HER-2, gp100, and MAGE-1 are expressed in human glioblastoma and recognized by cytotoxic T cells

TRP-2 / gp100 DNA vaccine and PD-1 checkpoint blockade combination for the treatment of intracranial tumors

Intracranial tumors present a significant therapeutic challenge due to their physiological location. Immunotherapy presents an attractive method for targeting these intracranial tumors due to relatively low toxicity and tumor specificity. Here we show that SCIB1, a TRP-2 and gp100 directed ImmunoBody® DNA vaccine, generates a strong TRP-2 specific immune response, as demonstrated by the high number of TRP2-specific IFNγ spots produced and the detection of a significant number of pentamer positive T cells in the spleen of vaccinated mice. Furthermore, vaccine-induced T cells were able to recognize and kill B16HHDII/DR1 cells after a short in vitro culture. Having found that glioblastoma multiforme (GBM) expresses significant levels of PD-L1 and IDO1, with PD-L1 correlating with poorer survival in patients with the mesenchymal subtype of GBM, we decided to combine SCIB1 ImmunoBody® with PD-1 immune checkpoint blockade to treat mice harboring intracranial tumors expressing TRP-2 and gp100. Time-to-death was significantly prolonged, and this correlated with increased CD4+ and CD8+ T cell infiltration in the tissue microenvironment (TME). However, in addition to PD-L1 and IDO, the GBM TME was found to contain a significant number of immunoregulatory T (Treg) cell-associated transcripts, and the presence of such cells is likely to significantly affect clinical outcome unless also tackled.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

Intracranial injection of natural killer cells engineered with a HER2-targeted chimeric antigen receptor in patients with recurrent glioblastoma

BACKGROUND

Glioblastoma (GB) is incurable at present without established treatment options for recurrent disease. In this phase I first-in-human clinical trial we investigated safety and feasibility of adoptive transfer of clonal chimeric antigen receptor (CAR)-NK cells (NK-92/5.28.z) targeting HER2, which is expressed at elevated levels by a subset of glioblastomas.

METHODS

Nine patients with recurrent HER2-positive GB were treated with single doses of 1 × 107, 3 × 107, or 1 × 108 irradiated CAR-NK cells injected into the margins of the surgical cavity during relapse surgery. Imaging at baseline and follow-up, peripheral blood lymphocyte phenotyping and analyses of the immune architecture by multiplex immunohistochemistry and spatial digital profiling were performed.

RESULTS

There were no dose-limiting toxicities, and none of the patients developed a cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. Five patients showed stable disease after relapse surgery and CAR-NK injection that lasted 7 to 37 weeks. Four patients had progressive disease. Pseudoprogression was found at injection sites in 2 patients, suggestive of a treatment-induced immune response. For all patients, median progression-free survival was 7 weeks, and median overall survival was 31 weeks. Furthermore, the level of CD8+ T-cell infiltration in recurrent tumor tissue prior to CAR-NK cell injection positively correlated with time to progression.

CONCLUSIONS

Intracranial injection of HER2-targeted CAR-NK cells is feasible and safe in patients with recurrent GB. 1 × 108 NK-92/5.28.z cells was determined as the maximum feasible dose for a subsequent expansion cohort with repetitive local injections of CAR-NK cells.

Optimizing CAR-T Therapy for Glioblastoma

Chimeric antigen receptor T-cell therapies have transformed the management of hematologic malignancies but have not yet demonstrated consistent efficacy in solid tumors. Glioblastoma is the most common primary malignant brain tumor in adults and remains a major unmet medical need. Attempts at harnessing the potential of chimeric antigen receptor T-cell therapy for glioblastoma have resulted in glimpses of promise but have been met with substantial challenges. In this focused review, we discuss current and future strategies being developed to optimize chimeric antigen receptor T cells for efficacy in patients with glioblastoma, including the identification and characterization of new target antigens, reversal of T-cell dysfunction with novel chimeric antigen receptor constructs, regulatable platforms, and gene knockout strategies, and the use of combination therapies to overcome the immune-hostile microenvironment.

Dendritic Cells Pulsed with Tumor Lysates Induced by Tetracyanotetra(aryl)porphyrazines-Based Photodynamic Therapy Effectively Trigger Anti-Tumor Immunity in an Orthotopic Mouse Glioma Model

Research in the past decade on immunogenic cell death (ICD) has shown that the immunogenicity of dying tumor cells is crucial for effective anticancer therapy. ICD induction leads to the emission of specific damage-associated molecular patterns (DAMPs), which act as danger signals and as adjuvants to activate specific anti-tumor immune responses, leading to the elimination of tumor cells and the formation of long-term immunological memory. ICD can be triggered by many anticancer treatment modalities, including photodynamic therapy (PDT). However, due to the variety of photosensitizers used and the lack of a universally adopted PDT protocol, there is a need to develop novel PDT with a proven ICD capability. In the present study, we characterized the abilities of two photoactive dyes to induce ICD in experimental glioma in vitro and in vivo. One dye was from the tetracyanotetra(aryl)porphyrazine group with 9-phenanthrenyl (pz I), and the other was from the 4-(4-fluorobenzyoxy)phenyl (pz III) group in the aryl frame of the macrocycle. We showed that after the photosensitizers penetrated into murine glioma GL261 cells, they localized predominantly in the Golgi apparatus and partially in the endoplasmic reticulum, providing efficient phototoxic activity against glioma GL261 cells upon light irradiation at a dose of 20 J/cm2 (λex 630 nm; 20 mW/cm2). We demonstrated that pz I-PDT and pz III-PDT can act as efficient ICD inducers when applied to glioma GL261 cells, facilitating the release of two crucial DAMPs (ATP and HMGB1). Moreover, glioma GL261 cells stimulated with pz I-PDT or pz III-PDT provided strong protection against tumor growth in a prophylactic subcutaneous glioma vaccination model. Finally, we showed that dendritic cell (DC) vaccines pulsed with the lysates of glioma GL261 cells pre-treated with pz-I-PDT or pz-III-PDT could act as effective inducers of adaptive anti-tumor immunity in an intracranial orthotopic glioma mouse model.

Bispecific T-Cell Engagers and Chimeric Antigen Receptor T-Cell Therapies in Glioblastoma: An Update

Glioblastoma is the most common malignant primary brain tumor in adults. The prognosis is extremely poor even with standard treatment of maximal safe resection, radiotherapy, and chemotherapy. Recurrence is inevitable within months, and treatment options are very limited. Chimeric antigen receptor T-cell therapy (CART) and bispecific T-cell engagers (TCEs) are two emerging immunotherapies that can redirect T-cells for tumor-specific killing and have shown remarkable success in hematological malignancies and been under extensive study for application in glioblastoma. While there have been multiple clinical trials showing preliminary evidence of safety and efficacy for CART, bispecific TCEs are still in the early stages of clinical testing, with preclinical studies showing very promising results. However, there are multiple shared challenges that need to be addressed in the future, including the route of delivery, antigen escape, the immunosuppressive tumor microenvironment, and toxicity resulting from the limited choice of tumor-specific antigens. Efforts are underway to optimize the design of both these treatments and find the ideal combination therapy to overcome these challenges. In this review, we describe the work that has been performed as well as novel approaches in glioblastoma and in other solid tumors that may be applicable in the future.

Efficacy and safety of innate and adaptive immunotherapy combined with standard of care in high-grade gliomas: a systematic review and meta-analysis

Background

Malignant glioma is the most common intracranial malignant tumor with the highest mortality. In the era of immunotherapy, it is important to determine what type of immunotherapy provides the best chance of survival.

Method

Here, the efficacy and safety of immunotherapy in high-grade glioma (HGG) were evaluated by systematic review and meta-analysis. The differences between various types of immunotherapy were explored. Retrieved hits were screened for inclusion in 2,317 articles. We extracted the overall survival (OS) and progression-free survival (PFS) hazard ratios (HRs) as two key outcomes for examining the efficacy of immunotherapy. We also analyzed data on the reported corresponding adverse events to assess the safety of immunotherapy. This study was registered with PROSPERO (CRD42019112356).

Results

We included a total of 1,271 patients, of which 524 received a combination of immunotherapy and standard of care (SOC), while 747 received SOC alone. We found that immunotherapy extended the OS (HR = 0.74; 95% confidence interval [CI], 0.56-0.99; Z = -2.00, P = 0.0458 < 0.05) and PFS (HR = 0.67; 95% CI, 0.45-0.99; Z = -1.99, P = 0.0466 < 0.05), although certain adverse events occurred (proportion = 0.0773, 95% CI, 0.0589-0.1014). Our data have demonstrated the efficacy of the dendritic cell (DC) vaccine in prolonging the OS (HR = 0.38; 95% CI, 0.21-0.68; Z = -3.23; P = 0.0012 < 0.05) of glioma patients. Oncolytic viral therapy (VT) only extended patient survival in a subgroup analysis (HR = 0.60; 95% CI, 0.45-0.80; Z = -3.53; P = 0.0004 < 0.05). By contrast, immunopotentiation (IP) did not prolong OS (HR = 0.69; 95% CI, 0.50-0.96; Z = -2.23; P = 0.0256).

Conclusion

Thus, DC vaccination significantly prolonged the OS of HGG patients, however, the efficacy of VT and IP should be explored in further studies. All the therapeutic schemes evaluated were associated with certain side effects.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=112356.

CAR-NK cell therapy for glioblastoma: what to do next?

Glioblastoma is a malignant tumor with the highest morbidity and mortality in the central nervous system. Conventional surgical resection combined with radiotherapy or chemotherapy has a high recurrence rate and poor prognosis. The 5-year survival rate of patients is less than 10%. In tumor immunotherapy, CAR-T cell therapy represented by chimeric antigen receptor-modified T cells has achieved great success in hematological tumors. However, the application of CAR-T cells in solid tumors such as glioblastoma still faces many challenges. CAR-NK cells are another potential adoptive cell therapy strategy after CAR-T cells. Compared with CAR-T cell therapy, CAR-NK cells have similar anti-tumor effects. CAR-NK cells can also avoid some deficiencies in CAR-T cell therapy, a research hotspot in tumor immunity. This article summarizes the preclinical research status of CAR-NK cells in glioblastoma and the problems and challenges faced by CAR-NK in glioblastoma.

Gene Targets of CAR-T Cell Therapy for Glioblastoma

Glioblastoma (GBM) is an aggressive primary brain tumor with a poor prognosis following conventional therapeutic interventions. Moreover, the blood-brain barrier (BBB) severely impedes the permeation of chemotherapy drugs, thereby reducing their efficacy. Consequently, it is essential to develop novel GBM treatment methods. A novel kind of pericyte immunotherapy known as chimeric antigen receptor T (CAR-T) cell treatment uses CAR-T cells to target and destroy tumor cells without the aid of the antigen with great specificity and in a manner that is not major histocompatibility complex (MHC)-restricted. It has emerged as one of the most promising therapy techniques with positive clinical outcomes in hematological cancers, particularly leukemia. Due to its efficacy in hematologic cancers, CAR-T cell therapy could potentially treat solid tumors, including GBM. On the other hand, CAR-T cell treatment has not been as therapeutically effective in treating GBM as it has in treating other hematologic malignancies. CAR-T cell treatments for GBM have several challenges. This paper reviewed the use of CAR-T cell therapy in hematologic tumors and the selection of targets, difficulties, and challenges in GBM.

Multivalent in vivo delivery of DNA-encoded bispecific T cell engagers effectively controls heterogeneous GBM tumors and mitigates immune escape

Glioblastoma multiforme (GBM) is among the most difficult cancers to treat with a 5-year survival rate less than 5%. An immunotherapeutic vaccine approach targeting GBM-specific antigen, EGFRvIII, previously demonstrated important clinical impact. However, immune escape variants were reported in the trial, suggesting that multivalent approaches targeting GBM-associated antigens may be of importance. Here we focused on multivalent in vivo delivery of synthetic DNA-encoded bispecific T cell engagers (DBTEs) targeting two GBM-associated antigens, EGFRvIII and HER2. We designed and optimized an EGFRvIII-DBTE that induced T cell-mediated cytotoxicity against EGFRvIII-expressing tumor cells. In vivo delivery in a single administration of EGFRvIII-DBTE resulted in durable expression over several months in NSG mice and potent tumor control and clearance in both peripheral and orthotopic animal models of GBM. Next, we combined delivery of EGFRvIII-DBTEs with an HER2-targeting DBTE to treat heterogeneous GBM tumors. In vivo delivery of dual DBTEs targeting these two GBM-associated antigens exhibited enhanced tumor control and clearance in a heterogeneous orthotopic GBM challenge, while treatment with single-target DBTE ultimately allowed for tumor escape. These studies support that combined delivery of DBTEs, targeting both EGFRvIII and HER2, can potentially improve outcomes of GBM immunotherapy, and such multivalent approaches deserve additional study.

Chimeric Antigen Receptor-Natural Killer Cells: A New Breakthrough in the Treatment of Solid Tumours

Natural killer (NK) cells can quickly and directly eradicate tumour cells without recognising tumour-specific antigens. NK cells also participate in immune surveillance, which arouses great interest in the development of novel cancer therapies. The chimeric antigen receptor (CAR) family is composed of receptor proteins that give immune cells extra capabilities to target specific antigen proteins or enhance their killing effects. CAR-T cell therapy has achieved initial success in haematological tumours, but is prone to adverse reactions, especially with cytokine release syndrome in clinical applications. Currently, CAR-NK cell therapy has been shown to successfully kill haematological tumour cells with allogeneic NK cells in clinical trials without adverse reactions, proving its potential to become an off-the-shelf product with broad clinical application prospects. Meanwhile, clinical trials of CAR-NK cells for solid tumours are currently underway. Here we will focus on the latest advances in CAR-NK cells, including preclinical and clinical trials in solid tumours, the advantages and challenges of CAR-NK cell therapy and new strategies to improve the safety and efficacy of CAR-NK cell therapy.

Activated T cell therapy targeting glioblastoma cancer stem cells

Naïve T cells become effector T cells following stimulation by antigen-loaded dendritic cells (DCs) and sequential cytokine activation. We aimed to develop procedures to efficiently activate T cells with tumor-associated antigens (TAAs) to glioblastoma (GBM) stem cells. To remove antigen presentation outside of the immunosuppressive tumor milieu, three different glioma stem cell (GSC) specific antigen sources to load DCs were compared in their ability to stimulate lymphocytes. An activated T cell (ATC) protocol including cytokine activation and expansion in culture to target GSCs was generated and optimized for a planned phase I clinical trial. We compared three different antigen-loading methods on DCs to effectively activate T cells, which were GBM patient-derived GSC-lysate, acid-eluate of GSCs and synthetic peptides derived from proteins expressed in GSCs. DCs derived from HLA-A2 positive blood sample were loaded with TAAs. Autologous T cells were activated by co-culturing with loaded DCs. Efficiency and cytotoxicity of ATCs were evaluated by targeting TAA-pulsed DCs or T2 cells, GSCs, or autologous PHA-blasts. Characteristics of ATCs were evaluated by Flow Cytometry and ELISpot assay, which showed increased number of ATCs secreting IFN-γ targeting GSCs as compared with non-activated T cells and unloaded target cells. Neither GSC-lysate nor acid-eluate loading showed enhancement in response of ATCs but the synthetic peptide pool showed significantly increased IFN-γ secretion and increased cytotoxicity towards target cells. These results demonstrate that ATCs activated using a TAA synthetic peptide pool efficiently enhance cytotoxicity specifically to target cells including GSC.

AAV-mediated gene transfer of a checkpoint inhibitor in combination with HER2-targeted CAR-NK cells as experimental therapy for glioblastoma

Glioblastoma (GB) is the most common primary brain tumor, which is characterized by low immunogenicity of tumor cells and prevalent immunosuppression in the tumor microenvironment (TME). Targeted local combination immunotherapy is a promising strategy to overcome these obstacles. Here, we evaluated tumor-cell specific delivery of an anti-PD-1 immunoadhesin (aPD-1) via a targeted adeno-associated viral vector (AAV) as well as HER2-specific NK-92/5.28.z (anti-HER2.CAR/NK-92) cells as components for a combination immunotherapy. In co-culture experiments, target-activated anti-HER2.CAR/NK-92 cells modified surrounding tumor cells and bystander immune cells by triggering the release of inflammatory cytokines and upregulation of PD-L1. Tumor cell-specific delivery of aPD-1 was achieved by displaying a HER2-specific designed ankyrin repeat protein (DARPin) on the AAV surface. HER2-AAV mediated gene transfer into GB cells correlated with HER2 expression levels, without inducing anti-viral responses in transduced cells. Furthermore, AAV-transduction did not interfere with anti-HER2.CAR/NK-92 cell-mediated tumor cell lysis. After selective transduction of HER2⁺ cells, aPD-1 expression was detected at the mRNA and protein level. The aPD-1 immunoadhesin was secreted in a time-dependent manner, bound its target on PD-1-expressing cells and was able to re-activate T cells by efficiently disrupting the PD-1/PD-L1 axis. Moreover, high intratumoral and low systemic aPD-1 concentrations were achieved following local injection of HER2-AAV into orthotopic tumor grafts in vivo. aPD-1 was selectively produced in tumor tissue and could be detected up to 10 days after a single HER2-AAV injection. In subcutaneous GL261-HER2 and Tu2449-HER2 immunocompetent mouse models, administration of the combination therapy significantly prolonged survival, including complete tumor control in several animals in the GL261-HER2 model. In summary, local therapy with aPD-1 encoding HER2-AAVs in combination with anti-HER2.CAR/NK-92 cells may be a promising novel strategy for GB immunotherapy with the potential to enhance efficacy and reduce systemic side effects of immune-checkpoint inhibitors.

Clinical and Translational Advances in Glioma Immunotherapy

Gliomas are highly treatment refractory against immune checkpoint blockade, an immunotherapeutic modality that revolutionized therapy for many tumors. At the same time, technological innovation has dramatically accelerated the development of immunotherapeutic approaches such as personalized tumor-specific vaccine production, dendritic cell vaccine manufacture, patient-individual target selection and chimeric antigen receptor, and T cell receptor T cell manufacture. Here we review recent clinical and translational advances in glioma immunotherapy with a focus on targets and their cognate immune receptor derivates as well as concepts to improve intratumoral T cell effector functions.

Chimeric Antigen Receptor (CAR) T Cell Therapy for Glioblastoma

Glioblastoma (GBM) are the most common and aggressive primary brain tumors in adults. Current mainstay treatments include surgery, chemotherapy, and radiation; however, these are ineffective. As a result, immunotherapy treatment strategies are being developed to harness the body's natural defense mechanisms against gliomas. Adoptive cell therapy with chimeric antigen receptor (CAR) T cells uses patients' own T cells that are genetically modified to target tumor-associated antigens. These cells are harvested from patients, engineered to target specific proteins expressed by the tumor and re-injected into the patient with the goal of destroying tumor cells. In this mini review, we outline the history of CAR T cell therapy, describe current antigen targets, and review challenges this treatment faces specifically in targeting GBM.

Emerging new therapeutic antibody derivatives for cancer treatment

Monoclonal antibodies constitute a promising class of targeted anticancer agents that enhance natural immune system functions to suppress cancer cell activity and eliminate cancer cells. The successful application of IgG monoclonal antibodies has inspired the development of various types of therapeutic antibodies, such as antibody fragments, bispecific antibodies, and antibody derivatives (e.g., antibody–drug conjugates and immunocytokines). The miniaturization and multifunctionalization of antibodies are flexible and viable strategies for diagnosing or treating malignant tumors in a complex tumor environment. In this review, we summarize antibodies of various molecular types, antibody applications in cancer therapy, and details of clinical study advances. We also discuss the rationale and mechanism of action of various antibody formats, including antibody–drug conjugates, antibody–oligonucleotide conjugates, bispecific/multispecific antibodies, immunocytokines, antibody fragments, and scaffold proteins. With advances in modern biotechnology, well-designed novel antibodies are finally paving the way for successful treatments of various cancers, including precise tumor immunotherapy, in the clinic.

CAR-T cells for pediatric brain tumors: Present and future

Chimeric Antigen Receptor T (CAR-T) cells are currently approved for B cell malignancies only, in children and adults. Despite a lack of robust evidence to approve such cellular immunotherapy for pediatric solid tumors, there is a growing interest for this approach in the treatment of pediatric brain tumors. Following the identification of tumor antigens as targets, the first clinical trials demonstrated some degree of clinical and biological responses to CAR-T cells for such tumor types. Additionaly, several preclinical studies have recently identified new attractive targets and antigen combination strategies, along with a superior tumor trafficking following locoregional administration. We review here the preclinical and clinical knowledge at the basis of the current clinical development of CAR-T cells for pediatric brain tumors.

Genetically Modified Cellular Therapies for Malignant Gliomas

Despite extensive preclinical research on immunotherapeutic approaches, malignant glioma remains a devastating disease of the central nervous system for which standard of care treatment is still confined to resection and radiochemotherapy. For peripheral solid tumors, immune checkpoint inhibition has shown substantial clinical benefit, while promising preclinical results have yet failed to translate into clinical efficacy for brain tumor patients. With the advent of high-throughput sequencing technologies, tumor antigens and corresponding T cell receptors (TCR) and antibodies have been identified, leading to the development of chimeric antigen receptors (CAR), which are comprised of an extracellular antibody part and an intracellular T cell receptor signaling part, to genetically engineer T cells for antigen recognition. Due to efficacy in other tumor entities, a plethora of CARs has been designed and tested for glioma, with promising signs of biological activity. In this review, we describe glioma antigens that have been targeted using CAR T cells preclinically and clinically, review their drawbacks and benefits, and illustrate how the emerging field of transgenic TCR therapy can be used as a potent alternative for cell therapy of glioma overcoming antigenic limitations.

Challenges and Prospects for Designer T and NK Cells in Glioblastoma Immunotherapy

Glioblastoma (GBM) is the most prevalent, aggressive primary brain tumour with a dismal prognosis. Treatment at diagnosis has limited efficacy and there is no standardised treatment at recurrence. New, personalised treatment options are under investigation, although challenges persist for heterogenous tumours such as GBM. Gene editing technologies are a game changer, enabling design of novel molecular-immunological treatments to be used in combination with chemoradiation, to achieve long lasting survival benefits for patients. Here, we review the literature on how cutting-edge molecular gene editing technologies can be applied to known and emerging tumour-associated antigens to enhance chimeric antigen receptor T and NK cell therapies for GBM. A tight balance of limiting neurotoxicity, avoiding tumour antigen loss and therapy resistance, while simultaneously promoting long-term persistence of the adoptively transferred cells must be maintained to significantly improve patient survival. We discuss the opportunities and challenges posed by the brain contexture to the administration of the treatments and achieving sustained clinical responses.

CAR-T therapy: Prospects in targeting cancer stem cells

Cancer stem cells (CSCs), a group of tumour cells with stem cell characteristics, have the ability of self-renewal, multi-lineage differentiation and tumour formation. Since CSCs are resistant to conventional radiotherapy and chemotherapy, their existence may be one of the root causes of cancer treatment failure and tumour progression. The elimination of CSCs may be effective for eventual tumour eradication. Because of the good therapeutic effects without major histocompatibility complex (MHC) restriction and the unique characteristics of CSCs, chimeric antigen receptor T-cell (CAR-T) therapy is expected to be an important method to eliminate CSCs. In this review, we have discussed the feasibility of CSCs-targeted CAR-T therapy for cancer treatment, summarized current research and clinical trials of targeting CSCs with CAR-T cells and forecasted the challenges and future direction from the perspectives of toxicity, persistence and potency, trafficking, infiltration, immunosuppressive tumour microenvironment, and tumour heterogeneity.

Current Immunotherapeutic Strategies for the Treatment of Glioblastoma

Glioblastoma (GBM) is a lethal primary brain tumor. Despite extensive effort in basic, translational, and clinical research, the treatment outcomes for patients with GBM are virtually unchanged over the past 15 years. GBM is one of the most immunologically "cold" tumors, in which cytotoxic T-cell infiltration is minimal, and myeloid infiltration predominates. This is due to the profound immunosuppressive nature of GBM, a tumor microenvironment that is metabolically challenging for immune cells, and the low mutational burden of GBMs. Together, these GBM characteristics contribute to the poor results obtained from immunotherapy. However, as indicated by an ongoing and expanding number of clinical trials, and despite the mostly disappointing results to date, immunotherapy remains a conceptually attractive approach for treating GBM. Checkpoint inhibitors, various vaccination strategies, and CAR T-cell therapy serve as some of the most investigated immunotherapeutic strategies. This review article aims to provide a general overview of the current state of glioblastoma immunotherapy. Information was compiled through a literature search conducted on PubMed and clinical trials between 1961 to 2021.

Specificity, Safety, Efficacy of EGFRvIII-Retargeted Oncolytic HSV for Xenotransplanted Human Glioblastoma

Glioblastoma is a lethal primary brain tumor lacking effective therapy. The secluded onset site, combined with the infiltrative properties of this tumor, require novel targeted therapies. In this scenario, the use of oncolytic viruses retargeted to glioblastoma cells and able to spread across the tumor cells represent an intriguing treatment strategy. Here, we tested the specificity, safety and efficacy of R-613, the first oncolytic HSV fully retargeted to EGFRvIII, a variant of the epidermal growth factor receptor carrying a mutation typically found in glioblastoma. An early treatment with R-613 on orthotopically transplanted EGFRvIII-expressing human glioblastoma significantly increased the median survival time of mice. In this setting, the growth of human glioblastoma xenotransplants was monitored by a secreted luciferase reporter and showed that R-613 is able to substantially delay the development of the tumor masses. When administered as late treatment to a well-established glioblastomas, R-613 appeared to be less effective. Notably the uninfected tumor cells derived from the explanted tumor masses were still susceptible to R-613 infection ex vivo, thus suggesting that multiple treatments could enhance R-613 therapeutic efficacy, making R-613 a promising oncolytic HSV candidate for glioblastoma treatment.

Chimeric Antigen Receptor T-Cell Therapy: Updates in Glioblastoma Treatment

Glioblastoma multiforme (GBM) are the most common and among the deadliest brain tumors in adults. Current mainstay treatments are insufficient to treat this tumor, and therefore, more effective therapies are desperately needed. Immunotherapy, which takes advantage of the body's natural defense mechanism, is an exciting emerging field in neuro-oncology. Adoptive cell therapy with chimeric antigen receptor (CAR) T cells provides a treatment strategy based on using patients' own selected and genetically engineered cells that target tumor-associated antigens. These cells are harvested from patients, modified to target specific proteins expressed by the tumor, and re-introduced into the patient with the goal of destroying tumor cells. Here, we review the history of CAR T-cell therapy, and describe the characteristics of various generations of CAR T therapies, and the challenges inherent to treatment of GBM. Finally, we describe recent and current CAR T clinical trials designed to combat GBM.

PMEL as a Prognostic Biomarker and Negatively Associated With Immune Infiltration in Skin Cutaneous Melanoma (SKCM)

Premelanosome protein (PMEL) is crucial for the formation of melanosomal fibrils through the transition from stage I to stage II melanosomes. It was used as a target antigen in some adoptive T-cell therapy of melanoma. The correlation of PMEL to prognosis and immune cell infiltration level are unknown in melanoma. The PMEL expression was evaluated via Tumor Immune Estimation Resource, Oncomine and Gene Expression Profiling Interactive Analysis (GEPIA). We also evaluate the influence of PMEL on overall survival via GEPIA, PrognoScan, and immunohistochemistry in human tissue microarray. The correlation between PMEL expression level and immune cell or gene markers of immune infiltration level was explored on Tumor Immune Estimation Resource and GEPIA. PMEL expression was significantly higher in skin cutaneous melanoma (SKCM) and SKCM-metastasis in comparison with the other cancers. In SKCM, PMEL expression in high levels was associated with poor overall survival. In both SKCM and SKCM-metastasis patients, PMEL expression is negatively correlated with the infiltration cells of CD8+ T cells, macrophages, and neutrophils. Programmed cell-death protein 1 just showed response rates ranging from 20% to 40% in patients with melanoma, so it is critical to discover a new therapeutic target. PMEL is negatively associated with immune cell infiltration and can be as a negative prognosis marker or new immunotherapy target in SKCM and SKCM-metastasis.

Targeting Tumor-Associated Antigen: A Promising CAR-T Therapeutic Strategy for Glioblastoma Treatment

Chimeric antigen receptor T cells (CAR-T) therapy is a prospective therapeutic strategy for blood cancers tumor, especially leukemia, but it is not effective for solid tumors. Glioblastoma (GBM) is a highly immunosuppressive and deadly malignant tumor with poor responses to immunotherapies. Although CAR-T therapeutic strategies were used for glioma in preclinical trials, the current proliferation activity of CAR-T is not sufficient, and malignant glioma usually recruit immunosuppressive cells to form a tumor microenvironment that hinders CAR-T infiltration, depletes CAR-T, and impairs their efficacy. Moreover, specific environments such as hypoxia and nutritional deficiency can hinder the killing effect of CAR-T, limiting their therapeutic effect. The normal brain lack lymphocytes, but CAR-T usually can recognize specific antigens and regulate the tumor immune microenvironment to increase and decrease pro- and anti-inflammatory factors, respectively. This increases the number of T cells and ultimately enhances anti-tumor effects. CAR-T therapy has become an indispensable modality for glioma due to the specific tumor-associated antigens (TAAs). This review describes the characteristics of CAR-T specific antigen recognition and changing tumor immune microenvironment, as well as ongoing research into CAR-T therapy targeting TAAs in GBM and their potential clinical application.

Immunotherapy and radiation for high-grade glioma: a narrative review

Glioblastoma and other high-grade gliomas (HGGs) are the most common and deadly primary brain tumors. Due to recent advances in immunotherapy and improved clinical outcomes in other disease sites, the study of immunotherapy in HGG has increased significantly. Herein, we summarize and evaluate existing evidence and ongoing clinical trials investigating the use of immunotherapy in the treatment of HGG, including therapeutic vaccination, immune checkpoint inhibition, adoptive lymphocyte transfer, and combinatorial approaches utilizing radiation and multiple modalities of immunotherapy. Special attention is given to the mechanisms by which radiation may improve immunogenicity in HGG, why this motivates the study of radiation in combination with immunotherapy, and how to determine optimal dosing and scheduling of radiation. Though larger randomized controlled trials have not consistently shown improvements in clinical outcomes, this area of research is still in its early stages and a number of important lessons can be taken away from the studies that have been completed to date. Many studies found a subset of patients who experienced durable responses, and analysis of their immune cells and tumor cells can be used to identify biomarkers that predict therapeutic response, as well as additional glioma-specific targets that can enhance therapeutic efficacy in a challenging tumor type.

Dry Formulation of Virus-Like Particles in Electrospun Nanofibers

Biologics can be combined with liquid polymer materials and electrospun to produce a dry nanofibrous scaffold. Unlike spray-drying and freeze-drying, electrospinning minimizes the physiological stress on sensitive materials, and nanofiber mat properties such as hydrophobicity, solubility, and melting temperature can be tuned based on the polymer composition. In this study, we explored the dry formulation of a virus-like particle (VLP) vaccine by electrospinning VLP derived from rabbit hemorrhagic disease virus modified to carry the MHC-I gp100 tumor-associated antigen epitope. VLP were added to a polyvinylpyrrolidone (PVP) solution (15% w/v) followed by electrospinning at 24 kV. Formation of a nanofibrous mat was confirmed by scanning electron microscopy, and the presence of VLP was confirmed by transmission electron microscopy and Western blot. VLP from the nanofibers induced T-cell activation and interferon- (IFN-) γ production in vitro. To confirm in vivo cytotoxicity, Pmel mice treated by injection with gp100 VLP from nanofibers induced a gp100 specific immune response, lysing approximately 65% of gp100-pulsed target cells, comparable to mice vaccinated with gp100 VLP in PBS. VLP from nanofibers also induced an antibody response. This work shows that electrospinning can be used to dry-formulate VLP, preserving both humoral and cell-mediated immunity.

The Current State of Oncolytic Herpes Simplex Virus for Glioblastoma Treatment

Glioblastoma (GBM) is a lethal primary malignant brain tumor with no current effective treatments. The recent emergence of immuno-virotherapy and FDA approval of T-VEC have generated a great expectation towards oncolytic herpes simplex viruses (oHSVs) as a promising treatment option for GBM. Since the generation and testing of the first genetically engineered oHSV in glioma in the early 1990s, oHSV-based therapies have shown a long way of great progress in terms of anti-GBM efficacy and safety, both preclinically and clinically. Here, we revisit the literature to understand the recent advancement of oHSV in the treatment of GBM. In addition, we discuss current obstacles to oHSV-based therapies and possible strategies to overcome these pitfalls.

Autologous CMV-specific T cells are a safe adjuvant immunotherapy for primary glioblastoma multiforme

BACKGROUNDThe recent failure of checkpoint-blockade therapies for glioblastoma multiforme (GBM) in late-phase clinical trials has directed interest toward adoptive cellular therapies (ACTs). In this open-label, first-in-human trial, we have assessed the safety and therapeutic potential of cytomegalovirus-specific (CMV-specific) ACT in an adjuvant setting for patients with primary GBM, with an ultimate goal to prevent or delay recurrence and prolong overall survival.METHODSTwenty-eight patients with primary GBM were recruited to this prospective study, 25 of whom were treated with in vitro-expanded autologous CMV-specific T cells. Participants were monitored for safety, progression-free survival, overall survival (OS), and immune reconstitution.RESULTSNo participants showed evidence of ACT-related toxicities. Of 25 evaluable participants, 10 were alive at the completion of follow-up, while 5 were disease free. Reconstitution of CMV-specific T cell immunity was evident and CMV-specific ACT may trigger a bystander effect leading to additional T cell responses to nonviral tumor-associated antigens through epitope spreading. Long-term follow-up of participants treated before recurrence showed significantly improved OS when compared with those who progressed before ACT (median 23 months, range 7-65 vs. median 14 months, range 5-19; P = 0.018). Gene expression analysis of the ACT products indicated that a favorable T cell gene signature was associated with improved long-term survival.CONCLUSIONData presented in this study demonstrate that CMV-specific ACT can be safely used as an adjuvant therapy for primary GBM and, if offered before recurrence, this therapy may improve OS of GBM patients.TRIAL REGISTRATIONanzctr.org.au: ACTRN12615000656538.FUNDINGPhilanthropic funding and the National Health and Medical Research Council (Australia).

Clinical implication of cellular vaccine in glioma: current advances and future prospects

Gliomas, especially glioblastomas, represent one of the most aggressive and difficult-to-treat human brain tumors. In the last few decades, clinical immunotherapy has been developed and has provided exceptional achievements in checkpoint inhibitors and vaccines for cancer treatment. Immunization with cellular vaccines has the advantage of containing specific antigens and acceptable safety to potentially improve cancer therapy. Based on T cells, dendritic cells (DC), tumor cells and natural killer cells, the safety and feasibility of cellular vaccines have been validated in clinical trials for glioma treatment. For TAA engineered T cells, therapy mainly uses chimeric antigen receptors (IL13Rα2, EGFRvIII and HER2) and DNA methylation-induced technology (CT antigen) to activate the immune response. Autologous dendritic cells/tumor antigen vaccine (ADCTA) pulsed with tumor lysate and peptides elicit antigen-specific and cytotoxic T cell responses in patients with malignant gliomas, while its pro-survival effect is biased. Vaccinations using autologous tumor cells modified with TAAs or fusion with fibroblast cells are characterized by both effective humoral and cell-mediated immunity. Even though few therapeutic effects have been observed, most of this therapy showed safety and feasibility, asking for larger cohort studies and better guidelines to optimize cellular vaccine efficiency in anti-glioma therapy.

Present and Future of Anti-Glioblastoma Therapies: A Deep Look into Molecular Dependencies/Features

Glioblastoma (GBM) is aggressive malignant tumor residing within the central nervous system. Although the standard treatment options, consisting of surgical resection followed by combined radiochemotherapy, have long been established for patients with GBM, the prognosis is still poor. Despite recent advances in diagnosis, surgical techniques, and therapeutic approaches, the increased patient survival after such interventions is still sub-optimal. The unique characteristics of GBM, including highly infiltrative nature, hard-to-access location (mainly due to the existence of the blood brain barrier), frequent and rapid recurrence, and multiple drug resistance mechanisms, pose challenges to the development of an effective treatment. To overcome current limitations on GBM therapy and devise ideal therapeutic strategies, efforts should focus on an improved molecular understanding of GBM pathogenesis. In this review, we summarize the molecular basis for the development and progression of GBM as well as some emerging therapeutic approaches.

The update of chimeric antigen receptor-T cells therapy in glioblastoma

Glioblastoma (GBM) is the most malignant central nervous system neoplasm and the outcome is difficult to break through for decades. Ninety percent of patients who suffered from treatment failed. Since 2010, the chimeric antigen receptor (CAR)-T cell therapy has achieved a durable effect in the treatment of B-cell hematologic malignancies. Although several preclinical and clinical trials have emerged as a potential option in solid tumor including high-grade gliomas, the results are limited at present. The challenges of CAR-T cells in GBM are including identification of tumor-specific antigens, preservation activity of T cell, trafficking of enough CAR-T cells to the tumor site, and reversed unique immune suppressive environment of the central nervous system. The success of targeting brain tumors with CAR-T cells has more consideration. In this review article, we will summarize the current key clinical trials of CAR-T therapies in this field. And will outline the obstacles of application of CAR-T cells for the treatment of GBM as well. This review is intended to help guide the future direction of CAR-T therapy in GBM that will move the outcome forward in the future.

Syngeneic murine model for prostate cancer using RM1 cells transfected with gp100

BACKGROUND

Prostate cancer (PC) is the most commonly diagnosed solid tumor in men. A major challenge in PC immunotherapy is the lack of an animal model that resembles human adenocarcinoma and allows for manipulation or monitoring of the immune response. Mouse models are needed for preclinical testing of new immunotherapies, whether used alone or in combination with established drugs, and to develop companion biomarkers that can be validated in clinical trials.

METHODS

To develop a syngeneic prostate adenocarcinoma model with a well-defined tumor antigen, murine RM1 PC cells were transfected with the endogenous mouse melanoma protein, gp100 (RM1-gp100). Gp100 was attractive because it is a self-protein and it instantly allowed us to use the large trove of immune research tools developed for melanoma research. A dendritic cell (DC) vaccine was used as model immunotherapy to demonstrate that adoptive immunotherapy against gp100 decreases the growth of RM1-gp100 but not RM1.

RESULTS

Expressing gp100 did not change the growth of RM1 cell in vitro or in vivo. The DCs pulsed with RM1-gp100 could be used to stimulate Pmel-1 lymphocyte proliferation and activation. Pmel-1 lymphocytes could be adoptively transferred into C57Bl/6 mice that were treated with DCs pulsed with RM1-gp100. The resulting Pmel-1 lymphocytes were monitored to assess the primary cellular immune response and memory response.

CONCLUSION

We describe a murine model for prostate adenocarcinoma with a well-characterized antigen that can be used in an immunologically intact mice to monitor the temporal CD8+ lymphocyte-mediated antitumor immunity.

Tumor-Specific T Cell Activation in Malignant Brain Tumors

Due to their delicate locations as well as aggressive and infiltrative behavior, malignant brain tumors remain a therapeutic challenge. Harnessing the efficacy and specificity of the T-cell response to counteract malignant brain tumor progression and recurrence, represents an attractive treatment option. With the tremendous advances in the current era of immunotherapy, ongoing studies aim to determine the best treatment strategies for mounting a tumor-specific immune response against malignant brain tumors. However, immunosuppression in the local tumor environment, molecular and cellular heterogeneity as well as a lack of suitable targets for tumor-specific vaccination impede the successful implementation of immunotherapeutic treatment strategies in neuro-oncology. In this review, we therefore discuss the role of T cell exhaustion, the genetic and antigenic landscape, potential pitfalls and ongoing efforts to overcome the individual challenges in order to elicit a tumor-specific T cell response.

CAR-Engineered NK Cells for the Treatment of Glioblastoma: Turning Innate Effectors Into Precision Tools for Cancer Immunotherapy

Glioblastoma (GB) is the most common and aggressive primary brain tumor in adults and currently incurable. Despite multimodal treatment regimens, median survival in unselected patient cohorts is <1 year, and recurrence remains almost inevitable. Escape from immune surveillance is thought to contribute to the development and progression of GB. While GB tumors are frequently infiltrated by natural killer (NK) cells, these are actively suppressed by the GB cells and the GB tumor microenvironment. Nevertheless, ex vivo activation with cytokines can restore cytolytic activity of NK cells against GB, indicating that NK cells have potential for adoptive immunotherapy of GB if potent cytotoxicity can be maintained in vivo. NK cells contribute to cancer immune surveillance not only by their direct natural cytotoxicity which is triggered rapidly upon stimulation through germline-encoded cell surface receptors, but also by modulating T-cell mediated antitumor immune responses through maintaining the quality of dendritic cells and enhancing the presentation of tumor antigens. Furthermore, similar to T cells, specific recognition and elimination of cancer cells by NK cells can be markedly enhanced through expression of chimeric antigen receptors (CARs), which provides an opportunity to generate NK-cell therapeutics of defined specificity for cancer immunotherapy. Here, we discuss effects of the GB tumor microenvironment on NK-cell functionality, summarize early treatment attempts with ex vivo activated NK cells, and describe relevant CAR target antigens validated with CAR-T cells. We then outline preclinical approaches that employ CAR-NK cells for GB immunotherapy, and give an overview on the ongoing clinical development of ErbB2 (HER2)-specific CAR-NK cells currently applied in a phase I clinical trial in glioblastoma patients.

CAR T-cell therapy for glioblastoma: recent clinical advances and future challenges

In patients with certain hematologic malignancies, the use of autologous T cells genetically modified to express chimeric antigen receptors (CARs) has led to unprecedented clinical responses. Although progress in solid tumors has been elusive, recent clinical studies have demonstrated the feasibility and safety of CAR T-cell therapy for glioblastoma. In addition, despite formidable barriers to T-cell localization and effector function in glioblastoma, signs of efficacy have been observed in select patients. In this review, we begin with a discussion of established obstacles to systemic therapy in glioblastoma and how these may be overcome by CAR T cells. We continue with a summary of previously published CAR T-cell trials in GBM, and end by outlining the key therapeutic challenges associated with the use of CAR T cells in this disease.

A Randomized Double-Blind Placebo-Controlled Phase II Trial of Dendritic Cell Vaccine ICT-107 in Newly Diagnosed Patients with Glioblastoma

PURPOSE

To evaluate the results of the randomized, double-blind, placebo-controlled phase II clinical trial of ICT-107 in patients with newly diagnosed glioblastoma.

PATIENTS AND METHODS

We conducted a double-blinded randomized phase II trial of ICT-107 in newly diagnosed patients with glioblastoma (GBM) and tested efficacy, safety, quality of life (QoL), and immune response. HLA-A1⁺ and/or -A2⁺-resected patients with residual tumor ≤1 cm³ received radiotherapy and concurrent temozolomide. Following completion of radiotherapy, 124 patients, randomized 2:1, received ICT-107 [autologous dendritic cells (DC) pulsed with six synthetic peptide epitopes targeting GBM tumor/stem cell-associated antigens MAGE-1, HER-2, AIM-2, TRP-2, gp100, and IL13Rα2] or matching control (unpulsed DC). Patients received induction ICT-107 or control weekly × 4 followed by 12 months of adjuvant temozolomide. Maintenance vaccinations occurred at 1, 3, and 6 months and every 6 months thereafter.

RESULTS

ICT-107 was well tolerated, with no difference in adverse events between the treatment and control groups. The primary endpoint, median overall survival (OS), favored ICT-107 by 2.0 months in the intent-to-treat (ITT) population but was not statistically significant. Progression-free survival (PFS) in the ITT population was significantly increased in the ICT-107 cohort by 2.2 months (P = 0.011). The frequency of HLA-A2 primary tumor antigen expression was higher than that for HLA-A1 patients, and HLA-A2 patients had higher immune response (via Elispot). HLA-A2 patients achieved a meaningful therapeutic benefit with ICT-107, in both the MGMT methylated and unmethylated prespecified subgroups, whereas only HLA-A1 methylated patients had an OS benefit.

CONCLUSIONS

PFS was significantly improved in ICT-107-treated patients with maintenance of QoL. Patients in the HLA-A2 subgroup showed increased ICT-107 activity clinically and immunologically.

Genetically Engineered T-Cells for Malignant Glioma: Overcoming the Barriers to Effective Immunotherapy

Malignant gliomas carry a dismal prognosis. Conventional treatment using chemo- and radiotherapy has limited efficacy with adverse events. Therapy with genetically engineered T-cells, such as chimeric antigen receptor (CAR) T-cells, may represent a promising approach to improve patient outcomes owing to their potential ability to attack highly infiltrative tumors in a tumor-specific manner and possible persistence of the adaptive immune response. However, the unique anatomical features of the brain and susceptibility of this organ to irreversible tissue damage have made immunotherapy especially challenging in the setting of glioma. With safety concerns in mind, multiple teams have initiated clinical trials using CAR T-cells in glioma patients. The valuable lessons learnt from those trials highlight critical areas for further improvement: tackling the issues of the antigen presentation and T-cell homing in the brain, immunosuppression in the glioma microenvironment, antigen heterogeneity and off-tumor toxicity, and the adaptation of existing clinical therapies to reflect the intricacies of immune response in the brain. This review summarizes the up-to-date clinical outcomes of CAR T-cell clinical trials in glioma patients and examines the most pressing hurdles limiting the efficacy of these therapies. Furthermore, this review uses these hurdles as a framework upon which to evaluate cutting-edge pre-clinical strategies aiming to overcome those barriers.

Current Options and Future Directions in Immune Therapy for Glioblastoma

Glioblastoma is in need of innovative treatment approaches. Immune therapy for cancer refers to the use of the body's immune system to target malignant cells in the body. Such immune therapeutics have recently been very successful in treating a diverse group of cancerous lesions. As a result, many new immune therapies have gained Food and Drug Administration approval for the treatment of cancer, and there has been an explosion in the study of immune therapeutics for cancer treatment over the past few years. However, the immune suppression of glioblastoma and the unique immune microenvironment of the brain make immune therapeutics more challenging to apply to the brain than to other systemic cancers. Here, we discuss the existing barriers to successful immune therapy for glioblastoma and the ongoing development of immune therapeutics. We will discuss the discovery and classification of immune suppressive factors in the glioblastoma microenvironment; the development of vaccine-based therapies; the use of convection-enhanced delivery to introduce tumoricidal viruses into the tumor microenvironment, leading to secondary immune responses; the emerging use of adoptive cell therapy in the treatment of glioblastoma; and future frontiers, such as the use of cerebral microdialysis for immune monitoring and the use of sequencing to develop patient-specific therapeutics. Armed with a better understanding of the challenges inherent in immune therapy for glioblastoma, we may soon see more successes in immune-based clinical trials for this deadly disease.

Irradiation to Improve the Response to Immunotherapeutic Agents in Glioblastomas

Purpose

Glioblastoma (GBM) remains an incurable disease despite extensive treatment with surgical resection, irradiation, and temozolomide. In line with many other forms of aggressive cancers, GBM is currently under consideration as a target for immunotherapy. However, GBM tends to be nonimmunogenic and exhibits a microenvironment with few or no effector T cells, a relatively low nonsynonymous somatic mutational load, and a low predicted neoantigen burden. GBM also exploits a multitude of immunosuppressive strategies.

Methods and Materials

A number of immunotherapeutic approaches have been tested with disappointing results. A rationale exists to combine immunotherapy and radiation therapy, which can induce an immunogenic form of cell death with T-cell activation and tumor infiltration.

Results

Various immunotherapy agents, including immune checkpoint modulators, transforming growth factor beta receptor inhibitors, and indoleamine-2,3-dioxygenase inhibitors, have been evaluated with irradiation in preclinical GBM models, with promising results, and are being further tested in clinical trials.

Conclusions

This review aims to present the basic rationale behind this emerging complementary therapeutic approach in GBM, appraise the current preclinical and clinical data, and discuss the future challenges in improving the antitumor immune response.

Bystander CD8+ T cells are abundant and phenotypically distinct in human tumour infiltrates

Various forms of immunotherapy, such as checkpoint blockade immunotherapy, are proving to be effective at restoring T cell-mediated immune responses that can lead to marked and sustained clinical responses, but only in some patients and cancer types^1-4. Patients and tumours may respond unpredictably to immunotherapy partly owing to heterogeneity of the immune composition and phenotypic profiles of tumour-infiltrating lymphocytes (TILs) within individual tumours and between patients^5,6. Although there is evidence that tumour-mutation-derived neoantigen-specific T cells play a role in tumour control^2,4,7-10, in most cases the antigen specificities of phenotypically diverse tumour-infiltrating T cells are largely unknown. Here we show that human lung and colorectal cancer CD8⁺ TILs can not only be specific for tumour antigens (for example, neoantigens), but also recognize a wide range of epitopes unrelated to cancer (such as those from Epstein-Barr virus, human cytomegalovirus or influenza virus). We found that these bystander CD8⁺ TILs have diverse phenotypes that overlap with tumour-specific cells, but lack CD39 expression. In colorectal and lung tumours, the absence of CD39 in CD8⁺ TILs defines populations that lack hallmarks of chronic antigen stimulation at the tumour site, supporting their classification as bystanders. Expression of CD39 varied markedly between patients, with some patients having predominantly CD39^- CD8⁺ TILs. Furthermore, frequencies of CD39 expression among CD8⁺ TILs correlated with several important clinical parameters, such as the mutation status of lung tumour epidermal growth factor receptors. Our results demonstrate that not all tumour-infiltrating T cells are specific for tumour antigens, and suggest that measuring CD39 expression could be a straightforward way to quantify or isolate bystander T cells.

CAR T-cell therapy for glioblastoma: ready for the next round of clinical testing?

INTRODUCTION

The outcome for patients with glioblastoma (GBM) remains poor, and there is an urgent need to develop novel therapeutic approaches. T cells genetically modified with chimeric antigen receptors (CARs) hold the promise to improve outcomes since they recognize and kill cells through different mechanisms than conventional therapeutics. Areas covered: This article reviews CAR design, tumor associated antigens expressed by GBMs that can be targeted with CAR T cells, preclinical and clinical studies conducted with CAR T cells, and genetic approaches to enhance their effector function. Expert commentary: While preclinical studies have highlighted the potent anti-GBM activity of CAR T cells, the initial foray of CAR T-cell therapies into the clinic resulted only in limited benefits for GBM patients. Additional genetic modification of CAR T cells has resulted in a significant increase in their anti-GBM activity in preclinical models. We are optimistic that clinical testing of these enhanced CAR T cells will be safe and result in improved anti-glioma activity in GBM patients.

Trivalent CAR T cells overcome interpatient antigenic variability in glioblastoma

Background

Glioblastoma (GBM) is the most common primary malignant brain cancer, and is currently incurable. Chimeric antigen receptor (CAR) T cells have shown promise in GBM treatment. While we have shown that combinatorial targeting of 2 glioma antigens offsets antigen escape and enhances T-cell effector functions, the interpatient variability in surface antigen expression between patients hinders the clinical impact of targeting 2 antigen pairs. This study addresses targeting 3 antigens using a single CAR T-cell product for broader application.

Methods

We analyzed the surface expression of 3 targetable glioma antigens (human epidermal growth factor receptor 2 [HER2], interleukin-13 receptor subunit alpha-2 [IL13Rα2], and ephrin-A2 [EphA2]) in 15 primary GBM samples. Accordingly, we created a trivalent T-cell product armed with 3 CAR molecules specific for these validated targets encoded by a single universal (U) tricistronic transgene (UCAR T cells).

Results

Our data showed that co-targeting HER2, IL13Rα2, and EphA2 could overcome interpatient variability by a tendency to capture nearly 100% of tumor cells in most tumors tested in this cohort. UCAR T cells made from GBM patients' blood uniformly expressed all 3 CAR molecules with distinct antigen specificity. UCAR T cells mediated robust immune synapses with tumor targets forming more polarized microtubule organizing centers and exhibited improved cytotoxicity and cytokine release over best monospecific and bispecific CAR T cells per patient tumor profile. Lastly, low doses of UCAR T cells controlled established autologous GBM patient derived xenografts (PDXs) and improved survival of treated animals.

Conclusion

UCAR T cells can overcome antigenic heterogeneity in GBM and lead to improved treatment outcomes.

Importance of immune monitoring approaches and the use of immune checkpoints for the treatment of diffuse intrinsic pontine glioma: From bench to clinic and vice versa (Review)

On the basis of immunological results, it is not in doubt that the immune system is able to recognize and eliminate transformed cells. A plethora of studies have investigated the immune system of patients with cancer and how it is prone to immunosuppression, due in part to the decrease in lymphocyte proliferation and cytotoxic activity. The series of experiments published following the demonstration by Dr Allison's group of the potential effect of anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) paved the way for a new perception in cancer immunotherapy: Immune checkpoints. Several T cell-co-stimulatory molecules including cluster of differentiation (CD)28, inducible T cell co-stimulatory, 4-1BB, OX40, glucocorticoid-induced tumor necrosis factor receptor-related gene and CD27, and inhibitory molecules including T cell immunoglobulin and mucin domain-containing-3, programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1), V-domain immunoglobulin suppressor of T cells activation, T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain, and B and T lymphocyte attenuator have been described in regulating T cell functions, and have been demonstrated to be essential targets in immunotherapy. In preclinical studies, glioblastoma multiforme, a high-grade glioma, the monotherapy targeting PD-1/PD-L1 and CTLA-4 resulted in increased survival times. An improved understanding of the pharmacodynamics and immune monitoring on glioma cancers, particularly in diffuse intrinsic pontine glioma (DIPG), an orphan type of cancer, is expected to have a major contribution to the development of novel therapeutic approaches. On the basis of the recent preclinical and clinical studies of glioma, but not of DIPG, the present review makes a claim for the importance of investigating the tumor microenvironment, the immune response and the use of immune checkpoints (agonists or antagonists) in preclinical/clinical DIPG samples by immune monitoring approaches and high-dimensional analysis. Evaluating the potential predictive and correlative biomarkers in preclinical and clinical studies may assist in answering certain crucial questions that may be useful to improve the clinical response in patients with DIPG.

Therapeutic Potential of Thymoquinone in Glioblastoma Treatment: Targeting Major Gliomagenesis Signaling Pathways

Glioblastoma multiforme (GBM) is one of the most devastating brain tumors with median survival of one year and presents unique challenges to therapy because of its aggressive behavior. Current treatment strategy involves surgery, radiotherapy, immunotherapy, and adjuvant chemotherapy even though optimal management requires a multidisciplinary approach and knowledge of potential complications from both the disease and its treatment. Thymoquinone (TQ), the main bioactive component of Nigella sativa L., has exhibited anticancer effects in numerous preclinical studies. Due to its multitargeting nature, TQ interferes in a wide range of tumorigenic processes and counteract carcinogenesis, malignant growth, invasion, migration, and angiogenesis. TQ can specifically sensitize tumor cells towards conventional cancer treatments and minimize therapy-associated toxic effects in normal cells. Its potential to enter brain via nasal pathway due to volatile nature of TQ adds another advantage in overcoming blood-brain barrier. In this review, we summarized the potential role of TQ in different signaling pathways in GBM that have undergone treatment with standard therapeutic modalities or with TQ. Altogether, we suggest further comprehensive evaluation of TQ in preclinical and clinical level to delineate its implied utility as novel therapeutics to combat the challenges for the treatment of GBM.

Branched multipeptide immunotherapy for glioblastoma using human leukocyte antigen-A*0201-restricted cytotoxic T-lymphocyte epitopes from ERBB2, BIRC5 and CD99

We investigated the use of cytotoxic T-lymphocyte (CTL) epitopes in peptide immunotherapy for glioblastoma. Three peptides (ERBB2, BIRC5 and CD99) were selected based on their peptide-T2 cell binding affinities and combined in a multipeptide cocktail or a branched multipeptide synthesized with mini-polyethylene glycol spacers. Dendritic cells (DCs) pulsed with the multipeptide cocktail or branched multipeptide were compared based on their immunophenotype and cytokine secretion. FACS analysis of alpha-type 1 polarized dendritic cells (αDC1s) revealed that both groups highly expressed CD80, CD83 and CD86, indicating that both treatments efficiently generated mature αDC1s with the expected phenotype. Production of IL-12p70, IL-12p40 and IL-10 also increased upon αDC1 maturation in both groups. CTLs stimulated by either αDC1 group (“DC-CTLs”) included numerous IFN-γ-secreting cells against T2 cells loaded with the corresponding multipeptides. Large numbers of IFN-γ-secreting cells were observed when human glioblastoma cell lines and primary cells were treated with multipeptide-pulsed DC-CTLs. Both multipeptide-pulsed DC-CTL groups exhibited cytotoxic activity of 40-60% against the U251 cell line and 60-80% against primary cells. Branched multipeptide from ERBB2, BIRC5 and CD99 stably bound with T2 cells, and its cytotoxicity toward target cells was similar to that of the multipeptide cocktail. Thus, branched multipeptides could be promising candidates for immunotherapeutic glioblastoma treatment.

Emerging immunotherapies for glioblastoma

INTRODUCTION

Immunotherapy for brain cancer has evolved dramatically over the past decade, owed in part to our improved understanding of how the immune system interacts with tumors residing within the central nervous system (CNS). Glioblastoma (GBM), the most common primary malignant brain tumor in adults, carries a poor prognosis (<15 months) and only few advances have been made since the FDA's approval of temozolomide (TMZ) in 2005. Importantly, several immunotherapies have now entered patient trials based on promising preclinical data, and recent studies have shed light on how GBM employs a slew of immunosuppressive mechanisms that may be targeted for therapeutic gain. Altogether, accumulating evidence suggests immunotherapy may soon earn its keep as a mainstay of clinical management for GBM.

AREAS COVERED

Here, we review cancer vaccines, checkpoint inhibitors, adoptive T-cell immunotherapy, and oncolytic virotherapy.

EXPERT OPINION

Checkpoint blockade induces antitumor activity by preventing negative regulation of T-cell activation. This platform, however, depends on an existing frequency of tumor-reactive T cells. GBM tumors are exceptionally equipped to prevent this, occupying low levels of antigen expression and elaborate mechanisms of immunosuppression. Therefore, checkpoint blockade may be most effective when used in combination with a DC vaccine or adoptively transferred tumor-specific T cells generated ex vivo. Both approaches have been shown to induce endogenous immune responses against tumor antigens, providing a rationale for use with checkpoint blockade where both primary and secondary responses may be potentiated.

Engineering challenges for brain tumor immunotherapy

Malignant brain tumors represent one of the most devastating forms of cancer with abject survival rates that have not changed in the past 60years. This is partly because the brain is a critical organ, and poses unique anatomical, physiological, and immunological barriers. The unique interplay of these barriers also provides an opportunity for creative engineering solutions. Cancer immunotherapy, a means of harnessing the host immune system for anti-tumor efficacy, is becoming a standard approach for treating many cancers. However, its use in brain tumors is not widespread. This review discusses the current approaches, and hurdles to these approaches in treating brain tumors, with a focus on immunotherapies. We identify critical barriers to immunoengineering brain tumor therapies and discuss possible solutions to these challenges.