HER2-specific T cells target primary glioblastoma stem cells and induce regression of autologous experimental tumors

Glioma stem cells and immunotherapy for the treatment of malignant gliomas

Stem cell research has led to the discovery of glioma stem cells (GSCs), and because these cells are resistant to chemotherapy and radiotherapy, analysis of their properties has been rapidly pursued for targeted treatment of malignant glioma. Recent studies have also revealed complex crosstalk between GSCs and their specialized environment (niche). Therefore, targeting not only GSCs but also their niche may be a principle for novel therapies of malignant glioma. One possible novel strategy for targeting GSCs and their niches is immunotherapy with different antitumor mechanism(s) from those of conventional therapy. Recent clinical studies of immunotherapy using peptide vaccines and antibodies have shown promising results. This review describes the recent findings related to GSCs and their niches, as well as immunotherapies for glioma, followed by discussion of immunotherapies that target GSCs for the treatment of malignant glioma.

Achieving graft-versus-tumor effect in brain tumor patients: from autologous progenitor cell transplant to active immunotherapy

Success in treating aggressive brain tumors like glioblastoma multiforme and medulloblastoma remains challenging, in part because these malignancies overcome CNS immune surveillance. New insights into brain tumor immunology have led to a rational development of immunotherapeutic strategies, including cytotoxic Tlymphocyte therapies and dendritic cell vaccines. However, these therapies are most effective when applied in a setting of minimal residual disease, so require prior use of standard cytotoxic therapies or cytoreduction by surgery. Myeloablative chemotherapy with autologous hematopoietic cell transplantation (autoHCT) can offer a platform upon which different cellular therapies can be effectively instituted. Specifically, this approach provides an inherent 'chemical debulking' through high-dose chemotherapy and a graft-versus-tumor effect through an autologous T-cell replete graft. Furthermore, autoHCT may be beneficial in 'resetting' the body's immune system, potentially 'breaking' tumor tolerance, and in providing a 'boost' of immune effector cells (NK cells or cytotoxic T lymphocytes), which could augment desired anti-tumor effects. As literature on the use of autoHCT in brain tumors is scarce, aspects of immunotherapies applied in non-CNS malignancies are reviewed as potential therapies that could be used in conjunction with autoHCT to eradicate brain tumors.

Cell-based immunotherapy against gliomas: from bench to bedside

Glioblastoma (GBM) comprises 51% of all gliomas and is the most malignant form of brain tumors with a median survival of 18-21 months. Standard-of-care treatment includes maximal surgical resection of the tumor mass in combination with radiation and chemotherapy. However, as the poor survival rate indicates, these treatments have not been effective in preventing disease progression. Cellular immunotherapy is currently being explored as therapeutic approach to treat malignant brain tumors. In this review, we discuss advances in active, passive, and vaccine-based immunotherapeutic strategies for gliomas both at the bench and in the clinic.

HER2-specific T lymphocytes kill both trastuzumab-resistant and trastuzumab-sensitive breast cell lines in vitro

OBJECTIVE

Although the development of trastuzumab has improved the outlook for women with human epidermal growth factor receptor 2 (HER2)-positive breast cancer, the resistance to anti-HER2 therapy is a growing clinical dilemma. We aim to determine whether HER2-specific T cells generated from dendritic cells (DCs) modified with HER2 gene could effectively kill the HER2-positive breast cancer cells, especially the trastuzumab-resistant cells.

METHODS

The peripheral blood mononuclear cells (PBMCs) from healthy donors, whose HLA haplotypes were compatible with the tumor cell lines, were transfected with reconstructive human adeno-association virus (rhAAV/HER2) to obtain the specific killing activities of T cells, and were evaluated by lactate dehydrogenase (LDH) releasing assay.

RESULTS

Trastuzumab produced a significant inhibiting effect on SK-BR-3, the IC50 was 100ng/ml. MDA-MB-453 was resistant to trastuzumab even at a concentration of 10,000 ng/ml in vitro. HER2-specific T lymphocytes killed effectively SK-BR-3 [(69.86±13.41)%] and MDA-MB-453 [(78.36±10.68)%] at 40:1 (effector:target ratio, E:T), but had no significant cytotoxicity against HER2-negative breast cancer cell lines MDA-MB-231 or MCF-7 (less than 10%).

CONCLUSION

The study showed that HER2-specific T lymphocytes generated from DCs modified by rhAAV/HER2 could kill HER2-positive breast cancer cell lines in a HER2-dependent manner, and result in significantly high inhibition rates on the intrinsic trastuzumab-resistant cell line MDA-MB-453 and the tastuzumab-sensitive cell line SK-BR-3. These results imply that this immunotherapy might be a potential treatment to HER2-positive breast cancer.

Focused ultrasound delivers targeted immune cells to metastatic brain tumors

Natural killer (NK) cells are cytotoxic lymphocytes involved in innate immunity. NK-92, a human NK cell line, may be targeted to tumor-associated antigens in solid malignancies where it exhibits antitumor efficacy, but its clinical utility for treating brain tumors is limited by an inability to cross the blood-brain barrier (BBB). We investigated the potential for focused ultrasound (FUS) to deliver targeted NK-92 cells to the brain using a model of metastatic breast cancer. HER2-expressing human breast tumor cells were implanted into the brain of nude rats. The NK-92-scFv(FRP5)-zeta cell line expressing a chimeric HER2 antigen receptor was transfected with superparamagnetic iron oxide nanoparticles before intravenous injection, before and following BBB disruption using focused ultrasound (551.5 kHz focused transducer, 0.33 MPa average peak rarefaction pressure) in the presence of a microbubble contrast agent. Baseline and posttreatment 1.5T and 7T MR imaging was done, and histology used to identify NK-92 cells post-mortem. Contrast-enhanced MRI showed reproducible and consistent BBB disruption. 7T MR images obtained at 16 hours posttreatment revealed a significant reduction in signal indicating the presence of iron-loaded NK-92 cells at the tumor site. The average ratio of NK-92 to tumor cells was 1:100 when NK cells were present in the vasculature at the time of sonication, versus 2:1,000 and 1:1,000 when delivered after sonication and without BBB disruption, respectively. Our results offer a preclinical proof-of-concept that FUS can improve the targeting of immune cell therapy of brain metastases.

Immunotherapy of malignant disease using chimeric antigen receptor engrafted T cells

Chimeric antigen receptor- (CAR-) based immunotherapy has been under development for almost 25 years, over which period it has progressed from a new but cumbersome technology to an emerging therapeutic modality for malignant disease. The approach involves the genetic engineering of fusion receptors (CARs) that couple the HLA-independent binding of cell surface target molecules to the delivery of a tailored activating signal to host immune cells. Engineered CARs are delivered most commonly to peripheral blood T cells using a range of vector systems, most commonly integrating viral vectors. Preclinical refinement of this approach has proceeded over several years to the point that clinical testing is now being undertaken at several centres, using increasingly sophisticated and therapeutically successful genetic payloads. This paper considers several aspects of the pre-clinical and clinical development of CAR-based immunotherapy and how this technology is acquiring an increasing niche in the treatment of both solid and haematological malignancies.

Passive immunotherapeutic strategies for the treatment of malignant gliomas

This review provides historical and recent perspectives related to passive immunotherapy for high-grade gliomas. The authors discuss approaches that use lymphokine-activated killer cells, cytotoxic T lymphocytes, and monoclonal antibodies.

Brain tumor immunotherapy: seeing the brain in the body

Brain tumor immunotherapy is often interpreted in terms of immune privilege and the blood-brain barrier (BBB), but a broader view is warranted. The delicate regulatory balance of the immune system is relevant at any site, as are the heterogeneity and plasticity of tumor growth. Criteria for tumor antigens, and often the antigens themselves, cut across tumor types. Here, this broader view, complemented by current understanding of privilege and the BBB, provides the context for review. Future success is likely to exploit simplified methods, used in combination; and similarities - more than differences - between the brain and other sites.

T cells redirected to EphA2 for the immunotherapy of glioblastoma

Outcomes for patients with glioblastoma (GBM) remain poor despite aggressive multimodal therapy. Immunotherapy with genetically modified T cells expressing chimeric antigen receptors (CARs) targeting interleukin (IL)-13Rα2, epidermal growth factor receptor variant III (EGFRvIII), or human epidermal growth factor receptor 2 (HER2) has shown promise for the treatment of gliomas in preclinical models and in a clinical study (IL-13Rα2). However, targeting IL-13Rα2 and EGFRvIII is associated with the development of antigen loss variants, and there are safety concerns with targeting HER2. Erythropoietin-producing hepatocellular carcinoma A2 (EphA2) has emerged as an attractive target for the immunotherapy of GBM as it is overexpressed in glioma and promotes its malignant phenotype. To generate EphA2-specific T cells, we constructed an EphA2-specific CAR with a CD28-ζ endodomain. EphA2-specific T cells recognized EphA2-positive glioma cells as judged by interferon-γ (IFN-γ) and IL-2 production and tumor cell killing. In addition, EphA2-specific T cells had potent activity against human glioma-initiating cells preventing neurosphere formation and destroying intact neurospheres in coculture assays. Adoptive transfer of EphA2-specific T cells resulted in the regression of glioma xenografts in severe combined immunodeficiency (SCID) mice and a significant survival advantage in comparison to untreated mice and mice treated with nontransduced T cells. Thus, EphA2-specific T-cell immunotherapy may be a promising approach for the treatment of EphA2-positive GBM.

Targeting the TGFβ signalling pathway in disease

Many drugs that target transforming growth factor-β (TGFβ) signalling have been developed, some of which have reached Phase III clinical trials for a number of disease applications. Preclinical and clinical studies indicate the utility of these agents in fibrosis and oncology, particularly in augmentation of existing cancer therapies, such as radiation and chemotherapy, as well as in tumour vaccines. There are also reports of specialized applications, such as the reduction of vascular symptoms of Marfan syndrome. Here, we consider why the TGFβ signalling pathway is a drug target, the potential clinical applications of TGFβ inhibition, the issues arising with anti-TGFβ therapy and how these might be tackled using personalized approaches to dosing, monitoring of biomarkers as well as brief and/or localized drug-dosing regimens.

Gene therapy-mediated reprogramming tumor infiltrating T cells using IL-2 and inhibiting NF-κB signaling improves the efficacy of immunotherapy in a brain cancer model

Immune-mediated gene therapy using adenovirus expressing Flt3 ligand and thymidine kinase followed by ganciclovir administration (Flt3/TK) effectively elicits tumor regression in preclinical glioma models. Herein, we assessed new strategies to optimize Flt3L/TK therapeutic efficacy in a refractory RG2 orthotopic glioblastoma model. Specifically, we aimed to optimize the therapeutic efficacy of Flt3L/TK treatment in the RG2 model by overexpressing the following genes within the brain tumor microenvironment: 1) a TK mutant with enhanced cytotoxicity (SR39 mutant TK), 2) Flt3L-IgG fusion protein that has a longer half-life, 3) CD40L to stimulate DC maturation, 4) T helper cell type 1 polarizing dendritic cell cytokines interleukin-12 or C-X-C motif ligand 10 chemokine (CXCL)-10, 5) C-C motif ligand 2 chemokine (CCL2) or C-C motif ligand 3 chemokine (CCL3) to enhance dendritic cell recruitment into the tumor microenvironment, 6) T helper cell type 1 cytokines interferon-γ or interleukin-2 to enhance effector T-cell functions, and 7) IκBα or p65RHD (nuclear factor kappa-B [NF-κB] inhibitors) to suppress the function of Foxp3+ Tregs and enhanced effector T-cell functions. Anti-tumor immunity and tumor specific effector T-cell functions were assessed by cytotoxic T lymphocyte assay and intracellular IFN-γ staining. Our data showed that overexpression of interferon-γ or interleukin-2, or inhibition of the nuclear factor kappa-B within the tumor microenvironment, enhanced cytotoxic T lymphocyte-mediated immune responses and successfully extended the median survival of rats bearing intracranial RG2 when combined with Flt3L/TK. These findings indicate that enhancement of T-cell functions constitutes a critical therapeutic target to overcome immune evasion and enhance therapeutic efficacy for brain cancer. In addition, our study provides novel targets to be used in combination with immune-therapeutic strategies for glioblastoma, which are currently being tested in the clinic.

Medulloblastoma-biology and microenvironment: a review

Medulloblastoma (MB) is a cancer of the cerebellum and the most common primary pediatric malignancy of the central nervous system. Classified as a primitive neural ectoderm tumor; it is thought to arise from granule cell precursors in the cerebellum. The standard of care consists of surgery, chemotherapy and age-dependent radiation therapy. Despite aggressive multimodality therapy; approximately 30% of MB patients remain incurable. Moreover, for long-term survivors, the treatment related sequelae are often debilitating. Side effects include cerebellar mutism, sterility, neurocognitive deficits, and a substantial risk of developing secondary cancers. In a quest for more effective and targeted therapies, scientists have begun to investigate the biological events that not only initiate but also sustain the malignant phenotype in MB. Of particular interest is, the role of the tumor microenvironment in tumor pathogenesis. This review seeks to highlight several key processes observed in cancer biology, particularly the involvement of the tumor microenvironment, with relevant examples from MB.

Generation of polyclonal CMV-specific T cells for the adoptive immunotherapy of glioblastoma

Glioblastoma (GBM) is the most common primary brain cancer in adults and is virtually incurable. Recent studies have shown that cytomegalovirus (CMV) is present in majority of GBMs. To evaluate whether the CMV antigens pp65 and IE1, which are expressed in GBMs, could be targeted by CMV-specific T cells, we measured the frequency of T cells targeting pp65 and IE1 in the peripheral blood of a cohort of 11 sequentially diagnosed CMV-seropositive GBM patients, and evaluated whether it was feasible to expand autologous CMV-specific T cells for future clinical studies. All 11 CMV-seropositive GBM patients had T cells specific for pp65 and IE1 in their peripheral blood assessed by IFNγ enzyme-linked immunospot assay. However, the precursor frequency of pp65-specific T cells was decreased in comparison with healthy donors (P=0.001). We successfully reactivated and expanded CMV-specific T cells from 6 out of 6 GBM patients using antigen-presenting cells transduced with an adenoviral vector encoding pp65 and IE1. CMV-specific T-cell lines contained CD4 as well as CD8 T cells, recognized pp65 and IE1 targets and killed CMV-infected autologous GBM cells. Infusion of such CMV-specific T-cell lines may extend the benefits of T-cell therapy to patients with CMV GBMs.

Challenges in the clinical utility of the serum test for HER2 ECD

Approximately 15-30% of breast cancers over-express the HER2/neu receptor. Historically, over-expression of HER2/neu has been identified using IHC or FISH, both of which are invasive approaches requiring tissue samples. Recent evidence has shown that some tumors identified as "negative" using these methods can respond to HER2/neu targeted therapy. Shedding of the extracellular domain (ECD) of the receptor into the circulation has led to the development of a serum test of HER2 ECD as an additional approach to probe HER2/neu overexpression. The serum test will be able to monitor the dynamic changes of HER2 status over the course of disease progression. Some studies further suggest that the serum HER2 ECD level and its change may serve as a biomarker to reflect patients' response to therapy. Yet more than 10years after the first serum HER2 ECD test was approved by the FDA, serum HER2 testing has yet to be widely used in clinical practice. In this article we will review the progress of the serum HER2 ECD test and discuss some obstacles impeding its incorporation into broad clinical practice. We will also discuss recent improvements in the sensitivity and specificity of the assay that offer some hope for the future of serum HER2 test.

Vaccines targeting cancer stem cells: are they within reach?

Increased appreciation of intraclonal heterogeneity of tumors in the past decade has led to the resurgence of the cancer stem cell hypothesis. This hypothesis also has potential implications for immunologic approaches targeting cancer, and it has been suggested that vaccines targeting cancer stem cells may be essential for durable antitumor immunity. Recent studies have provided novel insights into the nature of antigenic targets expressed on putative cancer stem cells and the capacity of both the innate and the adaptive immune system to target these cells, as well as the associated challenges. While the phenotypic properties of cancer stem cells may be plastic, their stemness and capacity for self-renewal may depend on a limited set of genes. Several of these genes overlap with those regulating stemness in embryonal stem cells and are also emerging as potential oncogenes in some cancers. Immunologic approaches targeting stemness-associated pathways in cancer may provide an important strategy for the prevention of diverse cancers, including those occurring in the context of regenerative therapies.

Cellular immunotherapy for high-grade glioma

The outcome for patients with the most common primary brain tumor, glioblastoma multiforme (GBM), remains poor. Several immunotherapeutic approaches are actively being pursued including antibodies and cell-based therapies. While the blood-brain barrier protects brain tumor cells from therapeutic antibodies, immune cells have the ability to traverse the blood-brain barrier and migrate into GBM tumors to exert their therapeutic function. Results of Phase I clinical studies with vaccines to induce GBM-specific T cells are encouraging and Phase II clinical trials are in progress. Nonvaccine-based cell therapy for GBM has been actively explored over the last four decades. Here we will review past clinical experience with adoptive cell therapies for GBM and summarize current strategies on how to improve these approaches.

Stem-like tumor-initiating cells isolated from IL13Rα2 expressing gliomas are targeted and killed by IL13-zetakine-redirected T Cells

PURPOSE

To evaluate IL13Rα2 as an immunotherapeutic target for eliminating glioma stem-like cancer initiating cells (GSC) of high-grade gliomas, with particular focus on the potential of genetically engineered IL13Rα2-specific primary human CD8(+) CTLs (IL13-zetakine(+) CTL) to target this therapeutically resistant glioma subpopulation.

EXPERIMENTAL DESIGN

A panel of low-passage GSC tumor sphere (TS) and serum-differentiated glioma lines were expanded from patient glioblastoma specimens. These glioblastoma lines were evaluated for expression of IL13Rα2 and for susceptibility to IL13-zetakine(+) CTL-mediated killing in vitro and in vivo.

RESULTS

We observed that although glioma IL13Rα2 expression varies between patients, for IL13Rα2(pos) cases this antigen was detected on both GSCs and more differentiated tumor cell populations. IL13-zetakine(+) CTL were capable of efficient recognition and killing of both IL13Rα2(pos) GSCs and IL13Rα2(pos) differentiated cells in vitro, as well as eliminating glioma-initiating activity in an orthotopic mouse tumor model. Furthermore, intracranial administration of IL13-zetakine(+) CTL displayed robust antitumor activity against established IL13Rα2(pos) GSC TS-initiated orthotopic tumors in mice.

CONCLUSIONS

Within IL13Rα2 expressing high-grade gliomas, this receptor is expressed by GSCs and differentiated tumor populations, rendering both targetable by IL13-zetakine(+) CTLs. Thus, our results support the potential usefullness of IL13Rα2-directed immunotherapeutic approaches for eradicating therapeutically resistant GSC populations.

Novel therapies in glioblastoma

Conventional treatment of glioblastoma has advanced only incrementally in the last 30 years and still yields poor outcomes. The current strategy of surgery, radiation, and chemotherapy has increased median survival to approximately 15 months. With the advent of molecular biology and consequent improved understanding of basic tumor biology, targeted therapies have become cornerstones for cancer treatment. Many pathways (RTKs, PI3K/AKT/mTOR, angiogenesis, etc.) have been identified in GBM as playing major roles in tumorigenesis, treatment resistance, or natural history of disease. Despite the growing understanding of the complex networks regulating GBM tumors, many targeted therapies have fallen short of expectations. In this paper, we will discuss novel therapies and the successes and failures that have occurred. One clear message is that monotherapies yield minor results, likely due to functionally redundant pathways. A better understanding of underlying tumor biology may yield insights into optimal targeting strategies which could improve the overall therapeutic ratio of conventional treatments.

Replication-competent herpes simplex virus retargeted to HER2 as therapy for high-grade glioma

Oncolytic herpes simplex viruses (HSVs) represent a novel frontier against tumors resistant to standard therapies, like glioblastoma (GBM). The oncolytic HSVs that entered clinical trials so far showed encouraging results; however, they are marred by the fact that they are highly attenuated. We engineered HSVs that maintain unimpaired lytic efficacy and specifically target cells that express tumor-specific receptors, thus limiting the cytotoxicity only to cancer cells, and leaving unharmed the neighboring tissues. We report on the safety and efficacy in a high-grade glioma (HGG) model of R-LM113, an HSV recombinant retargeted to human epidermal growth factor receptor 2 (HER2), frequently expressed in GBMs. We demonstrated that R-LM113 is safe in vivo as it does not cause encephalitis when intracranially injected in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, extremely sensitive to wild-type HSV. The efficacy of R-LM113 was assessed in a platelet-derived growth factor (PDGF)-induced infiltrative glioma model engineered to express HER2 and transplanted intracranially in adult NOD/SCID mice. Mice injected with HER2-engineered glioma cells infected with R-LM113 showed a doubled survival time compared with mice injected with uninfected cells. A doubling in survival time from the beginning of treatment was obtained also when R-LM113 was administered into already established tumors. These data demonstrate the efficacy of R-LM113 in thwarting tumor growth.

Auto T cells expressing chimeric antigen receptor derived from auto antibody might be a new treatment for osteosarcoma

Osteosarcoma is the most common primary malignant tumor of bone. Except for the improvement in five-year survival achieved by the adoption of neoadjuvant chemotherapy strategy, there are nearly no improvement for the treatment of osteosarcoma in the past 30 years, especially for the patients with metastatic disease. Immunotherapy has been successfully applied in some tumors. The survival of osteosarcoma patients enrolled in several clinical immunotherapy trials did be improved in the past. Immunotherapy might further improve the therapy result of osteosarcoma patients besides neoadjuvant chemotherapy. But there still are many problems needed to be solved before clinically successful application. Immune escape is one of the main obstacles hindering the immunotherapy for osteosarcoma. No effective tumor antigens, or in other words, attenuated immunogenicity is one of the main mechanisms of immune escape. So the key point of immunotherapy for osteosarcoma is to find out an effective target through which the immune system can recognize this tumor and attack it. Genetic modification of immune system may circumvent this problem by enhancing the capacity of immune system. Chimeric antigen receptor (CAR), an artificial receptor generated by genetic manipulation, is a promising technique. The CAR technique can circumvent the restriction of major histocompatibility in antigen recognition for T cells, and is more effective than the corresponding antibody to get rid of tumor cells. But short persistence of the CAR expressing T cells in vivo is the main problem of CAR technique in current research. This problem is believed to have some relation to the immunogenicity of the artificial receptor because the antigen recognizing portion of receptor is derived from monoclonal antibody. So we believe that the elimination of the immunogenicity of CAR might prolong the persistence of CAR expressing T cells in vivo and put forward a hypothesis that the antigen binding portion of CAR could be derived from the antibody against osteosarcoma antigen from the same patient with osteosarcoma by methods such as antibody phage display, BRASIL technique. We believe that CAR expressing T cells constructed by this strategy would persist longer and are more effective to eradicate osteosarcoma cells. In addition, this treatment strategy is an individualized treatment because an effective target specific to the CAR could be found. Therefore the immune escape of osteosarcoma would be surmounted and the survival of patients would be improved.

Immunotherapy targeting glioma stem cells--insights and perspectives

INTRODUCTION

Glioblastoma multiforme (GBM) is the most aggressive and lethal primary malignant brain tumor. Although progress has been made in current conventional therapies for GBM patients, the effect of these advances on clinical outcomes has been disappointing. Recent research into the origin of cancers suggest that GBM cancer stem cells (GSC) are the source of initial tumor formation, resistance to current conventional therapeutics and eventual patient relapse. Currently, there are very few studies that apply immunotherapy to target GSC.

AREAS COVERED

CD133, a cell surface protein, is used extensively as a surface marker to identify and isolate GSC in malignant glioma. We discuss biomarkers such as CD133, L1-cell adhesion molecule (L1-CAM), and A20 of GSC. We review developing novel treatment modalities, including immunotherapy strategies, to target GSC.

EXPERT OPINION

There are very few reports of preclinical studies targeting GSC. Identification and validation of unique molecular signatures and elucidation of signaling pathways involved in survival, proliferation and differentiation of GSC will significantly advance this field and provide a framework for the rational design of a new generation of antigen-specific, anti-GSC immunotherapy- and nanotechnology-based targeted therapyies. Combined with other therapeutic avenues, GSC-targeting therapies may represent a new paradigm to treat GBM patients.

Challenges in immunotherapy presented by the glioblastoma multiforme microenvironment

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. Despite intensive treatment, the prognosis for patients with GBM remains grim with a median survival of only 14.6 months. Immunotherapy has emerged as a promising approach for treating many cancers and affords the advantages of cellular-level specificity and the potential to generate durable immune surveillance. The complexity of the tumor microenvironment poses a significant challenge to the development of immunotherapy for GBM, as multiple signaling pathways, cytokines, and cell types are intricately coordinated to generate an immunosuppressive milieu. The development of new immunotherapy approaches frequently uncovers new mechanisms of tumor-mediated immunosuppression. In this review, we discuss many of the current approaches to immunotherapy and focus on the challenges presented by the tumor microenvironment.

Human glioblastoma stem-like cells are more sensitive to allogeneic NK and T cell-mediated killing compared with serum-cultured glioblastoma cells

Glioblastoma multiforme (GBM) is the most dramatic primary brain cancer with a very poor prognosis because of inevitable disease recurrence. The median overall survival is less than 1 year after diagnosis. Cancer stem cells have recently been disclosed in GBM. GBM stem-like cells (GSCs) exhibit resistance to radio/chemotherapeutic treatments and are therefore considered to play an important role in disease recurrence. GSCs are thus appealing targets for new treatments for GBM patients. In this study, we show that GBM cells with stem cell characteristics are resistant to lysis mediated by resting natural killer (NK) cells because of the expression of MHC class I molecules. However, GSCs are killed by lectin-activated NK cells. Furthermore, in experiments using the therapeutic antibody CetuximAb, we show that GSCs are sensitive to antibody-mediated cytotoxicity. We confirm the sensitivity of GSC to cytotoxicity carried out by IL2-activated NK cells and tumor-specific T cells. More importantly, we show that GSCs are more sensitive to NK and T cell-mediated lysis relatively to their corresponding serum-cultured GBM cells obtained from the same initial tumor specimen. Altogether, these results demonstrate the sensitivity of GSC to immune cell cytotoxicity and, therefore, strongly suggest that GSCs are suitable target cells for immunotherapy of GBM patients.

Highlights of the second international conference on "Immunotherapy in Pediatric Oncology"

The Second International Conference on Immunotherapy in Pediatric Oncology was held in Houston, Texas, USA, October 11-12, 2010, to discuss the progress and challenges that have occurred in cutting edge immunotherapeutic strategies currently being developed for pediatric oncology. Major topics included immune targeting of acute lymphoblastic leukemia and pediatric solid tumors, chimeric antigen receptors (CARs) for hematologic malignancies and solid tumors, enhancing graft-versus-leukemia for pediatric cancers, overcoming hurdles of immunotherapy, strategies to active the innate immune system, and moving immunotherapy beyond phase I studies. Significant progress has been made in the last 2 years both in the development of novel immunobiologics such as CARs, and in establishing survival benefits of an anti-GD2 monoclonal antibody in randomized studies. Although there is much excitement going forward, a great deal of laboratory and regulatory challenges lie ahead in improving the efficacy of each of these modalities as well as getting them to patients in a timely and cost-effective fashion. The resulting discussions will hopefully lead to new collaborations and insight for further translational and clinical studies.

Immunotherapy in human glioblastoma

Glioblastoma patients spontaneously develop anti-tumour immune responses. However, the tumour itself develops several mechanisms that allow the tumor to escape the immune system. Clinical trials using infusion of activated autologous immune cells, or active immunotherapy with tumor antigens and dendritic cells have successfully induced anti-tumour immunity and some radiological responses. More recently, approaches targeting the mechanisms of tolerance have shown promising data in melanoma, and are currently under investigations in gliomas. However, large randomised trials are still needed to prove the usefulness of cancer vaccines in brain tumors.

PiggyBac-mediated cancer immunotherapy using EBV-specific cytotoxic T-cells expressing HER2-specific chimeric antigen receptor

Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes (CTLs) can be modified to function as heterologous tumor directed effector cells that survive longer in vivo than tumor directed T cells without virus specificity, due to chronic stimulation by viral antigens expressed during persistent infection in seropositive individuals. We evaluated the nonviral piggyBac (PB) transposon system as a platform for modifying EBV-CTLs to express a functional human epidermal growth factor receptor 2-specific chimeric antigen receptor (HER2-CAR) thereby directing virus-specific, gene modified CTLs towards HER2-positive cancer cells. Peripheral blood mononuclear cells (PBMCs) were nucleofected with transposons encoding a HER2-CAR and a truncated CD19 molecule for selection followed by specific activation and expansion of EBV-CTLs. HER2-CAR was expressed in ~40% of T cells after CD19 selection with retention of immunophenotype, polyclonality, and function. HER2-CAR-modified EBV-CTLs (HER2-CTLs) killed HER2-positive brain tumor cell lines in vitro, exhibited transient and reversible increases in HER2-CAR expression following antigen-specific stimulation, and stably expressed HER2-CAR beyond 120 days. Adoptive transfer of PB-modified HER2-CTLs resulted in tumor regression in a murine xenograft model. Our results demonstrate that PB can be used to redirect virus-specific CTLs to tumor targets, which should prolong tumor-specific T cell survival in vivo producing more efficacious immunotherapy.

Crosstalk between medulloblastoma cells and endothelium triggers a strong chemotactic signal recruiting T lymphocytes to the tumor microenvironment

Cancer cells can live and grow if they succeed in creating a favorable niche that often includes elements from the immune system. While T lymphocytes play an important role in the host response to tumor growth, the mechanism of their trafficking to the tumor remains poorly understood. We show here that T lymphocytes consistently infiltrate the primary brain cancer, medulloblastoma. We demonstrate, both in vitro and in vivo, that these T lymphocytes are attracted to tumor deposits only after the tumor cells have interacted with tumor vascular endothelium. Macrophage Migration Inhibitory Factor (MIF)" is the key chemokine molecule secreted by tumor cells which induces the tumor vascular endothelial cells to secrete the potent T lymphocyte attractant "Regulated upon Activation, Normal T-cell Expressed, and Secreted (RANTES)." This in turn creates a chemotactic gradient for RANTES-receptor bearing T lymphocytes. Manipulation of this pathway could have important therapeutic implications.

Immunotherapy of brain cancers: the past, the present, and future directions

Treatment of brain cancers, especially high grade gliomas (WHO stage III and IV) is slowly making progress, but not as fast as medical researchers and the patients would like. Immunotherapy offers the opportunity to allow the patient's own immune system a chance to help eliminate the cancer. Immunotherapy's strength is that it efficiently treats relatively small tumors in experimental animal models. For some patients, immunotherapy has worked for them while not showing long-term toxicity. In this paper, we will trace the history of immunotherapy for brain cancers. We will also highlight some of the possible directions that this field may be taking in the immediate future for improving this therapeutic option.

Molecular alterations in glioblastoma: potential targets for immunotherapy

Glioblastoma is the most common and deadly brain tumor, possibly arising from genetic and epigenetic alterations in normal astroglial cells. Multiple cytogenetic, chromosomal, and genetic alterations have been identified in glioblastoma, with distinct expression of antigens (Ags) and biomarkers that may alter therapeutic potential of this aggressive cancer. Current therapy consists of surgical resection, followed by radiation therapy and chemotherapy. In spite of these treatments, the prognosis for glioblastoma patients is poor. Although recent studies have focused on the development of novel immunotherapeutics against glioblastoma, little is known about glioblastoma-specific immune responses. A better understanding of the molecular interactions among glioblastoma tumors, host immune cells, and the tumor microenvironment may give rise to novel integrated approaches for the simultaneous control of tumor escape pathways and the activation of antitumor immune responses. This review provides a detailed overview concerning genetic alterations in glioblastoma, their effects on Ag and biomarker expression, and the future design of chemoimmunotherapeutics against glioblastoma.

T-cell immunotherapy for malignant glioma: toward a combined approach

PURPOSE OF REVIEW

Immunotherapies using T lymphocytes are now considered as promising approaches for treating malignant glioma patients. This review discusses how basic understanding of antitumor T-cell responses in the brain are now leading to the rational planning of such novel therapeutic modalities.

RECENT FINDINGS

Clinical trials show that therapeutic vaccination with defined glioma antigens or dendritic cells pulsed with glioma lysates is feasible and generally well tolerated, but clinical efficacy has yet to be demonstrated in randomized trials. Preclinical data have established that effector T cells can be engineered to more efficiently recognize tumor cells via high-affinity T-cell receptors or chimeric antibody-like receptors. Animal studies have demonstrated that glioma immunotherapy is enhanced if immunosuppressive molecules (including transforming growth factor-beta) and glioma infiltrating regulatory T cells are inactivated. Clinical trials are under way assessing transforming growth factor-beta2 antisense oligonucleotides and regulatory T cell depletion. Combination of any of the above approaches with chemotherapy or radiotherapy is strongly supported by animal and clinical observations.

SUMMARY

Future T-cell immunotherapies will combine different strategies to deliver potent T cells to the glioma bed. The synergy of immunotherapies with radiotherapy and chemotherapy requires optimization, but it is now clear that these modalities are partners and not enemies.

Immune response against tumor antigens expressed on human cancer stem-like cells/tumor-initiating cells

Cancer stem-like cells (CSCs)/tumor-initiating cells (TICs) are a small population of cancer cells that have the properties of tumor-initiating ability, self-renewal and differentiation. These properties suggest that CSCs/TICs are essential for tumor maintenance, recurrence and distant metastasis. Thus, elimination of CSCs/TICs is essential to cure malignant diseases. However, there are several studies reporting that CSCs/TICs are more resistant to standard cancer therapies, including chemotherapy and radiotherapy, than non-CSC/TIC populations. How then, can we eliminate CSCs/TICs? Immunotherapy might be the possible answer. In recent analysis, innate immunity (natural killer cells and gammadeltaT cells) and also adaptive immunity (cytotoxic T lymphocyte-based cellular immunity and antibody-based humoral immunity) can recognize CSCs/TICs in vitro efficiently. Furthermore, CSC/TIC-specific monoclonal antibody therapies are also efficient in vivo. In this article, we describe the potency, possibilities and problems of CSC/TIC-targeting immunotherapy.

Cellular and vaccine therapeutic approaches for gliomas

Despite new additions to the standard of care therapy for high grade primary malignant brain tumors, the prognosis for patients with this disease is still poor. A small contingent of clinical researchers are focusing their efforts on testing the safety, feasibility and efficacy of experimental active and passive immunotherapy approaches for gliomas and are primarily conducting Phase I and II clinical trials. Few trials have advanced to the Phase III arena. Here we provide an overview of the cellular therapies and vaccine trials currently open for patient accrual obtained from a search of http://www.clinicaltrials.gov. The search was refined with terms that would identify the Phase I, II and III immunotherapy trials open for adult glioma patient accrual in the United States. From the list, those that are currently open for patient accrual are discussed in this review. A variety of adoptive immunotherapy trials using ex vivo activated effector cell preparations, cell-based and non-cell-based vaccines, and several combination passive and active immunotherapy approaches are discussed.

Overview of cellular immunotherapy for patients with glioblastoma

High grade gliomas (HGG) including glioblastomas (GBM) are the most common and devastating primary brain tumours. Despite important progresses in GBM treatment that currently includes surgery combined to radio- and chemotherapy, GBM patients' prognosis remains very poor. Immunotherapy is one of the new promising therapeutic approaches that can specifically target tumour cells. Such an approach could also maintain long term antitumour responses without inducing neurologic defects. Since the past 25 years, adoptive and active immunotherapies using lymphokine-activated killer cells, cytotoxic T cells, tumour-infiltrating lymphocytes, autologous tumour cells, and dendritic cells have been tested in phase I/II clinical trials with HGG patients. This paper inventories these cellular immunotherapeutic strategies and discusses their efficacy, limits, and future perspectives for optimizing the treatment to achieve clinical benefits for GBM patients.