Preventive vaccination with telomerase controls tumor growth in genetically engineered and carcinogen-induced mouse models of cancer

Expression of the membrane tetraspanin claudin 18 on cancer cells promotes T lymphocyte infiltration and antitumor immunity in pancreatic cancer

Tumors weakly infiltrated by T lymphocytes poorly respond to immunotherapy. We aimed to unveil malignancy-associated programs regulating T cell entrance, arrest, and activation in the tumor environment. Differential expression of cell adhesion and tissue architecture programs, particularly the presence of the membrane tetraspanin claudin (CLDN)18 as a signature gene, demarcated immune-infiltrated from immune-depleted mouse pancreatic tumors. In human pancreatic ductal adenocarcinoma (PDAC) and non-small cell lung cancer, CLDN18 expression positively correlated with more differentiated histology and favorable prognosis. CLDN18 on the cell surface promoted accrual of cytotoxic T lymphocytes (CTLs), facilitating direct CTL contacts with tumor cells by driving the mobilization of the adhesion protein ALCAM to the lipid rafts of the tumor cell membrane through actin. This process favored the formation of robust immunological synapses (ISs) between CTLs and CLDN18-positive cancer cells, resulting in increased T cell activation. Our data reveal an immune role for CLDN18 in orchestrating T cell infiltration and shaping the tumor immune contexture.

Pathways and molecules for overcoming immunotolerance in metastatic gastrointestinal tumors

Worldwide, gastrointestinal (GI) cancer is recognized as one of the leading malignancies diagnosed in both genders, with mortality largely attributed to metastatic dissemination. It has been identified that in GI cancer, a variety of signaling pathways and key molecules are modified, leading to the emergence of an immunotolerance phenotype. Such modifications are pivotal in the malignancy's evasion of immune detection. Thus, a thorough analysis of the pathways and molecules contributing to GI cancer's immunotolerance is vital for advancing our comprehension and propelling the creation of efficacious pharmacological treatments. In response to this necessity, our review illuminates a selection of groundbreaking cellular signaling pathways associated with immunotolerance in GI cancer, including the Phosphoinositide 3-kinases/Akt, Janus kinase/Signal Transducer and Activator of Transcription 3, Nuclear Factor kappa-light-chain-enhancer of activated B cells, Transforming Growth Factor-beta/Smad, Notch, Programmed Death-1/Programmed Death-Ligand 1, and Wingless and INT-1/beta-catenin-Interleukin 10. Additionally, we examine an array of pertinent molecules like Indoleamine-pyrrole 2,3-dioxygenase, Human Leukocyte Antigen G/E, Glycoprotein A Repetitions Predominant, Clever-1, Interferon regulatory factor 8/Osteopontin, T-cell immunoglobulin and mucin-domain containing-3, Carcinoembryonic antigen-related cell adhesion molecule 1, Cell division control protein 42 homolog, and caspases-1 and -12.

Multiparametric flow cytometry to characterize vaccine-induced polyfunctional T cell responses and T cell/NK cell exhaustion and memory phenotypes in mouse immuno-oncology models

Suitable methods to assess in vivo immunogenicity and therapeutic efficacy of cancer vaccines in preclinical cancer models are critical to overcome current limitations of cancer vaccines and enhance the clinical applicability of this promising immunotherapeutic strategy. In particular, availability of methods allowing the characterization of T cell responses to endogenous tumor antigens is required to assess vaccine potency and improve the antigen formulation. Moreover, multiparametric assays to deeply characterize tumor-induced and therapy-induced immune modulation are relevant to design mechanism-based combination immunotherapies. Here we describe a versatile multiparametric flow cytometry method to assess the polyfunctionality of tumor antigen-specific CD4⁺ and CD8⁺ T cell responses based on their production of multiple cytokines after short-term ex vivo restimulation with relevant tumor epitopes of the most common mouse strains. We also report the development and application of two 21-color flow cytometry panels allowing a comprehensive characterization of T cell and natural killer cell exhaustion and memory phenotypes in mice with a particular focus on preclinical cancer models.

Interrupting the nitrosative stress fuels tumor-specific cytotoxic T lymphocytes in pancreatic cancer

Background

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest tumors owing to its robust desmoplasia, low immunogenicity, and recruitment of cancer-conditioned, immunoregulatory myeloid cells. These features strongly limit the success of immunotherapy as a single agent, thereby suggesting the need for the development of a multitargeted approach. The goal is to foster T lymphocyte infiltration within the tumor landscape and neutralize cancer-triggered immune suppression, to enhance the therapeutic effectiveness of immune-based treatments, such as anticancer adoptive cell therapy (ACT).

Methods

We examined the contribution of immunosuppressive myeloid cells expressing arginase 1 and nitric oxide synthase 2 in building up a reactive nitrogen species (RNS)-dependent chemical barrier and shaping the PDAC immune landscape. We examined the impact of pharmacological RNS interference on overcoming the recruitment and immunosuppressive activity of tumor-expanded myeloid cells, which render pancreatic cancers resistant to immunotherapy.

Results

PDAC progression is marked by a stepwise infiltration of myeloid cells, which enforces a highly immunosuppressive microenvironment through the uncontrolled metabolism of L-arginine by arginase 1 and inducible nitric oxide synthase activity, resulting in the production of large amounts of reactive oxygen and nitrogen species. The extensive accumulation of myeloid suppressing cells and nitrated tyrosines (nitrotyrosine, N-Ty) establishes an RNS-dependent chemical barrier that impairs tumor infiltration by T lymphocytes and restricts the efficacy of adoptive immunotherapy. A pharmacological treatment with AT38 ([3-(aminocarbonyl)furoxan-4-yl]methyl salicylate) reprograms the tumor microenvironment from protumoral to antitumoral, which supports T lymphocyte entrance within the tumor core and aids the efficacy of ACT with telomerase-specific cytotoxic T lymphocytes.

Conclusions

Tumor microenvironment reprogramming by ablating aberrant RNS production bypasses the current limits of immunotherapy in PDAC by overcoming immune resistance.

T-cell tracking using Cerenkov and radioluminescence imaging

Cancer immunotherapy is a promising strategy based on the ability of the immune system to kill selected cells. In the development of an effective T-cell therapy, the noninvasive cell tracking methods play a crucial role. Here, we investigate the potentialities of T-cell marked with radionuclides in order to detect their localization with imaging techniques in small animal rodents. A protocol to label T-cells with ³² P-ATP was tested and evaluated. The homing of ³² P-ATP labeled T lymphocytes was investigated by Cerenkov luminescence imaging (CLI) and radioluminescence imaging (RLI). The first approach relies on the acquisition of Cerenkov photons produced by the beta particles emitted by the ³² P internalized by lymphocytes; the second one on the detection of photons coming from the conversion of radioactive energy in light done by scintillator crystals layered on the animals. The results show that T-cell biodistribution can be optically observed by both CLI and RLI in small animal rodents in in vivo and ex vivo acquisitions. T-cell localization in the tumor mass was definitively confirmed by flow cytometry.

Local endothelial complement activation reverses endothelial quiescence, enabling t-cell homing, and tumor control during t-cell immunotherapy

Cancer immunotherapy relies upon the ability of T cells to infiltrate tumors. The endothelium constitutes a barrier between the tumor and effector T cells, and the ability to manipulate local vascular permeability could be translated into effective immunotherapy. Here, we show that in the context of adoptive T cell therapy, antitumor T cells, delivered at high enough doses, can overcome the endothelial barrier and infiltrate tumors, a process that requires local production of C3, complement activation on tumor endothelium and release of C5a. C5a, in turn, acts on endothelial cells promoting the upregulation of adhesion molecules and T-cell homing. Genetic deletion of C3 or the C5a receptor 1 (C5aR1), and pharmacological blockade of C5aR1, impaired the ability of T cells to overcome the endothelial barrier, infiltrate tumors, and control tumor progression in vivo, while genetic chimera mice demonstrated that C3 and C5aR1 expression by tumor stroma, and not leukocytes, governs T cell homing, acting on the local endothelium. In vitro, endothelial C3 and C5a expressions were required for endothelial activation by type 1 cytokines. Our data indicate that effective immunotherapy is a consequence of successful homing of T cells in response to local complement activation, which disrupts the tumor endothelial barrier.

Effective control of acute myeloid leukaemia and acute lymphoblastic leukaemia progression by telomerase specific adoptive T-cell therapy

Telomerase (TERT) is a ribonucleoprotein enzyme that preserves the molecular organization at the ends of eukaryotic chromosomes. Since TERT deregulation is a common step in leukaemia, treatments targeting telomerase might be useful for the therapy of hematologic malignancies. Despite a large spectrum of potential drugs, their bench-to-bedside translation is quite limited, with only a therapeutic vaccine in the clinic and a telomerase inhibitor at late stage of preclinical validation. We recently demonstrated that the adoptive transfer of T cell transduced with an HLA-A2-restricted T-cell receptor (TCR), which recognize human TERT with high avidity, controls human B-cell chronic lymphocytic leukaemia (B-CLL) progression without severe side-effects in humanized mice. In the present report, we show the ability of our approach to limit the progression of more aggressive leukemic pathologies, such as acute myeloid leukaemia (AML) and B-cell acute lymphoblastic leukaemia (B-ALL). Together, our findings demonstrate that TERT-based adoptive cell therapy is a concrete platform of T cell-mediated immunotherapy for leukaemia treatment.

4PD Functionalized Dendrimers: A Flexible Tool for In Vivo Gene Silencing of Tumor-Educated Myeloid Cells

Myeloid cells play a key role in tumor progression and metastasis by providing nourishment and immune protection, as well as facilitating cancer invasion and seeding to distal sites. Although advances have been made in understanding the biology of these tumor-educated myeloid cells (TEMCs), their intrinsic plasticity challenges our further understanding of their biology. Indeed, in vitro experiments only mimic the in vivo setting, and current gene-knockout technologies do not allow the simultaneous, temporally controlled, and cell-specific silencing of multiple genes or pathways. In this article, we describe the 4PD nanoplatform, which allows the in vivo preferential transfection and in vivo tracking of TEMCs with the desired RNAs. This platform is based on the conjugation of CD124/IL-4Rα-targeting peptide with G5 PAMAM dendrimers as the loading surface and can convey therapeutic or experimental RNAs of interest. When injected i.v. in mice bearing CT26 colon carcinoma or B16 melanoma, the 4PD nanoparticles predominantly accumulate at the tumor site, transfecting intratumoral myeloid cells. The use of 4PD to deliver a combination of STAT3- and C/EBPβ-specific short hairpin RNA or miR-142-3p confirmed the importance of these genes and microRNAs in TEMC biology and indicates that silencing of both genes is necessary to increase the efficacy of immune interventions. Thus, the 4PD nanoparticle can rapidly and cost effectively modulate and assess the in vivo function of microRNAs and mRNAs in TEMCs.

Superior Immunologic and Therapeutic Efficacy of a Xenogeneic Genetic Cancer Vaccine Targeting Carcinoembryonic Human Antigen

We have generated a xenogeneic vaccine against human carcinoembryonic antigen (hCEACAM-5 or commonly hCEA) using as immunogen rhesus CEA (rhCEA). RhCEA cDNA was codon-usage optimized (rhCEAopt) and delivered by sequential DNA electro-gene-transfer (DNA-EGT) and adenoviral (Ad) vector. RhCEAopt was capable to break tolerance to CEA in hCEA transgenic mice and immune responses were detected against epitopes distributed over the entire length of the protein. Xenovaccination with rhCEA resulted in the activation of CD4+ T-cell responses in addition to self-reactive CD8+ T-cells, the development of high-titer antibodies against hCEA, and significant antitumor effects upon challenge with hCEA+ tumor cells. The superior activity of rhCEAopt compared with hCEAopt was confirmed in hCEA/HHD double-transgenic mice, where potent CD8+ T-cell responses against specific human HLA A*0201 hCEA epitopes were detected. Our data show that xenogeneic gene-based vaccination with rhCEA is a viable approach to break tolerance against CEA, thus suggesting further development in the clinical setting.

Novel metronomic chemotherapy and cancer vaccine combinatorial strategy for hepatocellular carcinoma in a mouse model

Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer and represents the third and the fifth leading cause of cancer-related death worldwide in men and women, respectively. Hepatitis B virus (HBV) and hepatitis C virus (HCV) chronic infections account for pathogenesis of more than 80 % of primary HCC. HCC prognosis greatly varies according to stage at beginning of treatment, but the overall 5-year survival rate is approximately 5-6 %. Given the limited number of effective therapeutic strategies available, immunotherapies and therapeutic cancer vaccines may help in improving the clinical outcome for HCC patients. However, the few clinical trials conducted to date have shown contrasting results, indicating the need for improvements. In the present study, a novel combinatorial strategy, based on metronomic chemotherapy plus vaccine, is evaluated in a mouse model. The chemotherapy is a multi-drug cocktail including taxanes and alkylating agents, which is administered in a metronomic-like fashion. The vaccine is a multi-peptide cocktail including HCV as well as universal tumor antigen TERT epitopes. The combinatorial strategy designed and evaluated in the present study induces an enhanced specific T cell response, when compared to vaccine alone, which correlates to a reduced Treg frequency. Such results are highly promising and may pave way to relevant improvements in immunotherapeutic strategies for HCC and beyond.

Mammalian models of chemically induced primary malignancies exploitable for imaging-based preclinical theragnostic research

Compared with transplanted tumor models or genetically engineered cancer models, chemically induced primary malignancies in experimental animals can mimic the clinical cancer progress from the early stage on. Cancer caused by chemical carcinogens generally develops through three phases namely initiation, promotion and progression. Based on different mechanisms, chemical carcinogens can be divided into genotoxic and non-genotoxic ones, or complete and incomplete ones, usually with an organ-specific property. Chemical carcinogens can be classified upon their origins such as environmental pollutants, cooked meat derived carcinogens, N-nitroso compounds, food additives, antineoplastic agents, naturally occurring substances and synthetic carcinogens, etc. Carcinogen-induced models of primary cancers can be used to evaluate the diagnostic/therapeutic effects of candidate drugs, investigate the biological influential factors, explore preventive measures for carcinogenicity, and better understand molecular mechanisms involved in tumor initiation, promotion and progression. Among commonly adopted cancer models, chemically induced primary malignancies in mammals have several advantages including the easy procedures, fruitful tumor generation and high analogy to clinical human primary cancers. However, in addition to the time-consuming process, the major drawback of chemical carcinogenesis for translational research is the difficulty in noninvasive tumor burden assessment in small animals. Like human cancers, tumors occur unpredictably also among animals in terms of timing, location and the number of lesions. Thanks to the availability of magnetic resonance imaging (MRI) with various advantages such as ionizing-free scanning, superb soft tissue contrast, multi-parametric information, and utility of diverse contrast agents, now a workable solution to this bottleneck problem is to apply MRI for noninvasive detection, diagnosis and therapeutic monitoring on those otherwise uncontrollable animal models with primary cancers. Moreover, it is foreseeable that the combined use of chemically induced primary cancer models and molecular imaging techniques may help to develop new anticancer diagnostics and therapeutics.

Targeting tumor vasculature: expanding the potential of DNA cancer vaccines

Targeting the tumor vasculature with anti-angiogenesis modalities is a bona fide validated approach that has complemented cancer treatment paradigms. Tumor vasculature antigens (TVA) can be immunologically targeted and offers multiple theoretical advantages that may enhance existing strategies against cancer. We focused on tumor endothelial marker 1 (TEM1/CD248) as a model TVA since it is broadly expressed on many different cancers. Our DNA-based vaccine approach demonstrated that CD248 can be effectively targeted immunologically; anti-tumor responses were generated in several mouse models; and CD8(+)/CD4(+) T cell responses were elicited against peptides derived from CD248 protein. Our work supports our contention that CD248 is a novel immunotherapeutic target for cancer treatment and highlights the efficient, safe and translatable use of DNA-based immunotherapy. We next briefly highlight ongoing investigations targeting CD248 with antibodies as a diagnostic imaging agent and as a therapeutic antibody in an early clinical trial. The optimal approach for generating effective DNA-based cancer vaccines for several tumor types may be a combinatorial approach that enhances immunogenicity such as combination with chemotherapy. Additional combination approaches are discussed and include those that alleviate the immunosuppressive tumor microenvironment induced by myeloid-derived suppressor cells and T regulatory cells. Targeting the tumor vasculature by CD248-based immunological modalities expands the armamentarium against cancer.

Prostate Cancer Immunotherapy: Exploiting the HLA Class II Pathway in Vaccine Design

Prostate cancer is the second most diagnosed cancer in men and current treatment of advanced prostate cancer is ineffective. Immunotherapy has emerged as a promising treatment option for metastatic prostate cancer but its clinical application is still in the early stages of development. In order to treat metastatic prostate tumors, new directions must be taken to improve current immunotherapeutic strategies. These include the identification of effective tumor antigens (Ags), the induction of the HLA class II pathway for Ag processing and CD4⁺ T cell activation, and the ability of tumor cells to act like Ag presenting cells. In this review, we suggest a model for tumor Ag selection, epitope modification and self-processing for presentation by class II proteins as a means of restoring immune activation and tumor clearance. We also outline the importance of a Gamma-IFN-inducible Lysosomal Thiol reductase (GILT) in Ag and modified peptide processing by tumor cells, generation of functional epitopes for T cell recognition, and inclusion of immune checkpoint blockers in cancer immunotherapy. Taken together, this review provides a framework for the future development of novel cancer vaccines and the improvement of existing immunotherapeutics in prostate cancer.

CD8+ T-cell responses rapidly select for antigen-negative tumor cells in the prostate

Stimulation of patients' immune systems for the treatment of solid tumors is an emerging therapeutic paradigm. The use of enriched autologous T cells for adoptive cell therapy or vaccination with antigen-loaded dendritic cells have shown clinical efficacy in melanoma and prostate cancer, respectively. However, the long-term effects of immune responses on selection and outgrowth of antigen-negative tumor cells in specific tumor types must be determined to understand and achieve long-term therapeutic effects. In this study, we have investigated the expression of a tumor-specific antigen in situ after treatment with tumor-specific CD8(+) T cells in an autochthonous mouse model of prostate cancer. After T-cell treatment, aggregates of dead antigen-positive tumor cells were concentrated in the lumen of the prostate gland and were eventually eliminated from the prostate tissue. Despite the elimination of antigen-positive tumor cells, prostate tumor continued to grow in T-cell-treated mice. Interestingly, the remaining tumor cells were antigen negative and downregulated MHC class I expression. These results show that CD8(+) T cells are effective in eliminating antigen-bearing prostate tumor cells but they also can select for the outgrowth of antigen-negative tumor cells. These findings provide insights into the requirements for an effective cancer immunotherapy within the prostate that not only induces potent immune responses but also avoids selection and outgrowth of antigen-negative tumor cells.

A novel minigene scaffold for therapeutic cancer vaccines

Genetic vaccines are emerging as a powerful modality to induce T-cell responses to target tumor associated antigens (TAA). Viral or plasmid DNA or RNA vectors harbor an expression cassette encoding the antigen of choice delivered in vivo by vaccination. In this context, immunizations with minigenes containing selected, highly antigenic, T-cell epitopes of TAAs may have several advantages relative to full-length proteins. The objective of this study was to identify an optimal scaffold for minigene construction. We generated a number of minigenes containing epitopes from the carcinoembryonic antigen (CEA) model TAA and utilized muscle DNA electro-gene-transfer (DNA-EGT) to vaccinate HLA-A*0201 (HHD) and CEA/HHD double transgenic mice. The components utilized to construct the minigenes included CD8⁺ T cell epitopes and (or) anchor modified analogs that were selected on the basis of their predicted binding to HLA-*A0201, their uniqueness in the human proteome, and the likelihood of cancer cell natural processing and presentation via MHC-I. Other candidate components comparatively tested included: helper CD4⁺ T-cell epitopes, flanking regions for optimal epitope processing (including both proteasome-dependent and furin-dependent polypeptide processing mechanisms), and immunoenhancing moieties. Through a series of comparative studies and iterations we have identified an optimal minigene scaffold comprising the following elements: human tissue plasminogen activator (TPA) signal peptide, T-cell epitopes connected by furin sensitive linkers, and the E. Coli enterotoxin B subunit. The selected epitope modified minigenes (EMM) delivered by DNA-EGT were able to break immune tolerance in CEA/HHD mice and induce a strong immune response against all epitopes tested, independently of their relative positions within the scaffold. Furthermore, the optimized EMMs delivered via DNA-EGT were more immunogenic and exerted more powerful antitumor effects in a B16-CEA/HHD metastatic melanoma model than a DNA vector encoding the full-length protein or a mixture of the same peptides injected subcutaneously. Our data may shed light on the optimal design of a universal vehicle for epitope-targeted, genetic cancer vaccines.

Highly optimized DNA vaccine targeting human telomerase reverse transcriptase stimulates potent antitumor immunity

High levels of human telomerase reverse transcriptase (hTERT) are detected in more than 85% of human cancers. Immunologic analysis supports that hTERT is a widely applicable target recognized by T cells and can be potentially studied as a broad cancer immunotherapeutic, or a unique line of defense against tumor recurrence. There remains an urgent need to develop more potent hTERT vaccines. Here, a synthetic highly optimized full-length hTERT DNA vaccine (phTERT) was designed and the induced immunity was examined in mice and non-human primates (NHP). When delivered by electroporation, phTERT elicited strong, broad hTERT-specific CD8 T-cell responses including induction of T cells expressing CD107a, IFN-γ, and TNF-α in mice. The ability of phTERT to overcome tolerance was evaluated in an NHP model, whose TERT is 96% homologous to that of hTERT. Immunized monkeys exhibited robust [average 1,834 spot forming unit (SFU)/10(6) peripheral blood mononuclear cells (PBMC)], diverse (multiple immunodominant epitopes) IFN-γ responses and antigen-specific perforin release (average 332 SFU/10(6) PBMCs), suggesting that phTERT breaks tolerance and induces potent cytotoxic responses in this human-relevant model. Moreover, in an HPV16-associated tumor model, vaccination of phTERT slows tumor growth and improves survival rate in both prophylactic and therapeutic studies. Finally, in vivo cytotoxicity assay confirmed that phTERT-induced CD8 T cells exhibited specific cytotoxic T lymphocyte (CTL) activity, capable of eliminating hTERT-pulsed target cells. These findings support that this synthetic electroporation-delivered DNA phTERT may have a role as a broad therapeutic cancer vaccine candidate.

Modeling protective anti-tumor immunity via preventative cancer vaccines using a hybrid agent-based and delay differential equation approach

A next generation approach to cancer envisions developing preventative vaccinations to stimulate a person's immune cells, particularly cytotoxic T lymphocytes (CTLs), to eliminate incipient tumors before clinical detection. The purpose of our study is to quantitatively assess whether such an approach would be feasible, and if so, how many anti-cancer CTLs would have to be primed against tumor antigen to provide significant protection. To understand the relevant dynamics, we develop a two-compartment model of tumor-immune interactions at the tumor site and the draining lymph node. We model interactions at the tumor site using an agent-based model (ABM) and dynamics in the lymph node using a system of delay differential equations (DDEs). We combine the models into a hybrid ABM-DDE system and investigate dynamics over a wide range of parameters, including cell proliferation rates, tumor antigenicity, CTL recruitment times, and initial memory CTL populations. Our results indicate that an anti-cancer memory CTL pool of 3% or less can successfully eradicate a tumor population over a wide range of model parameters, implying that a vaccination approach is feasible. In addition, sensitivity analysis of our model reveals conditions that will result in rapid tumor destruction, oscillation, and polynomial rather than exponential decline in the tumor population due to tumor geometry.

An innovative approach to treating cancer envisions developing preventative anti-cancer vaccines to train a person's immune cells to eliminate early-stage tumors close to genesis. The design of such a treatment strategy requires an understanding of the tumor and immune interactions leading to a successful anti-cancer immune response. To engage this problem, we formulate a mathematical model of the immune response against incipient tumours consisting of as low as hundreds to thousands of cancer cells, which is far below the clinical detection threshold of over 100,000 cells. The model considers the initial stimulation of the immune response and the resulting immune attack on the tumor mass and is formulated as a hybrid agent-based and delay differential equation model. We apply the model to test dynamics over a wide range of dynamic parameters, including immune and tumor cell growth rates and the size of the initial anti-cancer immune population. Our results show that an anti-cancer memory immune cell population of 3% or less can successfully eradicate an incipient tumor population over a wide range of dynamic parameters, indicating that a vaccination approach is feasible.

Genetic cancer vaccines: current status and perspectives

INTRODUCTION

The recent approval of the first therapeutic cancer vaccine by the US Regulatory Agency represents a breakthrough event in the history of cancer treatment. The past scepticism towards this type of therapeutic intervention is now replaced by great expectations. The field is now moving towards the development of alternative vaccination technologies, which are capable of generating stronger, more durable and efficient immune responses against specific tumour-associated antigens (TAAs) in combination with cheaper and more standardised manufacturing.

AREAS COVERED

In this context, genetic vaccines are emerging among the most promising methodologies. Several evidences point to combinations of different genetic immunisation modalities (heterologous prime/boost) as a powerful approach to induce superior immune responses and achieve greater clinical efficacy. In this review, we provide an overview of the current status of development of genetic cancer vaccines with particular emphasis on adenoviral vector prime/DNA boost vaccination schedules.

EXPERT OPINION

We believe that therapeutic genetic cancer vaccines have the strong potential to become an established therapeutic modality for cancer in next coming years, in a manner similar to what have now become monoclonal antibodies.

Chemokine nitration prevents intratumoral infiltration of antigen-specific T cells

Blocking CCL2 nitration in tumors promoted CD8⁺ influx and reduced tumor growth and prolonged survival in mice when combined with adoptive cell therapy.

Tumor-promoted constraints negatively affect cytotoxic T lymphocyte (CTL) trafficking to the tumor core and, as a result, inhibit tumor killing. The production of reactive nitrogen species (RNS) within the tumor microenvironment has been reported in mouse and human cancers. We describe a novel RNS-dependent posttranslational modification of chemokines that has a profound impact on leukocyte recruitment to mouse and human tumors. Intratumoral RNS production induces CCL2 chemokine nitration and hinders T cell infiltration, resulting in the trapping of tumor-specific T cells in the stroma that surrounds cancer cells. Preconditioning of the tumor microenvironment with novel drugs that inhibit CCL2 modification facilitates CTL invasion of the tumor, suggesting that these drugs may be effective in cancer immunotherapy. Our results unveil an unexpected mechanism of tumor evasion and introduce new avenues for cancer immunotherapy.

DNA vaccines delivered by human papillomavirus pseudovirions as a promising approach for generating antigen-specific CD8+ T cell immunity

Background

Human papillomavirus (HPV) pseudovirions have recently been shown to deliver DNA efficiently in vivo, resulting in the priming of antigen-specific CD8+ T cells in vaccinated mice. In the current study, we compare the different preparation methods for the generation of HPV pseudovirions for their ability to efficiently infect cells. We also compare the antigen-specific CD8+ T cell immune responses generated by different DNA delivery methods and several commonly used forms of vaccination with that of HPV pseudovirions.

Results

We found that the preparation method of pseudovirions is important for the efficient delivery of encapsidated DNA. We have shown that vaccination with DNA encoding model antigen ovalbumin (OVA) delivered by HPV-16 pseudovirions was capable of generating therapeutic antitumor effects against OVA-expressing tumor. In addition, vaccination with DNA encoding OVA delivered by HPV-16 pseudovirions generated the highest number of OVA-specific CD8+ T cells in mice in our system compared to DNA delivered by other delivery methods. We also found that vaccination with OVA DNA delivered by HPV-16 pseudovirions generated the highest number of OVA-specific CD8+ T cells in mice compared to other forms of antigen-specific vaccines. Furthermore, HPV-16 pseudovirions were capable of carrying DNA vaccine encoding clinically relevant antigen, telomerase reverse transcriptase, to generate antigen-specific CD8+ T cell immune responses.

Conclusions

Our data suggest that DNA vaccines delivered by HPV-16 pseudovirions may be advantageous compared to other delivery methods and other forms of antigen-specific vaccines for application to antigen-specific immunotherapy.

Virus-induced tumor inflammation facilitates effective DC cancer immunotherapy in a Treg-dependent manner in mice

Vaccination using DCs pulsed with tumor lysates or specific tumor-associated peptides has so far yielded limited clinical success for cancer treatment, due mainly to the low immunogenicity of tumor-associated antigens. In this study, we have identified intratumoral virus-induced inflammation as a precondition for effective antitumor DC vaccination in mice. Administration of a tumor-targeted DC vaccine during ongoing virus-induced tumor inflammation, a regimen referred to as oncolysis-assisted DC vaccination (ODC), elicited potent antitumoral CD8+ T cell responses. This potent effect was not replicated by TLR activation outside the context of viral infection. ODC-elicited immune responses mediated marked tumor regression and successful eradication of preestablished lung colonies, an essential prerequisite for potentially treating metastatic cancers. Unexpectedly, depletion of Tregs during ODC did not enhance therapeutic efficacy; rather, it abrogated antitumor cytotoxicity. This phenomenon could be attributed to a compensatory induction of myeloid-derived suppressor cells in Treg-depleted and thus vigorously inflamed tumors, which prevented ODC-mediated immune responses. Consequently, Tregs are not only general suppressors of immune responses, but are essential for the therapeutic success of multimodal and temporally fine-adjusted vaccination strategies. Our results highlight tumor-targeting, replication-competent viruses as attractive tools for eliciting effective antitumor responses upon DC vaccination.

Telomerase and primary T cells: biology and immortalization for adoptive immunotherapy

Telomeres are specialized repeats, present at the end of chromosomes, whose loss during cell division is followed by growth arrest, a central mechanism of replicative senescence in human cells. Telomere length in stem cells is maintained by telomerase, a specialized reverse transcriptase, whose function is to restore shortening telomeres. Unlike most somatic cell types, human T lymphocytes are capable of briefly reactivating telomerase expression at the time of stimulation. Telomerase expression in T lymphocytes is modulated by a variety of external stimuli and by viral infections. However, telomerase reactivation in stimulated, proliferating human T lymphocytes is limited and cannot prevent the ultimate onset of senescence. Ectopic telomerase expression can rescue human and macaque antigen-specific T cells from senescence. Primary T cells have been engineered with telomerase to have substantially extended replicative lifespans without the loss of primary cell functions or malignant transformation. 'Immortal' antigen-specific T-cell lines and clones overexpressing telomerase are an invaluable source of well-characterized quasi-primary T cells for research of T-cell biology and are potentially useful for immunotherapy of cancer and AIDS.

A vaccine targeting telomerase enhances survival of dogs affected by B-cell lymphoma

Canine cancers occur with an incidence similar to that of humans and share many features with human malignancies including histological appearance, tumor genetics, biological behavior, and response to conventional therapies. As observed in humans, the telomerase reverse transcriptase (TERT) activity is largely confined to tumor tissues and absent in the majority of normal dog tissues. Therefore, dog TERT (dTERT) can constitute a valid target for translational cancer immunotherapy. We have evaluated the ability of adenovirus serotype 6 (Ad6) and DNA electroporation (DNA-EP) to induce immune responses against dTERT in dogs affected by malignant lymphoma (ML). The vaccine was combined with standard chemotherapy regimen [cyclophosphamide, vincristine, prednisone (COP)]. dTERT-specific immune response was induced in 13 out of 14 treated animals (93%) and remained detectable and long-lasting with the absence of autoimmunity or other side effects. Most interestingly, the survival time of vaccine/Chemo-treated dogs was significantly increased over historic controls of Chemo-treated animals (>97.8 versus 37 weeks, respectively, P = 0.001). Our results show that Ad6/DNA-EP-based cancer vaccine against dTERT overcomes host immune tolerance, should be combined with chemotherapy, induces long-lasting immune responses, and significantly prolongs the survival of ML canine patients. These data support further evaluation of this approach in human clinical trials.

Tumor-induced tolerance and immune suppression depend on the C/EBPbeta transcription factor

Tumor growth is associated with a profound alteration in myelopoiesis, leading to recruitment of immunosuppressive cells known as myeloid-derived suppressor cells (MDSCs). We showed that among factors produced by various experimental tumors, the cytokines GM-CSF, G-CSF, and IL-6 allowed a rapid generation of MDSCs from precursors present in mouse and human bone marrow (BM). BM-MDSCs induced by GM-CSF+IL-6 possessed the highest tolerogenic activity, as revealed by the ability to impair the priming of CD8(+) T cells and allow long term acceptance of pancreatic islet allografts. Cytokines inducing MDSCs acted on a common molecular pathway and the immunoregulatory activity of both tumor-induced and BM-derived MDSCs was entirely dependent on the C/EBPbeta transcription factor. Adoptive transfer of tumor antigen-specific CD8(+) T lymphocytes resulted in therapy of established tumors only in mice lacking C/EBPbeta in the myeloid compartment, suggesting that C/EBPbeta is a critical regulator of the immunosuppressive environment created by growing cancers.

Telomerase inhibition alters telomere maintenance mechanisms in laryngeal squamous carcinoma cells

BACKGROUND AND PURPOSE

Telomere length must be maintained throughout cancer cell progression and proliferation. In most tumours, telomerase activity maintains telomere length. Therefore, telomerase is a target for cancer treatments. However, some cancer cells maintain telomere length through an alternative mechanism termed 'alternative lengthening of telomeres'. To determine how telomerase inhibition relates to the initiation of the alternative lengthening of telomeres pathway, we investigated telomerase activity and telomere maintenance in Hep-2 cells with and without reduced telomerase activity.

MATERIALS AND METHODS

We investigated telomerase activity levels in a normal Hep-2 cell line and in residual cells following telomerase inhibition treatment. Additionally, we looked for expression of a marker protein for the alternative lengthening of telomeres mechanism.

RESULTS AND CONCLUSIONS

In the residual cells, telomerase activity was eliminated. However, these cells had higher levels of the alternative lengthening of telomeres biomarker, suggesting an alternative mechanism for telomere maintenance following telomerase inhibition. These results could have a major impact on the design of new cancer treatments.

Vaccines based on abnormal self-antigens as tumor-associated antigens: immune regulation

Abnormal expression of "self" antigens on tumors compared with normal cells provides opportunities and challenges for development of cancer vaccines. We review recent work in pre-clinical transgenic mouse models and in clinical trials that has elucidated multiple regulatory mechanisms that interfere with the induction of effective immunity. We discuss these as being either part of the normal function of the immune system or being driven by the tumor microenvironment. Collectively this work shows that it is possible to design vaccines based on tumor-associated antigens and elicit effective immunity against abnormal expression of these antigens on tumors without causing autoimmunity.

A TLR9 agonist enhances therapeutic effects of telomerase genetic vaccine

The telomerase reverse transcriptase (TERT) is an attractive target for cancer vaccination because its expression is reactivated in most tumors. In this study, we have evaluated the ability of a genetic vaccine targeting murine TERT (mTERT) based on DNA electroporation (DNA-EP) and adenovirus serotype 6 (Ad6) to exert therapeutic effects in combination with a novel TLR9 agonist, referred to as immune modulatory oligonucleotide (IMO), as an adjuvant. IMO was administered to mice at the same time as vaccine. IMO induced dose-dependent cytokine secretion and activation of NK cells. Most importantly, vaccination of mice with IMO in combination with mTERT vaccine conferred therapeutic benefit in tumor bearing animals and this effect was associated with increased NK, DC and T cell tumor infiltration. These data show that appropriate combination of a DNA-EP/Ad6-based cancer vaccine against TERT with IMO induces multiple effects on innate and adaptive immune responses resulting in a significant antitumor efficacy.

Tumor immunogenicity and responsiveness to cancer vaccine therapy: the state of the art

Despite enormous effort, promising pre-clinical data in animal studies and over 900 clinical trials in the United States, no cancer vaccine has ever been approved for clinical use. Over the past decade a great deal of progress has been in both laboratory and clinical studies defining the interactions between developing tumors and the immune system. The results of these studies provide a rationale that may help explain the failure of recent therapeutic cancer vaccines in terms of vaccine principles, in selecting which tumors are the most appropriate to target and instruct the design and implementation of state-of-the-art cancer vaccines.

Autoimmune B-cell lymphopenia after successful adoptive therapy with telomerase-specific T lymphocytes

Telomerase reverse transcriptase (TERT) is a good candidate for cancer immunotherapy because it is overexpressed in 85% of all human tumors and implicated in maintenance of the transformed phenotype. TERT-based cancer vaccines have been shown to be safe, not inducing any immune-related pathology, but their impact on tumor progression is modest. Here we show that adoptive cell therapy with the use of high-avidity T lymphocytes reactive against telomerase can control the growth of different established tumors. Moreover, in transgenic adenocarcinoma mouse prostate mice, which develop prostate cancer, TERT-based adoptive cell therapy halted the progression to more aggressive and poorly differentiated tumors, significantly prolonging mouse survival. We also demonstrated that human tumors, including Burkitt lymphoma, and human cancer stem cells, are targeted in vivo by TERT-specific cytotoxic T lymphocytes. Effective therapy with T cells against telomerase, different from active vaccination, however, led to autoimmunity marked by a consistent, although transient, B-cell depletion in primary and secondary lymphoid organs, associated with alteration of the spleen cytoarchitecture. These results indicate B cells as an in vivo target of TERT-specific cytotoxic T lymphocytes during successful immunotherapy.

Targeting human telomerase reverse transcriptase with recombinant lentivector is highly effective to stimulate antitumor CD8 T-cell immunity in vivo

The success of active immunotherapy is based on the vaccine's ability to overcome immune tolerance through recalibrating the immune system so that it is able to recognize tumor antigens as foreign rather than self. In this study, we used a lentiviral vector system to target human telomerase reverse transcriptase (lv-hTERT), a widely expressed tumor antigen. Immunization of HLA-A*0201 transgenic HHD mice with recombinant lv-hTERT vector induces potent and diversified cytotoxic T lymphocyte responses that recognize in vitro murine tumor cells, which overexpress telomerase. Compared with peptide-based vaccinations, the lv-hTERT vector triggers better and more sustained CD8(+) T-cell response against self/TERT epitope in vivo. The study found that the additional use of a heterologous boosted vaccination drastically improves self/TERT-specific CD8 responses in lv-hTERT primed mice. Both primary and long-lasting self/TERT-specific CD8(+) T-cell responses induced with Iv-hTERT vector required the presence of CD4 T cells in vivo. This lv-hTERT-based active immunotherapy efficiently inhibits the growth of telomerase expressing tumors (B16/HLA-A2.1 murine melanoma) in HHD mice. These data show that targeting hTERT with lentivector is highly effective in stimulating a broad range of CD8 T-cell immunity that can be exploited for cancer immunotherapy.

In vivo administration of artificial antigen-presenting cells activates low-avidity T cells for treatment of cancer

The development of effective antitumor immune responses is normally constrained by low-avidity, tumor-specific CTLs that are unable to eradicate the tumor. Strategies to rescue antitumor activity of low-avidity melanoma-specific CTLs in vivo may improve immunotherapy efficacy. To boost the in vivo effectiveness of low-avidity CTLs, we immunized mice bearing lung melanoma metastases with artificial antigen-presenting cells (aAPC), made by covalently coupling (pep)MHC-Ig dimers and B7.1-Ig molecules to magnetic beads. aAPC treatment induced significant tumor reduction in a mouse telomerase antigen system, and complete tumor eradication in a mouse TRP-2 antigen system, when low-avidity CTLs specific for these antigens were adoptively transferred. In addition, in an in vivo treatment model of subcutaneous melanoma, aAPC injection also augmented the activity of adoptively transferred CTLs and significantly delayed tumor growth. In vivo tumor clearance due to aAPC administration correlated with in situ proliferation of the transferred CTL. In vitro studies showed that aAPC effectively stimulated cytokine release, enhanced CTL-mediated lysis, and TCR downregulation in low-avidity CTLs. Therefore, in vivo aAPC administration represents a potentially novel approach to improve cancer immunotherapy.

The choice of the antigen in the dendritic cell-based vaccine therapy for prostate cancer

Tumor antigens (TA) are promising candidates for targeted treatment of prostate cancer (PCa). Critical issues in the preparation of dendritic cell (DC)-based TA vaccines are the DC maturation state and the appropriateness of the TA. Prostate-specific antigen (PSA) and prostate acide pshosphatase (PAP) presented by DC have produced encouraging results and PAP-loaded DCs are at late-stage development for PCa patients. TAs indispensable for tumor survival and propagation are now emerging as first choice TAs for future vaccines. The increased expression and enzymatic activity of prostate specific membrane antigen (PSMA) and prostate stem cell antigen (PSCA) by aggressive prostate tumors is indicative of a unique, selective advantage on the part of cells expressing them. Human telomerase reverse transcriptase (hTERT) and survivin are both involved in tumor cell survival and considered universal TAs. The T cell epitope potential of peptides derived from these TAs has been defined by computer-assisted prediction programs and has been tested in vitro and in vivo in terms of their ability to recruit cytotoxic T lymphocytes (CTL) and to be recognised as CTL targets. Results, reviewed here, show that anti-tumor immunity can be induced in vivo by DC loaded with both whole TAs and TA peptides. The promising, but still limited clinical success suggests further exploration of this immune therapy in the more appropriate setting of minimal disease. In advanced stages, vaccine can still be effective when combined with systemic or local cytoreductive therapies, which may overcome antigen specific tolerance and subvert the tumor immunosuppressive environment.

Immunotherapy of pediatric brain tumor patients should include an immunoprevention strategy: a medical hypothesis paper

Adults diagnosed with Glioblastoma multiforme (GBM) are frequently faced with a 7% chance of surviving 2 years compared with pediatric patients with GBM who have a 26% survival rate. Our recent screen of possible glioma-associated antigen precursor protein (TAPP) profiles displayed from different types of pediatric brain tumors showed that pediatric patients contained a subset of the tumor antigens displayed by adult GBM patients. Adult GBM possess at least 27 tumor antigens that can potentially stimulate T cell immune responses, suggesting that these tumors are quite antigenic. In contrast, pediatric brain tumors only expressed nine tumor antigens with mRNA levels that were equivalent to those displayed by adult GBM. These tumor-associated antigens could be used as possible targets of therapeutic immunization for pediatric brain cancer patients. Children have developing immune systems that peak at puberty. An immune response mounted by these pediatric patients might account for their extended life spans, even though the pediatric brain tumors express far fewer total tumor-associated antigens. Here we present a hypothesis that pediatric brain tumor patients might be the best patients to show that immunotherapy can be used to successfully treat established cancers. We speculate that immunotherapy should include a panel of tumor antigens that might prevent the out-growth of more malignant tumor cells and thereby prevent the brain tumor relapse. Thus, pediatric brain tumor patients might provide an opportunity to prove the concept of immunoprevention.

Coadministration of telomerase genetic vaccine and a novel TLR9 agonist in nonhuman primates

The human telomerase reverse transcriptase (hTERT) is an attractive target for human cancer vaccination because its expression is reactivated in most human tumors. We have evaluated the ability of DNA electroporation (DNA-EP) and adenovirus serotype 6 (Ad6) to induce immune responses against hTERT in nonhuman primates (NHPs) (Macaca mulatta). Vaccination was effective in all treated animals, and the adaptive immune response remained detectable and long lasting without side effects. To further enhance the efficacy of the hTERT vaccine, we evaluated the combination of hTERT vaccine and a novel TLR9 agonist, referred to as immunomodulatory oligonucleotide (IMO). Monkeys were dosed weekly with IMO concurrently with the vaccine regimen and showed increases in cytokine secretion and activation of natural killer (NK) cells compared with the group that received vaccine alone. Using a peptide array, a specific profile of B-cell reactive epitopes was identified when hTERT vaccine was combined with IMO. The combination of IMO with hTERT genetic vaccine did not impact vaccine-induced TERT-specific cell-mediated immunity. Our results show that appropriate combination of a DNA-EP/Ad6-based cancer vaccine against hTERT with IMO induces multiple effects on innate and adaptive immune responses in NHPs.