Human adenovirus-specific CD8+ T-cell responses are not inhibited by E3-19K in the presence of gamma interferon

Adenoviral vector-based platforms for developing effective vaccines to combat respiratory viral infections

Since the development of the first vaccine against smallpox over two centuries ago, vaccination strategies have been at the forefront of significantly impacting the incidences of infectious diseases globally. However, the increase in the human population, deforestation and climate change, and the rise in worldwide travel have favored the emergence of new viruses with the potential to cause pandemics. The ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is a cruel reminder of the impact of novel pathogens and the suboptimal capabilities of conventional vaccines. Therefore, there is an urgent need to develop new vaccine strategies that allow the production of billions of doses in a short duration and are broadly protective against emerging and re-emerging infectious diseases. Extensive knowledge of the molecular biology and immunology of adenoviruses (Ad) has favored Ad vectors as platforms for vaccine design. The Ad-based vaccine platform represents an attractive strategy as it induces robust humoral and cell-mediated immune responses and can meet the global demand in a pandemic situation. This review describes the status of Ad vector-based vaccines in preclinical and clinical studies for current and emerging respiratory viruses, particularly coronaviruses, influenza viruses and respiratory syncytial viruses.

Intracellular Sequestration of the NKG2D Ligand MIC B by Species F Adenovirus

The enteric human adenoviruses of species F (HAdVs-F), which comprise HAdV-F40 and HAdV-F41, are significant pathogens that cause acute gastroenteritis in children worldwide. The early transcription unit 3 (E3) of HAdVs-F is markedly different from that of all other HAdV species. To date, the E3 proteins unique to HAdVs-F have not been characterized and the mechanism by which HAdVs-F evade immune defenses in the gastrointestinal (GI) tract is poorly understood. Here, we show that HAdV-F41 infection of human intestinal HCT116 cells upregulated the expression of MHC class I-related chain A (MIC A) and MIC B relative to uninfected cells. Our results also showed that, for MIC B, this response did not however result in a significant increase of MIC B on the cell surface. Instead, MIC B was largely sequestered intracellularly. Thus, although HAdV-F41 infection of HCT116 cells upregulated MIC B expression, the ligand remained inside infected cells. A similar observation could not be made for MIC A in these cells. Our preliminary findings represent a novel function of HAdVs-F that may enable these viruses to evade immune surveillance by natural killer (NK) cells in the infected gut, thereby paving the way for the future investigation of their unique E3 proteins.

Understanding Post Entry Sorting of Adenovirus Capsids; A Chance to Change Vaccine Vector Properties

Adenovirus vector-based genetic vaccines have emerged as a powerful strategy against the SARS-CoV-2 health crisis. This success is not unexpected because adenoviruses combine many desirable features of a genetic vaccine. They are highly immunogenic and have a low and well characterized pathogenic profile paired with technological approachability. Ongoing efforts to improve adenovirus-vaccine vectors include the use of rare serotypes and non-human adenoviruses. In this review, we focus on the viral capsid and how the choice of genotypes influences the uptake and subsequent subcellular sorting. We describe how understanding capsid properties, such as stability during the entry process, can change the fate of the entering particles and how this translates into differences in immunity outcomes. We discuss in detail how mutating the membrane lytic capsid protein VI affects species C viruses' post-entry sorting and briefly discuss if such approaches could have a wider implication in vaccine and/or vector development.

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.

Discovery of small molecule inhibitors of adenovirus by disrupting E3-19K/HLA-A2 interactions

The binding of the adenovirus (Ad) protein E3-19K with the human leukocyte antigen (HLA) plays an important role in Ad infections, which is the causative agent of a series of gastrointestinal, respiratory and ocular diseases. The objective of this research is to evaluate the essential interactions between E3-19K and HLA-A2 using the X-ray crystal structure of the E3-19K/HLA-A2 complex, and to identify small molecules that could potentially disrupt their binding. Computational methods, including molecular dynamic simulations, MM/GBSA calculations, and computational solvent mapping, were implemented to determine potential binding site(s) for small molecules. The previous experimentally determined hot spot residues, Q54 and E177 in HLA-A2, were also predicted to be the dominant residues for binding to E3-19K by our theoretical calculations. Several other residues were also found to play pivotal roles for the binding of E3-19K with HLA-A2. Residues adjacent to E177, including Q54 and several other residues theoretically predicted to be crucial in HLA-A2 were selected as a potential binding pocket to perform virtual screening with 1200 compounds from the Prestwick library. Seven hits were validated by surface plasmon resonance (SPR) as binders to HLA-A2 as a first step in identifying molecules that can perturb its association with the Ad E3-19K protein.

Small-size recombinant adenoviral hexon protein fragments for the production of virus-type specific antibodies

Background

Adenoviruses are common pathogens infecting animals and humans. They are classified based on serology, or genome sequence information. These methods have limitations due to lengthy procedures or lack of infectivity data. Adenoviruses are easy to produce and amenable to genetic and biochemical modifications, which makes them a powerful tool for biological studies, and clinical gene-delivery and vaccine applications. Antibodies directed against adenoviral proteins are important diagnostic tools for virus identification in vivo and in vitro, and are used to elucidate infection mechanisms, often in combination with genomic sequencing and type specific information from hyper-variable regions of structural proteins.

Results

Here we describe a novel and readily useable method for cloning, expressing and purifying small fragments of hyper-variable regions 1-6 of the adenoviral hexon protein. We used these polypeptides as antigens for generating polyclonal rabbit antibodies against human adenovirus 3 (HAdV-B3), mouse adenovirus 1 (MAdV-1) and MAdV-2 hexon. In Western immunoblots with lysates from cells infected from thirteen human and three mouse viruses, these antibodies bound to homologous full-length hexon protein and revealed variable levels of cross-reactivity to heterologous hexons. Results from immuno-fluorescence and electron microscopy studies indicated that HAdV-B3 and MAdV-2 hexon antibodies recognized native forms of hexon.

Conclusions

The procedure described here can in principle be applied to any adenovirus for which genome sequence information is available. It provides a basis for generating novel type-specific tools in diagnostics and research, and extends beyond the commonly used anti-viral antibodies raised against purified viruses or subviral components.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0822-5) contains supplementary material, which is available to authorized users.

Structure of the Adenovirus Type 4 (Species E) E3-19K/HLA-A2 Complex Reveals Species-Specific Features in MHC Class I Recognition

Adenoviruses (Ads) subvert MHC class I Ag presentation and impair host anti-Ad cellular activities. Specifically, the Ad-encoded E3-19K immunomodulatory protein targets MHC class I molecules for retention within the endoplasmic reticulum of infected cells. We report the x-ray crystal structure of the Ad type 4 (Ad4) E3-19K of species E bound to HLA-A2 at 2.64-Å resolution. Structural analysis shows that Ad4 E3-19K adopts a tertiary fold that is shared only with Ad2 E3-19K of species C. A comparative analysis of the Ad4 E3-19K/HLA-A2 structure with our x-ray structure of Ad2 E3-19K/HLA-A2 identifies species-specific features in HLA-A2 recognition. Our analysis also reveals common binding characteristics that explain the promiscuous, and yet high-affinity, association of E3-19K proteins with HLA-A and HLA-B molecules. We also provide structural insights into why E3-19K proteins do not associate with HLA-C molecules. Overall, our study provides new information about how E3-19K proteins selectively engage with MHC class I to abrogate Ag presentation and counteract activation of CD8(+) T cells. The significance of MHC class I Ag presentation for controlling viral infections, as well as the threats of viral infections in immunocompromised patients, underline our efforts to characterize viral immunoevasins, such as E3-19K.

Crystal structure of adenovirus E3-19K bound to HLA-A2 reveals mechanism for immunomodulation

E3-19K binds to and retains MHC class I molecules in the endoplasmic reticulum, suppressing anti-adenovirus activities of T cells. We determined the structure of the adenovirus serotype 2 (Ad2, species C) E3-19K-HLA-A2 complex to 1.95-Å resolution. Ad2 E3-19K binds to the N terminus of the HLA-A2 groove, contacting the α1, α2 and α3 domains and β(2)m. Ad2 E3-19K has a unique structure comprising a large N-terminal domain, formed by two partially overlapping β-sheets arranged in a V shape, and a C-terminal α-helix and tail. The structure reveals determinants in E3-19K and HLA-A2 that are important for complex formation; conservation of some of these determinants in E3-19K proteins of different species and MHC I molecules of different loci suggests a universal binding mode for all E3-19K proteins. Our structure is important for understanding the immunomodulatory function of E3-19K.

Comparison of human memory CD8 T cell responses to adenoviral early and late proteins in peripheral blood and lymphoid tissue

Treatment of invasive adenovirus (Ad) disease in hematopoietic stem cell transplant (SCT) recipients with capsid protein hexon-specific donor T cells is under investigation. We propose that cytotoxic T cells (CTLs) targeted to the late protein hexon may be inefficient in vivo because the early Ad protein E3-19K downregulates HLA class I antigens in infected cells. In this study, CD8+ T cells targeted to highly conserved HLA A2-restricted epitopes from the early regulatory protein DNA polymerase (P-977) and late protein hexon (H-892) were compared in peripheral blood (PB) and tonsils of naturally infected adults. In tonsils, epitope-specific pentamers detected a significantly higher frequency of P-977+CD8+ T cells compared to H-892+CD8+ T cells; this trend was reversed in PB. Tonsil epitope-specific CD8+ T cells expressed IFN-γ and IL-2 but not perforin or TNF-α, whereas PB T cells were positive for IFN-γ, TNF-α, and perforin. Tonsil epitope-specific T cells expressed lymphoid homing marker CCR7 and exhibited lower levels of the activation marker CD25 but higher proliferative potential than PB T cells. Finally, in parallel with the kinetics of mRNA expression, P-977-specific CTLs lysed targets as early as 8 hrs post infection. In contrast, H-892-specific CTLs did not kill unless infected fibroblasts were pretreated with IFN-γ to up regulate HLA class I antigens, and cytotoxicity was delayed until 16–24 hours. These data show that, in contrast to hexon CTLs, central memory type DNA polymerase CTLs dominate the lymphoid compartment and kill fibroblasts earlier after infection without requiring exogenous IFN-γ. Thus, use of CTLs targeted to both early and late Ad proteins may improve the efficacy of immunotherapy for life-threatening Ad disease in SCT recipients.

Adenovirus E3-19K proteins of different serotypes and subgroups have similar, yet distinct, immunomodulatory functions toward major histocompatibility class I molecules

Our understanding of the mechanism by which the E3-19K protein from adenovirus (Ad) targets major histocompatibility complex (MHC) class I molecules for retention in the endoplasmic reticulum is derived largely from studies of Ad serotype 2 (subgroup C). It is not well understood to what extent observations on the Ad2 E3-19K/MHC I association can be generalized to E3-19K proteins of other serotypes and subgroups. The low levels of amino acid sequence homology between E3-19K proteins suggest that these proteins are likely to manifest distinct MHC I binding properties. This information is important as the E3-19K/MHC I interaction is thought to play a critical role in enabling Ads to cause persistent infections. Here, we characterized interaction between E3-19K proteins of serotypes 7 and 35 (subgroup B), 5 (subgroup C), 37 (subgroup D), and 4 (subgroup E) and a panel of HLA-A, -B, and -C molecules using native gel, surface plasmon resonance (SPR), and flow cytometry. Results show that all E3-19K proteins exhibited allele specificity toward HLA-A and -B molecules; this was less evident for Ad37 E3-19K. The allele specificity for HLA-A molecules was remarkably similar for different serotypes of subgroup B as well as subgroup C. Interestingly, all E3-19K proteins characterized also exhibited MHC I locus specificity. Importantly, we show that Lys(91) in the conserved region of Ad2 E3-19K targets the C terminus of the α2-helix (MHC residue 177) on MHC class I molecules. From our data, we propose a model of interaction between E3-19K and MHC class I molecules.

Determinants of the endoplasmic reticulum (ER) lumenal-domain of the adenovirus serotype 2 E3-19K protein for association with and ER-retention of major histocompatibility complex class I molecules

The E3-19K immunomodulatory protein from adenoviruses (Ads) inhibits antigen presentation by major histocompatibility complex (MHC) class I molecules. As a result, the ability of Ad-specific cytotoxic T lymphocytes (CTLs) to lyse infected cells is suppressed. The ER-lumenal domain of E3-19K is subdivided into a variable (residues 1 to ∼78/81) and conserved (residues ∼79/82 to 98) region followed by a linker (residues 99-107). Using molecular and cellular approaches, we characterized in detail the properties of the ER-lumenal domain of E3-19K that enable it to target MHC class I molecules. Proteolysis of recombinant serotype 2 E3-19K (residues 1-100) (with six His residues) generated a large N-terminal (residues 1-88) and a small C-terminal fragment (residues 94-100) in solution. Neither of these fragments associates with HLA-A*1101 as shown by a native gel band-shift assay. In contrast, the N-terminal 1-93 residues of Ad2 E3-19K exhibited the same binding affinity to HLA-A*1101 as E3-19K. Using a site-directed mutational analysis and flow cytometry, we show that Tyr(93), but not Tyr(88), critically modulates the cell-surface expression of MHC class I molecules. Taken together, these results indicate that the sequence comprising residues 89-93 (M(89)SKQY(93)), and in particular Tyr(93), in the conserved region of E3-19K is critical for its immunomodulatory function. Residues 89-93 likely form a linker or loop in E3-19K. Overall, our data provide novel insights into the structure of E3-19K and identify key determinants for association with and ER-retention of its cellular target protein. This knowledge is important for our understanding of the molecular basis of Ad pathogenesis.

Evaluation of cross-reactive cell-mediated immune responses among human, bovine and porcine adenoviruses

The absence of preexisting immunity against porcine adenovirus (Ad) serotype 3 (PAd3) and bovine Ad serotype 3 (BAd3) in humans makes them attractive alternatives to human Ad serotype 5 (HAd5) vectors. To determine whether there is significant cross-reactivity among HAd5, BAd3, and PAd3 at the level of cell-mediated immune responses, BALB/c mice were inoculated intraperitoneally with wild type (WT) or replication-defective (RD) HAd5, BAd3, or PAd3. Thirty-five days after the first inoculation, cross-reactive CD8+ cytotoxic T cells, as well as CD4+ Th1- and Th2-helper T cells, in the spleen were analyzed by ELISPOT, flow cytometry and cytotoxic T lymphocyte (CTL) assays. Virus neutralization assays were used to evaluate humoral cross-reactivity. CD8+ or CD4+ T cells primed with WT or RD HAd5, PAd3, or BAd3 demonstrated significant (P <0.005) reactivity with homologous Ad antigens, whereas, only minimal cross-reactivity was observed upon stimulation with heterologous Ad antigens. Ad-neutralizing antibodies were found to be homologous Ad-specific. Overall, these results suggest that there is no significant immunological cross-reactivity among HAd5, BAd3, and PAd3, thereby supporting the rationale for the use of BAd3 and PAd3 as alternative HAd vectors to circumvent anti-HAd immunity in humans.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.

Adenovirus DNA polymerase is recognized by human CD8+ T cells

Donor lymphocytes have potential as a treatment for adenovirus (Ad) disease in haematopoietic stem cell transplant (SCT) recipients, but better understanding of Ad-specific T-cell responses is required. Most healthy adults exhibit memory T-cell responses to hexon, a capsid protein synthesized late after infection. However, since the Ad E3-19k downregulates major histocompatibility complex (MHC) class I molecules, cytotoxic T cells (CTLs) targeted to early viral proteins may be more effective in eliminating Ad-infected cells in vivo. Here we show that Ad-specific CTLs recognize the early region 2 proteins DNA polymerase (Pol) and DNA-binding protein (DBP). Firstly, memory Ad-specific CD8(+) T cells were amplified from healthy donors by in vitro stimulation with Ad-infected dendritic cells and found to exhibit MHC-restricted cytotoxicity to targets expressing Pol and DBP. Secondly, gamma interferon responses to HLA A2-binding motif peptides from Pol and DBP were directly detected in peripheral blood mononuclear cells (PBMCs) from a recently infected normal donor. Peptide-specific CTLs generated to Pol and DBP epitopes were confirmed to exhibit HLA A2-restricted killing of targets expressing Pol or DBP. Lastly, Pol-epitope-specific T cells were detected at similar or higher frequencies than hexon and DBP in three of three SCT recipients recovering from invasive Ad disease. Pol epitopes were well conserved among different Ad serotypes. Therefore, Pol is a promising target for immunotherapy of Ad disease.

Adenovirus E3/19K promotes evasion of NK cell recognition by intracellular sequestration of the NKG2D ligands major histocompatibility complex class I chain-related proteins A and B

The adenovirus (Ad) early transcription unit 3 (E3) encodes multiple immunosubversive functions that are presumed to facilitate the establishment and persistence of infection. Indeed, the capacity of E3/19K to inhibit transport of HLA class I (HLA-I) to the cell surface, thereby preventing peptide presentation to CD8(+) T cells, has long been recognized as a paradigm for viral immune evasion. However, HLA-I downregulation has the potential to render Ad-infected cells vulnerable to natural killer (NK) cell recognition. Furthermore, expression of the immediate-early Ad gene E1A is associated with efficient induction of ligands for the key NK cell-activating receptor NKG2D. Here we show that while infection with wild-type Ad enhances synthesis of the NKG2D ligands, major histocompatibility complex class I chain-related proteins A and B (MICA and MICB), their expression on the cell surface is actively suppressed. Both MICA and MICB are retained within the endoplasmic reticulum as immature endoglycosidase H-sensitive forms. By analyzing a range of cell lines and viruses carrying mutated versions of the E3 gene region, E3/19K was identified as the gene responsible for this activity. The structural requirements within E3/19K necessary to sequester MICA/B and HLA-I are similar. In functional assays, deletion of E3/19K rendered Ad-infected cells more sensitive to NK cell recognition. We report the first NK evasion function in the Adenoviridae and describe a novel function for E3/19K. Thus, E3/19K has a dual function: inhibition of T-cell recognition and NK cell activation.

The CD4+ T-cell response to adenovirus is focused against conserved residues within the hexon protein

Adenovirus is a significant pathogen in immunocompromised patients and is widely utilized as a gene delivery vector, so a detailed understanding of the human immune response to adenovirus infection is critical. This study characterized the adenovirus-specific CD4+ T-cell response of healthy donors by incubation with whole virus or with individual hexon and fiber proteins. Adenovirus-specific CD4+ T cells averaged 0.26 % of the CD4+ T-cell pool and were detectable in all donors. T cells recognizing the highly conserved hexon protein accounted for 0.09 %, whereas no response was observed against the fiber protein. A panel of hexon-specific CD4+ T-cell clones was generated and shown to lyse targets infected with adenovirus from different serotypes and species. Three CD4 T-cell epitopes are described, which map to highly conserved regions of the hexon protein.

Adenovirus infection after allogeneic stem cell transplantation

Adenovirus infection after allogeneic hematopoietic stem cell transplantation (HSCT) is an emerging pathogen causing relevant morbidity and mortality, with preponderance in children. During the last years, basic research on the biology of the virus and host immune response ameliorated the diagnostic, surveillance, and therapeutic strategies. Risk factors for infection commonly have an impact on T-cell reconstitution, such as T-cell depleted graft, unrelated or HLA-mismatched donor transplantation, and GvHD. Weekly surveillance by PCR in stool and blood till day 100 or longer post-HSCT and pre-emptive therapy with cidofovir are the mainstay of the current approach to adenoviral infections post-HSCT. Since a sufficient host T-cell response is essential to clear the virus, diagnostic procedures for detection of virus-specific T-cells have recently been developed to assess the risk of the infection. Furthermore, adoptive immunotherapy is a new treatment option for patients with absent specific T-cell response and present systemic adenoviral infection.

Allele- and Locus-Specific Recognition of Class I MHC Molecules by the Immunomodulatory E3-19K Protein from Adenovirus

The E3-19K protein from human adenoviruses (Ads) retains class I MHC molecules in the endoplasmic reticulum. As a consequence, the cell surface expression of class I molecules is suppressed, allowing Ads to evade immune surveillance. Using native gel electrophoresis, gel filtration chromatography, and surface plasmon resonance, we show that a soluble form of the Ad type 2 (Ad2) E3-19K protein associates with HLA-A and -B molecules; equilibrium dissociation constants were in the nanomolar range and approximately 2.5-fold higher affinity for HLA-A (-A*0201, -A*0301, -A*1101, -A*3301, and -Aw*6801) relative to HLA-B (-B*0702 and -B*0801) molecules. Among the alleles of the HLA-A locus examined, HLA-A*3101 associated approximately 15-fold less avidly with soluble E3-19K. Soluble E3-19K interacted only very weakly with HLA-Cw*0304, and no interaction with HLA-Cw*0401 could be detected under identical conditions. Site-directed mutagenesis and flow cytometry demonstrated that MHC residue 56 plays a critical role in the association and endoplasmic reticulum retention of HLA-A molecules by E3-19K. This delineates the spatial environment around residue 56 as a putative E3-19K interaction surface on class I molecules. Overall, our data imply that a link may exist between host genetic factors and the susceptibility of individuals to Ad infections.

Human CD4+ T cells stimulated by conserved adenovirus 5 hexon peptides recognize cells infected with different species of human adenovirus

The immune response against human adenovirus (HAdV) has gained interest because of the application of HAdV-based vectors in gene therapy and the high incidence of infections in pediatric recipients of allogeneic stem cell grafts. Because antiviral medication is frequently ineffective, the option of adoptive transfer of HAdV-specific donor-derived T cells in these immunocompromised patients is investigated. To generate good manufacturing practice-compatible reagents, a panel of 63 long, overlapping, peptides of the hexon protein was screened for recognition by T cells. Five conserved peptides of 30 amino acids were identified that were recognized by the majority of adult donors. CD4+ T cells from long-term cultures of PBMC, stimulated with this set of five peptides, recognized cells infected with HAdV serotypes belonging to different species. These data demonstrate that adult human T cells preferentially recognize conserved sequences of amino acid residues from a structural protein of HAdV. In the context of gene therapy, this observation may limit the beneficial effect of switching to HAdV-based vectors derived from less common serotypes of HAdV in an attempt to circumvent pre-existing immunity. However, this cross-reactivity benefits the application of HAdV-specific T cells for adoptive immunotherapy in immunocompromised transplant recipients.

Adenoviral Infections in Hematopoietic Stem Cell Transplantation

Adenoviruses are lytic DNA viruses that are ubiquitous in human communities. In total, 51 different serotypes with varying tissue tropisms have been identified. Adenovirus infections, although frequent, are rarely fatal in immunocompetent individuals who have potent innate and adaptive immunity. But in immunosuppressed individuals, adenoviruses are a significant cause of morbidity and mortality, with limited treatment options. In particular, pediatric recipients of allogeneic hematopoietic stem cell transplantation frequently develop infections early in the posttransplantation period. Because the endogenous recovery of adenovirus-specific T cells has proven important in controlling infection, we explore the potential of adoptive T-cell immunotherapy as a therapeutic strategy. We discuss the advantages and limitations of T-cell therapy for the prophylaxis and treatment of adenovirus infection posttransplantation.

Human CD8+ cytotoxic T cell responses to adenovirus capsid proteins

Adenoviruses (Ads) cause fatal disease in allogeneic stem cell transplant recipients, but there is no established therapy. Ad-specific CD8+ T cells were detected in PBMC from healthy adults at a mean frequency of 77 per 10(5) CD8+ T cells (range 8-260) by interferon-gamma ELISPOT and cytokine flow cytometry assays. CD8+ T cell lines from 7 of 7 donors exhibited MHC-class-I-restricted killing of targets expressing the capsid protein hexon. In contrast, cytotoxicity against the capsid proteins fiber and penton base was weaker or not detected. Two HLA-A2-restricted hexon epitopes and one HLA-B-restricted epitope were identified, all of which are adjacent to or overlap an HLA-DP4-restricted epitope in the highly conserved C-terminus. Thus, hexon is the immunodominant T cell target among capsid proteins and contains multiple C-terminal epitopes conserved among serotypes. These data support evaluation of donor lymphocyte infusions for treatment of Ad disease post-transplant.

Glioblastoma Patients Exhibit Circulating Tumor-Specific CD8+ T Cells

PURPOSE

There is growing interest in developing cellular immune therapies for glioblastoma multiforme, but little is known about tumor-specific T-cell responses. A glioblastoma multiforme-specific T-cell assay was developed using monocyte-derived dendritic cells to present tumor antigens from the established glioblastoma multiforme cell line U118.

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells (PBMC) and tumor cells were obtained from nine patients with newly diagnosed brain tumors: five glioblastoma multiforme, two oligodendroglioma, one ependymoma, and one astrocytoma. PBMCs were incubated overnight with autologous tumor cells or autologous dendritic cells loaded with a U118 cell lysate, and responses were detected by IFN-gamma ELISPOT and cytokine flow cytometry assays.

RESULTS

PBMCs from all glioblastoma multiforme patients exhibited IFN-gamma responses to autologous tumor but not to HLA-mismatched U118 cells. Glioblastoma multiforme-specific IFN-gamma responses were primarily mediated by CD8+ T cells and represented approximately 2% of total CD8+ T cells. Additionally, all glioblastoma multiforme patients responded to autologous dendritic cells loaded with U118 lysate but not with low-grade astrocytoma cell lysates. PBMCs from four patients with other brain tumor types and one normal donor failed to respond to U118 lysate-loaded autologous dendritic cells. These data indicate that the IFN-gamma responses to U118 lysate-loaded autologous dendritic cells are glioblastoma multiforme specific. Moreover, PBMCs stimulated 1 to 2 weeks with U118 lysate-loaded dendritic cells exhibited MHC class I-restricted cytotoxicity against autologous tumor cells.

CONCLUSIONS

Glioblastoma multiforme patients exhibit circulating tumor-specific CD8+ T cells that recognize shared tumor antigens from the glioblastoma multiforme cell line U118. These data show that glioblastoma multiformes are immunogenic and support the development of immunotherapy trials.

Adenovirus infections in stem cell transplant recipients: recent developments in understanding of pathogenesis, diagnosis and management

Adenovirus is increasingly recognized as an important pathogen in stem cell transplant recipients, reflecting increased awareness about the virus, together with changes in transplant practice such as the performance of more high-risk transplants, and improvements in diagnostic methods. In retrospective studies, the reported incidence of adenovirus infections ranged between 4-20% with a similar variation in the proportion of patients developing invasive disease. In contrast, the incidence of adenovirus infection varies between 20-30% in recent prospective studies on T-cell depleted or mismatched allografts and about 30-40% of these patients develop invasive disease. These prospective studies have established a relationship between the risk of invasive adenovirus disease and a number of factors such as the extent of T-cell depletion, the intensity of immunosuppressive therapy and the kinetics of lymphocyte recovery post-transplant. Polymerase chain reaction (PCR) assays to detect adenovirus DNA in peripheral blood have shown a strong correlation between viremia and the risk of disseminated adenovirus disease. These developments have led to the possibility of a preemptive antiviral treatment strategy for asymptomatic adenovirus infections. In addition, a better understanding of the interactions between adenovirus and host immune system in the post-transplant setting might enable development of effective immunotherapeutic strategies against adenovirus infections.

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.

Mechanisms of E3 Modulation of Immune and Inflammatory Responses

Adenoviruses contain genes that have evolved to control the host immune and inflammatory responses; however, it is not clear whether these genes function primarily to facilitate survival of the virus during acute infection or during its persistent phase. These issues have assumed greater importance as the use of adenoviruses as vectors for gene therapy has been expanded. This review will focus on the mechanism of immune evasion mediated by the proteins encoded within the early region 3 (E3) transcription region, which affect the functions of a number of cell surface receptors including Fas, intracellular cell signaling events involving NF-kappaB, and the secretion of pro-inflammatory molecules such as chemokines. The successful use of E3 genes in facilitating allogeneic transplantation and in preventing autoimmune diabetes in several transgenic mouse models will also be described.

Immune Evasion by Adenovirus E3 Proteins: Exploitation of Intracellular Trafficking Pathways

Adenoviruses (Ads) are nonenveloped viruses which replicate and assemble in the nucleus. Therefore, viral membrane proteins are not directly required for their multiplication. Yet, all human Ads encode integral membrane proteins in the early transcription unit 3 (E3). Previous studies on subgenus C Ads demonstrated that most E3 proteins exhibit immunomodulatory functions. In this review we focus on the E3 membrane proteins, which appear to be primarily devoted to remove critical recognition structures for the host immune system from the cell surface. The molecular mechanism for removal depends on the E3 protein involved: E3/19K prevents expression of newly synthesized MHC molecules by inhibition of ER export, whereas E3/10.4-14.5K down-regulate apoptosis receptors by rerouting them into lysosomes. The viral proteins mediating these processes contain typical transport motifs, such as KKXX, YXXphi, or LL. E3/49K, another recently discovered E3 protein, may require such motifs to reach a processing compartment essential for its presumed immunomodulatory activity. Thus, E3 membrane proteins exploit the intracellular trafficking machinery for immune evasion. Conspicuously, many E3 membrane proteins from Ads other than subgenus C also contain putative transport motifs. Close inspection of surrounding amino acids suggests that many of these are likely to be functional. Therefore, Ads might harbor more E3 proteins that exploit intracellular trafficking pathways as a means to manipulate immunologically important key molecules. Differential expression of such functions by Ads of different subgenera may contribute to their differential pathogenesis. Thus, an unexpected link emerges between viral manipulation of intracellular transport pathways and immune evasion.

Detection of equine arteritis virus (EAV)-specific cytotoxic CD8+ T lymphocyte precursors from EAV-infected ponies

Equine arteritis virus (EAV) causes a systemic infection in equids with variable outcome, ranging from subclinical infections to severe disease, and also has the capacity to induce abortion in pregnant mares and persistent infections in stallions. The serum virus-neutralizing antibody response that invariably develops in the infected animal lasts for many months or years and is believed to play an important role in virus clearance. However, very little is known about cellular immunity against EAV because of a lack of methods for evaluating these immune responses. In the present study, we describe methods for detecting cytotoxic T lymphocyte (CTL) precursors in the peripheral blood of EAV-convalescent ponies using a 51Cr release cytolysis assay. Primary equine dermal cells, used as CTL targets, were shown to express MHC I but not MHC II and to retain 51Cr efficiently and support EAV replication. Peripheral blood mononuclear cells (PBMC) collected from EAV-convalescent ponies that had been incubated with or without live EAV were used as effectors. EAV-induced PBMC cultures showed evidence of expansion and activation of lymphoblasts, with an increase in the CD8+/CD4+ ratio in comparison with mock-induced PBMC. The cytotoxicity induced by EAV-stimulated PBMC was virus specific, showed genetic restriction, was mediated by CD8+ T lymphocytes and could be detected for periods of 4 months to more than 1 year post-infection. These findings and methods will hopefully contribute to an understanding of virus–host interactions in horses, in particular the mechanisms of virus clearance occurring during EAV infection.

Adenovirus infection in hematopoietic stem cell transplantation: effect of ganciclovir and impact on survival

Adenoviruses (ADV) are emerging as important causes of morbidity and mortality in patients undergoing hematopoietic stem cell transplantation (HSCT). In mainly non-T-cell depleted HSCT recipients, we analyzed the incidence of ADV infection, risk factors for infection, the effect of ganciclovir administered for prevention of cytomegalovirus (CMV), and the impact of ADV infection on survival. The overall incidence of ADV, irrespective of the method of detection, was 8.5% (450/5233) and 12.3% (43/348) after the first or second allogeneic HSCT, and 6.3% (78/1219) and 6.5% (5/77) after the first or second autologous HSCT, respectively. The most frequent sites of infection and disease were stool and gastrointestinal tract, respectively. Statistically significant risk factors associated with ADV infections among allogeneic recipients included younger age, grade II to IV graft-versus-host disease, year of transplantation, and a second allogeneic HSCT. Furthermore, allogeneic patients seronegative for CMV at transplantation and seropositive allogeneic patients who did not receive ganciclovir, either at engraftment or as pre-emptive therapy on CMV reactivation, were at higher risk of developing ADV infections compared with seropositive patients who received ganciclovir (odds ratio=1.8, 95% confidence interval (CI) 1.2 to 2.8, P=.005 and odds ratio=3.4, 95% CI 2.1 to 5.55, P<.0001, respectively). The hazard of overall mortality was higher in patients who contracted ADV compared with those who did not (hazard ratio 1.5, 95% CI 1.3 to 1.7, P<.0001). This study shows that ADV infections are associated with poor transplantation outcome in T-cell repleted HSCT recipients. Ganciclovir, given for CMV prevention, may have a protective effect. Controlled treatment and prevention studies are warranted.

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 infections following allogeneic stem cell transplantation: incidence and outcome in relation to graft manipulation, immunosuppression, and immune recovery

Adenovirus infections occur in 5% to 21% of patients following stem cell transplantation (SCT), with an associated mortality of up to 50%. However, a lack of prospective studies has hampered further developments in the understanding and management of this infection in the posttransplantation setting. We prospectively studied the incidence and outcome of adenovirus infections after SCT using preemptive screening and a policy of reduction or withdrawal of immunosuppressive therapy if the virus was isolated. The incidence of adenovirus infection was 19.7% (15 of 76), and the virus was isolated exclusively in recipients of T-cell-depleted grafts. Patients receiving 50 or 100 mg alemtuzumab in vivo were at the greatest risk of adenovirus infection (45% probability) regardless of donor type, and this was related to the slower lymphocyte recovery. Six (40%) of the 15 adenovirus-infected patients developed adenovirus disease. Severe lymphocytopenia (less than 300/microL) at the time of first detection of adenovirus was a major risk factor for development of adenovirus disease (P =.001). In addition, failure to reduce immunosuppression (P =.04) and a positive result of adenovirus polymerase chain reaction (PCR) in blood at diagnosis (P =.01) were both associated with fatal adenovirus disease. On the basis of this study, we recommend active surveillance for adenovirus infection in T-cell-depleted SCT and withdrawal or reduction of immunosuppressive treatment, if possible, in patients with adenovirus infection. Preemptive antiviral therapy is warranted for patients with severe lymphocytopenia or positive blood PCR, and in those in whom immunosuppressive therapy cannot be reduced.

Quantitative analysis of adenovirus-specific CD4+ T-cell responses from healthy adults

Although nearly all adults are seropositive for adenoviruses, little is known about the cellular immune responses to these ubiquitous pathogens. We have previously identified adenovirus-specific proliferative T-cell responses in peripheral blood mononuclear cells (PBMC) from healthy adults. In this study, memory T-cell responses to adenovirus were further evaluated in healthy adult donors using a short term, quantitative enzyme-linked immunospot assay (ELISPOT) assay. Adenovirus antigen induced specific secretion of interferon-gamma (IFN-gamma) from PBMC within 12 hours of incubation. PBMC from 20 of 22 healthy donors (90.9%) expressed IFN-y in response to adenovirus. Responder cells were identified as CD4+ T cells by immunomagnetic depletion methods. Interleukin-4 (IL-4) secretion was not detected, consistent with a TH1 response. There was a 10-fold variation in the frequencies of adenovirus-specific CD4+ T cells between donors (range, 34 to 294; median, 122 per million PBMC). Adenovirus-specific T cell frequencies remained stable over periods up to 2 years among individual donors, but there was an inverse correlation between frequency and donor age. These quantitative data suggest that most adults retain adenovirus-specific cellular memory after childhood exposure. This assay may be useful for the evaluation of adenovirus-specific CD4+ T-cell responses in patients treated with adenovirus gene therapy vectors and the identification of major T-cell epitopes.

The adenovirus capsid protein hexon contains a highly conserved human CD4+ T-cell epitope

The immunogenicity of adenovirus vectors remains a major obstacle to their safe and efficacious use for gene therapy. In order to identify T-cell epitopes directly from adenoviruses, four viral protein sequences were screened for the well-characterized 9-mer HLA-A2 binding motif. Peripheral blood mononuclear cells (PBMC) from healthy adults were tested for responses to 17 selected viral peptides using a short-term interferon-gamma ELISPOT assay. Memory T-cell responses were identified to a single peptide derived from the major capsid protein hexon in 5 of 6 HLA-A2-positive donors. Unexpectedly, responses to this hexon peptide were also detected in 4 of 6 HLA-A2-negative donors, and responder cells were identified as CD4(+) T cells by immunomagnetic depletion experiments. A longer 15-mer peptide, H910-924, was identified as the optimal CD4(+) T-cell epitope. This hexon epitope induces strong proliferative T-cell responses that can be blocked by a monoclonal antibody against HLA-DR, and molecular HLA typing of donors suggests that the peptide response is restricted by multiple HLA-DR alleles. Additionally, quantitative analysis of responses to H910-924 and whole adenovirus reveals that the frequency of circulating CD4(+) T cells specific for this single hexon epitope (mean = 61 per 10(6) PBMC) represents up to one third of the total adenovirus-specific T-cell response. Finally, comparison of hexon sequences from over 20 different human adenovirus serotypes indicates that H910-924 is highly conserved. In most individuals, therefore, T-cell responses to this hexon epitope will be induced by all adenovirus vectors, including "gutted" vectors packaged with capsid proteins and vectors based on different serotypes.

Immunomodulatory functions encoded by the E3 transcription unit of adenoviruses

Persistent viruses have evolved multiple strategies to escape the host immune system. One important prerequisite for efficient viral reproduction in the face of an ongoing immune response is prevention of premature lysis of infected cells. A number of viruses achieve this goal by interfering with antigen presentation and recognition of infected cells by cytotoxic T cells (CTL). Another viral strategy aims to block apoptosis triggered by host defense mechanisms. Both types of strategies seem to be realized by human adenoviruses (Ads). The early transcription unit E3 of Ads encodes proteins that inhibit antigen presentation by MHC class I molecules as well as apoptosis induced by tumor necrosis factor alpha (TNF-alpha) and Fas ligand (FasL). Here, we will describe the organization of the E3 regions of different Ad subgroups and compare the structure and functions of the known immunomodulatory E3 proteins.

MHC class I-subversive gene functions of cytomegalovirus and their regulation by interferons-an intricate balance

Multiple glycoproteins of human cytomegalovirus (HCMV) encoded by the genes US2, US3, US6 and US11 interrupt the MHC class I pathway of antigen presentation at distinct checkpoints to avoid recognition of infected cells by cytotoxic CD8+ T lymphocytes. The action of cytokines like interferon (IFN)-gamma, IFN-alpha/beta and tumour necrosis factor alpha (TNF-alpha) compensate for the viral inhibition and restore antigen presentation in HCMV-infected cells. This finding was explained by their effects on cellular rather than viral genes and reflected by an increase in the production, assembly and maturation of MHC class I molecules resulting in an escape of MHC I from viral control. Here we reproduce the IFN-gamma-mediated effect when MHC I-subversive gene functions of HCMV are tested in isolation, but the efficacy of IFN-gamma to restore MHC I surface expression in US2-, US6- and US11-transfectants differs significantly. In addition, in HCMV-infected cells IFN-gamma strongly affects the synthesis of the US6-encoded glycoprotein. Despite the capability of HCMV to block the interferon signaling pathway the IFN-gamma driven enhancement of MHC class I and class II expression remains effective provided that cells are exposed to IFN-gamma before infection. Our findings illustrate a complex interplay between host immune factors and viral immune evasion functions.

Adenovirus E1A oncogene expression in tumor cells enhances killing by TNF-related apoptosis-inducing ligand (TRAIL)

Expression of the adenovirus serotype 5 (Ad5) E1A oncogene sensitizes cells to apoptosis by TNF-alpha and Fas-ligand. Because TNF-related apoptosis-inducing ligand (TRAIL) kills cells in a similar manner as TNF-alpha and Fas ligand, we asked whether E1A expression might sensitize cells to lysis by TRAIL. To test this hypothesis, we examined TRAIL-induced killing of human melanoma (A2058) or fibrosarcoma (H4) cells that expressed E1A following either infection with Ad5 or stable transfection with Ad5-E1A. E1A-transfected A2058 (A2058-E1A) or H4 (H4-E1A) cells were highly sensitive to TRAIL-induced killing, but Ad5-infected cells expressing equally high levels of E1A protein remained resistant to TRAIL. Infection of A2058-E1A cells with Ad5 reduced their sensitivity to TRAIL-dependent killing. Therefore, viral gene products expressed following infection with Ad5 inhibited the sensitivity to TRAIL-induced killing conferred by transfection with E1A. E1B and E3 gene products have been shown to inhibit TNF-alpha- and Fas-dependent killing. The effect of these gene products on TRAIL-dependent killing was examined by using Ad5-mutants that did not express either the E3 (H5dl327) or E1B-19K (H5dl250) coding regions. A2058 cells infected with H5dl327 were susceptible to TRAIL-dependent killing. Furthermore, TRAIL-dependent killing of A2058-E1A cells was not inhibited by infection with H5dl327. Infection with H5dl250 sensitized A2058 cells to TRAIL-induced killing, but considerably less than H5dl327-infection. In summary, expression of Ad5-E1A gene products sensitizes cells to TRAIL-dependent killing, whereas E3 gene products, and to a lesser extent E1B-19K, inhibit this effect.

Adenovirus infections following haematopoietic cell transplantation: is there a role for adoptive immunotherapy?

Adenovirus has been recognised as an important pathogen in BMT recipients, especially in patients with GVHD and those receiving T cell-depleted allografts. We report adenovirus infections from an ongoing surveillance study in four patients after a non-myeloablative transplant and their improved outcome following withdrawal of immunosuppression in two patients and donor lymphocyte infusion for relapsed disease in the others. We discuss the control of adenovirus infections following immune manipulations and the feasibility of adoptive immunotherapy for post-transplant adenovirus infections.

Immune response to recombinant adenovirus in humans: capsid components from viral input are targets for vector-specific cytotoxic T lymphocytes

We previously demonstrated that a single injection of 10(9) PFU of recombinant adenovirus into patients induces strong vector-specific immune responses (H. Gahéry-Ségard, V. Molinier-Frenkel, C. Le Boulaire, P. Saulnier, P. Opolon, R. Lengagne, E. Gautier, A. Le Cesne, L. Zitvogel, A. Venet, C. Schatz, M. Courtney, T. Le Chevalier, T. Tursz, J.-G. Guillet, and F. Farace, J. Clin. Investig. 100:2218-2226, 1997). In the present study we analyzed the mechanism of vector recognition by cytotoxic T lymphocytes (CTL). CD8(+) CTL lines were derived from two patients and maintained in long-term cultures. Target cell infections with E1-deleted and E1-plus E2-deleted adenoviruses, as well as transcription-blocking experiments with actinomycin D, revealed that host T-cell recognition did not require viral gene transcription. Target cells treated with brefeldin A were not lysed, indicating that viral input protein-derived peptides are associated with HLA class I molecules. Using recombinant capsid component-loaded targets, we observed that the three major proteins could be recognized. These results raise the question of the use of multideleted adenoviruses for gene therapy in the quest to diminish antivector CTL responses.

Successful ribavirin therapy for severe adenovirus hemorrhagic cystitis after allogeneic marrow transplant from close HLA donors rather than distant donors

Intravenous ribavirin was given to nine patients who had developed severe adenovirus-induced hemorrhagic cystitis (AD-HC) which was resistant to conventional therapy or where there was involvement of other organs after allogeneic BMT. Three patients recovered completely from AD-HC, two of whom had been resistant to vidarabine. All three had received sibling BMTs (2 HLA matched, 1 HLA mismatched). Five patients who received BMTs from related (2 HLA mismatched) or unrelated (1 HLA matched, 2 HLA mismatched) showed an improvement in symptoms but had recurrent AD-HC after discontinuation of ribavirin. Improvement in clinical symptoms and termination of virus excretion were well correlated. The last patient who received a mismatched unrelated BMT died during ribavirin therapy. Ribavirin was notably more effective among patients receiving BMTs from siblings in contrast to patients receiving BMTs from alternative donors (<0.05). One patient experienced severe pancytopenia during the second treatment with ribavirin after HC recurrence and recovered after ceasing ribavirin. Thus, ribavirin seems to be very effective for severe AD-HC for some recipients who receive transplants from a genetically close donor. Bone Marrow Transplantation (2000) 25, 545-548.

The amyloid precursor-like protein 2 associates with the major histocompatibility complex class I molecule K(d)

Amyloid precursor-like protein 2 (APLP2) is a member of a protein family related to the amyloid precursor protein, which is implicated in Alzheimer's disease. Little is known about the physiological function of this protein family. The adenovirus E3/19K protein binds to major histocompatibility complex (MHC) class I antigens in the endoplasmic reticulum, thereby preventing their transport to the cell surface. In cells coexpressing E3/19K and the MHC K(d) molecule, K(d) is associated with E3/19K and two cellular protein species with masses of 100 and 110 kDa, termed p100/110. Interestingly, p100/110 are released from the complex upon the addition of K(d)-binding peptides, suggesting a role for these proteins in peptide transfer to MHC molecules. Here we demonstrate by microsequencing, reactivity with APLP2-specific antibodies, and comparison of biochemical parameters that p100/110 is identical to human APLP2. We further show that the APLP2/K(d) association does not require the physical presence of E3/19K. Thus, APLP2 exhibits an intrinsic affinity for the MHC K(d) molecule. Similar to the binding of MHC molecules to the transporter associated with antigen processing, complex formation between APLP2 and K(d) strictly depends upon the presence of beta(2)-microglobulin. Conditions that prolong the residency of K(d) in the endoplasmic reticulum lead to a profound increase of the association and a drastic reduction of APLP2 transport. Therefore, this unexpected interplay between these unrelated molecules may have implications for both MHC antigen and APLP2 function.

Cellular immune responses of healthy individuals to intradermal administration of an E1-E3- adenovirus gene transfer vector

In animals, Ad-mediated gene transfer initiates anti-Ad host immune responses that vary, depending on vector design, dose, host, and transgene. To begin to understand whether the anti-Ad vector responses in humans simulate those in animals, Ad(GV)CD.10, an E1-E3- Ad5 vector encoding the E. coli cytosine deaminase gene, was administered by the intradermal route to six normal individuals (8 x 10(7) to 8 x 10(9) particle units, each dose administered to two sites; n = 2 per group). No adverse events were observed. Polymerase chain reaction/Southern analysis demonstrated vector genome in the skin through 28 days in all individuals except one of two at the lowest dose. Local induration, independent of vector dose and baseline systemic anti-Ad5 neutralizing antibodies, developed in all subjects (6 to 17 mm, peak by day 3). Biopsies revealed a mild to moderate T cell (CD3+, CD4+, CD8+), B cell, and macrophage infiltrate at day 3, all decreased by day 28. Langerhans cells accumulated primarily in the papillary dermis. The day 3 cellular response was dose independent. On day 28, CD4+ and CD8+ T lymphocytes and macrophages showed dose dependency. There was minimal systemic Ad5-specific lymphocyte proliferation induced by Ad vector administration in three individuals studied, and no Ad5-specific cytotoxic T lymphocytes (evaluated in two subjects) could be detected. Thus, intradermal administration of an E1-E3- Ad vector to normal subjects induces mild/moderate local cellular responses, even in Ad-immunized individuals. These observations provide a baseline to determine if these human anti-Ad vector host responses can be circumvented by using "stealth" vectors and/or immunosuppression.

Immune evasion by adenoviruses

Adenovirus is a human pathogen that infects mainly respiratory and gastrointestinal epithelia. While the pathology caused by this virus is generally not life threatening in immunocompetent individuals, there is a large literature describing its ability to establish a persistent infection. These persistent infections typically occur in apparently healthy individuals with no outward signs of disease. Such a long term and benign interaction between virus and immune system requires adenoviruses to dampen host antiviral effector mechanisms that would otherwise eliminate the virus and cause immune-mediated pathology to the host. Adenovirus devotes a significant portion of its genome to gene products whose sole function seems to be the modulation of host immune responses. This review focuses on what is currently understood about how these immunomodulatory mechanisms work and how they might play a role in maintaining the virus in a persistent state.

Extensive cross-reactivity of adenovirus-specific cytotoxic T cells

Although adenovirus is a major source of morbidity for immunocompromised individuals and a popular vector for gene therapy, little is known about the cellular immune responses it evokes in humans. Initial trials using adenovirus vectors have been disappointing, probably owing both to a preexisting immune response to Ad2 and Ad5, the most commonly used vector backbones, and to a response to the transgene. The former problem might be overcome by switching from the common type C adenoviruses, of which Ad2 and Ad5 are members, to other less common serotypes. Evidence for the feasibility of this approach has been provided by a rat model system. However, its success in humans depends on there being no immunological cross-reactivity between groups at the humoral or cellular level. Here, we examine the cross-reactivity of the cellular immune response to adenovirus in a human system, and find that human cytotoxic T lymphocytes (CTLs) prepared in vitro against an adenovirus from two of the six subgroups can lyse cells infected with adenoviruses from the other subgroups. Hence, the proposed use of adenovirus vectors from uncommon subgroups to evade memory immune response to subgroup C adenoviruses may not be successful. However, this same cross-reactivity indicates that adoptive transfer of CTLs generated in vitro against one adenovirus serotype may protect immunocompromised patients from infections by adenoviruses of all serotypes.

Phase I trial of recombinant adenovirus gene transfer in lung cancer. Longitudinal study of the immune responses to transgene and viral products

Animal studies indicate that the use of replication-deficient adenovirus for human gene therapy is limited by host antivector immune responses that result in transient recombinant protein expression and blocking of gene transfer when rechallenged. Therefore, we have examined immune responses to an adenoviral vector and to the beta-galactosidase protein in four patients with lung cancer given a single intratumor injection of 10(9) plaque-forming units of recombinant adenovirus. The beta-galactosidase protein was expressed in day-8 tumor biopsies from all patients at variable levels. Recombinant virus DNA was detected by PCR in day-30 and day-60 tumor biopsies from all patients except patient 1. A high level of neutralizing antiadenovirus antibodies was detected in patient 1 before Ad-beta-gal injection whereas it was low (patient 3) or undetectable in the other two patients. All patients developed potent CD4 type 1 helper T cell (Th1) responses to adenoviral particles which increased gradually over time after injection. Antiadenovirus cytotoxic T lymphocyte responses were consistently boosted in the two patients examined (patients 3 and 4). Sustained production of anti-beta-galactosidase IgG was observed in all patients except patient 1. Consistent with anti-beta-gal antibody production, all patients except patient 1 developed intense, dose-dependent Th1 responses to soluble beta-galactosidase which increased over time. Strong beta-galactosidase-specific cytotoxic T lymphocyte responses were detected in patients 2, 3, and 4. Our results clearly show that despite the intensity of antiadenovirus responses, transgene protein expression was sufficient to induce strong and prolonged immunity in three patients. Recombinant adenovirus injected directly into the tumor is a highly efficient vector for immunizing patients against the transgene protein.

Interference with antigen processing by viruses

Viruses that establish persistent infections in their host, such as herpesviruses, adenoviruses or HIV, express proteins designed to pre-empt or evade recognition and elimination by MHC class I restricted CD8+ T lymphocytes. Notable discoveries during the annual period of review have demonstrated that, in principle, each single step within the MHC class I pathway of antigen processing and presentation is fair game for manipulation by viral functions. The viral factors that are natural inhibitors of this pathway have been instrumental for the elucidation of the distinct molecular mechanisms that are exploited by viruses. The viral stealth strategies that downregulate MHC class I protein surface expression may lead, however, to a higher susceptibility of virus-infected cells to natural killer cell activity. Strikingly, there is evidence that some viruses counteract increased natural killer cell recognition by expressing viral MHC class I homologues that function as surrogate inhibitors of natural killer cell activity.

Amplification of recombinant adenoviral transgene products occurs by inhibition of histone deacetylase

n-Butyrate (butyrate) has been shown to amplify transgene expression in cells infected with E1-defective adenoviruses. The present studies were undertaken in order to better define the actions of butyrate in the context of adenovirus gene expression, and to attempt to elucidate the mechanism by which butyrate mediates the transgene amplification. It was found that butyrate amplified viral transgene expression over a concentration range of 0.5-5 mM, and that the amplification required an exposure of 12-24 hr for maximal effect. Western blot analysis of representative viral proteins showed that butyrate treatment amplified DNA-binding protein, but not fiber protein. A transient adenoviral replication system suggested that butyrate had a modest inhibitory effect on replication of the E1-defective adenovirus. Use of a specific inhibitor of histone deacetylase, trichostatin A (TSA), reproduced the amplification of the viral transgene product achieved with the butyrate. In contrast, adenoviral transgene expression could not be amplified by TSA treatment in a cell line known to have a TSA-resistant histone deacetylase. Butyrate amplified steady-state gene expression of the viral transgene, but had no detectable effects on either DNA-binding protein or fiber steady-state gene expression. Nuclear run-off experiments showed that both butyrate and TSA caused an increase in the viral transgene transcription. It was concluded that inhibitors of histone deacetylase amplify adenoviral transgene expression at the transcriptional level.