Immunotherapy for glioblastoma: concepts and challenges

Near-Complete Remission of Glioblastoma in a Patient Treated with an Allogenic Dendritic Cell-Based Vaccine: The Role of Tumor-Specific CD4+T-Cell Cytokine Secretion Pattern in Predicting Response and Recurrence

Immunotherapy has brought hope to the fight against glioblastoma, but its efficacy remains unclear. We present the case of CST, a 25-year-old female patient with a large right-hemisphere glioblastoma treated with a dendritic-tumor cell fusion vaccine. CST showed a near-complete tumor response, with a marked improvement in her functional status and simultaneous increases in tumor-specific CD8+ and CD4+ T cells. Two months before recurrence, the frequency of tumor-specific T cells decreased, while that of IL-17 and CD4+ T cells increased. CST passed away 15 months after enrollment. In this illustrative case, the tumor-specific CD4+ T-cell numbers and phenotype behaved as treatment efficacy biomarkers, highlighting the key role of the latter in glioblastoma immunotherapy.

GDF-15: Diagnostic, prognostic, and therapeutic significance in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the commonest primary malignant brain tumor and has a remarkably weak prognosis. According to the aggressive form of GBM, understanding the accurate molecular mechanism associated with GBM pathogenesis is essential. Growth differentiation factor 15 (GDF-15) belongs to transforming growth factor-β superfamily with important roles to control biological processes. It affects cancer growth and progression, drug resistance, and metastasis. It also can promote stemness in many cancers, and also can stress reactions control, bone generation, hematopoietic growth, adipose tissue performance, and body growth, and contributes to cardiovascular disorders. The role GDF-15 to develop and progress cancer is complicated and remains unclear. GDF-15 possesses tumor suppressor properties, as well as an oncogenic effect. GDF-15 antitumorigenic and protumorigenic impacts on tumor development are linked to the cancer type and stage. However, the GDF-15 signaling and mechanism have not yet been completely identified because of no recognized cognate receptor.

Monitoring innate immune cell dynamics in the glioma microenvironment by magnetic resonance imaging and multiphoton microscopy (MR-MPM)

Rationale: Glioblastoma is the most frequent, primary brain tumor that is characterized by a highly immunosuppressive tumor microenvironment (TME). The TME plays a key role for tumor biology and the effectiveness of immunotherapies. Composition of the TME correlates with overall survival and governs therapy response. Non invasive assessment of the TME has been notoriously difficult. Methods: We have designed an in vivo imaging approach to non invasively visualize innate immune cell dynamics in the TME in a mouse glioma model by correlated MRI and multiphoton microscopy (MR-MPM) using a bimodal, fluorescently labeled iron oxide nanoparticle (NP). The introduction of Teflon cranial windows instead of conventional Titanium rings dramatically reduced susceptibility artifacts on MRI and allowed longitudinal MR-MPM imaging for innate immune cell tracking in the same animal. Results: We visualized tumor associated macrophage and microglia (TAM) dynamics in the TME and dissect the single steps of NP uptake by blood-born monocytes that give rise to tumor-associated macrophages. Next to peripheral NP-loading, we identified a second route of direct nanoparticle uptake via the disrupted blood-brain barrier to directly label tissue resident TAMs. Conclusion: Our approach allows innate immune cell tracking by MRI and multiphoton microscopy in the same animal to longitudinally investigate innate immune cell dynamics in the TME.

Cold Atmospheric Plasma as an Adjunct to Immunotherapy for Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive form of brain cancer in adults. GBM carries a dismal prognosis because of its proliferative, invasive, and angiogenic capabilities and because of its ability to downregulate the immune system. Immune-based therapies under investigation for GBM have been unsuccessful in vivo because of this downregulation. Cold atmospheric plasma (CAP) is a high-energy state of matter that can be applied directly or indirectly to tumor tissue to serve as an adjunct to immunotherapy in the treatment of GBM because it upregulates the immune system by the induction of reactive oxygen species. CAP has the potential to improve the efficacy of existing and investigative immunotherapies for GBM.

The surgical perspective in precision treatment of diffuse gliomas

Over the last decade, advances in molecular and imaging-based biomarkers have induced a more versatile diagnostic classification and prognostic evaluation of glioma patients. This, in combination with a growing therapeutic armamentarium, enables increasingly individualized, risk-benefit-optimized treatment strategies. This path to precision medicine in glioma patients requires surgical procedures to be reassessed within multidimensional management considerations. This article attempts to integrate the surgical intervention into a dynamic network of versatile diagnostic characterization, prognostic assessment, and multimodal treatment options in the light of the latest 2016 World Health Organization (WHO) classification of diffuse brain tumors, WHO grade II, III, and IV. Special focus is set on surgical aspects such as resectability, extent of resection, and targeted surgical strategies including minimal invasive stereotactic biopsy procedures, convection enhanced delivery, and photodynamic therapy. Moreover, the influence of recent advances in radiomics/radiogenimics on the process of surgical decision-making will be touched.

Evolutionary basis of a new gene- and immune-therapeutic approach for the treatment of malignant brain tumors: from mice to clinical trials for glioma patients

Glioma cells are one of the most aggressive and malignant tumors. Following initial surgery, and radio-chemotherapy they progress rapidly, so that patients' median survival remains under two years. They invade throughout the brain, which makes them difficult to treat, and are universally lethal. Though total resection is always attempted it is not curative. Standard of care in 2016 comprises surgical resection, radiotherapy and chemotherapy (temozolomide). Median survival is currently ~14-20months post-diagnosis though it can be higher in high complexity medical university centers, or during clinical trials. Why the immune system fails to recognize the growing brain tumor is not completely understood. We believe that one reason for this failure is that the brain lacks cells that perform the role that dendritic cells serve in other organs. The lack of functional dendritic cells from the brain causes the brain to be deficient in priming systemic immune responses to glioma antigens. To overcome this drawback we reconstituted the brain immune system for it to initiate and prime anti-glioma immune responses from within the brain. To achieve brain immune reconstitution adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1 derived thymidine kinase which converts ganciclovir into phospho-ganciclovir which becomes cytotoxic to dividing cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine for dendritic cells. This results in HSV-1/ganciclovir killing of tumor cells, and the release of tumor antigens, which are then taken up by dendritic cells recruited to the brain tumor microenvironment by Flt3L. Concomitant release of HMGB1, a TLR2 agonist that activates dendritic cells, stimulates dendritic cells loaded with glioma antigens to migrate to the cervical lymph nodes to prime a systemic CD8+ T cytotoxic killing of brain tumor cells. This induced immune response causes glioma-specific cytotoxicity, induces immunological memory, and does not cause brain toxicity or autoimmunity. A Phase I Clinical Trial, to test our hypothesis in human patients, was opened in December 2013 (see: NCT01811992, Combined Cytotoxic and Immune-Stimulatory Therapy for Glioma, at ClinicalTrials.gov). This trial is a first in human trial to test whether the re-engineering of the brain immune system can serve to treat malignant brain tumors. The long and winding road from the laboratory to the clinical trial follows below.

Nanotheranostics: Emerging Strategies for Early Diagnosis and Therapy of Brain Cancer

Nanotheranostics have demonstrated the development of advanced platforms that can diagnose brain cancer at early stages, initiate first-line therapy, monitor it, and if needed, rapidly start subsequent treatments. In brain nanotheranostics, therapeutic as well as diagnostic entities are loaded in a single nanoplatform, which can be further developed as a clinical formulation for targeting various modes of brain cancer. In the present review, we concerned about theranostic nanosystems established till now in the research field. These include gold nanoparticles, carbon nanotubes, magnetic nanoparticles, mesoporous silica nanoparticles, quantum dots, polymeric nanoparticles, upconversion nanoparticles, polymeric micelles, solid lipid nanoparticles and dendrimers for the advanced detection and treatment of brain cancer with advanced features. Also, we included the role of three-dimensional models of the BBB and cancer stem cell concept for the advanced characterization of nanotheranostic systems for the unification of diagnosis and treatment of brain cancer. In future, brain nanotheranostics will be able to provide personalized treatment which can make brain cancer even remediable or at least treatable at the primary stages.

Immunotherapeutic Potential of Oncolytic H-1 Parvovirus: Hints of Glioblastoma Microenvironment Conversion towards Immunogenicity

Glioblastoma, one of the most aggressive primary brain tumors, is characterized by highly immunosuppressive microenvironment. This contributes to glioblastoma resistance to standard treatment modalities and allows tumor growth and recurrence. Several immune-targeted approaches have been recently developed and are currently under preclinical and clinical investigation. Oncolytic viruses, including the autonomous protoparvovirus H-1 (H-1PV), show great promise as novel immunotherapeutic tools. In a first phase I/IIa clinical trial (ParvOryx01), H-1PV was safe and well tolerated when locally or systemically administered to recurrent glioblastoma patients. The virus was able to cross the blood-brain (tumor) barrier after intravenous infusion. Importantly, H-1PV treatment of glioblastoma patients was associated with immunogenic changes in the tumor microenvironment. Tumor infiltration with activated cytotoxic T cells, induction of cathepsin B and inducible nitric oxide (NO) synthase (iNOS) expression in tumor-associated microglia/macrophages (TAM), and accumulation of activated TAM in cluster of differentiation (CD) 40 ligand (CD40L)-positive glioblastoma regions was detected. These are the first-in-human observations of H-1PV capacity to switch the immunosuppressed tumor microenvironment towards immunogenicity. Based on this pilot study, we present a tentative model of H-1PV-mediated modulation of glioblastoma microenvironment and propose a combinatorial therapeutic approach taking advantage of H-1PV-induced microglia/macrophage activation for further (pre)clinical testing.

NKG2D-Dependent Antitumor Effects of Chemotherapy and Radiotherapy against Glioblastoma

Purpose: NKG2D is a potent activating immune cell receptor, and glioma cells express the cognate ligands (NKG2DL). These ligands are inducible by cellular stress and temozolomide (TMZ) or irradiation (IR), the standard treatment of glioblastoma, could affect their expression. However, a role of NKG2DL for the efficacy of TMZ and IR has never been addressed.Experimental Design: We assessed the effect of TMZ and IR on NKG2DL in vitro and in vivo in a variety of murine and human glioblastoma models, including glioma-initiating cells, and a cohort of paired glioblastoma samples from patients before and after therapy. Functional effects were studied with immune cell assays. The relevance of the NKG2D system for the efficacy of TMZ and IR was assessed in vivo in syngeneic orthotopic glioblastoma models with blocking antibodies and NKG2D knockout mice.Results: TMZ or IR induced NKG2DL in vitro and in vivo in all glioblastoma models, and glioblastoma patient samples had increased levels of NKG2DL after therapy with TMZ and IR. This enhanced the immunogenicity of glioma cells in a NGK2D-dependent manner, was independent from cytotoxic or growth inhibitory effects, attenuated by O⁶-methylguanine-DNA-methyltransferase (MGMT), and required the DNA damage response. The survival benefit afforded by TMZ or IR relied on an intact NKG2D system and was decreased upon inhibition of the NKG2D pathway.Conclusions: The immune system may influence the activity of convential cancer treatments with particular importance of the NKG2D pathway in glioblastoma. Our data provide a rationale to combine NKG2D-based immunotherapies with TMZ and IR. Clin Cancer Res; 24(4); 882-95. ©2017 AACR.

Current State of Immune-Based Therapies for Glioblastoma

Glioblastoma is one of the most aggressive solid tumors, and, despite treatment options such as surgery, radiation, and chemotherapy, its prognosis remains grim. Novel approaches are needed to improve survival. Immunotherapy has proven efficacy for melanoma, lung cancer, and kidney cancer and is now a focus for glioblastoma. In this article, glioblastoma-mediated immunosuppression will be discussed and two exciting immune approaches, checkpoint inhibitors and viral-based therapies, will be reviewed.

Control of glioma cell migration and invasiveness by GDF-15

Growth and differentiation factor (GDF)-15 is a member of the transforming growth factor (TGF)-β family of proteins. GDF-15 levels are increased in the blood and cerebrospinal fluid of glioblastoma patients. Using a TCGA database interrogation, we demonstrate that high GDF-15 expression levels are associated with poor survival of glioblastoma patients. To elucidate the role of GDF-15 in glioblastoma in detail, we confirmed that glioma cells express GDF-15 mRNA and protein in vitro. To allow for a detailed functional characterization, GDF-15 expression was silenced using RNA interference in LNT-229 and LN-308 glioma cells. Depletion of GDF-15 had no effect on cell viability. In contrast, GDF-15-deficient cells displayed reduced migration and invasion, in the absence of changes in Smad2 or Smad1/5/8 phosphorylation. Conversely, exogenous GDF-15 stimulated migration and invasiveness. Large-scale expression profiling revealed that GDF-15 gene silencing resulted in minor changes in the miRNA profile whereas several genes, including members of the plasminogen activator/inhibitor complex, were deregulated at the mRNA level. One of the newly identified genes induced by GDF-15 gene silencing was the serpin peptidase inhibitor, clade E nexin group 1 (serpine1) which is induced by TGF-β and known to inhibit migration and invasiveness. However, serpine1 down-regulation alone did not mediate GDF-15-induced promotion of migration and invasiveness. Our findings highlight the complex contributions of GDF-15 to the invasive phenotype of glioma cells and suggest anti-GDF-15 approaches as a promising therapeutic strategy.

Immunological effects of chemotherapy and radiotherapy against brain tumors

INTRODUCTION

The mainstays of brain tumor therapy are surgery, radiotherapy and chemotherapy. Cancer immunotherapy is explored as an additional treatment modality. However, emerging evidence indicates that also radio- and chemotherapy have immunological effects in addition to their cytotoxic and cytostatic activities.

AREA COVERED

We summarize the literature on radio- and chemotherapy-mediated immunological effects in primary and secondary brain tumors and outline open questions within the field. To this end, a literature search was performed using the terms 'brain tumor', 'immune system', 'immunogenic cell death', 'vaccination', 'checkpoint inhibition', 'radiotherapy', 'chemotherapy' and derivations thereof. Expert commentary: Immunological effects of chemo- and radiotherapy in brain tumors involve direct immunogenic modulations of tumor cells, changes of the microenvironment and functional alterations of innate and adaptive immune cells. Each treatment modality can exert various effects that comprise both immune-stimulatory and immunosuppressive mechanisms. A detailed knowledge of these mechanisms is indispensable for an optimal combination of conventional anti-tumor treatments and novel immunotherapeutic approaches.

Human Leukocyte Antigen (HLA) Peptides Derived from Tumor Antigens Induced by Inhibition of DNA Methylation for Development of Drug-facilitated Immunotherapy

Treatment of cancer cells with anticancer drugs often fails to achieve complete remission. Yet, such drug treatments may induce alteration in the tumor's gene expression patterns, including those of Cancer/Testis Antigens (CTA). The degradation products of such antigens can be presented as HLA peptides on the surface of the tumor cells and be developed into anticancer immunotherapeutics. For example, the DNA methyl transferase inhibitor, 5-aza-2'-deoxycytidine (Decitabine) has limited antitumor efficacy, yet it induces the expression of many genes, including CTAs that are normally silenced in the healthy adult tissues. In this study, the presentation of many new HLA peptides derived from CTAs and induced by Decitabine was demonstrated in three human Glioblastoma cell lines. Such presentation of CTA-derived HLA peptides can be exploited for development of new treatment modalities, combining drug treatment with anti-CTA targeted immunotherapy. The Decitabine-induced HLA peptidomes include many CTAs that are not normally detected in healthy tissues or in cancer cells, unless treated with the drug. In addition, the study included large-scale analyses of the simultaneous effects of Decitabine on the transcriptomes, proteomes and HLA peptidomes of the human Glioblastoma cells. It demonstrates the poor correlations between these three levels of gene expression, both in their total levels and in their response to the drug. The proteomics and HLA peptidomics data are available via ProteomeXchange with identifier PXD003790 and the transcriptomics data are available via GEO with identifier GSE80137.

Immunotherapy of Brain Cancer

The brain has long been considered an immune-privileged site precluding potent immune responses. Nevertheless, because of the failure of conventional anti-cancer treatments to achieve sustained control of intracranial neoplasms, immunotherapy has been considered as a promising strategy for decades. However, several efforts aimed at exploiting the immune system as a therapeutic weapon were largely unsuccessful. The situation only changed with the introduction of the checkpoint inhibitors, which target immune cell receptors that interfere with the activation of immune effector cells. Following the observation of striking effects of drugs that target CTLA-4 or PD-1 against melanoma and other tumor entities, it was recognized that these drugs may also be active against metastatic tumor lesions in the brain. Their therapeutic activity against primary brain tumors is currently being investigated within clinical trials. In parallel, other immunotherapeutics such as peptide vaccines are at an advanced stage of clinical development. Further immunotherapeutic strategies currently under investigation comprise adoptive immune cell transfer as well as inhibitors of metabolic pathways involved in the local immunosuppression frequently found in brain tumors. Thus, the ongoing implementation of immunotherapeutic concepts into clinical routine may represent a powerful addition to the therapeutic arsenal against various brain tumors.

The Long and Winding Road: From the High-Affinity Choline Uptake Site to Clinical Trials for Malignant Brain Tumors

Malignant brain tumors are one of the most lethal cancers. They originate from glial cells which infiltrate throughout the brain. Current standard of care involves surgical resection, radiotherapy, and chemotherapy; median survival is currently ~14-20 months postdiagnosis. Given that the brain immune system is deficient in priming systemic immune responses to glioma antigens, we proposed to reconstitute the brain immune system to achieve immunological priming from within the brain. Two adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1-derived thymidine kinase which converts ganciclovir into a compound only cytotoxic to dividing glioma cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine that attracts dendritic cells to the brain. HSV-1/ganciclovir killing of tumor cells releases tumor antigens that are taken up by dendritic cells within the brain tumor microenvironment. Tumor killing also releases HMGB1, an endogenous TLR2 agonist that activates dendritic cells. HMGB1-activated dendritic cells, loaded with glioma antigens, migrate to cervical lymph nodes to stimulate a systemic CD8+ T cells cytotoxic immune response against glioma. This immune response is specific to glioma tumors, induces immunological memory, and does neither cause brain toxicity nor autoimmune responses. An IND was granted by the FDA on 4/7/2011. A Phase I, first in person trial, to test whether reengineering the brain immune system is potentially therapeutic is ongoing.

Pharmacotherapies for the treatment of glioblastoma - current evidence and perspectives

INTRODUCTION

Glioblastoma, the most common malignant brain tumor, exhibits a poor prognosis with little therapeutic progress in the last decade. Novel treatment strategies beyond the established standard of care with temozolomide-based radiotherapy are urgently needed.

AREAS COVERED

We reviewed the literature on glioblastoma with a focus on phase III trials for pharmacotherapies and/or innovative concepts until December 2015.

EXPERT OPINION

In the last decade, phase III trials on novel compounds largely failed to introduce efficacious pharmacotherapies beyond temozolomide in glioblastoma. So far, inhibition of angiogenesis by compounds such as bevacizumab, cediranib, enzastaurin or cilengitide as well as alternative dosing schedules of temozolomide did not prolong survival, neither at primary diagnosis nor at recurrent disease. Promising strategies of pharmacotherapy currently under evaluation represent targeting epidermal growth factor receptor (EGFR) with biomarker-stratified patient populations and immunotherapeutic concepts including checkpoint inhibition and vaccination. The clinical role of the medical device delivering 'tumor-treating fields' in newly diagnosed glioblastoma which prolonged overall survival in a phase III study has remained controversial. After failure of several phase III trials with previously promising agents, improvement of concepts and novel compounds are urgently needed to expand the still limited therapeutic options for the treatment of glioblastoma.