Induction of anti-glioma natural killer cell response following multiple low-dose intracerebral CpG therapy

Applications of nanotechnology in remodeling the tumour microenvironment for glioblastoma treatment

With the increasing research and deepening understanding of the glioblastoma (GBM) tumour microenvironment (TME), novel and more effective therapeutic strategies have been proposed. The GBM TME involves intricate interactions between tumour and non-tumour cells, promoting tumour progression. Key therapeutic goals for GBM treatment include improving the immunosuppressive microenvironment, enhancing the cytotoxicity of immune cells against tumours, and inhibiting tumour growth and proliferation. Consequently, remodeling the GBM TME using nanotechnology has emerged as a promising approach. Nanoparticle-based drug delivery enables targeted delivery, thereby improving treatment specificity, facilitating combination therapies, and optimizing drug metabolism. This review provides an overview of the GBM TME and discusses the methods of remodeling the GBM TME using nanotechnology. Specifically, it explores the application of nanotechnology in ameliorating immune cell immunosuppression, inducing immunogenic cell death, stimulating, and recruiting immune cells, regulating tumour metabolism, and modulating the crosstalk between tumours and other cells.

Immunological nanomaterials to combat cancer metastasis

Metastasis causes greater than 90% of cancer-associated deaths, presenting huge challenges for detection and efficient treatment of cancer due to its high heterogeneity and widespread dissemination to various organs. Therefore, it is imperative to combat cancer metastasis, which is the key to achieving complete cancer eradication. Immunotherapy as a systemic approach has shown promising potential to combat metastasis. However, current clinical immunotherapies are not effective for all patients or all types of cancer metastases owing to insufficient immune responses. In recent years, immunological nanomaterials with intrinsic immunogenicity or immunomodulatory agents with efficient loading have been shown to enhance immune responses to eliminate metastasis. In this review, we would like to summarize various types of immunological nanomaterials against metastasis. Moreover, this review will summarize a series of immunological nanomaterial-mediated immunotherapy strategies to combat metastasis, including immunogenic cell death, regulation of chemokines and cytokines, improving the immunosuppressive tumour microenvironment, activation of the STING pathway, enhancing cytotoxic natural killer cell activity, enhancing antigen presentation of dendritic cells, and enhancing chimeric antigen receptor T cell therapy. Furthermore, the synergistic anti-metastasis strategies based on the combinational use of immunotherapy and other therapeutic modalities will also be introduced. In addition, the nanomaterial-mediated imaging techniques (e.g., optical imaging, magnetic resonance imaging, computed tomography, photoacoustic imaging, surface-enhanced Raman scattering, radionuclide imaging, etc.) for detecting metastasis and monitoring anti-metastasis efficacy are also summarized. Finally, the current challenges and future prospects of immunological nanomaterial-based anti-metastasis are also elucidated with the intention to accelerate its clinical translation.

M-MDSCs mediated trans-BBB drug delivery for suppression of glioblastoma recurrence post-standard treatment

We found that immunosuppressive monocytic-myeloid-derived suppressor cells (M-MDSCs) were more likely to be recruited by glioblastoma (GBM) through adhesion molecules on GBM-associated endothelial cells upregulated post-chemoradiotherapy. These cells are continuously generated during tumor progression, entering tumors and expressing PD-L1 at a high level, allowing GBM to exhaust T cells and evade attack from the immune system, thereby facilitating GBM relapse. αLy-6C-LAMP is composed of (i) drug cores with slightly negative charges condensed by cationic protamine and plasmids encoding PD-L1 trap protein, (ii) pre-formulated cationic liposomes targeted to Ly-6C for encapsulating the drug cores, and (iii) a layer of red blood cell membrane on the surface for effectuating long-circulation. αLy-6C-LAMP persistently targets peripheral, especially splenic, M-MDSCs and delivers secretory PD-L1 trap plasmids, leveraging M-MDSCs to transport the plasmids crossing the blood-brain barrier (BBB), thus expressing PD-L1 trap protein in tumors to inhibit PD-1/PD-L1 pathway. Our proposed drug delivery strategy involving intermediaries presents an efficient cross-BBB drug delivery concept that incorporates live-cell targeting and long-circulating nanotechnology to address GBM recurrence.

IGFBP5, as a Prognostic Indicator Promotes Tumor Progression and Correlates with Immune Microenvironment in Glioma

Background: Insulin-like growth factor binding protein 5 (IGFBP5) is highly expressed in multiple human cancers, including glioma. Despite this, it remains unclear what role it plays in glioma. The aim of the present study was to analyze whether IGFBP5 could be used as a predictor of prognosis and immune infiltration in glioma. Methods: Glioma patients' clinical information was collected from the Cancer Genome Atlas (TCGA), the Chinese Glioma Genome Atlas (CGGA), Rembrandt, and Gravendeel databases. The diagnostic and prognostic roles of IGFBP5 were assessed by the Kaplan-Meier survival curves, diagnostic receiver operating characteristic (ROC) curves, nomogram model, Cox regression analysis and Enrichment analysis by R software. Moreover, the correlation between IGFBP5 expression and immune cell infiltration, and immune checkpoint genes was conducted. Immunohistochemistry staining, CCK8, colony formation, scratch and transwell assays and western blot were used to interrogate the expression and function of IGFBP5 in glioma. Results: IGFBP5 levels were obviously increased in glioma with higher malignancy and predicted poor outcomes by Univariate and multivariate Cox analysis. The biological function analysis revealed that IGFBP5 correlated closely with immune signatures. Moreover, IGFBP5 expression was associated with tumor infiltration of B cells, T cells, macrophages, and NK cells. IGFBP5 affected glioma cell proliferation, migration, and invasion probably involved in the epithelial-to-mesenchymal transition (EMT) and Hippo-YAP signaling pathway. Further study showed that IGFBP5 induced the expression of PD-L1 and CXCR4. Conclusions: IGFBP5 as an oncogene is a useful biomarker of prognosis and correlates with progression and immune infiltration in glioma.

NK cell exhaustion in the tumor microenvironment

Natural killer (NK) cells kill mutant cells through death receptors and cytotoxic granules, playing an essential role in controlling cancer progression. However, in the tumor microenvironment (TME), NK cells frequently exhibit an exhausted status, which impairs their immunosurveillance function and contributes to tumor immune evasion. Emerging studies are ongoing to reveal the properties and mechanisms of NK cell exhaustion in the TME. In this review, we will briefly introduce the maturation, localization, homeostasis, and cytotoxicity of NK cells. We will then summarize the current understanding of the main mechanisms underlying NK cell exhaustion in the TME in four aspects: dysregulation of inhibitory and activating signaling, tumor cell-derived factors, immunosuppressive cells, and metabolism and exhaustion. We will also discuss the therapeutic approaches currently being developed to reverse NK cell exhaustion and enhance NK cell cytotoxicity in the TME.

Combination of local immunogenic cell death-inducing chemotherapy and DNA vaccine increases the survival of glioblastoma-bearing mice

Immunotherapy efficacy as monotherapy is negligible for glioblastoma (GBM). We hypothesized that combining therapeutic vaccination using a plasmid encoding an epitope derived from GBM-associated antigen (pTOP) with local delivery of immunogenic chemotherapy using mitoxantrone-loaded PEGylated PLGA-based nanoparticles (NP-MTX) would improve the survival of GBM-bearing mice by stimulating an antitumor immune response. We first proved that MTX retained its ability to induce cytotoxicity and immunogenic cell death of GBM cells after encapsulation. Intratumoral delivery of MTX or NP-MTX increased the frequency of IFN-γ-secreting CD8 T cells. NP-MTX mixed with free MTX in combination with pTOP DNA vaccine increased the median survival of GL261-bearing mice and increased M1-like macrophages in the brain. The addition of CpG to this combination abolished the survival benefit but led to increased M1 to M2 macrophage ratio and IFN-γ-secreting CD4 T cell frequency. These results highlight the benefits of combination strategies to potentiate immunotherapy and improve GBM outcome.

Combination of hyaluronic acid conjugates with immunogenic cell death inducer and CpG for glioblastoma local chemo-immunotherapy elicits an immune response and induces long-term survival

The efficacy of standard glioblastoma (GBM) treatments has been limited due to the highly immunosuppressive tumor immune microenvironment, interpatient tumor heterogenicity and anatomical barriers, such as the blood brain barrier. In the present work, we hypothesized that a new local therapy based on the combination of doxorubicin (DOX) as an immunogenic cell death (ICD) inducer and CpG, a Toll-like receptor (TLR)-9 agonist, would act synergistically to eradicate GBM. DOX and CpG were first tested in an orthotopic GL261 GBM model showing enhanced survival. To improve the outcome with a reduced dose, we designed bioresponsive hyaluronic acid (HA)-drug conjugates for effective in situ chemoimmunotherapy. HA was derivatized with CpG. The new HA-CpG conjugate showed high efficacy in re-educating protumoral M2-like microglia into an antitumoral M1-like phenotype, inducing the expression of immune-stimulatory cytokines. DOX was also conjugated to HA. DOX conjugation increased ICD induction in GL261 cells. Finally, a combination of the conjugates was explored in an orthotopic GL261 GBM model. The local delivery of combined HA-DOX + HA-CpG into the tumor mass elicited antitumor CD8⁺ T cell responses in the brain tumor microenvironment and reduced the infiltration of M2-like tumor-associated macrophages and myeloid-derived suppressor cells. Importantly, the combination of HA-DOX and HA-CpG induced long-term survival in >66% of GBM-bearing animals than other treatments (no long-term survivor observed), demonstrating the benefits of conjugating synergistic drugs to HA nanocarrier. These results emphasize that HA-drug conjugates constitute an effective drug delivery platform for local chemoimmunotherapy against GBM and open new perspectives for the treatment of other brain cancers and brain metastasis.

Advances in NK cell therapy for brain tumors

Despite advances in treatment regimens that comprise surgery, chemotherapy, and radiation, outcome of many brain tumors remains dismal, more so when they recur. The proximity of brain tumors to delicate neural structures often precludes complete surgical resection. Toxicity and long-term side effects of systemic therapy remain a concern. Novel therapies are warranted. The field of NK cell-based cancer therapy has grown exponentially and currently constitutes a major area of immunotherapy innovation. This provides a new avenue for the treatment of cancerous lesions in the brain. In this review, we explore the mechanisms by which the brain tumor microenvironment suppresses NK cell mediated tumor control, and the methods being used to create NK cell products that subvert immune suppression. We discuss the pre-clinical studies evaluating NK cell-based immunotherapies that target several neuro-malignancies and highlight advances in molecular imaging of NK cells that allow monitoring of NK cell-based therapeutics. We review current and ongoing NK cell based clinical trials in neuro-oncology.

Construction of an immune-related gene signature for the prognosis and diagnosis of glioblastoma multiforme

Background

Increasing evidence has suggested that inflammation is related to tumorigenesis and tumor progression. However, the roles of immune-related genes in the occurrence, development, and prognosis of glioblastoma multiforme (GBM) remain to be studied.

Methods

The GBM-related RNA sequencing (RNA-seq), survival, and clinical data were acquired from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), Chinese Glioma Genome Atlas (CGGA), and Gene Expression Omnibus (GEO) databases. Immune-related genes were obtained from the Molecular Signatures Database (MSigDB). Differently expressed immune-related genes (DE-IRGs) between GBM and normal samples were identified. Prognostic genes associated with GBM were selected by Kaplan-Meier survival analysis, Least Absolute Shrinkage and Selection Operator (LASSO)-penalized Cox regression analysis, and multivariate Cox analysis. An immune-related gene signature was developed and validated in TCGA and CGGA databases separately. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to explore biological functions of the signature. The correlation between immune cell infiltration and the signature was analyzed by single-sample gene set enrichment analysis (ssGSEA), and the diagnostic value was investigated. The gene set enrichment analysis (GSEA) was performed to explore the potential function of the signature genes in GBM, and the protein-protein interaction (PPI) network was constructed.

Results

Three DE-IRGs [Pentraxin 3 (PTX3), TNFSF9, and bone morphogenetic protein 2 (BMP2)] were used to construct an immune-related gene signature. Receiver operating characteristic (ROC) curves and Cox analyses confirmed that the 3-gene-based prognostic signature was a good independent prognostic factor for GBM patients. We found that the signature was mainly involved in immune-related biological processes and pathways, and multiple immune cells were disordered between the high- and low-risk groups. GSEA suggested that PTX3 and TNFSF9 were mainly correlated with interleukin (IL)-17 signaling pathway, nuclear factor kappa B (NF-κB) signaling pathway, tumor necrosis factor (TNF) signaling pathway, and Toll-like receptor signaling pathway, and the PPI network indicated that they could interact directly or indirectly with inflammatory pathway proteins. Quantitative real-time PCR (qRT-PCR) indicated that the three genes were significantly different between target tissues.

Conclusion

The signature with three immune-related genes might be an independent prognostic factor for GBM patients and could be associated with the immune cell infiltration of GBM patients.

ApoE-mediated systemic nanodelivery of granzyme B and CpG for enhanced glioma immunotherapy

The response of malignant glioma to immunotherapy remains gloomy due to its discrete immunological environment and poor brain penetration of immunotherapeutic agents. Here, we disclose that ApoE peptide-mediated systemic nanodelivery of granzyme B (GrB) and CpG ODN co-stimulates enhanced immunotherapy of murine malignant LCPN glioma model. ApoE peptide-functionalized polymersomes encapsulating GrB (ApoE-PS-GrB) could effectively penetrate the blood-brain barrier-mimicking endothelial cell monolayer in vitro and further be taken up by LCPN cells, inducing strong immunogenic cell death (ICD). The co-administration of ApoE-PS-GrB and ApoE-PS-CpG in orthotopic LCPN glioma-bearing mice co-stimulated cytokine production, maturation of dendritic cells (DCs), infiltration of cytotoxic T lymphocytes (CTLs) while reduction of regulatory T lymphocytes (T_reg) and M2 phenotype macrophages in the tumor microenvironment, leading to greatly delayed tumor progression and significantly prolonged survival time compared with all controls. The ApoE-mediated systemic nanodelivery of GrB and CpG ODN opens a new pathway for potent immunotherapy of malignant glioma.

In situ targeting nanoparticles-hydrogel hybrid system for combined chemo-immunotherapy of glioma

It is well known that glioma is currently the most malignant brain tumor. Because of the existence of blood-brain barrier (BBB) and tumor cell heterogeneity, systemic chemotherapy exerts unsatisfied therapeutic effect for the treatment of glioma after surgical resection and may even damage the body's immune system. Here, we developed an in situ sustained-release hydrogel delivery system for combined chemo-immunotherapy of glioma by combined chemotherapy drug and immunoadjuvant through the resection cavity local delivery. Briefly, glioma homing peptide modified paclitaxel targeting nanoparticles (PNP_PTX) and mannitolated immunoadjuvant CpG targeting nanoparticles (MNP_CpG) were embedded into PLGA₁₇₅₀-PEG₁₅₀₀-PLGA₁₇₅₀ thermosensitive hydrogel framework (PNP_PTX&MNP_CpG@Gel). The in vitro and in vivo results showed that the targeting nanoparticles-hydrogel hybrid system could cross-link into a gel drug reservoir when injected into the resection cavity of glioma. And then, the sustained-release PNP_PTX could target the residual infiltration glioma cells and produce tumor antigens. Meanwhile, MNP_CpG targeted and activated the antigen-presenting cells, which enhanced the tumor antigen presentation ability and activated CD8⁺T and NK cells to reverse immunosuppression of glioma microenvironment. This study indicated that the PNP_PTX&MNP_CpG@Gel system could enhance the therapeutic effect of glioma by chemo-immunotherapy.

Transdermal vaccination via 3D-printed microneedles induces potent humoral and cellular immunity

Vaccination is an essential public health measure for infectious disease prevention. The exposure of the immune system to vaccine formulations with the appropriate kinetics is critical for inducing protective immunity. In this work, faceted microneedle arrays were designed and fabricated utilizing a three-dimensional (3D)-printing technique called continuous liquid interface production (CLIP). The faceted microneedle design resulted in increased surface area as compared with the smooth square pyramidal design, ultimately leading to enhanced surface coating of model vaccine components (ovalbumin and CpG). Utilizing fluorescent tags and live-animal imaging, we evaluated in vivo cargo retention and bioavailability in mice as a function of route of delivery. Compared with subcutaneous bolus injection of the soluble components, microneedle transdermal delivery not only resulted in enhanced cargo retention in the skin but also improved immune cell activation in the draining lymph nodes. Furthermore, the microneedle vaccine induced a potent humoral immune response, with higher total IgG (Immunoglobulin G) and a more balanced IgG1/IgG2a repertoire and achieved dose sparing. Furthermore, it elicited T cell responses as characterized by functional cytotoxic CD8⁺ T cells and CD4⁺ T cells secreting Th1 (T helper type 1)-cytokines. Taken together, CLIP 3D-printed microneedles coated with vaccine components provide a useful platform for a noninvasive, self-applicable vaccination.

Innovative and Promising Strategies to Enhance Effectiveness of Immunotherapy for CNS Tumors: Where Are We?

Although there are several immunotherapy approaches for the treatment of Central Nervous System (CNS) tumors under evaluation, currently none of these approaches have received approval from the regulatory agencies. CNS tumors, especially glioblastomas, are tumors characterized by highly immunosuppressive tumor microenvironment, limiting the possibility of effectively eliciting an immune response. Moreover, the peculiar anatomic location of these tumors poses relevant challenges in terms of safety, since uncontrolled hyper inflammation could lead to cerebral edema and cranial hypertension. The most promising strategies of immunotherapy in neuro-oncology consist of the use of autologous T cells redirected against tumor cells through chimeric antigen receptor (CAR) constructs or genetically modified T-cell receptors. Trials based on native or genetically engineered oncolytic viruses and on vaccination with tumor-associated antigen peptides are also under evaluation. Despite some sporadic complete remissions achieved in clinical trials, the outcome of patients with CNS tumors treated with different immunotherapeutic approaches remains poor. Based on the lessons learned from these unsatisfactory experiences, novel immune-therapy approaches aimed at overcoming the profound immunosuppressive microenvironment of these diseases are bringing new hope to reach the cure for CNS tumors.

CX3CL1 Recruits NK Cells Into the Central Nervous System and Aggravates Brain Injury of Mice Caused by Angiostrongylus cantonensis Infection

Background

Angiostrongylus cantonensis (A. cantonensis), is a food-borne zoonotic parasite that can cause central nervous system (CNS) injury characterized by eosinophilic meningitis. However, the pathogenesis of angiostrongylosis remains elusive. Natural killer cells (NK cells) are unique innate lymphocytes important in early defense against pathogens. The aim of this study was to investigate the role of NK cells in A. cantonensis infection and to elucidate the key factors that recruit NK cells into the CNS.

Methods

Mouse model of A. cantonensis infection was established by intragastric administration of third-stage larvae. The expression of cytokines and chemokines at gene and protein levels was analyzed by qRT-PCR and ELISA. Distribution of NK cells was observed by immunohistochemistry and flow cytometry. NK cell-mediated cytotoxicity against YAC-1 cells was detected by LDH release assay. The ability of NK cells to secrete cytokines was determined by intracellular flow cytometry and ELISA. Depletion and adoptive transfer of NK cells in vivo was induced by tail vein injection of anti-asialo GM1 rabbit serum and purified splenic NK cells, respectively. CX₃CL1 neutralization experiment was performed by intraperitoneal injection of anti-CX₃CL1 rat IgG.

Results

The infiltration of NK cells in the CNS of A. cantonensis-infected mice was observed from 14 dpi and reached the peak on 18 and 22 dpi. Compared with uninfected splenic NK cells, the CNS-infiltrated NK cells of infected mice showed enhanced cytotoxicity and increased IFN-γ and TNF-α production ability. Depletion of NK cells alleviated brain injury, whereas adoptive transfer of NK cells exacerbated brain damage in A. cantonensis-infected mice. The expression of CX₃CL1 in the brain tissue and its receptor CX₃CR1 on the CNS-infiltrated NK cells were both elevated after A. cantonensis infection. CX₃CL1 neutralization reduced the percentage and absolute number of the CNS-infiltrated NK cells and relieved brain damage caused by A. cantonensis infection.

Conclusions

Our results demonstrate that the up-regulated CX₃CL1 in the brain tissue recruits NK cells into the CNS and aggravates brain damage caused by A. cantonensis infection. The findings improve the understanding of the pathogenesis of angiostrongyliasis and expand the therapeutic intervention in CNS disease.

Tumor cell and immune cell profiles in primary human glioblastoma: Impact on patient outcome

The distribution and role of tumor-infiltrating leucocytes in glioblastoma (GBM) remain largely unknown. Here, we investigated the cellular composition of 55 primary (adult) GBM samples by flow cytometry and correlated the tumor immune profile with patient features at diagnosis and outcome. GBM single-cell suspensions were stained at diagnosis (n = 44) and recurrence following radiotherapy and chemotherapy (n = 11) with a panel of 8-color monoclonal antibody combinations for the identification and enumeration of (GFAP+ CD45- ) tumor and normal astrocytic cells, infiltrating myeloid cells -i.e. microglial and blood-derived tumor-associated macrophages (TAM), M1-like, and M2-like TAM, neutrophils. and myeloid-derived suppressor cells (MDSC)- and tumor-infiltrating lymphocytes (TIL) -i.e. CD3+ T-cells and their TCD4+ , TCD8+ , TCD4- CD8- , and (CD25+ CD127lo ) regulatory (T-regs) subsets, (CD19+ CD20+ ) B-cells, and (CD16+ ) NK-cells-. Overall, GBM samples consisted of a major population (mean ± 1SD) of tumor and normal astrocytic cells (73% ± 16%) together with a significant but variable fraction of immune cells (24% ± 18%). Within myeloid cells, TAM predominated (13% ± 12%) including both microglial cells (10% ± 11%) and blood-derived macrophages (3% ± 5%), in addition to a smaller proportion of neutrophils (5% ± 9%) and MDSC (4% ± 8%). Lymphocytes were less represented and mostly included TCD4+ (0.5% ± 0.7%) and TCD8+ cells (0.6% ± 0.7%), together with lower numbers of TCD4- CD8- T-cells (0.2% ± 0.4%), T-regs (0.1% ± 0.2%), B-lymphocytes (0.1% ± 0.2%) and NK-cells (0.05% ± 0.05%). Overall, three distinct immune profiles were identified: cases with a minor fraction of leucocytes, tumors with a predominance of TAM and neutrophils, and cases with mixed infiltration by TAM, neutrophils, and T-lymphocytes. Untreated GBM patients with mixed myeloid and lymphoid immune infiltrates showed a significantly shorter patient overall survival versus the other two groups, in the absence of gains of the EGFR gene (p = 0.02). Here we show that immune cell infiltrates are systematically present in GBM, with highly variable levels and immune profiles. Patients with mixed myeloid and T-lymphoid infiltrates showed a worse outcome.

Polyethyleneimine-CpG Nanocomplex as an In Situ Vaccine for Boosting Anticancer Immunity in Melanoma

Cancer immunotherapy is redefining the field of cancer therapy. However, current cancer immunotherapies are limited by insufficient immune activation, which results in low response rate. Herein, polyethyleneimine-CpG nanocomplex (CpG@PEI) is reported as an in situ vaccine for boosting anticancer immunity in melanoma. CpG, a Toll-like receptor (TLR) 9 agonist, can activate antigen-presenting cells and increase the expression of costimulatory molecules, while PEI can help to enhance the stability and cellular internalization of CpG. It is proved that PEI loading can significantly enhance the cellular internalization and immune stimulation ability of CpG, and the CpG@PEI nanocomplex can effectively inhibit murine B16F10 melanoma growth after intratumoral injection. Further analysis reveals that this CpG@PEI nanocomplex therapy elicits both innate and adaptive immunity, with much increased natural killer (NK) cells and T cells infiltration in the tumor, as well as CD80 expression on the dendritic cells (DCs). This study will inspire more attempts in directly using single nanoparticle-loaded pattern recognition receptor (PRR) agonists for cancer immunotherapy.

The Role of NK Cells and Innate Lymphoid Cells in Brain Cancer

The brain is considered an immune privileged site due to the high selectivity of the blood-brain barrier which restricts the passage of molecules and cells into the brain parenchyma. Recent studies have highlighted active immunosurveillance mechanisms in the brain. Here we review emerging evidence for the contribution of innate lymphoid cells (ILCs) including natural killer (NK) cells to the immunosurveillance of brain cancers focusing on glioblastoma, one of the most aggressive and most common malignant primary brain tumors diagnosed in adults. Moreover, we discuss how the local tissue microenvironment and unique cellular interactions influence ILC functions in the brain and how these interactions might be successfully harnessed for cancer immunotherapy using insights gained from the studies of autoimmunity, aging, and CNS injury.

Pulmonary Delivery of Nanoparticle-Bound Toll-like Receptor 9 Agonist for the Treatment of Metastatic Lung Cancer

CpG oligodeoxynucleotides are potent toll-like receptor (TLR) 9 agonists and have shown promise as anticancer agents in preclinical studies and clinical trials. Binding of CpG to TLR9 initiates a cascade of innate and adaptive immune responses, beginning with activation of dendritic cells and resulting in a range of secondary effects that include the secretion of pro-inflammatory cytokines, activation of natural killer cells, and expansion of T cell populations. Recent literature suggests that local delivery of CpG in tumors results in superior antitumor effects as compared to systemic delivery. In this study, we utilized PRINT (particle replication in nonwetting templates) nanoparticles as a vehicle to deliver CpG into murine lungs through orotracheal instillations. In two murine orthotopic metastasis models of non-small-cell lung cancer-344SQ (lung adenocarcinoma) and KAL-LN2E1 (lung squamous carcinoma), local delivery of PRINT-CpG into the lungs effectively promoted substantial tumor regression and also limited systemic toxicities associated with soluble CpG. Furthermore, cured mice were completely resistant to tumor rechallenge. Additionally, nanodelivery showed extended retention of CpG within the lungs as well as prolonged elevation of antitumor cytokines in the lungs, but no elevated levels of proinflammatory cytokines in the serum. These results demonstrate that PRINT-CpG is a potent nanoplatform for local treatment of lung cancer that has collateral therapeutic effects on systemic disease and an encouraging toxicity profile and may have the potential to treat lung metastasis of other cancer types.

Plant Virus-Like Particle In Situ Vaccine for Intracranial Glioma Immunotherapy

Despite aggressive multi-modality treatment with surgery, radiation and chemotherapies, malignant glioma inevitably recurs and has dismal survival rates. Recent progress in immunotherapy has led to a resurgence of interest, and immunotherapies are being investigated for treatment of glioma. However, the unique brain anatomy and a highly immunosuppressive glioma microenvironment pose significant challenges to achieving efficacy. Thus, there is a critical need for assessment of next-generation immunotherapies for glioma. In this study, we have investigated the efficacy of the nanoparticle platform technology based on plant-derived Cowpea mosaic virus like particles (empty CPMV or eCPMV) to instigate a potent immune response against intracranial glioma. CPMV immunotherapy has been shown to efficiently reverse the immunosuppressive tumor microenvironments in pre-clinical murine models of dermal melanoma and metastatic melanoma, metastatic breast cancer, intraperitoneal ovarian cancer and in canine patients with oral melanoma. In the present study, we demonstrate that in situ administration of CPMV immunotherapy in the setting of glioma can effectively recruit unique subset of effector innate and adaptive immune cells to the brain parenchyma while reducing immune suppressive cellular population, leading to regression of intracranial glioma. The in situ CPMV nanoparticle vaccine offers a potent yet safe and localized immunotherapy for intracranial glioma.

Anti-glioma effect of intracranial vaccination with tumor cell lysate plus flagellin in mice

The adjuvant effects of flagellin on regulation of immune response have been proved; whether flagellin could assist tumor cell lysate (TCL) to enhance anti-glioma immunity remains to be investigated. This study tests a hypothesis that therapeuticly intracranial administration with flagellin plus TCL enhances the effects of specific immunotherapy on glioma in mice. In this study, GL261 cells were transferred into C57BL/6 mice and the GL261-bearing mice were subcutaneously or intracranially inoculated with flagellin plus TCL, flagellin, TCL or saline. Our results showed that prophylacticly subcutaneous administration with TCL and flagellin could induce potent cytotoxic T lymphocyte (CTL) and prolong the survival of GL261-bearing mice significantly, but therapeuticly subcutaneous administration failed to. However, therapeuticly intracranial administration of TCL plus flagellin could prolong the survival. Moreover, intracranial administration of flagellin could recruit CD4⁺ T cells and CD8⁺ T cells to brain tissues, induce proliferation of natural killer (NK) cells, CD4⁺ T cells and CD8⁺ T cells in peripheral blood mononuclear cells and induce to splenomegaly. The results suggested that flagellin could be acted as an efficient adjuvant for TCL based vaccine.

S100B suppression alters polarization of infiltrating myeloid-derived cells in gliomas and inhibits tumor growth

S100B, a member of the multigene family of Ca²⁺-binding proteins, is overexpressed by most malignant gliomas but its biological role in gliomagenesis is unclear. Recently, we demonstrated that low concentrations of S100B attenuated microglia activation through the induction of STAT3. Furthermore, S100B downregulation in a murine glioma model inhibited macrophage trafficking and tumor growth. Based on these observations, we hypothesized that S100B inhibitors may have antiglioma properties through modulation of tumor microenvironment.

To discover novel S100B inhibitors, we developed a high-throughput screening cell-based S100B promoter-driven luciferase reporter assay. Initial screening of 768 compounds in the NIH library identified 36 hits with >85% S100B inhibitory activity. Duloxetine (Dul, an SNRI) was selected for the initial proof-of-concept studies. At low concentrations (1–5 μM) Dul inhibited S100B and CCL2 production in mouse GL261 glioma cells, but had minimal cytotoxic activity in vitro. In vivo, however, Dul (30 mg/kg/14 days) inhibited S100B production, altered the polarization and trafficking of tumor-associated myeloid-derived cells, and inhibited the growth of intracranial GL261 gliomas. Dul therapeutic efficacy, however, was not observed in the K-Luc glioma model that expresses low levels of S100B. These findings affirm the role of S100B in gliomagenesis and justify the development of more potent S100B inhibitors for glioma therapy.

Immunotherapies for malignant glioma

Glioblastoma multiforme (GBM) is a highly malignant primary brain cancer with a dreadful overall survival and for which treatment options are limited. Recent breakthroughs in novel immune-related treatment strategies for cancer have spurred interests in usurping the power of the patient's immune system to recognize and eliminate GBM. Here, we discuss the unique properties of GBM's tumor microenvironment, the effects of GBM standard on care therapy on tumor-associated immune cells, and review several approaches aimed at therapeutically targeting the immune system for GBM treatment. We believe that a comprehensive understanding of the intricate micro-environmental landscape of GBM will abound into the development of novel immunotherapy strategies for GBM patients.

Myeloid-derived suppressor cells and myeloid regulatory cells in cancer and autoimmune disorders

Myeloid-derived suppressor cells (MDSCs) were originally described as a heterogeneous population of immature cells derived from myeloid progenitors with immune-suppressive functions in tumor-bearing hosts. In recent years, increasing number of studies have described various populations of myeloid cells with MDSC-like properties in murine models of cancer and autoimmune diseases. These studies have observed that the populations of MDSCs are increased during inflammation and autoimmune conditions. In addition, MDSCs can effectively suppress T cell responses and modulate the activity of natural killer cells and other myeloid cells. MDSCs have also been implicated in the induction of regulatory T cell production. Furthermore, these cells have the potential to suppress the autoimmune response, thereby limiting tissue injury. Myeloid regulatory cells (Mregs) are recently attracting increasing attention, since they function in proinflammatory and immune suppression in autoimmune diseases, as well as in various types of cancer. Currently, research focus is directed from MDSCs to Mregs in cancer and autoimmune diseases. The present study reviewed the suppressive roles of MDSCs in various autoimmune murine models, the immune modulation of MDSCs to T helper 17 lymphocytes, as well as the proinflammatory and immunosuppressive roles of Mregs in various types of cancer and autoimmune diseases.

Characterization of Arginase Expression in Glioma-Associated Microglia and Macrophages

Microglia (MG) and macrophages (MPs) represent a significant component of the inflammatory response to gliomas. When activated, MG/MP release a variety of pro-inflammatory cytokines, however, they also secrete anti-inflammatory factors that limit their cytotoxic function. The balance between pro and anti-inflammatory functions dictates their antitumor activity. To evaluate potential variations in MG and MP function in gliomas, we isolated these cells (and other Gr1⁺ cells) from intracranial GL261 murine gliomas by FACS and evaluated their gene expression profiles by microarray analysis. As expected, arginase 1 (Arg1, M2 marker) was highly expressed by tumor-associated Gr1⁺, MG and MP. However, in contrast to MP and Gr1⁺ cells that expressed Arg1 shortly after tumor trafficking, Arg1 expression in MG was delayed and occurred in larger tumors. Interestingly, depletion of MPs in tumors did not prevent MG polarization, suggesting direct influence of tumor-specific factors on MG Arg1 upregulation. Finally, Arg1 expression was confirmed in human GBM samples, but most Arg1⁺ cells were neutrophils and not MPs. These findings confirm variations in tumor MG and MP polarization states and its dependency on tumor microenvironmental factors.

The multidrug-resistance transporter Abcc3 protects NK cells from chemotherapy in a murine model of malignant glioma

Abcc3, a member of the ATP-binding cassette transporter superfamily, plays a role in multidrug resistance. Here, we found that Abcc3 is highly expressed in blood-derived NK cells but not in CD8(+) T cells. In GL261 glioma-bearing mice treated with the alkylating agent temozolomide (TMZ) for 5 d, an early increased frequency of NK cells was observed. We also found that Abcc3 is strongly upregulated and functionally active in NK cells from mice treated with TMZ compared to controls. We demonstrate that Abcc3 is critical for NK cell survival during TMZ administration; more importantly, Akt, involved in lymphocyte survival, is phosphorylated only in NK cells expressing Abcc3. The resistance of NK cells to chemotherapy was accompanied by increased migration and homing in the brain at early time points. Cytotoxicity, evaluated by IFNγ production and specific lytic activity against GL261 cells, increased peripherally in the later phases, after conclusion of TMZ treatment. Intra-tumor increase of the NK effector subset as well as in IFNγ, granzymes and perforin-1 expression, were found early and persisted over time, correlating with a profound modulation on glioma microenvironment induced by TMZ. Our findings reveal an important involvement of Abcc3 in NK cell resistance to chemotherapy and have important clinical implications for patients treated with chemo-immunotherapy.

Tumor infiltrating immune cells in gliomas and meningiomas

Tumor-infiltrating immune cells are part of a complex microenvironment that promotes and/or regulates tumor development and growth. Depending on the type of cells and their functional interactions, immune cells may play a key role in suppressing the tumor or in providing support for tumor growth, with relevant effects on patient behavior. In recent years, important advances have been achieved in the characterization of immune cell infiltrates in central nervous system (CNS) tumors, but their role in tumorigenesis and patient behavior still remain poorly understood. Overall, these studies have shown significant but variable levels of infiltration of CNS tumors by macrophage/microglial cells (TAM) and to a less extent also lymphocytes (particularly T-cells and NK cells, and less frequently also B-cells). Of note, TAM infiltrate gliomas at moderate numbers where they frequently show an immune suppressive phenotype and functional behavior; in contrast, infiltration by TAM may be very pronounced in meningiomas, particularly in cases that carry isolated monosomy 22, where the immune infiltrates also contain greater numbers of cytotoxic T and NK-cells associated with an enhanced anti-tumoral immune response. In line with this, the presence of regulatory T cells, is usually limited to a small fraction of all meningiomas, while frequently found in gliomas. Despite these differences between gliomas and meningiomas, both tumors show heterogeneous levels of infiltration by immune cells with variable functionality. In this review we summarize current knowledge about tumor-infiltrating immune cells in the two most common types of CNS tumors-gliomas and meningiomas-, as well as the role that such immune cells may play in the tumor microenvironment in controlling and/or promoting tumor development, growth and control.

Metronomic Doses of Temozolomide Enhance the Efficacy of Carbon Nanotube CpG Immunotherapy in an Invasive Glioma Model

Even when treated with aggressive current therapies, most patients with glioblastoma survive less than two years. Rapid tumor growth, an invasive nature, and the blood-brain barrier, which limits the penetration of large molecules into the brain, all contribute to the poor tumor response associated with conventional therapies. Immunotherapy has emerged as a therapeutic approach that may overcome these challenges. We recently reported that single-walled carbon nanotubes (SWCNTs) can be used to dramatically increase the immunotherapeutic efficacy of CpG oligonucleotides in a mouse model of glioma. Following implantation in the mouse brain, the tumor cell line used in these previous studies (GL261) tends to form a spherical tumor with limited invasion into healthy brain. In order to evaluate SWCNT/CpG therapy under more clinically-relevant conditions, here we report the treatment of a more invasive mouse glioma model (K-Luc) that better recapitulates human disease. In addition, a CpG sequence previously tested in humans was used to formulate the SWCNT/CpG which was combined with temozolomide, the standard of care chemotherapy for glioblastoma patients. We found that, following two intracranial administrations, SWCNT/CpG is well-tolerated and improves the survival of mice bearing invasive gliomas. Interestingly, the efficacy of SWCNT/CpG was enhanced when combined with temozolomide. This enhanced anti-tumor efficacy was correlated to an increase of tumor-specific cytotoxic activity in splenocytes. These results reinforce the emerging understanding that immunotherapy can be enhanced by combining it with chemotherapy and support the continued development of SWCNT/CpG.

Biological Response Modifier in Cancer Immunotherapy

Biological response modifiers (BRMs) emerge as a lay of new compounds or approaches used in improving cancer immunotherapy. Evidences highlight that cytokines, Toll-like receptor (TLR) signaling, and noncoding RNAs are of crucial roles in modulating antitumor immune response and cancer-related chronic inflammation, and BRMs based on them have been explored. In particular, besides some cytokines like IFN-α and IL-2, several Toll-like receptor (TLR) agonists like BCG, MPL, and imiquimod are also licensed to be used in patients with several malignancies nowadays, and the first artificial small noncoding RNA (microRNA) mimic, MXR34, has entered phase I clinical study against liver cancer, implying their potential application in cancer therapy. According to amounts of original data, this chapter will review the regulatory roles of TLR signaling, some noncoding RNAs, and several key cytokines in cancer and cancer-related immune response, as well as the clinical cases in cancer therapy based on them.

Immunotherapy with dendritic cells loaded with glioblastoma stem cells: from preclinical to clinical studies

Different approaches have been explored to raise effective antitumor responses against glioblastoma (GBM), the deadliest of primary brain tumors. In many clinical studies, cancer vaccines have been based on dendritic cells (DCs) loaded with peptides, representing one or more specific tumor antigens or whole lysates as a source of multiple antigens. Randomized clinical trials using DCs are ongoing, and results of efficacy are not yet available. Such strategies are feasible and safe; however, immune-suppressive microenvironment, absence of appropriate specific epitopes to target, and cancer immunoediting can limit their efficacy. The aim of this review is to describe how the definition of novel and more specific targets may increase considerably the possibility of successful DC immunotherapy. By proposing to target glioblastoma stem-like cells (GSCs), the immune response will be pointed to eradicating factors and pathways highly relevant to GBM biology. Preclinical observations on efficacy, and preliminary results of immunotherapy trials, encourage exploring the clinical efficacy of DC immunotherapy in GBM patients using high-purity, GSC-loaded DC vaccines.

MicroRNA-mediated down-regulation of NKG2D ligands contributes to glioma immune escape

Malignant gliomas are intrinsic brain tumors with a dismal prognosis. They are well-adapted to hypoxic conditions and poorly immunogenic. NKG2D is one of the major activating receptors of natural killer (NK) cells and binds to several ligands (NKG2DL).

Here we evaluated the impact of miRNA on the expression of NKG2DL in glioma cells including stem-like glioma cells. Three of the candidate miRNA predicted to target NKG2DL were expressed in various glioma cell lines as well as in glioblastomas in vivo: miR-20a, miR-93 and miR-106b. LNA inhibitor-mediated miRNA silencing up-regulated cell surface NKG2DL expression, which translated into increased susceptibility to NK cell-mediated lysis. This effect was reversed by neutralizing NKG2D antibodies, confirming that enhanced lysis upon miRNA silencing was mediated through the NKG2D system. Hypoxia, a hallmark of glioblastomas in vivo, down-regulated the expression of NKG2DL on glioma cells, associated with reduced susceptibility to NK cell-mediated lysis. This process, however, was not mediated through any of the examined miRNA. Accordingly, both hypoxia and the expression of miRNA targeting NKG2DL may contribute to the immune evasion of glioma cells at the level of the NKG2D recognition pathway. Targeting miRNA may therefore represent a novel approach to increase the immunogenicity of glioblastoma.

4T1 Murine Mammary Carcinoma Cells Enhance Macrophage-Mediated Innate Inflammatory Responses

Tumor progression and the immune response are intricately linked. While it is known that cancers alter macrophage inflammatory responses to promote tumor progression, little is known regarding how cancers affect macrophage-dependent innate host defense. In this study, murine bone-marrow-derived macrophages (BMDM) were exposed to murine carcinoma-conditioned media prior to assessment of the macrophage inflammatory response. BMDMs exposed to 4T1 mammary carcinoma-conditioned medium demonstrated enhanced production of pro-inflammatory cytokines tumor necrosis factor α, interleukin-6, and CCL2 in response to lipopolysaccharide (LPS) while production of interleukin-10 remained unchanged. The increased LPS-induced production of pro-inflammatory cytokines was transient and correlated with enhanced cytokine production in response to other Toll-like receptor agonists, including peptidoglycan and flagellin. In addition, 4T1-conditioned BMDMs exhibited strengthened LPS-induced nitric oxide production and enhanced phagocytosis of Escherichia coli. 4T1-mediated augmentation of macrophage responses to LPS was partially dependent on the NFκB pathway, macrophage-colony stimulating factor, and actin polymerization, as well as the presence of 4T1-secreted extracellular vesicles. Furthermore, peritoneal macrophages obtained from 4T1 tumor-bearing mice displayed enhanced pro-inflammatory cytokine production in response to LPS. These results suggest that uptake of 4T1-secreted factors and actin-mediated ingestion of 4T1-secreted exosomes by macrophages cause a transient enhancement of innate inflammatory responses. Mammary carcinoma-mediated regulation of innate immunity may have significant implications for our understanding of host defense and cancer progression.

RB mutation and RAS overexpression induce resistance to NK cell-mediated cytotoxicity in glioma cells

Several theories aim to explain the malignant transformation of cells, including the mutation of tumor suppressors and proto-oncogenes. Deletion of Rb (a tumor suppressor), overexpression of mutated Ras (a proto-oncogene), or both, are sufficient for in vitro gliomagenesis, and these genetic traits are associated with their proliferative capacity. An emerging hallmark of cancer is the ability of tumor cells to evade the immune system. Whether specific mutations are related with this, remains to be analyzed. To address this issue, three transformed glioma cell lines were obtained (Rb^−/−, Ras^V12, and Rb^−/−/Ras^V12) by in vitro retroviral transformation of astrocytes, as previously reported. In addition, Ras^V12 and Rb^−/−/Ras^V12 transformed cells were injected into SCID mice and after tumor growth two stable glioma cell lines were derived. All these cells were characterized in terms of Rb and Ras gene expression, morphology, proliferative capacity, expression of MHC I, Rae1δ, and Rae1αβγδε, mult1, H60a, H60b, H60c, as ligands for NK cell receptors, and their susceptibility to NK cell-mediated cytotoxicity. Our results show that transformation of astrocytes (Rb loss, Ras overexpression, or both) induced phenotypical and functional changes associated with resistance to NK cell-mediated cytotoxicity. Moreover, the transfer of cell lines of transformed astrocytes into SCID mice increased resistance to NK cell-mediated cytotoxicity, thus suggesting that specific changes in a tumor suppressor (Rb) and a proto-oncogene (Ras) are enough to confer resistance to NK cell-mediated cytotoxicity in glioma cells and therefore provide some insight into the ability of tumor cells to evade immune responses.

Enhancement of glioma-specific immunity in mice by "NOBEL", an insulin-like growth factor 1 receptor antisense oligodeoxynucleotide

Autologous glioblastoma multiforme tumor cells treated with an antisense oligodeoxynucleotide (AS-ODN) targeting insulin-like growth factor receptor-1 (IGF-1R) are the basis of a vaccine with therapeutic effects on tumor recurrence in a pilot clinical trial. As a preface to continued clinical investigation of this vaccination strategy, we have studied the contribution of an optimized IGF-1R AS-ODN, designated "NOBEL", to the induction of immunity to mouse GL261 glioma cells. The impact of NOBEL on mechanisms contributing to the development of GL261 immunity was first examined in the periphery. GL261 cells are naturally immunogenic when implanted into the flanks of congenic C57BL/6 mice, immunizing rather than forming tumors in around 50 % of these animals but causing tumors in the majority of mice lacking T and B lymphocytes. Overnight treatment with NOBEL in vitro reduces IGF-1R expression by GL261 cells but has minimal effect on cell viability and does not reduce the capacity of the cells to form tumors upon implantation. In contrast, tumors are extremely rare when GL261 cells are mixed with NOBEL at inoculation into the flanks of C57BL/6, and the recipient mice become immune to subcutaneous and intracranial challenge with untreated GL261. Adaptive immune mechanisms contribute to this effect, as immunocompromised mice fail to either fully control tumor formation or develop immunity following flank administration of the GL261/NOBEL mix. NOBEL's structure has known immunostimulatory motifs that likely contribute to the immunogenicity of the mix, but its specificity for IGF-1R mRNA is also important as a similarly structured sense molecule is not effective.

Recent advances in the role of toll-like receptors and TLR agonists in immunotherapy for human glioma

Gliomas are extremely aggressive brain tumors with a very poor prognosis. One of the more promising strategies for the treatment of human gliomas is targeted immunotherapy where antigens that are unique to the tumors are exploited to generate vaccines. The approach, however, is complicated by the fact that human gliomas escape immune surveillance by creating an immune suppressed microenvironment. In order to oppose the glioma imposed immune suppression, molecules and pathways involved in immune cell maturation, expansion, and migration are under intensive clinical investigation as adjuvant therapy. Toll-like receptors (TLRs) mediate many of these functions in immune cell types, and TLR agonists, thus, are currently primary candidate molecules to be used as important adjuvants in a variety of cancers. In animal models for glioma, TLR agonists have exhibited antitumor properties by facilitating antigen presentation and stimulating innate and adaptive immunity. In clinical trials, several TLR agonists have achieved survival benefit, and many more trials are recruiting or ongoing. However, a second complicating factor is that TLRs are also expressed on cancer cells where they can participate instead in a variety of tumor promoting activities including cell growth, proliferation, invasion, migration, and even stem cell maintenance. TLR agonists can, therefore, possibly play dual roles in tumor biology. Here, how TLRs and TLR agonists function in glioma biology and in anti-glioma therapies is summarized in an effort to provide a current picture of the sophisticated relationship of glioma with the immune system and the implications for immunotherapy.

RAGE expression in tumor-associated macrophages promotes angiogenesis in glioma

Interaction of RAGE (the receptor for advanced glycation endproducts) with its ligands can promote tumor progression, invasion, and angiogenesis. Although blocking RAGE signaling has been proposed as a potential anticancer strategy, functional contributions of RAGE expression in the tumor microenvironment (TME) have not been investigated in detail. Here, we evaluated the effect of genetic depletion of RAGE in TME on the growth of gliomas. In both invasive and noninvasive glioma models, animal survival was prolonged in RAGE knockout (Ager(-/-)) mice. However, the improvement in survival in Ager(-/-) mice was not due to changes in tumor growth rate but rather to a reduction in tumor-associated inflammation. Furthermore, RAGE ablation in the TME abrogated angiogenesis by downregulating the expression of proangiogenic factors, which prevented normal vessel formation, thereby generating a leaky vasculature. These alterations were most prominent in noninvasive gliomas, in which the expression of VEGF and proinflammatory cytokines were also lower in tumor-associated macrophages (TAM) in Ager(-/-) mice. Interestingly, reconstitution of Ager(-/-) TAM with wild-type microglia or macrophages normalized tumor vascularity. Our results establish that RAGE signaling in glioma-associated microglia and TAM drives angiogenesis, underscoring the complex role of RAGE and its ligands in gliomagenesis.

Systemic injection of TLR1/2 agonist improves adoptive antigen-specific T cell therapy in glioma-bearing mice

Adoptive immunotherapy is an attractive strategy for glioma treatment. However, some obstacles still need be overcome. In this study, GL261-bearing mice treated with adoptively transferred antigen-specific T cells and systemic injection of bacterial lipoprotein (BLP), a TLR1/2 agonist, got a long-term survival and even immune protection. By analyzing adoptive T cells, it was found that BLP maintained T cell survival, proliferation and anti-tumor efficacy in the brains of tumor-bearing hosts. Moreover, tumor microenvironment was modified by up-regulating IFN-γ-secreting CD8+ T cells and down-regulating MDSC, which might be related with high CXCL10 and low CCL2 expression. In addition, TLR2 deficiency abrogated therapeutic effect with increased MDSC accumulation and decreased IFN-γ-secreting CD8+ T cells in the brains. Thus, the systemic injection of BLP could improve the adoptive T cell therapy by maintaining T cell persistence, modifying the tumor microenvironment and even inducing systemic anti-tumor immunity, which might offer a clinically promising immunotherapeutic strategy for glioma.

A new hope in immunotherapy for malignant gliomas: adoptive T cell transfer therapy

Immunotherapy emerged as a promising therapeutic approach to highly incurable malignant gliomas due to tumor-specific cytotoxicity, minimal side effect, and a durable antitumor effect by memory T cells. But, antitumor activities of endogenously activated T cells induced by immunotherapy such as vaccination are not sufficient to control tumors because tumor-specific antigens may be self-antigens and tumors have immune evasion mechanisms to avoid immune surveillance system of host. Although recent clinical results from vaccine strategy for malignant gliomas are encouraging, these trials have some limitations, particularly their failure to expand tumor antigen-specific T cells reproducibly and effectively. An alternative strategy to overcome these limitations is adoptive T cell transfer therapy, in which tumor-specific T cells are expanded ex vivo rapidly and then transferred to patients. Moreover, enhanced biologic functions of T cells generated by genetic engineering and modified immunosuppressive microenvironment of host by homeostatic T cell expansion and/or elimination of immunosuppressive cells and molecules can induce more potent antitumor T cell responses and make this strategy hold promise in promoting a patient response for malignant glioma treatment. Here we will review the past and current progresses and discuss a new hope in adoptive T cell therapy for malignant gliomas.

Proteomic comparison of 3D and 2D glioma models reveals increased HLA-E expression in 3D models is associated with resistance to NK cell-mediated cytotoxicity

Three-dimensional cell culture techniques can better reflect the in vivo characteristics of tumor cells compared with traditional monolayer cultures. Compared with their 2D counterparts, 3D-cultured tumor cells showed enhanced resistance to the cytotoxic T cell-mediated immune response. However, it remains unclear whether 3D-cultured tumor cells have an enhanced resistance to NK cell cytotoxicity. In this study, a total of 363 differentially expressed proteins were identified between the 2D- and 3D-cultured U251 cells by comparative proteomics, and an immune-associated protein-protein interaction (PPI) network based on these differential proteins was constructed by bioinformatics. Within the network, HLA-E, as a molecule for inhibiting NK cell activation, was significantly up-regulated in the 3D-cultured tumor cells. Then, we found that the 3D-cultured U251 cells exhibited potent resistance to NK cell cytotoxicity in vitro and were prone to tumor formation in vivo. The resistance of the 3D-cultured tumor cells to NK cell lysis was mediated by the HLA-E/NKG2A interaction because the administration of antibodies that block either HLA-E or NKG2A completely eliminated this resistance and significantly decreased tumor formation. Taken together, our findings indicate that HLA-E up-regulation in 3D-cultured cells may result in enhanced tumor resistance to NK cell-mediated immune response.

Effective immunotherapy of rat glioblastoma with prolonged intratumoral delivery of exogenous heat shock protein Hsp70

Chaperone Hsp70 can activate adaptive immunity suggesting its possible application as an antitumor vaccine. To assess the therapeutic capacity of Hsp70 we administered purified chaperone into a C6 glioblastoma brain tumor and explored the viability and tumor size as well as interferon gamma (IFNγ) production and cytotoxicity of lymphocytes in the treated animals. Targeted intratumoral injection of Hsp70 resulted in its distribution within the area of glioblastoma, and caused significant inhibition of tumor progression as confirmed by magnetic resonance imaging. The delay in tumor growth corresponded to the prolonged survival of tumor-bearing animals of up to 31 days versus 20 days in control. Continuous administration of Hsp70 with an osmotic pump increased survival even further (39 days). Therapeutic efficacy was associated with infiltration to glioblastoma of NK cells (Ly-6c+) and T lymphocytes (CD3+, CD4+ and CD8+) as well as with an increase in the activity of NK cells (granzyme B production) and CD8+ T lymphocytes as shown by IFNγ ELISPOT assay. Furthermore, we found that Hsp70 treatment caused concomitantly, with a tenfold elevated IFNγ production, an increase in anti-C6 tumor cytotoxicity of lymphocytes. In conclusion, continuous intratumoral delivery of Hsp70 demonstrates high therapeutic potential and therefore could be applied in the treatment of glioblastoma.

Natural killer cells in intracranial neoplasms: presence and therapeutic efficacy against brain tumours

Natural killer (NK) cells are lymphocytes that play an important role in anti-tumour immunity. Their potential against brain cancer has been demonstrated in vitro and in vivo, both as a direct anti-tumour agent and in experimental therapies stimulating endogenous NK cell cytotoxicity. However, the clinical translation of these promising results requires detailed knowledge about the immune status of brain tumour patients, with focus on the NK cell population. In this report, we provide an overview of the studies investigating NK cell infiltration into the tumour, emphasizing the need of revision of the methodologies and further research in this field. We also discuss the potential of using autologous or allogeneic NK cells as effector cells in cellular therapy against brain cancer and developing immunotherapies stimulating endogenous NK cell-mediated anti-tumour response, such as blocking inhibitory killer immunoglobulin-like receptors. Combination of NK cell adoptive transfer with targeted therapies, such as anti-EGFR therapeutic antibody (CetuximAb) could also be a potent strategy.

Treg depletion followed by intracerebral CpG-ODN injection induce brain tumor rejection

Using brain lymphoma model, we demonstrate that immunotherapy combining Treg depletion (using anti-CD25 mAb PC61) followed by intracranial CpG-ODN administration induced tumor rejection in all treated mice and led to the establishment of a memory antitumor immune response in 60% of them. This protective effect was associated with a recruitment of NK cells and, to a lesser extent, of dendritic cells, B cells and T lymphocytes. NK cell depletion abolished the protective effect of the treatment, confirming a major role of NK cells in brain tumor elimination. Each treatment used alone failed to protect brain tumor bearing mice, revealing the therapeutic benefit of combining Treg depletion and local CpG-ODN injection.

Production of bioactive soluble interleukin-15 in complex with interleukin-15 receptor alpha from a conditionally-replicating oncolytic HSV-1

Oncolytic type-1 herpes simplex viruses (oHSVs) lacking the γ134.5 neurovirulence gene are being evaluated for treatment of a variety of malignancies. oHSVs replicate within and directly kill permissive cancer cells. To augment their anti-tumor activity, oHSVs have been engineered to express immunostimulatory molecules, including cytokines, to elicit tumor-specific immune responses. Interleukin-15 (IL-15) holds potential as an immunotherapeutic cytokine because it has been demonstrated to promote both natural killer (NK) cell-mediated and CD8(+) T cell-mediated cytotoxicity against cancer cells. The purpose of these studies was to engineer an oHSV producing bioactive IL-15. Two oHSVs were constructed encoding murine (m)IL-15 alone (J100) or with the mIL-15 receptor α (mIL-15Rα, J100D) to determine whether co-expression of these proteins is required for production of bioactive mIL-15 from oHSV. The following were demonstrated: i) both oHSVs retain replication competence and cytotoxicity in permissive tumor cell lines. ii) Enhanced production of mIL-15 was detected in cell lysates of neuro-2a cells following J100D infection as compared to J100 infection, suggesting that mIL-15Rα improved mIL-15 production. iii) Soluble mIL-15 in complex with mIL-15Rα was detected in supernates from J100D-infected, but not J100-infected, neuro-2a, GL261, and CT-2A cells. These cell lines vary in permissiveness to oHSV replication and cytotoxicity, demonstrating soluble mIL-15/IL-15Rα complex production from J100D was independent of direct oHSV effects. iv) The soluble mIL-15/IL-15Rα complex produced by J100D was bioactive, stimulating NK cells to proliferate and reduce the viability of syngeneic GL261 and CT-2A cells. v) J100 and J100D were aneurovirulent inasmuch as no neuropathologic effects were documented following direct inoculation into brains of CBA/J mice at up to 1x10(7) plaque forming units. The production of mIL-15/mIL-15Rα from multiple tumor lines, as well as the lack of neurovirulence, renders J100D suitable for investigating the combined effects of oHSV and mIL-15/IL-15Rα in various cancer models.

NK cells in central nervous system disorders

NK cells are important players in immunity against pathogens and neoplasms. As a component of the innate immune system, they are one of the first effectors on sites of inflammation. Through their cytokine production capacities, NK cells participate in the development of a potent adaptive immune response. Furthermore, NK cells were found to have regulatory functions to limit and prevent autoimmunity via killing of autologous immune cells. These paradoxical functions of NK cells are reflected in CNS disorders. In this review, we discuss the phenotypes and functional features of peripheral and brain NK cells in brain tumors and infections, neurodegenerative diseases, acute vascular and traumatic damage, as well as mental disorders. We also discuss the implication of NK cells in neurotoxicity and neuroprotection following CNS pathology, as well as the crosstalk between NK cells and brain-resident immune cells.

Targeting the cytosolic innate immune receptors RIG-I and MDA5 effectively counteracts cancer cell heterogeneity in glioblastoma

Cellular heterogeneity, for example, the intratumoral coexistence of cancer cells with and without stem cell characteristics, represents a potential root of therapeutic resistance and a significant challenge for modern drug development in glioblastoma (GBM). We propose here that activation of the innate immune system by stimulation of innate immune receptors involved in antiviral and antitumor responses can similarly target different malignant populations of glioma cells. We used short-term expanded patient-specific primary human GBM cells to study the stimulation of the cytosolic nucleic acid receptors melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene I (RIG-I). Specifically, we analyzed cells from the tumor core versus "residual GBM cells" derived from the tumor resection margin as well as stem cell-enriched primary cultures versus specimens without stem cell properties. A portfolio of human, nontumor neural cells was used as a control for these studies. The expression of RIG-I and MDA5 could be induced in all of these cells. Receptor stimulation with their respective ligands, p(I:C) and 3pRNA, led to in vitro evidence for an effective activation of the innate immune system. Most intriguingly, all investigated cancer cell populations additionally responded with a pronounced induction of apoptotic signaling cascades revealing a second, direct mechanism of antitumor activity. By contrast, p(I:C) and 3pRNA induced only little toxicity in human nonmalignant neural cells. Granted that the challenge of effective central nervous system (CNS) delivery can be overcome, targeting of RIG-I and MDA5 could thus become a quintessential strategy to encounter heterogeneous cancers in the sophisticated environments of the brain.