Enhancement of antitumor immune response in glioma models in mice by genetically modified dendritic cells pulsed with Semliki forest virus-mediated complementary DNA

Semliki Forest virus-based immunotherapy for cancer

Introduction: Immunotherapy has been introduced as a modern alternative for the treatment of various cancers, including the stimulation of the immune system by introduction of immunostimulatory molecules. Application of viral and non-viral vectors have provided a substantial contribution to improved delivery and expression of these immunostimulators.Areas covered: Alphavirus vectors, based on Semliki Forest virus, have allowed immunization with self-replicating RNA, recombinant virus particles, and layered DNA/RNA vectors. The attractive features of alphaviruses comprise their broad host range and extreme RNA replication in infected cells resulting in very high recombinant protein expression levels providing enhanced immune responses and an excellent basis for immunotherapy.Expert opinion: Immunization studies in animal tumor models have elicited strong humoral and cellular immune response, have provided prophylactic protection against tumor challenges, and have generated therapeutic efficacy in tumor-bearing animals. Clinical trials have indicated safe use of alphavirus vectors, making them attractive for cancer immunotherapy.

Trial watch: dendritic cell vaccination for cancer immunotherapy

Dendritic- cells (DCs) have received considerable attention as potential targets for the development of anticancer vaccines. DC-based anticancer vaccination relies on patient-derived DCs pulsed with a source of tumor-associated antigens (TAAs) in the context of standardized maturation-cocktails, followed by their reinfusion. Extensive evidence has confirmed that DC-based vaccines can generate TAA-specific, cytotoxic T cells. Nonetheless, clinical efficacy of DC-based vaccines remains suboptimal, reflecting the widespread immunosuppression within tumors. Thus, clinical interest is being refocused on DC-based vaccines as combinatorial partners for T cell-targeting immunotherapies. Here, we summarize the most recent preclinical/clinical development of anticancer DC vaccination and discuss future perspectives for DC-based vaccines in immuno-oncology.

Trial watch: Dendritic cell-based anticancer immunotherapy

Dendritic cell (DC)-based vaccines against cancer have been extensively developed over the past two decades. Typically DC-based cancer immunotherapy entails loading patient-derived DCs with an appropriate source of tumor-associated antigens (TAAs) and efficient DC stimulation through a so-called "maturation cocktail" (typically a combination of pro-inflammatory cytokines and Toll-like receptor agonists), followed by DC reintroduction into patients. DC vaccines have been documented to (re)activate tumor-specific T cells in both preclinical and clinical settings. There is considerable clinical interest in combining DC-based anticancer vaccines with T cell-targeting immunotherapies. This reflects the established capacity of DC-based vaccines to generate a pool of TAA-specific effector T cells and facilitate their infiltration into the tumor bed. In this Trial Watch, we survey the latest trends in the preclinical and clinical development of DC-based anticancer therapeutics. We also highlight how the emergence of immune checkpoint blockers and adoptive T-cell transfer-based approaches has modified the clinical niche for DC-based vaccines within the wide cancer immunotherapy landscape.

Gene Therapy Applications of Viral Vectors

Viral vectors have frequently been applied in gene therapy with the final goal of treating various diseases in the areas of neurology, neurodegeneration, metabolic disease, and cancer. Vectors have been engineered based on AAV, adenoviruses, alphaviruses, herpes simplex viruses, lentiviruses, and retroviruses. Some vectors are suitable for short-term episomal transgene expression, whereas others are integrated into the host cell genome to provide long-term expression. Additionally, hybrid vectors with favorable features from different viruses have been developed. Therapeutic genes of choice have typically been toxic genes such as thymidine kinase, pro-apoptotic genes like Bax, and immunostimulatory genes (for instance, interleukin-12). A large number of animal studies have demonstrated proof of concept of viral gene therapy. Many types of viral vectors have been employed in more than 700 clinical trials that have been carried out or are currently in progress.

Alphavirus-based vaccines in melanoma: rationale and potential improvements in immunotherapeutic combinations

Immune checkpoint blockade has formally demonstrated the clinical benefit of immunotherapy against melanoma. New immunotherapeutic modalities are currently explored to improve the management of relapsing/refractory patients. Potent antitumor vaccines would have the advantage to promote long-lasting tumor control while limiting autoimmunity. Alphavirus vectors and nonreplicating particles offer versatile platforms to deliver antigen expression and immunize against cancer. They have shown promising preclinical results and initial proof of clinical activity in melanoma. The growing number of clinically available immunomodulatory agents provides a tremendous opportunity to exploit and revisit anticancer vaccines in the setting of powerful immunotherapeutic combinations. Accelerating the evaluation of alphavirus-based vaccines in patients with immune sensitive, but still very deadly malignancies, such as melanoma, is thus extremely important.

Alphavirus vectors as tools in neuroscience and gene therapy

Alphavirus-based vectors have been engineered for in vitro and in vivo expression of heterelogous genes. The rapid and easy generation of replication-deficient recombinant particles and the broad range of host cell infection have made alphaviruses attractive vehicles for applications in neuroscience and gene therapy. Efficient delivery to primary neurons and hippocampal slices has allowed localization studies of gene expression and electrophysiological recordings of ion channels. Alphavirus vectors have also been applied for in vivo delivery to rodent brain. Due to the strong local transient expression provided by alphavirus vectors a number of immunization and gene therapy approaches have demonstrated both therapeutic and prophylactic efficacy in various animal models.

Alphaviruses in gene therapy

Alphavirus vectors present an attractive approach for gene therapy applications due to the rapid and simple recombinant virus particle production and their broad range of mammalian host cell transduction. Mainly three types of alphavirus vectors, namely naked RNA, recombinant particles and DNA/RNA layered vectors, have been subjected to preclinical studies with the goal of achieving prophylactic or therapeutic efficacy, particularly in oncology. In this context, immunization with alphavirus vectors has provided protection against challenges with tumor cells. Moreover, alphavirus intratumoral and systemic delivery has demonstrated substantial tumor regression and significant prolonged survival rates in various animal tumor models. Recent discoveries of the strong association of RNA interference and disease have accelerated gene therapy based approaches, where alphavirus-based gene delivery can play an important role.

Trial watch: Dendritic cell-based anticancer therapy

The use of patient-derived dendritic cells (DCs) as a means to elicit therapeutically relevant immune responses in cancer patients has been extensively investigated throughout the past decade. In this context, DCs are generally expanded, exposed to autologous tumor cell lysates or loaded with specific tumor-associated antigens (TAAs), and then reintroduced into patients, often in combination with one or more immunostimulatory agents. As an alternative, TAAs are targeted to DCs in vivo by means of monoclonal antibodies, carbohydrate moieties or viral vectors specific for DC receptors. All these approaches have been shown to (re)activate tumor-specific immune responses in mice, often mediating robust therapeutic effects. In 2010, the first DC-based preparation (sipuleucel-T, also known as Provenge®) has been approved by the US Food and Drug Administration (FDA) for use in humans. Reflecting the central position occupied by DCs in the regulation of immunological tolerance and adaptive immunity, the interest in harnessing them for the development of novel immunotherapeutic anticancer regimens remains high. Here, we summarize recent advances in the preclinical and clinical development of DC-based anticancer therapeutics.

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.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

Alphavirus-based vaccines

Alphavirus vectors have demonstrated high levels of transient heterologous gene expression both in vitro and in vivo and, therefore, possess attractive features for vaccine development. The most commonly used delivery vectors are based on three single-stranded encapsulated alphaviruses, namely Semliki Forest virus, Sindbis virus and Venezuelan equine encephalitis virus. Alphavirus vectors have been applied as replication-deficient recombinant viral particles and, more recently, as replication-proficient particles. Moreover, in vitro transcribed RNA, as well as layered DNA vectors have been applied for immunization. A large number of highly immunogenic viral structural proteins expressed from alphavirus vectors have elicited strong neutralizing antibody responses in multispecies animal models. Furthermore, immunization studies have demonstrated robust protection against challenges with lethal doses of virus in rodents and primates. Similarly, vaccination with alphavirus vectors expressing tumor antigens resulted in prophylactic protection against challenges with tumor-inducing cancerous cells. As certain alphaviruses, such as Chikungunya virus, have been associated with epidemics in animals and humans, attention has also been paid to the development of vaccines against alphaviruses themselves. Recent progress in alphavirus vector development and vaccine technology has allowed conducting clinical trials in humans.

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.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a privileged position at the interface between innate and adaptive immunity, orchestrating a large panel of responses to both physiological and pathological cues. In particular, whereas the presentation of antigens by immature DCs generally results in the development of immunological tolerance, mature DCs are capable of priming robust, and hence therapeutically relevant, adaptive immune responses. In line with this notion, functional defects in the DC compartment have been shown to etiologically contribute to pathological conditions including (but perhaps not limited to) infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. Thus, the possibility of harnessing the elevated immunological potential of DCs for anticancer therapy has attracted considerable interest from both researchers and clinicians over the last decade. Alongside, several methods have been developed not only to isolate DCs from cancer patients, expand them, load them with tumor-associated antigens and hence generate highly immunogenic clinical grade infusion products, but also to directly target DCs in vivo. This intense experimental effort has culminated in 2010 with the approval by the US FDA of a DC-based preparation (sipuleucel-T, Provenge®) for the treatment of asymptomatic or minimally symptomatic metastatic castration-refractory prostate cancer. As an update to the latest Trial Watch dealing with this exciting field of research (October 2012), here we summarize recent advances in DC-based anticancer regimens, covering both high-impact studies that have been published during the last 13 mo and clinical trials that have been launched in the same period to assess the antineoplastic potential of this variant of cellular immunotherapy.

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.

Alphavirus vectors for cancer therapy

Alphaviruses contain a single strand RNA genome that can be easily modified to express heterologous genes at very high levels in a broad variety of cells, including tumor cells. Alphavirus vectors can be used as viral particles containing a packaged vector RNA, or directly as nucleic acids in the form of RNA or DNA. In the latter case alphavirus RNA is cloned within a DNA vector downstream of a eukaryotic promoter. Expression mediated by these vectors is generally transient due to the induction of apoptosis. The high expression levels, induction of apoptosis, and activation of type I IFN response are the key features that have made alphavirus vectors very attractive for cancer treatment and vaccination. Alphavirus vectors have been successfully used as vaccines to induce protective and therapeutic immune responses against many tumor-associated antigens in animal models of mastocytoma, melanoma, mammary, prostate, and virally induced tumors. Alphavirus vectors have also shown a high antitumoral efficacy by expressing antitumoral molecules in tumor cells, which include cytokines, antiangiogenic factors or toxic proteins. In these studies induction of apoptosis in tumor cells contributed to the antitumoral efficacy by the release of tumor antigens that can be uptaken by antigen presenting cells, enhancing immune responses against tumors. The potential use of alphaviruses as oncolytic agents has also been evaluated for avirulent strains of Semliki Forest virus and Sindbis virus. The fact that this latter virus has a natural tropism for tumor cells has led to many studies in which this vector was able to reach metastatic tumors when administered systemically. Other "artificial" strategies to increase the tropism of alphavirus for tumors have also been evaluated and will be discussed.

Dendritic cells transduced with Rsf-1/HBXAP gene generate specific cytotoxic T lymphocytes against ovarian cancer in vitro

Recently, some studies have indicated that Rsf-1/HBXAP plays a role in chromatin remodeling and transcriptional regulation that may contribute to tumorigenesis in ovarian cancer. The present study demonstrates that using dendritic cells (DCs) from human cord blood CD34(+) cells transduced with Rsf-1/HBXAP DNA plasmids by nucleofection generate specific cytotoxic T lymphocytes (CTL) against ovarian cancer in vitro. After transfection, DCs were analyzed for Rsf-1/HBXAP mRNA expression by RT-PCR and protein expression by Western blot. Then the DC phenotypes, T-cell stimulatory capacity, endocytic activity and migration capacity were explored by flow cytometry analysis, allogeneic mixed lymphocyte reaction, endocytosis and transwell chemotaxis assay, respectively. After transfection, Rsf-1/HBXAP expression was detected at mRNA and protein levels. Allogeneic T-cell proliferation induced by transfected DCs was obviously higher than non-transfected DCs, but the endocytosis capacity and migratory ability were not different. Rsf-1/HBXAP gene-transduced DCs could induce antigen-specific CTL and generate a very potent cytotoxicity to OVCAR3 cells. These data suggest that Rsf-1/HBXAP gene-transduced DCs may be a potential adjuvant immunotherapy for ovarian cancer in clinical applications.

Effects of herpes simplex virus amplicon transduction on murine dendritic cells

The herpes simplex virus (HSV)-based amplicon is a versatile vaccine platform that has been preclinically vetted as a gene-based immunotherapeutic for cancer, HIV, and neurodegenerative disorders. Although it is well known that injection of dendritic cells (DCs) transduced ex vivo with helper virus-free HSV amplicon vectors expressing disease-relevant antigens induces antigen-specific immune responses, the cellular receptor(s) by which the amplicon virion gains entry into DCs, as well as the effects that viral vector transduction impinges on the physiological status of these cells, is less understood. Herein, we examine the effects of amplicon transduction on mouse bone marrow-derived DCs. We demonstrate that HSV-1 cellular receptors HveC and HveA are expressed on the cell surface of murine DCs, and that HSV amplicons transduce DCs at high efficiency (>90%) with minimal effects on cell viability. Transduction of dendritic cells with amplicons induces a transient DC maturation phenotype as represented by self-limited upregulation of MHCII and CD11c markers. Mature DCs are less sensitive to HSV amplicon transduction than immature DCs regarding DC-related surface marker maintenance. From this and our previous work, we conclude that HSV amplicons transduce DCs efficiently, but impart differential and transient physiological effects on mature and immature DC pools, which will facilitate fine-tuning of this vaccination platform and further exploit its potential in immunotherapy.

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.

Alphaviruses in gene therapy

Alphaviruses are enveloped single stranded RNA viruses, which as gene therapy vectors provide high-level transient gene expression. Semliki Forest virus (SFV), Sindbis virus (SIN) and Venezuelan Equine Encephalitis (VEE) virus have been engineered as efficient replication-deficient and -competent expression vectors. Alphavirus vectors have frequently been used as vehicles for tumor vaccine generation. Moreover, SFV and SIN vectors have been applied for intratumoral injections in animals implanted with tumor xenografts. SIN vectors have demonstrated natural tumor targeting, which might permit systemic vector administration. Another approach for systemic delivery of SFV has been to encapsulate replication-deficient viral particles in liposomes, which can provide passive targeting to tumors and allow repeated administration without host immune responses. This approach has demonstrated safe delivery of encapsulated SFV particles to melanoma and kidney carcinoma patients in a phase I trial. Finally, the prominent neurotropism of alphaviruses make them attractive for the treatment of CNS-related diseases.

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.

Antitumor effects of vaccination with dendritic cells transfected with modified receptor for hyaluronan-mediated motility mRNA in a mouse glioma model

OBJECT

The receptor for hyaluronan-mediated motility (RHAMM) is frequently overexpressed in brain tumors and was recently identified as an immunogenic antigen by using serological screening of cDNA expression libraries. In this study, which was conducted using a mouse glioma model, the authors tested the hypothesis that vaccination with dendritic cells transfected with RHAMM mRNA induces strong immunological antitumor effects.

METHODS

The authors constructed a plasmid for transduction of the mRNAs transcribed in vitro into dendritic cells, which were then used to transport the intracellular protein RHAMM efficiently into major histocompatibility complex class II compartments by adding a late endosomal-lysosomal sorting signal to the RHAMM gene. The dendritic cells transfected with this RHAMM mRNA were injected intraperitoneally into the mouse glioma model 3 and 10 days after tumor cell implantation. The antitumor effects of the vaccine were estimated by the survival rate, histological analysis, and immunohistochemical findings for immune cells. Mice in the group treated by vaccination therapy with dendritic cells transfected with RHAMM mRNA survived significantly longer than those in the control groups. Immunohistochemical analysis revealed that greater numbers of T lymphocytes containing T cells activated by CD4+, CD8+, and CD25+ were found in the group vaccinated with dendritic cells transfected with RHAMM mRNA.

CONCLUSIONS

These results demonstrate the therapeutic potential of vaccination with dendritic cells transfected with RHAMM mRNA for the treatment of malignant glioma.

Cellules dendritiques et gliomes : un espoir en immunothérapie ?

Immunotherapy has been explored for several decades to try to improve the prognosis of gliomas, but until recently no therapeutic benefit has been achieved. The discovery of dendritic cells, the most potent professional antigen presenting cells to initiate specific immune response, and the possibility of producing them ex vivo gave rise to new protocols of active immunotherapy. In oncology, promising experimental and clinical therapeutic results were obtained using these dendritic cells loaded with tumor antigen. Patients bearing gliomas have deficit antigen presentation making this approach rational. In several experimental glioma models, independent research teams have showed specific antitumor responses using these dendritic cells. Phase I/II clinical trials have demonstrated the feasibility and the tolerance of this immunotherapeutic approach. In neuro-oncology, the efficiency of such an approach remains to be established, similarly in oncology where positive phase III studies are missing. Nevertheless, dendritic cells comprise a complex network which is only partially understood and capable of generating either immunotolerance or immune response. Numerous parameters remain to be explored before any definitive conclusion about their utility as an anticancer weapon can be drawn. It seems however logical that immunotherapy with dendritic cells could prevent or delay tumor recurrence in patients with minor active disease. A review on glioma and dendritic cells is presented.

Prolongation of the survival of breast cancer-bearing mice immunized with GM-CSF-secreting syngeneic/allogeneic fibroblasts transfected with a cDNA expression library from breast cancer cells

Breast cancer cells, like other types of neoplastic cells, form weakly immunogenic tumor-associated antigens. The antigenic properties of the tumor-associated antigens can be enhanced if they are expressed by highly immunogenic cells. In this study, a cancer vaccine was prepared by transfer of a cDNA expression library from SB5b breast carcinoma into mouse fibroblast cells of C3H/He mouse origin (H-2(k)), that had been previously modified to secrete GM-CSF and to express allogeneic class I-determinants (H-2(b)). The transfected syngeneic/allogeneic fibroblasts secreting GM-CSF were used as a vaccine in C3H/He mice. Robust cell-mediated immunity toward the breast cancer cells was generated in mice immunized with the cDNA-based vaccine. The immunity, mediated predominantly by CD8(+) T lymphocytes, was directed toward the breast cancer cells, but not against either of two other non-cross-reactive neoplasms of C3H/He mice. The immunity was sufficient to prolong the survival of mice with established breast cancer. Among other advantages, preparation of the vaccine by cDNA-transfer into a fibroblast cell line enabled the recipient cells to be modified in advance of DNA-transfer to augment their immunogenic properties. As the transferred DNA is replicated as the transfected cells divide, the vaccine could be prepared from microgram quantities of tumor tissue.

Semliki forest virus vectors engineered to express higher IL-12 levels induce efficient elimination of murine colon adenocarcinomas

To evaluate the use of alphavirus vectors for tumor treatment we have constructed and compared two Semliki Forest virus (SFV) vectors expressing different levels of IL-12. SFV-IL-12 expresses both IL-12 subunits from a single subgenomic promoter, while in SFV-enhIL-12 each IL-12 subunit is expressed from an independent subgenomic promoter fused to the SFV capsid translation enhancer. This latter strategy provided an eightfold increase of IL-12 expression. We chose the poorly immunogenic MC38 colon adenocarcinoma model to evaluate the therapeutic potential of SFV vectors. A single intratumoral injection of 10(8) viral particles of SFV-IL-12 or SFV-enh-IL-12 induced>or=80% complete tumor regressions with long-term tumor-free survival. However, lower doses of SFV-enhIL-12 were more efficient than SFV-IL-12 in inducing antitumoral responses, indicating a positive correlation between the IL-12 expression level and the therapeutic effect. Moreover, repeated intratumoral injections of suboptimal doses of SFV-enhIL-12 increased the antitumoral response. In all cases SFV vectors were more efficient at eliminating tumors than a first-generation adenovirus vector expressing IL-12. In addition, the antitumoral effect of SFV vectors was only moderately affected by preimmunization of animals with high doses of SFV vectors. This antitumoral effect was produced, at least partially, by a potent CTL-mediated immune response.

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.

Tumor lysate and IL-18 loaded dendritic cells elicits Th1 response, tumor-specific CD8+ cytotoxic T cells in patients with malignant glioma

In this study, we demonstrate that tumor lysate-loaded dendritic cells can elicit a specific CD8+ cytotoxic T lymphocyte response against autologous tumor cells in patients with malignant glioma. CTL from three of five patients expressed strong cytolytic activity against autologous glioma cells, did not lyse autologous lymphoblasts and were variably cytotoxic against the LAK-sensitive cell line Daudi. Also, DCs pulsed normal brain lysate failed to induce cytolytic activity against autologous glioma cells, suggesting the lack of autoimmune response. Two of five patients CD8+ T cells expressed a modest cytotoxicity against autologous glioma cells. CD8+ T cells isolated during these ineffective primings secreted large amounts of IL-10, less amounts of IFN-gamma as detected by ELISA, Type 2 bias in the CD8+ T cell response accounts for the lack of cytotoxic effector function from these patients. Cytotoxicity against autologous glioma cells could be significantly inhibited by anti-HLA class I antibody. These data demonstrate that tumor lysate-loaded DC can be an effective tool in inducing glioma-specific CD8+ CTL able to kill autologous glioma cells in vitro. However, high levels of tumor specific tolerance in some patients may account for a significant barrier to therapeutic vaccination. Moreover, cytotoxic responses were augmented by transfecting DC with the gene for IL-18. For all five patients, CD8+T cells treated with IL18 transfected DC produced Th1 response. These results may have important implications for the treatment of malignant glioma patients with immunotherapy. DCs loaded with total tumor lysate and IL-18 may represent a method for inducing Th1 immunoresponses against the entire repertoire of glioma antigens.

Clinical evaluation of dendritic cell vaccination for patients with recurrent glioma: results of a clinical phase I/II trial

PURPOSE

To investigate the safety and the immunologic and clinical responses of dendritic cell therapy for patients with recurrent malignant glioma.

EXPERIMENTAL DESIGN

Twenty-four patients with recurrent malignant glioma (6 grade 3 and 18 grade 4 patients) were evaluated in a phase I/II clinical study of dendritic cell therapy. All patients were resistant to the standard maximum therapy. The patient's peripheral blood dendritic cells were generated with granulocyte macrophage colony-stimulating factor, plus interleukin 4 with or without OK-432, and pulsed with an autologous tumor lysate. Dendritic cells were injected intradermally, or both intratumorally and intradermally every 3 weeks.

RESULTS

The protocols were well tolerated with only local redness and swelling at the injection site in several cases. Clinical responses were as follows: 1 patient with partial response, 3 patients with minor response, 10 patients with stable disease, and 10 patients with progressive disease. The patients whose dendritic cells were matured with OK-432 had longer survival times than the dendritic cells from patients without OK-432 maturation. The patients with both intratumoral and intradermal administrations had a longer survival time than the patients with intradermal administration only. Increased ELISPOT and delayed-type hypersensitivity responses after vaccination could provide good laboratory markers to predict the clinical outcome of patients receiving dendritic cell vaccination. The overall survival of patients with grade 4 glioma was 480 days, which was significantly better than that in the control group.

CONCLUSIONS

This study showed the safety and clinical response of autologous tumor lysate-pulsed dendritic cell therapy for patients with malignant glioma. Dendritic cell therapy is recommended for further clinical studies in malignant glioma patients.

Induction of antigen-specific immune responses against malignant brain tumors by intramuscular injection of sindbis DNA encoding gp100 and IL-18

We constructed pSin-SV40-HDV-SV40pA, an improved Sindbis DNA expression vector, and evaluated the potential of this vector system for brain tumor therapy. We investigated whether immunizing mice with xenogeneic DNA encoding human gp100 and mouse IL-18 would enhance the antitumor responses. To study the immune mechanisms involved in tumor regression, we examined tumor growth in B16-gp100-implanted brain tumor models using T-cell subset-depleted and IFN-gamma-neutralized mice. Hugp100/mIL-18 vaccination was also investigated for its antitumor effects against the wild-type murine B16 tumor, which expresses the murine gp100 molecule. Genetic immunization using plasmid pSin 9001 DNA codelivery of human gp100 and mouse IL-18 resulted in enhanced protective and therapeutic effects on the malignant brain tumors. The antitumor and protective effects were mediated by both CD4(+)/CD8(+) T cells and IFN-gamma. Vaccination with hugp100/mIL-18 conferred a significant survival merit to wild-type B16 tumor-harboring mice. Immunogene therapy with the improved Sindbis virus vector expressing xenogeneic gp100 and syngeneic IL-18 may be an excellent approach for developing a new treatment protocol. Thus, the Sindbis DNA system may represent a novel approach for the treatment of malignant brain tumors.

Dendritic Cell-Based Immunotherapy of Malignant Gliomas

The failure of conventional treatment modalities for gliomas, in spite of tremendous progress in research in the past two decades, has led to increasing interest in alternative treatment strategies, including immunotherapy. It has become evident that vaccination with dendritic cells (DC), designed to express tumor antigens, is a potent strategy to elicit anti-tumor immune response in both pre-clinical and clinical settings. Various methods have been applied in order to induce DC to express tumor antigens including: pulsing with isolated tumor peptides or whole tumor lysate; fusion with tumor cells; and pulsing with apoptotic tumor cells. Herein, we review the recent progress in DC biology with regard to tumor immunity and discuss current DC-based strategies and future prospects in immunotherapy for malignant gliomas.

Viral and non-viral vectors in gene therapy: technology development and clinical trials

Gene therapy as part of modern molecular medicine holds great promise for the treatment of both acute and chronic diseases and has the potential to bring a revolutionary era to cancer treatment. Gene therapy has been named the medicine of the future. For the past 10 years various viral and non-viral vectors have been engineered for improved gene and drug delivery. Although various diseases have been targeted, cancer therapy has been addressed to a large extent because of the straight forward approach. Delivery of toxic or immunostimulatory genes by viral and non-viral vectors has been investigated and encouraging results have been obtained in animal models. A large number of clinical trials have been conducted with some highly promising outcome. We propose that combinations of viruses with liposomes or polymers will solve the problem of systemic viral delivery and tumor targeting, bringing a revolution in molecular medicine and in applications of gene therapy in humans.

Development of improved Sindbis virus-based DNA expression vector

We have constructed an improved DNA expression vector based on the Sindbis virus. Several DNA-based Sindbis virus vectors were constructed to investigate the efficiency of transgene expression. These vectors, when transfected into mammalian cells, have been used to express heterologous genes. A recombinant genome of Sindbis plasmid DNA, in which the structural genes were replaced by a polylinker cassette to allow for insertion of heterologous genes, was placed under the control of a simian virus (SV 40) promoter with a hepatitis delta virus (HDV) antigenomic ribozyme and a polyadenylation signal. Transfection of mammalian cells with this Sindbis-based plasmid vector, pSin-SV40-HDV-SV40pA, resulted in transient high-level expression of the beta-galactosidase reporter gene. The expression level of beta-galactosidase from pSin-SV40-HDV-SV40pA was more than 16-fold higher than that of pSin-Lux originally reported by Herweijer et al. In vivo expression was also detected after injection of plasmid DNA into mouse quadriceps. In vivo expression was transient and undetectable after day 14. Furthermore, we demonstrate that the transfection of cells with this Sindbis virus vector results in apoptotic death on glioma cells. We have demonstrated a high-level expression of the exogenous beta-galactosidase gene from the pSin-SV40-HDV-SV40pA construct using a Sindbis replication system.

Venezuelan Equine Encephalitis Replicon Immunization Overcomes Intrinsic Tolerance and Elicits Effective Anti-tumor Immunity to the ‘Self’ tumor-associated antigen, neu in a Rat Mammary Tumor Model

Many tumor-associated antigens (TAAs) represent 'self' antigens and as such, are subject to the constraints of immunologic tolerance. There are significant barriers to eliciting anti-tumor immune responses of sufficient magnitude. We have taken advantage of a Venezuelan equine encephalitis-derived alphavirus replicon vector system with documented in vivo tropism for immune system dendritic cells. We have overcome the intrinsic tolerance to the 'self' TAA rat neu and elicited an effective anti-tumor immune response using this alphavirus replicon vector system and a designed target antigen in a rigorous rat mammary tumor model. We have demonstrated the capacity to generate 50% protection in tumor challenge experiments (p = 0.004) and we have confirmed the establishment of immunologic memory by both second tumor challenge and Winn Assay (p = 0.009). Minor antibody responses were identified and supported the establishment of T helper type 1 (Th1) anti-tumor immune responses by isotype. Animals surviving in excess of 300 days with established effective anti-tumor immunity showed no signs of autoimmune phenomena. Together these experiments support the establishment of T lymphocyte dependent, Th1-biased anti-tumor immune responses to a non-mutated 'self' TAA in an aggressive tumor model. Importantly, this tumor model is subject to the constraints of immunologic tolerance present in animals with normal developmental, temporal, and anatomical expression of a non-mutated TAA. These data support the continued development and potential clinical application of this alphaviral replicon vector system and the use of appropriately designed target antigen sequences for anti-tumor immunotherapy.

Vaccination of recurrent glioma patients with tumour lysate-pulsed dendritic cells elicits immune responses: results of a clinical phase I/II trial

In this Phase I/II trial, the patient's peripheral blood dendritic cells were pulsed with an autologous tumour lysate of the glioma. Seven patients with glioblastoma and three patients with anaplastic glioma, ranging in age from 20 to 69 years, participated in this study. The mean numbers of vaccinations of tumour lysate-pulsed dendritic cells were 3.7 times intradermally close to a cervical lymph node, and 3.2 times intratumorally via an Ommaya reservoir. The percentage of CD56-positive cells in the peripheral blood lymphocytes increased after immunisation. There were two minor responses and four no-change cases evaluated by radiological findings. Dendritic cell vaccination elicited T-cell-mediated antitumour activity, as evaluated by the ELISPOT assay after vaccination in two of five tested patients. Three patients showed delayed-type hypersensitivity reactivity to the autologous tumour lysate, two of these had a minor clinical response, and two had an increased ELISPOT result. Intratumoral CD4+ and CD8+ T-cell infiltration was detected in two patients who underwent reoperation after vaccination. This study demonstrated the safety and antitumour effects of autologous tumour lysate-pulsed dendritic cell therapy for patients with malignant glioma.

Induction of an antitumor immunological response by an intratumoral injection of dendritic cells pulsed with genetically engineered Semliki Forest virus to produce interleukin-18 combined with the systemic administration of interleukin-12

OBJECT

The aim of this study was to investigate further immunogene treatment of malignant brain tumor to improve its therapeutic efficacy.

METHODS

Intratumoral dendritic cells pulsed with Semliki Forest virus (SFV)-interleukin-18 (IL-18) and/or systemic IL-12 were injected into mice bearing the B16 brain tumor. To study the immune mechanisms involved in tumor regression, we monitored the growth of implanted B16 brain tumor cells in T cell-depleted mice and IFNgamma-neutralized mice. To analyze the protective immunity created by tumor inoculation, B16 cells were injected into the left thighs of mice that had received an inoculation, and tumor growth was monitored. The local delivery of dendritic cells pulsed with IL-18 bound by SFV combined with the systemic administration of IL-12 enhanced the induction of the T helper type 1 response from tumor-specific CD4+ and CD8+ T cells and natural killer cells as well as antitumor immunity. Interferon-gamma is partly responsible for this IL-18-mediated antitumor immunity. Furthermore, the protective immunity is mediated mainly by CD8+ T cells.

CONCLUSIONS

Immunogene therapy that combines the local administration of dendritic cells pulsed with IL-18 bound by SFV and the systemic administration of IL-12 may be an excellent candidate for the development of a new treatment protocol. A self-replicating SFV system may therefore open a novel approach for the treatment of malignant brain tumor.

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.

The history, evolution, and clinical use of dendritic cell-based immunization strategies in the therapy of brain tumors

Despite advancements in therapeutic regimens, the prognosis remains poor for patients with malignant gliomas. Specificity has been an elusive goal for current modalities, but immunotherapy has emerged as a potential means of designing more tumor-specific treatments. Dendritic cells (DC) are the specialized antigen presenting cells of the immune system and have served now as a platform for therapeutic immunizations against such cancers as lymphoma, multiple myeloma, melanoma, prostate cancer, renal cell carcinoma, non-small cell lung carcinoma, colon cancer, and even malignant gliomas. DC-based immunizations offer a number of advantages over traditional immunotherapeutic approaches to brain tumors, approaches that have proved promising despite concerns over central nervous system immune privilege and glioma-mediated immunosuppression. The future success of clinical trials will depend on the optimization and standardizing of procedures for DC generation, loading, and administration.

Semliki Forest virus vectors for gene therapy

Semliki Forest virus (SFV) vectors transduce a broad range of mammalian and non-mammalian cells, generating high levels of transient expression of heterologous proteins. Generally, they induce apoptosis in mammalian host cells, leading to rapid cell death. These features have made SFV attractive for various gene therapy applications. Recombinant particles, naked RNA and plasmid DNA containing SFV replicons, demonstrate a strong immune response against recombinantly expressed proteins, which has shown protection against tumour challenges. Intratumoural injection of SFV particles has resulted in tumour regression. SFV vectors have been used for production of retrovirus-like particles. Recently, encapsulation of SFV particles into liposomes has generated highly efficient targeting to tumours. Novel SFV vectors based on point mutations in the non-structural genes, and avirulent SFV strains, have further widened the application range.

Immunogene therapy of recurrent glioblastoma multiforme with a liposomally encapsulated replication-incompetent Semliki forest virus vector carrying the human interleukin-12 gene--a phase I/II clinical protocol

Glioblastoma multiforme (GBM) is an incurable brain tumor resistant to standard treatment modalities such as surgery, radiation, and chemotherapy. Since recurrent GBM tends to develop predominantly within the infiltrative rim surrounding the primary tumor focus, novel therapy strategies need in addition to focal tumor destruction to target this somewhat diffuse area. This is a phase I/II clinical study in adult patients with recurrent GBM which is aimed at evaluating biological safety, maximum tolerated dose, and antitumor efficacy of a genetically modified replication-disabled Semliki forest virus vector (SFV) carrying the human interleukin 12 (IL-12) gene and encapsulated in cationic liposomes (LSFV-IL12). The vector will be administered in doses of 1 x 10(7)-1 x 10(9) infectious particles by continuous intratumoral infusion, thus exploiting the advantages of convection-enhanced drug delivery in the brain. The present protocol is also designed to investigate systemic and local immune response and to identify factors predicting tumor response to LSFV-IL12 therapy, such as volume of extracellular space of the tumor, volume of contrast enhancing lesion, and immune status of the patients. SFV, an insect alphavirus, infects mitotic and non-mitotic cells and triggers apoptosis in tumor cells within 48-72 h. Preclinical work with the LSFV-IL12 vector in breast and prostate cancer animal models demonstrated its biosafety and some antitumor efficacy. An ongoing phase I clinical study in patients with melanoma and renal cell carcinoma seems also to confirm the biosafety of intravenously administered vectors. This protocol will be the first study of SFV-IL12 therapy of human recurrent GBM.

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.

Cell-mediated immunotherapy: a new approach to the treatment of malignant glioma

BACKGROUND

The dismal prognosis for patients harboring intracranial gliomas has prompted an intensive search for effective treatment alternatives such as immunotherapy. Our increased knowledge in basic immunology, glioma immunobiology, and molecular biology may lead to the development of effective, rational immunotherapy approaches.

METHODS

The authors reviewed the literature on glioma immunology, the status of tumor vaccine therapy and on novel techniques to monitor the tumor-specific immune response.

RESULTS

Experimental conditions currently exist whereby potent antitumor cell-mediated immune responses can be generated. However, clinically, no therapeutic regimen has proven effective. Obstacles to establishing an effective immunotherapy regimen are the lack of a well-defined glioma-specific antigen, the heterogeneity of tumor cells in gliomas, and the modulating effect of the glioma itself on the immune system. Unique strategies to overcome these barriers are being developed.

CONCLUSIONS

Novel strategies to generate an anti-glioma immune response through use of dendritic cell vaccination, directed cytokine delivery, gene-based immunotherapy, and reversal of tumor-induced immunosuppression are promising. These strategies carry the potential of overcoming the resistance of gliomas to immunotherapeutic manipulation and, undoubtedly, will become a part of our future therapeutic armamentarium.

Advances in dendritic cell-based vaccine of cancer

Dendritic cells (DCs) are potent antigen presenting cells that exist in virtually every tissue, and from which they capture antigens and migrate to secondary lymphoid organs where they activate naïve T cells. Although DCs are normally present in extremely small numbers in the circulation, recent advances in DC biology have allowed the development of methods to generate large numbers of these cells in vitro. Because of their immunoregulatory capacity, vaccination with tumor antigen-presenting DCs has been proposed as a treatment modality for cancer. In animal models, vaccination with DCs pulsed with tumor peptides, lysates, or RNA or loaded with apoptotic/necrotic tumor cells could induce significant antitumor CTL responses and antitumor immunity. However, the results from early clinical trails pointed to a need for additional improvement of DC-based vaccines before they could be considered as practical alternatives to the existing cancer treatment strategies. In this regard, subsequent studies have shown that DCs that express transgenes encoding tumor antigens are more potent primers of antitumor immunity both in vitro and in vivo than DCs simply pulsed with tumor peptides. Furthermore, DCs that have been engineered to express certain cytokines or chemokines can display a substantially improved maturation status, capacity to migrate to secondary lymphoid organs in vivo, and abilities to stimulate tumor-specific T cell responses and induce tumor immunity in vivo. In this review we also discuss a number of factors that are important considerations in designing DC vaccine strategies, including (i) the type and concentrations of tumor peptides used for pulsing DCs; (ii) the timing and intervals for DC vaccination/boostable data on DC vaccination portends bright prospects for this approach to tumor immune therapy, either alone or in conjunction with other therapies.

A potential role of macrophage activation in the treatment of cancer

One of the functions of macrophages is to provide a defense mechanism against tumor cells. In the last decades the mechanism of tumor cell killing by macrophages have been studied extensively. The tumor cytotoxic function of macrophages requires stimulation either with bacterial cell wall products such as lipopolysaccharide (LPS) or muramyldipeptide (MDP) or with cytokines such as interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Activated macrophages secrete several substances that are directly involved in tumor cell killing i.e. tumor necrosis factor (TNF) and nitric oxide (NO). On the other hand, substances are secreted that are able to stimulate tumor cell growth, depending on the stage and the nature of the tumor. Several clinical trials have been performed aiming at the activation of macrophages or dendritic cells, a subpopulation of the macrophages. In this review we will summarize and discuss experimental studies and clinical trials based on the activation of macrophages.

Clinical immunotherapy for brain tumors

As an immunization platform for brain tumors, dendritic cells supply an impressive host of advantages. On the simplest level, they provide the safety and tumor-specificity so wanted by current therapeutic options. Yet, in addition, as the fundamental antigen-presenting cell, they circumvent many of the immunologic challenges that gliomas and the CNS proffer and that other immunotherapeutic modes fail to overcome. Directions to take now include the identification of new tumor-specific and tumor-associated antigens; the determination of the optimal dendritic cell subtype, generation, loading method, maturation state, dose, and route of delivery for immunizations; the further characterization of dendritic cells and their activities; and, potentially, the discovery of ways to pulse dendritic cells efficiently in vivo. Preclinical studies continue to play an important role in refining this form of active immunotherapy.

Administration of interleukin-12 and -18 enhancing the antitumor immunity of genetically modified dendritic cells that had been pulsed with Semliki forest virus-mediated tumor complementary DNA

OBJECT

Immunogene therapy for malignant gliomas was further investigated in this study to improve its therapeutic efficacy.

METHODS

Dendritic cells (DCs) were isolated from bone marrow and pulsed with phosphate-buffered saline or Semliki Forest virus (SFV)-mediated 203 glioma complementary (c)DNA with or without systemic administration of interleukin (IL)-12 and IL-18 to treat mice bearing the 203 glioma. To study the immune mechanisms involved in tumor regression, the authors investigated tumor growth of an implanted 203 glioma model in T cell subset-depleted mice and in interferon (IFN) gamma-neutralized mice. To examine the protective immunity produced by tumor inoculation, a repeated challenge of 203 glioma cells was given by injecting the cells into the left thighs of surviving mice and the growth of these cells was monitored. The authors demonstrated that the combined administration of SFV-cDNA, IL-12, and IL-18 produced significant antitumor effects against the growth of murine glioma cells in vivo and also can induce specific antitumor immunity. The synergic effects of the combination of SFV-cDNA, IL-12, and IL-18 in vivo were also observed to coincide with markedly augmented IFN-gamma production. The antitumor effects of this combined therapy are mediated by CD4+ and CD8+ T cells and by NK cells. These results indicate that the use of IL-18 and IL-12 in DC-based immunotherapy for malignant glioma is beneficial.

CONCLUSIONS

Immunogene therapy combined with DC therapy, IL-12, and IL-18 may be an excellent candidate in the development of a new treatment protocol. The self-replicating SFV system may therefore provide a novel approach for the treatment of malignant gliomas.

Marked enhancement of antitumor immune responses in mouse brain tumor models by genetically modified dendritic cells producing Semliki Forest virus-mediated interleukin-12

OBJECT

The authors evaluated dendritic cell (DC)-based immunotherapy for malignant brain tumor to improve its therapeutic efficacy.

METHODS

Dendritic cells were isolated from bone marrow and pulsed with phosphate-buffered saline, Semliki Forest virus (SFV)-LacZ, retrovirus vector GCsap-interleukin (IL)-12, and SFV-IL-12, respectively, to treat mice bearing brain tumors of the B16 cell line. The results indicated that therapeutic immunization with DCs pulsed with SFV-IL-12 prolonged the survival of mice with established tumors. Semliki Forest virus induced apoptosis in DCs, which in turn facilitated the uptake of apoptotic cells by other DCs, thus providing a potential mechanism for enhanced immunogenicity.

CONCLUSIONS

Therapy with DCs that have been pulsed with SFV-mediated IL-12 may be an excellent step in the development of new cancer vaccines. Intratumorally injected DCs that have been transiently transduced with IL-12 do not require pulsing of a source of tumor antigens to induce tumor regression.

Induction of therapeutic antitumor antiangiogenesis by intratumoral injection of genetically engineered endostatin-producing Semliki Forest virus

Antiangiogenic therapy using Semliki Forest virus (SFV) carrying Endostatin gene for malignant brain tumor was investigated to improve the therapeutic efficacy. The efficiency of SFV-mediated gene delivery was first evaluated for B 16 cells and compared with the efficiency in cells of endothelial origin (HMVECs). HMVECs are more susceptible to SFV infection than B 16 cells. For the in vivo treatment model, phosphate-buffered saline, SFV-LacZ, retrovirus vector GCsap-Endostatin, and SFV-Endostatin were injected to mice bearing B 16 brain tumors. A very significant inhibition of tumor growth was observed in the group that had been treated with SFV-Endostatin. A marked reduction of intratumoral vascularization was seen in the tumor sections from the SFV-Endostatin group compared with tumor sections from the SFV-LacZ or GCsap-Endostatin groups. Moreover, at day 7 after intravenous administration of SFV-Endostatin, the serum level of endostatin was augmented more than 3-fold compared to that after intravenous administration of GCsap-Endostatin. The results indicated that treatment with SFV-Endostatin inhibited the angiogenesis with established tumors. Gene therapy with Endostatin delivered via SFV may be a candidate for the development of new therapy for brain tumors.