Dendritic Cell Therapy of Primary Brain Tumors

The Role of Cellular Immunity and Adaptive Immunity in Pathophysiology of Brain and Spinal Cord Tumors

Major advances have been made in our understanding of CNS tumors, especially glioma, however, the survival of patients with malignant glioma remains poor. While radiation and chemotherapy have increased overall survival, glioblastoma multiforme (GBM) still has one of the worst 5-year survival rates of all human cancers. Here, in this chapter, the authors review the abrogation of the immune system in the tumor setting, revealing many plausible targets for therapy and the current immunotherapy treatment strategies employed. Notably, glioma has also been characterized as a subset of primary spinal cord tumor and current treatment recommendations are outlined here.

Immunotherapeutic Strategies for Malignant Glioma

BACKGROUND

Despite advances in surgery, radiation therapy, and chemotherapy, only modest improvement has been achieved in the survival of patients with malignant gliomas.

METHODS

The authors review the immunologic aspects of gliomas, potential targets for therapy, and issues surrounding current immunotherapeutic strategies directed against malignant gliomas.

RESULTS

The blood-brain barrier and the purported immunological privilege of the brain are not necessarily insurmountable obstacles to effective immunotherapy for brain tumors. Preclinical studies suggest a number of potential therapeutic avenues. Translational studies offer the prospect of providing substantial new information about immunological trafficking in the nervous system and suggesting the most fruitful approaches to immunotherapy for malignant gliomas.

CONCLUSIONS

More effective adjuvant treatments for malignant gliomas are needed. The applicability of immunological approaches in the treatment of these tumors warrants continued study.

Dendritic cell-based immunotherapy for malignant gliomas

Despite dramatic advances in surgical techniques, imaging and adjuvant radiotherapy or chemotherapy, the prognosis for patients with malignant glial tumors remains dismal. Based on the current knowledge regarding immune responses in the healthy CNS and glioma-bearing hosts, this review discusses dendritic cell-based immunotherapeutic approaches for malignant gliomas and the relevance of recent clinical trials and their outcomes. It is now recognized that the CNS is not an immunologically tolerated site and clearance of arising glioma cells is a routine physiologic function of the normal, noncompromised immune system. To escape from immune surveillance, however, clinically apparent gliomas develop complex mechanisms that suppress tumoricidal immune responses. Although the use of dendritic cells for the treatment of glioma patients may be the most appropriate approach, an effective treatment paradigm for these tumors may eventually require the use of several types of treatment. Additionally, given the heterogeneity of this disease process and an immune-refractory tumor cell population, the series use of rational multiple modalities that target disparate tumor characteristics may be the most effective therapeutic strategy to treat malignant gliomas.

Dendritic cell vaccines

Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. Among the new treatments currently being investigated, immunotherapy is theoretically very attractive since it offers the potential for high tumor-specific cytotoxicity. Increasing numbers of reports demonstrate that systemic immunotherapy using dendritic cells is capable of inducing an antiglioma response. Therefore, dendritic cell-based immunotherapy could be a new treatment modality for patients with glioma. In this chapter, we will discuss the implications of these findings for glioma therapy, reviewing current literature on dendritic cell-based glioma immunotherapy. We will overview the role of dendritic cells in immunobiology, the central nervous system and tumor immunology, before outlining dendritic cell therapy results in clinical trials and future directions. Dendritic cell-based immunotherapy strategies appear promising as an approach to successfully induce an antitumor immune response in patients with glioma, where it seems to be safe and without major side effects. The development of methods for manipulating dendritic cells for the purpose of vaccination will enhance the clinical usefulness of these cells for biotherapy. Its efficacy should be further determined in randomized, controlled clinical trials.

Effect of double-stranded DNA on maturation of dendritic cells in vitro

A preparation of human genomic fragmented double-stranded DNA (dsDNA) was used as maturation stimulus in cultures of human dendritic cells (DCs) generated in compliance with the interferon protocol. Culturing of the DCs in medium with 5μg/ml of the DNA preparation was associated with a decrease in the relative proportion of CD14 + cells and an increase in that of CD83 + cells. These changes are markers of DC maturation. The efficiency with which the DNA preparation was able to elicit DC maturation was commensurate with that of lypopolysaccharide from bacterial cell, the standard inducer of DC maturation. Generated ex vivo, matured in the presence of the human DNA preparation, pulsed with tumor antigens mouse DCs were used as a vaccine in biological tests for its antitumor activity. The experimental results demonstrate that reinfusion of mature pulsed with tumor antigens DCs cause a statistically significant suppression of tumor graft growth.

Dendritic cell vaccines for brain tumors

Over the past decade, dendritic cell-based immunotherapy for central nervous system tumors has progressed from preclinical rodent models and safety assessments to phase I/II clinical trials in over 200 patients, which have produced measurable immunologic responses and some prolonged survival rates. Many questions regarding the methods and molecular mechanisms behind this new treatment option, however, remain unanswered. Results from currently ongoing and future studies will help to elucidate which dendritic cell preparations, treatment protocols, and adjuvant therapeutic regimens will optimize the efficacy of dendritic cell vaccination. As clinical studies continue to report results on dendritic cell-mediated immunotherapy, it will be critical to continue refining treatment methods and developing new ways to augment this promising form of glioma treatment.

Glioma stem cell research for the development of immunotherapy

Glioma, especially high-grade glioblastoma multiforme (GBM), is the most common and aggressive type of brain tumor, accounting for about half of all the primary brain tumors. Despite continued advances in surgery, chemotherapy, and radiotherapy, the clinical outcomes remain dismal. The 2-year survival rate of GBM is less than 30%. Better understanding of GBM biology is needed to develop novel therapies. Recent studies have demonstrated the existence of a small subpopulation of cells with stemlike features called cancer stem cells (CSCs). These GBM CSCs are self renewable and highly tumorigenic. They not only are chemo-radio resistant but also often contain multidrug resistance genes and drug transporter genes. These characteristics enable GBM CSCs to survive standard cytotoxic therapies. Among GBM CSCs, CD133(+) cells are a well-defined population and are prospectively isolated by their cell-surface marker. Increasing data show that the presence of CD133(+) CSCs highly correlates with patient survival, making these cells an ideal immunotherapy target population. The authors have reviewed recent studies related with GBM CSCs (particularly CD133(+) CSCs) and the novel therapeutic strategies targeting these cells.

Use of interferon-alpha-induced dendritic cells in the therapy of patients with malignant brain gliomas

Clinical and immunological analysis of the efficiency of combined immunotherapy with the use dendritic cells for the treatment of malignant glioma of the brain was carried out. Dendritic cells generated in the presence of granulocyte-macrophage CSF and IFN-alpha retain their functional characteristics in patients with gliomas, which suggests the possibility of their use for the treatment of malignant tumors (glioma) of the brain. Combined therapy using interferon-induced dendritic cells was associated with generation of antigen-specific immune response during vaccinations. The results indicate satisfactory tolerance of combined immunotherapy using dendritic cells and the absence of toxic side effects at the stage of adoptive immunotherapy and at the stage of vaccinations with dendritic cells. Clinical trials showed that vaccinations with dendritic cells included into combined immunotherapy improved the quality of life and survival of patients with malignant gliomas.

Brain tumor stem cells: new targets for clinical treatments?

✓ The observation of similarities between the self-renewal mechanisms of stem cells and cancer cells has led to the new concept of the cancer stem cell. In cases of leukemia, multiple myeloma, and breast cancer, cells with a high self-renewal potential have been identified. Furthermore, investigators have shown these cells' ability to drive the formation and growth of the tumor. Brain tumors have also been reported to possess a subpopulation of cancer stemlike cells that have the ability to proliferate, self-renew, and be multipotent. When grafted into mice, these cells are also able to generate a tumor that recapitulates that of the patient from whom the cells were derived. The identification and characterization of this new category of cells call for new therapies capable of selectively targeting and killing these multifaceted cells.

Dendritic cell vaccination in glioblastoma patients induces systemic and intracranial T-cell responses modulated by the local central nervous system tumor microenvironment

PURPOSE

We previously reported that autologous dendritic cells pulsed with acid-eluted tumor peptides can stimulate T cell-mediated antitumor immune responses against brain tumors in animal models. As a next step in vaccine development, a phase I clinical trial was established to evaluate this strategy for its feasibility, safety, and induction of systemic and intracranial T-cell responses in patients with glioblastoma multiforme.

EXPERIMENTAL DESIGN

Twelve patients were enrolled into a multicohort dose-escalation study and treated with 1, 5, or 10 million autologous dendritic cells pulsed with constant amounts (100 mug per injection) of acid-eluted autologous tumor peptides. All patients had histologically proven glioblastoma multiforme. Three biweekly intradermal vaccinations were given; and patients were monitored for adverse events, survival, and immune responses. The follow-up period for this trial was almost 5 years.

RESULTS

Dendritic cell vaccinations were not associated with any evidence of dose-limiting toxicity or serious adverse effects. One patient had an objective clinical response documented by magnetic resonance imaging. Six patients developed measurable systemic antitumor CTL responses. However, the induction of systemic effector cells did not necessarily translate into objective clinical responses or increased survival, particularly for patients with actively progressing tumors and/or those with tumors expressing high levels of transforming growth factor beta(2) (TGF-beta(2)). Increased intratumoral infiltration by cytotoxic T cells was detected in four of eight patients who underwent reoperation after vaccination. The magnitude of the T-cell infiltration was inversely correlated with TGF-beta(2) expression within the tumors and positively correlated with clinical survival (P = 0.047).

CONCLUSIONS

Together, our results suggest that the absence of bulky, actively progressing tumor, coupled with low TGF-beta(2) expression, may identify a subgroup of glioma patients to target as potential responders in future clinical investigations of dendritic cell-based vaccines.

Cytotoxicity of rat marrow stromal cells against malignant glioma cells

OBJECTS

Marrow stromal cells (MSCs) have been shown to have the capacity of orthodox and unorthodox plasticity. In this study, the authors tried to access in vitro cytotoxicity of MSCs from rat and also to differentiate MSCs into immune effector cell.

METHODS

Rat MSCs (rMSCs) were isolated by standard methodology and were activated by interleukin-2 (IL-2), interleukin-15 (IL-15), granulocyte macrophage colony stimulating factor, and combinations, which were effector cells. Cytotoxicity of rMSCs and activated rMSCs against the target cells (9L rat glioma cell line) was estimated using visual survival cell assay. Phenotypes of these various activated cells were determined using flow cytometry. The secreted protein from effector cells was estimated by enzyme-linked immunosorbent assay. The expression of immune response-related genes in activated cells was measured.

RESULTS

There was a significant cytotoxicity of rMSCs activated with various cytokine combinations. After various cytokine activations of rMSCs, the population of immune effector cells (CD8, CD161a) and immune reaction-related proteins (IL-4, gamma-INF) might increase. Apoptosis may be one of the lysis mechanisms of target cells by activated rMSCs. The contributing genes could be gamma-INF, FasL, and perforin.

CONCLUSION

This study suggests that rMSC may be used as adoptive transfer therapy in patients suffering from malignant brain tumor, but we have to investigate orthotopic animal study for the proper translation.

Highly Successful Therapeutic Vaccinations Combining Dendritic Cells and Tumor Cells Secreting Granulocyte Macrophage Colony-stimulating Factor

In an attempt to induce potent immune antitumor activities, we investigated, within the rat 9L gliosarcoma model, distal therapeutic vaccinations associating three therapies: dendritic cell vaccination, intratumoral granulocyte macrophage colony-stimulating factor (GM-CSF) gene transfer, and tumor apoptosis induction. Vaccines of dendritic cells coinjected with processed GM-CSF secreting 9L cells induced systemic responses, resulting in the complete regression of distant preimplanted 9L tumor masses in, with the best strategy, 94% of male rats. All of the cured rats developed a long-term resistance to a rechallenge with parental cells. The curative responses were correlated with the detection of elevated specific cytotoxic activities and a CD4+, CD8+ T cell-, and natural killer (NK) cell-mediated IFN-gamma production. The survival rate of the rat seemed more directly linked to the amount of GM-CSF secreted by the transduced tumor cells, which in turn depended on the toxicity of the apoptosis-inducing treatment, than to the level of apoptosis induced. Unexpectedly, alive GM-CSF secreting 9L cells became apoptotic when injected in vivo. Thus we documented the positive role of apoptosis in the induction of therapeutic antitumor responses by comparing, at equal GM-CSF exogenous supply, the effects of dendritic cells coinjected with apoptotic or necrotic 9L cells. The data showed the superior therapeutic efficiency of combined vaccines containing apoptotic tumor cells. In conclusion, vaccinations with dendritic cells associated with apoptotic tumor cells secreting GM-CSF show a very high therapeutic potency that should show promise for the treatment of human cancer.

Systematic Comparison of Dendritic Cell-based Immunotherapeutic Strategies for Malignant Gliomas: In Vitro Induction of Cytolytic and Natural Killer-like T Cells

OBJECTIVE

To compare the efficacy of various immunotherapeutic strategies of loading dendritic cells (DCs) with whole-glioma cell antigens and characterize the effector responses induced.

METHODS

DCs were either fused with major histocompatibility complex (MHC)-matched glioma cells (Fusion) or pulsed with apoptotic tumor cells (DC/Apo), total tumor ribonucleic acid (RNA) (DC/RNA), or tumor lysate (DC/Lys). These tumor-DC preparations were then assessed for their phenotype, cytokine profile, and capacity to stimulate autologous peripheral blood mononuclear cells (PBMCs) in vitro. Phenotype and tumor-specific cytolytic activities of various effector cell populations were characterized and compared.

RESULTS

The various tumor-DC preparations exhibited similar phenotype and cytokine profiles irrespective of the method of loading tumor-cell antigens. However, the fusion, DC/Apo, and DC/RNA induced superior tumor cytolytic activities in PBMCs compared with DC/Lys or DC and tumor controls. DC/Apo induced the greatest expansion of tumor-specific lymphocytes, as detected by trypan blue exclusion and thymidine incorporation assays. Flow cytometric analyses also revealed the highest relative percentages of T helper cells (CD3+CD4+), cytotoxic T lymphocytes (CTLs) (CD3+CD8+), and natural killer (NK)-like T cells (CD3+CD56+) in the DC/Apo group among all the groups studied, indicating that DC/Apo induced expansion of PBMCs bearing multiple T and NK cell markers. Interestingly, isolated NK-like T cells demonstrated significantly higher tumor cytotoxicity compared with CTLs isolated from the same groups and was also non-MHC-restricted.

CONCLUSION

Apoptotic tumor cells may be an optimal source of whole-tumor-cell antigen for immunotherapy of gliomas. The study also demonstrates for the first time that both CTLs and NK-like T cells are expanded and stimulated by mature, tumor-pulsed DCs.

Human autologous dendritic cell-glioma fusions: feasibility and capacity to stimulate T cells with proliferative and cytolytic activity

Gliomas are the most common primary neoplasm of the central nervous system. The failure of conventional treatment modalities to improve outcome over the last two decades has led to interest in alternative treatment modalities. Dendritic cell (DC)-based immunotherapy has utilized DC pulsed with tumor lysate or peptide to induce an antitumor immune response mediated largely by CD8 T cells. While this has been effective in preclinical studies, clinical efficacy remains unproven. Recently, hybrid cells produced by fusions of tumor and autologous DC have demonstrated remarkable efficacy for stimulating an anti-tumor immune response in both preclinical and clinical studies of extra-cranial neoplasms. The advantage of generating such hybrid cells is that the entire cellular material of the tumor is processed and presented in both endogenous and exogenous pathways. This leads to activation of both MHC class I restricted CD8 cells as well as MHC class II restricted CD4 T cells. Here, we examined in vitro T cell stimulatory capacity of autologous human DC-glioma fusion in comparison to DC loaded with apoptotic glioma. DC fused with autologous tumor or loaded with apoptotic tumor cells (DC/apo) were first used to stimulate autologous non-adherent peripheral blood mononuclear cells (PBMC), in vitro. The PBMC were then examined for phenotype (CD3, CD4, CD8) and intracellular IFN-gamma using flow cytometry. Lymphocyte proliferation and cytolytic responses were also assessed. Lymphocytes stimulated in vitro with fusion or DC/apo cells showed significantly enhanced cytotoxicity and proliferation against autologous tumor cells compared with PBMC stimulated with tumor cells or DC alone. Both strategies had similar efficacy. Tumor-cytolytic responses were enhanced by the addition of CD40 ligand (CD40L), and partially blocked by anti-MHC class I antibody. Flow cytometric analysis detected CD3+ CD8+ T cells, which also stained positive for intracellular IFN-gamma. The study suggests that DC/glioma fusion and DC/apo have comparable efficacy for stimulation of CTL with cytolytic and proliferative activity against human malignant gliomas. These findings may have implications for future studies of DC-based immunotherapy in malignant gliomas.

T-cell immune responses in the brain and their relevance for cerebral malignancies

In order that cellular immune responses afford protection without risk to sensitive normal tissue, they must be adapted to individual tissues of the body. Nowhere is this more critical than for the brain, where various passive and active mechanisms maintain a state of immune privilege that can limit high magnitude immune responses. Nevertheless, it is now clear that immune responses are induced to antigens in the brain, including those expressed by cerebral malignancies. We discuss hypotheses of how this can occur, although details such as which antigen presenting cells are involved remain to be clarified. Antitumor responses induced spontaneously are insufficient to eradicate malignant astrocytomas; many studies suggest that this can be explained by a combination of low level immune response induction and tumor mediated immunosuppression. A clinical objective currently pursued is to use immunotherapy to ameliorate antitumour immunity. This will necessitate a high level immune response to ensure sufficient effector cells reach the tumor bed, focused cytotoxicity to eradicate malignant cells with little collateral damage to critical normal cells, and minimal inflammation. To achieve these aims, priority should be given to identifying more target antigens in astrocytoma and defining those cells present in the brain parenchyma that are essential to maintain antitumour effector function without exacerbating inflammation. If we are armed with better understanding of immune interactions with brain tumor cells, we can realistically envisage that immunotherapy will one day offer hope to patients with currently untreatable neoplastic diseases of the CNS.