Inflammatory leukocytes associated with increased immunosuppression by glioblastoma

BAMBI promotes macrophage proliferation and differentiation in gliomas

The present study investigated the capacity of Bone morphogenic protein and activin membrane‑bound inhibitor homolog (BAMBI) to regulate the migration and differentiation of macrophages in gliomas. Using a migration assay, it was determined that BAMBI stimulated monocytes migration in a dose‑dependent effect. When induced by phorbol myristate acetate (PMA) the monocytes differentiated into macrophages, and BAMBI also increased the migration of PMA‑induced macrophages compared with control cells. The expression of CD68 and BAMBI protein and mRNA in glioma and normal specimens were detected using immunohistochemistry and reverse transcription‑quantitative polymerase chain reaction, respectively. The localization of BAMBI was primarily in macrophages, as demonstrated by staining for the macrophage marker CD68, and the mRNA expression of CD68 and BAMBI were higher in gliomas compared to normal tissues. In addition, the mRNA expression of CD68 and BAMBI were positively correlated (R2=0.64). After treatment with 50 nM PMA and 10 nM BAMBI for 48 h, RAW 264.7 macrophages were exhibited dendrite‑like morphology, indicating that the co‑treatment promoted the differentiation of monocytes to macrophages. The expression of specific markers of M1 [inducible nitric oxide synthase (iNOS) and interleukin (IL)-12] and M2 (IL-10 and arginase 1) type macrophages was determined following 10 nM BAMBI treatment. BAMBI promoted the expression of M1 markers, whereas the M2 markers were not affected, which indicated that BAMBI induced differentiation of M1 type macrophages. These results indicate that BAMBI may be involved in macrophage differentiation in gliomas.

Resistance to cytotoxicity and sustained release of interleukin-6 and interleukin-8 in the presence of decreased interferon-γ after differentiation of glioblastoma by human natural killer cells

Natural killer (NK) cells are functionally suppressed in the glioblastoma multiforme (GBM) tumor microenvironment. We have recently shown that survival and differentiation of cancer stem-like cells (CSCs)/poorly differentiated tumors are controlled through two distinct phenotypes of cytotoxic and non-cytotoxic/split anergized NK cells, respectively. In this paper, we studied the function of NK cells against brain CSCs/poorly differentiated GBM and their NK cell-differentiated counterparts. Brain CSCs/poorly differentiated GBM, differentiated by split anergized NK supernatants (supernatants from NK cells treated with IL-2 + anti-CD16mAb) expressed higher levels of CD54, B7H1 and MHC-I and were killed less by the NK cells, whereas their CSCs/poorly differentiated counterparts were highly susceptible to NK cell lysis. Resistance to NK cells and differentiation of brain CSCs/poorly differentiated GBM by split anergized NK cells were mediated by interferon (IFN)-γ and tumor necrosis factor (TNF)-α. Brain CSCs/poorly differentiated GBM expressed low levels of TNFRs and IFN-γRs, and when differentiated and cultured with IL-2-treated NK cells, they induced increased secretion of pro-inflammatory cytokine interleukin (IL)-6 and chemokine IL-8 in the presence of decreased IFN-γ secretion. NK-induced differentiation of brain CSCs/poorly differentiated GBM cells was independent of the function of IL-6 and/or IL-8. The inability of NK cells to lyse GBM tumors and the presence of a sustained release of pro-inflammatory cytokines IL-6 and chemokine IL-8 in the presence of a decreased IFN-γ secretion may lead to the inadequacy of NK cells to differentiate GBM CSCs/poorly differentiated tumors, thus failing to control tumor growth.

Immunological Evasion in Glioblastoma

Glioblastoma is the most aggressive tumor in Central Nervous System in adults. Among its features, modulation of immune system stands out. Although immune system is capable of detecting and eliminating tumor cells mainly by cytotoxic T and NK cells, tumor microenvironment suppresses an effective response through recruitment of modulator cells such as regulatory T cells, monocyte-derived suppressor cells, M2 macrophages, and microglia as well as secretion of immunomodulators including IL-6, IL-10, CSF-1, TGF-β, and CCL2. Other mechanisms that induce immunosuppression include enzymes as indolamine 2,3-dioxygenase. For this reason it is important to develop new therapies that avoid this immune evasion to promote an effective response against glioblastoma.

Increased diffusion in the normal appearing white matter of brain tumor patients: is this just tumor infiltration?

Altered diffusion in the normal appearing white matter (NAWM) of glioma patients has been explained by tumor infiltration. The goal of the present study was to test this explanation indirectly by examining whether these alterations were also present in the contralateral NAWM of non-infiltrative tumors like meningiomas; and to search for other possible reasons for this abnormality. Twenty-seven patients with histologically verified glioma (grade II-IV), 22 meningioma patients and two groups of age- and sex-matched healthy controls underwent diffusion weighted imaging (DWI) on a 3T MR. All patients were examined before treatment. Apparent diffusion coefficient (ADC) values were calculated in the entire NAWM of the hemisphere contralateral to the tumor. ADC values of the NAWM were compared between groups with Mann-Whitney U-test and multiple linear regression. The relations of ADC in NAWM to glioma grade and to tumor volume were also investigated. ADC values of the contralateral NAWM were significantly higher in both glioma and meningioma patients compared to controls (P = 0.0006 and 0.0099, respectively). ADC value was higher in the NAWM of high grade gliomas than in low grade gliomas (P = 0.0181) and in healthy control subjects (P = 0.0003). ADC did not depend on tumor volume in any of the patient groups. Elevated ADC in the NAWM of both glioma and meningioma patients might indicate that the effect of infiltrating tumor cells is not the only reason for the alteration as it has been previously suggested. Although the role of mass effect was not proved, other mechanisms might also contribute to ADC elevation.

Reciprocal Supportive Interplay between Glioblastoma and Tumor-Associated Macrophages

Glioblastoma multiforme (GBM) is the most lethal and aggressive type of primary brain malignancy. Failures of the traditional therapies in treating GBMs raise the urgent requirement to develop new approaches with more responsive targets. The phenomenon of the high infiltration of tumor-associated macrophages (TAMs) into GBMs has been observed for a long time. Regardless of the limited knowledge about TAMs, the high percentage of supportive TAM in GBM tumor mass makes it possible to be a good target for GBM treatment. In this review, we discussed the unique features of TAMs in GBMs, including their origin, the tumor-supportive properties, the secreted cytokines, and the relevant mechanisms. In addition, we tried to interpret the current understandings about the interplay between GBM cancer cells and TAMs. Finally, the translational studies of targeting TAMs were also described.

Immunobiology of malignant gliomas

The immune system of patients with malignant gliomas is profoundly suppressed. The suppression involves both the cellular and humoral immunity and it is mainly attributable to selective depletion and malfunction of helper T cells. Malignant glioma cells express potent immunosuppressive factors such as transforming growth factor-beta(2), inteleukin-10 and prostaglandin E(2). Malignant glioma cells also produce chemoattractants and immunostimulatory cytokines which may activate the immune cells. However, the production of these stimulatory cytokines is not self-destructive to glioma cells because of the immunosuppression. Rather, the tumour cells use them to gain a growth advantage. Indeed the cytokines may act as a growth stimulator of the tumour cells themselves (autocrine mechanism), they may act as angiogenic factors to endothelial cells (paracrine mechanism) or induce the attracted immune cells to secrete angiogenic factors. Some cytokines produced by malignant glioma cells are known to be growth inhibitory to normal astrocytes. Recent studies on tumour suppressor genes suggest a close link between the aberrant genes and the immunobiologic features of malignant glioma cells.

Induction of selective blood-tumor barrier permeability and macromolecular transport by a biostable kinin B1 receptor agonist in a glioma rat model

Treatment of malignant glioma with chemotherapy is limited mostly because of delivery impediment related to the blood-brain tumor barrier (BTB). B1 receptors (B1R), inducible prototypical G-protein coupled receptors (GPCR) can regulate permeability of vessels including possibly that of brain tumors. Here, we determine the extent of BTB permeability induced by the natural and synthetic peptide B1R agonists, LysdesArg⁹BK (LDBK) and SarLys[dPhe⁸]desArg⁹BK (NG29), in syngeneic F98 glioma-implanted Fischer rats. Ten days after tumor inoculation, we detected the presence of B1R on tumor cells and associated vasculature. NG29 infusion increased brain distribution volume and uptake profiles of paramagnetic probes (Magnevist and Gadomer) at tumoral sites (T₁-weighted imaging). These effects were blocked by B1R antagonist and non-selective cyclooxygenase inhibitors, but not by B2R antagonist and non-selective nitric oxide synthase inhibitors. Consistent with MRI data, systemic co-administration of NG29 improved brain tumor delivery of Carboplatin chemotherapy (ICP-Mass spectrometry). We also detected elevated B1R expression in clinical samples of high-grade glioma. Our results documented a novel GPCR-signaling mechanism for promoting transient BTB disruption, involving activation of B1R and ensuing production of COX metabolites. They also underlined the potential value of synthetic biostable B1R agonists as selective BTB modulators for local delivery of different sized-therapeutics at (peri)tumoral sites.

The molecular profile of microglia under the influence of glioma

Microglia, which contribute substantially to the tumor mass of glioblastoma, have been shown to play an important role in glioma growth and invasion. While a large number of experimental studies on functional attributes of microglia in glioma provide evidence for their tumor-supporting roles, there also exist hints in support of their anti-tumor properties. Microglial activities during glioma progression seem multifaceted. They have been attributed to the receptors expressed on the microglia surface, to glioma-derived molecules that have an effect on microglia, and to the molecules released by microglia in response to their environment under glioma control, which can have autocrine effects. In this paper, the microglia and glioma literature is reviewed. We provide a synopsis of the molecular profile of microglia under the influence of glioma in order to help establish a rational basis for their potential therapeutic use. The ability of microglia precursors to cross the blood-brain barrier makes them an attractive target for the development of novel cell-based treatments of malignant glioma.

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-β, 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.

Antigen-receptor gene-modified T cells for treatment of glioma

Immunological effector cells and molecules have been shown to access intracranial tumor sites despite the existence of blood brain barrier (BBB) or immunosuppressive mechanisms associated with brain tumors. Recent progress in T-cell biology and tumor immunology made possible to develop strategies of tumor-associated antigen-specific immunotherapeutic approaches such as vaccination with defined antigens and adoptive T-cell therapy with antigen-specific T cells including gene-modified T cells for the treatment of patients with brain tumors. An array of recent reports on the trials of active and passive immunotherapy for patients with brain tumors have documented safety and some preliminary clinical efficacy, although the ultimate judgment for clinical benefits awaits rigorous evaluation in trials of later phases. Nevertheless, treatment with lymphocytes that are engineered to express tumor-specific receptor genes is a promising immunotherapy against glioma, based on the significant efficacy reported in the trials for patients with other types of malignancy. Overcoming the relative difficulty to apply immunotherapeutic approach to intracranial region, current advances in the understanding of human tumor immunology and the gene-therapy methodology will address the development of effective immunotherapy of brain tumors.

Microglial cell origin and phenotypes in health and disease

Microglia - resident myeloid-lineage cells in the brain and the spinal cord parenchyma - function in the maintenance of normal tissue homeostasis. Microglia also act as sentinels of infection and injury, and participate in both innate and adaptive immune responses in the central nervous system. Microglia can become activated and/or dysregulated in the context of neurodegenerative disease and cancer, and thereby contribute to disease severity. Here, we discuss recent studies that provide new insights into the origin and phenotypes of microglia in health and disease.

Short hairpin RNA-mediated fibronectin knockdown delays tumor growth in a mouse glioma model

Glioblastoma multiforme is the most common and lethal primary brain tumor. Glioma progression depends on the rapid proliferation of tumor cells accompanied by an acute immunosuppressive environment, facilitated mainly by tumor infiltration of regulatory T cells (Tregs). In this study, we characterize the role of fibronectin, a high-molecular weight extracellular matrix glycoprotein secreted by tumor cells, in controlling glioma progression and in mediating immunosuppression. Fibronectin binds to membrane-spanning integrin receptors and plays an important role in cell signaling, in defining cellular shape, in mobility, and in regulating the cell cycle. We found that inhibition of fibronectin expression in glioma cells, using short hairpin RNA-mediated silencing of gene expression, delayed cell proliferation in vitro. This delayed growth is explained, in part, by the observed reduced expression of integrin β(1) fibronectin receptor, which was restored by the inhibition of proteosomal activity. In our analysis of the downstream signaling targets of integrin β(1), we demonstrated reduced phosphorylation of Src kinase and STAT-3. We also observed reduced survivin expression that induced a three-fold increased accumulation of fibronectin-knockdown cells in the G(2)/M phase. In an experimental animal model, the fibronectin knockdown tumors had a mean survival advantage of 23 days over wild-type tumors. Moreover, brain samples of animals bearing fibronectin-knockdown tumors showed delayed Treg recruitment. Collectively, we propose that fibronectin is a key mediator of glioma progression because its inhibition delays both tumor progression and immunosuppression.

Immunostimulants for malignant gliomas

Several immunostimulant approaches have been studied in the treatment of gliomas. The advent of recombinant DNA technology led to a nonspecific immunostimulation via systemic administration of cytokines. Recently, in attempts to more closely mimic their natural activity, cytokines have been delivered by implanting genetically transduced cells or by using in vivo gene transfer techniques. The latest efforts have focused on immunostimulatory agents that act directly on antigen-presenting cells and effector cells of the immune system via pattern recognition receptors. Combining these strategies with more than one mode of immunotherapy may provide better clinical results.

Immunotherapeutic approaches for glioma

The development of effective immunotherapy strategies for glioma requires adequate understanding of the unique immunological microenvironment in the central nervous system (CNS) and CNS tumors. Although the CNS is often considered to be an immunologically privileged site and poses unique challenges for the delivery of effector cells and molecules, recent advances in technology and discoveries in CNS immunology suggest novel mechanisms that may significantly improve the efficacy of immunotherapy against gliomas. In this review, we first summarize recent advances in the CNS and CNS tumor immunology. We address factors that may promote immune escape of gliomas. We also review advances in passive and active immunotherapy strategies for glioma, with an emphasis on lessons learned from recent early-phase clinical trials. We also discuss novel immunotherapy strategies that have been recently tested in non-CNS tumors and show great potential for application to gliomas. Finally, we discuss how each of these promising strategies can be combined to achieve clinical benefit for patients with gliomas.

A North American brain tumor consortium phase II study of poly-ICLC for adult patients with recurrent anaplastic gliomas

This phase II study was designed to determine the objective response rate and 6-month progression free survival of adult patients with recurrent supratentorial anaplastic glioma when treated with the immune modulator, polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly-ICLC). This was an open-labeled, single arm phase II study. Patients were treated with poly-ICLC alone. Patients may have had treatment for no more than two prior relapses. Treatment with poly-ICLC continued until tumor progression. Fifty five patients were enrolled in the study. Ten were ineligible after central review of pathology. Eleven percent of patients (5 of 45) had a radiographic response. Time to progression was known for 39 patients and 6 remain on treatment. The estimated 6-month progression free survival was 24%. The median survival time was 43 weeks. Poly-ICLC was well tolerated, but there was no improvement in 6-month progression free survival compared to historical database nor was there an encouraging objective radiographic response rate. Based on this study, poly-ICLC does not improve 6moPFS in patients with recurrent anaplastic gliomas but may be worth further study in combination with agents such as temozolomide.

A phase II clinical trial of poly-ICLC with radiation for adult patients with newly diagnosed supratentorial glioblastoma: a North American Brain Tumor Consortium (NABTC01-05)

PURPOSE

This phase II study was designed to determine the overall survival time of adults with supratentorial glioblastoma treated with the immune modulator, polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly-ICLC), in combination with and following radiation therapy (RT).

METHODS AND MATERIALS

This was an open-label, single arm phase II study. Patients were treated with RT in combination with poly-ICLC followed by poly-ICLC as a single agent. Poly-ICLC was initiated 7-28 days after the surgical procedure that established the diagnosis; radiotherapy began within 7 days of the first dose of poly-ICLC and within 35 days of surgical diagnosis. Treatment with poly-ICLC continued following the completion of RT to a maximum of 1 year or until tumor progression.

RESULTS

31 patients were enrolled in this study. One patient did not have a Glioblastoma mutiforme and was deemed ineligible. For the 30 eligible patients, time to progression was known for 27 patients and 3 were censored. The estimated 6-month progression-free survival was 30% and the estimated 1-year progression-free survival was 5%. Median time to progression was as 18 weeks. The 1-year survival was 69% and the median survival was 65 weeks.

CONCLUSIONS

The combined therapy was relatively well-tolerated. This study suggests a survival advantage compared to historical studies using RT without chemotherapy but no survival advantage compared to RT with adjuvant nitrosourea or non-temozolomide chemotherapy. Our results suggest that poly-ICLC has activity against glioblastoma and may be worth further study in combination with agents such as temozolomide.

Association of preoperative depression and survival after resection of malignant brain astrocytoma

BACKGROUND

Clinical depression has been shown to negatively influence the morbidity and mortality of multiple disease states. It remains unclear if clinical depression affects survival after surgical management of malignant brain astrocytoma. We set out to determine whether patients with a diagnosis of clinical depression before surgery experienced decreased survival independent of treatment modality or degree of disability.

METHODS

One thousand fifty-two patients undergoing surgical management for malignant brain astrocytoma (WHO grade 3 or 4) performed at a single institution from 1995 to 2006 were retrospectively reviewed. The independent association of depression prior to surgery and subsequent survival was assessed via multivariate proportional hazards regression analysis.

RESULTS

Surgical management consisted of primary resection in 605 (58%) patients, secondary resection in 410 (39%), and biopsy in 37 patients (3.5%). Pathology was WHO grade IV in 829 (79%) and grade III in 223 (21%). Forty-nine patients (5%) carried the diagnosis of depression at the time of surgery. Mean age and KPS on admission was 51 +/- 16 and 80 +/- 10 years, respectively. Two hundred ninety patients (28%) received Gliadel (BCNU MGI Pharma, Inc., Bloomington, MN, USA) wafer implantation and 274 (26%) received postoperative temozolomide (concomitant in 102, delayed adjuvant in 172 patients). Subsequent resection was performed at the time of recurrence in 135 (13%) patients a mean of 10 +/- 6 months after surgery. Adjusting for all variables associated with survival in this model, age (P < .001), KPS (P < .001), WHO grade III vs IV (P < .001), primary versus secondary resection (P < .001), gross-total resection (P < .001), Gliadel wafer implantation (P = .048), postoperative temozolomide therapy (P < .001), and subsequent resection at time of recurrence (P < .001); preoperative depression was independently associated with decreased survival (relative risk [95% CI]: 1.41 [1.1-1.96], P < .05). The difference in percent survival between the depression and nondepression cohorts was most notable at 12 months (15% vs 41%) and 20 months (0% vs 21%) after surgery.

CONCLUSION

In our experience, patients who are actively depressed at the time of surgery were associated with decreased survival after surgical management of malignant astrocytoma, independent of degree of disability, tumor grade, or subsequent treatment modalities. In our opinion, the presence of an association between preoperative depression and survival warrants further investigation.

Results of a phase I dendritic cell vaccine trial for malignant astrocytoma: potential interaction with adjuvant chemotherapy

Dendritic cell vaccination has been applied to the treatment of a variety of cancers, including malignant astrocytoma. We have treated 13 patients with malignant astrocytoma using dendritic cell vaccination and have shown that this treatment is safe and is likely to be effective in combination with standard adjuvant therapy. Future studies should prospectively incorporate dendritic cell vaccination together with chemotherapy. Ideally, dendritic cell vaccination should be tested in a prospective fashion, in a coordinated trial involving multiple centres.

Expression and localization of VEGF-C and VEGFR-3 in glioblastomas and haemangioblastomas

Primary human brain tumours account for approximately 2% of all cancers. High levels of expression of vascular endothelial growth factor-A (VEGF-A), a potent angiogenic factor, are linked to poor prognosis. In contrast, the potential role in human brain tumour biology of newer VEGF family members, VEGF-C and VEGF-D, both of which are lymphangiogenic factors, is poorly understood. In the present study, the expression of all VEGFs (VEGF-A, -B, -C, and -D) and their receptors (VEGFR-1, -2, and -3) has been assessed in 39 primary human brain tumours. The well-established findings were confirmed with VEGF-A. Surprisingly, however, VEGF-C and VEGF-D, as well as VEGFR-3, were expressed in some tumour types such as haemangioblastomas and glioblastomas, despite their lack of lymphatic vessels. VEGF-C and VEGFR-3 transcripts were localized to the tumour palisade around necrotic areas in glioblastomas and were evenly distributed throughout haemangioblastomas. VEGF-C protein was localized by immunohistochemistry to the palisade layer in glioblastomas. More than 50% of VEGF-C-positive cells also expressed the intermediate-stage inflammatory macrophage marker CD163; however, a significant proportion of VEGF-C-positive cells were CD163-negative. These data demonstrate the presence of molecules, primarily described as regulators of lymphangiogenesis, in normal human brain and brain tumours that are devoid of lymphatics. Their localization in macrophages points to a role in tumour-associated inflammation.

T-cell apoptosis in human glioblastoma multiforme: Implications for immunotherapy

We used immunohistochemistry and flow cytometry to assess apoptosis in human glioblastoma multiforme (GBM). Our immunohistochemical study revealed apoptosis of glioma cells expressing glial fibrillary acidic protein and of CD3(+) T cells infiltrating GBM. To quantify and phenotype the apoptotic T cells, we performed flow cytometry on lymphocytes separated from GBM. The cells were stained with annexin-V-FLUOS/propidium iodide to identify apoptosis. We found that high proportions of both the CD4(+) and CD8(+) T cells were apoptotic. In particular, we found that T cells expressing Fas ligand (Fas-L, CD95L) were eight times more vulnerable to apoptosis than those not expressing Fas-L, which suggests that the T-cell apoptosis is induced by overactivation of the T-cell receptor, possibly in the absence of appropriate costimulation. Our results have implications for the design of immunotherapies for GBM.

Glioblastomas induce T-lymphocyte death by two distinct pathways involving gangliosides and CD70

Here we report that glioblastoma multiforme (GBM) mediates immunosuppression by promoting T-cell death via tumor-associated CD70 and gangliosides that act through receptor-dependent and receptor-independent pathways, respectively. GBM lines cocultured with T cells induced lymphocyte death. The GBM lines were characterized for their expression of CD70, Fas ligand (FasL), and tumor necrosis factor-alpha (TNF-alpha), and the possible participation of those molecules in T-cell killing was assessed by doing GBM/T cell cocultures in the presence of anti-CD70 antibodies, Fas fusion proteins, or anti-TNF-alpha antibodies. CD70 but not TNF-alpha or FasL is responsible for initiating T-cell death via the receptor-dependent pathway. Of the four GBM cell lines that induced T-cell death, three highly expressed CD70. Two nonapoptogenic GBM lines (CCF3 and U138), on the other hand, had only minimally detectable CD70 expression. Blocking experiments with the anti-CD70 antibody confirmed that elevated CD70 levels were involved in the apoptogenicity of the three GBM lines expressing that molecule. Gangliosides were found to participate in the induction of T-cell apoptosis, because the glucosylceramide synthase inhibitor (PPPP) significantly reduced the abilities of all four apoptogenic lines to kill the lymphocytes. High-performance liquid chromatography (HPLC) and mass spectroscopy revealed that GM2, GM2-like gangliosides, and GD1a were synthesized in abundance by all four apoptogenic GBM lines but not by the two GBMs lacking activity. Furthermore, gangliosides isolated from GBM lines as well as HPLC fractions containing GM2 and GD1a were directly apoptogenic for T cells. Our results indicate that CD70 and gangliosides are both products synthesized by GBMs that may be key mediators of T-cell apoptosis and likely contribute to the T-cell dysfunction observed within the tumor microenvironment.

An experimental study of dendritic cells-mediated immunotherapy against intracranial gliomas in rats

OBJECT

To investigate the effect of dendritic cells(DC) pulsed with apoptotic tumor cells for treatment of intracranial gliomas in rats.

METHODS

C6 glioma cells were injected into brain of Wistar rats under stereotactic monitor to establish an animal model of glioma. The precursors of DCs were isolated from bone marrow of rats, stimulated in vitro with recombinent rat granulocyte-macrophage colony-stimulating factor (rrGM-CSF) and interleukin-4 (rrIL-4). These DCs were then pulsed ex vivo with apoptotic C6 glioma cells induced by heating and subsequently injected subcutaneously into rats harboring intracranial C6 glioma. Rats were treated with five weekly subcutaneous injections of either control media, unpulsed DCs, or DCs pulsed with apoptotic tumor cells. The animals were followed for survival, volume of tumor by MRI, CD8 + T cells, cytotoxicity assay in vitro and proliferational function of lymphocytes in peripheral blood were determined by flow cytometry(FCM). The concentration of cytokines interferon-gamma (IFN-gamma) and interleukin-10(IL-10) were monitored through enzyme-linked immunosorbent assay(ELISA) using ELISAkit.

RESULTS

Our results indicated that C6 glioma model rats treated with apoptotic tumor cells pulsed DCs prolonged survival, inhibited the tumor growth and increased the level of CD8 + T lymphocytes in peripheral blood comparing with control group. Cytotoxicity assay suggested that vaccination with these apoptotic cells pulsed DCs can induce cytotoxic T lymphocytes response against C6 tumor cells compared with control group. Furthermore, significantly enhanced IFN-gamma and reduced IL-10(even undetectable) were observed in peripheral blood of rats treated with pulsed-DCs. No evident autoimmune response were detected.

CONCLUSIONS

Our data demonstrated that systemic vaccination with DCs pulsed with apoptotic cells is a safe and effective immunotherapy for intracranial glioma.

Neural precursor cells and their role in neuro-oncology

Neural precursor cells (NPCs) provide a new mode for delivery of genes and proteins to brain tumors. These cells exist both in the developing and the adult nervous systems of all mammalian organisms. They have the ability to self-renew, migrate to diseased areas of the brain and differentiate into neurons, astrocytes and oligodendrocytes. The migratory ability of NPCs and their capacity to differentiate into all neural phenotypes provides a powerful tool for the treatment of both diffuse and localized neurological disorders. NPCs have been used in transplantation to replace damaged cells and in cancer therapy to provide therapeutic proteins and vectors to eliminate malignant cells in the brain. This review focuses on the characteristics of NPCs and their experimental use in the therapy for brain tumors. Examples are provided of monitoring migration of NPCs by bioluminescence imaging in living animals and of using them to deliver the apoptotic protein, TRAIL, to kill tumor cells.

Uptake and presentation of malignant glioma tumor cell lysates by monocyte-derived dendritic cells

Malignant glioma of the CNS is a tumor with a very bad prognosis. Development of adjuvant immunotherapy is hampered by interindividual and intratumoral antigenic heterogeneity of gliomas. To evaluate feasibility of tumor vaccination with (autologous) tumor cells, we have studied uptake of tumor cell lysates by dendritic cells (DCs), and the T-cell stimulatory capacity of the loaded DCs. DCs are professional antigen-presenting cells, which have already been used as natural adjuvants to initiate immune responses in human cancer. An efficacious uptake of tumor cell proteins, followed by processing and presentation of tumor-associated antigens by the DCs, is indeed one of the prerequisites for a potent and specific stimulation of T lymphocytes. Human monocytes were differentiated in vitro to immature DCs, and these were loaded with FITC-labeled tumor cell proteins. Uptake of the tumor cell proteins and presentation of antigens in the context of both MHC class I and II could be demonstrated using FACS analysis and confocal microscopy. After further maturation, the loaded DCs had the capacity to induce specific T-cell cytotoxic activity against tumor cells. We conclude that DCs loaded with crude tumor lysate are efficacious antigen-presenting cells able to initiate a T-cell response against malignant glioma tumor cells.

Downregulation of major histocompatibility complex antigens in invading glioma cells: stealth invasion of the brain

Invasion into surrounding brain tissue is a fundamental feature of gliomas and the major reason for treatment failure. The process of brain invasion in gliomas is not well understood. Differences in gene expression and/or gene products between invading and noninvading glioma cells may identify potential targets for new therapies. To look for genes associated with glioma invasion, we first employed Affymetrix microarray Genechip technology to identify genes differentially expressed in migrating glioma cells in vitro and in invading glioma cells in vivo using laser capture microdissection. We observed upregulation of a variety of genes, previously reported to be linked to glioma cell migration and invasion. Remarkably, major histocompatiblity complex (MHC) class I and II genes were significantly downregulated in migrating cells in vitro and in invading cells in vivo. Decreased MHC expression was confirmed in migrating glioma cells in vitro using RT-PCR and in invading glioma cells in vivo by immunohistochemical staining of human and murine glioblastomas for beta2 microglobulin, a marker of MHC class I protein expression. To the best of our knowledge, this report is the first to describe the downregulation of MHC class I and II antigens in migrating and invading glioma cells, in vitro and in vivo, respectively. These results suggest that the very process of tumor invasion is associated with decreased expression of MHC antigens allowing glioma cells to invade the surrounding brain in a 'stealth'-like manner.

Immunotherapy for malignant gliomas: emphasis on strategies of active specific immunotherapy using autologous dendritic cells

REVIEW

In this review, we discuss immunotherapy for malignant gliomas.

EMPHASIS

The emphasis is on the novel strategy of active specific immunotherapy using dendritic cells as antigen-presenting cells, especially its theoretical concepts and advantages, specific requirements, critical issues, pre-clinical and early clinical experience. Dendritic cell vaccination is situated in the diversity of other immunotherapeutical approaches.

FURTHER DISCUSSION

Future directions, challenges, and drawbacks will be discussed.

Combining cytotoxic and immune-mediated gene therapy to treat brain tumors

Glioblastoma (GBM) is a type of intracranial brain tumor, for which there is no cure. In spite of advances in surgery, chemotherapy and radiotherapy, patients die within a year of diagnosis. Therefore, there is a critical need to develop novel therapeutic approaches for this disease. Gene therapy, which is the use of genes or other nucleic acids as drugs, is a powerful new treatment strategy which can be developed to treat GBM. Several treatment modalities are amenable for gene therapy implementation, e.g. conditional cytotoxic approaches, targeted delivery of toxins into the tumor mass, immune stimulatory strategies, and these will all be the focus of this review. Both conditional cytotoxicity and targeted toxin mediated tumor death, are aimed at eliminating an established tumor mass and preventing further growth. Tumors employ several defensive strategies that suppress and inhibit anti-tumor immune responses. A better understanding of the mechanisms involved in eliciting anti-tumor immune responses has identified promising targets for immunotherapy. Immunotherapy is designed to aid the immune system to recognize and destroy tumor cells in order to eliminate the tumor burden. Also, immune-therapeutic strategies have the added advantage that an activated immune system has the capability of recognizing tumor cells at distant sites from the primary tumor, therefore targeting metastasis distant from the primary tumor locale. Pre-clinical models and clinical trials have demonstrated that in spite of their location within the central nervous system (CNS), a tissue described as 'immune privileged', brain tumors can be effectively targeted by the activated immune system following various immunotherapeutic strategies. This review will highlight recent advances in brain tumor immunotherapy, with particular emphasis on advances made using gene therapy strategies, as well as reviewing other novel therapies that can be used in combination with immunotherapy. Another important aspect of implementing gene therapy in the clinical arena is to be able to image the targeting of the therapeutics to the tumors, treatment effectiveness and progression of disease. We have therefore reviewed the most exciting non-invasive, in vivo imaging techniques which can be used in combination with gene therapy to monitor therapeutic efficacy over time.

Surgery and adjuvant dendritic cell-based tumour vaccination for patients with relapsed malignant glioma, a feasibility study

Patients with relapsed malignant glioma have a poor prognosis. We developed a strategy of vaccination using autologous mature dendritic cells loaded with autologous tumour homogenate. In total, 12 patients with a median age of 36 years (range: 11–78) were treated. All had relapsing malignant glioma. After surgery, vaccines were given at weeks 1 and 3, and later every 4 weeks. A median of 5 (range: 2–7) vaccines was given. There were no serious adverse events except in one patient with gross residual tumour prior to vaccination, who repetitively developed vaccine-related peritumoral oedema. Minor toxicities were recorded in four out of 12 patients. In six patients with postoperative residual tumour, vaccination induced one stable disease during 8 weeks, and one partial response. Two of six patients with complete resection are in CCR for 3 years. Tumour vaccination for patients with relapsed malignant glioma is feasible and likely beneficial for patients with minimal residual tumour burden.

C6 glioma cells retrovirally engineered to express IL-18 and Fas exert FasL-dependent cytotoxicity against glioma formation

The decreased antitumor immune response significantly contributes to the progression of glioma. To evaluate whether the antitumor immunity is restored by stable co-expression of IL-18 and Fas receptor, we retrovirally introduced these two genes into rat C6 glioma cells. We found that IL-18-transduced glioma cells secreted IL-18 and induced PBMC IFN-gamma production in vitro. We also found that Fas-transduced glioma cells were susceptible to Fas-mediated apoptosis. In vivo, we found that IL-18 expression and Fas expression synergistically inhibited C6 cell tumorigenesis with the glioma cells being subcutaneously injected in rat flank. Furthermore, we found that co-expression of IL-18 and Fas also produced a marked survival advantage with the rats being intracerebrally implanted with the glioma cells. Finally, we demonstrated that FasL-dependent PBMC cytotoxicity participated in the anti-glioma immunity induced by IL-18 and Fas expression. Taken together, these findings demonstrate that increasing IL-18 production in tumor microenvironment and prompting functional Fas receptor expression of tumor cells could enhance FasL-dependent cytotoxic antitumor immunity.

Intratumoral T cell subset ratios and Fas ligand expression on brain tumor endothelium

INTRODUCTION

T cell presence in TIL, and the ratio of CD8+ and CD4+ T cell subsets in particular, can correlate with tumor prognosis in some tumors, although the significance of such infiltration into glioma is controversial. However, gliomas represent a lower extreme in their extent of T cell infiltration, and are thus useful in assessing factors that can decrease T cell presence within tumor tissue. Fas ligand, a pro-apoptotic cell surface protein, may play a key role in reduction of T cells in tumor tissue.

OBJECTIVE

To assess the level of FasL expression on brain tumor endothelium and to correlate this with relative levels of CD4+ and CD8+ T cell subsets in TIL from brain tumors.

METHODS

CD3+, CD4+, and CD8+ cells were quantified in fresh TIL by flow cytometry. Paraffin embedded sections of tumors, including meningiomas and gliomas as well as extracranial malignancies, underwent immunohistochemical staining for FasL and Von-Willebrand's factor (Factor VIII) to determine expression levels of endothelial FasL.

RESULTS

FasL expression was high in aggressive intracranial malignancies compared to more indolent neoplasms, and correlated inversely with CD8+/CD4+ TIL ratios in all tumor classes combined (ANOVA, p < 0.05).

CONCLUSION

Low levels of T cells within TIL, as well as low CD8+/CD4+ TIL ratios appear to be a property of parenchymal tumor presence. Together with the inverse correlation seen between FasL expression and CD8+/CD4+ TIL ratios, the high levels of endothelial FasL expression in gliomas suggests that FasL decreases T cell presence in brain tumors in a subset-selective manner, thus contributing to glioma immune privilege.

Intratumoral dendritic cell vaccination elicits potent tumoricidal immunity against malignant glioma in rats

Dendritic cells (DC) are attractive candidates for innovative cancer immunotherapy by virtue of their ability to function as powerful antigen presenting cells and elicit potent antitumor cytotoxic immune responses. With the aim of generating antitumor immunity, the authors sought to enhance in vivo tumor antigen presentation by using an intratumoral DC vaccination strategy in the setting of partially irradiated intracranial brain tumors. Fisher rats, implanted with 9L gliomas in the right corpus striatum, were treated with freshly cultured, unpulsed syngeneic DC inoculated directly into the tumor bed. Intracranially inoculated DCs were found to drain to ipsilateral deep cervical lymph nodes. This was associated with increased local and systemic antitumor cytoxicity, as evidenced by robust infiltration of treated tumors with CD4 and CD8 T cells as well as by increased IFN-gamma protein and message levels in in vitro restimulated splenic lymphocytes. DC therapy resulted in prolonged survival and immunity to subsequent intracranial tumor re-challenge. These results demonstrate the viability of intratumoral DC vaccination as an effective therapeutic strategy for intracranial glioma.

Treatment of intracranial glioma with in situ interferon-gamma and tumor necrosis factor-alpha gene transfer

Interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) are potent immunostimulatory cytokines with demonstrated tumoricidal effects in a variety of cancers. With the aim of investigating their ability to generate antitumor immune responses in malignant brain tumors, we describe the use of in situ adenoviral-mediated IFNgamma and TNFalpha gene transfer in glioma-bearing rodents. Survival was prolonged in mice treated with AdmIFNgamma or AdTNFalpha compared to AdLacZ- and saline-inoculated controls, and AdmIFNgamma- or AdTNFalpha-treated animals revealed significantly smaller tumors. These effects were accompanied by significant up-regulation of tumor MHC-I expression in AdmIFNgamma-inoculated animals, and of MHC-II in AdTNFalpha-treated tumors. Significantly enhanced intratumoral infiltration with CD4(+) and CD8(+) T cells was visible in animals treated with AdmIFNgamma, AdTNFalpha, or a combination of AdmIFNgamma and AdTNFalpha. In addition, AdTNFalpha therapy down-regulated the expression of endothelial Fas ligand, a cell membrane protein implicated as a contributor to immune privilege in cancer. These findings demonstrate the effectiveness of local IFNgamma and TNFalpha gene transfer as a treatment strategy for glioma and illustrate possible physiological pathways responsible for the therapeutic benefit observed.

Analysis of interleukin-6 gene expression in primary human gliomas, glioblastoma xenografts, and glioblastoma cell lines

Our previous study showed that high-grade astrocytomas often expressed high interleukin (IL)-1beta production. Coexpression of IL-1beta and IL-6 has been found in a number of glioma samples and glioma cell lines. To characterize the expression of IL-6 in the human glioma microenvironment, we investigated surgically excised human gliomas, human glioblastoma xenografts, and human glioblastoma cell lines using the reverse transcriptase-polymerase chain reaction (RT-PCR), immunohistochemistry (IHC), and enzyme-linked immunosorbent assay (ELISA). In the 29 primary gliomas, transcripts of IL-6 were less frequently detectable (55.6%) than those of IL-1beta (72.4%) or those of IL-10, IL-8, or IL-1alpha (>80% each). As for IL-6 gene expression, little or no transcription was observed in low-grade astrocytomas, oligodendroglial tumors, and 1 ependymoma. Strong IL-6 gene expression was found in only 5 of 9 glioblastomas. Immunohistochemically, IL-6 antigen was localized in the tumor cells and macrophages in 4 of 7 glioblastomas. In 3 glioblastomas transplanted into nude mice, both IL-1beta and IL-6 were detected only in 1, but othercytokines (IL-8, IL-10, and IL-1alpha) were detected in all 3 xenografts by RT-PCR. Two cell lines both showed IL-6 expression at the mRNA level, and in a cell line with a high level of IL-6 and IL-1beta transcripts, significant production of IL-6 was observed by IHC and ELISA. We concluded that IL-6 produced in tumor tissue may be involved in tumor progression in some glioblastomas, but not in low-grade astrocytomas and oligodendroglial tumors, and that IL-6 gene expression is closely correlated with IL-1beta expression in biopsy tissue, xenografts, and cultures of human gliomas.

Changes in the immunologic phenotype of human malignant glioma cells after passaging in vitro

Although immunotherapeutic strategies against glioblastomas have been promising both in vitro and in animal models, similar successes have not been realized in human clinical trials. One reason may be that immunotherapeutic strategies are based on prior studies that primarily have used human glioblastoma cell lines passaged in vitro, which may not accurately reflect the in vivo properties of glioblastoma cells. In this report, we used flow cytometry to quantify the expression of immunological cell surface molecules on human glioblastomas directly ex vivo (prior to any in vitro culturing) and after varying passages in vitro. Furthermore, we used ELISA to quantitate cytokine secretion after various passages in vitro. We demonstrate that in vitro culturing of established cell lines led to increases in the cell surface expression of MHC class I and ICAM-1 and secretion of IL-6 and TGF-beta(2). Furthermore, there were significant changes in the expression of MHC class I, MHC class II, B7-2, ICAM-1, and FasL when comparing ex vivo tumor cells to those after a single passage in vitro. After passaging once in vitro, there were also significant changes in the secretion of TGF-beta(2) and IL-10. This report indicates that in vitro culturing leads to significant changes in both cell surface molecules and secreted cytokines, which are known to affect the ability of immune cells to initiate an anti-tumor immune response. These changes in the immunological phenotype of glioblastomas after in vitro culturing may in part explain the limited success of immunotherapeutic strategies against glioblastomas in human clinical trials.

Modified immunoregulation associated with interferon-gamma treatment of rat glioma

Little is known about modulation by cytokines of major histocompatibility complex (MHC) antigen expression on intracranial tumors in vivo. The ability of cytokines to up-regulate MHC class-1 (MHC-1) antigen expression was investigated first in vitro using three rat glioma cell lines. Immunohistochemistry showed that incubation with recombinant rat interferon-gamma (rrIFN-gamma) increased MHC-1 antigen expression in RG2, C6, and 9L cell lines. Flow cytometric analysis revealed different baseline levels of MHC-1 antigen expression in each line (RG2 lowest, C6 highest), and that these levels increased in all lines after stimulation with 100 U ml(-1) or more of rrIFN-gamma. The antitumor effect of rrIFN-gamma in vivo was evaluated by assessing survival of rats with implanted intracerebral RG2 gliomas after intracarotid infusion of rrIFN-gamma. A high dose of rrIFN-gamma (2.4 x 10(5) U kg(-1)) significantly increased the survival, compared to control (p < 0.02). Intracarotid pre-treatment with the bradykinin analogue RMP-7 did not further increase survival. Immunohistochemical staining of tumor sections after in vivo rrIFN-gamma, infusion showed no clear increase in MHC-1 antigen expression on tumor cells but increased staining for ED2 antigen within tumor tissue, presumably from perivascular cells with MHC class-2 antigen.

Antigen-presenting capability of glial cells under glioma-harboring conditions and the effect of glioma-derived factors on antigen presentation

The antigen-presenting capability of syngeneic rat glial cells was investigated under glioma-harboring conditions. Microglia induced a significant proliferation of glioma-primed splenocytes, but astrocytes did not. Furthermore, astrocytes suppressed the accessory cell function of microglia. The presence of both indomethacin and anti-interleukin (IL)-10 neutralizing antibody during priming of microglia enhanced splenocyte proliferation. The glioma culture supernatants down-regulated the interferon-gamma-induced expression of major histocompatibility complex class II molecules on microglia. The down-regulation was blocked by indomethacin and anti-IL-10 antibody. The results suggest that microglia but not astrocytes may function as antigen-presenting cells in glioma, and that glioma may suppress the antigen-presenting abilities of microglia.

Glioma immunology and immunotherapy

OBJECTIVE

Despite advances in conventional therapy, the prognosis for most glioma patients remains dismal. This has prompted an intensive search for effective treatment alternatives. Immunotherapy, one such alternative, has long been recognized as a potentially potent cancer treatment but has been limited by an inadequate understanding of the immune system. Now, increased insight into immunology is suggesting more rational approaches to immunotherapy. In this article, we explore key aspects of modern immunology and discuss their implications for glioma therapy.

METHODS

A thorough literature review of glioma immunology and immunotherapy was undertaken to inquire into the basic immunology, central nervous system immunology, glioma immunobiology, standard glioma immunotherapy, and recent immunotherapeutic advances in glioma treatment.

RESULTS

Although gliomas express tumor-associated antigens and appear potentially sensitive to immune responses, many factors work together to inhibit antiglioma immunity. Not surprisingly, most clinical attempts at glioma immunotherapy have met with little success to date. However, novel immunostimulatory strategies, such as immunogene therapy, directed cytokine delivery, and dendritic cell manipulation, have recently yielded dramatic preclinical results in glioma models. This suggests that glioma-derived immunosuppression can be overcome.

CONCLUSION

Modern molecular biology and immunology techniques have yielded a wealth of new data about glioma immunobiology. Armed with this information, many investigators have proposed novel means to stimulate antiglioma immune responses. Although definitive clinical results remain to be seen, the current renaissance in glioma immunology and immunotherapy shows great promise for the future.

Immune defects observed in patients with primary malignant brain tumors

Malignant glioblastomas (gliomas) account for approximately one third of all diagnosed brain tumors. Yet, a decade of research has made little progress in advancing the treatment of these tumors. In part this lack of progress is linked to the challenge of discovering how glial tumors are capable of both modulating host immune function and neutralizing immune-based therapies. Patients with gliomas exhibit a broad suppression of cell-mediated immunity. The impaired cell-mediated immunity observed in patients with gliomas appears to result from immunosuppressive factor(s) secreted by the tumor. This article reviews what has been elucidated about the immune defects of patients harboring glioma and the glioma-derived factors which mediate this immunosuppression. A model involving systemic cytokine dysregulation is presented to suggest how the immune defects arise in these individuals.

Fluorescence automatic cell sorter and immunohistochemical investigation of CD68-positive cells in meningioma

Infiltration of brain neoplasms by mononuclear cells including monocytes/macrophages has attracted little attention since they have marked morphological heterogeneity. Twenty-seven meningiomas were studied by anti-CD68 antibody-gated flow cytometry and by immunohistochemical analysis using the anti-CD68 antibodies. Flow cytometric analysis divided cells contained within tumor tissues into CD68-positive and -negative cells. In addition, eight gliomas, eight metastatic brain tumor, and 12 pituitary adenomas were investigated in the same way to compare meningiomas. The mean contents of CD68-positive cells were 24.0 +/- 3.7% in meningiomas, 4.4 +/- 1.4% in gliomas, 9.5 +/- 3.9% in metastatic brain tumors, and 4.5 +/- 1.8% in pituitary adenomas. Immunohistochemically, CD68-positive cells showed significant heterogeneity and were detected as round, rod-shaped, ameboid and ramified cells in meningiomas. Although the infiltrated mononuclear cells in gliomas have been investigated to some degree and showed that they express cytokines and/or growth factors, these infiltrated cells in meningioma have barely been studied. The CD68-positive cells detected in this study are likely to be monocytes, macrophages and microglias, and are presumed to be in various functional stages and to play important roles in growth regulation in meningioma.

Inhibition of experimental rat glioma growth by decorin gene transfer is associated with decreased microglial infiltration

Decorin gene therapy for experimental malignant glioma is thought to involve antagonism of immunosuppression induced by glioma-derived transforming growth factor-beta (TGF-beta). TGF-beta is chemotactic for cells of the monocyte macrophage lineage but inhibits their functional activity in many in vitro paradigms. Here, we examined changes in the patterns of microglial infiltration of rat C6 gliomas expressing a decorin transgene. We find that the number of OX42/ED-1-positive microglial cells is reduced rather than enhanced in the presence of decorin. Decorin-expressing gliomas contain lower numbers of MHC class II antigen-expressing microglial cells whereas the relative frequency of MHC I immunoreactivity among microglial cells is increased. Interestingly, the reduction of TGF-beta levels in the tumors by decorin is associated with the de novo expression of inducible nitric oxide synthase (iNOS) in a minority of microglial cells. These data suggest that microglial cells do not participate in the regression of decorin-expressing rat C6 gliomas.

Diminished monocytic HLA-DR expression and ex vivo cytokine secretion capacity in patients with glioblastoma: effect of tumor extirpation

Severe immunodysregulation on lymphocyte level has been described in patients with glioblastoma and is likely involved into its unfavorable prognosis. Although the major importance of monocytic cells for immunoregulation is well established, only very limited data exist regarding the monocyte status in glioblastoma patients. Here we demonstrate a markedly diminished monocytic HLA-DR expression and ex vivo cytokine secretion capacity (TNF-alpha, IL-1beta, IL-10) as signs for monocyte deactivation in glioblastoma patients but not in patients with astrocytoma. As known in immunocompromised patients from other reasons, monocyte deactivation indicate global immunodepression associated with an enhanced risk of infectious complications. Interestingly, tumor resection resulted in partial recovery from the monocytic deactivation. This suggests that the glioblastoma itself contributed to this phenomenon. However, IL-10 and the active forms of transforming growth factor-beta2 and -beta1, which are produced by glioblastoma cells and known to inhibit monocyte function, were not detectable in plasma in our patients. Moreover, low levels of the adrenocorticotropic hormone and cortisol excluded hypothalamo-pituitary-adrenal axis involvement. So, further investigations are necessary to clarify the mechanism. The demonstrated severe glioblastoma-associated monocytic deactivation may contribute to its unfavorable prognosis. Therefore, monocytes may represent target cells for new adjuvant immunotherapies in glioblastoma.

Granulocyte-macrophage colony-stimulating factor and B7-2 combination immunogene therapy in an allogeneic Hu-PBL-SCID/beige mouse-human glioblastoma multiforme model

Glioblastoma multiforme is the most common primary central nervous system neoplasm. Its dismal prognosis has led to investigation of new treatment strategies such as immunogene therapy. We transduced the human glioblastoma cell line D54MG in vitro with genes encoding the proinflammatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF), the T cell co-stimulatory molecule B7-2, or both (in a bicistronic vector) via retroviral vectors. Therapeutic gene expression by D54MG was high after transduction and selection (30 ng/10(6) cells/day for GM-CSF and > 2 orders of magnitude fluorescence shift on flow cytometry for B7-2). The effect of GM-CSF and/or B7-2 transduction on D54MG tumor growth in vivo was monitored in a novel allogeneic human peripheral blood lymphocyte-severe combined immunodeficiency mouse (Hu-PBL-SCID) model. GM-CSF- or B7-2-transduced tumors showed growth suppression in hu-PBL-reconstituted mice compared to untransduced and/or unreconstituted controls. Growth suppression was greatest for B7-2. Furthermore, vaccination with irradiated GM-CSF/B7-2-transduced tumor cells markedly inhibited growth of wild-type tumors at distant sites. Thus, this study illustrates a potential gene therapy strategy for glioblastoma multiforme patients using GM-CSF and/or B7-2 transduced tumor vaccines. Although extension of these allogeneic studies to an autologous system is critical, this is the first demonstration of in vivo efficacy of combination GM-CSF and B7-2 immunogene therapy for human glioblastoma multiforme.

TGF-B2 and soluble p55 TNFR modulate VCAM-1 expression in glioma cells and brain derived endothelial cells

Transforming growth factor beta-2 (TGF-B2) is secreted by glioma cells and is known to decrease leukocyte-endothelium interaction. TGF-B2 alone and in conjunction with soluble tumor necrosis factor (TNF) p55 receptor, was found to decrease the expression of TNF induced VCAM-1 on the malignant glioma cell line A-172 and human cerebral microvessel endothelial (CNS-EC) cells. Co-culture of A-172 glioma cells led to a decrease in VCAM-1 expression; this effect on CNS-EC in co-culture could be simulated by glioma supernatant alone. These results suggest that malignant gliomas, by secreting TGF-B2 and releasing soluble TNF receptors, modulate adhesion molecules.

Human retinoblastoma: a morphological study of apoptotic, leukocytic, and vascular elements

Retinoblastoma (Rb), derived from retinal neuroepithelial progenitor cells, is the most common intraocular malignancy of childhood. This study examined 10 human Rb biopsy specimens with light and electron microscopy for histopathological features not previously described in detail, including cell death, leukocytic infiltration, and the tumor vasculature. Rb is a solid well-vascularized tumor with regions of viable tumor cells surrounding vessels, interspersed with zones of necrosis; apoptotic cells were seen in all specimens. Mononuclear phagocyte series (MPS) cells and lymphocytes often colocalized, adjacent to tumor vessels, and MPS cells frequently invested the perivascular space. Lymphocytes were rarely seen within areas of viable tumor. Tumor vessels at early stages of formation resembled normal developing retinal vessels. While junctions were often seen between endothelial calls, disruption of these junctions and endothelial fenestrae was sometimes evident. Müller cells and astrocytes extended processes around tumor cells and blood vessels, and contributed to the formation of the vascular glia limitans, which in some mature vessels was disrupted and discontinuous. Overall, this study provides further morphological details of cell death within Rb, particularly apoptotic involution, and describes the presence of a vascular-associated leukocytic infiltration in Rb. Evidence of compromise of the normal blood-retinal barrier (BRB) within the Rb tumor vessels is presented.

Glioblastoma-associated circulating monocytes and the release of epidermal growth factor

Monocytes/macrophages frequently infiltrate malignant gliomas and play a central role in the tumor-associated immune response as they process tumor antigen and present it to T-lymphocytes. Findings have accumulated that peripheral blood monocytes leaving the cerebral circulation become microglial cells and vice versa and that monocytes/macrophages may stimulate malignant tumor growth by some unknown mechanism. Most malignant gliomas express growth factor receptors, for example epidermal growth factor receptor (EGFR). The aim of this study was to determine whether peripheral blood monocytes of glioma patients release EGF, the appropriate ligand of gliomacell membrane-bound EGFR. Long-term cultured peripheral blood monocytes from 14 patients with malignant gliomas were compared to those from 12 controls (seven with nontumorous disease and five healthy individuals). Using an enzyme-linked immunosorbent assay for EGF, the EGF content of cell culture supernatants was determined at Days 7, 21, and 100 of culture. The EGF content (mean +/- standard error) of supernatants was 5.9 +/- 0.2 pg/ml/10(3) glioma monocytes versus 1.3 +/- 0.1 pg/ml/10(3) control monocytes at Day 7 of culture, 22.9 +/- 0.8 pg/ml/10(3) glioma monocytes versus 1.8 +/- 0.9 pg/ml/10(3) control monocytes at Day 21 of culture, and 23.4 +/- 0.7 pg/ml/10(3) glioma monocytes, and below detection levels for control monocytes at Day 100 of culture. Steroid treatment of glioma patients did not influence the EGF release of cultured monocytes. These data indicate that glioblastoma-associated peripheral blood monocytes may be distinct from those of healthy individuals. Moreover, this study indicates that subtypes of glioma-associated peripheral blood monocytes may support immunosuppression and promote growth of malignant glioma by releasing unusually high amounts of EGF.

The failure of current immunotherapy for malignant glioma. Tumor-derived TGF-beta, T-cell apoptosis, and the immune privilege of the brain

Human malignant gliomas are rather resistant to all current therapeutic approaches including surgery, radiotherapy and chemotherapy as well as antibody-guided or cellular immunotherapy. The immunotherapy of malignant glioma has attracted interest because of the immunosuppressed state of malignant glioma patients which resides mainly in the T-cell compartment. This T-cell suppression has been attributed to the release by the glioma cells of immunosuppressive factors like transforming growth factor-beta (TGF-beta) and prostaglandins. TGF-beta has multiple effects in the immune system, most of which are inhibitory. TGF-beta appears to control downstream elements of various cellular activation cascades and regulates the expression of genes that are essential for cell cycle progression and mitosis. Since TGF-beta-mediated growth arrest of T-cell lines results in their apoptosis in vitro, glioma-derived TGF-beta may prevent immune-mediated glioma cell elimination by inducing apoptosis of tumor-infiltrating lymphocytes in vivo. T-cell apoptosis in the brain may be augmented by the absence of professional antigen-presenting cells and of appropriate costimulating signals. Numerous in vitro studies predict that tumor-derived TGF-beta will incapacitate in vitro-expanded and locally administered lymphokine-activated killer cells (LAK-cells) or tumor-infiltrating lymphocytes. Thus, TGF-beta may be partly responsible for the failure of current adoptive cellular immunotherapy of malignant glioma. Recent experimental in vivo studies on non-glial tumors have corroborated that neutralization of tumor-derived TGF-beta activity may facilitate immune-mediated tumor rejection. Current efforts to improve the efficacy of immunotherapy for malignant glioma include various strategies to enhance the immunogenicity of glioma cells and the cytotoxic activity of immune effector cells, e.g., by cytokine gene transfer. Future strategies of cellular immunotherapy for malignant glioma will have to focus on rendering glioma cell-targeting immune cells resistent to local inactivation and apoptosis which may be induced by TGF-beta and other immunosuppressive molecules at the site of neoplastic growth. Cytotoxic effectors targeting Fas/APO-1, the receptor protein for perforin-independent cytotoxic T-cell killing, might be promising, since Fas/APO-1 is expressed by glioma cells but not by untransformed brain cells, and since Fas/APO-1-mediated killing in vitro is not inhibited by TGF-beta.