The adenovirus E3-14.7K protein and the E3-10.4K/14.5K complex of proteins, which independently inhibit tumor necrosis factor (TNF)-induced apoptosis, also independently inhibit TNF-induced release of arachidonic acid

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.

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.

Mechanisms of pathogenesis of emerging adenoviruses

Periodic outbreaks of human adenovirus infections can cause severe illness in people with no known predisposing conditions. The reasons for this increased viral pathogenicity are uncertain. Adenoviruses are constantly undergoing mutation during circulation in the human population, but related phenotypic changes of the viruses are rarely detected because of the infrequency of such outbreaks and the limited biological studies of the emergent strains. Mutations and genetic recombinations have been identified in these new strains. However, the linkage between these genetic changes and increased pathogenicity is poorly understood. It has been observed recently that differences in virus-induced immunopathogenesis can be associated with altered expression of non-mutant viral genes associated with changes in viral modulation of the host innate immune response. Initial small animal studies indicate that these changes in viral gene expression can be associated with enhanced immunopathogenesis in vivo. Available evidence suggests the hypothesis that there is a critical threshold of expression of certain viral genes that determines both the sustainability of viral transmission in the human population and the enhancement of immunopathogenesis. Studies of this possibility will require extension of the analysis of outbreak viral strains from a sequencing-based focus to biological studies of relationships between viral gene expression and pathogenic responses. Advances in this area will require increased coordination among public health organizations, diagnostic microbiology laboratories, and research laboratories to identify, catalog, and systematically study differences between prototype and emergent viral strains that explain the increased pathogenicity that can occur during clinical outbreaks.

Diverse mechanisms evolved by DNA viruses to inhibit early host defenses

In mammalian cells, early defenses against infection by pathogens are mounted through a complex network of signaling pathways shepherded by immune-modulatory pattern-recognition receptors. As obligate parasites, the survival of viruses is dependent on the evolutionary acquisition of mechanisms that tactfully dismantle and subvert the cellular intrinsic and innate immune responses. Here, we review the diverse mechanisms by which viruses that accommodate DNA genomes are able to circumvent activation of cellular immunity. We start by discussing viral manipulation of host defense protein levels by either transcriptional regulation or protein degradation. We next review viral strategies used to repurpose or inhibit these cellular immune factors by molecular hijacking or by regulating their post-translational modification status. Additionally, we explore the infection-induced temporal modulation of apoptosis to facilitate viral replication and spread. Lastly, the co-evolution of viruses with their hosts is highlighted by the acquisition of elegant mechanisms for suppressing host defenses via viral mimicry of host factors. In closing, we present a perspective on how characterizing these viral evasion tactics both broadens the understanding of virus-host interactions and reveals essential functions of the immune system at the molecular level. This knowledge is critical in understanding the sources of viral pathogenesis, as well as for the design of antiviral therapeutics and autoimmunity treatments.

STAT1 interaction with E3-14.7K in monocytes affects the efficacy of oncolytic adenovirus

Oncolytic viruses based on adenovirus type 5 (Ad5) have been developed as a new class of therapeutic agents for cancers that are resistant to conventional therapies. Clinical experience shows that these agents are safe, but virotherapy alone has not achieved long-term cure in cancer patients. The vast majority of oncolytic adenoviruses used in clinical trials to date have deletion of the E3B genes. It has been demonstrated that the antitumor potency of the E3B-deleted mutant (dl309) is inferior to adenovirus with E3B genes intact. Tumors treated with dl309 show markedly greater macrophage infiltration than E3B-intact adenovirus. However, the functional mechanisms for this were not previously known. Here, we demonstrate that deletion of E3B genes increases production of chemokines by monocytes after adenovirus infection and increases monocyte migration. The E3B 14,700-Da protein (E3B-14.7K) inhibits STAT1 function by preventing its phosphorylation and nuclear translocation. The STAT1 inhibitor, fludarabine, rescues the effect of E3B-14.7K deletion by downregulating target chemokine expression in human and murine monocytes and results in an enhanced antitumor efficacy with dl309 in vivo. These findings have important implications for clinical use of E3B-deleted oncolytic adenovirus and other E3B-deleted adenovirus vector-based therapy.

Cytokine patterns associated with a serotype 8 fowl adenovirus infection

This study examined cytokine gene expression patterns associated with fowl adenovirus (FAdV) infection. The selected cytokine mRNA was quantified by quantitative real-time reverse transcription-PCR in spleen, liver, and cecal tonsil during the course of infection of chickens with a serotype 8 FAdV (FAdV-8). Compared to uninfected chickens, infected birds had higher mRNA expression of interleukin (IL)-18 and IL-10 in spleen and liver, respectively. Interferon gamma (IFN-γ) mRNA expressed in spleen and liver of infected chickens was significantly upregulated, while the expression of IL-8 mRNA in spleen and liver of infected chickens was significantly downregulated. There was no significant difference between infected and uninfected groups in terms of cytokine gene expression in cecal tonsil. These results indicate that these four cytokines might play an important role in driving the immune responses following FAdV-8 infection.

Oncolytic viruses & their specific targeting to tumour cells

Cancer is one of the major causes of death worldwide. In spite of achieving significant successes in medical sciences in the past few decades, the number of deaths due to cancer remains unchecked. The conventional chemotherapy and radiotherapy have limited therapeutic index and a plethora of treatment related side effects. This situation has provided an impetus for search of novel therapeutic strategies that can selectively destroy the tumour cells, leaving the normal cells unharmed. Viral oncotherapy is such a promising treatment modality that offers unique opportunity for tumour targeting. Numerous viruses with inherent anti-cancer activity have been identified and are in different phases of clinical trials. In the era of modern biotechnology and with better understanding of cancer biology and virology, it has become feasible to engineer the oncolytic viruses (OVs) to increase their tumour selectivity and enhance their oncolytic activity. In this review, the mechanisms by which oncolytic viruses kill the tumour cells have been discussed as also the development made in virotherapy for cancer treatment with emphasis on their tumour specific targeting.

Oncolytic adenoviral gene therapy in ovarian cancer: why we are not wasting our time

Preclinical gene-therapy studies in the past 15 years have repeatedly raised hopes that we were about to enter a brave new era. However, many clinical trials have disappointed. For tumor types with poor response rates to first-line conventional cytotoxic chemotherapy and/or high rates of chemorefractory disease, there remain very few treatment options. In this article we review gene therapy within the context of ovarian cancer. We examine why clinical data have been discouraging and discuss how the lessons learned from earlier trials are being applied to current research.

Deletion of the E3-6.7K/gp19K region reduces the persistence of wild-type adenovirus in a permissive tumor model in Syrian hamsters

A partial deletion of the adenovirus E3 region, comprising the overlapping 6.7K/gp19K genes, has been described for the incorporation of therapeutic genes in 'armed' oncolytic adenoviruses. This deletion allows the insertion of up to 2.5 kb genetic material into the virus and ensures strong expression of transgenes without reducing the replication and cytolytic potency of viruses in vitro. E3-gp19K and 6.7K proteins are involved in avoiding recognition and elimination of infected cells by the host immune system. Therefore, we have studied the effect of this deletion on the replication and transgene expression of the virus in immunocompetent models based on Syrian hamsters. Tumors were established by intrahepatic injection of pancreatic cancer cells with moderate (HaP-T1, HP-1) or low (H2T) permissivity for adenovirus replication. The wild-type human adenovirus 5 (Ad5) or a modified version containing the luciferase gene in the E3-6.7K/gp19K locus (Ad-WTLuc) were injected intratumorally. We found that elimination of Ad-WTLuc was faster than Ad5 in HaP-T1 and HP-1 tumors. In contrast, no differences were observed when the same tumor was established in severely immunocompromised NOD-scid IL2Rgamma(null) mice. In addition, virus-mediated luciferase expression was more stable in these animals. These results suggest that the lack of E3-6.7K/gp19K genes may accelerate the clearance of oncolytic adenoviruses in some immunocompetent tumor models.

Prevention of hepatocyte allograft rejection in rats by transferring adenoviral early region 3 genes into donor cells

Hepatocyte transplantation is being evaluated as an alternative to liver transplantation for metabolic support during liver failure and for definitive treatment of inherited liver diseases. However, as with liver transplantation, transplantation of allogeneic hepatocytes requires prolonged immunosuppression with its associated untoward effects. Therefore, we explored strategies for the genetic modification of donor hepatocytes that could eliminate allograft rejection, obviating the need for immunosuppression. Products of early region 3 (AdE3) of the adenoviral genome are known to protect infected cells from immune recognition and destruction. In the present study we showed that immortalized rat hepatocytes that had been stably transduced with AdE3 before transplantation into fully MHC-mismatched rats are protected from allograft rejection. Quantitative real-time PCR analysis showed that a similar number of engrafted AdE3-transfected hepatocytes had survived in syngeneic and allogeneic recipients. AdE3 expression did not reduce expression of MHC class I on the surfaces of donor hepatocytes. Consistent with this, the in vivo cytotoxic cell-mediated alloresponse was attenuated but not abolished in recipients of AdE3-transfected allogeneic hepatocytes. In contrast, graft survival correlated with a marked reduction in cell-surface localization of Fas receptor in the transplanted cells and inhibition of Fas-mediated apoptosis, which are related to the antiapoptotic functions of the AdE3 proteins.

CONCLUSION

AdE3 gene products prevent hepatocyte allograft rejection mainly by protecting the cells from the effector limb of the host immune response and could be used as a tool to facilitate allogeneic hepatocyte transplantation.

Adenovirus RIDalphabeta complex inhibits lipopolysaccharide signaling without altering TLR4 cell surface expression

The transmembrane heterotrimer complex 10.4K/14.5K, also known as RID (for "receptor internalization and degradation"), is encoded by the adenovirus E3 region, and it down-regulates the cell surface expression of several unrelated receptors. We recently showed that RID expression correlates with down-regulation of the cell surface expression of the tumor necrosis factor (TNF) receptor 1 in several human cells. This observation provided the first mechanistic explanation for the inhibition of TNF alpha-induced chemokines by RID. Here we analyze the immunoregulatory activities of RID on lipopolysaccharide (LPS) and interleukin-1 beta (IL-1beta)-mediated responses. Although both signaling pathways are strongly inhibited by RID, the chemokines up-regulated by IL-1beta stimulation are only marginally inhibited. In addition, RID inhibits signaling induced by LPS without affecting the expression of the LPS receptor Toll-like receptor 4, demonstrating that RID need not target degradation of the receptor to alter signal transduction. Taken together, our data demonstrate the inhibitory effect of RID on two additional cell surface receptor-mediated signaling pathways involved in inflammatory processes. The data suggest that RID has intracellular targets that impair signal transduction and chemokine expression without evidence of receptor down-regulation.

Viruses with deletions in antiapoptotic genes as potential oncolytic agents

Replication-selective oncolytic viruses have emerged as a new treatment platform for cancers. However, selectivity and potency need to be improved before virotherapy can become a standard treatment modality. In addition, mechanisms that can be incorporated to enable targeting a broad range of cancer types are highly desirable. Cancer cells are well known to have multiple blocks in apoptosis pathways. On the other hand, viruses have evolved to express numerous antiapoptotic genes to antagonize apoptosis induced upon infection. Viruses with deletions in antiapoptotic genes can therefore be complemented by antiapoptotic genetic changes in cancer cells for efficient replication and oncolysis. In this review, we summarize the recent development of this concept, the potential obstacles, and future directions for optimization.

Adenovirus immunoregulatory E3 proteins prolong transplants of human cells in immunocompetent mice

The majority of proteins encoded in the early 3 (E3) region of human subgroup C adenoviruses function to modulate the host immune response. For example, gp19K, one of these E3 proteins, prevents the major histocompatibility complex type I (MHC-I) from presenting viral antigens on the surface of the infected cell. Other E3 proteins, such as the RID and 14.7K proteins, counteract the effector phase of the cellular immune response. In order to study further the effects of these proteins, we constructed an E1-/E3- adenovirus vector, Ad/E3, that contains all the E3 genes with the exception of the cytolytic adp gene, inserted into the deleted E1 region. The transcription of the E3 genes in this vector is driven by a CMV promoter in place of the native E3 promoter. Ad/E3 expressed close to wild-type adenovirus levels of all E3 proteins, and these proteins appear to function normally in cell culture. For example, in Ad/E3-infected cells, surface expression of MHC-I was down-regulated, as was cell surface display of death receptors Fas and TRAIL Receptor 1. A human cell line of lung origin (A549), which was rapidly rejected after transplantation into C57BL/6 mice, was protected for an extended time from the host immune response after infection with an Ad/E3, and went through a number of divisions in immunocompetent mice. These latter results indicate that the E3 proteins protect cells from destruction by the immune system.

Adenoviral-mediated transduction of human pancreatic islets: importance of adenoviral genome for cell viability and association with a deficient antiviral response

As adenoviral vectors are extensively used for genetic manipulation of insulin-producing cells in vitro, there is an increasing need to evaluate their effects on the function, morphology, and viability of transduced pancreatic islets. In the present study we observed that specific adenoviral genotypes, carrying E4 and E1/E3 deletions, correlate with differential induction of necrosis in pancreatic islet cells. In particular, the adenovirus death protein encoded from the E3 region of the adenoviral genome was able to modulate the changes induced in the morphology and viability of the transduced cells. We also propose a putative role for the transcriptional regulator pIX. Although human islet cells showed an increased resistance in terms of viral concentrations required for the induction of cell toxicity, our results showed that they were unable to build up an efficient antiviral response after transduction and that their survival was dependent on the exogenous addition of alpha-interferon. An intact and fully functional beta-cell is crucial for the successful application of gene therapy approaches in type 1 diabetes, and therefore, the implications of our findings need to be considered when designing vectors for gene transfer into pancreatic beta-cells.

ADP-overexpressing adenovirus elicits enhanced cytopathic effect by induction of apoptosis

Replication-competent adenoviruses (Ad's) are emerging as a promising new modality for treatment of cancer. Selective replication of viral agents in tumor may lead to improved efficacy over nonreplicating Ad's due to their inherent ability to multiply, lyse, and spread to surrounding cells. We have previously shown that an E1B 55 kDa-deleted adenovirus (YKL-1) exhibits tumor-specific replication and cell lysis, but its cytolytic effects were reduced in comparison to the wild-type adenovirus. To increase the oncolytic potency of YKL-1, we have reintroduced the Ad death protein (ADP) gene under the control of either a CMV or an MLP promoter at the E3 region of YKL-1, generating YKL-cADP and YKL-mADP Ad's, respectively. ADP is an 11.6 kDa protein encoded by the E3 transcription unit, and is required to kill adenovirus-infected cells efficiently. However, to date, the mechanism by which ADP mediates cell death has not been clearly defined. In this study, we report that ADP-overexpressing Ad markedly enhanced cytolytic effect (up to 100-fold) against all tumor cell lines tested, but did not increase cytopathic effect in normal skin fibroblast, BJ. Moreover, plaque size formed by YKL-cADP was substantially larger than that of YKL-1, indicating an enhancement in cell lysis. TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assay and Annexin-V/PI double staining indicate that ADP-mediated cytotoxicity was largely driven by apoptosis. Finally, YKL-cADP adenovirus also showed superior antitumor effect than YKL-1 and YKL-mADP in C33A cervical and Hep3B hepatoma xenograft tumor models. Taken together, these lines of evidence demonstrate that the newly generated adenovirus expressing ADP under the CMV promoter induces efficient but tumor-selective cell lysis, which is critical for adding therapeutic value to replicating adenovirus for its use in cancer gene therapy.

Sequence polymorphism in the E3 7.7K ORF of subspecies B1 human adenoviruses

Sequences corresponding to the 7.7K open-reading frame (ORF) of the E3 region of subspecies B1 adenoviruses (Ads) were compared with prototype strains of Ad3, Ad7, Ad16, Ad21, and Ad50 and field isolates representing a variety of genome restriction types of Ad3 and Ad7 to better assess the extent of genetic variation in this intriguing region of the viral genome encoding a product whose function is still unknown. Alignment of 55 species B1 Ad sequences revealed a marked polymorphism in the 7.7K ORF and allowed the identification of eight distinct sequence profiles (SPs) characterized by (1) deletions that retain or change the reading frame, (2) single-base mutations (SBMs) that change the start codon (ATG to ATT or ATC), and (3) other SBMs. mRNAs of expected size for the observed sequence polymorphisms were identified by RT-PCR from DNAse I-treated total RNA extracts of infected cells. Predicted proteins ranged from 0 to 94 amino acids corresponding to molecular masses of 0-11 K. Together with the hypervariable regions of the hexon gene, the E3 7.7K ORF appears to be another area of the Ad genome in which genetic diversity may be generated by illegitimate recombination.

Adenovirus E3-6.7K protein is required in conjunction with the E3-RID protein complex for the internalization and degradation of TRAIL receptor 2

Adenoviruses (Ads) encode several proteins within the early region 3 (E3) transcription unit that help protect infected cells from elimination by the immune system. Among these immunomodulatory proteins, the receptor internalization and degradation (RID) protein complex, which is composed of the RIDalpha (formerly E3-10.4K) and RIDbeta (formerly E3-14.5K) subunits, stimulates the internalization and degradation of certain members of the tumor necrosis factor (TNF) receptor superfamily, thus blocking apoptosis initiated by Fas and TNF-related apoptosis-inducing ligand (TRAIL). The experiments reported here show that TRAIL receptor 2 (TR2) is cleared from the cell surface in Ad-infected cells. Virus mutants containing deletions that span E3 were used to show that the RID and E3-6.7K proteins are both necessary for the internalization and degradation of TR2, whereas only the RID protein is required for TRAIL receptor 1 downregulation. In addition, replication-defective Ad vectors that express individual E3 proteins were used to establish that the RID and E3-6.7K proteins are sufficient to clear TR2. These data demonstrate that E3-6.7K is an important component of the antiapoptosis arsenal encoded by the E3 transcription unit of subgroup C Ads.

Tumor-specific intravenous gene delivery using oncolytic adenoviruses

In this report, we describe a vector system that specifically delivers transgene products to tumors following intravenous (i.v.) administration. The Escherichia coli cytosine deaminase (CD) gene was placed in the E3B region of the tumor-selective, replication-competent adenovirus ONYX-411, under the control of endogenous viral late gene regulatory elements. Thus, CD expression was directly coupled to the tumor-selective replication of the viral vector. In vitro, CD was expressed efficiently in various human cancer cell lines tested but not in cultured normal human cells, including human hepatocytes. Following i.v. administration into nude mice carrying human tumor xenografts, robust CD activity was detected only in tumors but not in liver or other normal tissues. Levels of CD activity in the tumors increased progressively following i.v. virus administration, correlating closely with virus replication in vivo. Subsequent administration of 5-fluorocytosine (5-FC) demonstrated a trend to improve the antitumor efficacy of these viruses in a mouse xenograft model, presumably due to the intratumoral conversion of 5-FC to the chemotherapeutic drug 5-fluorouracil. We show that the combination of a highly selective oncolytic virus, ONYX-411, with the strategic use of the viral E3B region for transgene insertion provides a powerful platform that allows for tumor-specific, persistent and robust transgene expression after i.v. administration. This technology provides an opportunity to enhance greatly both safety and efficacy of cancer gene therapy.

An E1B-19 kDa gene deletion mutant adenovirus demonstrates tumor necrosis factor-enhanced cancer selectivity and enhanced oncolytic potency

Oncolytic adenoviruses hold promise as a new treatment platform for cancer, but limitations have been identified, including limited spread and potency. The adenoviral protein E1B-19 kDa is a Bcl-2 homologue that blocks apoptosis induction via the intrinsic and extrinsic pathways, specifically including tumor necrosis factor-mediated cell death. We demonstrate that an E1B-19 kDa gene deletion mutant had tumor necrosis factor-enhanced cancer selectivity, in vitro and in vivo, due to genetic blocks in apoptosis pathways in cancer cells. In addition, this mutant demonstrated significantly enhanced viral spread and antitumoral potency relative to dl1520 (aka Onyx-015) and wild-type adenovirus in vitro. Significant antitumoral efficacy was demonstrated in vivo by intratumoral and intravenous routes of administration. E1B-19 kDa deletion should be considered as a feature of oncolytic adenoviruses to enhance their safety, spread, and efficacy.

Functions and mechanisms of action of the adenovirus E3 proteins

In the evolutionary battle between viruses and their hosts, viruses have armed themselves with weapons to defeat the host's attacks on infected cells. Various proteins encoded in the adenovirus (Ad) E3 transcription unit protect cells from killing mediated by cytotoxic T cells and death-inducing cytokines such as tumor necrosis factor (TNF), Fas ligand, and TNF-related apoptosis-inducing ligand (TRAIL). The viral protein E3-gp19 K blocks MHC class-I-restricted antigen presentation, which diminishes killing by cytotoxic T cells. The receptor internalization and degradation (RID) complex (formerly E3-10.4 K/14.5 K) stimulates the clearance from the cell surface and subsequent degradation of the receptors for Fas ligand and TRAIL, thereby preventing the action of these important immune mediators. RID also downmodulates the epidermal growth factor receptor (EGFR), although what role, if any, this function has in immune regulation is uncertain. In addition, RID antagonizes TNF-mediated apoptosis and inflammation through a mechanism that does not primarily involve receptor downregulation. E3-6.7 K functions together with RID in downregulating some TRAIL receptors and may block apoptosis independently of other E3 proteins. Furthermore, E3-14.7 K functions as a general inhibitor of TNF-mediated apoptosis and blocks TRAIL-induced apoptosis. Finally, after expending great effort to maintain cell viability during the early part of the virus replication cycle, Ads lyse the cell to allow efficient virus release and dissemination. To perform this task subgroup C Ads synthesize a protein late in infection named ADP (formerly E3-11.6 K) that is required for efficient virus release. This review focuses on recent experiments aimed at discovering the mechanism of action of these critically important viral proteins.

Distinct domains in the adenovirus E3 RIDalpha protein are required for degradation of Fas and the epidermal growth factor receptor

Adenovirus (Ad) types 2 and 5 encode at least five proteins within the E3 transcription unit that help the virus evade the immune system. Two such proteins, RIDalpha (formerly E3-10.4K) and RIDbeta (formerly E3-14.5K), form the RID (receptor internalization and degradation) complex (formerly E3-10.4K/14.5K). RID mediates clearance from the cell surface and lysosomal degradation of a number of important members in the tumor necrosis factor receptor (TNFR) superfamily and the receptor tyrosine kinase receptor family. Affected receptors include Fas, TRAIL (TNF-related apoptosis-inducing ligand) receptor 1 (TR1), TR2, and epidermal growth factor receptor (EGFR). Degradation of Fas and TRAIL receptors protects Ad-infected cells from apoptosis. To investigate the mechanism of action of RIDalpha, 14 mutant RIDalpha proteins, each containing a three- to five-amino-acid deletion, were constructed and then expressed from the E3 region of a replication-competent recombinant Ad in the same context as wild-type RIDalpha. Each mutant protein was characterized with regard to five physical properties associated with wild-type RIDalpha, namely, protein stability, proteolytic cleavage, insertion into the membrane, complex formation with RIDbeta, and transport to the cell surface. Additionally, the mutant proteins were tested for their ability to mediate internalization and degradation of EGFR and Fas and to protect cells from Fas-mediated apoptosis. The majority of mutant RIDalpha proteins (8 out of 14) were physically similar to wild-type RIDalpha. With regard to functional characteristics, the cytoplasmic domain of RIDalpha is largely unimportant for receptor internalization and degradation and the extracellular domain of RIDalpha is important for down-regulation of EGFR but not Fas.

E3 gene manipulations affect oncolytic adenovirus activity in immunocompetent tumor models

Oncolytic replication-selective adenoviruses constitute a rapidly growing therapeutic platform for cancer. However, the role of the host immune response and the E3 immunoregulatory genes of the human adenovirus were unknown until now. We identified four mouse carcinoma lines of variable permissivity for adenoviral gene expression, cytopathic effects and/or burst size. To determine E3 gene effects in immunocompetent tumor-bearing hosts, we injected tumors with one of three adenoviruses: Ad5 (E3 wild type), dl309 (del. E3 10.4/14.5, 14.7 kDa) or dl704 (del. E3 gp19 kDa). Compared with Ad5 and dl704, dl309 was cleared much more rapidly and/or its activity was lower in all four models. Intratumoral injection with dl309 resulted in markedly greater macrophage infiltration and expression of both tumor necrosis factor and interferon-gamma. Adenovirus replication, CD8(+) lymphocyte infiltration and efficacy were similar upon intratumoral injection with either dl704 or Ad5. E3-dependent differences were not evident in athymic mice. These findings have important implications for the design of oncolytic adenoviruses and may explain the rapid clearance of E3-10.4/14.5,14.7-deleted adenoviruses in patients.

Novel immunocompetent murine tumor models for the assessment of replication-competent oncolytic adenovirus efficacy

Oncolytic replication-selective adenoviruses constitute a rapidly expanding experimental approach to the treatment of cancer. However, due to the lack of an immunocompetent and replication-competent efficacy model, the role of the host immune response and viral E3 immunoregulatory genes remained unknown. We screened nine murine carcinoma lines for adenovirus (Ad5) uptake, gene expression, replication, and cytopathic effects. In seven of these murine cell lines the infectability and cytopathic effects were similar to those seen with human carcinoma lines. Surprisingly, productive viral replication was demonstrated in several lines; replication varied from levels similar to those for some human carcinoma lines (e.g., CMT-64) to very low levels. Seven of these lines were grown as subcutaneous xenografts in immunocompetent mice and were subsequently injected directly with Ad5, saline, or a replication-deficient control adenovirus particle to assess intratumoral viral gene expression, replication, and antitumoral effects. E1A, coat protein expression, and cytopathic effects were documented in five xenografts; Ad5 replication was demonstrated in CMT-64 and JC xenografts. Ad5 demonstrated significant efficacy compared to saline and nonreplicating control Ad particles in both replication-permissive xenografts (CMT-64, JC) and poorly permissive tumors (CMT-93); efficacy against CMT-93 tumors was significantly greater in immunocompetent mice compared to athymic mice. These murine tumor xenograft models have potential for elucidating viral and host immune mechanisms involved in oncolytic adenovirus antitumoral effects.

Inducible nitric oxide synthase expression inhibition by adenovirus E1A

Nitric oxide (NO) is an antiviral effector of the innate immune system. Viruses that can interfere with NO synthesis may be able to replicate more rapidly than viruses that cannot limit NO synthesis. We show that the adenovirus E1A protein inhibits NO production by decreasing expression of the inducible NO synthase (NOS2). The amino-terminal portion of E1A decreases transactivation of the NOS2 5'-flanking region, limiting the DNA binding activity of NF-kappaB and inhibiting NOS2 expression. E1A is thus able to deactivate a critical component of the host defense against viral infection. Viral inhibition of NO production is a mechanism that may enable certain viruses to evade the host innate immune system.

Adenovirus early region 3 antiapoptotic 10.4K, 14.5K, and 14.7K genes decrease the incidence of autoimmune diabetes in NOD mice

Genes in the early region 3 (E3) of the adenovirus genome allow the virus to evade host immune responses by interfering with major histocompatibility (MHC) class I-mediated antigen presentation and tumor necrosis factor-alpha (TNF-alpha)- or Fas-induced apoptosis of infected cells. Autoimmune type 1 diabetes (T1D) is inhibited in NOD mice transgenically expressing all E3 genes under control of a rat insulin promoter (RIPE3/NOD). For dissecting the protective mechanisms afforded by various E3 genes, they were subdivided into RIP-driven transgene constructs. Strong T1D protection mediated at the beta-cell level characterized DL704/NOD mice lacking the E3 gp19K gene suppressing MHC class I expression but retaining the 10.4K, 14.5K, and 14.7K genes inhibiting Fas- or TNF-alpha-induced apoptosis and TNF-alpha-induced NF-kB activation. Much weaker protection characterized DL309/NOD mice expressing the gp19K but not the 10.4K, 14.5K, and 14.7K genes. While RIPE3/NOD splenocytes had an unexpected decrease in ability to adoptively transfer T1D, splenocytes from both the DL704 and DL309 stocks efficiently did so. These findings indicate that all E3 genes must be expressed to inhibit the diabetogenic potential of NOD immune cells. They also demonstrate that the antiapoptotic E3 genes most effectively protect pancreatic beta-cells from diabetogenic immune responses.

Overexpression of the ADP (E3-11.6K) protein increases cell lysis and spread of adenovirus

Adenoviruses replicate in the nucleus and induce lytic cell death. We have shown previously that efficient cell lysis and release of adenovirus from infected cells requires an 11.6-kDa protein named Adenovirus Death Protein (ADP). The adp gene is located in the early E3 transcription unit, but the gene is expressed primarily at very late stages of infection. The putative function of ADP was discerned previously from the use of virus mutants that lack functional ADP. Here we describe two adenovirus mutants, named VRX-006 and VRX-007, that overexpress ADP. VRX-006 lacks all other genes in the E3 region, and VRX-007 lacks all other E3 genes except 12.5K. VRX-006 and VRX-007 display the phenotype predicted by the proposed function for ADP: they produce early cytopathic effect, early cell lysis, large plaques, and increased cell-to-cell spread. They grow as well in cultured cells as does adenovirus type 5. These results are consistent with the conclusion that ADP functions in adenovirus infections to promote virus release from cells at the culmination of infection.

Subversion of host defense mechanisms by adenoviruses

Adenoviruses (Ads) cause acute and persistent infections. Alike the much more complex herpesviruses, Ads encode numerous immunomodulatory functions. About a third of the viral genome is devoted to counteract both the innate and the adaptive antiviral immune response. Immediately upon infection, E1A blocks interferon-induced gene expression and the VA-RNA inhibits interferon-induced PKR activity. At the same time, E1A reprograms the cell for DNA synthesis and induces the intrinsic cellular apoptosis program that is interrupted by E1B/19K and E1B/55K proteins, the latter inhibits p53-mediated apoptosis. Most other viral stealth functions are encoded by a separate transcription units, E3. Several E3 products prevent death receptor-mediated apoptosis. E3/14.7K seems to interfere with the cytolytic and pro-inflammatory activities of TNF while E3/10.4K and 14.5K proteins remove Fas and TRAIL receptors from the cell surface by inducing their degradation in lysosomes. These and other functions that may afect granule-mediated cell death might drastically limit lysis by NK cells and cytotoxic T cells (CTL). Moreover, Ads interfere with recognition of infected cell by CTL. The paradigmatic E3/19K protein subverts antigen presentation by MHC class I molecules by inhibiting their transport to the cell surface. In concert, these viral countermeasures ensure prolonged survival in the infected host and, as a consequence, facilitate transmission. Elucidating the molecular mechanisms of Ad-mediated immune evasion has stimulated corresponding research on other viruses. This knowledge will also be instrumental for designing better vectors for gene therapy and vaccination, and may lead to a more rational treatment of life-threatening Ad infections, e.g. in transplantation patients.

Adenovirus RIDbeta subunit contains a tyrosine residue that is critical for RID-mediated receptor internalization and inhibition of Fas- and TRAIL-induced apoptosis

The adenovirus-encoded receptor internalization and degradation (RID) protein (previously named E3-10.4K/14.5K), which is composed of RIDalpha and RIDbeta subunits, down-regulates a number of cell surface receptors in the tumor necrosis factor (TNF) receptor superfamily, namely Fas, TRAIL receptor 1, and TRAIL receptor 2. Down-regulation of these "death" receptors protects adenovirus-infected cells from apoptosis induced by the death receptor ligands Fas ligand and TRAIL. RID also down-regulates certain tyrosine kinase cell surface receptors, especially the epidermal growth factor receptor (EGFR). RID-mediated Fas and EGFR down-regulation occurs via endocytosis of the receptors into endosomes followed by transport to and degradation within lysosomes. However, the molecular interactions underlying this function of RID are unknown. To investigate the molecular determinants of RIDbeta that are involved in receptor down-regulation, mutations within the cytoplasmic tail of RIDbeta were constructed and the mutant proteins were analyzed for their capacity to internalize and degrade Fas and EGFR and to protect cells from death receptor ligand-induced apoptosis. The results demonstrated the critical nature of a tyrosine residue near the RIDbeta C terminus; mutation of this residue to alanine abolished RID function. Mutating the tyrosine to phenylalanine did not abolish the function of RID, arguing that phosphorylation of the tyrosine is not required for function. These data suggest that this tyrosine residue forms part of a tyrosine-based sorting signal (Yxxphi). Additional mutations that target another potential sorting motif and several possible protein-protein interaction motifs had no discernible effect on RID function. It was also demonstrated that mutation of serine 116 to alanine eliminated phosphorylation of RIDbeta but did not affect any of the functions of RID that were examined. These results suggest a model in which the tyrosine-based sorting signal in RID plays a role in RID's ability to down-regulate receptors.

Construction and characterization of E1-minus replication-defective adenovirus vectors that express E3 proteins from the E1 region

Previous research has indicated that the adenovirus protein complex named RID, derived from the E3 transcription unit, functions to remove the receptors named Fas/Apo1/CD95 (Fas) and epidermal growth factor receptor (EGFR) from the surface of cells. (The RID complex is composed of the RIDalpha and RIDbeta polypeptides, previously named 10.4K and 14.5K, respectively.) In response to RID, Fas and EGFR appear to be internalized into endosomes and degraded in lysosomes. Fas is a death receptor in the tumor necrosis factor (TNF) receptor superfamily. RID inhibits apoptosis via the Fas pathway, presumably because RID gets rid of Fas. Earlier work further showed that another adenovirus E3-coded protein, E3-14.7K, inhibits apoptosis induced by TNF. Most of the above studies have been conducted using viable virus mutants that lack one or more of the genes for RID, E3-14.7K, or E1B-19K (this protein, coded by the E1B transcription unit, also inhibits apoptosis via the TNF and Fas pathways). Some studies have also been conducted with the genes for RID or E3-14.7K transiently or stably transfected into cells. We now report a new approach to studying the E3 genes. We have constructed four E1-minus replication-defective vectors that have all the E3 genes deleted from their natural position and then reinserted, in different permutations, into the deleted E1 region under control of the cytomegalovirus immediate early promoter. Vector Ad/RID only has the genes for RIDalpha and RIDbeta. Vector Ad/14.7K only has the gene for E3-14.7K. Vector Ad/RID/14.7K only has the genes for RIDalpha, RIDbeta, and E3-14.7K. Vector Ad/E3 has all E3 genes, but there are two missense mutations in the gene for Adenovirus Death Protein. These vectors expressed RID and/or E3-14.7K, as expected. The RID-expressing vectors forced the internalization and degradation of Fas and EGFR, and they inhibited apoptosis induced through the Fas pathway. These vectors should be useful reagents to study the E3 proteins.

Adenoviral inhibitors of apoptotic cell death

Adenoviruses (Ads) are endemic in the human population and the well-studied group C Ads typically cause an acute infection in the respiratory epithelium. A growing body of evidence suggests that these viruses also establish a persistent infection. The Ad genome encodes several proteins that counteract the host anti-viral mechanisms, which function to limit viral infections. This review describes the adenovirus immuno-regulatory proteins and how they function to block apoptosis of infected cells. In addition to facilitating the successful completion of the viral replication cycle and spread of progeny virus, these functions may help maintain the virus in a persistent state.

Inhibition of chemokine expression by adenovirus early region three (E3) genes

Adenoviruses (Ad) have a variety of immunoregulatory genes, many of which are clustered in a 3.5-kb segment of DNA known as early region 3 (E3). Ad E3 codes for proteins that downregulate surface expression of class I major histocompatibility antigens and also inhibit tumor necrosis factor alpha (TNF-alpha)- and Fas-induced cytolysis. We were interested in determining whether chemokine production or activity might also be inhibited by Ad E3 and we have studied this function in a human astrocytoma cell line, U373. Astrocytes constitute a part of the blood-brain barrier, and chemokines (IP-10, IL-8, MCP-1-4, and MIPs) expressed by them may contribute to leukocyte infiltration within the brain during inflammation. When U373 cells are activated by the proinflammatory molecule TNF-alpha, the increase in chemokine MCP-1, IL-8, and IP-10 transcripts is blocked by a recombinant Ad expressing the E3 genes under cytomegalovirus promoter control. Comparable Ads expressing green fluorescent protein in place of E3 have no effect on these chemokines. Ads also have been extensively studied as gene therapy vectors and most have a deletion of the E3 region to permit the insertion of larger fragments of foreign DNA. Our results suggest that construction of Ad vectors to include E3 expression cassettes will improve the efficacy and safety of such viral-based gene therapy protocols.

A time to kill: viral manipulation of the cell death program

Many viruses have as part of their arsenal the ability to modulate the apoptotic pathways of the host. It is counter-intuitive that such simple organisms would be efficient at regulating this the most crucial pathway within the host, given the relative complexity of the host cells. Yet, viruses have the potential to initiate or stay the onset of programmed cell death through the manipulation of a variety of key apoptotic proteins. It is the intention of this review to provide an overview of viral gene products that are able to promote or inhibit apoptotic death of the host cell and to discuss their mechanisms of action. It is not until recently that the depth at which viruses exploit the apoptotic pathways of their host has been seen. This understanding may provide a great opportunity for future therapeutic ventures.

Constitutive expression of the adenovirus E3-14.7K protein does not prolong adenovirus vector DNA persistence but protects mice against lipopolysaccharide-induced acute hepatitis

First-generation adenovirus vectors, deleted in the E1 and E3 regions of the genome, induce a strong inflammatory response that affects persistence of vector DNA in transduced organs and causes toxicity in the host. Wild-type adenovirus encodes a number of proteins that are nonessential for viral propagation in vitro but that dampen the inflammatory and immune responses mounted by the host during infection. The adenovirus E3 region-encoded 14.7K protein inhibits tumor necrosis factor alpha (TNF-alpha)-induced apoptosis and arachidonic acid synthesis. To evaluate the impact of constitutive expression of the 14.7K protein on vector-induced pathology, toxicity, and DNA persistence, we constructed vectors that contain a cytomegalovirus promoter-driven 14.7K expression cassette. Although these vectors inhibit TNF-alpha-induced apoptosis in vitro, they do not show better vector DNA persistence, or lower inflammation or pathology than E3-deleted first-generation vector in mouse models. However, the 14.7K protein is functional in mice because animals injected intravenously with a 14.7K-constitutive vector were fully protected against a lethal dose of lipopolysaccharide 5 days after vector administration. These results open new applications for the E3-encoded 14.7K protein, which can be used to protect organs against inflammatory reactions and TNF-alpha-mediated apoptosis.

Adenovirus E3-6.7K maintains calcium homeostasis and prevents apoptosis and arachidonic acid release

E3-6.7K is a small and hydrophobic membrane glycoprotein encoded by the E3 region of subgroup C adenovirus. Recently, E3-6.7K has been shown to be required for the downregulation of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors by the adenovirus E3/10.4K and E3/14.5K complex of proteins. We demonstrate here that E3-6.7K has additional protective roles, independent of other virus proteins. In transfected Jurkat T-cell lymphoma cells, E3-6.7K was found to maintain endoplasmic reticulum-Ca(2+) homeostasis and inhibit the induction of apoptosis by thapsigargin. The presence of E3-6.7K also lead to a reduction in the TNF-induced release of arachidonic acid from transfected U937 human histiocytic lymphoma cells. In addition, E3-6.7K protected cells against apoptosis induced through Fas, TNF receptor, and TRAIL receptors. Therefore, E3-6.7K confers a wide range of protective effects against both Ca(2+) flux-induced and death receptor-mediated apoptosis.

Poliovirus protein 3A inhibits tumor necrosis factor (TNF)-induced apoptosis by eliminating the TNF receptor from the cell surface

Viral infections often trigger host defensive reactions by activating intrinsic (intracellular) and extrinsic (receptor-mediated) apoptotic pathways. Poliovirus is known to encode an antiapoptotic function(s) suppressing the intrinsic pathway. Here, the effect of poliovirus nonstructural proteins on cell sensitivity to tumor necrosis factor (TNF)-induced (i.e., receptor-mediated) apoptosis was studied. This sensitivity is dramatically enhanced by the viral proteinase 2A, due, most likely, to inhibition of cellular translation. On the other hand, cells expressing poliovirus noncapsid proteins 3A and 2B exhibit strong TNF resistance. Expression of 3A neutralizes the proapoptotic activity of 2A and results in a specific suppression of TNF signaling, including the lack of activation of NF-kappaB, due to elimination of the TNF receptor from the cell surface. In agreement with this, poliovirus infection results in a dramatic decrease in TNF receptor abundance on the surfaces of infected cells as early as 4 h postinfection. Poliovirus proteins that confer resistance to TNF interfere with endoplasmic reticulum-Golgi protein trafficking, and their effect on TNF signaling can be imitated by brefeldin A, suggesting that the mechanism of poliovirus-mediated resistance to TNF is a result of aberrant TNF receptor trafficking.

Inhibition of TRAIL-induced apoptosis and forced internalization of TRAIL receptor 1 by adenovirus proteins

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis through two receptors, TRAIL-R1 (also known as death receptor 4) and TRAIL-R2 (also known as death receptor 5), that are members of the TNF receptor superfamily of death domain-containing receptors. We show that human adenovirus type 5 encodes three proteins, named RID (previously named E3-10.4K/14.5K), E3-14.7K, and E1B-19K, that independently inhibit TRAIL-induced apoptosis of infected human cells. This conclusion was derived from studies using wild-type adenovirus, adenovirus replication-competent mutants that lack one or more of the RID, E3-14.7K, and E1B-19K genes, and adenovirus E1-minus replication-defective vectors that express all E3 genes, RID plus E3-14.7K only, RID only, or E3-14.7K only. RID inhibits TRAIL-induced apoptosis when cells are sensitized to TRAIL either by adenovirus infection or treatment with cycloheximide. RID induces the internalization of TRAIL-R1 from the cell surface, as shown by flow cytometry and indirect immunofluorescence for TRAIL-R1. TRAIL-R1 was internalized in distinct vesicles which are very likely to be endosomes and lysosomes. TRAIL-R1 is degraded, as indicated by the disappearance of the TRAIL-R1 immunofluorescence signal. Degradation was inhibited by bafilomycin A1, a drug that prevents acidification of vesicles and the sorting of receptors from late endosomes to lysosomes, implying that degradation occurs in lysosomes. RID was also shown previously to internalize and degrade another death domain receptor, Fas, and to prevent apoptosis through Fas and the TNF receptor. RID was shown previously to force the internalization and degradation of the epidermal growth factor receptor. E1B-19K was shown previously to block apoptosis through Fas, and both E1B-19K and E3-14.7K were found to prevent apoptosis through the TNF receptor. These findings suggest that the receptors for TRAIL, Fas ligand, and TNF play a role in limiting virus infections. The ability of adenovirus to inhibit killing through these receptors may prolong acute and persistent infections.

Marek's disease herpesvirus transforming protein MEQ: a c-Jun analogue with an alternative life style

In order to adapt to and to cope with an often hostile host environment, many viruses have evolved to encode products that are homologous to cellular proteins. These proteins exploit the existing host machinery and allow viruses to readily integrate into the host functional network. As a result, viruses are able to maneuver their journey seemingly effortlessly inside the host cell to achieve ultimate survival. Such molecular mimicries sometime go overboard, allowing viruses to overtake the cellular pathways or evade the immune system as do many of the retroviral oncogenes. Retroviral oncogenes are derived directly from host genes, and they are virtually identical to host genes in sequences except those mutations that make them unregulatable by host. Oncogenic herpesviruses also encode oncogenes, or transforming genes, which have independently evolved and are distantly related to host genes. However, these genes do share consensus structural motifs with cellular genes involved in cell growth and apoptosis and are functional analogues to host genes. The Marek's disease virus oncoprotein, MEQ, is one such example. MEQ is a basic region-leucine zipper (bZIP) transactivator which shares extensive homology with the Jun/Fos family of transcription factors within the bZIP domain, but not in other regions. Like all other bZIP proteins, MEQ is capable of dimerizing with itself and with a variety of bZIP partners including c-Jun, B-Jun, c-Fos, CREB, ATF-1, ATF-2, and SNF. MEQ-Jun heterodimers bind to a TRE/CRE-like sequence in the meq promoter region and have been shown to up-regulate MEQ expression in both chicken embryo fibroblasts and F9 cells. In addition, the bZIP and transactivation domains are interchangeable between MEQ and c-Jun in terms of transforming potential; i.e. MEQ can functionally substitute for c-Jun. These properties enable MEQ to engage in host cell processes by disguising itself as c-Jun. On the other hand, there are properties of MEQ notably different from c-Jun, which include its capability to bind RNA, to bind a CACAC-bent DNA structure as a homodimer, to inhibit apoptosis, and to interact with CDK2. MEQ's subcellular localization in the nucleolus and coiled body, is also different from Jun/Fos family of transactivators. These unique features may provide the MEQ with additional facility in regulating MDV replication, establishing latency, and cellular transformation. In this review, we will attempt to summarize the past research progress on MDV meq, with a focused on the similarities and differences between MEQ and cellular proteins, and between MEQ and other viral oncoproteins.

Adenovirus-mediated transfer of an Na+/K+-ATPase beta1 subunit gene improves alveolar fluid clearance and survival in hyperoxic rats

Pulmonary edema is cleared via active Na(+) transport by alveolar epithelial Na(+)/K(+)-ATPases and Na(+) channels. Rats exposed to acute hyperoxia have a high mortality rate, decreased Na(+)/K(+)-ATPase function, and decreased alveolar fluid clearance (AFC). We hypothesized that Na(+)/K(+)-ATPase subunit gene overexpression could improve AFC in rats exposed to hyperoxia. We delivered 4 x 10(9) PFU of recombinant adenoviruses containing rat alpha(1) and beta(1) Na(+)/K(+)-ATPase subunit cDNAs (adalpha(1) and adbeta(1), respectively) to rat lungs 7 days prior to exposure to 100% O(2) for 64 hr. As compared with controls and ad alpha(1), AFC in the adbeta(1) rats was increased by >300%. Permeability for large solutes was less in the ad beta(1) than in the other hyperoxia groups. Glutathione oxidation, but not superoxide dismutase activity, was increased only in the adbeta(1) group. Survival through 14 days of hyperoxia was 100% in the adbeta(1) group but was not different from hyperoxic controls in animals given adalpha(1). Our data show that overexpression of a beta(1) Na(+)/K(+)-ATPase subunit augments AFC and improves survival in this model of acute lung injury via antioxidant-independent mechanisms. Conceivably, restoration of AFC via gene transfer of Na(+)/K(+)-ATPase subunit genes may prove useful for the treatment of acute lung injury and pulmonary edema.

Rb-independent induction of apoptosis by bovine papillomavirus type 1 E7 in response to tumor necrosis factor alpha

Bovine papillomavirus type 1 (BPV-1) is a small DNA virus that causes fibropapillomas of the host. BPV-1 has served as the prototype for studies of the molecular biology of the papillomaviruses. BPV-1 efficiently induces anchorage-independent growth and focus formation in murine C127 cells. The transforming properties of BPV-1 primarily reside in two genes, E5 and E6. Each of these genes is sufficient to transform cells. Although no independent transformation activity has been detected for E7, it was shown to be required for full transformation of C127 by BPV-1. We investigated the biological activities of BPV-1 E7 in several assays. Our results indicate that expression of BPV-1 E7 sensitizes cells to tumor necrosis factor alpha (TNF)-induced apoptosis. The TNF-induced apoptosis in E7-expressing cells was accompanied by increased release of arachidonic acid, indicating that phospholipase A(2) was activated. Unlike the E7 proteins from the cancer-related human papillomaviruses, the BPV-1 E7 protein does not associate efficiently with the retinoblastoma protein (pRB) in vitro, nor does it significantly affect the pRB levels in cultured cells. Furthermore, BPV-1 E7 sensitizes Rb-null cells to TNF-induced apoptosis. These studies indicate that BPV-1 E7 can sensitize cells to apoptosis through mechanisms that are independent of pRB.

Soluble CD8 attenuates cytotoxic T cell responses against replication-defective adenovirus affording transprotection of transgenes in vivo

The T cell coreceptor, CD8, enhances T cell-APC interactions. Because soluble CD8alpha homodimers can antagonize CD8 T cell activation in vitro, we asked whether secretion of soluble CD8 would effect cytotoxic T cell responses in vivo. Production of soluble CD8 by a replication-defective adenovirus vector allowed persistent virus expression for up to 5 mo in C57BL/6 mice and protected a second foreign transgene from rapid deletion. Soluble CD8 selectively inhibited CD8 T cell proliferation and IFN-gamma production and could also attenuate peptide-specific CD8 T cell responses in vivo. These finding suggest that gene vector delivery of soluble CD8 may have therapeutic applications.

a controlled trial of intratumoral ONYX-015, a selectively-replicating adenovirus, in combination with cisplatin and 5-fluorouracil in patients with recurrent head and neck cancer

ONYX-015 is an adenovirus with the E1B 55-kDa gene deleted, engineered to selectively replicate in and lyse p53-deficient cancer cells while sparing normal cells. Although ONYX-015 and chemotherapy have demonstrated anti-tumoral activity in patients with recurrent head and neck cancer, disease recurs rapidly with either therapy alone. We undertook a phase II trial of a combination of intratumoral ONYX-015 injection with cisplatin and 5-fluorouracil in patients with recurrent squamous cell cancer of the head and neck. There were substantial objective responses, including a high proportion of complete responses. By 6 months, none of the responding tumors had progressed, whereas all non-injected tumors treated with chemotherapy alone had progressed. The toxic effects that occurred were acceptable. Tumor biopsies obtained after treatment showed tumor-selective viral replication and necrosis induction.

Identification and characterization of a 30K protein (Ad4E3-30K) encoded by the E3 region of human adenovirus type 4

Human adenovirus type 4 (Ad4), the sole member of subgroup E, contains an open reading frame in the E3 region predicted to encode a unique 30-kDa protein (named Ad4E3-30K). Ad4E3-30K is predicted to be an integral membrane protein containing an N-terminal signal sequence, a lumenal domain, a transmembrane domain near the C-terminus, and a 37-amino-acid cytoplasmic tail. To determine whether this protein is expressed, rabbit polyclonal antisera were raised against 30K-containing fusion proteins expressed in bacteria. A 30K protein was detected by immunoprecipitation from cell-free translation products and from Ad4-infected A549 cells radiolabeled in the presence of tunicamycin. The protein was detected at only low levels in infected cells. It was not synthesized by a mutant with a large E3 deletion that includes the Ad4E3-30K gene. This mutant grows as well as wild-type Ad4 in culture. Features of Ad4E3-30K were characterized in different transient expression systems. The protein underwent glycosylation by addition of approximately six asparagine-linked oligosaccharides. These glycans were sensitive to endoglycosidase H, indicating that they were either high-mannose or hybrid types, but not complex types, and that the protein did not pass through the Golgi apparatus. Immunofluorescence staining of transfected cells revealed that Ad4E3-30K was localized primarily in the endoplasmic reticulum and nuclear envelope.

Viral subversion of the immune system

This review describes the diverse array of pathways and molecular targets that are used by viruses to elude immune detection and destruction. These include targeting of pathways for major histocompatibility complex-restricted antigen presentation, apoptosis, cytokine-mediated signaling, and humoral immune responses. The continuous interactions between host and pathogens during their coevolution have shaped the immune system, but also the counter measures used by pathogens. Further study of their interactions should improve our ability to manipulate and exploit the various pathogens.

Adenoviral E3-14.7K protein in LPS-induced lung inflammation

The adenoviral E3-14.7K protein is a cytoplasmic protein synthesized after adenoviral infection. To assess the contribution of E3-14. 7K-sensitive pathways in the modulation of inflammation by the respiratory epithelium, inflammatory responses to intratracheal lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-alpha were assessed in transgenic mice bearing the adenoviral E3-14.7K gene under the direction of the surfactant protein (SP) C promoter. When E3-14.7K transgenic mice were administered LPS intratracheally, lung inflammation as indicated by macrophage and neutrophil accumulation in bronchoalveolar lavage fluid was decreased compared with wild-type control mice. Lung inflammation and epithelial cell injury were decreased in E3-14.7K mice 24 and 48 h after LPS administration. Intracellular staining for surfactant proprotein (proSP) B, proSP-C, and SP-B was decreased and extracellular staining was markedly increased in wild-type mice after LPS administration, consistent with LPS-induced lung injury. In contrast, intense intracellular staining of proSP-B, proSP-C, and SP-B persisted in type II cells of E3-14.7K mice, whereas extracellular staining of proSP-B and proSP-C was absent. Inhibitory effects of intratracheal LPS on SP-C mRNA were ameliorated by expression of the E3-14.7K gene. Similar to the response to LPS, lung inflammation after intratracheal administration of TNF-alpha was decreased in E3-14.7K transgenic mice. Levels of TNF-alpha after LPS administration were similar in wild-type and E3-14.7K-bearing mice. Cell-selective expression of E3-14.7K in the respiratory epithelium inhibited LPS- and TNF-alpha-mediated lung inflammation, demonstrating the critical role of respiratory epithelial cells in LPS- and TNF-alpha-induced lung inflammation.

Viruses and apoptosis

Successful viral replication requires not only the efficient production and spread of progeny, but also evasion of host defense mechanisms that limit replication by killing infected cells. In addition to inducing immune and inflammatory responses, infection by most viruses triggers apoptosis or programmed cell death of the infected cell. This cell response often results as a compulsory or unavoidable by-product of the action of critical viral replicative functions. In addition, some viruses seem to use apoptosis as a mechanism of cell killing and virus spread. In both cases, successful replication relies on the ability of certain viral products to block or delay apoptosis until sufficient progeny have been produced. Such proteins target a variety of strategic points in the apoptotic pathway. In this review we summarize the great amount of recent information on viruses and apoptosis and offer insights into how this knowledge may be used for future research and novel therapies.