Imaging tryptophan uptake with positron emission tomography in glioblastoma patients treated with indoximod.

INTRODUCTION: Glioblastoma (GBM) is the most frequent and aggressive primary tumor of the central nervous system, accounting for over 50% of all primary malignant gliomas arising in the adult brain. Even after surgical resection, adjuvant radiotherapy (RT) and temozolomide (TMZ) chemotherapy, as well as tumor-treating fields, the median survival is only 15-20 months. We have identified a pathogenic mechanism that contributes to the tumor-induced immunosuppression in the form of increased indoleamine 2,3 dioxygenase 1 (IDO1) expression; an enzyme that metabolizes the essential amino acid, tryptophan (Trp), into kynurenine (Kyn). However, real-time measurements of IDO1 activity has yet to become mainstream in clinical protocols for assessing IDO1 activity in GBM patients. METHODS: Pre-treatment and on-treatment α-[11C]-methyl-L-Trp (AMT) positron emission tomography (PET) with co-registered MRI was performed on patients with recurrent GBM treated with the IDO1 pathway inhibitor indoximod (D1-MT) and TMZ. RESULTS: Regional intratumoral variability of AMT within enhancing and non-enhancing tumor was noted at baseline. On treatment imaging revealed decreased regional uptake suggesting IDO1 pathway modulation with treatment. CONCLUSIONS: Here, we have validated the ability to use PET of the Trp probe, AMT, for use in visualizing and quantifying intratumoral Trp uptake in GBM patients treated with an IDO1 pathway inhibitor. These data serve as rationale to utilize AMT-PET imaging in the future evaluation of GBM patients treated with IDO1 enzyme inhibitors.

Newly Diagnosed Glioblastoma: A Review on Clinical Management.

Glioblastoma is an aggressive primary tumor of the central nervous system. This review will focus on clinical developments and management of newly diagnosed disease, including a discussion about the incorporation of molecular features into the classification of glioblastoma. Such advances will continue to shape our thinking about the disease and how to best manage it. With regards to treatment, the role of surgical resection, radiotherapy, chemotherapy, and tumor-treating fields will be presented. Pivotal studies defining our current standard of care will be highlighted, as will key ongoing trials that may influence our management of glioblastoma in the near future.

Non-tumor cell IDO1 predominantly contributes to enzyme activity and response to CTLA-4/PD-L1 inhibition in mouse glioblastoma.

Glioblastoma (GBM) is the most common malignant brain tumor in adults with a median survival of 14.6months. A contributing factor to GBM aggressiveness is the intratumoral expression of the potently immunosuppressive enzyme, indoleamine 2,3 dioxygenase 1 (IDO1). The enzymatic activity of IDO1 is associated with the conversion of tryptophan into downstream kynurenine (Kyn), which has previously been hypothesized to contribute toward the suppression of tumor immunity. Utilizing the syngeneic, immunocompetent, intracranial GL261 cell GBM model, we previously demonstrated that tumor cell, but not non-tumor cell IDO1, suppresses T cell-mediated brain tumor regression in mice. Paradoxically, we also showed that the survival advantage mediated by immune checkpoint blockade is abrogated by non-tumor cell IDO1 deficiency. Here, we have built on our past observations and confirm the maladaptive role of tumor cell IDO1 in a novel mouse GBM model. We also demonstrate that, non-tumor cells, rather than mouse GBM cells, are the dominant contributor to IDO1-mediated enzyme activity. Finally, we show the novel associations between maximally-effective immune-checkpoint blockade-mediated survival, non-tumor cell IDO1 and intra-GBM Kyn levels. These data suggest for the first time that, GBM cell-mediated immunosuppression is IDO1 enzyme independent, while the survival benefits of immune checkpoint blockade require non-tumor cell IDO1 enzyme activity. Given that current clinical inhibitors vary in their mechanism of action, in terms of targeting IDO1 enzyme activity versus enzyme-independent effects, this work suggests that choosing an appropriate IDO1 pharmacologic will maximize the effectiveness of future immune checkpoint blockade approaches.

Dendritic Cell-Based Vaccines that Utilize Myeloid Rather than Plasmacytoid Cells Offer a Superior Survival Advantage in Malignant Glioma.

Dendritic cells (DCs) are professional APCs that are traditionally divided into two distinct subsets, myeloid DC (mDCs) and plasmacytoid DC (pDCs). pDCs are known for their ability to secrete large amounts of IFN-α. Apart from IFN-α production, pDCs can also process Ag and induce T cell immunity or tolerance. In several solid tumors, pDCs have been shown to play a critical role in promoting tumor immunosuppression. We investigated the role of pDCs in the process of glioma progression in the syngeneic murine model of glioma. We show that glioma-infiltrating pDCs are the major APC in glioma and are deficient in IFN-α secretion (p < 0.05). pDC depletion leads to increased survival of the mice bearing intracranial tumor by decreasing the number of regulatory T cells (Tregs) and by decreasing the suppressive capabilities of Tregs. We subsequently compared the ability of mDCs and pDCs to generate effective antiglioma immunity in a GL261-OVA mouse model of glioma. Our data suggest that mature pDCs and mDCs isolated from naive mice can be effectively activated and loaded with SIINFEKL Ag in vitro. Upon intradermal injection in the hindleg, a fraction of both types of DCs migrate to the brain and lymph nodes. Compared to mice vaccinated with pDC or control mice, mice vaccinated with mDCs generate a robust Th1 type immune response, characterized by high frequency of CD4(+)T-bet(+) T cells and CD8(+)SIINFEKEL(+) T cells. This robust antitumor T cell response results in tumor eradication and long-term survival in 60% of the animals (p < 0.001).

Updates from the Neuro-Oncology Section of the 2015 American Neurological Association Annual Meeting.

American Neurological Association Annual Meeting, Chicago, IL, USA, 27-29 September 2015 The American Neurological Association (ANA) held its annual meeting in Chicago, IL, USA on 27-29 September 2015. The Scientific Programming Advisory Committee was chaired by Dr. S Pleasure from the University of California-San Francisco (CA, USA). The Neuro-Oncology session, chaired by Dr. A Pruitt from the University of Pennsylvania (PA, USA) and cochaired by Dr. J Laterra from Johns Hopkins University (MD, USA), was held on 27 September 2015. Speakers included Dr. D Wainwright (Northwestern University, IL, USA), Dr. N Kolb (University of Utah, UT, USA), Dr. A Nath (NINDS/NIH, MD, USA), Dr. D Franz (Cincinnati Children's Hospital, OH, USA) and Dr. R Lukas (University of Chicago, IL, USA). A summary of key presentations from the Neuro-Oncology section of the 2015 American Neurological Association annual meeting is reported. Preclinical and clinical advances in the use of immunotherapies for the treatment of primary and metastatic CNS tumors are covered. Particular attention is paid to the enzyme indoleamine dioxygenase and the immune checkpoints CTLA4 and PD1 and their ligands. Specific nervous system toxicities associated with novel immunotherapies are also discussed. The recent success of targeting the mTOR pathway in the neurocutaneous syndrome tuberous sclerosis is detailed. Finally, important early steps in our understanding of the common toxicity of chemotherapy induced neuropathy are reviewed.

The role of IDO in brain tumor immunotherapy.

Malignant glioma comprises the majority of primary brain tumors. Coincidently, most of those malignancies express an inducible tryptophan catabolic enzyme, indoleamine 2,3 dioxygenase 1 (IDO1). While IDO1 is not normally expressed at appreciable levels in the adult central nervous system, it's rapidly induced and/or upregulated upon inflammatory stimulus. The primary function of IDO1 is associated with conversion of the essential amino acid, tryptophan, into downstream catabolites known as kynurenines. The depletion of tryptophan and/or accumulation of kynurenine has been shown to induce T cell deactivation, apoptosis and/or the induction of immunosuppressive programming via the expression of FoxP3. This understanding has informed immunotherapeutic design for the strategic development of targeted molecular therapeutics that inhibit IDO1 activity. Here, we review the current knowledge of IDO1 in brain tumors, pre-clinical studies targeting this enzymatic pathway, alternative tryptophan catabolic mediators that compensate for IDO1 loss and/or inhibition, as well as proposed clinical strategies and questions that are critical to address for increasing future immunotherapeutic effectiveness in patients with incurable brain cancer.

Blood-brain barrier permeable gold nanoparticles: an efficient delivery platform for enhanced malignant glioma therapy and imaging.

The blood-brain barrier (BBB) remains a formidable obstacle in medicine, preventing efficient penetration of chemotherapeutic and diagnostic agents to malignant gliomas. Here, a transactivator of transcription (TAT) peptide-modified gold nanoparticle platform (TAT-Au NP) with a 5 nm core size is demonstrated to be capable of crossing the BBB efficiently and delivering cargoes such as the anticancer drug doxorubicin (Dox) and Gd(3+) contrast agents to brain tumor tissues. Treatment of mice bearing intracranial glioma xenografts with pH-sensitive Dox-conjugated TAT-Au NPs via a single intravenous administration leads to significant survival benefit when compared to the free Dox. Furthermore, it is demonstrated that TAT-Au NPs are capable of delivering Gd(3+) chelates for enhanced brain tumor imaging with a prolonged retention time of Gd(3+) when compared to the free Gd(3+) chelates. Collectively, these results show promising applications of the TAT-Au NPs for enhanced malignant brain tumor therapy and non-invasive imaging.

Anti-aquaporin-4 immunoglobulin G/anti-myelin oligodendrocyte glycoprotein immunoglobulin G double-positive paraneoplastic neurological syndrome in a patient with triple-negative breast cancer.

We report a rare case of paraneoplastic neurological syndrome with dual seropositivity of anti-aquaporin-4 and myelin oligodendrocyte glycoprotein antibodies in a 40 year-old woman with metastatic triple-negative breast cancer. She received multiple lines of anti-neoplastic treatment, including immunotherapy with pembrolizumab, as well as cytotoxic chemotherapy. Paraneoplastic meningoencephalomyelitis developed 2 years after diagnosis of breast cancer and 1 year after discontinuation of immunotherapy with pembrolizumab. She first developed longitudinally extending transverse myelitis followed by left optic neuritis and meningoencephalitis with new enhancing lesions in the brain and spinal leptomeninges. Cerebrospinal fluid analysis during both episodes showed normal glucose and protein, and elevated white blood cell count. Cytology was negative for malignancy. Cerebrospinal fluid was positive for neuromyelitis optica immunoglobulin G antibody anti-aquaporin-4, and autoimmune myelopathy panel was positive for myelin oligodendrocyte glycoprotein antibody. The patient had significant clinical and radiographic improvement after completion of five cycles of plasmapheresis followed by intravenous immunoglobulin. She did not have recurrence of paraneoplastic syndrome with maintenance rituximab every 6 months and daily low-dose prednisone. She succumbed to progressive systemic metastatic disease 4.5 years after her breast cancer diagnosis. This case shows that these antibodies can occur concurrently and cause clinical features, such as both neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein antibody disease, in a patient with a singular type of cancer. We highlight the importance of testing for paraneoplastic etiology in cancer patients with radiographic menigoencephalomyelitis or meningitis with atypical symptoms of meningeal carcinomatosis and/or cerebrospinal fluid profile negative for leptomeningeal carcinomatosis.

CD8+ T cells sustain antitumor response by mediating crosstalk between adenosine A2A receptor and glutathione/GPX4.

Antitumor responses of CD8+ T cells are tightly regulated by distinct metabolic fitness. High levels of glutathione (GSH) are observed in the majority of tumors, contributing to cancer progression and treatment resistance in part by preventing glutathione peroxidase 4-dependent (GPX4-dependent) ferroptosis. Here, we show the necessity of adenosine A2A receptor (A2AR) signaling and the GSH/GPX4 axis in orchestrating metabolic fitness and survival of functionally competent CD8+ T cells. Activated CD8+ T cells treated ex vivo with simultaneous inhibition of A2AR and lipid peroxidation acquire a superior capacity to proliferate and persist in vivo, demonstrating a translatable means to prevent ferroptosis in adoptive cell therapy. Additionally, we identify a particular cluster of intratumoral CD8+ T cells expressing a putative gene signature of GSH metabolism (GMGS) in association with clinical response and survival across several human cancers. Our study addresses a key role of GSH/GPX4 and adenosinergic pathways in fine-tuning the metabolic fitness of antitumor CD8+ T cells.

Lactate dehydrogenase A regulates tumor-macrophage symbiosis to promote glioblastoma progression.

Abundant macrophage infiltration and altered tumor metabolism are two key hallmarks of glioblastoma. By screening a cluster of metabolic small-molecule compounds, we show that inhibiting glioblastoma cell glycolysis impairs macrophage migration and lactate dehydrogenase inhibitor stiripentol emerges as the top hit. Combined profiling and functional studies demonstrate that lactate dehydrogenase A (LDHA)-directed extracellular signal-regulated kinase (ERK) pathway activates yes-associated protein 1 (YAP1)/ signal transducer and activator of transcription 3 (STAT3) transcriptional co-activators in glioblastoma cells to upregulate C-C motif chemokine ligand 2 (CCL2) and CCL7, which recruit macrophages into the tumor microenvironment. Reciprocally, infiltrating macrophages produce LDHA-containing extracellular vesicles to promote glioblastoma cell glycolysis, proliferation, and survival. Genetic and pharmacological inhibition of LDHA-mediated tumor-macrophage symbiosis markedly suppresses tumor progression and macrophage infiltration in glioblastoma mouse models. Analysis of tumor and plasma samples of glioblastoma patients confirms that LDHA and its downstream signals are potential biomarkers correlating positively with macrophage density. Thus, LDHA-mediated tumor-macrophage symbiosis provides therapeutic targets for glioblastoma.

Aging amplifies a gut microbiota immunogenic signature linked to heightened inflammation.

Aging is associated with low-grade inflammation that increases the risk of infection and disease, yet the underlying mechanisms remain unclear. Gut microbiota composition shifts with age, harboring microbes with varied immunogenic capacities. We hypothesized the gut microbiota acts as an active driver of low-grade inflammation during aging. Microbiome patterns in aged mice strongly associated with signs of bacterial-induced barrier disruption and immune infiltration, including marked increased levels of circulating lipopolysaccharide (LPS)-binding protein (LBP) and colonic calprotectin. Ex vivo immunogenicity assays revealed that both colonic contents and mucosa of aged mice harbored increased capacity to activate toll-like receptor 4 (TLR4) whereas TLR5 signaling was unchanged. We found patterns of elevated innate inflammatory signaling (colonic Il6, Tnf, and Tlr4) and endotoxemia (circulating LBP) in young germ-free mice after 4 weeks of colonization with intestinal contents from aged mice compared with young counterparts, thus providing a direct link between aging-induced shifts in microbiota immunogenicity and host inflammation. Additionally, we discovered that the gut microbiota of aged mice exhibited unique responses to a broad-spectrum antibiotic challenge (Abx), with sustained elevation in Escherichia (Proteobacteria) and altered TLR5 immunogenicity 7 days post-Abx cessation. Together, these data indicate that old age results in a gut microbiota that differentially acts on TLR signaling pathways of the innate immune system. We found that these age-associated microbiota immunogenic signatures are less resilient to challenge and strongly linked to host inflammatory status. Gut microbiota immunogenic signatures should be thus considered as critical factors in mediating chronic inflammatory diseases disproportionally impacting older populations.

NKG2C/KLRC2 tumor cell expression enhances immunotherapeutic efficacy against glioblastoma.

BACKGROUND: Activating and inhibitory receptors of natural killer (NK) cells such as NKp, NKG2, or CLEC are highly relevant to cold tumors including glioblastoma (GBM). Here, we aimed to characterize the expression of these receptors in GBM to gain insight into their potential role as modulators of the intratumoral microenvironment. METHODS: We performed a transcriptomic analysis of several NK receptors with a focus on the activating receptor encoded by KLRC2, NKG2C, among bulk and single-cell RNA sequencing GBM data sets. We also evaluated the effects of KLRC2-overexpressing GL261 cells in mice treated with or without programmed cell death protein-1 (PD-1) monoclonal antibody (mAb). Finally, we analyzed samples from two clinical trials evaluating PD-1 mAb effects in patients with GBM to determine the potential of NKG2C to serve as a biomarker of response. RESULTS: We observed significant expression of several inhibitory NK receptors on GBM-infiltrating NK and T cells, which contrasts with the strong expression of KLRC2 on tumor cells, mainly at the infiltrative margin. Neoplastic KLRC2 expression was associated with a reduction in the number of myeloid-derived suppressor cells and with a higher level of tumor-resident lymphocytes. A stronger antitumor activity after PD-1 mAb treatment was observed in NKG2Chigh-expressing tumors both in mouse models and patients with GBM whereas the expression of inhibitory NK receptors showed an inverse association. CONCLUSIONS: This study explored the role of neoplastic NKG2C/KLRC2 expression in shaping the immune profile of GBM and suggests that it is a predictive biomarker for positive responses to immune checkpoint inhibitor treatment in patients with GBM. Future studies could further validate this finding in prospective trials.

Age-stratified comorbid and pharmacologic analysis of patients with glioblastoma.

Background: Increased age is a strong and unfavorable prognostic factor for patients with glioblastoma (GBM). However, the relationships between stratified patient age, comorbidities, and medications have yet to be explored in GBM patient survival analyses. Objective: To evaluate co-morbid conditions, tumor-related symptoms, medication prescriptions, and subject age for patients with GBM and to establish potential targets for prospective studies. Methods: Electronic health records for 565 patients with IDHwt GBM were evaluated at a single center between January 1, 2000 and August 9, 2021 were retrospectively assessed. Data were stratified by MGMT promoter methylation status when available and were used to construct multivariable time-dependent cox models and intra-cohort hazards. Results: Younger (<65 years of age) but not older (≥65 years) GBM patients demonstrated a worse prognosis with movement related disabilities (P < 0.0001), gait/balance difficulty (P = 0.04) and weakness (P = 0.007), as well as psychiatric conditions, mental health disorders (P = 0.002) and anxiety (P = 0.001). In contrast, older but not younger GBM patients demonstrated a worse prognosis with epilepsy (P = 0.039). Both groups had worse survival with confusion/altered mental status (P = 0.023 vs < 0.000) and an improved survival with a Temozolomide prescription. Older but not younger GBM patients experienced an improved hazard with a prescription of ace-inhibitor medications (P = 0.048). Conclusion: Age-dependent novel associations between clinical symptoms and medications prescribed for co-morbid conditions were demonstrated in patients with GBM. The results of the current work support future mechanistic studies that investigate the negative relationship(s) between increased age, comorbidities, and drug therapies for differential clinical decision-making across the lifespan of patients with GBM.

Characterization and immunotherapeutic implications for a novel antibody targeting interleukin (IL)-13 receptor α2.

The high affinity interleukin-13 receptor α2 (IL13Rα2) is selectively expressed at a high frequency by glioblastoma multiforme (GBM) as well as several other tumor types. One approach for targeting this tumor-specific receptor utilizes the cognate ligand, IL-13, conjugated to cytotoxic molecules. However, this approach lacks specificity because the lower affinity receptor for IL-13, IL13Rα1, is widely expressed by normal tissues. Here, we aimed to develop and characterize a novel monoclonal antibody (mAb) specific to IL13Rα2 for the therapeutic purpose of targeting IL13Rα2-expressing tumors. Hybridoma cell lines were generated and compared for binding affinities to recombinant human IL13Rα2 (rhIL13Rα2). Clone 47 demonstrated binding to the native conformation of IL13Rα2 and was therefore chosen for further studies. Clone 47 bound specifically and with high affinity (K(D) = 1.39 × 10(-9) M) to rhIL13Rα2 but not to rhIL13Rα1 or murine IL13Rα2. Furthermore, clone 47 specifically recognized wild-type IL13Rα2 expressed on the surface of CHO and HEK cells as well as several glioma cell lines. Competitive binding assays revealed that clone 47 also significantly inhibited the interaction between human soluble IL-13 and IL13Rα2 receptor. Moreover, we found that N-linked glycosylation of IL13Rα2 contributes in part to the interaction of the antibody to IL13Rα2. In vivo, the IL13Rα2 mAb improved the survival of nude mice intracranially implanted with a human U251 glioma xenograft. Collectively, these data warrant further investigation of this novel IL13Rα2 mAb with an emphasis on translational implications for therapeutic use.

Nanoparticle-programmed self-destructive neural stem cells for glioblastoma targeting and therapy.

A 3-step glioblastoma-tropic delivery and therapy method using nanoparticle programmed self-destructive neural stem cells (NSCs) is demonstrated in vivo: 1) FDA-approved NSCs for clinical trials are loaded with pH-sensitive MSN-Dox; 2) the nanoparticle conjugates provide a delayed drug-releasing mechanism and allow for NSC migration towards a distant tumor site; 3) NSCs eventually undergo cell death and release impregnated MSN-Dox, which subsequently induces toxicity towards surrounding glioma cells.

LDHA-regulated tumor-macrophage symbiosis promotes glioblastoma progression.

Abundant macrophage infiltration and altered tumor metabolism are two key hallmarks of glioblastoma. By screening a cluster of metabolic small-molecule compounds, we show that inhibiting glioblastoma cell glycolysis impairs macrophage migration and lactate dehydrogenase (LDH) inhibitor stiripentol (an FDA-approved anti-seizure drug for Dravet Syndrome) emerges as the top hit. Combined profiling and functional studies demonstrate that LDHA-directed ERK pathway activates YAP1/STAT3 transcriptional co-activators in glioblastoma cells to upregulate CCL2 and CCL7, which recruit macrophages into the tumor microenvironment. Reciprocally, infiltrating macrophages produce LDHA-containing extracellular vesicles to promote glioblastoma cell glycolysis, proliferation, and survival. Genetic and pharmacological inhibition of LDHA-mediated tumor-macrophage symbiosis markedly suppresses tumor progression and macrophage infiltration in glioblastoma mouse models. Analysis of tumor and plasma samples of glioblastoma patients confirms that LDHA and its downstream signals are potential biomarkers correlating positively with macrophage density. Thus, LDHA-mediated tumor-macrophage symbiosis provides therapeutic targets for glioblastoma.

Advanced Age in Humans and Mouse Models of Glioblastoma Show Decreased Survival from Extratumoral Influence.

PURPOSE: Glioblastoma (GBM) is the most common aggressive primary malignant brain tumor in adults with a median age of onset of 68 to 70 years old. Although advanced age is often associated with poorer GBM patient survival, the predominant source(s) of maladaptive aging effects remains to be established. Here, we studied intratumoral and extratumoral relationships between adult patients with GBM and mice with brain tumors across the lifespan. EXPERIMENTAL DESIGN: Electronic health records at Northwestern Medicine and the NCI SEER databases were evaluated for GBM patient age and overall survival. The commercial Tempus and Caris databases, as well as The Cancer Genome Atlas were profiled for gene expression, DNA methylation, and mutational changes with varying GBM patient age. In addition, gene expression analysis was performed on the extratumoral brain of younger and older adult mice with or without a brain tumor. The survival of young and old wild-type or transgenic (INK-ATTAC) mice with a brain tumor was evaluated after treatment with or without senolytics and/or immunotherapy. RESULTS: Human patients with GBM ≥65 years of age had a significantly decreased survival compared with their younger counterparts. While the intra-GBM molecular profiles were similar between younger and older patients with GBM, non-tumor brain tissue had a significantly different gene expression profile between young and old mice with a brain tumor and the eradication of senescent cells improved immunotherapy-dependent survival of old but not young mice. CONCLUSIONS: This work suggests a potential benefit for combining senolytics with immunotherapy in older patients with GBM.

CD4+ T cell-mediated neuroprotection is independent of T cell-derived BDNF in a mouse facial nerve axotomy model.

BACKGROUND: The production of neurotrophic factors, such as BDNF, has generally been considered an important mechanism of immune-mediated neuroprotection. However, the ability of T cells to produce BDNF remains controversial. METHODS: In the present study, we examined mRNA and protein of BDNF using RT-PCR and western blot, respectively, in purified and reactivated CD4(+) T cells. In addition, to determine the role of BDNF derived from CD4(+) T cells, the BDNF gene was specifically deleted in T cells using the Cre-lox mouse model system. RESULTS: Our results indicate that while both mRNA expression and protein secretion of BDNF in reactivated T cells were detected at 24 h, only protein could be detected at 72 h after reactivation. The results suggest a transient up-regulation of BDNF mRNA in reactivated T cells. Furthermore, in contrast to our hypothesis that the BDNF expression is necessary for CD4(+) T cells to mediate neuroprotection, mice with CD4(+) T cells lacking BDNF expression demonstrated a similar level of facial motoneuron survival compared to their littermates that expressed BDNF, and both levels were comparable to wild-type. The results suggest that the deletion of BDNF did not impair CD4(+) T cell-mediated neuroprotection. CONCLUSION: Collectively, while CD4(+) T cells are a potential source of BDNF after nerve injury, production of BDNF is not necessary for CD4(+) T cells to mediate their neuroprotective effects.

Recent developments on immunotherapy for brain cancer.

INTRODUCTION: Brain tumors are a unique class of cancers since they are anatomically shielded from normal immunosurveillance by the blood-brain barrier, lack a normal lymphatic drainage system and reside in a potently immunosuppressive environment. Of the primary brain cancers, glioblastoma multiforme (GBM) is the most common and aggressive in adults. Although treatment options include surgery, radiation and chemotherapy, the average lifespan of GBM patients remains at only 14.6 months post-diagnosis. AREAS COVERED: A review of key cellular and molecular immune system mediators in the context of brain tumors including TGF-ß, cytotoxic T cells, Tregs, CTLA-4, PD-1 and IDO is discussed. In addition, prognostic factors, currently utilized immunotherapeutic strategies, ongoing clinical trials and a discussion of new or potential immunotherapies for brain tumor patients are considered. EXPERT OPINION: Current drugs that improve the quality of life and overall survival in patients with brain tumors, especially for GBM, are poorly effective. This disease requires a reanalysis of currently accepted treatment strategies, as well as newly designed approaches. Here, we review the fundamental aspects of immunosuppression in brain tumors, new and promising immunotherapeutic drugs as well as combinatorial strategies that focus on the simultaneous inhibition of immunosuppressive hubs, both in immune and brain tumor cells, which is critical to consider for achieving future success for the treatment of this devastating disease.

Next Steps for Immunotherapy in Glioblastoma.

Outcomes for glioblastoma (GBM) patients undergoing standard of care treatment remain poor. Here we discuss the portfolio of previously investigated immunotherapies for glioblastoma, including vaccine therapy and checkpoint inhibitors, as well as novel emerging therapeutic approaches. In addition, we explore the factors that potentially influence response to immunotherapy, which should be considered in future research aimed at improving immunotherapy efficacy.