Preclinical investigation of combined gene-mediated cytotoxic immunotherapy and immune checkpoint blockade in glioblastoma

Antigen presentation deficiency, mesenchymal differentiation, and resistance to immunotherapy in the murine syngeneic CT2A tumor model

Background

The GL261 and CT2A syngeneic tumor lines are frequently used as immunocompetent orthotopic mouse models of human glioblastoma (huGBM) but demonstrate distinct differences in their responses to immunotherapy.

Methods

To decipher the cell-intrinsic mechanisms that drive immunotherapy resistance in CT2A-luc and to define the aspects of human cancer biology that these lines can best model, we systematically compared their characteristics using whole exome and transcriptome sequencing, and protein analysis through immunohistochemistry, Western blot, flow cytometry, immunopeptidomics, and phosphopeptidomics.

Results

The transcriptional profiles of GL261-luc2 and CT2A-luc tumors resembled those of some huGBMs, despite neither line sharing the essential genetic or histologic features of huGBM. Both models exhibited striking hypermutation, with clonal hotspot mutations in RAS genes (Kras p.G12C in GL261-luc2 and Nras p.Q61L in CT2A-luc). CT2A-luc distinctly displayed mesenchymal differentiation, upregulated angiogenesis, and multiple defects in antigen presentation machinery (e.g. Tap1 p.Y488C and Psmb8 p.A275P mutations) and interferon response pathways (e.g. copy number losses of loci including IFN genes and reduced phosphorylation of JAK/STAT pathway members). The defect in MHC class I expression could be overcome in CT2A-luc by interferon-γ treatment, which may underlie the modest efficacy of some immunotherapy combinations. Additionally, CT2A-luc demonstrated substantial baseline secretion of the CCL-2, CCL-5, and CCL-22 chemokines, which play important roles as myeloid chemoattractants.

Conclusion

Although the clinical contexts that can be modeled by GL261 and CT2A for huGBM are limited, CT2A may be an informative model of immunotherapy resistance due to its deficits in antigen presentation machinery and interferon response pathways.

Therapeutic Targeting of Glioblastoma and the Interactions with Its Microenvironment

Glioblastoma (GBM) is the most common primary malignant brain tumour, and it confers a dismal prognosis despite intensive multimodal treatments. Whilst historically, research has focussed on the evolution of GBM tumour cells themselves, there is growing recognition of the importance of studying the tumour microenvironment (TME). Improved characterisation of the interaction between GBM cells and the TME has led to a better understanding of therapeutic resistance and the identification of potential targets to block these escape mechanisms. This review describes the network of cells within the TME and proposes treatment strategies for simultaneously targeting GBM cells, the surrounding immune cells, and the crosstalk between them.

NamiRNA-mediated high expression of KNSTRN correlates with poor prognosis and immune infiltration in hepatocellular carcinoma

Introduction

Mutations of kinetochore-localized astrin/sperm-associated antigen 5 (KNSTRN) can interfere with chromatid cohesion, increase aneuploidy in tumours, and enhance tumourigenesis. However, the role of the KNSTRN-binding protein in hepatocellular carcinoma (HCC) remains unclear.

Material and methods

Using The Cancer Genome Atlas databases, we investigated the potential oncogenic functions of KNSTRN in HCC along with R and various computational tools.

Results

Detailed results revealed that elevated expression of KNSTRN was considerably associated with poor overall survival (HR = 1.48, 95% CI: 1.05-2.09, p = 0.027) and progress-free interval (HR = 1.41, 95% CI: 1.05-1.89, p = 0.021) in HCC. Gene ontology/Kyoto Encyclopedia of Genes and Genomes functional enrichment analysis showed that KNSTRN is closely related to organelle fission, chromosomal region, tubulin binding, and cell cycle signalling pathway. TIMER database analysis showed the correlations between KNSTRN expression and tumour-infiltrating immune cells, biomarkers of immune cells, and immune checkpoint expression. Moreover, the KNSTRN level was significantly positively associated with immunosuppressive cells in the tumour microenvironment, including regulatory T-cells, myeloid-derived suppressor cells, and cancer-associated fibrocytes. Finally, a possible nuclear activating miRNA (NamiRNA)-enhancer network of hsa-miR-107, which activates the KNSTRN expression in liver hepatocellular carcinoma, was constructed by correlation analysis.

Conclusions

NamiRNA-mediated upregulation of KNSTRN correlated with poor prognosis and tumour immune infiltration in HCC. KNSTRN could serve as an effective biomarker for the diagnosis and prognosis of HCC and support the development of novel therapeutic strategies.

Clinical Efficacy and Safety of AdV-tk Gene Therapy for Patients with Cervical Squamous Intraepithelial Lesion: A Prospective Study

Cervical cancer is the fourth most common type of cancer for women in 2020, and many more women have cervical precancerous lesion-squamous intraepithelial lesion (SIL). Early treatment of cervical SIL to reverse or delay its progression is an important approach to reduce the incidence of cervical cancer. The efficacy and safety of adenovirus-based vectors expressing the thymidine kinase gene (AdV-tk) in the treatment of multiple types of cancers shows promise for its use in gynecology. We aim to provide relevant clinical efficacy and safety data after introducing AdV-tk for the treatment of cervical SIL for the first time through this prospective study. We conducted a maximum of 6 sessions to administer AdV-tk gene therapy to 23 patients (mean age: 35 years old) with cervical low-/high-grade SIL (LSIL/HSIL) who were enrolled from August 2015 to April 2018 and analyzed the clinical characteristics and follow-up outcomes (mean follow-up period: 7.3 months). The present study consisted of 17 patients (73.9%) with cervical HSIL and 6 patients with LSIL confirmed by colposcopy-directed biopsy. We observed an overall histological remission and regression rate of 87.0% (20/23, 95% confidence interval [95% CI]: 73.2-100, p < 0.001) after AdV-tk gene therapy. Eight patients (34.8%) were detected with human papillomavirus (HPV) 16/18 subtypes and 13 patients were found to be positive with at least one of the other 13 high-risk HPV (HR-HPV) subtypes, while 2 patients did not have any of the 15 HR-HPV subtypes. The overall clearance rate of HR-HPV was 76.2% (16/21, 95% CI: 58.0-94.4, p = 0.016) after AdV-tk gene therapy. For safety evaluation, no severe complications were reported in any of the 23 patients. The most commonly reported symptom was fever in 52.2% (12/23) of patients and all symptoms were fully resolved after symptomatic treatment. Our data indicate that AdV-tk gene therapy has high efficacy and safety in the treatment of cervical SIL among gynecological patients. Our findings provide clinical evidence on the potential promotion and application of AdV-tk in the treatment of cervical SIL, and potentially for cervical cancer, among gynecological patients.

Opportunities and challenges of combining adoptive cellular therapy with oncolytic virotherapy

The use of oncolytic viruses (OVs) and adoptive cell therapies (ACT) have independently emerged as promising approaches for cancer immunotherapy. More recently, the combination of such agents to obtain a synergistic anticancer effect has gained attention, particularly in solid tumors, where immune-suppressive barriers of the microenvironment remain a challenge for desirable therapeutic efficacy. While adoptive cell monotherapies may be restricted by an immunologically cold or suppressive tumor microenvironment (TME), OVs can serve to prime the TME by eliciting a wave of cancer-specific immunogenic cell death and inducing enhanced antitumor immunity. While OV/ACT synergy is an attractive approach, immune-suppressive barriers remain, and methods should be considered to optimize approaches for such combination therapy. In this review, we summarize current approaches that aim to overcome these barriers to enable optimal synergistic antitumor effects.

Updates in Glioblastoma Immunotherapy: An Overview of the Current Clinical and Translational Scenario

Glioblastoma (GBM) is the most common and aggressive central nervous system tumor, requiring multimodal management. Due to its malignant behavior and infiltrative growth pattern, GBM is one of the most difficult tumors to treat and gross total resection is still considered to be the first crucial step. The deep understanding of GBM microenvironment and the possibility of manipulating the patient's innate and adaptive immune system to fight the neoplasm represent the base of immunotherapeutic strategies that currently express the future for the fight against GBM. Despite the immunotherapeutic approach having been successfully adopted in several solid and haematologic neoplasms, immune resistance and the immunosuppressive environment make the use of these strategies challenging in GBM treatment. We describe the most recent updates regarding new therapeutic strategies that target the immune system, immune checkpoint inhibitors, chimeric antigen receptor T cell therapy, peptide and oncolytic vaccines, and the relevant mechanism of immune resistance. However, no significant results have yet been obtained in studies targeting single molecules/pathways. The future direction of GBM therapy will include a combined approach that, in contrast to the inescapable current treatment modality of maximal resection followed by chemo- and radiotherapy, may combine a multifaceted immunotherapy treatment with the dual goals of directly killing tumor cells and activating the innate and adaptive immune response.

Barriers to overcoming immunotherapy resistance in glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor, known for its poor prognosis and high recurrence rate. Current standard of care includes surgical resection followed by combined radiotherapy and chemotherapy. Although immunotherapies have yielded promising results in hematological malignancies, their successful application in GBM remains limited due to a host of immunosuppressive factors unique to GBM. As a result of these roadblocks, research efforts have focused on utilizing combinatorial immunotherapies that target networks of immune processes in GBM with promising results in both preclinical and clinical trials, although limitations in overcoming the immunosuppressive factors within GBM remain. In this review, we aim to discuss the intrinsic and adaptive immune resistance unique to GBM and to summarize the current evidence and outcomes of engineered and non-engineered treatments targeted at overcoming GBM resistance to immunotherapy. Additionally, we aim to highlight the most promising strategies of targeted GBM immunotherapy combinatorial treatments and the insights that may directly improve the current patient prognosis and clinical care.

Role of Nanomedicine-Based Therapeutics in the Treatment of CNS Disorders

Central nervous system disorders, especially neurodegenerative diseases, are a public health priority and demand a strong scientific response. Various therapy procedures have been used in the past, but their therapeutic value has been insufficient. The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier is two of the barriers that protect the central nervous system (CNS), but are the main barriers to medicine delivery into the CNS for treating CNS disorders, such as brain tumors, Parkinson's disease, Alzheimer's disease, and Huntington's disease. Nanotechnology-based medicinal approaches deliver valuable cargos targeting molecular and cellular processes with greater safety, efficacy, and specificity than traditional approaches. CNS diseases include a wide range of brain ailments connected to short- and long-term disability. They affect millions of people worldwide and are anticipated to become more common in the coming years. Nanotechnology-based brain therapy could solve the BBB problem. This review analyzes nanomedicine's role in medication delivery; immunotherapy, chemotherapy, and gene therapy are combined with nanomedicines to treat CNS disorders. We also evaluated nanotechnology-based approaches for CNS disease amelioration, with the intention of stimulating the immune system by delivering medications across the BBB.

Optimal timing of PD-1 blockade in combination with oncolytic virus therapy

Anti-PD-1 and oncolytic viruses (OVs) have non-overlapping anti-tumor mechanisms, since each agent works at different steps of the cancer-immunity cycle. Evidence suggests that OVs improve therapeutic responses to anti-PD-1 therapy by reversing immunosuppressive factors, increasing the number and diversity of infiltrating lymphocytes, and promoting PD-L1 expression in both injected and non-injected tumors. Many studies in preclinical models suggest that the timing of anti-PD-1 administration influences the therapeutic success of the combination therapy (anti-PD-1 + OV). Therefore, determining the appropriate sequencing of agents is of critical importance to designing a rationale OV-based combinational clinical trial. Currently, the combination of anti-PD-1 and OVs are being delivered using various schedules, and we have classified the timing of administration of anti-PD-1 and OVs into five categories: (i) anti-PD-1 lead-in → OV; (ii) concurrent administration; (iii) OV lead-in → anti-PD-1; (iv) concurrent therapy lead-in → anti-PD-1; and (v) OV lead-in → concurrent therapy. Based on the reported preclinical and clinical literature, the most promising treatment strategy to date is hypothesized to be OV lead-in → concurrent therapy. In the OV lead-in → concurrent therapy approach, initial OV treatment results in T cell priming and infiltration into tumors and an immunologically hot tumor microenvironment (TME), which can be counterbalanced by engagement of PD-L1 to PD-1 receptor on immune cells, leading to T cell exhaustion. Therefore, after initial OV therapy, concurrent use of both OV and anti-PD-1 is critical through which OV maintains T cell priming and an immunologically hot TME, whereas PD-1 blockade helps to overcome PD-L1/PD-1-mediated T cell exhaustion. It is important to note that the hypothetical conclusion drawn in this review is based on thorough literature review on current understanding of OV + anti-PD-1 combination therapies and rhythm of treatment-induced cancer-immunity cycle. A variety of confounding factors such as tumor types, OV types, presence or absence of cytokine transgenes carried by an OV, timing of treatment initiation, varying dosages and treatment frequencies/duration of OV and anti-PD-1, etc. may affect the validity of our conclusion that will need to be further examined by future research (such as side-by-side comparative studies using all five treatment schedules in a given tumor model).

A Phase 2 Trial of Enhancing Immune Checkpoint Blockade by Stereotactic Radiation and In Situ Virus Gene Therapy in Metastatic Triple-Negative Breast Cancer

PURPOSE

A Phase 2 trial of stereotactic radiotherapy and in situ cytotoxic virus therapy in patients with metastatic triple-negative breast cancer (mTNBC) followed by pembrolizumab (STOMP) was designed to evaluate dual approach of enhancing single-agent immune checkpoint blockade with adenovirus-mediated expression of herpes-simplex-virus thymidine-kinase (ADV/HSV-tk) plus valacyclovir gene therapy and stereotactic body radiotherapy (SBRT) in patients with mTNBC.

PATIENTS AND METHODS

In this single-arm, open-label Phase 2 trial, patients with mTNBC were treated with ADV/HSV-tk [5 × 1011 virus particles (vp)] intratumoral injection, followed by SBRT to the injected tumor site, then pembrolizumab (200 mg, every 3 weeks). The primary endpoint was clinical benefit rate [CBR; complete response (CR), partial response (PR), or stable disease (SD) ≥ 24 weeks per RECIST version1.1 at non-irradiated site]. Secondary endpoints included duration on treatment (DoT), overall survival (OS), and safety. Exploratory endpoints included immune response to treatment assessed by correlative tissue and blood-based biomarkers.

RESULTS

Twenty-eight patients were enrolled and treated. CBR was seen in 6 patients (21.4%), including 2 CR (7.1%), 1 PR (3.6%), and 3 SD (10.7%). Patients with clinical benefit had durable responses, with median DoT of 9.6 months and OS of 14.7 months. The median OS was 6.6 months in the total population. The combination was well tolerated. Correlative studies with Cytometry by Time of Flight (CyTOF) and imaging mass cytometry (IMC) revealed a significant increase of CD8 T cells in responders and of myeloid cells in non-responders.

CONCLUSIONS

The median OS increased by more than 2-fold in patients with clinical benefit. The therapy is a well-tolerated treatment in heavily pretreated patients with mTNBC. Early detection of increased effector and effector memory CD8 T cells and myeloids correlate with response and non-response, respectively.

Perturbing DDR signaling enhances cytotoxic effects of local oncolytic virotherapy and modulates the immune environment in glioma

CAN-2409 is a replication-deficient adenovirus encoding herpes simplex virus (HSV) thymidine kinase (tk) currently in clinical trials for treatment of glioblastoma. The expression of tk in transduced cancer cells results in conversion of the pro-drug ganciclovir into a toxic metabolite causing DNA damage, inducing immunogenic cell death and immune activation. We hypothesize that CAN-2409 combined with DNA-damage-response inhibitors could amplify tumor cell death, resulting in an improved response. We investigated the effects of ATR inhibitor AZD6738 in combination with CAN-2409 in vitro using cytotoxicity, cytokine, and fluorescence-activated cell sorting (FACS) assays in glioma cell lines and in vivo with an orthotopic syngeneic murine glioma model. Tumor immune infiltrates were analyzed by cytometry by time of flight (CyTOF). In vitro, we observed a significant increase in the DNA-damage marker γH2AX and decreased expression of PD-L1, pro-tumorigenic cytokines (interleukin-1β [IL-1β], IL-4), and ligand NKG2D after combination treatment compared with monotherapy or control. In vivo, long-term survival was increased after combination treatment (66.7%) compared with CAN-2409 (50%) and control. In a tumor re-challenge, long-term immunity after combination treatment was not improved. Our results suggest that ATR inhibition could amplify CAN-2409's efficacy in glioblastoma through increased DNA damage while having complex immunological ramifications, warranting further studies to determine the ideal conditions for maximized therapeutic benefit.

Translational landscape of glioblastoma immunotherapy for physicians: guiding clinical practice with basic scientific evidence

Despite recent advances in cancer therapeutics, glioblastoma (GBM) remains one of the most difficult cancers to treat in both the primary and recurrent settings. GBM presents a unique therapeutic challenge given the immune-privileged environment of the brain and the aggressive nature of the disease. Furthermore, it can change phenotypes throughout the course of disease—switching between mesenchymal, neural, and classic gene signatures, each with specific markers and mechanisms of resistance. Recent advancements in the field of immunotherapy—which utilizes strategies to reenergize or alter the immune system to target cancer—have shown striking results in patients with many types of malignancy. Immune checkpoint inhibitors, adoptive cellular therapy, cellular and peptide vaccines, and other technologies provide clinicians with a vast array of tools to design highly individualized treatment and potential for combination strategies. There are currently over 80 active clinical trials evaluating immunotherapies for GBM, often in combination with standard secondary treatment options including re-resection and anti-angiogenic agents, such as bevacizumab. This review will provide a clinically focused overview of the immune environment present in GBM, which is frequently immunosuppressive and characterized by M2 macrophages, T cell exhaustion, enhanced transforming growth factor-β signaling, and others. We will also outline existing immunotherapeutic strategies, with a special focus on immune checkpoint inhibitors, chimeric antigen receptor therapy, and dendritic cell vaccines. Finally, we will summarize key discoveries in the field and discuss currently active clinical trials, including combination strategies, burgeoning technology like nucleic acid and nanoparticle therapy, and novel anticancer vaccines. This review aims to provide the most updated summary of the field of immunotherapy for GBM and offer both historical perspective and future directions to help inform clinical practice.

Emerging therapies for glioblastoma: current state and future directions

Glioblastoma (GBM) is the most common high-grade primary malignant brain tumor with an extremely poor prognosis. Given the poor survival with currently approved treatments for GBM, new therapeutic strategies are urgently needed. Advances in decades of investment in basic science of glioblastoma are rapidly translated into innovative clinical trials, utilizing improved genetic and epigenetic profiling of glioblastoma as well as the brain microenvironment and immune system interactions. Following these encouraging findings, immunotherapy including immune checkpoint blockade, chimeric antigen receptor T (CAR T) cell therapy, oncolytic virotherapy, and vaccine therapy have offered new hope for improving GBM outcomes; ongoing studies are using combinatorial therapies with the aim of minimizing adverse side-effects and augmenting antitumor immune responses. In addition, techniques to overcome the blood-brain barrier (BBB) for targeted delivery are being tested in clinical trials in patients with recurrent GBM. Here, we set forth the rationales for these promising therapies in treating GBM, review the potential novel agents, the current status of preclinical and clinical trials, and discuss the challenges and future perspectives in glioblastoma immuno-oncology.

Oncolytic measles vaccines encoding PD-1 and PD-L1 checkpoint blocking antibodies to increase tumor-specific T cell memory

PD-1/PD-L1 checkpoint blockade has achieved unprecedented success in cancer immunotherapy. Nevertheless, many immune-excluded tumors are resistant to therapy. Combination with oncolytic virotherapy may overcome resistance by inducing acute inflammation, immune cell recruitment, and remodeling of the tumor immune environment. Here, we assessed the combination of oncolytic measles vaccine (MV) vectors and PD-1/PD-L1 blockade. In the MC38cea model of measles virus oncolysis, MV combined with anti-PD-1 and MV vectors encoding anti-PD-1 or anti-PD-L1 antibodies achieved modest survival benefits compared with control MV or vectors encoding the antibody constant regions only. Analyses of tumor samples and tumor-draining lymph nodes revealed slight increases in intratumoral T cell effector cytokines as well as a shift toward an effector memory phenotype in the T cell compartment. Importantly, increased IFN-γ recall responses were observed in tumor rechallenge experiments with mice in complete tumor remission after treatment with MV encoding anti-PD-1 or anti-PD-L1 compared with control MV. These results prompted us to generate MV encoding the clinically approved agents pembrolizumab and nivolumab. Previously, we have generated MV encoding atezolizumab. We demonstrated the functionality of the novel vectors in vitro. We envision these vectors as therapeutics that induce and support durable anti-tumor immune memory.

Systemic high-dose dexamethasone treatment may modulate the efficacy of intratumoral viral oncolytic immunotherapy in glioblastoma models

Background

Intratumoral viral oncolytic immunotherapy is a promising new approach for the treatment of a variety of solid cancers. CAN-2409 is a replication-deficient adenovirus that delivers herpes simplex virus thymidine kinase to cancer cells, resulting in local conversion of ganciclovir or valacyclovir into a toxic metabolite. This leads to highly immunogenic cell death, followed by a local immune response against a variety of cancer neoantigens and, next, a systemic immune response against the injected tumor and uninjected distant metastases. CAN-2409 treatment has shown promising results in clinical studies in glioblastoma (GBM). Patients with GBM are usually given the corticosteroid dexamethasone to manage edema. Previous work has suggested that concurrent dexamethasone therapy may have a negative effect in patients treated with immune checkpoint inhibitors in patients with GBM. However, the effects of dexamethasone on the efficacy of CAN-2409 treatment have not been explored.

Methods

In vitro experiments included cell viability and neurosphere T-cell killing assays. Effects of dexamethasone on CAN-2409 in vivo were examined using a syngeneic murine GBM model; survival was assessed according to Kaplan-Meier; analyses of tumor-infiltrating lymphocytes were performed with mass cytometry (CyTOF - cytometry by time-of-flight). Data were analyzed using a general linear model, with one-way analysis of variance followed by Dunnett’s multiple comparison test, Kruskal-Wallis test, Dunn’s multiple comparison test or statistical significance analysis of microarrays.

Results

In a mouse model of GBM, we found that high doses of dexamethasone combined with CAN-2409 led to significantly reduced median survival (29.0 days) compared with CAN-2409 treatment alone (39.5 days). CyTOF analyses of tumor-infiltrating immune cells demonstrated potent immune stimulation induced by CAN-2409 treatment. These effects were diminished when high-dose dexamethasone was used. Functional immune cell characterization suggested increased immune cell exhaustion and tumor promoting profiles after dexamethasone treatment.

Conclusion

Our data suggest that concurrent high-dose dexamethasone treatment may impair the efficacy of oncolytic viral immunotherapy of GBM, supporting the notion that dexamethasone use should be balanced between symptom control and impact on the therapeutic outcome.

Self-assembled ruthenium and osmium nanosystems display a potent anticancer profile by interfering with metabolic activity

Amphiphilic ruthenium and osmium complexes auto-assemble to nanosystems that poison mitochondria and show highly promising in vitro and in vivo anticancer activity.

An overview of current therapeutic strategies for glioblastoma and the role of CD73 as an alternative curative approach

Glioblastoma multiforme (GBM) is a complicated and heterogeneous brain tumor with short-term survival outcomes. Commercial therapies are not practical due to cell infiltration capacity, high proliferative rate, and blood-brain barrier. In this context, recognition of the molecular mechanism of tumor progression might help the development of new cancer therapeutics. Recently, more evidence has supported CD73 and downstream adenosine A2A/A2B receptor signaling playing a crucial role in glioblastoma pathogenesis; therefore, targeting CD73 in murine tumor models can reduce tumor development. CD73 is an ecto-enzyme inducing tumor metastasis, angiogenesis, and immune escape via the production of extracellular adenosine in the tumor microenvironment. In this review, we provided information about clinical characteristics as well as the therapeutic management of glioblastoma. Then, we focused on newly available experimental evidence distinguishing between the essential role of CD73 on this tumor growth and a new method for the treatment of GBM patients.

Anti-PD-1 checkpoint blockade monotherapy in the orthotopic GL261 glioma model: the devil is in the detail

The GL261 cell line, syngeneic on the C57BL/6 background, has, since its establishment half a century ago in 1970, become the most commonly used immunocompetent murine model of glioblastoma. As immunotherapy has entered the mainstream of clinical discourse in the past decade, this model has proved its worth as a formidable opponent against various immunotherapeutic combinations. Although advances in surgical, radiological, and chemotherapeutic interventions have extended mean glioblastoma patient survival by several months, 5-year survival postdiagnosis remains below 5%. Immunotherapeutic interventions, such as the ones explored in the murine GL261 model, may prove beneficial for patients with glioblastoma. However, even common immunotherapeutic interventions in the GL261 model still have unclear efficacy, with wildly discrepant conclusions being made in the literature regarding this topic. Here, we focus on anti-PD-1 checkpoint blockade monotherapy as an example of this pattern. We contend that a fine-grained analysis of how biological variables (age, sex, tumor location, etc.) predict treatment responsiveness in this preclinical model will better enable researchers to identify glioblastoma patients most likely to benefit from checkpoint blockade immunotherapy moving forward.

PI3Kγ inhibition suppresses microglia/TAM accumulation in glioblastoma microenvironment to promote exceptional temozolomide response

Precision medicine in oncology leverages clinical observations of exceptional response. Toward an understanding of the molecular features that define this response, we applied an integrated, multiplatform analysis of RNA profiles derived from clinically annotated glioblastoma samples. This analysis suggested that specimens from exceptional responders are characterized by decreased accumulation of microglia/macrophages in the glioblastoma microenvironment. Glioblastoma-associated microglia/macrophages secreted interleukin 11 (IL11) to activate STAT3-MYC signaling in glioblastoma cells. This signaling induced stem cell states that confer enhanced tumorigenicity and resistance to the standard-of-care chemotherapy, temozolomide (TMZ). Targeting a myeloid cell restricted an isoform of phosphoinositide-3-kinase, phosphoinositide-3-kinase gamma isoform (PI3Kγ), by pharmacologic inhibition or genetic inactivation disrupted this signaling axis by reducing microglia/macrophage-associated IL11 secretion in the tumor microenvironment. Mirroring the clinical outcomes of exceptional responders, PI3Kγ inhibition synergistically enhanced the anti-neoplastic effects of TMZ in orthotopic murine glioblastoma models. Moreover, inhibition or genetic inactivation of PI3Kγ in murine glioblastoma models recapitulated expression profiles observed in clinical specimens isolated from exceptional responders. Our results suggest key contributions from tumor-associated microglia/macrophages in exceptional responses and highlight the translational potential for PI3Kγ inhibition as a glioblastoma therapy.

Immune Checkpoints in Pediatric Solid Tumors: Targetable Pathways for Advanced Therapeutic Purposes

The tumor microenvironment (TME) represents a complex network between tumor cells and a variety of components including immune, stromal and vascular endothelial cells as well as the extracellular matrix. A wide panel of signals and interactions here take place, resulting in a bi-directional modulation of cellular functions. Many stimuli, on one hand, induce tumor growth and the spread of metastatic cells and, on the other hand, contribute to the establishment of an immunosuppressive environment. The latter feature is achieved by soothing immune effector cells, mainly cytotoxic T lymphocytes and B and NK cells, and/or through expansion of regulatory cell populations, including regulatory T and B cells, tumor-associated macrophages and myeloid-derived suppressor cells. In this context, immune checkpoints (IC) are key players in the control of T cell activation and anti-cancer activities, leading to the inhibition of tumor cell lysis and of pro-inflammatory cytokine production. Thus, these pathways represent promising targets for the development of effective and innovative therapies both in adults and children. Here, we address the role of different cell populations homing the TME and of well-known and recently characterized IC in the context of pediatric solid tumors. We also discuss preclinical and clinical data available using IC inhibitors alone, in combination with each other or administered with standard therapies.

Radiotherapy, Temozolomide, and Antiprogrammed Cell Death Protein 1 Treatments Modulate the Immune Microenvironment in Experimental High-Grade Glioma

BACKGROUND

The lack of immune synergy with conventional chemoradiation could explain the failure of checkpoint inhibitors in current clinical trials for high-grade gliomas (HGGs).

OBJECTIVE

To analyze the impact of radiotherapy (RT), Temozolomide (TMZ) and antiprogrammed cell death protein 1 (αPD1) (as single or combined treatments) on the immune microenvironment of experimental HGGs.

METHODS

Mice harboring neurosphere /CT-2A HGGs received RT (4 Gy, single dose), TMZ (50 mg/kg, 4 doses) and αPD1 (100 μg, 3 doses) as monotherapies or combinations. The influence on survival, tumor volume, and tumor-infiltrating immune cells was analyzed.

RESULTS

RT increased total T cells (P = .0159) and cluster of differentiation (CD)8+ T cells (P = .0078) compared to TMZ. Lymphocyte subpopulations resulting from TMZ or αPD1 treatment were comparable with those of controls. RT reduced M2 tumor-associated macrophages/microglia (P = .0019) and monocytic myeloid derived suppressor cells (mMDSCs, P = .0003) compared to controls. The effect on mMDSC was also seen following TMZ and αPD1 treatment, although less pronounced (P = .0439 and P = .0538, respectively). Combining RT with TMZ reduced CD8+ T cells (P = .0145) compared to RT alone. Adding αPD1 partially mitigated this effect as shown by the increased CD8+ T cells/Tregs ratio, even if this result failed to reach statistical significance (P = .0973). Changing the combination sequence of RT, TMZ, and αPD1 did not alter survival nor the immune effects.

CONCLUSION

RT, TMZ, and αPD1 modify the immune microenvironment of HGG. The combination of RT with TMZ induces a strong immune suppression which cannot be effectively counteracted by αPD1.

Development of Immunotherapy Combination Strategies in Cancer

Harnessing the immune system to treat cancer through inhibitors of CTLA4 and PD-L1 has revolutionized the landscape of cancer. Rational combination strategies aim to enhance the antitumor effects of immunotherapies, but require a deep understanding of the mechanistic underpinnings of the immune system and robust preclinical and clinical drug development strategies. We review the current approved immunotherapy combinations, before discussing promising combinatorial approaches in clinical trials and detailing innovative preclinical model systems being used to develop rational combinations. We also discuss the promise of high-order immunotherapy combinations, as well as novel biomarker and combinatorial trial strategies. SIGNIFICANCE: Although immune-checkpoint inhibitors are approved as dual checkpoint strategies, and in combination with cytotoxic chemotherapy and angiogenesis inhibitors for multiple cancers, patient benefit remains limited. Innovative approaches are required to guide the development of novel immunotherapy combinations, ranging from improvements in preclinical tumor model systems to biomarker-driven trial strategies.

Tumor‐associated macrophages as treatment targets in glioma

Gliomas, the most common primary tumors in the central nervous system (CNS), can be categorized into 4 grades according to the World Health Organization. The most malignant glioma type is grade Ⅳ, also named glioblastoma multiforme (GBM). However, the standard treatment of concurrent temozolomide (TMZ) chemotherapy and radiotherapy after maximum resection does not improve overall survival in patients with GBM. Targeting components of the CNS microenvironment represents a new strategy for improving the efficacy of glioma treatment. Most recent studies focused on T cells. However, there is a growing body of evidence that tumor‐associated macrophages (TAMs) play an important role in tumor progression and can be regulated by a wide array of cytokines or chemokines. New TAM‐associated immunotherapies may improve clinical outcomes by blocking tumor progression and prolonging survival. However, understanding the exact roles and possible mechanisms of TAMs in the tumor environment is necessary for developing this promising therapeutic target and identifying potential diagnostic markers for improved prognosis. This review summarizes the possible interactions between TAMs and glioma progression and discusses the potential therapeutic directions for TAM‐associated immunotherapies.

Human gut microbial communities dictate efficacy of anti-PD-1 therapy in a humanized microbiome mouse model of glioma

Background

Although immunotherapy works well in glioblastoma (GBM) preclinical mouse models, the therapy has not demonstrated efficacy in humans. To address this anomaly, we developed a novel humanized microbiome (HuM) model to study the response to immunotherapy in a preclinical mouse model of GBM.

Methods

We used 5 healthy human donors for fecal transplantation of gnotobiotic mice. After the transplanted microbiomes stabilized, the mice were bred to generate 5 independent humanized mouse lines (HuM1-HuM5).

Results

Analysis of shotgun metagenomic sequencing data from fecal samples revealed a unique microbiome with significant differences in diversity and microbial composition among HuM1-HuM5 lines. All HuM mouse lines were susceptible to GBM transplantation, and exhibited similar median survival ranging from 19 to 26 days. Interestingly, we found that HuM lines responded differently to the immune checkpoint inhibitor anti-PD-1. Specifically, we demonstrate that HuM1, HuM4, and HuM5 mice are nonresponders to anti-PD-1, while HuM2 and HuM3 mice are responsive to anti-PD-1 and displayed significantly increased survival compared to isotype controls. Bray-Curtis cluster analysis of the 5 HuM gut microbial communities revealed that responders HuM2 and HuM3 were closely related, and detailed taxonomic comparison analysis revealed that Bacteroides cellulosilyticus was commonly found in HuM2 and HuM3 with high abundances.

Conclusions

The results of our study establish the utility of humanized microbiome mice as avatars to delineate features of the host interaction with gut microbial communities needed for effective immunotherapy against GBM.

Neoadjuvant Gene-Mediated Cytotoxic Immunotherapy for Non-Small-Cell Lung Cancer: Safety and Immunologic Activity

Gene-mediated cytotoxic immunotherapy (GMCI) is an immuno-oncology approach involving local delivery of a replication-deficient adenovirus expressing herpes simplex thymidine kinase (AdV-tk) followed by anti-herpetic prodrug activation that promotes immunogenic tumor cell death, antigen-presenting cell activation, and T cell stimulation. This phase I dose-escalation pilot trial assessed bronchoscopic delivery of AdV-tk in patients with suspected lung cancer who were candidates for surgery. A single intra-tumoral AdV-tk injection in three dose cohorts (maximum 1012 viral particles) was performed during diagnostic staging, followed by a 14-day course of the prodrug valacyclovir, and subsequent surgery 1 week later. Twelve patients participated after appropriate informed consent. Vector-related adverse events were minimal. Immune biomarkers were evaluated in tumor and blood before and after GMCI. Significantly increased infiltration of CD8+ T cells was found in resected tumors. Expression of activation, inhibitory, and proliferation markers, such as human leukocyte antigen (HLA)-DR, CD38, Ki67, PD-1, CD39, and CTLA-4, were significantly increased in both the tumor and peripheral CD8+ T cells. Thus, intratumoral AdV-tk injection into non-small-cell lung cancer (NSCLC) proved safe and feasible, and it effectively induced CD8+ T cell activation. These data provide a foundation for additional clinical trials of GMCI for lung cancer patients with potential benefit if combined with other immune therapies.

Zika virus oncolytic activity requires CD8+ T cells and is boosted by immune checkpoint blockade

Glioblastoma multiforme (GBM) is a fatal human cancer in part because GBM stem cells are resistant to therapy and recurrence is inevitable. Previously, we demonstrated Zika virus (ZIKV) targets GBM stem cells and prevents death of mice with gliomas. Here, we evaluated the immunological basis of ZIKV-mediated protection against GBM. Introduction of ZIKV into the brain tumor increased recruitment of CD8⁺ T and myeloid cells to the tumor microenvironment. CD8⁺ T cells were required for ZIKV-dependent tumor clearance because survival benefits were lost with CD8⁺ T cell depletion. Moreover, while anti–PD-1 antibody monotherapy moderately improved tumor survival, when coadministered with ZIKV, survival increased. ZIKV-mediated tumor clearance also resulted in durable protection against syngeneic tumor rechallenge, which also depended on CD8⁺ T cells. To address safety concerns, we generated an immune-sensitized ZIKV strain, which was effective alone or in combination with immunotherapy. Thus, oncolytic ZIKV treatment can be leveraged by immunotherapies, which may prompt combination treatment paradigms for adult patients with GBM.

Regulation of tumor immune suppression and cancer cell survival by CXCL1/2 elevation in glioblastoma multiforme

The invasiveness and high immune suppression of glioblastoma multiforme (GBM) produce poor survival of afflicted patients. Unfortunately, in the past decades, no therapeutic approach has remarkably improved the survival time of patients with GBM. Our analysis of the TCGA database and brain tumor tissue arrays indicated that CXCL1 and CXCL2 overexpression is closely associated with GBM's aggressiveness. Our results showed that elevation of CXCL1 or CXCL2 facilitated myeloid cell migration and simultaneously disrupted CD8⁺ T cell accumulation at tumor sites, causing accelerated tumor progression. Yet, blockade of CXCL1/2 significantly prevented myeloid-derived suppressor cell migration and thereby increased CD8⁺ T cell accumulation in vitro and in vivo. CXCL1/2 also promoted the paracrine factor S100A9 and further activated Erk1/2 and p70S60k, whereas blocking CXCL1/2 down-regulated these prosurvival factors. The combination of targeting CXCL1/2 and standard temozolomide chemotherapy improved upon the antitumor efficacy of chemotherapy alone, extending the overall survival time in GBM.

Immunocompetent Mouse Models in the Search for Effective Immunotherapy in Glioblastoma

Glioblastoma (GBM) is the most aggressive intrinsic brain tumor in adults. Despite maximal therapy consisting of surgery and radio/chemotherapy, GBM remains largely incurable with a median survival of less than 15 months. GBM has a strong immunosuppressive nature with a multitude of tumor and microenvironment (TME) derived factors that prohibit an effective immune response. To date, all clinical trials failed to provide lasting clinical efficacy, despite the relatively high success rates of preclinical studies to show effectivity of immunotherapy. Various factors may explain this discrepancy, including the inability of a single mouse model to fully recapitulate the complexity and heterogeneity of GBM. It is therefore critical to understand the features and limitations of each model, which should probably be combined to grab the full spectrum of the disease. In this review, we summarize the available knowledge concerning immune composition, stem cell characteristics and response to standard-of-care and immunotherapeutics for the most commonly available immunocompetent mouse models of GBM.

Effects of oncolytic viruses and viral vectors on immunity in glioblastoma

Glioblastoma (GBM) is regarded as an incurable disease due to its poor prognosis and limited treatment options. Virotherapies were once utilized on cancers for their oncolytic effects. And they are being revived on GBM treatment, as accumulating evidence presents the immunogenic effects of virotherapies in remodeling immunosuppressive GBM microenvironment. In this review, we focus on the immune responses induced by oncolytic virotherapies and viral vectors in GBM. The current developments of GBM virotherapies are briefly summarized, followed by a detailed depiction of their immune response. Limitations and lessons inferred from earlier experiments and trials are discussed. Moreover, we highlight the importance of engaging the immune responses induced by virotherapies into the multidisciplinary management of GBM.

Combination of rAd-p53 in situ gene therapy and anti-PD-1 antibody immunotherapy induced anti-tumor activity in mouse syngeneic urogenital cancer models

In this study we undertook a novel combination therapy using rAd-p53 in situ gene therapy and immunotherapy with immune checkpoint inhibitor (ICI) anti-PD-1 antibody for urogenital cancers. Three mouse syngeneic tumor cell lines, TRAMP-C2 (prostate cancer derived from C57BL/6 mice), MBT-2 (bladder cancer derived from C3H mice) and Renca (kidney cancer derived from BALB/c mice) were used in this study. The highest coxsackie and adenovirus receptor (CAR) mRNA expression was observed in TRAMP-C2 cells, followed by Renca and then MBT-2 cells. Consistent with the CAR expressions, rAd-p53 at 160 multiplicity of infection (MOI) significantly inhibited the cell proliferation of TRAMP-C2 and Renca cells, but not MBT-2 cells. In in vivo experiments, the combination of intratumoral injections of rAd-p53 (1 × 10⁹ plaque-forming units) every other day and intraperitoneal injections of anti-mouse PD-1 antibody (200 μg) twice a week suppressed tumor growth and prolonged survival compared to rAd-p53 or anti-PD-1 antibody monotherapy in both the TRAMP-C2 and Renca models. Our results encourage the clinical development of combination therapy comprised of in situ gene therapy with rAd-p53 and immunotherapy with an ICI anti-PD-1 antibody for urogenital cancers.

Nanomedicine-based immunotherapy for central nervous system disorders

Central nervous system (CNS) disorders represent a broad spectrum of brain ailments with short- and long-term disabilities, and nanomedicine-based approaches provide a new therapeutic approach to treating CNS disorders. A variety of potential drugs have been discovered to treat several neuronal disorders; however, their therapeutic success can be limited by the presence of the blood-brain barrier (BBB). Furthermore, unique immune functions within the CNS provide novel target mechanisms for the amelioration of CNS diseases. Recently, various therapeutic approaches have been applied to fight brain-related disorders, with moderate outcomes. Among the various therapeutic strategies, nanomedicine-based immunotherapeutic systems represent a new era that can deliver useful cargo with promising pharmacokinetics. These approaches exploit the molecular and cellular targeting of CNS disorders for enhanced safety, efficacy, and specificity. In this review, we focus on the efficacy of nanomedicines that utilize immunotherapy to combat CNS disorders. Furthermore, we detailed summarize nanomedicine-based pathways for CNS ailments that aim to deliver drugs across the BBB by mimicking innate immune actions.

Modulation of temozolomide dose differentially affects T-cell response to immune checkpoint inhibition

BACKGROUND

The changes induced in host immunity and the tumor microenvironment by chemotherapy have been shown to impact immunotherapy response in both a positive and a negative fashion. Temozolomide is the most common chemotherapy used to treat glioblastoma (GBM) and has been shown to have variable effects on immune response to immunotherapy. Therefore, we aimed to determine the immune modulatory effects of temozolomide that would impact response to immune checkpoint inhibition in the treatment of experimental GBM.

METHODS

Immune function and antitumor efficacy of immune checkpoint inhibition were tested after treatment with metronomic dose (MD) temozolomide (25 mg/kg × 10 days) or standard dose (SD) temozolomide (50 mg/kg × 5 days) in the GL261 and KR158 murine glioma models.

RESULTS

SD temozolomide treatment resulted in an upregulation of markers of T-cell exhaustion such as LAG-3 and TIM-3 in lymphocytes which was not seen with MD temozolomide. When temozolomide treatment was combined with programmed cell death 1 (PD-1) antibody therapy, the MD temozolomide/PD-1 antibody group demonstrated a decrease in exhaustion markers in tumor infiltrating lymphocytes that was not observed in the SD temozolomide/PD-1 antibody group. Also, the survival advantage of PD-1 antibody therapy in a murine syngeneic intracranial glioma model was abrogated by adding SD temozolomide to treatment. However, when MD temozolomide was added to PD-1 inhibition, it preserved the survival benefit that was seen by PD-1 antibody therapy alone.

CONCLUSION

The peripheral and intratumoral immune microenvironments are distinctively affected by dose modulation of temozolomide.

Tumor Interferon Signaling Is Regulated by a lncRNA INCR1 Transcribed from the PD-L1 Locus

Tumor interferon (IFN) signaling promotes PD-L1 expression to suppress T cell-mediated immunosurveillance. We identify the IFN-stimulated non-coding RNA 1 (INCR1) as a long noncoding RNA (lncRNA) transcribed from the PD-L1 locus and show that INCR1 controls IFNγ signaling in multiple tumor types. Silencing INCR1 decreases the expression of PD-L1, JAK2, and several other IFNγ-stimulated genes. INCR1 knockdown sensitizes tumor cells to cytotoxic T cell-mediated killing, improving CAR T cell therapy. We discover that PD-L1 and JAK2 transcripts are negatively regulated by binding to HNRNPH1, a nuclear ribonucleoprotein. The primary transcript of INCR1 binds HNRNPH1 to block its inhibitory effects on the neighboring genes PD-L1 and JAK2, enabling their expression. These findings introduce a mechanism of tumor IFNγ signaling regulation mediated by the lncRNA INCR1 and suggest a therapeutic target for cancer immunotherapy.

Combination therapy with oncolytic viruses and immune checkpoint inhibitors

Introduction: Immune checkpoint inhibitors (ICI) have dramatically improved the outcome for cancer patients across multiple tumor types. However the response rates to ICI monotherapy remain relatively low, in part due to some tumors cultivating an inherently 'cold' immune microenvironment. Oncolytic viruses (OV) have the capability to promote a 'hotter' immune microenvironment which can improve the efficacy of ICI.Areas covered: In this article we conducted a literature search through Pubmed/Medline to identify relevant articles in both the pre-clinical and clinical settings for combining OVs with ICIs and discuss the impact of this approach on treatment as well as changes within the tumor microenvironment. We also explore the future directions of this novel combination strategy.Expert opinion: The imminent results of the Phase 3 study combining pembrolizumab with or without T-Vec injection are eagerly awaited. OV/ICI combinations remain one of the most promising avenues to explore in the success of cancer immunotherapy.

Fractalkine/CX3CL1 in Neoplastic Processes

Fractalkine/CX3C chemokine ligand 1 (CX3CL1) is a chemokine involved in the anticancer function of lymphocytes-mainly NK cells, T cells and dendritic cells. Its increased levels in tumors improve the prognosis for cancer patients, although it is also associated with a poorer prognosis in some types of cancers, such as pancreatic ductal adenocarcinoma. This work focuses on the 'hallmarks of cancer' involving CX3CL1 and its receptor CX3CR1. First, we describe signal transduction from CX3CR1 and the role of epidermal growth factor receptor (EGFR) in this process. Next, we present the role of CX3CL1 in the context of cancer, with the focus on angiogenesis, apoptosis resistance and migration and invasion of cancer cells. In particular, we discuss perineural invasion, spinal metastasis and bone metastasis of cancers such as breast cancer, pancreatic cancer and prostate cancer. We extensively discuss the importance of CX3CL1 in the interaction with different cells in the tumor niche: tumor-associated macrophages (TAM), myeloid-derived suppressor cells (MDSC) and microglia. We present the role of CX3CL1 in the development of active human cytomegalovirus (HCMV) infection in glioblastoma multiforme (GBM) brain tumors. Finally, we discuss the possible use of CX3CL1 in immunotherapy.

Phase I study of gene-mediated cytotoxic immunotherapy with AdV-tk as adjuvant to surgery and radiation for pediatric malignant glioma and recurrent ependymoma

BACKGROUND

Gene-mediated cytotoxic immunotherapy (GMCI) is a tumor-specific immune stimulatory strategy implemented through local delivery of aglatimagene besadenovec (AdV-tk) followed by anti-herpetic prodrug. GMCI induces T-cell dependent tumor immunity and synergizes with radiotherapy. Clinical trials in adult malignant gliomas demonstrated safety and potential efficacy. This is the first trial of GMCI in pediatric brain tumors.

METHODS

This phase I dose escalation study was conducted to evaluate GMCI in patients 3 years of age or older with malignant glioma or recurrent ependymoma. AdV-tk at doses of 1 × 1011 and 3 × 1011 vector particles (vp) was injected into the tumor bed at the time of surgery followed by 14 days of valacyclovir. Radiation started within 8 days of surgery, and if indicated, chemotherapy began after completion of valacyclovir.

RESULTS

Eight patients (6 glioblastoma, 1 anaplastic astrocytoma, 1 recurrent ependymoma) were enrolled and completed therapy: 3 on dose level 1 and 5 on dose level 2. Median age was 12.5 years (range 7-17) and Lansky/Karnofsky performance scores were 60-100. Five patients had multifocal/extensive tumors that could not be resected completely and 3 had gross total resection. There were no dose-limiting toxicities. The most common possibly GMCI-related adverse events included Common Terminology Criteria for Adverse Events grade 1-2 fever, fatigue, and nausea/vomiting. Three patients, in dose level 2, lived more than 24 months, with 2 alive without progression 37.3 and 47.7 months after AdV-tk injection.

CONCLUSIONS

GMCI can be safely combined with radiation therapy with or without temozolomide in pediatric patients with brain tumors and the present results strongly support further investigation.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov NCT00634231.

Modeling Oncolytic Viral Therapy, Immune Checkpoint Inhibition, and the Complex Dynamics of Innate and Adaptive Immunity in Glioblastoma Treatment

Oncolytic viruses are of growing interest to cancer researchers and clinicians, due to their selectivity for tumor cells over healthy cells and their immunostimulatory properties. The immune response to an oncolytic virus plays a critical role in treatment efficacy. However, uncertainty remains regarding the circumstances under which the immune system either assists in eliminating tumor cells or inhibits treatment via rapid viral clearance, leading to the cessation of the immune response. In this work, we develop an ordinary differential equation model of treatment for a lethal brain tumor, glioblastoma, using an oncolytic Herpes Simplex Virus. We use a mechanistic approach to model the interactions between distinct populations of immune cells, incorporating both innate and adaptive immune responses to oncolytic viral therapy (OVT), and including a mechanism of adaptive immune suppression via the PD-1/PD-L1 checkpoint pathway. We focus on the tradeoff between viral clearance by innate immune cells and the innate immune cell-mediated recruitment of antiviral and antitumor adaptive immune cells. Our model suggests that when a tumor is treated with OVT alone, the innate immune cells' ability to clear the virus quickly after administration has a much larger impact on the treatment outcome than the adaptive immune cells' antitumor activity. Even in a highly antigenic tumor with a strong innate immune response, the faster recruitment of antitumor adaptive immune cells is not sufficient to offset the rapid viral clearance. This motivates our subsequent incorporation of an immunotherapy that inhibits the PD-1/PD-L1 checkpoint pathway by blocking PD-1, which we combine with OVT within the model. The combination therapy is most effective for a highly antigenic tumor or for intermediate levels of innate immune localization. Extreme levels of innate immune cell activity either clear the virus too quickly or fail to activate a sufficiently strong adaptive response, yielding ineffective combination therapy of GBM. Hence, we show that the innate and adaptive immune interactions significantly influence treatment response and that combining OVT with an immune checkpoint inhibitor expands the range of immune conditions that allow for tumor size reduction or clearance.

Oncolytic Viruses: Priming Time for Cancer Immunotherapy

New immuno-oncology therapies are improving cancer treatments beyond the former standard of care, as evidenced by the recent and continuing clinical approvals for immunotherapies in a broad range of indications. However, a majority of patients (particularly those with immunologically cold tumors) still do not benefit, highlighting the need for rational combination approaches. Oncolytic viruses (OV) both directly kill tumor cells and inflame the tumor microenvironment. While OV spread can be limited by the generation of antiviral immune responses, the initial local tumor cell killing can reverse the immunosuppressive tumor microenvironment, resulting in more effective release of tumor-associated antigens (TAAs), cross-presentation, and antitumoral effector T cell recruitment. Moreover, many OVs can be engineered to express immunomodulatory genes. Rational combination approaches to cancer immunotherapy include the use of OVs in combination with immune checkpoint inhibitors (ICIs) or adoptive T cell therapy (ACT) to promote sustained antitumoral immune responses. OV combinations have additive or synergistic efficacy in preclinical tumor models with ICIs or ACT. Several preclinical studies have confirmed systemic reactivation and proliferation of adoptively transferred antitumoral T cells in conjunction with oncolytic OVs (expressing cytokines or TAAs) resulting from the specific tumor cell killing and immunostimulation of the tumor microenvironment which leads to increased tumor trafficking, activity, and survival. Recent clinical trials combining OVs with ICIs have shown additive effects in melanoma. Additional clinical data in an expanded range of patient indications are eagerly awaited. The relative timings of OV and ICI combination remains under-studied and is an area for continued exploration. Studies systematically exploring the effects of systemic ICIs prior to, concomitantly with, or following OV therapy will aid in the future design of clinical trials to enhance efficacy and increase patient response rates.

Combined-therapeutic strategies synergistically potentiate glioblastoma multiforme treatment via nanotechnology

Glioblastoma multiforme (GBM) is a highly aggressive and devastating brain tumor characterized by poor prognosis and high rates of recurrence. Numerous therapeutic strategies and delivery systems are developed to prolong the survival time. They exhibit enhanced therapeutic effects in animal models, whereas few of them is applied in clinical trials. Taking into account the drug-resistance and high recurrence of GBM, combined-therapeutic strategies are exploited to maximize therapeutic efficacy. The combined therapies demonstrate superior results than those of single therapies against GBM. The co-therapeutic agents, the timing of therapeutic strategies and the delivery systems greatly affect the overall outcomes. Herein, the current advances in combined therapies for glioblastoma via systemic administration are exhibited in this review. And we will discuss the pros and cons of these combined-therapeutic strategies via nanotechnology, and provide the guidance for developing rational delivery systems to optimize treatments against GBM and other malignancies in central nervous system.

Suicide gene therapy for the treatment of high-grade glioma: past lessons, present trends, and future prospects

Suicide gene therapy has represented an experimental cancer treatment modality for nearly 40 years. Among the various cancers experimentally treated by suicide gene therapy, high-grade gliomas have been the most prominent both in preclinical and clinical settings. Failure of a number of promising suicide gene therapy strategies in the clinic pointed toward a bleak future of this approach for the treatment of high-grade gliomas. Nevertheless, the development of new vectors and suicide genes, better prodrugs, more efficient delivery systems, and new combinatorial strategies represent active research areas that may eventually lead to better efficacy of suicide gene therapy. These trends are evident by the current increasing focus on suicide gene therapy for high-grade glioma treatment both in the laboratory and in the clinic. In this review, we give an overview of different suicide gene therapy approaches for glioma treatment and discuss clinical trials, delivery issues, and immune responses.

Functional Change of Effector Tumor-Infiltrating CCR5+CD38+HLA-DR+CD8+ T Cells in Glioma Microenvironment

Human glioma facilitates an impaired anti-tumor immunity response, including defects in circulation of T lymphocytes. The level of CD8⁺ T-cell activation acts as an immune regulator associated with disease progression. However, little is known about the characteristics of peripheral and tumor-infiltrating CD8⁺ T cells in patients with glioma. In this study, we examined the level of CD8⁺ T-cell activation in a group of 143 patients with glioma and determined that peripheral CD3⁺ T cells decreased in accordance with disease severity. The patients' peripheral CD8⁺ T-cell populations were similar to that of healthy donors, and a small amount of CD8⁺ tumor-infiltrating lymphocytes was identified in glioma tissues. An increase in activated CD8⁺ T cells, characterized as CD38⁺HLA-DR⁺, and their association with disease progression were identified in the patients' peripheral blood and glioma, and shown to display enriched CCR5⁺ and TNFR2⁺ expression levels. Ex vivo examination of CD38⁺HLA-DR⁺CD8⁺ T cells indicated that this subset of cells displayed stronger secretion of IFN-γ and IL-2 before and after a 6-h stimulation with phorbol 12-myristate 13-acetate (PMA) and ionomycin (ION) relative to healthy CD38⁺HLA-DR⁺CD8⁺ T cells, indicating the functional feasibility of CD38⁺HLA-DR⁺CD8⁺ T cells. Higher CCL5 protein and mRNA levels were identified in glioma tissues, which was consistent with the immunohistochemistry results revealing both CCL5 and CD38⁺HLA-DR⁺CD8⁺ T cell expression. Patients' CCR5⁺CD38⁺HLA-DR⁺CD8⁺ T cells were further validated and shown to display increases in CD45RA⁺CCR7^- and T-bet⁺ accompanied by substantial CD107-a, IFN-γ, and Granzyme B levels in response to glioma cells.

Oncolytic adenoviruses: a game changer approach in the battle between cancer and the immune system

INTRODUCTION

Oncolytic adenoviruses are among the most studied oncolytic viruses because of their tumor selectivity, safety, and transgene-delivery capability. With a growing number of different immunotherapies against cancer, the extraordinary immunogenicity of the adenovirus has emerged as a differentiating strength. Enabling T-cell related therapies with oncolytic adenoviruses appears a promising approach due to its inherent ability to elicit responses from the adaptive immune compartment.

AREAS COVERED

These viruses have successfully enhanced both adoptive T-cell therapies and immune-checkpoint therapies. Oncolytic viruses induce several effects at the tumor and on the systemic level that help to circumvent current limitations of T-cells and related therapies, such as T-cell trafficking, tumor immune suppressivity and antigen spreading

EXPERT OPINION

Taking into account the multitude of possibilities of treating cancer with immunotherapies, learning to optimize the combinations and administration strategies of these drugs, could lead to durable responses in patients with currently incurable cancers.

Updates on Oncolytic Virus Immunotherapy for Cancers

The 2018 annual Cambridge Healthtech Institute's International Immuno-Oncology Summit in Boston, MA convened late August, and academic and industry researchers were allowed to debate and discuss oncolytic virology during the virus immunotherapy portion of the conference. The breakthrough agent, TVEC/IMLYGIC, as well as most other oncolytic viruses (OVs) in clinical trials, are demonstrating an immense synergy with T cell checkpoint inhibitors. To this extent, the marriage of T cell checkpoint inhibitors and OV is now vastly accepted, indicating the next phase in OVs is the recruitment of the immune system, and tailoring the immune response toward tumor clearance is a far better strategy than directly lysing the tumor outright with virus. The next field-shaping question for OVs is how to convert a patient's immune response against their tumor. The talks this year focused on whether OVs can cause the emergence of a strong anti-tumor immunity intrinsically or whether vectors, which educate the immune system to detect tumor antigens, were more efficacious. Speakers presented novel transgenes to arm OVs and systems biology approaches to discover the best viral backbones to engineer into vectors. Here we summarize the meeting's keynote talks, thematic principles running through the summit, and current developments in the OV field.

Measles Virus-Based Treatments Trigger a Pro-inflammatory Cascade and a Distinctive Immunopeptidome in Glioblastoma

Glioblastoma is an aggressive primary brain tumor with bad prognosis. On the other hand, oncolytic measles virus (MeV) therapy is an experimental glioma treatment strategy with clinical safety and first evidence of anti-tumoral efficacy. Therefore, we investigated the combination of MeV with conventional therapies by cytotoxic survival assays in long-term glioma cell lines LN229, LNZ308, and glioma stem-like GS8 cells, as well as the basal viral infectivity in primary glioblastoma cultures T81/16, T1094/17, and T708/16. We employed Chou-Talalay analysis to identify the synergistic treatment sequence chemotherapy, virotherapy, and finally radiotherapy (CT-VT-RT). RNA sequencing and immunopeptidome analyses were used to delineate treatment-induced molecular and immunological profiles. CT-VT-RT displayed synergistic anti-glioma activity and initiated a type 1 interferon response, along with canonical Janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling, and downstream interferon-stimulated genes were induced, resulting in apoptotic cascades. Furthermore, antigen presentation along with immunostimulatory chemokines was increased in CT-VT-RT-treated glioma cells, indicating a treatment-induced pro-inflammatory phenotype. We identified novel treatment-induced viral and tumor-associated peptides through HLA ligandome analysis. Our data delineate an actionable treatment-induced molecular and immunological signature of CT-VT-RT, and they could be exploited for the design of novel tailored treatment strategies involving virotherapy and immunotherapy.

Glioblastoma Treatments: An Account of Recent Industrial Developments

The different drugs and medical devices, which are commercialized or under industrial development for glioblastoma treatment, are reviewed. Their different modes of action are analyzed with a distinction being made between the effects of radiation, the targeting of specific parts of glioma cells, and immunotherapy. Most of them are still at a too early stage of development to firmly conclude about their efficacy. Optune, which triggers antitumor activity by blocking the mitosis of glioma cells under the application of an alternating electric field, seems to be the only recently developed therapy with some efficacy reported on a large number of GBM patients. The need for early GBM diagnosis is emphasized since it could enable the treatment of GBM tumors of small sizes, possibly easier to eradicate than larger tumors. Ways to improve clinical protocols by strengthening preclinical studies using of a broader range of different animal and tumor models are also underlined. Issues related with efficient drug delivery and crossing of blood brain barrier are discussed. Finally societal and economic aspects are described with a presentation of the orphan drug status that can accelerate the development of GBM therapies, patents protecting various GBM treatments, the different actors tackling GBM disease, the cost of GBM treatments, GBM market figures, and a financial analysis of the different companies involved in the development of GBM therapies.

Oncolytic virus and PD-1/PD-L1 blockade combination therapy

Oncolytic viruses are lytic for many types of cancers but are attenuated or replication-defective in normal tissues. Aside from tumor lysis, oncolytic viruses can induce host immune responses against cancer cells and may thus be viewed as a form of immunotherapy. Although recent successes with checkpoint inhibitors have shown that enhancing antitumor immunity can be effective, the dynamic nature of the immunosuppressive tumor microenvironment presents significant hurdles to the broader application of these therapies. Targeting one immune-suppressive pathway may not be sufficient to eliminate tumors. Here we focus on the development of the combination of oncolytic virotherapy with checkpoint inhibitors designed to target the programmed cell death protein 1 and programmed cell death ligand 1 signaling axis. We also discuss future directions for the clinical application of this novel combination therapy.

Quo Vadis-Do Immunotherapies Have a Role in Glioblastoma?

PURPOSE OF REVIEW

More effective therapies for glioblastoma are urgently needed. Immunotherapeutic strategies appear particularly promising and are therefore intensively studied. This article reviews the current understanding of the immunosuppressive glioblastoma microenvironment, discusses the rationale behind various immunotherapies, and outlines the findings of several recently published clinical studies.

RECENT FINDINGS

The results of CheckMate-143 indicated that nivolumab is not superior to bevacizumab in patients with recurrent glioblastoma. A first-in man exploratory study evaluating EGFRvIII-specific CAR T cells for patients with newly diagnosed glioblastoma demonstrated overall safety of CAR T cell therapy and effective target recognition. A pilot study evaluating treatment with adoptively transferred CMV-specific T cells combined with a CMV-specific DC vaccine was found to be safe and resulted in increased polyclonality of CMV-specific T cells in vivo. Despite the success of immunotherapies in many cancers, clinical evidence supporting their efficacy for patients with glioblastoma is still lacking. Nevertheless, the recently published studies provide important proof-of-concept in several areas of immunotherapy research. The careful and critical interpretation of these results will enhance our understanding of the opportunities and challenges of immunotherapies for high-grade gliomas and improve the immunotherapeutic strategies investigated in future clinical trials.