Exploitation of immune mechanisms in the treatment of central nervous system cancer

Dendritic cell-based immunotherapy for malignant glioma

The immunotherapy for malignant glioma faces unique difficult, due to some anatomical and immunological characteristics including the existence of blood brain barrier, the absence of lymphatic tissues and dendritic cells (DCs) in the central nervous system (CNS) parenchyma, and the presence of an immunosuppressive microenvironment. Therefore, immunotherapeutic approaches will not be beneficial unless the compromised immune status in malignant glioma patients is overcome. DC-based immunotherapy, vaccinating cancer patients with DCs pulsed with various tumor antigens, is one of the most promising immunotherapeutic approaches for treatment of malignant glioma because it seems able to overcome, at least partially, the immunosuppressive state associated with primary malignancies. The preparation of DCs, choice of antigen, and route and schedule of administration are improving and optimizing with rapid development of molecular biology and gene engineering technology. DC vaccination in humans, after a number of pre-clinical models and clinical trials, would increase the clinical benefits for malignant glioma immunotherapy.

Recent advances in the treatment of childhood brain tumors

Pediatric brain tumors are the commonest cause of cancer-related death in children. The last four decades have seen only a 35% increase in 5-year survival rate of children with these tumors. The therapeutic successes achieved are due to advances in neuroimaging, surgical techniques, radiotherapy, and induction of newer chemotherapeutic agents along with molecular targeted therapy. Neuroimaging advances include the use of MRA, MRS, DSA, and PET scans. With the use of stereotactic surgery, intraoperative mapping, and imaging, surgical resection has improved with significant decrease in morbidity. A major development has been the use of precision guided radiotherapy utilizing technologies like 3D-CRT, SRS, and IMRT, thereby decreasing radiation to normal tissues. Induction of newer drugs and high-dose chemotherapy with peripheral stem cell support has improved survival and delayed radiation in younger children and infants with brain tumors. Intense ongoing research is profiling novel molecular targets for therapeutic intervention. Newer therapeutic strategies like blood brain barrier disruption, immunotherapy, and gene therapy are in clinical trials. This review article intends to give the reader an overview of current therapeutic strategies and research involved in the treatment of children with brain tumors.

Proton radiation and TNF-alpha/Bax gene therapy for orthotopic C6 brain tumor in Wistar rats

High-grade tumors of the brain remain virtually incurable with current therapeutic regimens, new approaches to augment existing therapies need to be explored. The major goal of this pilot study was to evaluate the feasibility of gene therapy using plasmid DNA encoding tumor necrosis factor-alpha and bax together with proton radiation in an immunocompetent animal model with orthotopic brain tumor. C6 glioma cells were stereotactically implanted into the left hemibrain of Wistar rats (day 0). On day 5, the appropriate groups received intratumoral pGL1-TNF-a and pGL1-Bax (10 microg each), parental plasmid pWS4 (20 microg), or PBS. Hemibrain proton irradiation (10 Gy, 90 MeV, single fraction) was delivered 18-20 hr later. Rats were euthanized when signs of illness appeared. In addition, a subset of animals from each group was euthanized on day 9 for immune and other assays. By day 9, 25%, 20%, and 10% of rats treated with PBS, pWS4, or pGL1-TNF-alpha/pGL1-Bax, respectively, had been euthanized due to weight loss or other signs of illness, whereas all rats treated with pGL1-TNF-alpha/pGL1-Bax + radiation or radiation alone were healthy (P<0.05). At this same time, the pGL1-TNF-alpha/pGL1-Bax + radiation group had significantly elevated lymphocyte percentages (P<0.005 or less) and a relatively high level of lymphocytic infiltrate within tumors. Although the rats treated with pGL1-TNF-alpha/pGL1-Bax had the highest levels of activated T helper (CD4+/CD71+) and T cytotoxic (CD8+/CD71+) cells, the values were not significantly different compared to the pWS4-injected control group. Splenocytes in all tumor cell-injected groups had higher mean values for DNA and protein synthesis compared to the non-tumor cell injected control group, whereas oxygen radical production by phagocytes was consistently higher in groups injected with plasmid or treated with radiation. Body, hemibrain, and spleen masses, white blood cell, red blood cell and platelet counts, hemoglobin, hematocrit, and transforming growth factor-beta1 levels in plasma were similar among groups. The results demonstrate that treatment with pGL1-TNF-alpha/pGL1-Bax combined with proton hemibrain irradiation is safe under the conditions used. Overall, these data support further investigation of this unique combination therapy.

Antitumor vaccination of patients with glioblastoma multiforme: a pilot study to assess feasibility, safety, and clinical benefit

PURPOSE

Prognosis of patients with glioblastoma is poor. Therefore, in glioblastoma patients, we analyzed whether antitumor vaccination with a virus-modified autologous tumor cell vaccine is feasible and safe. Also, we determined the influence on progression-free survival and overall survival and on vaccination-induced antitumor reactivity.

PATIENTS AND METHODS

In a nonrandomized study, 23 patients were vaccinated and compared with nonvaccinated controls (n = 87). Vaccine was prepared from patient's tumor cell cultures by infection of the cells with Newcastle Disease Virus, followed by gamma-irradiation, and applied up to eight times. Antitumor immune reactivity was determined in skin, blood, and relapsed tumor by delayed-type hypersensitivity skin reaction, ELISPOT assay, and immunohistochemistry, respectively.

RESULTS

Establishment of tumor cell cultures was successful in approximately 90% of patients. After vaccination, we observed no severe side effects. The median progression-free survival of vaccinated patients was 40 weeks (v 26 weeks in controls; log-rank test, P = .024), and the median overall survival of vaccinated patients was 100 weeks (v 49 weeks in controls; log-rank test, P < .001). Forty-five percent of the controls survived 1 year, 11% survived 2 years, and there were no long-term survivors (> or = 3 years). Ninety-one percent of vaccinated patients survived 1 year, 39% survived 2 years, and 4% were long-term survivors. In the vaccinated group, immune monitoring revealed significant increases of delayed-type hypersensitivity reactivity, numbers of tumor-reactive memory T cells, and numbers of CD8(+) tumor-infiltrating T-lymphocytes in secondary tumors.

CONCLUSION

Postoperative vaccination with virus-modified autologous tumor cells seems to be feasible and safe and to improve the prognosis of patients with glioblastomas. This could be substantiated by the observed antitumor immune response.

Justification of glioma biology beyond a cellular basis of interpretation

Gliomas as neoplasms primarily arising from and constituted by glial cells would appear to implicate cell types that inherently reflect variation of aspects of a putative reparative process. The prominence of an astrocytic type cell of origin would further perhaps constitute a system of malignant transformation based on aberrant progression in cell proliferation and of cell pathology related to aspects on one hand of a gliosis and on the other of an autonomous process of progressiveness. In such terms, perhaps, one might consider the molecular aspects of gliomatous pathogenesis as simply a process of integral aberration of various aspects of astrocytic or glial cell responsiveness outside the normal confines of the normal reparative process and inherently beyond a strict cellular basis of interpretation in pathobiologic terms of such processes as anti-apoptosis and amplification of growth factor receptivity.

Autologous adjuvant linked fibroblasts induce anti-glioma immunity: implications for development of a glioma vaccine

OBJECTIVES

Adjuvant-linked vaccines have been shown to induce anti-tumor immunity in patients with a variety of solid tumors. In this study we describe an in vitro model of active immunotherapy using autologous fibroblasts as immunogen. Correlative results from glioma patients immunized with autologous fibroblasts are also described.

METHODS

Peripheral blood lymphocytes (PBLs) from normal subjects were immunized in vitro against autologous skin fibroblasts coupled to the adjuvant muramyl dipeptide. The lymphocytes developed cell-mediated cytotoxicity that was measured with a short-term chromium release assay. Results of in vitro experiments were compared to data derived from glioma patients immunized with subcutaneous injection of an autologous adjuvant-linked fibroblast vaccine. Glioma target cells and fibroblast immunogens were derived from early passage primary tissue culture.

RESULTS

A comparison of autologous vs. homologous immunogen indicated that major histocompatibility complex matching was required at the sensitization stage of immunity (17.2 +/- 3.4% specific lysis vs. 0.4 +/- 3.1%, P < 0.01). Pre-treatment of fibroblast immunogen cells with interferon gamma (IFN-gamma) was found to significantly increase immunity (42.2 +/- 10.0%, P < 0.01), as did IFN-gamma pre-treatment of tumor target cells (35.8 +/- 9.0%, P < 0.01). The positive effect of IFN-gamma was diminished by treatment of cells with IFN-alpha. These in vitro results correlated well with in vivo data derived from glioma patients immunized with an autologous adjuvant-linked fibroblast vaccine. PBLs from patients developed direct cell-mediated cytotoxicity against autologous tumor cells. Lysis of tumor targets after in vivo immunization increased over a three-week interval (from 1.2 +/- 3.0% to 21.0 +/- 3.4%, P < 0.01) while lysis of a non-MHC matched control cell line remained essentially unchanged.

CONCLUSIONS

Specific lysis of glioma targets in vitro was achieved after in vivo sensitization with autologous adjuvant-linked fibroblasts. Collectively, the data indicate that biochemically modified autologous cells can stimulate anti-glioma immunity in humans. The degree of specific immunity seen in our patients compares favorably with other published series using glioma cells as an antigenic source. Accordingly, fibroblasts may represent a practical alternative to glioma cells for vaccine construction.

7-Hydroxystaurosporine-induced apoptosis in 9L glioma cells provides an effective antigen source for dendritic cells and yields a potent vaccine strategy in an intracranial glioma model

OBJECTIVE

On the basis of recent studies indicating that tumoral apoptotic bodies may provide a potent source of antigen for delivery to antigen-presenting cells, as well as observations that signal transduction modulation may constitute a promising approach for inducing glioma cell apoptosis, we explored the efficacy of vaccination with glioma apoptotic body-pulsed dendritic cells (DCs) for inhibiting tumor growth in the syngeneic 9L glioma/Fischer rat model.

METHODS

For induction of apoptosis, 7-hydroxystaurosporine (UCN-01) (200-300 ng/ml), a selective protein kinase C inhibitor, was co-incubated with 9L cells in vitro for 72 or 96 hours. After this pretreatment period, glioma cells and DCs were mixed, and the interaction between DCs and apoptotic 9L tumor cells was assessed using two-color flow cytometry. In a series of experiments, the efficacy of vaccination strategies using DCs co-cultured with apoptotic 9L cells was then examined in animals harboring intracranial tumors.

RESULTS

Pretreatment of 9L cells with UCN-01 resulted in approximately 50% of cells' being observed to undergo apoptosis as compared with less than 3% of controls. After subsequent co-culture, two-color flow cytometry demonstrated a time-dependent physical association of DCs with the apoptotic glioma cells. Survival in animals harboring intracranial tumors was significantly longer for the animals treated with a glioma apoptotic body-pulsed DC vaccine than in the animals that received apoptotic glioma cells and DCs alone or vehicle (i.e., the controls), especially those that underwent a sequential vaccination strategy (P < 0.0001). Long-term survival (>90 d) was demonstrated in 6 (75%) of 8 animals that underwent this vaccination approach versus 0 (0%) of 16 controls. In contrast, no survival benefit was observed in animals that received DCs that were co-cultured with vehicle-treated (non-apoptotic) 9L cells. Three of four long-term survivors that were rechallenged intracranially with tumor cells also survived over the long term.

CONCLUSION

These studies suggest that induction of apoptosis in glioma cells by use of UCN-01 may promote the uptake of tumor antigens by DCs. This finding is important because apoptotic body-stimulated DCs may hold promise in promoting a host response against an established intracranial glioma, particularly if the parameters for apoptotic induction, duration of co-culture, and vaccination can be optimized.

Combination of stereotactic radiosurgery and cytokine gene-transduced tumor cell vaccination: a new strategy against metastatic brain tumors

OBJECT

To determine if the combination of radiosurgery and tumor cell vaccine would enhance the therapy of metastatic lesions of the central nervous system (CNS), the authors examined the antitumoral effects of radiosurgery and cytokine-transduced tumor cell vaccine.

METHODS

Fifty-five rats underwent intracranial implantation of 5 x 10(3) MADB 106 cells. On Day 3 after tumor implantation, 34 rats were inoculated in the flank with nonirradiated MADB 106 cells that had been retrovirally transduced to express granulocyte-macrophage colony-stimulating factor or interleukin-4. Twenty-seven rats (17 animals that had received the vaccine and 10 that had not) underwent radiosurgery performed using a gamma knife at maximum doses of 32 Gy on Day 5. No animals in the untreated group or in the vaccine-alone groups survived longer than 21 days. Animals treated by ra diosurgery alone displayed prolonged survival in comparison with untreated animals (p < 0.0001), but only one of 10 animals survived longer than 55 days. In contrast, 14 of 17 animals that received the combination therapy of radiosurgery and vaccination survived longer than 55 days (p = 0.0003 compared with animals that underwent radiosurgery alone). On Day 55, the long-term survivors were challenged by parental MADB 106 cells, which were implanted in the contralateral hemisphere. All animals from the combination therapy groups survived longer than 50 days after this challenge, but the single survivor from the radiosurgery-alone group died of tumor growth in 27 days.

CONCLUSIONS

The combination of radiosurgery and cytokine gene-transduced tumor cell vaccine markedly prolonged animal survival and protected animals from a subsequent challenge by parental tumor cells placed in the CNS. The data provided by this study indicate that this combination therapy represents a strategy that may have clinical applicability for single and/or multiple metastatic brain tumors.

Gliomagenesis: genetic alterations and mouse models

Glioblastoma multiforme is the most malignant of the primary brain tumours and is almost always fatal. The treatment strategies for this disease have not changed appreciably for many years and most are based on a limited understanding of the biology of the disease. However, in the past decade, characteristic genetic alterations have been identified in gliomas that might underlie the initiation or progression of the disease. Recent modelling experiments in mice are helping to delineate the molecular aetiology of this disease and are providing systems to identify and test novel and rational therapeutic strategies.