Current Advances in Immunotherapy for Glioblastoma.

PURPOSE OF REVIEW: This review seeks to inform oncology clinicians and researchers about the development of novel immunotherapies for the treatment of glioblastoma. An enumeration of ongoing and recently completed clinical trials will be discussed with special attention given to current technologies implemented to overcome central nervous system-specific challenges including barriers to the peripheral immune system, impaired antigen presentation, and T cell dysfunction. RECENT FINDINGS: The success of immunotherapy in other solid cancers has served as a catalyst to explore its application in glioblastoma, which has limited response to other treatments. Recent developments include multi-antigen vaccines that seek to overcome the heterogeneity of glioblastoma, as well as immune checkpoint inhibitors, which could amplify the adaptive immune response and may have promise in combinatorial approaches. Additionally, oncolytic and retroviruses have opened the door to a plethora of combinatorial approaches aiming to leverage their immunogenicity and/or ability to carry therapeutic transgenes. Treatment of glioblastoma remains a serious challenge both with regard to immune-based as well as other therapeutic strategies. The disease has proven to be highly resistant to treatment due to a combination of tumor heterogeneity, adaptive expansion of resistant cellular subclones, evasion of immune surveillance, and manipulation of various signaling pathways involved in tumor progression and immune response. Immunotherapeutics that are efficacious in other cancer types have unfortunately not enjoyed the same success in glioblastoma, illustrating the challenging and complex nature of this disease and demonstrating the need for development of multimodal treatment regimens utilizing the synergistic qualities of immune-mediated therapies.

The current state of immunotherapy for primary and secondary brain tumors: similarities and differences.

Treatment and resolution of primary and metastatic brain tumors have long presented a challenge to oncologists. In response to the dismal survival outcomes associated with conventional therapies, various immunotherapy modalities, such as checkpoint inhibitors, vaccine, cellular immunotherapy and viral immunotherapy have been actively explored over the past couple of decades. Although improved patient survival has been more frequently noted in treatment of brain metastases, little progress has been made in improving patient survival in cases of primary brain tumors, specifically glioblastoma, which is the representative primary brain tumor discussed in this review. Herein, we will first overview the findings of recent clinical studies for treatment of primary and metastatic brain tumors with immunotherapeutic interventions. The clinical efficacy of these immunotherapies will be discussed in the context of their ability or inability to overcome inherent characteristics of the tumor as well as restricted antigen presentation and its immunosuppressive microenvironment. Additionally, this review aims to briefly inform clinicians in the field of neuro-oncology on the relevant aspects of the immune system as it pertains to the central nervous system, with special focus on the differing modes of antigen presentation and tumor microenvironment of primary and metastatic brain tumors and the role these differences may play in the efficacy of immunotherapy in eradicating the tumor.

A mass cytometry approach to track the evolution of T cell responses during infection and immunotherapy by paired T cell receptor repertoire and T cell differentiation state analysis.

T cell receptor (TCR) recognition followed by clonal expansion is a fundamental feature of adaptive immune responses. Here, we developed a mass cytometric (CyTOF) approach combining antibodies specific for different TCR Vα- and Vß-chains with antibodies against T cell activation and differentiation proteins to identify antigen-specific expansions of T cell subsets and assess aspects of cellular function. This strategy allowed for the identification of expansions of specific Vß and Vα chain expressing CD8+ and CD4+ T cells with varying differentiation states in response to Listeria monocytogenes, tumors, and respiratory influenza infection. Expanded Vß chain expressing T cells could be directly linked to the recognition of specific antigens from Listeria, tumor cells, or influenza. In the setting of influenza infection, we showed that the common therapeutic approaches of intramuscular vaccination or convalescent serum transfer altered the clonal diversity and differentiation state of responding T cells. Thus, we present a new method to monitor broad changes in TCR specificity paired with T cell differentiation during adaptive immune responses.

Inhibition of D-2HG leads to upregulation of a proinflammatory gene signature in a novel HLA-A2/HLA-DR1 transgenic mouse model of IDH1R132H-expressing glioma.

BACKGROUND: Long-term prognosis of WHO grade II, isocitrate dehydrogenase (IDH)-mutated low-grade glioma (LGG) is poor due to high risks of recurrence and malignant transformation into high-grade glioma. Immunotherapy strategies are attractive given the relatively intact immune system of patients with LGG and the slow tumor growth rate. However, accumulation of the oncometabolite D-2-hydroxyglutarate (D-2HG) in IDH-mutated gliomas leads to suppression of inflammatory pathways in the tumor microenvironment, thereby contributing to the 'cold' tumor phenotype. Inhibiting D-2HG production presents an opportunity to generate a robust antitumor response following tumor antigen vaccination and immune checkpoint blockade. METHODS: An IDH1R132H glioma model was created in syngeneic HLA-A2/HLA-DR1-transgenic mice, allowing us to evaluate the vaccination with the human leukocyte antigens (HLA)-DR1-restricted, IDH1R132H mutation-derived neoepitope. The effects of an orally available inhibitor of mutant IDH1 and IDH2, AG-881, were evaluated as monotherapy and in combination with the IDH1R132H peptide vaccination or anti-PD-1 immune checkpoint blockade. RESULTS: The HLA-A2/HLA-DR1-syngeneic IDH1R132H cell line expressed the IDH1 mutant protein and formed D-2HG producing orthotopic gliomas in vivo. Treatment of tumor-bearing mice with AG-881 resulted in a reduction of D-2HG levels in IDH1R132H glioma cells (10 fold) and tumor-associated myeloid cells, which demonstrated high levels of intracellular D-2HG in the IDH1R132H gliomas. AG-881 monotherapy suppressed the progression of IDH1R132H gliomas in a CD4+ and CD8+ cell-dependent manner, enhanced proinflammatory IFNγ-related gene expression, and increased the number of CD4+ tumor-infiltrating T-cells. Prophylactic vaccination with the HLA-DR1-restricted IDH1R132H peptide or tumor-associated HLA-A2-restricted peptides did not enhance survival of tumor-bearing animals; however, vaccination with both HLA-A2-IDH1R132H and DR1-IDH1R132H peptides in combination with the IDH inhibitor significantly prolonged survival. Finally, tumor-bearing mice treated with both AG-881 and a PD-1 blocking antibody demonstrated improved survival when compared with either treatment alone. CONCLUSION: The development of effective IDH1R132H-targeting vaccine may be enhanced by integration with HLA class I-restricted cytotoxic T cell epitopes and AG-881. Our HLA-A2/HLA-DR1-syngeneic IDH1R132H glioma model should allow us to evaluate key translational questions related to the development of novel strategies for patients with IDH-mutant glioma.

Novel EGFRvIII-CAR transgenic mice for rigorous preclinical studies in syngeneic mice.

BACKGROUND: Rigorous preclinical studies of chimeric antigen receptor (CAR) immunotherapy will require large quantities of consistent and high-quality CAR-transduced T (CART) cells that can be used in syngeneic mouse glioblastoma (GBM) models. To this end, we developed a novel transgenic (Tg) mouse strain with a fully murinized CAR targeting epidermal growth factor receptor variant III (EGFRvIII). METHODS: We first established the murinized version of EGFRvIII-CAR and validated its function using a retroviral vector (RV) in C57BL/6J mice bearing syngeneic SB28 GBM expressing EGFRvIII. Next, we created C57BL/6J-background Tg mice carrying the anti-EGFRvIII-CAR downstream of a Lox-Stop-Lox cassette in the Rosa26 locus. We bred these mice with CD4-Cre Tg mice to allow CAR expression on T cells and evaluated the function of the CART cells both in vitro and in vivo. To inhibit immunosuppressive myeloid cells within SB28 GBM, we also evaluated a combination approach of CART and an anti-EP4 compound (ONO-AE3-208). RESULTS: Both RV- and Tg-CART cells demonstrated specific cytotoxic activities against SB28-EGFRvIII cells. A single intravenous infusion of EGFRvIII-CART cells prolonged the survival of glioma-bearing mice when preceded by a lymphodepletion regimen with recurrent tumors displaying profound EGFRvIII loss. The addition of ONO-AE3-208 resulted in long-term survival in a fraction of CART-treated mice and those survivors demonstrated delayed growth of subcutaneously re-challenged both EGFRvIII+ and parental EGFRvIII- SB28. CONCLUSION: Our new syngeneic CAR Tg mouse model can serve as a useful tool to address clinically relevant questions and develop future immunotherapeutic strategies.

Gut germinal center regeneration and enhanced antiviral immunity by mesenchymal stem/stromal cells in SIV infection.

Although antiretroviral therapy suppresses HIV replication, it does not eliminate viral reservoirs or restore damaged lymphoid tissue, posing obstacles to HIV eradication. Using the SIV model of AIDS, we investigated the effect of mesenchymal stem/stromal cell (MSC) infusions on gut mucosal recovery, antiviral immunity, and viral suppression and determined associated molecular/metabolic signatures. MSC administration to SIV-infected macaques resulted in viral reduction and heightened virus-specific responses. Marked clearance of SIV-positive cells from gut mucosal effector sites was correlated with robust regeneration of germinal centers, restoration of follicular B cells and T follicular helper (Tfh) cells, and enhanced antigen presentation by viral trapping within the follicular DC network. Gut transcriptomic analyses showed increased antiviral response mediated by pathways of type I/II IFN signaling, viral restriction factors, innate immunity, and B cell proliferation and provided the molecular signature underlying enhanced host immunity. Metabolic analysis revealed strong correlations between B and Tfh cell activation, anti-SIV antibodies, and IL-7 expression with enriched retinol metabolism, which facilitates gut homing of antigen-activated lymphocytes. We identified potentially new MSC functions in modulating antiviral immunity for enhanced viral clearance predominantly through type I/II IFN signaling and B cell signature, providing a road map for multipronged HIV eradication strategies.