during the production of GLAd. These two undesirable contaminants have raised safety concerns and hindered the clinical applications of GLAd. Recently, we developed helper virus-free gutless adenovirus (HF-GLAd), a new version of GLAd, which is produced by a helper plasmid instead of a helper adenovirus. Utilization of this helper plasmid eliminated the helper adenovirus and RCA contamination in the production of GLAd. HF-GLAd, devoid of helper adenovirus and RCA contaminants, will facilitate its clinical applications. In this review, we discuss the characteristics of adenoviruses, the evolution and production of adenoviral vectors, and the unique features of HF-GLAd as a new platform for gene therapy. Furthermore, we highlight the potential applications of HF-GLAd as a gene delivery vector for the treatment of various inherited genetic diseases.

Helper virus-free gutless adenovirus (HF-GLAd): a new platform for gene therapy

Gene therapy is emerging as a treatment option for inherited genetic diseases. The success of this treatment approach greatly depends upon gene delivery vectors. Researchers have attempted to harness the potential of viral vectors for gene therapy applications over many decades. Among the viral vectors available, gutless adenovirus (GLAd) has been recognized as one of the most promising vectors for in vivo gene delivery. GLAd is constructed by deleting all the viral genes from an adenovirus. Owing to this structural feature, the production of GLAd requires a helper that supplies viral proteins in trans. Conventionally, the helper is an adenovirus. Although the helper adenovirus efficiently provides helper functions, it remains as an unavoidable contaminant and also generates replicationcompetent adenovirus (RCA) during the production of GLAd. These two undesirable contaminants have raised safety concerns and hindered the clinical applications of GLAd. Recently, we developed helper virus-free gutless adenovirus (HF-GLAd), a new version of GLAd, which is produced by a helper plasmid instead of a helper adenovirus. Utilization of this helper plasmid eliminated the helper adenovirus and RCA contamination in the production of GLAd. HF-GLAd, devoid of helper adenovirus and RCA contaminants, will facilitate its clinical applications. In this review, we discuss the characteristics of adenoviruses, the evolution and production of adenoviral vectors, and the unique features of HF-GLAd as a new platform for gene therapy. Furthermore, we highlight the potential applications of HF-GLAd as a gene delivery vector for the treatment of various inherited genetic diseases. [BMB Reports 2020; 53(11): 565-575].

Cancer stem cell plasticity in glioblastoma multiforme: a perspective on future directions in oncolytic virotherapy

The cancer stem cell (CSC) hypothesis suggests that a rare population of stem-like cells underpin tumorigenesis. Oncolytic viruses (OVs) demonstrate novel mechanisms of targeting the elusive CSCs with greater selectivity - promising therapeutic potential against solid tumors such as glioblastoma (GBM) that are resistant to conventional treatment. In general, OVs have failed to translate the efficacy from bench to bedside. The success of OVs rely on the hypothesis that eliminating CSCs is key to preventing recurrence. However, newly emerging evidence of CSC plasticity challenge this hypothesis by proposing that the CSC pool can be regenerated from non-CSCs post-treatment. We review this evidence surrounding the CSC hypothesis to propose an original perspective on why several advanced OVs may be failing to reflect their true potential in clinical trials. We argue that preventing non-CSC to CSC dedifferentiation may be critical to achieving long-term treatment efficacy in future OV clinical trials.

The Adenovirus Death Protein - a small membrane protein controls cell lysis and disease

Human adenoviruses (HAdVs) cause widespread acute and persistent infections. Infections are usually mild and controlled by humoral and cell-based immunity. Reactivation of persistently infected immune cells can lead to a life-threatening disease in immunocompromised individuals, especially children and transplant recipients. To date, no effective therapy or vaccine against HAdV disease is available to the public. HAdV-C2 and C5 are the best-studied of more than 100 HAdV types. They persist in infected cells and release their progeny by host cell lysis to neighbouring cells and fluids, a process facilitated by the adenovirus death protein (ADP). ADP consists of about 100 amino acids and harbours a single membrane-spanning domain. It undergoes post-translational processing in endoplasmic reticulum and Golgi compartments, before localizing to the inner nuclear membrane. Here, we discuss the current knowledge on how ADP induces membrane rupture. Membrane rupture is essential for both progression of disease and efficacy of therapeutic viruses in clinical applications, in particular oncolytic therapy.

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.

The UPR sensor IRE1α and the adenovirus E3-19K glycoprotein sustain persistent and lytic infections

Persistent viruses cause chronic disease, and threaten the lives of immunosuppressed individuals. Here, we elucidate a mechanism supporting the persistence of human adenovirus (AdV), a virus that can kill immunosuppressed patients. Cell biological analyses, genetics and chemical interference demonstrate that one of five AdV membrane proteins, the E3-19K glycoprotein specifically triggers the unfolded protein response (UPR) sensor IRE1α in the endoplasmic reticulum (ER), but not other UPR sensors, such as protein kinase R-like ER kinase (PERK) and activating transcription factor 6 (ATF6). The E3-19K lumenal domain activates the IRE1α nuclease, which initiates mRNA splicing of X-box binding protein-1 (XBP1). XBP1s binds to the viral E1A-enhancer/promoter sequence, and boosts E1A transcription, E3-19K levels and lytic infection. Inhibition of IRE1α nuclease interrupts the five components feedforward loop, E1A, E3-19K, IRE1α, XBP1s, E1A enhancer/promoter. This loop sustains persistent infection in the presence of the immune activator interferon, and lytic infection in the absence of interferon.

Adenovirus (AdV) can cause persistent infections, but underlying mechanisms are poorly understood. Here, Prasad et al. show that the AdV glycoprotein E3-19K activates the unfolded protein response sensor IRE1α, and that this triggers a feedforward loop that sustains persistent infection in the presence of interferon.

Deep splicing plasticity of the human adenovirus type 5 transcriptome drives virus evolution

Viral genomes have high gene densities and complex transcription strategies rendering transcriptome analysis through short-read RNA-seq approaches problematic. Adenovirus transcription and splicing is especially complex. We used long-read direct RNA sequencing to study adenovirus transcription and splicing during infection. This revealed a previously unappreciated complexity of alternative splicing and potential for secondary initiating codon usage. Moreover, we find that most viral transcripts tend to shorten polyadenylation lengths as infection progresses. Development of an open reading frame centric bioinformatics analysis pipeline provided a deeper quantitative and qualitative understanding of adenovirus's genetic potential. Across the viral genome adenovirus makes multiple distinctly spliced transcripts that code for the same protein. Over 11,000 different splicing patterns were recorded across the viral genome, most occurring at low levels. This low-level use of alternative splicing patterns potentially enables the virus to maximise its coding potential over evolutionary timescales.

A Novel Role for PX, a Structural Protein of Fowl Adenovirus Serotype 4 (FAdV4), as an Apoptosis-Inducer in Leghorn Male Hepatocellular Cell

Hydropericardium-Hepatitis Syndrome (HHS) caused by Fowl Adenovirus Serotype 4 (FAdV4) infection is a severe threat to the poultry industry worldwide, especially in China since 2015. Recent studies show that FAdV4 induces liver injury through apoptosis. However, the underlying molecular mechanism is still unclear. We report here that FAdV4 infection caused apoptosis in Leghorn male hepatocellular (LMH) cells and that PX, a structural protein of FAdV4, acted as a major viral factor inducing apoptosis. Furthermore, the nuclear localization of PX is determined by the R/K regions of PX and required for PX-induced apoptosis. Moreover, alanines 11 and 129 of PX are crucial to PX-induced apoptosis. Inhibition of FAdV4-induced apoptosis by caspase inhibitors retarded viral replication, suggesting that PX serves as a virulence factor for FAdV4 infection, which may further our understandings of the pathogenesis of FAdV4 infection.

Human adenovirus type 5 increases host cell fucosylation and modifies Ley antigen expression

Certain viral infections are known to modify the glycosylation profile of infected cells through the overexpression of specific host cell fucosyltransferases (FUTs). Infection with CMV (cytomegalovirus), HCV (hepatitis C virus), HSV-1 (herpes simplex virus type-1) and VZV (varicella-zoster virus) increase the expression of fucosylated epitopes, including antigens sLex (Siaα2-3 Galβ1-4(Fucα1-3)GlcNAcβ1-R) and Ley (Fucα1-2 Galβ1-4(Fucα1-3)GlcNAcβ1-R). The reorganization of the glycocalyx induced by viral infection may favor the spread of viral progeny, and alter diverse biological functions mediated by glycans, including recognition by the adaptive immune system. In this work, we aimed to establish whether infection with human adenovirus type 5 (HAd5), a well-known viral vector and infectious agent, causes changes in the glycosylation profile of A549 cells, used as a model of lung epithelium, a natural target of HAd5. We demonstrate for the first time that HAd5 infection causes a significant increase in the cell surface de novo fucosylation, as assessed by metabolic labeling, and that such modification is dependent on the expression of viral genes. The main type of increased fucosylation was determined to be in α1-2 linkage, as assessed by UEA-I lectin binding and supported by the overexpression of FUT1 and FUT2. Also, HAd5-infected cells showed a heterogeneous change in the expression profile of the bi-fucosylated Ley antigen, an antigen associated with enhanced cell proliferation and inhibition of apoptosis.

Immune evasion by adenoviruses: a window into host-virus adaptation

Human adenoviruses (HAdVs) are widespread pathogens that cause a number of partially overlapping, species-specific infections associated with respiratory, urinary, gastrointestinal, and ocular diseases. The early 3 (E3) region of adenoviruses is highly divergent between different species, and it encodes a multitude of proteins with immunomodulatory functions. The study of genetic diversity in the E3 region offers a unique opportunity to gain insight into how the various HAdVs have evolutionarily adapted in response to the selection pressures exerted by host immune defenses. The objective of this review was to discuss subversion of host antiviral immune responses by HAdVs, with a focus on suppression of MHC class I antigen presentation, as a window into host-HAdV adaptation.

Genomic characterization of human adenovirus type 4 strains isolated worldwide since 1953 identifies two separable phylogroups evolving at different rates from their most recent common ancestor

Species Human mastadenovirus E (HAdV-E) comprises several simian types and a single human type: HAdV-E4, a respiratory and ocular pathogen. RFLP analysis for the characterization of intratypic genetic variability has previously distinguished two HAdV-E4 clusters: prototype (p)-like and a-like. Our analysis of whole genome sequences confirmed two distinct lineages, which we refer to as phylogroups (PGs). PGs I and II comprise the p- and a-like genomes, respectively, and differ significantly in their G + C content (57.7% ± 0.013 vs 56.3% ± 0.015). Sequence differences distinguishing the two clades map to several regions of the genome including E3 and ITR. Bayesian analyses showed that the two phylogroups diverged approximately 602 years before the present. A relatively faster evolutionary rate was identified for PG II. Our data provide a rationale for the incorporation of phylogroup identity to HAdV-E4 strain designation to reflect the identified unique genetic characteristics that distinguish PGs I and II.

Adenovirus early region 3 RIDα protein limits NFκB signaling through stress-activated EGF receptors

The host limits adenovirus infections by mobilizing immune systems directed against infected cells that also represent major barriers to clinical use of adenoviral vectors. Adenovirus early transcription units encode a number of products capable of thwarting antiviral immune responses by co-opting host cell pathways. Although the EGF receptor (EGFR) was a known target for the early region 3 (E3) RIDα protein encoded by nonpathogenic group C adenoviruses, the functional role of this host-pathogen interaction was unknown. Here we report that incoming viral particles triggered a robust, stress-induced pathway of EGFR trafficking and signaling prior to viral gene expression in epithelial target cells. EGFRs activated by stress of adenoviral infection regulated signaling by the NFκB family of transcription factors, which is known to have a critical role in the host innate immune response to infectious adenoviruses and adenovirus vectors. We found that the NFκB p65 subunit was phosphorylated at Thr254, shown previously by other investigators to be associated with enhanced nuclear stability and gene transcription, by a mechanism that was attributable to ligand-independent EGFR tyrosine kinase activity. Our results indicated that the adenoviral RIDα protein terminated this pathway by co-opting the host adaptor protein Alix required for sorting stress-exposed EGFRs in multivesicular endosomes, and promoting endosome-lysosome fusion independent of the small GTPase Rab7, in infected cells. Furthermore RIDα expression was sufficient to down-regulate the same EGFR/NFκB signaling axis in a previously characterized stress-activated EGFR trafficking pathway induced by treatment with the pro-inflammatory cytokine TNF-α. We also found that cell stress activated additional EGFR signaling cascades through the Gab1 adaptor protein that may have unappreciated roles in the adenoviral life cycle. Similar to other E3 proteins, RIDα is not conserved in adenovirus serotypes associated with potentially severe disease, suggesting stress-activated EGFR signaling may contribute to adenovirus virulence.

Drug development against human adenoviruses and its advancement by Syrian hamster models

The symptoms of human adenovirus infections are generally mild and self-limiting. However, these infections have been gaining importance in recent years because of a growing number of immunocompromised patients. Solid organ and hematopoietic stem cell transplant patients are subjected to severe immunosuppressive regimes and cannot efficaciously eliminate virus infections. In these patients, adenovirus infections can develop into deadly multi-organ disseminated disease. Presently, in the absence of approved therapies, physicians rely on drugs developed for other purposes to treat adenovirus infections. As there is a need for anti-adenoviral therapies, researchers have been developing new agents and repurposing existing ones to treat adenovirus infections. There are several small molecule drugs that are being tested for their efficacy against human adenoviruses; some of these have reached clinical trials, while others are still in the preclinical phase. Besides these compounds, research on immunotherapy against adenoviral infection has made significant progress, promising another modality for treatment. The availability of an animal model confirmed the activity of some drugs already in clinical use while proving that others are inactive. This led to the identification of several lead compounds that await further development. In the present article, we review the current status of anti-adenoviral therapies and their advancement by in vivo studies in the Syrian hamster model.

Viral CD229 (Ly9) homologs as new manipulators of host immunity

The signaling lymphocytic activation molecule family (SLAMF) of receptors plays crucial roles during innate and adaptive immune responses. The SLAMF member CD229 (Ly9, SLAMF3) is a homophilic receptor predominantly expressed on the surface of B and T cells. CD229 acts as a cosignaling molecule, regulating lymphocyte homoeostasis and activation. To promote viral replication and survival in their hosts, viruses have developed sophisticated mechanisms to combat and avoid immune surveillance. Many of these strategies rely on host defense genes captured during the process of virus-host coevolution. In particular, large DNA viruses devote a wide range of proteins to interfere with almost every host immune pathway. Given that CD229 is critically involved in regulating immune responses, it is not surprising that viruses have designed tactics to mimic or interfere with this receptor. The discovery, in recent years, that some viruses have hijacked CD229 genes from their hosts, incorporating them as an integral part of their genomes, or have evolved proteins to directly target CD229, indicates that this is the case. While it is still an emerging area of research, the present review discusses these viral molecules and their potential in immune modulation. A more detailed understanding of the mechanisms of action and the functional implications of these new viral CD229 mimics may not only provide seminal information on viral immune evasion mechanisms but also, unveil unrecognized aspects of CD229 immune functions.

A Survey of Recent Adenoviral Respiratory Pathogens in Hong Kong Reveals Emergent and Recombinant Human Adenovirus Type 4 (HAdV-E4) Circulating in Civilian Populations

Human adenovirus type 4 (HAdV-E4), which is intriguingly limited to military populations, causes acute respiratory disease with demonstrated morbidity and mortality implications. This respiratory pathogen contains genome identity with chimpanzee adenoviruses, indicating zoonotic origins. A signature of these “old” HAdV-E4 is the absence of a critical replication motif, NF-I, which is found in all HAdV respiratory pathogens and most HAdVs. However, our recent survey of flu-like disease in children in Hong Kong reveals that the emergent HAdV-E4 pathogens circulating in civilian populations contain NF-I, indicating recombination and reflecting host-adaptation that enables the “new” HAdV-E4 to replicate more efficiently in human cells and foretells more potential HAdV-E4 outbreaks in immune-naïve civilian populations. Special attention should be paid by clinicians to this emergent and recombinant HAdV-E4 circulating in civilian populations.

Molecular Evolution of Human Adenovirus (HAdV) Species C

Currently, 88 different Human Adenovirus (HAdV) types are grouped into seven HAdV species A to G. Most types (57) belong to species HAdV-D. Recombination between capsid genes (hexon, penton and fiber) is the main factor contributing to the diversity in species HAdV-D. Noteworthy, species HAdV-C contains so far only five types, although species HAdV-C is highly prevalent and clinically significant in immunosuppressed patients. Therefore, the evolution of species HAdV-C was studied by generating 51 complete genome sequences from circulating strains. Clustering of the whole genome HAdV-C sequences confirmed classical typing results (fifteen HAdV-C1, thirty HAdV-C2, four HAdV-C5, two HAdV-C6). However, two HAdV-C2 strains had a novel penton base sequence and thus were re-labeled as the novel type HAdV-C89. Fiber and early gene region 3 (E3) sequences clustered always with the corresponding prototype sequence but clustering of the E4 region indicated recombination events in 26 out of the 51 sequenced specimens. Recombination of the E1 gene region was detected in 16 circulating strains. As early gene region sequences are not considered in the type definition of HAdVs, evolution of HAdV-C remains on the subtype level. Nonetheless, recombination of the E1 and E4 gene regions may influence the virulence of HAdV-C strains.

Characterization, functional and signaling elucidation of pigeon (Columba livia) interferon-α: Knockdown p53 negatively modulates antiviral response

The regulation of interferon-α signaling pathways is essential to protect the host from infection with a broad range of viruses. However, information regarding antiviral response and the specific molecular mechanism of Columba livia interferon-α (CoIFN-α) has not been reported to date. In this study, we cloned a 723bp complete ORF of CoIFN-α gene. The specific antiviral activity of CoIFN-α in VSV (TCID₅₀ = 10^-5.87/100 μL)-infected CEFs reached 5.5 × 10⁵ U/mg. Moreover, our result indicated that the anti-VSV efficient of CoIFN-α might depend on the expression of NF-κB. CoIFN-α also showed high sensitivity to trypsin and relatively stable after acid, alkali or heat treatment. Moreover, CoIFN-α activated STAT/Jak signaling and autophagy to inhibit VSV-induced apoptosis. Although the expression of p53 was further increased, apoptosis was not involved in CoIFN-α against VSV. Notably, although STAT signaling was efficiently activated, knockdown p53 did inhibit the antiviral activity of the CoIFN-α via decreasing the expression of Mx1 but not weakened Jak phosphorylation. Moreover, VSV aggravated the apoptosis and the expression of cleaved Mdm2 in knockdown p53 under preincubated CoIFN-α. Taken together, p53 might as a highly interconnected regulator in IFN-α antiviral response and cleaved Mdm2 might as a dominant-negative regulator by competing with full length Mdm2 for p53 binding in virus infection. Overall, our research not only enriches CoIFN-α antiviral features but also helps explain that p53 enhance the CoIFN-α antiviral response against pigeon viral diseases.

Porcine Adenovirus Type 3 E3 Encodes a Structural Protein Essential for Capsid Stability and Production of Infectious Progeny Virions

The adenovirus E3 region encodes proteins that are not essential for viral replication in vitro The porcine adenovirus type 3 (PAdV-3) E3 region encodes three proteins, including 13.7K. Here, we report that 13.7K is expressed as an early protein, which localizes to the nucleus of infected cells. The 13.7K protein is a structural protein, as it is incorporated in CsCl-purified virions. The 13.7K protein appears to be essential for PAdV-3 replication, as mutant PAV13.7^3A expressing a mutated 13.7K could be isolated only in VIDO AS2 cells expressing the 13.7K protein. Analysis of PAV13.7^3A suggested that even in the presence of reduced levels of some late viral proteins, there appeared to be no effect on virus assembly and production of mature virions. Further analysis of CsCl-purified PAV13.7^3A by transmission electron microscopy revealed the presence of disrupted/broken capsids, suggesting that inactivation of 13.7K protein expression may produce fragile capsids. Our results suggest that the PAdV-3 E3 region-encoded 13.7K protein is a capsid protein, which appears to be essential for the formation of stable capsids and production of infectious progeny virions.IMPORTANCE Although E3 region-encoded proteins are involved in the modulation of leukocyte functions (N. Arnberg, Proc Natl Acad Sci U S A 110:19976-19977, 2013) and inducing a lytic infection of lymphocytes (V. K. Murali, D. A. Ornelles, L. R. Gooding, H. T. Wilms, W. Huang, A. E. Tollefson, W. S. Wold, and C. Garnett-Benson, J Virol 88:903-912, 2014), none of the E3 proteins appear to be a component of virion capsid or required for replication of adenovirus. Here, we demonstrate that the 13.7K protein encoded by the E3 region of porcine adenovirus type 3 is a component of progeny virion capsids and appears to be essential for maintaining the integrity of virion capsid and production of infectious progeny virions. To our knowledge, this is the first report to suggest that an adenovirus E3-encoded protein is an essential structural protein.

Adenoviromics: Mining the Human Adenovirus Species D Genome

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

A compendium of adenovirus genetic modifications for enhanced replication, oncolysis, and tumor immunosurveillance in cancer therapy

In this review, we specifically focus on genetic modifications of oncolytic adenovirus 5 (Ad5)-based vectors that enhance replication, oncolysis/spread, and virus-mediated tumor immunosurveillance. The finding of negative regulation of minor core protein V by SUMOylation led to the identification of amino acid residues, which when mutated increase adenovirus replication and progeny yield. Suppression of Dicer and/or RNAi pathway with shRNA or p19 tomato bushy stunt protein also results in significant enhancement of adenovirus replication and progeny yield. Truncation mutations in E3-19K or i-leader sequence or overexpression of adenovirus death protein (ADP) potently increase adenovirus progeny release and spread without affecting virus yield. Moreover, E3-19K protein, which was found to inhibit both major histocompatibility complex I (MHCI) and MHC-I chain-related A and B proteins (MICA/MICB) expression on the cell surface, protecting infected cells from T-lymphocyte and natural killer (NK) cell attack, may be tailored to selectively target only MHCI or MICA/MICB, or to lose the ability to downregulate both. At last, E3-19K protein may be exploited to deliver tumor-associated epitopes directly to the endoplasmic reticulum for loading MHCI in the transporter associated with antigen processing (TAP)-deregulated cells.

Hacking the Cell: Network Intrusion and Exploitation by Adenovirus E1A

As obligate intracellular parasites, viruses are dependent on their infected hosts for survival. Consequently, viruses are under enormous selective pressure to utilize available cellular components and processes to their own advantage. As most, if not all, cellular activities are regulated at some level via protein interactions, host protein interaction networks are particularly vulnerable to viral exploitation. Indeed, viral proteins frequently target highly connected “hub” proteins to “hack” the cellular network, defining the molecular basis for viral control over the host. This widespread and successful strategy of network intrusion and exploitation has evolved convergently among numerous genetically distinct viruses as a result of the endless evolutionary arms race between pathogens and hosts. Here we examine the means by which a particularly well-connected viral hub protein, human adenovirus E1A, compromises and exploits the vulnerabilities of eukaryotic protein interaction networks. Importantly, these interactions identify critical regulatory hubs in the human proteome and help define the molecular basis of their function.

Suppression of Type I Interferon Signaling by E1A via RuvBL1/Pontin

Suppression of interferon signaling is of paramount importance to a virus. Interferon signaling significantly reduces or halts the ability of a virus to replicate; therefore, viruses have evolved sophisticated mechanisms that suppress activation of the interferon pathway or responsiveness of the infected cell to interferon. Adenovirus has multiple modes of inhibiting the cellular response to interferon. Here, we report that E1A, previously shown to regulate interferon signaling in multiple ways, inhibits interferon-stimulated gene expression by modulating RuvBL1 function. RuvBL1 was previously shown to affect type I interferon signaling. E1A binds to RuvBL1 and is recruited to RuvBL1-regulated promoters in an interferon-dependent manner, preventing their activation. Depletion of RuvBL1 impairs adenovirus growth but does not appear to significantly affect viral protein expression. Although RuvBL1 has been shown to play a role in cell growth, its depletion had no effect on the ability of the virus to replicate its genome or to drive cells into S phase. E1A was found to bind to RuvBL1 via the C terminus of E1A, and this interaction was important for suppression of interferon-stimulated gene transcriptional activation and recruitment of E1A to interferon-regulated promoters. Here, we report the identification of RuvBL1 as a new target for adenovirus in its quest to suppress the interferon response.IMPORTANCE For most viruses, suppression of the interferon signaling pathway is crucial to ensure a successful replicative cycle. Human adenovirus has evolved several different mechanisms that prevent activation of interferon or the ability of the cell to respond to interferon. The viral immediate-early gene E1A was previously shown to affect interferon signaling in several different ways. Here, we report a novel mechanism reliant on RuvBL1 that E1A uses to prevent activation of interferon-stimulated gene expression following infection or interferon treatment. This adds to the growing knowledge of how viruses are able to inhibit interferon and identifies a novel target used by adenovirus for modulation of the cellular interferon pathway.

The tripartite leader sequence is required for ectopic expression of HAdV-B and HAdV-E E3 CR1 genes

The unique repertoire of genes that characterizes the early region 3 (E3) of the different species of human adenovirus (HAdV) likely contributes to their distinct pathogenic traits. The function of many E3 CR1 proteins remains unknown possibly due to unidentified intrinsic properties that make them difficult to express ectopically. This study shows that the species HAdV-B- and HAdV-E-specific E3 CR1 genes can be expressed from vectors carrying the HAdV tripartite leader (TPL) sequence but not from traditional mammalian expression vectors. Insertion of the TPL sequence upstream of the HAdV-B and HAdV-E E3 CR1 open reading frames was sufficient to rescue protein expression from pCI-neo constructs in transfected 293T cells. The detection of higher levels of HAdV-B and HAdV-E E3 CR1 transcripts suggests that the TPL sequence may enhance gene expression at both the transcriptional and translational levels. Our findings will facilitate the characterization of additional AdV E3 proteins.