Isocitrate dehydrogenase mutations suppress STAT1 and CD8+ T cell accumulation in gliomas.

Mutations in the isocitrate dehydrogenase genes IDH1 and IDH2 are among the first genetic alterations observed during the development of lower-grade glioma (LGG). LGG-associated IDH mutations confer gain-of-function activity by converting α-ketoglutarate to the oncometabolite R-2-hydroxyglutarate (2HG). Clinical samples and gene expression data from The Cancer Genome Atlas (TCGA) demonstrate reduced expression of cytotoxic T lymphocyte-associated genes and IFN-γ-inducible chemokines, including CXCL10, in IDH-mutated (IDH-MUT) tumors compared with IDH-WT tumors. Given these findings, we have investigated the impact of IDH mutations on the immunological milieu in LGG. In immortalized normal human astrocytes (NHAs) and syngeneic mouse glioma models, the introduction of mutant IDH1 or treatment with 2HG reduced levels of CXCL10, which was associated with decreased production of STAT1, a regulator of CXCL10. Expression of mutant IDH1 also suppressed the accumulation of T cells in tumor sites. Reductions in CXCL10 and T cell accumulation were reversed by IDH-C35, a specific inhibitor of mutant IDH1. Furthermore, IDH-C35 enhanced the efficacy of vaccine immunotherapy in mice bearing IDH-MUT gliomas. Our findings demonstrate a mechanism of immune evasion in IDH-MUT gliomas and suggest that specific inhibitors of mutant IDH may improve the efficacy of immunotherapy in patients with IDH-MUT gliomas.

Induction of robust type-I CD8+ T-cell responses in WHO grade 2 low-grade glioma patients receiving peptide-based vaccines in combination with poly-ICLC.

PURPOSE: WHO grade 2 low-grade gliomas (LGG) with high risk factors for recurrence are mostly lethal despite current treatments. We conducted a phase I study to evaluate the safety and immunogenicity of subcutaneous vaccinations with synthetic peptides for glioma-associated antigen (GAA) epitopes in HLA-A2(+) adults with high-risk LGGs in the following three cohorts: (i) patients without prior progression, chemotherapy, or radiotherapy (RT); (ii) patients without prior progression or chemotherapy but with prior RT; and (iii) recurrent patients. EXPERIMENTAL DESIGN: GAAs were IL13Rα2, EphA2, WT1, and Survivin. Synthetic peptides were emulsified in Montanide-ISA-51 and given every 3 weeks for eight courses with intramuscular injections of poly-ICLC, followed by q12 week booster vaccines. RESULTS: Cohorts 1, 2, and 3 enrolled 12, 1, and 10 patients, respectively. No regimen-limiting toxicity was encountered except for one case with grade 3 fever, fatigue, and mood disturbance (cohort 1). ELISPOT assays demonstrated robust IFNγ responses against at least three of the four GAA epitopes in 10 and 4 cases of cohorts 1 and 3, respectively. Cohort 1 patients demonstrated significantly higher IFNγ responses than cohort 3 patients. Median progression-free survival (PFS) periods since the first vaccine are 17 months in cohort 1 (range, 10-47+) and 12 months in cohort 3 (range, 3-41+). The only patient with large astrocytoma in cohort 2 has been progression-free for more than 67 months since diagnosis. CONCLUSION: The current regimen is well tolerated and induces robust GAA-specific responses in WHO grade 2 glioma patients. These results warrant further evaluations of this approach. Clin Cancer Res; 21(2); 286-94. ©2014 AACR.

Immune-checkpoint blockade and active immunotherapy for glioma.

Cancer immunotherapy has made tremendous progress, including promising results in patients with malignant gliomas. Nonetheless, the immunological microenvironment of the brain and tumors arising therein is still believed to be suboptimal for sufficient antitumor immune responses for a variety of reasons, including the operation of "immune-checkpoint" mechanisms. While these mechanisms prevent autoimmunity in physiological conditions, malignant tumors, including brain tumors, actively employ these mechanisms to evade from immunological attacks. Development of agents designed to unblock these checkpoint steps is currently one of the most active areas of cancer research. In this review, we summarize recent progresses in the field of brain tumor immunology with particular foci in the area of immune-checkpoint mechanisms and development of active immunotherapy strategies. In the last decade, a number of specific monoclonal antibodies designed to block immune-checkpoint mechanisms have been developed and show efficacy in other cancers, such as melanoma. On the other hand, active immunotherapy approaches, such as vaccines, have shown encouraging outcomes. We believe that development of effective immunotherapy approaches should ultimately integrate those checkpoint-blockade agents to enhance the efficacy of therapeutic approaches. With these agents available, it is going to be quite an exciting time in the field. The eventual success of immunotherapies for brain tumors will be dependent upon not only an in-depth understanding of immunology behind the brain and brain tumors, but also collaboration and teamwork for the development of novel trials that address multiple layers of immunological challenges in gliomas.

Soluble factors secreted by glioblastoma cell lines facilitate recruitment, survival, and expansion of regulatory T cells: implications for immunotherapy.

In patients with glioma, the tumor microenvironment can significantly impact pro-inflammatory immune cell functions. However, the mechanisms by which this occurs are poorly defined. Because immunosuppressive regulatory T cells (Treg) are over represented in the tumor microenvironment compared with peripheral blood, we hypothesized that the tumor may have an effect on Treg survival, migration, expansion, and/or induction of a regulatory phenotype from non-Treg conventional CD4+ T cells. We defined the impact of soluble factors produced by tumor cells on Treg from healthy patients in vitro to determine mechanisms by which gliomas influence T cell populations. We found that tumor-derived soluble factors allowed for preferential proliferation and increased chemotaxis of Treg, compared with conventional T cells, indicating that these mechanisms may contribute to the increased Treg in the tumor microenvironment. Conventional T cells also exhibited a significantly increased expression of pro-apoptotic transcripts in the presence of tumor-derived factors, indicating that survival of Treg in the tumor site is driven by exposure to soluble factors produced by the tumor. Together, these data suggest that tumor burden may induce increased Treg infiltration, proliferation, and survival, negating productive anti-tumor immune responses in patients treated with immunotherapies. Collectively, our data indicate that several mechanisms of Treg recruitment and retention in the tumor microenvironment exist and may need to be addressed to improve the specificity of immunotherapies seeking to eliminate Treg in patients with glioma.

The complement cascade as a mediator of tissue growth and regeneration.

Recent evidence has demonstrated that the complement cascade is involved in a variety of physiologic and pathophysiologic processes in addition to its role as an immune effector. Research in a variety of organ systems has shown that complement proteins are direct participants in maintenance of cellular turnover, healing, proliferation and regeneration. As a physiologic housekeeper, complement proteins maintain tissue integrity in the absence of inflammation by disposing of cellular debris and waste, a process critical to the prevention of autoimmune disease. Developmentally, complement proteins influence pathways including hematopoietic stem cell engraftment, bone growth, and angiogenesis. They also provide a potent stimulus for cellular proliferation including regeneration of the limb and eye in animal models, and liver proliferation following injury. Here, we describe the complement cascade as a mediator of tissue growth and regeneration.

TGF-beta downregulates the activating receptor NKG2D on NK cells and CD8+ T cells in glioma patients.

The activating receptor NKG2D, expressed by natural killer (NK) cells and CD8(+) T cells, has a role in the specific killing of transformed cells. We examined NKG2D expression in patients with glioblastoma multiforme and found that NKG2D was downregulated on NK cells and CD8(+) T cells. Expression of NKG2D on lymphocytes significantly increased following tumor resection and correlated with an increased ability to kill NKG2D ligand-positive tumor targets. Despite the presence of soluble NKG2D ligands in the sera of glioblastoma patients, NKG2D downregulation was primarily caused by tumor-derived tumor growth factor-beta, suggesting that blocking of this cytokine may have therapeutic benefit.

Clinical characteristics and outcomes for a modern series of primary gliosarcoma patients.

BACKGROUND: Primary gliosarcoma (PGS) is a rare central nervous system tumor with limited experience reported in the literature. In the current study, the authors present a modern series of confirmed PGS cases treated in the era of magnetic resonance imaging (MRI), after the accepted glioblastoma management of resection, radiation, and temozolomide. METHODS: Using a retrospective review, patients with confirmed PGS were identified (1996-2008). Cases were determined to be PGS by central pathology review using the 2007 World Health Organization criteria. Extensive chart review was performed to gather clinical and pathologic data on these cases. RESULTS: All but 1 patient had undergone a preoperative MRI, with 1 patient receiving a computed tomography scan due to a cardiac pacemaker. A total of 10 patients received radiotherapy with concurrent and adjuvant temozolomide chemotherapy, and 8 patients received radiotherapy alone or in combination with other chemotherapeutic agents. In 2 patients, the history of adjuvant treatment could not be confirmed. The overall median survival was 13.9 months (range, 2.2-22.9 months). Patients with gliosarcomas resembling meningioma were found to have a significantly prolonged median survival compared with patients harboring gliosarcoma resembling glioblastoma multiforme (16 months vs 9.6 months; P = .011). However, no difference in survival was noted between patients who received concurrent radiotherapy and temozolomide compared with those who did not (10.4 months vs 13.9 months; P = .946). CONCLUSIONS: The results of the current study support previous hypotheses that there are 2 distinct types of PGS. The type mimicking the appearance of a meningioma appears to carry a significantly more favorable prognosis, most likely due to an increased chance at achieving macroscopic total resection.

Cranial chondrosarcoma and recurrence.

The literature regarding recurrences in patients with cranial chondrosarcoma is limited to small series performed at single institutions, raising the question if these data precisely reflect the true recurrence of this tumor for guiding the clinician in the management of these patients. An extensive systematic review of the English literature was performed. The patients were stratified according to treatment modality, treatment history, histological subtype, and histological grade, and the recurrence rates were analyzed. A total of 560 patients treated for cranial chondrosarcoma were included. Five-year recurrence rate among all patients was 22% with median follow-up of 60 months and median disease-free interval of 16 months. Tumor recurrence was more common in patients who only received surgery or had mesenchymal subtype tumors. Our systematic review closely reflects the actuarial recurrence rate and provides predictive factors in the recurrence of cranial chondrosarcoma.

Secondary gliosarcoma after diagnosis of glioblastoma: clinical experience with 30 consecutive patients.

OBJECT: Gliosarcoma can arise secondarily, after conventional adjuvant treatment of high-grade glioma. The current literature on the occurrence of secondary gliosarcoma (SGS) after glioblastoma multiforme (GBM) is limited, with only 12 reported cases. The authors present a large series of histologically confirmed SGSs, with follow-up to describe the clinical and radiological presentation, pathological diagnosis, and treatment outcomes. METHODS: Gliosarcoma cases were identified using the University of California, San Francisco's Departments of Neurological Surgery and Neuropathology databases. Through a retrospective chart review, cases of gliosarcoma were considered SGS if the following inclusion criteria were met: 1) the patient had a previously diagnosed intracranial malignant glioma that did not have gliosarcoma components; and 2) the histopathological tissue diagnosis of the recurrence confirmed gliosarcoma according to the most current WHO criteria. Extensive review of clinical, surgical, and pathology notes was performed to gather clinical and pathological data on these cases. RESULTS: Thirty consecutive patients in whom SGS had been diagnosed between 1996 and 2008 were included in the analysis. All patients had previously received a diagnosis of malignant glioma. For the initial malignant glioma, all patients underwent resection, and 25 patients received both external-beam radiation and chemotherapy. Three patients received radiotherapy alone, 1 patient was treated with chemotherapy alone, and 1 patient's tumor rapidly recurred as gliosarcoma, requiring surgical intervention prior to initiation of adjuvant therapy. The median time from diagnosis of the initial tumor to diagnosis of gliosarcoma was 8.5 months (range 0.5-25 months). All but 1 patient (who only had a biopsy) underwent a second operation for gliosarcoma; 8 patients went on to receive radiotherapy (4 had brachytherapy, 3 had external-beam radiation, and 1 had Gamma Knife surgery); and 14 patients received additional chemotherapy. The median length of survival from the time of gliosarcoma diagnosis was 4.4 months (range 0.7-46 months). The median survival from the time of the original GBM diagnosis was 12.6 months (range 5.7-47.4 months). Patients who had received concurrent and adjuvant temozolomide for GBM had worse outcomes than those who had not (4.3 and 10.5 months, respectively; p = 0.045). There was no difference in time to diagnosis of gliosarcoma in these 2 groups (8 and 8.5 months; p = 0.387). Two patients who had not received radiation therapy for GBM had an anecdotally very prolonged survival (20.9 and 46.4 months). CONCLUSIONS: The data underscore the difficulty associated with management of this disease. The strikingly poor survival of patients with SGS who had previously received combined radiation and temozolomide chemotherapy for GBM may reflect a unique molecular profile of GBM that eventually recurs as SGS. Further work will be required, controlling for multiple prognostic factors with larger numbers of patients.

Gamma interferon-mediated superinduction of B7-H1 in PTEN-deficient glioblastoma: a paradoxical mechanism of immune evasion.

B7 homolog 1 (B7-H1) is a recently discovered immunoresistance protein that is regulated posttranscriptionally after PTEN loss in malignant glioma, a deadly form of brain tumor. Here, the impact of gamma-interferon-mediated activation of B7-H1 was investigated in glioblastoma patients with PTEN loss. Lymphocytes and T cells were selected for apoptosis assays after 1 : 1 coculture with autologous glioma cells. Gamma interferon treatment of PTEN-deficient tumors resulted in superinduction of B7-H1 protein that correlated with increased T-cell apoptosis, an effect dependent upon activation of the PI3-kinase pathway. The combination of PTEN loss and gamma-interferon exposure in glioblastoma patients results in an exceptionally immunoresistant phenotype that may negate adaptive immunity through induction of T-cell apoptosis.

A systematic review of intracranial chondrosarcoma and survival.

Most data regarding survival in patients with chondrosarcoma are limited to case studies and small series performed at single institutions. A systematic review was performed to study the relationship between potential prognostic factors and survival. The survival rates were analyzed according to modality of treatment, treatment history, histological subtype, and histological grade. A total of 560 patients with intracranial chondrosarcoma were analyzed. Median follow-up time was 60 months. The 5-year mortality among all patients was 11.5% with median survival of 24 months. Mortality at 5 years was significantly greater for patients with tumors of higher grade, or of the mesenchymal subtype, or who had received surgical resection alone. The results of our systematic review provide useful data in predicting survival among intracranial chondrosarcoma patients.