Dendritic cell vaccine trials in gliomas: Untangling the lines

Glioblastoma is a deadly brain tumor without any significantly successful treatments to date. Tumor antigen-targeted immunotherapy platforms including peptide and dendritic cell (DC) vaccines, have extended survival in hematologic malignancies. The relatively "cold" tumor immune microenvironment and heterogenous nature of glioblastoma have proven to be major limitations to translational application and efficacy of DC vaccines. Furthermore, many DC vaccine trials in glioblastoma are difficult to interpret due to a lack of contemporaneous controls, absence of any control comparison, or inconsistent patient populations. Here we review glioblastoma immunobiology aspects that are relevant to DC vaccines, review the clinical experience with DC vaccines targeting glioblastoma, discuss challenges in clinical trial design, and summarize conclusions and directions for future research for the development of effective DC vaccines for patients.

Reproducibility of outcomes in sequential trials using CMV-targeted dendritic cell vaccination for glioblastoma

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Background: Vaccination with dendritic cells (DCs) fares poorly in primary and recurrent glioblastoma (GBM). Moreover, GBM vaccine trials are often underpowered due to limited sample size. Methods: To address these limitations, we conducted three sequential clinical trials utilizing Cytomegalovirus (CMV)-specific DC vaccines in patients with newly diagnosed GBM eligible to receive standard of care resection and adjuvant radiation therapy and temozolomide chemotherapy. Autologous DCs were generated and electroporated with mRNA encoding for the CMV protein pp65. Serial vaccination was given throughout adjuvant temozolomide cycles, and 111Indium radiolabeling was implemented to assess migration efficiency of DC vaccines. Patients were followed for median overall survival (mOS) and OS. Results: Our initial study was the phase II ATTAC study (NCT00639639; total n = 12) with 6 patients randomized to vaccine site preconditioning with tetanus-diphtheria (Td) toxoid. This led to an expanded cohort trial (ATTAC-GM; NCT00639639) of 11 patients receiving CMV DC vaccines containing granulocyte-macrophage colony-stimulating factor (GM-CSF). Follow-up data from ATTAC and ATTAC-GM revealed 5-year OS rates of 33.3% (mOS 38.3 months; CI95 17.5-undefined) and 36.4% (mOS 37.7 months; CI95 18.2-109.1), respectively. ATTAC additionally revealed a significant increase in DC migration to draining lymph nodes following Td preconditioning ( P = 0.049). Increased DC migration was associated with OS (Cox proportional hazards model, HR = 0.820, P = 0.023). Td-mediated increased migration has been recapitulated in our larger confirmatory trial ELEVATE (NCT02366728) of 43 patients randomized to preconditioning (Wilcoxon rank sum, Td n = 24, unpulsed DC n = 19; 24h, P = 0.031 and 48h, P = 0.0195). In ELEVATE, median follow-up of 42.2 months revealed significantly longer OS in patients randomized to Td ( P = 0.026). The 3-year OS for Td-treated patients in ELEVATE was 34% (CI95 19-63%) compared to 6% given unpulsed DCs (CI95 1-42%). Conclusions: We report reproducibility of our findings across three sequential clinical trials using CMV pp65 DCs. Despite their small numbers, these successive trials demonstrate consistent survival outcomes, thus supporting the efficacy of CMV DC vaccine therapy in GBM. Clinical trial information: NCT00639639, NCT02366728.

Resolution of radiation necrosis with bevacizumab following radiation therapy for primary CNS lymphoma

IMPORTANCE

Radiation necrosis (RN) is a rare but serious adverse effect following treatment with radiation therapy. No standard of care exists for the management of RN, and efforts to prevent and treat RN are limited by a lack of insight into the pathomechanics and molecular drivers of RN. This case series describes the outcomes of treatment with bevacizumab (BV) in two primary CNS lymphoma (PCNSL) patients who developed symptomatic biopsy-proven RN after whole brain radiation (WBRT) with a stereotactic radiosurgery (SRS) boost.

OBSERVATIONS

Patient 1 is a 52 year-old female with PCNSL treated with WBRT followed by an SRS boost. She developed symptomatic biopsy-proven RN, and initial treatment with tocopherol and pentoxifylline was unsuccessful. A 100% clinical and radiographic response was achieved with 4 cycles of BV. Patient 2, a 48 year-old male with PCNSL, presented with seizures and biopsy-proven RN after radiation therapy. Initial empiric treatment with tocopherol and pentoxifylline was unsuccessful. A 100% clinical and radiographic response was achieved with 3 cycles of BV.

CONCLUSIONS AND RELEVANCE

Monitoring for RN in patients with PCNSL treated with radiation therapy is warranted. BV is an efficacious treatment and a viable alternative to corticosteroids or surgical intervention.

Designing Clinical Trials for Combination Immunotherapy: A Framework for Glioblastoma

Immunotherapy has revolutionized treatment for many hard-to-treat cancers but has yet to produce significant improvement in outcomes for patients with glioblastoma. This reflects the multiple and unique mechanisms of immune evasion and escape in this highly heterogeneous tumor. Glioblastoma engenders profound local and systemic immunosuppression and is remarkably effective at inducing T-cell dysfunction, posing a challenge to any immunotherapy-based approach. To overcome these mechanisms, multiple disparate modes of immune-oriented therapy will be required. However, designing trials that can evaluate these combinatorial approaches requires careful consideration. In this review, we explore the immunotherapy resistance mechanisms that have been encountered to date and how combinatorial approaches may address these. We also describe the unique aspects of trial design in both preclinical and clinical settings and consider endpoints and markers of response best suited for an intervention involving multiple agents.

Generation of Tumor Targeted Dendritic Cell Vaccines with Improved Immunogenic and Migratory Phenotype

Our group has employed methodologies for effective ex vivo generation of dendritic cell (DC) vaccines for patients with primary malignant brain tumors. In order to reliably produce the most potent, most representational vaccinated DC that will engender an antitumor response requires the ability to orchestrate multiple methodologies that address antigen cross-presentation, T-cell costimulation and polarization, and migratory capacity. In this chapter, we describe a novel method for augmenting the immunogenicity and migratory potential of DCs for their use as vaccines. We have elucidated methodologies to avoid the phenomenon known as immunodominance in generating cancer vaccines. We have found that culturing DC progenitors in serum-free conditions for the duration of the differentiation protocol results in a more homogeneously mature population of DCs that exhibit enhanced immunogenicity compared to DCs generated in serum-containing culture conditions. Furthermore, we demonstrate our method for generating high mobility DCs that readily migrate toward lymphoid organ chemoattractants using CCL3 protein. The combination of these two approaches represents a facile and clinically tractable methodology for generating highly mature DCs with excellent migratory capacity.

Once, Twice, Three Times a Finding: Reproducibility of Dendritic Cell Vaccine Trials Targeting Cytomegalovirus in Glioblastoma

Despite standard of care for glioblastoma, including gross total resection, high-dose radiation, and dose-limited chemotherapy, this tumor remains one of the most aggressive and therapeutically challenging. The relatively small number of patients with this diagnosis compared with more common solid tumors in clinical trials commits new glioblastoma therapies to testing in small, underpowered, nonrandomized settings. Among approximately 200 registered glioblastoma trials identified between 2005 and 2015, nearly half were single-arm studies with sample sizes not exceeding 50 patients. These constraints have made demonstrating efficacy for novel therapies difficult in glioblastoma and other rare and aggressive cancers. Novel immunotherapies for glioblastoma such as vaccination with dendritic cells (DC) have yielded mixed results in clinical trials. To address limited numbers, we sequentially conducted three separate clinical trials utilizing cytomegalovirus (CMV)-specific DC vaccines in patients with newly diagnosed glioblastoma whereby each follow-up study had nearly doubled in sample size. Follow-up data from the first blinded, randomized phase II clinical trial (NCT00639639) revealed that nearly one third of this cohort is without tumor recurrence at 5 years from diagnosis. A second clinical trial (NCT00639639) resulted in a 36% survival rate at 5 years from diagnosis. Results of the first two-arm trial (NCT00639639) showed increased migration of the DC vaccine to draining lymph nodes, and this increased migration has been recapitulated in our larger confirmatory clinical study (NCT02366728). We have now observed that nearly one third of the glioblastoma study patient population receiving CMV-specific DC vaccines results in exceptional long-term survivors.

Antigen-loaded monocyte administration induces potent therapeutic antitumor T cell responses

Efficacy of dendritic cell (DC) cancer vaccines is classically thought to depend on their antigen-presenting cell (APC) activity. Studies show, however, that DC vaccine priming of cytotoxic T lymphocytes (CTLs) requires the activity of endogenous DCs, suggesting that exogenous DCs stimulate antitumor immunity by transferring antigens (Ags) to endogenous DCs. Such Ag transfer functions are most commonly ascribed to monocytes, implying that undifferentiated monocytes would function equally well as a vaccine modality and need not be differentiated to DCs to be effective. Here, we used several murine cancer models to test the antitumor efficacy of undifferentiated monocytes loaded with protein or peptide Ag. Intravenously injected monocytes displayed antitumor activity superior to DC vaccines in several cancer models, including aggressive intracranial glioblastoma. Ag-loaded monocytes induced robust CTL responses via Ag transfer to splenic CD8+ DCs in a manner independent of monocyte APC activity. Ag transfer required cell-cell contact and the formation of connexin 43-containing gap junctions between monocytes and DCs. These findings demonstrate the existence of an efficient gap junction-mediated Ag transfer pathway between monocytes and CD8+ DCs and suggest that administration of tumor Ag-loaded undifferentiated monocytes may serve as a simple and efficacious immunotherapy for the treatment of human cancers.

Abstract A80: The effects of CCL3 on dendritic cell migration and immune cell activation

Glioblastoma (GBM) remains uniformly lethal and current therapy is ineffective and incapacitating. Standard therapies are limited by nonspecific toxicity, and the median overall survival for patients with GBM remains <15 months. Immunotherapy for GBM holds significant promise, as substantial evidence suggests that T cells can eradicate large, well-established tumors in mice and humans. Dendritic cell (DC) vaccines can, in some cases, effectively stimulate such T-cell responses as shown by several remarkable cases of individual patient responders. However, overall objective responses in early-phase clinical trials with tumor-targeted DC vaccination have remained under 15%. In a recent study in patients with newly diagnosed GBM published in Nature, we demonstrated that unilaterally preconditioning one vaccine site with the inflammatory recall antigens Tetanus/diphtheria toxoid (Td) resulted in increased bilateral DC migration to the draining lymph nodes and a significant increase in progression-free survival and overall survival—with half of the Td-treated patients living past 4.5 years. The benefit of vaccine site preconditioning could be recapitulated in a mouse model, as we found that Td increased DC migration to the draining lymph nodes and suppressed tumor growth in an antigen-dependent manner. In a search for potential mediators of these effects, we found that the only cytokine or chemokine significantly upregulated after Td preconditioning in both patients and mice was the chemokine (C-C motif) ligand 3 (CCL3). Furthermore, our data show that a source for CCL3 appears to be Td-specific CD4+ memory effector T cells (CD4Td-mem). In experiments where wild-type mice received either CCL3(-/-) or wild-type CD4Td-mem, DC migration was increased only in the wild-type CD4Td-mem setting, signifying that CCL3 from these cells is necessary for DC migration. Finally, we have found that exogenous CCL3 alone can enhance bilateral DC migration to the draining lymph nodes and reduce tumor growth similar to Td preconditioning, suggesting that exogenous CCL3 may be used to treat patients and increase objective responses associated with DC vaccines.

Citation Format: Teilo H. Schaller, Kristen A. Batich, Kelly Hotchkiss, Xiuyu Cui, Luis Sanchez-Perez, John H. Sampson. The effects of CCL3 on dendritic cell migration and immune cell activation [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A80.

Recurrent Extradural Myxopapillary Ependymoma With Oligometastatic Spread

Myxopapillary ependymomas are a slow-growing, grade I type glial tumor in the lumbosacral region. More rarely, they can present as extradural, subcutaneous sacrococcygeal, or perisacral masses, and it is under these circumstances that they are more likely to spread. Here, we report the presentation of a sacrococcygeal mass in patient that was initially resected confirming extradural myxopapillary ependymoma. At initial resection, multiple small pulmonary nodules were detected. This mass recurred 2 years later at the resection site with an interval increase in the previously imaged pulmonary nodules. Resection of both the post-sacral mass and largest lung metastasis confirmed recurrent myxopapillary ependymoma with oligometastatic spread. Because these tumors are rare, with extradural presentation being even more infrequent, to this date there are no definitive therapeutic guidelines for initial treatment and continued surveillance. For myxopapillary ependymoma, current standard of care is first-line maximal surgical resection with or without postoperative radiotherapy depending on the extent of disease and extent of resection. However, there remains insufficient evidence on the role of radiotherapy to oligometastatic foci in providing any further survival benefit or extending time to recurrence. Thus, prospective studies assessing the role of upfront treatment of oligometastases with local resection and adjuvant radiotherapy are needed for improved understanding of extradural myxopapillary ependymoma.

Operative and peri-operative considerations in the management of brain metastasis

The number of patients who develop metastatic brain lesions is increasing as the diagnosis and treatment of systemic cancers continues to improve, resulting in longer patient survival. The role of surgery in the management of brain metastasis (BM), particularly multiple and recurrent metastases, remains controversial and continues to evolve. However, with appropriate patient selection, outcomes after surgery are typically favorable. In addition, surgery is the only means to obtain a tissue diagnosis and is the only effective treatment modality to quickly relieve neurological complications or life‐threatening symptoms related to significant mass effect, CSF obstruction, and peritumoral edema. As such, a thorough understanding of the role of surgery in patients with metastatic brain lesions, as well as the factors associated with surgical outcomes, is essential for the effective management of this unique and growing patient population.

Immunotherapy Is Changing First-Line Treatment of Metastatic Renal-Cell Carcinoma

The incidence of renal-cell carcinoma has been increasing each year, with nearly one third of new cases diagnosed at advanced or metastatic stage. The advent of targeted therapies for metastatic renal-cell carcinoma (mRCC) has underscored the need to subtype tumors according to tumor-immune expression profiles that may more reliably predict treatment outcomes. Over the past 2 decades, several vascular endothelial growth factor (VEGF) and tyrosine kinase inhibitors have been the mainstay for first- and second-line treatment of mRCC. Very recently, immunotherapy checkpoint inhibitors have significantly changed the treatment landscape for patients with mRCC, particularly for first-line treatment of intermediate to poor risk mRCC patients. Now, combination immunotherapy as well as combinations of immunotherapy with targeted agents can significantly alter disease outcomes. The field of immuno-oncology for mRCC has unveiled a deeper understanding of the immunoreactivity inherent to these tumors, and as a result combination therapy is evolving as a first-line modality. This review provides a timeline of advances and controversies in first-line treatment of mRCC, describes recent advances in understanding the immunoreactivity of these tumors, and addresses the future of combination anti-VEGF and immunotherapeutic platforms.

Monocytes outperform ex vivo generated dendritic cells as cellular vaccines to trigger cytotoxic T lymphocyte responses against cancer in pre-clinical models

Conventional dendritic cell (DC) vaccines using ex vivo generated DC have been widely tested in clinical trials in the treatment of human cancers. These DC vaccines have often displayed limited efficacy despite a complex manufacturing process. Although the efficacy of DC vaccines is generally thought to depend on their antigen-presenting cell function, several lines of evidence suggest that, instead of directly presenting antigen (Ag) to naïve T cells, administered DC trigger cytotoxic T lymphocyte (CTL) responses in vivo mainly by transferring Ag to lymphoid-resident conventional DC (cDC). We tested here whether monocytes, known to transfer Ag to cDC in vivo, can be directly loaded with tumor Ag to trigger robust anti-tumor CTL responses. We found that IV administered monocytes loaded with protein or peptide Ag triggered stronger Ag-specific CTL responses than conventional adjuvant-based and DC vaccines. In several murine cancer models, including intra-cranial glioblastoma, we showed that monocyte vaccination suppressed tumor growth better than conventional adjuvant-based, GVAX and DC vaccines. Such anti-tumor activities could be further enhanced with immune checkpoint inhibition. Ag-loaded monocytes did not directly activate naïve CD8+T cells. Instead, they formed stable physical contacts with and transferred Ag to splenic CD8+cDC. This Ag transfer required the formation of connexin 43-containing gap junctions between monocytes and CD8+cDC. Our findings demonstrated that gap junctions are an efficient Ag transfer pathway in vivo between monocytes and splenic CD8+cDC and suggested that IV administered Ag-loaded monocytes may serve as a simple and efficacious cellular vaccine platform for the treatment of human cancers.

Multidimensional flow characterization of circulating immune cells in cisplatin-resistant metastatic urothelial cancer (mUC) patients (pts) treated with pembrolizumab (P) with or without acalabrutinib (acala)

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Background: Immunotherapy checkpoint inhibitors (ICIs) are now standard treatments (txs) in mUC, with response rates ranging 15-25%. A phase 2 randomized study (NCT02351739) treated 75 pts with mUC with either P or PA. We profiled peripheral blood mononuclear cells (PBMCs) to understand changes on tx. Methods: Comprehensive immune profiling of PBMCs was performed at baseline, weeks (wk) 4, 7, and 10. The Wilcoxon rank sum (WRS) test was used to compare tx arms, as well as pts with complete and partial response (CR/PR) vs disease progression (PD). Using the Benjamini-Hochberg (BH) method, results were deemed significant if they had false discovery rate (FDR) of 0.1 or less. Results: Clinical responses did not differ between tx arms (Zhang T et al, ESMO, 2017). The majority of patients showed largest immune changes from baseline at wk7. Comparing P vs PA pts, the PA group had statistically significant increases in PD-L1+ monocytes; CD8 T cells expressing: CD39, CTLA-4, ICOS, PD-1, TIM3, HLA-DR, Ki67, CD39/HLA-DR, CD39/Ki67, and PD-1/TIM-3; and exhausted (CD28-) CD8 T cells expressing ICOS and PD-L1 (Table). Comparing CR/PR vs PD pts, Treg subsets expressing CCR4/HLA-DR and CD39/HLA-DR were significant by WRS but not FDR criteria. Conclusions: From this extensive, exploratory, non-functional flow analysis of PBMCs, PA may potentiate immune changes of PD-L1+ monocytes and CD8+ T cell subsets. Increasing activated peripheral Tregs in CR/PR pts in either arm may indicate marginalization of Tregs from the tumor microenvironment. [Table: see text]

Temozolomide lymphodepletion enhances CAR abundance and correlates with antitumor efficacy against established glioblastoma

Adoptive transfer of T cells expressing chimeric antigen receptors (CARs) is an effective immunotherapy for B-cell malignancies but has failed in some solid tumors clinically. Intracerebral tumors may pose challenges that are even more significant. In order to devise a treatment strategy for patients with glioblastoma (GBM), we evaluated CARs as a monotherapy in a murine model of GBM. CARs exhibited poor expansion and survival in circulation and failed to treat syngeneic and orthotopic gliomas. We hypothesized that CAR engraftment would benefit from host lymphodepletion prior to immunotherapy and that this might be achievable by using temozolomide (TMZ), which is standard treatment for these patients and has lymphopenia as its major side effect. We modelled standard of care temozolomide (TMZSD) and dose-intensified TMZ (TMZDI) in our murine model. Both regimens are clinically approved and provide similar efficacy. Only TMZDI pretreatment prompted dramatic CAR proliferation and enhanced persistence in circulation compared to treatment with CARs alone or TMZSD + CARs. Bioluminescent imaging revealed that TMZDI + CARs induced complete regression of 21-day established brain tumors, which correlated with CAR abundance in circulation. Accordingly, TMZDI + CARs significantly prolonged survival and led to long-term survivors. These findings are highly consequential, as it suggests that GBM patients may require TMZDI as first line chemotherapy prior to systemic CAR infusion to promote CAR engraftment and antitumor efficacy. On this basis, we have initiated a phase I trial in patients with newly diagnosed GBM incorporating TMZDI as a preconditioning regimen prior to CAR immunotherapy (NCT02664363).

Dendritic Cells Enhance Polyfunctionality of Adoptively Transferred T Cells That Target Cytomegalovirus in Glioblastoma

Median survival for glioblastoma (GBM) remains <15 months. Human cytomegalovirus (CMV) antigens have been identified in GBM but not normal brain, providing an unparalleled opportunity to subvert CMV antigens as tumor-specific immunotherapy targets. A recent trial in recurrent GBM patients demonstrated the potential clinical benefit of adoptive T-cell therapy (ATCT) of CMV phosphoprotein 65 (pp65)-specific T cells. However, ex vivo analyses from this study found no change in the capacity of CMV pp65-specific T cells to gain multiple effector functions or polyfunctionality, which has been associated with superior antitumor efficacy. Previous studies have shown that dendritic cells (DC) could further enhance tumor-specific CD8+ T-cell polyfunctionality in vivo when administered as a vaccine. Therefore, we hypothesized that vaccination with CMV pp65 RNA-loaded DCs would enhance the frequency of polyfunctional CMV pp65-specific CD8+ T cells after ATCT. Here, we report prospective results of a pilot trial in which 22 patients with newly diagnosed GBM were initially enrolled, of which 17 patients were randomized to receive CMV pp65-specific T cells with CMV-DC vaccination (CMV-ATCT-DC) or saline (CMV-ATCT-saline). Patients who received CMV-ATCT-DC vaccination experienced a significant increase in the overall frequencies of IFNγ+, TNFα+, and CCL3+ polyfunctional, CMV-specific CD8+ T cells. These increases in polyfunctional CMV-specific CD8+ T cells correlated (R = 0.7371, P = 0.0369) with overall survival, although we cannot conclude this was causally related. Our data implicate polyfunctional T-cell responses as a potential biomarker for effective antitumor immunotherapy and support a formal assessment of this combination approach in a larger randomized study.Significance: A randomized pilot trial in patients with GBM implicates polyfunctional T-cell responses as a biomarker for effective antitumor immunotherapy. Cancer Res; 78(1); 256-64. ©2017 AACR.

Chemokines as adjuvants for immunotherapy: implications for immune activation with CCL3

INTRODUCTION

Immunotherapy embodies any approach that manipulates the immune system for therapeutic benefit. In this regard, various clinical trials have employed direct vaccination with patient-specific dendritic cells or adoptive T cell therapy to target highly aggressive tumors. Both modalities have demonstrated great specificity, an advantage that is unmatched by other treatment strategies. However, their full potential has yet to be realized. Areas covered: In this review, we provide an overview of chemokines in pathogen and anti-tumor immune responses and discuss further improving immunotherapies by arming particular chemokine axes. Expert commentary: The chemokine macrophage inflammatory protein-1 alpha (MIP-1α, CCL3) has emerged as a potent activator of both innate and adaptive responses. Specifically, CCL3 plays a critical role in recruiting distinct immune phenotypes to intratumoral sites, is a pivotal player in regulating lymph node homing of dendritic cell subsets, and induces antigen-specific T cell responses. The recent breadth of literature outlines the various interactions of CCL3 with these cellular subsets, which have now served as a basis for immunotherapeutic translation.

Emerging immunotherapies for glioblastoma

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Long-term Survival in Glioblastoma with Cytomegalovirus pp65-Targeted Vaccination

Purpose: Patients with glioblastoma have less than 15-month median survival despite surgical resection, high-dose radiation, and chemotherapy with temozolomide. We previously demonstrated that targeting cytomegalovirus pp65 using dendritic cells (DC) can extend survival and, in a separate study, that dose-intensified temozolomide (DI-TMZ) and adjuvant granulocyte macrophage colony-stimulating factor (GM-CSF) potentiate tumor-specific immune responses in patients with glioblastoma. Here, we evaluated pp65-specific cellular responses following DI-TMZ with pp65-DCs and determined the effects on long-term progression-free survival (PFS) and overall survival (OS).Experimental Design: Following standard-of-care, 11 patients with newly diagnosed glioblastoma received DI-TMZ (100 mg/m2/d × 21 days per cycle) with at least three vaccines of pp65 lysosome-associated membrane glycoprotein mRNA-pulsed DCs admixed with GM-CSF on day 23 ± 1 of each cycle. Thereafter, monthly DI-TMZ cycles and pp65-DCs were continued if patients had not progressed.Results: Following DI-TMZ cycle 1 and three doses of pp65-DCs, pp65 cellular responses significantly increased. After DI-TMZ, both the proportion and proliferation of regulatory T cells (Tregs) increased and remained elevated with serial DI-TMZ cycles. Median PFS and OS were 25.3 months [95% confidence interval (CI), 11.0-∞] and 41.1 months (95% CI, 21.6-∞), exceeding survival using recursive partitioning analysis and matched historical controls. Four patients remained progression-free at 59 to 64 months from diagnosis. No known prognostic factors [age, Karnofsky performance status (KPS), IDH-1/2 mutation, and MGMT promoter methylation] predicted more favorable outcomes for the patients in this cohort.Conclusions: Despite increased Treg proportions following DI-TMZ, patients receiving pp65-DCs showed long-term PFS and OS, confirming prior studies targeting cytomegalovirus in glioblastoma. Clin Cancer Res; 23(8); 1898-909. ©2017 AACR.

Preconditioning Vaccine Sites for mRNA-Transfected Dendritic Cell Therapy and Antitumor Efficacy

Messenger RNA (mRNA)-transfected dendritic cell (DC) vaccines have been shown to be a powerful modality for eliciting antitumor immune responses in mice and humans; however, their application has not been fully optimized since many of the factors that contribute to their efficacy remain poorly understood. Work stemming from our laboratory has recently demonstrated that preconditioning the vaccine site with a recall antigen prior to the administration of a dendritic cell vaccine creates systemic recall responses and resultantly enhances dendritic cell migration to the lymph nodes with improved antitumor efficacy. This chapter describes the generation of murine mRNA-transfected DC vaccines, as well as a method for vaccine site preconditioning with protein antigen formulations that create potent recall responses.

Tetanus toxoid and CCL3 improve dendritic cell vaccines in mice and glioblastoma patients

Upon stimulation, dendritic cells (DCs) mature and migrate to draining lymph nodes to induce immune responses¹. As such, autologous DCs generated ex vivo have been pulsed with tumor antigens and injected back into patients as immunotherapy. While DC vaccines have shown limited promise in the treatment of patients with advanced cancers^2–4 including glioblastoma (GBM),^5–7 the factors dictating DC vaccine efficacy remain poorly understood. Here we demonstrate that pre-conditioning the vaccine site with a potent recall antigen such as tetanus/diphtheria (Td) toxoid can significantly improve the lymph node homing and efficacy of tumor antigen-specific DCs. To assess the impact of vaccine site pre-conditioning in humans, we randomized patients with GBM to pre-conditioning with mature DCs⁸ or Td unilaterally before bilateral vaccination with Cytomegalovirus pp65 RNA-pulsed DCs. We and other laboratories have shown that pp65 is expressed in > 90% of GBM specimens but not surrounding normal brain^9–12, providing an unparalleled opportunity to subvert this viral protein as a tumor-specific target. Patients given Td had enhanced DC migration bilaterally and significantly improved survival. In mice, Td pre-conditioning also enhanced bilateral DC migration and suppressed tumor growth in a manner dependent on the chemokine CCL3. Our clinical studies and corroborating investigations in mice suggest that pre-conditioning with a potent recall antigen may represent a viable strategy to improve antitumor immunotherapy.

Peptide vaccines for the treatment of glioblastoma

Glioblastoma multiforme (GBM) is an extremely malignant brain tumor for which current therapies do little to remedy. Despite aggressive treatment with surgery, radiation therapy, and chemotherapy, tumors inevitably recur as a direct consequence of the infiltrative nature of GBM. The poor prognosis of patients with GBM underscores the clear and urgent need for more precise and potent therapies. Immunotherapy is emerging as a promising means to treat GBM based on the immune system's capacity to mediate tumor-specific cytotoxicity. In this review, we will discuss the use of peptide vaccines for the treatment of GBM. The simplicity of peptide vaccines and their ability to elicit tumor antigen-specific immune responses make them an invaluable tool for the study of brain tumor immunotherapy.

Enhancing dendritic cell-based vaccination for highly aggressive glioblastoma

INTRODUCTION

Patients with primary glioblastoma (GBM) have a dismal prognosis despite standard therapy, which can induce potentially deleterious side effects. Arming the immune system is an alternative therapeutic approach, as its cellular effectors and inherent capacity for memory can be utilized to specifically target invasive tumor cells, while sparing collateral damage to otherwise healthy brain parenchyma.

AREAS COVERED

Active immunotherapy is aimed at eliciting a specific immune response against tumor antigens. Dendritic cells (DCs) are one of the most potent activators of de novo and recall immune responses and are thus a vehicle for successful immunotherapy. Currently, investigators are optimizing DC vaccines by enhancing maturation status and migratory potential to induce more potent antitumor responses. An update on the most recent DC immunotherapy trials is provided.

EXPERT OPINION

Targeting of unique antigens restricted to the tumor itself is the most important parameter in advancing DC vaccines. In order to overcome intrinsic mechanisms of immune evasion observed in GBM, the future of DC-based therapy lies in a multi-antigenic vaccine approach. Successful targeting of multiple antigens will require a comprehensive understanding of all immunologically relevant oncological epitopes present in each tumor, thereby permitting a rational vaccine design.

Standard of care and future pharmacological treatment options for malignant glioma: an urgent need for screening and identification of novel tumor-specific antigens

INTRODUCTION

Malignant gliomas (MGs) represent the most common primary brain tumors in adults, the most deadly of which is grade IV glioblastoma. Patients with glioblastoma undergoing current standard-of-care therapy have a median survival of 12 - 15 months.

AREAS COVERED

Over the past 25 years, there have been modest advancements in the treatment of MGs. Assessment of therapeutic responses has continued to evolve to account for the increasing number of agents being tested in the clinic. Currently approved therapies for primary tumors have been extended for use in the setting of recurrent disease with modest efficacy. Agents initially approved for recurrent gliomas have begun to demonstrate efficacy against de novo tumors but will ultimately need to be evaluated in future studies for scheduling, timing and dosing relative to chemotherapy.

EXPERT OPINION

Screening and identification of tumor-specific mutations is critical for the advancement of effective therapy that is both safe and precise for the patient. Two unique antigens found in glioblastoma are currently being employed as targets for immunotherapeutic vaccines, one of which has advanced to Phase III testing. Whole genome sequencing of MGs has yielded two other novel mutations that offer great promise for the development of molecular inhibitors.

Complete response to steroids in dural inflammatory pseudotumor associated with Still's disease

We report a unique case of a dural-based inflammatory pseudotumor (IPT) arising in the left cavernous sinus of a patient with a history of juvenile Still's disease. The patient presented with hemi-facial paresthesias, dull, constant headaches, and transient episodes of sharp pain along the temporalis region. Treatment with oral steroid therapy resulted in complete regression of the lesion and accompanied neuralgia symptoms. Because intracranial IPT can mimic meningiomas both clinically and radiographically and can be associated with systemic arthritic diseases, neurosurgeons should be familiar with this entity in order to avoid unnecessary radical surgery and alternatively consider a tapering course of steroid therapy.