Human adenovirus type 52: a type 41 in disguise?

Isolation of a recombinant simian adenovirus encoding the human adenovirus G52 hexon suggests a simian origin for human adenovirus G52

Human adenoviruses (HAdVs) are causative agents of morbidity and mortality throughout the world. These double-stranded DNA viruses are phylogenetically classified into seven different species (A-G). HAdV-G52, originally isolated in 2008 from a patient presenting with gastroenteritis, is the sole human-derived member of species G. Phylogenetic analysis previously suggested that HAdV-G52 may have a simian origin, indicating a potential zoonotic spillover into humans. However, evidence of HAdV-G52 in either human or simian populations has not been reported since. Here, we describe the isolation and in vitro characterization of rhesus (rh)AdV-69, a novel simian AdV with clear evidence of recombination with HAdV-G52, from the stool of a rhesus macaque. Specifically, the rhAdV-69 hexon capsid protein is 100% identical to that of HAdV-G52, whereas the remainder of the genome is most similar to rhAdV-55, sharing 95.36% nucleic acid identity. A second recombination event with an unknown adenovirus (AdV) is evident at the short fiber gene. From the same sample, we also isolated a second, highly related recombinant AdV (rhAdV-68) that harbors a distinct hexon gene but nearly identical backbone compared to rhAdV-69. In vitro, rhAdV-68 and rhAdV-69 demonstrate comparable growth kinetics and tropisms in human cell lines, nonhuman cell lines, and human enteroids. Furthermore, we show that coinfection of highly related AdVs is not unique to this sample since we also isolated coinfecting rhAdVs from two additional rhesus macaque stool samples. Our data collectively contribute to elucidating the origins of HAdV-G52 and provide insights into the frequency of coinfections and subsequent recombination in AdV evolution.IMPORTANCEUnderstanding the host origins of adenoviruses (AdVs) is critical for public health as transmission of viruses from animals to humans can lead to emergent viruses. Recombination between animal and human AdVs can also produce emergent viruses. HAdV-G52 is the only human-derived member of the HAdV G species. It has been suggested that HAdV-G52 has a simian origin. Here, we isolated from a rhesus macaque, a novel rhAdV, rhAdV-69, that encodes a hexon protein that is 100% identical to that of HAdV-G52. This observation suggests that HAdV-G52 may indeed have a simian origin. We also isolated a highly related rhAdV, differing only in the hexon gene, from the same rhesus macaque stool sample as rhAdV-69, illustrating the potential for co-infection of closely related AdVs and recombination at the hexon gene. Furthermore, our study highlights the critical role of whole-genome sequencing in understanding AdV evolution and monitoring the emergence of pathogenic AdVs.

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.

Genotypes and phylogenetic analysis of adenovirus in children with respiratory infection in Buenos Aires, Argentina (2000-2018)

Human adenoviruses (HAdV) are one of the most frequent causes of respiratory infections around the world, causing mild to severe disease. In Argentina, many studies focused on the association of HAdV respiratory infection with severe disease and fatal outcomes leading to the discovery in 1984 of a genomic variant 7h associated with high fatality. Although several molecular studies reported the presence of at least 4 HAdV species (B, C, D and E) in Argentina, few sequences were available in the databases. In this study, sequences from the hexon gene region were obtained from 141 patients as a first approach to assess the genetic diversity of HAdVs circulating in Buenos Aires, Argentina. Phylogenetic analysis of these sequences and others recovered from public databases confirmed the circulation of the four above-mentioned species represented by 11 genotypes, with predominance in species B and C and shifts in their proportion in the studied period (2000 to 2018). The variants detected in Argentina, for most of the genotypes, were similar to those already described in other countries. However, uncommon lineages belonging to genotypes C2, C5 and E4 were detected, which might indicate the circulation of local variants and will deserve further studies of whole-genome sequences.

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.

An Analysis of Adenovirus Genomes Using Whole Genome Software Tools

The evolution of sequencing technology has lead to an enormous increase in the number of genomes that have been sequenced. This is especially true in the field of virus genomics. In order to extract meaningful biological information from these genomes, whole genome data mining software tools must be utilized. Hundreds of tools have been developed to analyze biological sequence data. However, only some of these tools are user-friendly to biologists. Several of these tools that have been successfully used to analyze adenovirus genomes are described here. These include Artemis, EMBOSS, pDRAW, zPicture, CoreGenes, GeneOrder, and PipMaker. These tools provide functionalities such as visualization, restriction enzyme analysis, alignment, and proteome comparisons that are extremely useful in the bioinformatics analysis of adenovirus genomes.

Viruses Causing Gastroenteritis: The Known, The New and Those Beyond

The list of recently discovered gastrointestinal viruses is expanding rapidly. Whether these agents are actually involved in a disease such as diarrhea is the essential question, yet difficult to answer. In this review a summary of all viruses found in diarrhea is presented, together with the current knowledge about their connection to disease.

Evaluation of new immunochromatographic assay kit for adenovirus detection in throat swab: comparison with culture and real-time PCR results

A new immunochromatographic (IC) assay kit, BD Veritor System Adeno was evaluated to comparing with commercial available kit, BD Adeno Examan, cell culture, and real-time PCR using throat swab samples. Specimens were collected from 146 pediatric patients between July 2011 and January 2012. Mean age of patients was 4 years (8 months-15 years old). Patients were diagnosed with pharyngitis (n = 67), tonsillitis (n = 45), pharyngoconjunctival fever (n = 26), upper respiratory tract infection (n = 6), conjunctivitis (n = 1), or bronchitis (n = 1). Thirty-one of the patients (21.2%) had more than one disease. Among all samples, 61 (41.8%) were positive for adenovirus with BD Veritor System Adeno; 68 (46.6%) with BD Adeno Examan; 63 (43.2%) with real-time PCR; and 65 (44.5%) with cell culture. Serotype 3 (n = 41; 63.1%) was predominant among the 65 adenovirus isolates, followed by serotype 2 (n = 12; 18.5%), 1 (n = 6; 9.2%), 5 (n = 4; 6.2%), and 4 (n = 2; 3.1%). Relative sensitivity and specificity of BD Veritor System Adeno, BD Adeno Examan, and real-time PCR were 93.8% and 98.7%, 96.9% and 93.8%, and 96.9% and 100%, respectively. Positive predictive and negative predictive values for these methods were 98.4% and 95.1%, 92.6% and 97.4%, and 100% and 97.6%, respectively. The sensitivity and specificity of real-time PCR was greater than that of IC assay kits. However, IC assay kits also showed high sensitivity and specificity appropriate for clinical use.

High prevalence and diversity of species D adenoviruses (HAdV-D) in human populations of four Sub-Saharan countries

BACKGROUND

Human adenoviruses of species D (HAdV-D) can be associated with acute respiratory illness, epidemic keratoconjunctivitis, and gastroenteritis, but subclinical HAdV-D infections with prolonged shedding have also been observed, particularly in immunocompromised hosts. To expand knowledge on HAdV-D in Sub-Saharan Africa, we investigated the prevalence, epidemiology and pathogenic potential of HAdV-D in humans from rural areas of 4 Sub-Saharan countries, Côte d'Ivoire (CI), Democratic Republic of the Congo (DRC), Central African Republic (CAR) and Uganda (UG).

METHODS

Stool samples were collected from 287 people living in rural regions in CI, DRC, CAR and UG. HAdV-D prevalence and diversity were determined by PCR and sequencing. A gene block, spanning the genes pV to hexon, was used for analysis of genetic distance. Correlation between adenovirus infection and disease symptoms, prevalence differences, and the effect of age and gender on infection status were analyzed with cross tables and logistic regression models.

RESULTS

The prevalence of HAdV-D in the investigated sites was estimated to be 66% in CI, 48% in DRC, 28% in CAR (adults only) and 65% in UG (adults only). Younger individuals were more frequently infected than adults; there was no difference in HAdV-D occurrence between genders. No correlation could be found between HAdV-D infection and clinical symptoms. Highly diverse HAdV-D sequences were identified, among which a number are likely to stand for novel types.

CONCLUSIONS

HAdV-D was detected with a high prevalence in study populations of 4 Sub-Saharan countries. The genetic diversity of the virus was high and further investigations are needed to pinpoint pathological potential of each of the viruses. High diversity may also favor the emergence of recombinants with altered tropism and pathogenic properties.

Ocular tropism of respiratory viruses

Respiratory viruses (including adenovirus, influenza virus, respiratory syncytial virus, coronavirus, and rhinovirus) cause a broad spectrum of disease in humans, ranging from mild influenza-like symptoms to acute respiratory failure. While species D adenoviruses and subtype H7 influenza viruses are known to possess an ocular tropism, documented human ocular disease has been reported following infection with all principal respiratory viruses. In this review, we describe the anatomical proximity and cellular receptor distribution between ocular and respiratory tissues. All major respiratory viruses and their association with human ocular disease are discussed. Research utilizing in vitro and in vivo models to study the ability of respiratory viruses to use the eye as a portal of entry as well as a primary site of virus replication is highlighted. Identification of shared receptor-binding preferences, host responses, and laboratory modeling protocols among these viruses provides a needed bridge between clinical and laboratory studies of virus tropism.

Serotype-specific neutralizing antibody epitopes of human adenovirus type 3 (HAdV-3) and HAdV-7 reside in multiple hexon hypervariable regions

Human adenovirus types 3 and 7 (HAdV-3 and HAdV-7) occur epidemically and contribute greatly to respiratory diseases, but there is no currently available licensed recombinant HAdV-3/HAdV-7 bivalent vaccine. Identification of serotype-specific neutralizing antibody (NAb) epitopes for HAdV-3 and HAdV-7 will be beneficial for development of recombinant HAdV-3/HAdV-7 bivalent vaccines. In this study, four NAb epitopes within hexon hypervariable regions (HVRs) were predicted for HAdV-3 and HAdV-7, respectively, by using bioinformatics. Eight hexon chimeric adenovirus vectors with the alternation of only one predicted neutralizing epitope were constructed. Further in vitro and in vivo neutralization assays indicated that E2 (residing in HVR2) and E3 (residing in HVR5) are NAb epitopes for HAdV-7, and E3 plays a more important role in generating NAb responses. Cross-neutralization assays indicated that all four predicted epitopes, R1 to R4, are NAb epitopes for HAdV-3, and R1 (residing in HVR1) plays the most important role in generating NAb responses. Humoral immune responses elicited by the recombinant rAdH7R1 (containing the R1 epitope) were significantly and durably suppressed by HAdV-3-specific NAbs. Surprisingly, the rAdΔE3GFP-specific neutralizing epitope responses induced by rAdMHE3 (R3 replaced by E3) and rAdMHE4 (R4 replaced by E4) were weaker than those of rAdMHE1 (R1 replaced by E1) or rAdMHE2 (R2 relaced by E2) in vitro and in vivo. Furthermore, rAdMHE4 replicated more slowly in HEp-2 cells, and the final yield was about 10-fold lower than that of rAdΔE3GFP. The current findings contribute not only to the development of new adenovirus vaccine candidates, but also to the construction of new gene delivery vectors.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

The revolution in viral genomics as exemplified by the bioinformatic analysis of human adenoviruses

Over the past 30 years, genomic and bioinformatic analysis of human adenoviruses has been achieved using a variety of DNA sequencing methods; initially with the use of restriction enzymes and more currently with the use of the GS FLX pyrosequencing technology. Following the conception of DNA sequencing in the 1970s, analysis of adenoviruses has evolved from 100 base pair mRNA fragments to entire genomes. Comparative genomics of adenoviruses made its debut in 1984 when nucleotides and amino acids of coding sequences within the hexon genes of two human adenoviruses (HAdV), HAdV-C2 and HAdV-C5, were compared and analyzed. It was determined that there were three different zones (1-393, 394-1410, 1411-2910) within the hexon gene, of which HAdV-C2 and HAdV-C5 shared zones 1 and 3 with 95% and 89.5% nucleotide identity, respectively. In 1992, HAdV-C5 became the first adenovirus genome to be fully sequenced using the Sanger method. Over the next seven years, whole genome analysis and characterization was completed using bioinformatic tools such as blastn, tblastx, ClustalV and FASTA, in order to determine key proteins in species HAdV-A through HAdV-F. The bioinformatic revolution was initiated with the introduction of a novel species, HAdV-G, that was typed and named by the use of whole genome sequencing and phylogenetics as opposed to traditional serology. HAdV bioinformatics will continue to advance as the latest sequencing technology enables scientists to add to and expand the resource databases. As a result of these advancements, how novel HAdVs are typed has changed. Bioinformatic analysis has become the revolutionary tool that has significantly accelerated the in-depth study of HAdV microevolution through comparative genomics.

Applying genomic and bioinformatic resources to human adenovirus genomes for use in vaccine development and for applications in vector development for gene delivery

Technological advances and increasingly cost-effect methodologies in DNA sequencing and computational analysis are providing genome and proteome data for human adenovirus research. Applying these tools, data and derived knowledge to the development of vaccines against these pathogens will provide effective prophylactics. The same data and approaches can be applied to vector development for gene delivery in gene therapy and vaccine delivery protocols. Examination of several field strain genomes and their analyses provide examples of data that are available using these approaches. An example of the development of HAdV-B3 both as a vaccine and also as a vector is presented.