Generation of cytotoxic T lymphocytes against immunorecessive epitopes after multiple immunizations with adenovirus vectors is dependent on haplotype

Combined bacterial and viral treatment: a novel anticancer strategy

An idea for a new combination therapy will be described herein. It is a proposition to combine viral and bacterial anticancer therapies and make them fight cancer in concert. We analyzed biological anticancer therapies and found overlapping advantages and disadvantages which led us to the conclusion that the combination therapy has the potential to create a new therapeutic quality. It is surprising how many weaknesses of viral anticancer therapy are the strengths of bacterial anticancer therapies and the other way round. We review the facts behind this concept and try to assess its value. We propose a few strategies how to combine these two therapies but as far as the review can go, final answers will have to come from the experiments. This review is the first attempt to describe a new strategy and understand the means for this idea but also to raise new questions and discuss new ways to look at anti-cancer treatment.

Oncolytic viruses from the perspective of the immune system

Cancer treatment with oncolytic viruses is at a crucial intersection from where two very different routes can be taken. The key role of the immune system needs to be addressed proactively to succeed. An immunocentric point of view posits that the intense immunosuppression induced by tumors can be outbalanced by the natural immunogenicity of viruses. To their advantage, viruses can be safely armed to be even more immunostimulatory. The microbe-associated inflammatory response is optimal for antigen presentation and helps to reveal the hidden tumor antigens. The induced immune effector cells patrol the organs to destroy disseminated tumor cells out of the reach of the oncolytic virus. However, as tumor immunosuppression is localized, this concept needs to be revisited because every tumor focus will have to be reached by the oncolytic virus. By contrast, virocentrics see the immune system as an obstacle to virotherapy. A virus is so immunogenic that it dominates all the elicited immunity to the detriment of a response towards tumor antigens. For them immunosuppression is the way to go, and the intense immunosuppression in and around the tumor is now an advantage, offering a privileged site for virus replication. A better oncolytic virus evades the immune system, but such a virus should be very tumor-selective to be safe. Although the trend favors immunocentrics, clinical results have been more often documented in immunocompromised patients. Trials of comparative interventions on the immune system will validate immunocentrism or virocentrism. What seems clear is that at this intersection one should take one route or the other to overcome the current limitations of virotherapy.

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.

Parenchymal expression of CD86/B7.2 contributes to hepatitis C virus-related liver injury

Hepatitis C virus (HCV) infection is a major global health problem. Hepatic expression of immune costimulatory signaling molecules (e.g., B7) is known to be associated with ongoing liver injury in hepatitis C patients. However, due to the general lack of viral culture systems and adequate animal models, the function of these molecules in disease pathogenesis is poorly understood. To investigate the role of CD86 in HCV-related liver injury, we developed two transgenic mouse lineages with inducible expression of HCV structural proteins and constitutive expression of the costimulatory molecule CD86/B7.2 in the liver. Using a hydrodynamic-based, nonviral delivery protocol, we induced HCV transgene expression in the livers of HCV and CD86 single- and double-transgenic mice. We found that hepatic CD86 expression resulted in increased activation of and cytokine production (e.g., interleukin-2 and gamma interferon) by CD4+ T cells and that the retention of these cells was associated with more pronounced necroinflammatory lesions in the liver. Taken together, these data suggest that augmented, parenchymal antigen presentation conferred by hepatocyte CD86 expression alters homeostasis and effector functions of CD4+ T cells and contributes to liver injury. This study provides an additional rationale for exploring immunomodulation-based therapies that could reduce disease progression in individuals with chronic HCV infection.

Conserved CTL epitopes on the adenovirus hexon protein expand subgroup cross-reactive and subgroup-specific CD8+ T cells

Adenoviruses often cause lethal infections in immunocompromised individuals. Adoptive transfer of immune T cells offers a therapeutic option, but this strategy has been hindered by the paucity of information on molecular targets of cellular immunity and by the immunologic heterogeneity of the 51 human adenoviruses, which are grouped from A to F on the basis of genome size, composition, homology, and organization. Clonal analysis of the adenovirus-specific cytotoxic T lymphocyte (CTL) responses of seropositive individuals identified 5 novel CD8+ T-cell epitopes, all located in conserved regions of the capsid protein hexon. Reactive T cells were cross-reactive between 2 to 4 groups, while no T cells specific for a single subgroup were detected. Thus, by exploiting these peptide targets, it is possible to prepare a T-cell population capable of reacting with most adenoviruses that cause disease in immunocompromised patients.

Neutralizing antibodies and CD8+ T lymphocytes both contribute to immunity to adenovirus serotype 5 vaccine vectors

The high prevalence of preexisting immunity to adenovirus serotype 5 (Ad5) in human populations will likely limit the immunogenicity and clinical utility of recombinant Ad5 vector-based vaccines for human immunodeficiency virus type 1 and other pathogens. Ad5-specific neutralizing antibodies (NAbs) are thought to contribute substantially to anti-Ad5 immunity, but the potential importance of Ad5-specific T lymphocytes in this setting has not been fully characterized. Here we assess the relative contributions of Ad5-specific humoral and cellular immune responses in blunting the immunogenicity of a rAd5-Env vaccine in mice. Adoptive transfer of Ad5-specific NAbs resulted in a dramatic abrogation of Env-specific immune responses following immunization with rAd5-Env. Interestingly, adoptive transfer of Ad5-specific CD8(+) T lymphocytes also resulted in a significant and durable suppression of rAd5-Env immunogenicity. These data demonstrate that NAbs and CD8(+) T lymphocytes both contribute to immunity to Ad5. Novel adenovirus vectors that are currently being developed to circumvent the problem of preexisting anti-Ad5 immunity should therefore be designed to evade both humoral and cellular Ad5-specific immune responses.

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.

Fiber-modified adenoviruses generate subgroup cross-reactive, adenovirus-specific cytotoxic T lymphocytes for therapeutic applications

Adenovirus (Ad) infections are responsible for considerable morbidity and mortality, particularly in pediatric hematopoietic stem cell transplant (HSCT) recipients. To date there is no therapy. The present study was motivated by the potential for using adoptive immunotherapy as either prophylaxis or treatment for Ad infections and associated diseases. The authors have developed a protocol to reactivate Ad-specific memory T cells from peripheral blood mononuclear cells (PBMCs) using a clinical-grade adenoviral vector. Such lines contain a specific CD4 and CD8 T-cell component and are capable of recognizing and lysing target cells infected with wild-type Ad serotypes from different Ad groups. Furthermore, the frequency of Ad-specific precursors can be determined in PBMCs ex vivo and used as a means to assess changes in Ad-specific T-cell memory responses after infusion. This is the first report of a simple and reproducible method to activate and expand Ad-specific cytotoxic T lymphocytes (CTLs), which should be protective against the range of different Ad subtypes that affect transplant recipients.

Stable integration of transgenes delivered by a retrotransposon-adenovirus hybrid vector

Helper-dependent adenoviruses show great promise as gene delivery vectors. However, because they do not integrate into the host chromosome, transgene expression cannot be maintained indefinitely. To overcome these limitations, we have inserted an L1 retrotransposon/transgene element into a helper-dependent adenovirus to create a novel chimeric gene delivery vector. Efficient adenovirus-mediated delivery of the L1 element into cultured human cells results in subsequent retrotransposition and stable integration of the transgene. L1 retrotransposition frequency was found to correlate with increasing multiplicity of infection by the chimeric vector, and further retrotransposition from newly integrated elements was not observed on prolonged culture. Therefore, this vector, which utilizes components of low immunogenic potential, represents a novel two-stage gene delivery system capable of achieving high titers via the initial helper-dependent adenovirus stage and permanent transgene integration via the retrotransposition stage.

Activation of HIV-1-specific immune responses to an HIV-1 vaccine constructed from a replication-defective adenovirus vector using various combinations of immunization protocols

We constructed a recombinant replication defective adenovirus vector containing the env gene (Ad-Bal) derived from macrophage-trophic HIV-1 (HIV-1 Bal). We then immunized mice with this vector using several administration routes and protocols, and examined the immune response. When the Ad-Bal viral vector (over 1 x 10(7) pfu) was injected subcutaneously, both humoral and cell-mediated immunities were induced. However, immune response induced by the Ad-Bal vector alone was weaker than that induced by the recombinant vaccinia viral vector. We then employed the following three immunization protocols: (l) DNA vaccination followed by immunization with the Ad-Bal; (2) vaccination using the Ad-Bal vector followed by DNA vaccination; and (3) DNA vaccination followed by Ad-Bal infection and passive transfer of dendritic cells (DCs) infected with the Ad-Bal. Among the three protocols, the last gave the strongest humoral and cell-mediated immunity. These results suggest that the combination of DNA vaccination, Ad-Bal vector infection and passive transfer of Ad-Bal-infected DCs can induce strong immunity against HIV-1 Bal.

An immunomodulatory procedure that stabilizes transgene expression and permits readministration of E1-deleted adenovirus vectors

Immune responses against E1-deleted adenovirus vectors and/or their transgene products result in the rapid elimination of vector-transduced cells and the generation of neutralizing antibodies. Different strategies of immunomodulation to stabilize transgene expression at therapeutic levels and to permit productive vector readministration have been examined. Our previous studies have shown that depletion of macrophages from spleen and liver decreases hepatic inflammation, significantly prolongs transgene expression, and delays the onset of humoral immune responses after systemic administration of an E1-deleted adenovirus vector. In the present study, we have examined the effects of macrophage depletion in combination with temporary blockade of CD40 ligation on E1-deleted adenovirus vector-mediated gene transfer. Alone, each of these treatments significantly inhibited the humoral immune response against the transgene product and prolonged its expression. Together, these treatments completely stabilized transgene expression and inhibited the production of neutralizing anti-adenovirus antibodies, permitting successful vector readministration. Animals rendered immunologically unresponsive to vector and transgene antigens regained their ability to mount productive immune responses against the vector after recovery of immune function, but remained unresponsive to the transgene product. These experiments demonstrate that this treatment is transient and antigen-specific.

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.

Implication of interfering antibody formation and apoptosis as two different mechanisms leading to variable duration of adenovirus-mediated transgene expression in immune-competent mice

This study explores the genetic and immunologic factors involved in the differences in duration of transgene expression following in vivo transduction with recombinant adenoviruses. Different strains of mice (C3H/HeJ [C3H], C57BL/6J [B6], BALB/cJ [Balb/c], C. B10-H2(b)/LiMcdJ [Balb.B], CB6F1/J [(Balb/c x B6)F1], B6C3F1/J [(B6 x C3H)F1], and BALB/cj SCID) received 5 x 10(9) PFU of the first-generation adenovirus, which expresses human alpha1-antitrypsin (Ad/RSVhAAT). While all strains studied showed similar patterns of anti-adenovirus antibody formation, only Balb/c and C3H mice developed significant levels of anti-hAAT antibodies by 8 weeks posttransduction. In addition, while all strains had quantitatively comparable amounts of adenovirus genomes and hAAT mRNA transcripts in the liver 9 days posttransduction, only Balb/c mice had undetectable adenovirus vector genomes and hAAT mRNA in the liver 40 days posttransduction. Terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling staining of liver sections from control and Ad/RSVhAAT-infected mice 5, 9, and 40 days posttransduction suggested that apoptosis was involved in the rapid elimination of transduced hepatocytes in Balb/c mice. Persistent expression of hAAT protein observed in BALB/cj SCID mice suggests that antigen-dependent immunity was essential for this apoptotic process in transduced Balb/c hepatocytes. In contrast to Balb/c mice, the loss of expression in C3H mice did not correlate with the loss of vector genomes or hAAT mRNA. Instead, the anti-hAAT antibodies in C3H but not Balb/c mice were found to interfere with detection of hAAT in the serum. In Balb. B and B6 mice, vector genome, hAAT mRNA transcripts, and hAAT protein levels persisted for at least 40 days posttransduction. This persistence correlated with poor anti-hAAT antibody formation and minimal hepatocyte toxicity. The expression of hAAT in (Balb/c x B6)F1 pups was found to be intermediate between the duration observed in the parental strains, while in (C3H x B6)F1 pups hAAT expression was similar to that seen in the B6 parents, which together support polygenic control of the immune responses in these mice. In summary, these findings suggest that there are three different profiles and at least two defined immune system-mediated mechanisms resulting in the loss of hAAT expression in mice and that different strains differ in the capacity to utilize these mechanisms.

Detection and induction of equine infectious anemia virus-specific cytotoxic T-lymphocyte responses by use of recombinant retroviral vectors

Cytotoxic T lymphocytes (CTL) appear to be critical in resolving or reducing the severity of lentivirus infections. Retroviral vectors expressing the Gag/Pr or SU protein of the lentivirus equine infectious anemia virus (EIAV) were constructed and used to evaluate EIAV-specific CTL responses in horses. Three promoters, cytomegalovirus, simian virus SV40, and Moloney murine sarcoma virus (MoMSV) long terminal repeat (LTR), were used, and there was considerable variation in their ability to direct expression of Gag/Pr and SU. Vectors expressing EIAV proteins under the direction of MoMSV LTR and using the gibbon ape leukemia virus (GALV) Env for internalization were efficient at transducing equine kidney (EK) target cells and were effective targets for EIAV-specific CTL lysis. CTL from EIAV-infected horses caused lysis of retroviral vector-transduced EK cells expressing either Gag/Pr or SU in an ELA-A-restricted manner. In contrast, lysis of recombinant vaccinia virus-infected EK cells expressing Gag/Pr and SU/TM was often non-LA-A restricted. Five horses were immunized by direct intramuscular injection with a mixture of retroviral vectors expressing Gag/Pr or SU, and one responded with EIAV-specific CTL. This result indicates that retroviral vector stimulation of CTL in horses needs to be optimized, perhaps by inclusion of appropriate cytokine genes in the constructs. However, the studies demonstrated that retroviral vector-transduced target cells were very effective for in vitro dissection of EIAV-specific CTL responses.

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.

Role of a subdominant H-2Kd-restricted SV40 tumor antigen cytotoxic T lymphocyte epitope in tumor rejection

SV40-transformed mKSA cells (H-2d) readily induce progressively growing tumors in adult syngeneic BALB/c mice while expressing the full complement of H-2d MHC class I antigens. BALB/c mice previously immunized with SV40, soluble SV40 T antigen, or irradiated SV40-transformed syngeneic, allogeneic, or xenogeneic cells reject an mKSA tumor challenge even though these mice have been considered low- or nonresponders to T antigen due to difficulty in demonstrating SV40 T antigen-specific CTL. We have investigated the role of H-2d-restricted CTL in the rejection of SV40 tumors in BALB/c mice. Immunization of BALB/c mice with SV40 induced T antigen-specific CTL which were largely. H-2Ld-restricted. However, following repeated in vitro restimulation with mKSA cells, CTL emerged which recognized a subdominant H-2Kd-restricted epitope corresponding to T antigen residues 499-507. Immunization of BALB/c mice with a recombinant vaccinia virus expressing the T499-507 epitope provided partial protection against a challenge of syngeneic mKSA tumor cells and induced the generation of T499-507-specific CTL. These results indicate that a subdominant H-2Kd-restricted CTL epitope can participate in the rejection of SV40 tumors in BALB/c mice.

Cytotoxic T-lymphocyte target proteins and their major histocompatibility complex class I restriction in response to adenovirus vectors delivered to mouse liver

The activation of cytotoxic T lymphocytes (CTLs) to cells infected with adenovirus vectors contributes to problems of inflammation and transient gene expression that attend their use in gene therapy. The goal of this study was to identify in a murine model of liver gene therapy the proteins that provide targets to CTLs and to characterize the major histocompatibility complex (MHC) class I restricting elements. Mice of different MHC haplotypes were infected with an E1-deleted adenovirus expressing human alkaline phosphatase (ALP) or beta-galactosidase as a reporter protein, and splenocytes were harvested for in vitro CTL assays to aid in the characterization of CTL epitopes. A library of vaccinia viruses was created to express individual viral open reading frames, as well as the ALP and lacZ transgenes. The MHC haplotype had a dramatic impact on the distribution of CTL targets: in C57BL/6 mice, the hexon protein presented by both H-2Kb and H2Db was dominant, and in C3H mice, H-2Dk-restricted presentation of ALP was dominant. Adoptive transfer of CTLs specific for various adenovirus proteins or transgene products into either Rag-I or C3H-scid mice infected previously with an E1-deleted adenovirus verified the in vivo relevance of the adenovirus-specific CTL targets identified in vitro. The results of these experiments illustrate the impact of lr gene control on the response to gene therapy with adenovirus vectors and suggest that the efficacy of therapy with adenovirus vectors may exhibit considerable heterogeneity when applied in human populations.