Therapeutic effect of a T helper cell supported CTL response induced by a survivin peptide vaccine against murine cerebral glioma

Revolutionizing Glioblastoma Treatment: A Comprehensive Overview of Modern Therapeutic Approaches

Glioblastoma is the most common malignant primary brain tumor in the adult population, with an average survival of 12.1 to 14.6 months. The standard treatment, combining surgery, radiotherapy, and chemotherapy, is not as efficient as we would like. However, the current possibilities are no longer limited to the standard therapies due to rapid advancements in biotechnology. New methods enable a more precise approach by targeting individual cells and antigens to overcome cancer. For the treatment of glioblastoma, these are gamma knife therapy, proton beam therapy, tumor-treating fields, EGFR and VEGF inhibitors, multiple RTKs inhibitors, and PI3K pathway inhibitors. In addition, the increasing understanding of the role of the immune system in tumorigenesis and the ability to identify tumor-specific antigens helped to develop immunotherapies targeting GBM and immune cells, including CAR-T, CAR-NK cells, dendritic cells, and immune checkpoint inhibitors. Each of the described methods has its advantages and disadvantages and faces problems, such as the inefficient crossing of the blood-brain barrier, various neurological and systemic side effects, and the escape mechanism of the tumor. This work aims to present the current modern treatments of glioblastoma.

Peptide-based vaccine for cancer therapies

Different strategies based on peptides are available for cancer treatment, in particular to counter-act the progression of tumor growth and disease relapse. In the last decade, in the context of therapeutic strategies against cancer, peptide-based vaccines have been evaluated in different tumor models. The peptides selected for cancer vaccine development can be classified in two main type: tumor-associated antigens (TAAs) and tumor-specific antigens (TSAs), which are captured, internalized, processed and presented by antigen-presenting cells (APCs) to cell-mediated immunity. Peptides loaded onto MHC class I are recognized by a specific TCR of CD8+ T cells, which are activated to exert their cytotoxic activity against tumor cells presenting the same peptide-MHC-I complex. This process is defined as active immunotherapy as the host's immune system is either de novo activated or restimulated to mount an effective, tumor-specific immune reaction that may ultimately lead to tu-mor regression. However, while the preclinical data have frequently shown encouraging results, therapeutic cancer vaccines clinical trials, including those based on peptides have not provided satisfactory data to date. The limited efficacy of peptide-based cancer vaccines is the consequence of several factors, including the identification of specific target tumor antigens, the limited immunogenicity of peptides and the highly immunosuppressive tumor microenvironment (TME). An effective cancer vaccine can be developed only by addressing all such different aspects. The present review describes the state of the art for each of such factors.

Phase IIa Study of SurVaxM Plus Adjuvant Temozolomide for Newly Diagnosed Glioblastoma

PURPOSE

Despite intensive treatment with surgery, radiation therapy, temozolomide (TMZ) chemotherapy, and tumor-treating fields, mortality of newly diagnosed glioblastoma (nGBM) remains very high. SurVaxM is a peptide vaccine conjugate that has been shown to activate the immune system against its target molecule survivin, which is highly expressed by glioblastoma cells. We conducted a phase IIa, open-label, multicenter trial evaluating the safety, immunologic effects, and survival of patients with nGBM receiving SurVaxM plus adjuvant TMZ following surgery and chemoradiation (ClinicalTrials.gov identifier: NCT02455557).

METHODS

Sixty-four patients with resected nGBM were enrolled including 38 men and 26 women, in the age range of 20-82 years. Following craniotomy and fractionated radiation therapy with concurrent TMZ, patients received four doses of SurVaxM (500 μg once every 2 weeks) in Montanide ISA-51 plus sargramostim (granulocyte macrophage colony-stimulating factor) subcutaneously. Patients subsequently received adjuvant TMZ and maintenance SurVaxM concurrently until progression. Progression-free survival (PFS) and overall survival (OS) were reported. Immunologic responses to SurVaxM were assessed.

RESULTS

SurVaxM plus TMZ was well tolerated with no serious adverse events attributable to SurVaxM. Of the 63 patients who were evaluable for outcome, 60 (95.2%) remained progression-free 6 months after diagnosis (prespecified primary end point). Median PFS was 11.4 months and median OS was 25.9 months measured from first dose of SurVaxM. SurVaxM produced survivin-specific CD8+ T cells and antibody/immunoglobulin G titers. Apparent clinical benefit of SurVaxM was observed in both methylated and unmethylated patients.

CONCLUSION

SurVaxM appeared to be safe and well tolerated. The combination represents a promising therapy for nGBM. For patients with nGBM treated in this manner, PFS may be an acceptable surrogate for OS. A large randomized clinical trial of SurVaxM for nGBM is in progress.

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.

The long multi-epitope peptide vaccine combined with adjuvants improved the therapeutic effects in a glioblastoma mouse model

Emerging data have suggested that single short peptides have limited success as a cancer vaccine; however, extending the short peptides into longer multi-epitope peptides overcame the immune tolerance and induced an immune response. Moreover, the combination of adjuvants such as lenalidomide and anti-programmed cell death protein 1 (PD1) with a peptide vaccine showed potential vaccine effects in previous studies. Therefore, the effects of a long multi-epitope peptide vaccine in combination with lenalidomide and anti-PD1 were analyzed in this study. Long multi-epitope peptides from two MHCI peptides (BIRC597-104 and EphA2682-689) and the pan-human leukocyte antigen-DR isotype (HLA-DR) binding epitope (PADRE) were synthesized. The therapeutic effects of long multi-epitope peptides in combination with lenalidomide and anti-PD1 were confirmed in the murine GL261 intracranial glioma model. Immune cells’ distribution and responses to the long multi-epitope peptides in combination with these adjuvants were also estimated in the spleens, lymph nodes, and tumor tissues. The difference between long multi-epitope peptides and a cocktail of multi-epitope peptides combined with lenalidomide and anti-PD1 was also clarified. As a result, long multi-epitope peptides combined with lenalidomide and anti-PD1 prolonged the survival of mice according to the suppression of tumor growth in an intracranial mouse model. While long multi-epitope peptides combined with these adjuvants enhanced the percentages of activated and memory effector CD8+ T cells, the increase in percentages of regulatory T cells (Tregs) was observed in a cocktail of multi-epitope peptides combined with lenalidomide and anti-PD1 group in the tumors. Long multi-epitope peptides combined with these adjuvants also enhanced the function of immune cells according to the enhanced pro-inflammatory cytokines and cytotoxicity against GL261 cells in ex vivo. In conclusion, long multi-epitope peptides composed of MHCI peptides, BIRC5 and EphA2, and the MHCII peptide, PADRE, in combination with lenalidomide and anti-PD1 has the potential to improve the therapeutic effects of a vaccine against GBM.

Development of immunotherapy for high-grade gliomas: Overcoming the immunosuppressive tumor microenvironment

The preclinical and clinical development of novel immunotherapies for the treatment of central nervous system (CNS) tumors is advancing at a rapid pace. High-grade gliomas (HGG) are aggressive tumors with poor prognoses in both adult and pediatric patients, and innovative and effective therapies are greatly needed. The use of cytotoxic chemotherapies has marginally improved survival in some HGG patient populations. Although several challenges exist for the successful development of immunotherapies for CNS tumors, recent insights into the genetic alterations that define the pathogenesis of HGG and their direct effects on the tumor microenvironment (TME) may allow for a more refined and targeted therapeutic approach. This review will focus on the TME in HGG, the genetic drivers frequently found in these tumors and their effect on the TME, the development of immunotherapy for HGG, and the practical challenges in clinical trials employing immunotherapy for HGG. Herein, we will discuss broadly the TME and immunotherapy development in HGG, with a specific focus on glioblastoma multiforme (GBM) as well as additional discussion in the context of the pediatric HGG diagnoses of diffuse midline glioma (DMG) and diffuse hemispheric glioma (DHG).

Using a Prime-Boost Vaccination Strategy That Proved Effective for High Resolution Epitope Mapping to Characterize the Elusive Immunogenicity of Survivin

Simple Summary

The generation of tumor-specific T cells remains a pillar of modern cancer immunotherapy. Exogenous vaccines often rely on targeting tumor-associated antigens. The anti-apoptotic protein survivin has been deemed a high priority target due to its overexpression in a wide variety of tumor types. To support the analysis of tumor-associated T cell responses, optimization of epitope mapping would be valuable. A heterologous prime-boost vaccination strategy was designed to target survivin to induce anti-tumor immune responses. However, survivin-specific T cell responses could not be detected in mice. Potential mechanisms to explain this failure were explored. To confirm the robustness of the vaccination platform, enhanced green fluorescent protein (eGFP) was targeted since it has been defined as a protein with relatively low immunogenicity. In this context the vaccination strategy uncovered novel T cell epitopes from eGFP in two strains of mice. This research highlighted the utility of the vaccine platform to triage potential target antigens based on their immunogenicity.

Abstract

Survivin is a member of the inhibitor of apoptosis family of proteins and has been reported to be highly expressed in a variety of cancer types, making it a high priority target for cancer vaccination. We previously described a heterologous prime-boost strategy using a replication-deficient adenovirus, followed by an oncolytic rhabdovirus that generates unprecedented antigen-specific T cell responses. We engineered each vector to express a mutated version of full-length murine survivin. We first sought to uncover the complete epitope map for survivin-specific T cell responses in C57BL/6 and BALB/c mice by flow cytometry. However, no T cell responses were detected by intracellular cytokine staining after re-stimulation of T cells. Survivin has been found to be expressed by activated T cells, which could theoretically cause T cell-mediated killing of activated T cells, known as fratricide. We were unable to recapitulate this phenomenon in experiments. Interestingly, the inactivated survivin construct has been previously shown to directly kill tumor cells in vitro. However, there was no evidence in our models of induction of death in antigen-presenting cells due to treatment with a survivin-expressing vector. Using the same recombinant virus-vectored prime-boost strategy targeting the poorly immunogenic enhanced green fluorescent protein proved to be a highly sensitive method for mapping T cell epitopes, particularly in the context of identifying novel epitopes recognized by CD4⁺ T cells. Overall, these results suggested there may be unusually robust tolerance to survivin in commonly used mouse strains that cannot be broken, even when using a particularly potent vaccination platform. However, the vaccination method shows great promise as a strategy for identifying novel and subdominant T cell epitopes.

Dendritic Cell Vaccination of Glioblastoma: Road to Success or Dead End

Glioblastomas (GBM) are the most frequent and aggressive malignant primary brain tumor and remains a therapeutic challenge: even after multimodal therapy, median survival of patients is only 15 months. Dendritic cell vaccination (DCV) is an active immunotherapy that aims at inducing an antitumoral immune response. Numerous DCV trials have been performed, vaccinating hundreds of GBM patients and confirming feasibility and safety. Many of these studies reported induction of an antitumoral immune response and indicated improved survival after DCV. However, two controlled randomized trials failed to detect a survival benefit. This raises the question of whether the promising concept of DCV may not hold true or whether we are not yet realizing the full potential of this therapeutic approach. Here, we discuss the results of recent vaccination trials, relevant parameters of the vaccines themselves and of their application, and possible synergies between DCV and other therapeutic approaches targeting the immunosuppressive microenvironment of GBM.

Mouse models of glioblastoma for the evaluation of novel therapeutic strategies

Glioblastoma (GBM) is an incurable brain tumor with a median survival of approximately 15 months despite an aggressive standard of care that includes surgery, chemotherapy, and ionizing radiation. Mouse models have advanced our understanding of GBM biology and the development of novel therapeutic strategies for GBM patients. However, model selection is crucial when testing developmental therapeutics, and each mouse model of GBM has unique advantages and disadvantages that can influence the validity and translatability of experimental results. To shed light on this process, we discuss the strengths and limitations of 3 types of mouse GBM models in this review: syngeneic models, genetically engineered mouse models, and xenograft models, including traditional xenograft cell lines and patient-derived xenograft models.

Host Immunity Following Near-Infrared Photoimmunotherapy Is Enhanced with PD-1 Checkpoint Blockade to Eradicate Established Antigenic Tumors

Near-infrared photoimmunotherapy (NIR-PIT) induces immunogenic cell death but has mostly failed to induce durable antitumor responses in syngenic tumor mouse models. We hypothesized that adaptive immune resistance could be limiting durable responses after treatmemt with NIR-PIT. We investigated the effects of combining NIR-PIT targeting cell-surface CD44 and PD-1 blockade in multiple syngeneic tumor models. In two of three models, NIR-PIT monotherapy halted tumor growth, enhanced dendritic cell tumor infiltration, and induced de novo tumor antigen-specific T-cell responses absent at baseline. The addition of PD-1 blockade reversed adaptive immune resistance, resulting in both enhanced preexisting tumor antigen-specific T-cell responses and enhanced de novo T-cell responses induced by NIR-PIT. Enhanced immune responses correlated with shared tumor antigen expression, suggesting that antigenicity is a major determinant of response to combination NIR-PIT and PD-1 blockade. Combination treatment induced complete rejection of MC38 tumors treated with NIR-PIT, as well as untreated, distant tumors. Accordingly, tumor antigen-specific T-cell responses were measured in both treated and untreated tumors, validating the development of systemic antitumor immunity. Mice that cleared tumors resisted subsequent tumor challenge, indicating the presence of systemic immune memory. Cumulatively, these results demonstrate reversal of adaptive immune resistance following induction of innate and adaptive immunity by NIR-PIT, resulting in high rates of tumor rejection and/or significant tumor growth control in antigenic syngeneic models of cancer.

Combination immunotherapy with Survivin and luteinizing hormone-releasing hormone fusion protein in murine breast cancer model

AIM

To investigate the therapeutic potential of two recombinant proteins, Survivin and luteinizing hormone-releasing hormone (LHRH) fusion protein [LHRH(6leu)-LTB] for immunotherapy of breast cancer.

METHODS

Murine 4T-1 breast cancer model was used to evaluate the efficacy of recombinant proteins in vivo. Twenty four Balb/c mice were divided into 4 groups of 6 mice each. Recombinant Survivin and LHRH fusion protein, alone or in combination, were administered along with immunomodulator Mycobacterium indicus pranii (MIP) in Balb/c mice. Unimmunized or control group mice were administered with phosphate buffer saline. Each group was then challenged with syngeneic 4T-1 cells to induce the growth of breast tumor. Tumor growth was monitored to evaluate the efficacy of immune-response in preventing the growth of cancer cells.

RESULTS

Preventive immunization with 20 µg recombinant Survivin and MIP was effective in suppressing growth of 4T-1 mouse model of breast cancer (P = 0.04) but 50 µg dose was ineffective in suppressing tumor growth. However, combination of Survivin and LHRH fusion protein was more effective in suppressing tumor growth (P = 0.02) as well as metastasis in vivo in comparison to LHRH fusion protein as vaccine antigen alone.

CONCLUSION

Recombinant Survivin and MIP suppress tumor growth significantly. Combining LHRH fusion protein with Survivin and MIP enhances tumor suppressive effects marginally which provides evidence for recombinant Survivin and LHRH fusion protein as candidates for translating the combination cancer immunotherapy approaches.

High Therapeutic Efficacy of a New Survivin LSP-Cancer Vaccine Containing CD4+ and CD8+ T-Cell Epitopes

The efficacy of an antitumoral vaccine relies both on the choice of the antigen targeted and on its design. The tumor antigen survivin is an attractive target to develop therapeutic cancer vaccines because of its restricted over-expression and vital functions in most human tumors. Accordingly, several clinical trials targeting survivin in various cancer indications have been conducted. Most of them relied on short peptide-based vaccines and showed promising, but limited clinical results. In this study, we investigated the immunogenicity and therapeutic efficacy of a new long synthetic peptide (LSP)-based cancer vaccine targeting the tumor antigen survivin (SVX). This SVX vaccine is composed of three long synthetic peptides containing several CD4⁺ and CD8⁺ T-cell epitopes, which bind to various HLA class II and class I molecules. Studies in healthy individuals showed CD4⁺ and CD8⁺ T-cell immunogenicity of SVX peptides in human, irrespective of the individual's HLA types. Importantly, high frequencies of spontaneous T-cell precursors specific to SVX peptides were also detected in the blood of various cancer patients, demonstrating the absence of tolerance against these peptides. We then demonstrated SVX vaccine's high therapeutic efficacy against four different established murine tumor models, associated with its capacity to generate both specific cytotoxic CD8⁺ and multifunctional Th1 CD4⁺ T-cell responses. When tumors were eradicated, generated memory T-cell responses protected against rechallenge allowing long-term protection against relapses. Treatment with SVX vaccine was also found to reshape the tumor microenvironment by increasing the tumor infiltration of both CD4⁺ and CD8⁺ T cells but not Treg cells therefore tipping the balance toward a highly efficient immune response. These results highlight that this LSP-based SVX vaccine appears as a promising cancer vaccine and warrants its further clinical development.

Recent advances in nanomedicine and survivin targeting in brain cancers

Brain cancer is a highly lethal disease, especially devastating toward both the elderly and children. This cancer has no therapeutics available to combat it, predominately due to the blood-brain barrier (BBB) preventing treatments from maintaining therapeutic levels within the brain. Recently, nanoparticle technology has entered the forefront of cancer therapy due to its ability to deliver therapeutic effects while potentially passing physiological barriers. Key nanoparticles for brain cancer treatment include glutathione targeted PEGylated liposomes, gold nanoparticles, superparamagnetic iron oxide nanoparticles and nanoparticle-albumin bound drugs, with these being discussed throughout this review. Recently, the survivin protein has gained attention as it is over-expressed in a majority of tumors. This review will briefly discuss the properties of survivin, while focusing on how both nanoparticles and survivin-targeting treatments hold potential as brain cancer therapies. This review may provide useful insight into new brain cancer treatment options, particularly survivin inhibition and nanomedicine.

Clinical study of a survivin long peptide vaccine (SurVaxM) in patients with recurrent malignant glioma

Survivin is an anti-apoptotic protein that is highly expressed in many cancers, including malignant gliomas. Preclinical studies established that the conjugated survivin peptide mimic SurVaxM (SVN53-67/M57-KLH) could stimulate an anti-tumor immune response against murine glioma in vivo, as well as human glioma cells ex vivo. The current clinical study was conducted to test safety, immunogenicity and clinical effects of the vaccine. Recurrent malignant glioma patients whose tumors were survivin-positive, and who had either HLA-A*02 or HLA-A*03 MHC class I allele-positivity, were given subcutaneous injections of SurVaxM (500 μg) in Montanide ISA 51 with sargramostim (100 μg) at 2-week intervals. SurVaxM was well tolerated with mostly grade one adverse events (AE) and no serious adverse events (SAE) attributable to the study drug. Six patients experienced local injection site reactions; three patients reported fatigue (grades 1 and 2), and 2 patients experienced myalgia (grade 1). Six of eight immunologically evaluable patients developed both cellular and humoral immune responses to vaccine. The vaccine also stimulated HLA-A*02, HLA-A*03 and HLA-A*24 restricted T cell responses. Three patients maintained a partial clinical response or stable disease for more than 6 months. Median progression-free survival was 17.6 weeks, and median overall survival was 86.6 weeks from study entry with seven of nine patients surviving more than 12 months.

Overview of current immunotherapeutic strategies for glioma

In the last decade, numerous studies of immunotherapy for malignant glioma (glioblastoma multiforme) have brought new knowledge and new hope for improving the prognosis of this incurable disease. Some clinical trials have reached Phase III, following positive outcomes in Phase I and II, with respect to safety and immunological end points. Results are encouraging especially when considering the promise of sustained efficacy by inducing antitumor immunological memory. Progress in understanding the mechanisms of tumor-induced immune suppression led to the development of drugs targeting immunosuppressive checkpoints, which are used in active clinical trials for glioblastoma multiforme. Insights related to the heterogeneity of the disease bring new challenges for the management of glioma and underscore a likely cause of therapeutic failure. An emerging therapeutic strategy is represented by a combinatorial, personalized approach, including the standard of care: surgery, radiation, chemotherapy with added active immunotherapy and multiagent targeting of immunosuppressive checkpoints.

PolyI:C and mouse survivin artificially embedding human 2B peptide induce a CD4+ T cell response to autologous survivin in HLA-A*2402 transgenic mice

CD4(+) T cell effectors are crucial for establishing antitumor immunity. Dendritic cell maturation by immune adjuvants appears to facilitate subset-specific CD4(+) T cell proliferation, but the adjuvant effect for CD4 T on induction of cytotoxic T lymphocytes (CTLs) is largely unknown. Self-antigenic determinants with low avidity are usually CD4 epitopes in mutated proteins with tumor-associated class I-antigens (TAAs). In this study, we made a chimeric version of survivin, a target of human CTLs. The chimeric survivin, where human survivin-2B containing a TAA was embedded in the mouse survivin frame (MmSVN2B), was used to immunize HLA-A-2402/K(b)-transgenic (HLA24(b)-Tg) mice. Subcutaneous administration of MmSVN2B or xenogeneic human survivin (control HsSNV2B) to HLA24(b)-Tg mice failed to induce an immune response without co-administration of an RNA adjuvant polyI:C, which was required for effector induction in vivo. Although HLA-A-2402/K(b) presented the survivin-2B peptide in C57BL/6 mice, 2B-specific tetramer assays showed that no CD8(+) T CTLs specific to survivin-2B proliferated above the detection limit in immunized mice, even with polyI:C treatment. However, the CD4(+) T cell response, as monitored by IFN-γ, was significantly increased in mice given polyI:C+MmSVN2B. The Th1 response and antibody production were enhanced in the mice with polyI:C. The CD4 epitope responsible for effector function was not Hs/MmSNV13-27, a nonconserved region between human and mouse survivin, but region 53-67, which was identical between human and mouse survivin. These results suggest that activated, self-reactive CD4(+) helper T cells proliferate in MmSVN2B+polyI:C immunization and contribute to Th1 polarization followed by antibody production, but hardly participate in CTL induction.

Survivin as a potential mediator to support autoreactive cell survival in myasthenia gravis: a human and animal model study

The mechanisms that underlie the development and maintenance of autoimmunity in myasthenia gravis are poorly understood. In this investigation, we evaluate the role of survivin, a member of the inhibitor of apoptosis protein family, in humans and in two animal models. We identified survivin expression in cells with B lymphocyte and plasma cells markers, and in the thymuses of patients with myasthenia gravis. A portion of survivin-expressing cells specifically bound a peptide derived from the alpha subunit of acetylcholine receptor indicating that they recognize the peptide. Thymuses of patients with myasthenia gravis had large numbers of survivin-positive cells with fewer cells in the thymuses of corticosteroid-treated patients. Application of a survivin vaccination strategy in mouse and rat models of myasthenia gravis demonstrated improved motor assessment, a reduction in acetylcholine receptor specific autoantibodies, and a retention of acetylcholine receptor at the neuromuscular junction, associated with marked reduction of survivin-expressing circulating CD20+ cells. These data strongly suggest that survivin expression in cells with lymphocyte and plasma cell markers occurs in patients with myasthenia gravis and in two animal models of myasthenia gravis. Survivin expression may be part of a mechanism that inhibits the apoptosis of autoreactive B cells in myasthenia gravis and other autoimmune disorders.

The combined effect of survivin-targeted shRNA and emodin on the proliferation and invasion of ovarian cancer cells

Survivin has been shown to be highly expressed in ovarian cancers, but not normal ovarian tissue, which makes it an attractive target for ovarian cancer treatment. Emodin is a traditional Chinese medicine that has been found to inhibit proliferation and induce apoptosis in ovarian cancer cells. Thus, in our study, we combined survivin-targeted shRNA (sur-shRNA) with emodin and tested the effects of this combination on ovarian cancer cells to identify more effective therapeutics against ovarian cancer. A sur-shRNA plasmid was constructed and transfected into the ovarian cancer cell lines SKOV3 and HO8910, and the cells were cultured for 24 h. The cells were then treated with emodin for specific time periods and assessed for viability and apoptosis using the MTT assay and flow cytometry, respectively. Cell invasion was also measured using a Matrigel invasion assay. The shRNA specific for survivin effectively reduced the expression of survivin at the mRNA and protein levels in SKOV3 and HO8910 cells. Both emodin and shRNA-mediated knockdown of survivin significantly inhibited cell proliferation, induced apoptosis, and suppressed invasion in SKOV3 and HO8910 cells (P<0.05). Moreover, the combination of the agents significantly enhanced these effects (P<0.05). We found that the combination of sur-shRNA and emodin could be effective in the treatment of ovarian cancer.

Combination therapy with local radiofrequency ablation and systemic vaccine enhances antitumor immunity and mediates local and distal tumor regression

Purpose

Radiofrequency ablation (RFA) is a minimally invasive energy delivery technique increasingly used for focal therapy to eradicate localized disease. RFA-induced tumor-cell necrosis generates an immunogenic source of tumor antigens known to induce antitumor immune responses. However, RFA-induced antitumor immunity is insufficient to control metastatic progression. We sought to characterize (a) the role of RFA dose on immunogenic modulation of tumor and generation of immune responses and (b) the potential synergy between vaccine immunotherapy and RFA aimed at local tumor control and decreased systemic progression.

Experimental Design

Murine colon carcinoma cells expressing the tumor-associated (TAA) carcinoembryonic antigen (CEA) (MC38-CEA⁺) were studied to examine the effect of sublethal hyperthermia in vitro on the cells’ phenotype and sensitivity to CTL-mediated killing. The effect of RFA dose was investigated in vivo impacting (a) the phenotype and growth of MC38-CEA⁺ tumors and (b) the induction of tumor-specific immune responses. Finally, the molecular signature was evaluated as well as the potential synergy between RFA and poxviral vaccines expressing CEA and a TRIad of COstimulatory Molecules (CEA/TRICOM).

Results

In vitro, sublethal hyperthermia of MC38-CEA⁺ cells (a) increased cell-surface expression of CEA, Fas, and MHC class I molecules and (b) rendered tumor cells more susceptible to CTL-mediated lysis. In vivo, RFA induced (a) immunogenic modulation on the surface of tumor cells and (b) increased T-cell responses to CEA and additional TAAs. Combination therapy with RFA and vaccine in CEA-transgenic mice induced a synergistic increase in CD4⁺ T-cell immune responses to CEA and eradicated both primary CEA⁺ and distal CEA^– s.c. tumors. Sequential administration of low-dose and high-dose RFA with vaccine decreased tumor recurrence compared to RFA alone. These studies suggest a potential clinical benefit in combining RFA with vaccine in cancer patients, and augment support for this novel translational paradigm.

Integration of epidemiology, immunobiology, and translational research for brain tumors

We recently identified a pivotal role for the host type I interferon (IFN) pathway in immunosurveillance against de novo mouse glioma development, especially through the regulation of immature myeloid cells (IMCs) in the glioma microenvironment. The present paper summarizes our published work in a number of areas. We have identified single-nucleotide polymorphisms (SNPs) in human IFN genes that dictate altered prognosis of patients with glioma. One of these SNPs (rs12553612) is located in the promoter of IFNA8 and influences its activity. Conversely, recent epidemiologic data show that chronic use of nonsteroidal anti-inflammatory drugs lowers the risk of glioma. We translated these findings back to our de novo glioma model and found that cyclooxygenase-2 inhibition enhances antiglioma immunosurveillance by reducing glioma-associated IMCs. Taken together, these findings suggest that alterations in myeloid cell function condition the brain for glioma development. Finally, in preliminary work, we have begun applying novel immunotherapeutic approaches to patients with low-grade glioma with the aim of preventing malignant transformation. Future research will hopefully better integrate epidemiological, immunobiological, and translational techniques to develop novel, preventive approaches for malignant gliomas.

Natural HLA class I ligands from glioblastoma: extending the options for immunotherapy

Glioblastoma multiforme is the most frequent and most malignant primary brain tumor with poor prognosis despite surgical removal and radio-chemotherapy. In this setting, immunotherapeutical strategies have great potential, but the reported repertoire of tumor associated antigens is only for HLA-A 02 positive tumors. We describe the first analysis of HLA-peptide presentation patterns in HLA-A 02 negative glioma tissue combined with gene expression profiling of the tumor samples by oligonucleotide microarrays. We identified numerous candidate peptides for immunotherapy. These are peptides derived from proteins with a well-described role in glioma tumor biology and suitable gene expression profiles such as PTPRZ1, EGFR, SEC61G and TNC. Information obtained from complementary analyses of HLA-A 02 negative tumors not only contributes to the discovery of novel shared glioma antigens, but most importantly provides the opportunity to tailor a patient-individual cocktail of tumor-associated peptides for a personalized, targeted immunotherapeutic approach in HLA-A 02 negative patients.

Tumor-associated antigens for specific immunotherapy of prostate cancer

Prostate cancer (PCa) is the most common noncutaneous cancer diagnosis and the second leading cause of cancer-related deaths among men in the United States. Effective treatment modalities for advanced metastatic PCa are limited. Immunotherapeutic strategies based on T cells and antibodies represent interesting approaches to prevent progression from localized to advanced PCa and to improve survival outcomes for patients with advanced disease. CD8⁺ cytotoxic T lymphocytes (CTLs) efficiently recognize and destroy tumor cells. CD4⁺ T cells augment the antigen-presenting capacity of dendritic cells and promote the expansion of tumor-reactive CTLs. Antibodies mediate their antitumor effects via antibody-dependent cellular cytotoxicity, activation of the complement system, improving the uptake of coated tumor cells by phagocytes, and the functional interference of biological pathways essential for tumor growth. Consequently, several tumor-associated antigens (TAAs) have been identified that represent promising targets for T cell- or antibody-based immunotherapy. These TAAs comprise proteins preferentially expressed in normal and malignant prostate tissues and molecules which are not predominantly restricted to the prostate, but are overexpressed in various tumor entities including PCa. Clinical trials provide evidence that specific immunotherapeutic strategies using such TAAs represent safe and feasible concepts for the induction of immunological and clinical responses in PCa patients. However, further improvement of the current approaches is required which may be achieved by combining T cell- and/or antibody-based strategies with radio-, hormone-, chemo- or antiangiogenic therapy.

Experimental immunotherapy for malignant glioma: lessons from two decades of research in the GL261 model

Nearly twenty years of experimental immunotherapy for malignant glioma yielded important insights in the mechanisms governing glioma immunology. Still considered promising, it is clear that immunotherapy does not on its own represent the magic bullet in glioma therapy. In this review, we summarize the major immunotherapeutic achievements in the mouse GL261 glioma model, which has emerged as the gold standard syngeneic model for experimental glioma therapy. Gene therapy, monoclonal antibody treatment, cytokine therapy, cell transfer strategies and dendritic cell therapy were hereby considered. Apart from the considerable progress made in understanding glioma immunology in this model, we also addressed its most pertinent issues and shortcomings. Despite these, the GL261 model will remain indispensable in glioma research since it is a fast, highly reproducible and easy-to-establish model system.

Is survivin the potential Achilles' heel of cancer?

Survivin, the smallest member of the inhibitors of apoptosis proteins (IAPs), plays an important role in the control of apoptosis, cell division, and cell migration/metastasis. Survivin is expressed and required for normal fetal development but is then generally no longer present in most adult tissues. However, reexpression of survivin is observed in numerous human cancers where presence of the protein is associated with enhanced proliferation, metastasis, poor prognosis, and decreased patient survival. Given the relatively selective expression in cancer cells, but not in normal tissue (tumor-associated antigen), and its importance in tumor cell biology, survivin has emerged as an attractive target for cancer treatment. Here, we discuss some aspects of survivin biology by focusing on why the protein appears to be so important for cancer cells and then discuss strategies that harness this dependence to eradicate tumors and situate survivin as a potential Achilles' heel of cancer.

Molecular alterations in glioblastoma: potential targets for immunotherapy

Glioblastoma is the most common and deadly brain tumor, possibly arising from genetic and epigenetic alterations in normal astroglial cells. Multiple cytogenetic, chromosomal, and genetic alterations have been identified in glioblastoma, with distinct expression of antigens (Ags) and biomarkers that may alter therapeutic potential of this aggressive cancer. Current therapy consists of surgical resection, followed by radiation therapy and chemotherapy. In spite of these treatments, the prognosis for glioblastoma patients is poor. Although recent studies have focused on the development of novel immunotherapeutics against glioblastoma, little is known about glioblastoma-specific immune responses. A better understanding of the molecular interactions among glioblastoma tumors, host immune cells, and the tumor microenvironment may give rise to novel integrated approaches for the simultaneous control of tumor escape pathways and the activation of antitumor immune responses. This review provides a detailed overview concerning genetic alterations in glioblastoma, their effects on Ag and biomarker expression, and the future design of chemoimmunotherapeutics against glioblastoma.

Antitumor cytotoxic T-cell response induced by a survivin peptide mimic

Survivin is a tumor-associated antigen with significant potential as a cancer vaccine target. We have identified a survivin peptide mimic containing human MHC class I epitopes and a potential class II ligand that induces a potent antitumor response in C57BL/6 mice with GL261 cerebral gliomas. This peptide is able to elicit both CD8+ CTL and T helper cell responses in C57BL/6 mice. The corresponding region of the human survivin molecule represented by peptide SVN53-67 is 100% homologous to the murine protein, but SVN53-67 is weakly immunogenic in man. We evaluated several amino acid substitutions in putative human MHC I anchor positions in SVN53-67 to identify potential peptide mimics that could provide an enhanced antitumor immune response against human glioma and primary central nervous system lymphoma (PCNSL) cells in culture. We evaluated survivin peptides with predicted binding to human HLA-A*0201 antigen using peptide-loaded dendritic cells from PBMC of patients with these malignancies. One alteration (M57) led to binding to HLA-A*0201 with significantly higher affinity. We compared the ability of autologous dendritic cells loaded with SVN53-67 peptide and SVN53-67/M57 in CTL assays against allomatched and autologous, survivin-expressing, human malignant glioma and PCNSL cells. Both SVN53-67 and SVN53-67/M57 produced CTL-mediated killing of malignant target cells; however, SVN53-67/M57 was significantly more effective than SVN53-67. Thus, SVN53-67/M57 may act as a peptide mimic to induce an enhanced antitumor CTL response in tumor patients. The use of SVN53-67/M57 as a cancer vaccine might have application for cancer vaccine therapy.

Novel cancer vaccine based on genes of Salmonella pathogenicity island 2

Although tumors express potentially immunogenic tumor-associated antigens (TAAs), cancer vaccines often fail because of inadequate antigen delivery and/or insufficient activation of innate immunity. Engineering nonpathogenic bacterial vectors to deliver TAAs of choice may provide an efficient way of presenting TAAs in an immunogenic form. In this study, we used genes of Salmonella pathogenicity island 2 (SPI2) to construct a novel cancer vaccine in which a TAA, survivin, was fused to SseF effector protein and placed under control of SsrB, the central regulator of SPI2 gene expression. This construct uses the type III secretion system (T3SS) of Salmonella and allows preferential delivery of tumor antigen into the cytosol of antigen-presenting cells for optimal immunogenicity. In a screen of a panel of attenuated strains of Salmonella, we found that a double attenuated strain of Salmonella typhimurium, MvP728 (purD/htrA), was not toxic to mice and effectively expressed and translocated survivin protein inside the cytosol of murine macrophages. We also found that a ligand for CD1d-reactive natural killer T (NKT) cells, alpha-glucuronosylceramide (GSL1), enhanced MvP728-induced interleukin-12 production in human dendritic cells and that in vivo coadministration of a NKT ligand with MvP728-Llo or MvP728-survivin enhanced effector-memory cytotoxic T lymphocyte (CTL) responses. Furthermore, combined use of MvP728-survivin with GSL1 produced antitumor activity in mouse models of CT26 colon carcinoma and orthotopic DBT glioblastoma. Therefore, the use of TAA delivery via SPI-2-regulated T3SS of Salmonella and NKT ligands as adjuvants may provide a foundation for new cancer vaccines.

Intradermal DNA electroporation induces survivin-specific CTLs, suppresses angiogenesis and confers protection against mouse melanoma

Survivin is an intracellular tumor-associated antigen that is broadly expressed in a large variety of tumors and also in tumor associated endothelial cells but mostly absent in differentiated tissues. Naked DNA vaccines targeting survivin have been shown to induce T cell as well as humoral immune responses in mice. However, the lack of epitope-specific CD8+ T cell detection and modest tumor protection observed highlight the need for further improvements to develop effective survivin DNA vaccination approaches. Here, the efficacy of a human survivin DNA vaccine delivered by intradermal electroporation (EP) was tested. The CD8+ T cell epitope surv(20-28) restricted to H-2 Db was identified based on in-silico epitope prediction algorithms and binding to MHC class I molecules. Intradermal DNA EP of mice with a human survivin encoding plasmid generated CD8+ cytotoxic T lymphocyte (CTL) responses cross-reactive with the mouse epitope surv(20-28), as determined by intracellular IFN-gamma staining, suggesting that self-tolerance has been broken. Survivin-specific CTLs displayed an activated effector phenotype as determined by CD44 and CD107 up-regulation. Vaccinated mice displayed specific cytotoxic activity against B16 and peptide-pulsed RMA-S cells in vitro as well as against surv(20-28) peptide-pulsed target cells in vivo. Importantly, intradermal EP with a survivin DNA vaccine suppressed angiogenesis in vivo and elicited protection against highly aggressive syngeneic B16 melanoma tumor challenge. We conclude that intradermal EP is an attractive method for delivering a survivin DNA vaccine that should be explored also in clinical studies.

Dendritic cell therapy of high-grade gliomas

The prognosis of patients with malignant glioma is poor in spite of multimodal treatment approaches consisting of neurosurgery, radiochemotherapy and maintenance chemotherapy. Among innovative treatment strategies like targeted therapy, antiangiogenesis and gene therapy approaches, immunotherapy emerges as a meaningful and feasible treatment approach for inducing long-term survival in at least a subpopulation of these patients. Setting up immunotherapy for an inherent immunosuppressive tumor located in an immune-privileged environment requires integration of a lot of scientific input and knowledge of both tumor immunology and neuro-oncology. The field of immunotherapy is moving into the direction of active specific immunotherapy using autologous dendritic cells (DCs) as vehicle for immunization. In the translational research program of the authors, the whole cascade from bench to bed to bench of active specific immunotherapy for malignant glioma is covered, including proof of principle experiments to demonstrate immunogenicity of patient-derived mature DCs loaded with autologous tumor lysate, preclinical in vivo experiments in a murine orthotopic glioma model, early phase I/II clinical trials for relapsing patients, a phase II trial for patients with newly diagnosed glioblastoma (GBM) for whom immunotherapy is integrated in the current multimodal treatment, and laboratory analyses of patient samples. The strategies and results of this program are discussed in the light of the internationally available scientific literature in this fast-moving field of basic science and translational clinical research.

Identification and characterization of survivin-derived H-2Kb-restricted CTL epitopes

Survivin is overexpressed in several malignancies and in tumor-associated endothelium making it an attractive target for therapeutic cytotoxic T-cell responses. Thus, it would be important to test this notion in preclinical models. Consequently, we screened the murine survivin sequence for potential binding K(b)-restricted octamer peptide epitopes. Two epitopes, which bind strongly to K(b), were selected to test their immunogenicity in vivo. Spleen cells from mice vaccinated by intradermal injection of mature DC pulsed with these peptides displayed reactivity to the respective epitopes. The natural processing and presentation of these epitopes by tumor cells was evident by the killing of murine melanoma cells by vaccination-induced T cells. Subcutaneous challenge with syngeneic melanoma demonstrated the protective immunity of this vaccination. Notably, analysis of the vessel density in subcutaneous tumors revealed that survivin-specific vaccination significantly reduced the number of intratumoral vessels. In summary, we demonstrated the immunogenicity of two K(b)-restricted peptide epitopes derived from the murine survivin protein; moreover, survivin-specific vaccination not only resulted in a reduction of tumor cells but also the tumor supplying blood vessels. The presented preclinical model for survivin-directed vaccination may serve as a valuable tool to improve already running clinical trials in a syngeneic tumor model.

Harnessing T-Cell Immunity to Target Brain Tumors

T-cell mediated immunotherapy is a conceptually attractive treatment option to envisage for glioma, since T lymphocytes can actively seek out neoplastic cells in the brain, and they have the potential to safely and specifically eliminate tumor. Some antigenic targets on glioma cells are already defined, and we can be optimistic that more will be discovered from progress in T-cell epitope identification and gene expression profiling of brain tumors. In parallel, advances in immunology (regional immunology, neuroimmunology, tumor immunology) now equip us to build upon the results from current immunotherapy trials in which the safety and feasibility of brain tumor immunotherapy have already been confirmed. We can now look to the next phase of immunotherapy, in which we must harness the most promising basic science advances and existing clinical expertise, and apply these to randomized clinical trials to determine the real clinical impact and applicability of these approaches for treating patients with currently incurable malignant brain tumors.