Molecular basis of immune evasion strategies by adenoviruses

Prolonged mechanical support in children with severe adenoviral infections: a case series and review of the literature

Adenovirus infections occur primarily in infants and children less than 5 years of age, accounting for 2% to 5% of respiratory illnesses in the pediatric population and 4% to 10% of childhood pneumonias. Although the majority of children with adenovirus disease develop mild upper respiratory tract disease, more severe disease may occur with involvement of the lower respiratory tract characterized by pneumonitis and/or small airways disease. The authors present a case series of 3 high-risk children with severe lower respiratory tract adenoviral infections. These cases demonstrate the potential for the development of severe respiratory involvement from adenovirus in infants and children with comorbid conditions and illustrate that there may be a rapid progression of the disease as well as the need, in selected circumstances, for prolonged mechanical support. We review the role of adenovirus in lower respiratory tract infections in infants and children, its potential to result in life-threatening complications in pediatric patients with comorbid conditions, and the potential life-saving role of mechanical ventilation and extracorporeal life support (ECLS) in these children.

Improving adenovirus based gene transfer: strategies to accomplish immune evasion

Adenovirus (Ad) based gene transfer vectors continue to be the platform of choice for an increasing number of clinical trials worldwide. In fact, within the last five years, the number of clinical trials that utilize Ad based vectors has doubled, indicating growing enthusiasm for the numerous positive characteristics of this gene transfer platform. For example, Ad vectors can be easily and relatively inexpensively produced to high titers in a cGMP compliant manner, can be stably stored and transported, and have a broad applicability for a wide range of clinical conditions, including both gene therapy and vaccine applications. Ad vector based gene transfer will become more useful as strategies to counteract innate and/or pre-existing adaptive immune responses to Ads are developed and confirmed to be efficacious. The approaches attempting to overcome these limitations can be divided into two broad categories: pre-emptive immune modulation of the host, and selective modification of the Ad vector itself. The first category of methods includes the use of immunosuppressive drugs or specific compounds to block important immune pathways, which are known to be induced by Ads. The second category comprises several innovative strategies inclusive of: (1) Ad-capsid-display of specific inhibitors or ligands; (2) covalent modifications of the entire Ad vector capsid moiety; (3) the use of tissue specific promoters and local administration routes; (4) the use of genome modified Ads; and (5) the development of chimeric or alternative serotype Ads. This review article will focus on both the promise and the limitations of each of these immune evasion strategies, and in the process delineate future directions in developing safer and more efficacious Ad-based gene transfer strategies.

Exhaustion of type I interferon response following an acute viral infection

Viral infections often cause a period of heightened susceptibility to a secondary infection but the cause of this phenomenon is unknown. We found that a primary viral infection in mice rapidly triggers an IFN-I-dependent partial activation state in the majority of B and T lymphocytes, which reverts to a resting phenotype within 5 days. When a secondary infection with an unrelated virus occurred 5 to 9 days after the primary infection, no recurrence of marked activation of lymphocytes was observed. This was not due to an inherent inability of the previously activated cells to undergo renewed partial activation, because they responded when challenged with virus after transfer into "naive" recipients. Instead, the failure to respond optimally resided in the original host's incapacity to mount an IFN-I response to the secondary infection during this time period. Thus, transient immunosuppression through exhaustion of IFN-I production during an acute viral infection creates a time period of enhanced susceptibility to secondary infection.

Fatal Type 3 Adenoviral Pneumonia in Immunocompetent Adult Identical Twins

We describe adult twin sisters who developed severe adenoviral pneumonia with relative leukopenia, progressive focal infiltrates, shock, and hypoxia. Potential determinants of severe adenoviral disease are discussed.

Genetic 'budget' of viruses and the cost to the infected host: a theory on the relationship between the genetic capacity of viruses, immune evasion, persistence and disease

The nature of the pathogen-host relationship is recognized as being a dynamic coevolutionary process where the immune system has required ongoing adaptation and improvement to combat infection. Under survival pressure from sophisticated immune responses, adaptive processes for microbes, including viruses, have manifested as immune evasion strategies. This paper proposes a theory that virus immune evasion can be broadly classified into 'acquisition' or 'erroneous replication' strategies. Acquisition strategies are characteristic of large genome dsDNA viruses, which (i) replicate in the cell nucleus; (ii) have acquired host genes that can be used to directly manipulate responses to infection; (iii) are often latent for the lifetime of the host; and (iv) have little or no serious impact on health. Alternatively, erroneous replication strategies are characteristic of small genome RNA viruses, which are recognized as being the cause of many serious diseases in humans. It is proposed that this propensity for disease is due to the cytoplasmic site of replication and truncated temporal relationship with the host, which has limited or removed the evolutionary opportunity for RNA viruses to have acquired host genes. This has resulted in RNA viruses relying on error-prone replication strategies which, while allowing survival and persistence, are more likely to lead to disease due to the lack of direct viral control over potentially host-deleterious inflammatory and immune responses to infection.

Efficient expression of the tumor-associated antigen MAGE-3 in human dendritic cells, using an avian influenza virus vector

Dendritic cells (DCs) are the most potent inducers of immune reactions. Genetically modified DCs, which express tumor-associated antigens (TAA), can efficiently induce antitumor immunity and thus have a high potential as tools in cancer therapy. The gene delivery is most efficiently achieved by viral vectors. Here, we explored the capacity of influenza virus vectors to transduce TAA genes. These viruses abortively infect DCs without interfering with their antigen-presenting capacity. In contrast to other viruses used for DC transduction, influenza viruses can be efficiently controlled by antiviral pharmaceuticals, lack the ability to integrate into host chromosomes, and fail to establish persistent infections. Genes encoding a melanoma-derived TAA (MAGE-3), or the green fluorescence protein (GFP), were introduced into a high-expression avian influenza virus vector. Monocyte-derived mature DCs infected by these recombinants efficiently produced GFP or MAGE-3. More than 90% of the infected DCs can express a transduced gene. Importantly, these transduced DCs retained their characteristic phenotype and their potent allogeneic T cell stimulatory capacity, and were able to stimulate MAGE-3-specific CD8(+) cytotoxic T cells. Thus influenza virus vectors provide a highly efficient gene delivery system in order to transduce human DCs with TAA, which consequently stimulate TAA-specific T cells.

Adenovirus-Induced Liver Pathology Is Mediated Through TNF Receptors I and II but Is Independent of TNF or Lymphotoxin

Mice infected with an adenovirus mutant in which the E3 region is deleted, including TNF-resistance genes, develop fatal liver pathology within 3–4 days after infection. At least 10-fold more wild-type virus was needed to cause comparable pathology. These results indicate that the E3 region is critically involved in modulating the pathogenesis of adenovirus infection and that TNF may play a role in liver damage. To explore the latter possibility, the course of disease was examined in infected mice lacking TNFR-I and/or TNFRII, TNF only, or both TNF and lymphotoxin-α. Only mice lacking both TNFRI and TNFRII were protected from the lethal affects of the mutant adenovirus. Mice deficient in TNF or TNF and lymphotoxin-α displayed the fatal pathology. This outcome is consistent with the existence of another related ligand that binds TNFRI/II to mediate liver damage during infection with this mutant.

Detection of adenoviral genome in the myocardium of adult patients with idiopathic left ventricular dysfunction

BACKGROUND

The use of molecular biological techniques has demonstrated the importance of enteroviral infection of the myocardium in the pathogenesis of myocarditis and dilated cardiomyopathy in adults and adenovirus and enterovirus infection in children. The aim of this study was to determine the frequency of adenoviral infection of the myocardium of adults with impaired left ventricular function of unknown origin.

METHODS AND RESULTS

Nested polymerase chain reaction (nPCR) was used to determine the frequency of detection of adenoviral DNA and enteroviral RNA in myocardial tissue samples from 94 adult patients with idiopathic left ventricular dysfunction and 14 control patients. Histological and immunohistological analyses were performed to detect myocardial inflammation. Adenoviral genomic DNA was detected by nPCR in 12 of the 94 patients with left ventricular dysfunction (in each case, adenovirus type 2), whereas enteroviral RNA was detected in another 12 patients. All control samples were negative for both viruses. In all patients, active myocarditis was excluded according to the Dallas criteria. However, there was significantly decreased CD2, CD3, and CD45RO T lymphocyte counts in the adenovirus-positive group compared with the adenovirus-negative group (P<0.05), whereas no differences were associated with enterovirus infection.

CONCLUSIONS

Although enteroviruses are an important causative agent in the pathogenesis of myocarditis and dilated cardiomyopathy, this study shows that adenovirus infection is also important in the pathogenesis of left ventricular failure in adults. However, the pathogenetic basis of disease associated with adenovirus infection may be different than that after infection with other agents, particularly with respect to activation of the host immune response.

Existing antilisterial immunity does not inhibit the development of a Listeria monocytogenes-specific primary cytotoxic T-lymphocyte response

Infection of BALB/c mice with Listeria monocytogenes stimulates an antilisterial immune response evident by the appearance of H2-Kd-restricted CD8(+) cytotoxic T lymphocytes (CTLs) specific for the nanomer peptides amino acids (aa) 91 to 99 of listeriolysin O (LLO 91-99) and aa 217 to 225 of the p60 molecule (p60 217-225). We have introduced point mutations at anchor residues within LLO 91-99 (92F) or p60 217-225 (218F), and BALB/c mice infected with L. monocytogenes strains containing these point mutations do not develop CTLs specific for LLO 91-99 or p60 217-225, respectively. We have used these strains to test whether primary CTL responses against L. monocytogenes-derived determinants can be stimulated within an environment of existing antilisterial immunity. We found that the development of a primary L. monocytogenes-specific CTL response is not altered by existing immunity to L. monocytogenes. For example, primary immunization with the p60 218F strain of L. monocytogenes followed by a secondary immunization with wild-type L. monocytogenes results in stimulation of p60 217-225-specific CTLs at primary response levels and LLO 91-99-specific effectors at levels consistent with a memory CTL response. Similarly, primary immunization with the 92F strain of L. monocytogenes followed by a secondary immunization with wild-type L. monocytogenes results in stimulation of LLO 91-99-specific CTLs at primary response levels and p60 217-225-specific effectors at levels consistent with a memory CTL response. These results provide additional support for the use of L. monocytogenes as a recombinant vaccine vector and show that antivector immunity does not inhibit the development of a primary CTL response when the epitope is delivered by L. monocytogenes as the vaccine strain.

Pathogen interactions with cytokines and host defence: an overview

This review summarises some of the immune evasion tactics adopted by pathogens. They include the antagonism of immune function through the use of homologues of cytokine receptors, expression of viral proteins which interact with cytokine signal transduction and expression of cytokine mimics and host proteins that influence the Type I or II cytokine responses. Some of the viral defense molecules that interfere with the functions of cytokines include the EBV protein BCRF1 (viral IL-10) which blocks synthesis of cytokines such as IFN-gamma, viral IL-17 and IL-8 receptor encoded by the herpesvirus saimiri genome and chemokine receptor homologues of Epstein-Barr virus, herpesvirus saimiri and cytomegalovirus. These immunomodulatory tactics function to protect the host from the lethal inflammatory effects as well as inhibit the local inflammatory response elicited to kill the foreign pathogen. Other strategies include the alterations in cytokine expression such as demonstrated with the hepatitis B virus (HBV) core protein and terminal protein which can inhibit interferon-beta gene expression, the interactions of the hepatitis C virus core protein to lymphotoxin-beta receptor and the effects of the interferon signal transduction pathway by adenovirus EIA oncogene and HBV by reducing levels or activity of the cytosolic latent transcriptional factors (STATS). Immune evasive strategies of helminth parasites related to cytokine activities will also be briefly discussed.

Reversal of biochemical and functional abnormalities in erythrocytes secondary to selenium deficiency

A patient with multiple enterocutaneous fistulae on total parenteral nutrition for 14 months developed low erythrocyte selenium and low erythrocyte glutathione peroxidase. Erythrocyte hexose monophosphate shunt activity stimulated with an H2O2 generating system was approximately one-fourth that of control. Hexose monophosphate shunt activity stimulated with methylene blue showed little difference between patient and control. With selenium supplementation erythrocyte selenium, glutathione peroxidase, and hexose monophosphate shunt activity became normal. Thus, the biochemical and functional consequences of selenium deficiency can be corrected with selenium supplementation.