Adenoviruses

Azra Adilce Selma Fatic

OVERVIEW

1. Introduction

2.Structure of adenoviruses

3.Classification of adenoviruses

4.The adenovirus genome

5.Replication & Transcripton

6. Pathogenesis & Epidemiology 7. Scientific article

Introduction • Adenovirus, a DNA virus, was first isolated in the 1950s in adenoid tissue–

derived cell cultures, hence the name.

• Adenoviruses are now known to be a common cause of asymptomatic respiratory tract infection that produces in vitro cytolysis in these tissues.

• The adenoviruses are common pathogens of humans and animals.

• More than 100 serologically distinct types of adenovirus have been identified, including 49 types that infect humans.

• It is transmitted via direct inoculation to the conjunctiva, a fecal-oral route, aerosolized droplets, or exposure to infected tissue or blood.

• Adenoviruses are a group of common viruses that infect the lining of your eyes, airways and lungs, intestines, urinary tract, and nervous system. They're common causes of fever, coughs, sore throats, diarrhea, and pink eye.

Important Properties of Adenoviruses

Virion: Icosahedral, 70–90 nm in diameter, 252 capsomeres; fiber projects from each vertex

Composition: DNA (13%), protein (87%)

Genome: Double-stranded DNA, linear, 26–45 kbp, protein-bound to termini, infectious

Proteins: Important antigens (hexon, penton base, fiber) are associated with the major outer capsid proteins

Envelope: None

Replication: Nucleus

Outstanding characteristic: Excellent models for molecular studies of eukaryotic cell processes

Structure of Adenoviruses

• The adenovirus particle consists of an icosahedral protein shell surrounding a protein core that contains the linear, double-stranded DNA genome.

• The shell, which is 70 to 100 nm in diameter, is made up of 252 structural capsomeres.

• The 12 vertices of the icosahedron are occupied by units called pentons, each of which has a slender projection called a fiber.

• The shell also contains some additional, minor polypeptide elements. The core particle is made up of two major proteins (polypeptide V and polypeptide VII) and a minor arginine-rich protein (μ)

• The capsid contains 252 capsomers arranged as icosahedrons with 20 triangular facets and 12 vertices

• 240 are called hexons

• 12 are called as penton base and a fiber

• fiber: viral attachment of proteins, can act as a hemagglutinin

• penton base and fiber are: toxic to cell, carry type-specific antigens

Classification of adenoviuses

Adenoviruses have been recovered from a wide variety of species and grouped into 4 genera, and we most important for humans on just two:

• Mastadenoviruses -the mammalian adenoviruses-all

human adenoviruses are in this group;

• Aviadenoviruses -the avian adenoviruses- Infect bird;

They infect only homologues species with the exception of

oncogenic human adenovirus;

• The adenovirus genome

-linear, non-segmented double standed DNA which is around 30-38 Kbp. This alows the virus to theoreticaly carry 30-40 genes. Althrough this is significally larger than other viruses in its Baltimore group. It's still a very simple virus and is heavily reliant on the host cell for survival and replication.

Replication

• Host cells differ in permissivity for adenovirus types. In permissive cells, the

virus multiplies productively and kills the host cell. Other cells are semipermissive, allowing replication at low efficiency, whereas in still others replication is blocked and the infection is abortive.

• Adenovirus replicates inside the nucleus . By the DNA replication process, the adenovirus multiplication cycle is separated into two phases, an early phase and a late phase.

• In both phases a primary transcript is formed which is spliced to produce monocistronic mRNA which is comparable with the host’s ribosome. This allows the translation of mRNAs. Mainly non-structural and regulatory proteins are expressed by the early genes.

Transcription

• Most of the adenovirus genes are transcribed by the host DNA-

dependent RNA polymerase II in a complex transcriptional program.

• This program is regulated by the nucleotide sequences and the structure of the viral promoters and by a host of cell-encoded transcription factors that recognize specific upstream and downstream nucleotide sequence motifs in the promoters.

• Genes in the E1A region of the adenovirus genome are the first to be transcribed. One protein product of this gene region is a transactivator that is essential for the activation of all other viral genes. This immediate-early viral function can also activate or inactivate certain cellular genes.

Pathogenesis

The site of entry generally determines the site of infection; respiratory tract infection infections result from droplet inhalation, while gastrointestinal tract involvement results from fecal-oral transmission. Upon infection with adenovirus, one of three different interactions with the cells may occur:

1. The first is lytic infection, which occurs when an adenovirus enters human epithelial cells and continues through an entire replication cycle, which results in cytolysis, cytokine production, and induction of host inflammatory response.

2. The second is chronic or latent infection, the exact mechanism of which is unknown, which frequently involves asymptomatic infection of lymphoid tissue.

3. Lastly, oncogenic transformation has been observed in rats. During oncogenesis, the replication cycle is truncated, and adenoviral DNA is then integrated into the host cell’s DNA. Thereafter, adenovirus produces potent E1A proteins that immortalize primary rodent cells by altering cellular transcription, ultimately leading to deregulation of apoptosis and malignant transformation.

Epidemiology

• Adenovirus infections are widely distributed in human populations. The highest susceptibility is found among children from 6 months to 2 years of age and extends to the group of 5 to 9 year old children. Types 2, 1, 3, 5, 7, and 6 (in that order) are most frequently isolated from adenovirus-infected children, with types 1 and 2 constituting some 60 percent of all isolates. Nevertheless, adenovirus infections are responsible for only 2 to 5 percent of acute respiratory infections in children.

• Infections happen in children more often than in adults, but anyone can get them. Most kids will have at least one type of adenovirus infection by the time they’re 10.

• The infections usually cause only mild symptoms and get better on their own in a few days. But they can be more serious in people with weak immune systems, especially children.

• Adenoviruses have been isolated from severely immunocompromised

patients, such as those with acquired immune deficiency syndrome (AIDS). Many of these isolates, including the adenovirus types 42 to 47, are found in the urine of AIDS patients.

Ilnesses associated with adnoviruses

Phase I Study of DNX-2401 (Delta-

24-RGD) Oncolytic Adenovirus:

Replication and

Immunotherapeutic Effects in

Recurrent Malignant Glioma

OVERVİEW

of

RESEARCH PAPER

• Introduction

• Method

• Result

INTRODUCTION • Tumor selectivity is achieved by a 24-base pair deletion in the

E1A gene, which renders the virus unable to replicate in normal cells that maintain a functional Rb pathway but fully replication competent in tumor cells.

• To enhance potency, an RGD-motif was engineered into the fiber H-loop, enabling the virus to use avb3 or avb5 integrins to enter cells. These integrins are typically enriched on tumor cells, including glioma stem cells.

• 20% of patients (five of 25) survived more than 3 years after single DNX-2401 administration, and three of these five patients had 95% reduction in tumor volumes that evolved over several months after treatment.

METHOD

• Patients were enrolled in one of two groups.

• Group A was a treatment-only group.

• Group B was treat-resect-treat group.

• All patients were older than 18.

• Medical history, MRI, blood counts, and chemistry values were documented.

Expriment Design

METHOD CONT.

• Pretreatment biopsy specimens obtained before injection were stained with hematoxylin and eosin and evaluated by a certified neuro-pathologist to document recurrent tumor. Post-treatment surgical specimens were immunostained for adenovirus proteins and for immune cell infiltrates.

RESULT

• Authors show that DNX-2401, a novel tumor-selective adenovirus, is safe and capable of robust viral replication and killing of recurrent high-grade glioma cells. Secondary antiglioma immune-mediated responses were observed. Importantly,these biologic mechanisms translated into clinical benefit, including three dramatic responses ($ 95% reduction in tumor size) with long progression-free intervals and long-term survival after treatment with DNX-2401

• By marking the injection with a catheter, we were

able to localize the site of virus injection and assess

viral replication. DNX-2401 infection, replication, and

killing followed the three-concentric zone pattern

that we described in preclinical animal models.

• Although viral replication was evident in post treatment specimens

collected 2 weeks after treatment, specimens taken beyond 1

month did not show evidence of virus, suggesting that DNX- 2401

does not persist long term or falls below the detection limit over

time, consistent with observations in immunocompetent animal

models.However, clinical responses ($ 95% reduction in tumor size)

were typically first evident at more than 3 months after

treatment,pointing to a robust secondary antitumor immune effect.

• Immune responses were observed after a single injection of

DNX-2401 into human glioma.

• Examination of a recurrent enhancing nodule

located away from the originally injected tumor 2.5

years after a complete response to DNX-2401.

• Also tumor infection induced a decrease in TIM-3

expression (Fig 3E), indicating that DNX-2401 may

partially overcome some features of T-cell ex-

haustion and suggesting that combining DNX-2401

with checkpoint-based therapies may further

augment clinical benefit.

• In all, these results provide the first clinical

correlates that DNX-2401 can induce a direct

oncolytic effect followed by an antitumor immune

response.

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