Intratumoral Immunosuppression Research Articles

Abstract 2681: Blockade of SIRPα in glioblastoma cells inhibits mitochondrial fatty acid β-oxidation and increase immune cell mediated cytotoxicity

Abstract Glioblastoma (GBM) is the most malignant brain tumor with limited immunotherapeutic options, likely due to significant GBM-associated systemic and intra-tumoral immunosuppression. The binding of SIRPα on myeloid cells to CD47 on cancer cells restricts immuno-phagocytosis against cancer cells. However, less attention has been given to SIRPα is also expressed in cancer cells, and the role of SIRPα on cancer cells is still unclear. Immunohistochemistry (IHC) staining was used to examine the expression of SIRPα in normal brain tissues and GBM. A single-cell database on the Broad Institute Portal was utilized to analyze the SIRPα expression in different cell types. SIRPα antisense morpholino was applied for gene knockdown. Established stable SIRPα overexpressed GBM cell lines were used to examine the mitochondrial function through the Seahorse Mito Stress test. In vitro, immune cell-mediated cytotoxicity was measured by Agilent xCELLigence Real-Time Cell Analysis. Patient biopsies show a 2-fold increase in SIRPα expression in GBM tumors compared to the normal adjacent (n=14-21; p < 0.01). Single-cell RNA-seq data on GBM tumors shows that SIRPα is expressed not only in the myeloid compartment but also in malignant cells. Studies have shown that mitochondrial function and fatty acid β-oxidation (FAO) play a critical role in GBM progression. Respirometry data revealed that blocking SIRPα in murine GBM cell line (CT2A) decreases mitochondrial ATP production. Seahorse Mito Stress test combined with fuel inhibitors showed that SIRPα expression mainly affects the usage of FAO (approximately 50%). In addition, stably, the GFP-tagged SIRPα overexpressed GBM cell line showed an increase of mitochondrial respiration with enhanced FAO ratio compared to the GFP control cell line. These suggested that SIRPα regulates mitochondrial FAO. Studies have shown that tumor-intrinsic FAO confers cell resistance to immune cell-mediated cytotoxicity. Interestingly, by coculturing with microglia, the innate immune population in the brain, our data showed that SIRPα blockade on GBM enhanced microglia-mediated cytotoxicity. Our data showed that targeting SIRPα on GBM may be a prospective therapeutic option by inhibiting FAO in mitochondria and increasing immune cell-mediated cytotoxicity. Citation Format: Yu-Ting Tsai, Glenn J. Lesser, David R. Soto-Pantoja. Blockade of SIRPα in glioblastoma cells inhibits mitochondrial fatty acid β-oxidation and increase immune cell mediated cytotoxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2681.

Immunosuppressive Microenvironment in H3K27 Mutant Pediatric Diffuse Midline Glioma: Single-Cell and Bioinformatics Insights on CD8A, IL7R, and ICAM1.

Diffuse midline gliomas (DMG) pose a grave threat as a malignant tumor primarily affecting children in the pons region. These tumors exhibit a distinct and heightened resistance to therapeutic interventions, coupled with exceptionally aggressive behavior. In this study, we accessed DMG data from the Gene Expression Omnibus (GEO) database. Subsequently, we performed functional annotation and conducted pathway enrichment analysis as well as gene set enrichment analysis (GSEA). Constructing a protein-protein interaction (PPI) network, we identified pivotal hub genes. To evaluate the impact of these hub genes on immune infiltration, we employed the CIBERSORT algorithm. Furthermore, to bolster our findings, we conducted a single-cell analysis. Our findings indicate the involvement of CD8A, IL7R, and ICAM1 in immune responses targeting diverse immune cell types, such as T cells, neutrophils, NK cells, dendritic cells, γδ T cells, and Macrophages M1. Additionally, the presence of immune checkpoints, including IDO1 and TIGIT, likely contributes to intratumoral immunosuppression, thereby fostering the development of an aggressive phenotype and resistance in pediatric DMG. In conclusion, the collective findings of our study suggest the potential role of CD8A, IL7R, and ICAM1 as innovative biomarkers for diagnosing and prognosticating pediatric DMG. Moreover, these molecules hold promise as therapeutic targets in the management of this disease. The implications of our research underscore the importance of exploring these novel avenues for improved patient outcomes.

IMMU-22. BLOCKADE OF CD47 RESULTS IN METABOLIC REPROGRAMMING TO ENHANCE IMMUNE CELL-MEDIATED CYTOTOXICITY OF GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most aggressive and malignant brain tumor. There is growing interest in using immunotherapy to treat GBM, however, clinical trials with immune checkpoints have shown little efficacy, likely due to significant GBM-associated systemic and intra-tumoral immunosuppression. The expression of the transmembrane protein CD47 contributes significantly to immunosuppression limiting innate and adaptive anti-tumor responses. Our new data shows that patient biopsies showed strong immunoreactivity to CD47 in GBM compared to normal adjacent tissue. Furthermore, high CD47 expression in GBM patients resulted in poor survival, indicating that CD47 may be a potential target for GBM treatment. Beyond the “don’t eat me signal”, CD47 facilitates its intracellular signaling through PLIC1 and it still unknown how CD47-related can influence metabolic reprogramming in the tumor microenvironment. Previous studies that upregulated fatty acid oxidation (FAO) provide GBM cells with metabolic plasticity to accommodate its dynamic nutrient microenvironment. Respirometry data revealed that blocking CD47 in murine cell line (CT2A) reduces mitochondrial function and ATP production by over 40-50% respectively (p*< 0.02). The reduction in mitochondrial respiration is linked to an over 50% reduction in FAO (*p< 0.004). This was associated with significant decreases in CPT1a, FASN, ATGL, and CD36 indicating a reduction in FA metabolism mediators. On the other hand, blocking CD47 on murine microglia (SIMA9), showed an opposite result from cancer cells, with increasing mitochondrial respiration and FAO. Initial shows differential responses may be due to the engagement of PLIC1 to CD47. Furthermore, blocking CD47 on microglia increased three-fold of the immune cell-mediated GBM cell cytotoxicity (*p< 0.005), suggesting that metabolic reprogramming associated with CD47 blockade could result in the improvement of immune adaptive responses in the GBM microenvironment. Taken together, our data indicated that CD47 blockade may be a prospective treatment to reduce GBM metabolic plasticity and increase microglia-mediated GBM killing.

Abstract 6442: Role of TWEAK-Fn14 axis in driving immunosuppression in glioblastoma multiforme

Abstract Cellular heterogeneity within glioblastoma multiforme (GBM) is a key driver of resistance to standard-of-care therapeutic approaches such as DNA damage (temozolomide, TMZ), angiogenesis inhibition (Bevacizumab, BM), radiation necrosis, and surgical resection. As such, understanding and targeting heterogeneous tumor-associated populations is a critical aim of ongoing GBM research. Central nervous system (CNS) resident microglia constitute significant percentages of primary GBM samples, often up to 50% of bulk tumor. Additionally, glioblastoma-associated microglia have been implicated in intra-tumoral immunosuppression, and are thus a key barrier to successful implementation of immunotherapies that seek to enhance T-cell mediated anti-tumoral cytotoxicity. As such, insight into targetable pathways that upregulate immunosuppressive cytokines within GBM-associated microglia is necessary for overcoming immuno-therapeutic failure. Here, we identify expression of the cytokine TWEAK (TNFSF12) and its receptor Fn14 (TNFRSF12A) within the myeloid compartment of primary GBM samples via scRNA-seq. Furthermore, we demonstrate TWEAK-mediated reprogramming of GBM-associated microglia towards an immunosuppressive phenotype capable of inhibiting CD8+ T cell activation and proliferation. These findings unveil a potent, targetable axis of immunosuppression within GBM and are thus an exciting step towards enhancing efficacy of existing T-cell based anti-cancer strategies for GBM patients. Citation Format: Angad Beniwal, Ryan Eghlimi, Kenneth D. Alexander, Mylan R. Blomquist, Nhan Tran. Role of TWEAK-Fn14 axis in driving immunosuppression in glioblastoma multiforme [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6442.

Cationic lipid potentiated the adjuvanticity of polysaccharide derivative-modified liposome vaccines

Antigen carriers that can selectively deliver antigens to antigen presenting cells and which can simultaneously activate these cells (adjuvant property) are necessary for efficient cancer immunotherapy or vaccination. Delivery of a model antigen into dendritic cell cytosol has been achieved by pH-responsive polymer-modified liposomes via destabilization of endosomal membranes responding to acidic pH, which impelled antigen-specific cellular immunity. Furthermore, β-glucan-based pH-responsive polysaccharides have shown not only cytosolic antigen delivery performance but also adjuvant property, which further heightened cellular immune responses. Because pH-responsive polysaccharides have anionic carboxy groups, cationic lipid was introduced to liposomes in this study to improve the modification efficiency of pH-responsive polysaccharides and to improve their adjuvanticity and immunity-inducing functions. Introduction of cationic lipids increased the amounts of polysaccharide derivatives on the liposome and increased the cellular association of the liposomes to dendritic cells. Liposomes containing β-glucan-based pH-responsive polysaccharides and cationic lipids increased cytokine production from dendritic cells much more than other polysaccharide derivatives did. Furthermore, through improvement of intra-tumoral immunosuppression and induction of antigen-specific cellular immunity, administering these liposomes impelled tumor suppression even with a small antigen dose. These results suggest that introducing cationic lipids and using pH-responsive polysaccharides having intrinsically adjuvant function are effective for producing liposomal nanovaccines showing strong immunity-inducing function.

Gold Nanocage-Based Photothermal Ablation Facilitates In Situ Vaccination for Melanoma Therapy.

Cancer immunotherapy represents a medical breakthrough, but there are still many patients unable to benefit from it because of the low response rate. The immunosuppressive tumor microenvironment (TME) is the main barrier to immunotherapy. Alleviating intratumoral immunosuppression is critical for improving the immune therapeutic efficacy. This work developed an in situ vaccination strategy by using gold nanocage (AuNC)-based photothermal effect in combination with an adjuvant and PD-L1 suppressor. In specific, this therapeutic strategy included three components: AuNCs as an inducer for tumor antigen production via photothermal ablation, CpG oligodeoxynucleotides as an adjuvant to amplify immune responses, and JQ1 as a PD-L1 suppressor to inhibit an immune checkpoint. The results showed that the in situ vaccination efficiently activated dendritic cells and primed T cells and exhibited a high therapeutic efficacy in the melanoma-bearing mice. This therapeutic strategy can increase the infiltration of cytotoxic T lymphocytes, suppress the PD-L1 expression in the tumor, and repolarize tumor-associated macrophages from pro-tumor M2 to the anti-tumor M1 phenotype, thereby remodeling the TME via regulating the innate immune and adaptive immune responses.

Abstract 6321: Anti-BTN1A1 exhibits synergistic anti-tumor immunotherapeutic efficacy in combination with radiation therapy

Abstract Chronic inflammation is a critical risk factor in the context of cancer development that promotes the expression of immune checkpoint proteins including PD-1, PD-L1, LAG-3, and TIM-3, which in turn suppress T-cell mediated cytotoxic tumor cell killing. Inflammation induced by treatments including chemotherapy and radiotherapy (RT) can also promote immune checkpoint upregulation and consequent tumor immune escape. However, whether the acute inflammation associated with standard chemotherapy and RT can engage distinct immune checkpoints to further support tumor persistence remains unknown. Using an in vivo screening platform in which tumors were irradiated with high-dose γ-radiation, we identified the B7-related immunoglobulin superfamily protein butyrophilin 1A1 (BTN1A1) as an acute stress-inducible immune checkpoint. Herein, we aimed to investigate how BTN1A1 contributes to post-irradiation intratumoral immunosuppression. To assess BTN1A1 induction in response to γ-radiation, human cell lines were exposed to a range of radiation doses, and cell death and BTN1A1 expression were examined by flow cytometry. Radiation promoted apoptosis and BTN1A1 expression in a dose-dependent manner, and PD-L1 was downregulated by increasing the dosage of γ-radiation. As radiation-induced cell death results in cytosolic DNA accumulation within tumors, which in turn activates the production of type I interferons (IFNs) via the cGAS/STING pathway, we examined the effect of BTN1A1 on cGAS and STING expression. BTN1A1 overexpression in human prostate adenocarcinoma PC3 cells suppressed cGAS and STING expression. IFNs can promote antigen presenting cell activation, thus priming T cell responses. We then examined the impact of BTN1A1 overexpression on type I IFN production as assessed via qRT-PCR, revealing that BTN1A1 overexpression enhanced IFN-β expression in the presence of the STING agonist cGAMP. BTN1A1 was also found to harbor a C-terminal B30.2 domain that was able to specifically interact with xanthine oxidoreductase (XOR), an oxidizing enzyme involved in purine metabolism. BTN1A1 expression induced high levels of intracellular reactive oxygen species (ROS), which have the potential to be more toxic in lymphocytes as compared to tumor cells, and BTN1A1 knockdown decreased these ROS levels. In light of these observations, we assessed the combination therapeutic efficacy of RT and anti-BTN1A1 antibodies in a syngeneic murine Lewis lung carcinoma (LLC) model system, revealing that these two treatments exhibited synergistic anti-tumor activity. FACS and IHC further confirmed that BTN1A1 was upregulated within tumors following irradiation. Together, these data offer new insights regarding the immunomodulatory role of radiation-induced BTN1A1 within tumors, providing a more robust foundation for the development of BTN1A1 as an immunologic target for cancer therapy. Citation Format: Ezra Chung, Young-Seung Kim, Andrew Park, Steven H. Lin, Hyunjin Jung, Stephen S. Yoo. Anti-BTN1A1 exhibits synergistic anti-tumor immunotherapeutic efficacy in combination with radiation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6321.

Immune suppressive checkpoint interactions in the tumour microenvironment of primary liver cancers.

Liver cancer is one of the most prevalent cancers, and the third most common cause of cancer-related mortality worldwide. The therapeutic options for the main types of primary liver cancer-hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA)-are very limited. HCC and CCA are immunogenic cancers, but effective immune-mediated tumour control is prevented by their immunosuppressive tumour microenvironment. Despite the critical involvement of key co-inhibitory immune checkpoint interactions in immunosuppression in liver cancer, only a minority of patients with HCC respond to monotherapy using approved checkpoint inhibitor antibodies. To develop effective (combinatorial) therapeutic immune checkpoint strategies for liver cancer, in-depth knowledge of the different mechanisms that contribute to intratumoral immunosuppression is needed. Here, we review the co-inhibitory pathways that are known to suppress intratumoral T cells in HCC and CCA. We provide a detailed description of insights from preclinical studies in cellular crosstalk within the tumour microenvironment that results in interactions between co-inhibitory receptors on different T-cell subsets and their ligands on other cell types, including tumour cells. We suggest alternative immune checkpoints as promising targets, and draw attention to the possibility of combined targeting of co-inhibitory and co-stimulatory pathways to abrogate immunosuppression.

Intratumoral immunosuppression profiles in 11q-deleted neuroblastomas provide new potential therapeutic targets.

High-risk neuroblastoma (NB) patients with 11q deletion frequently undergo late but consecutive relapse cycles with fatal outcome. To date, no actionable targets to improve current multimodal treatment have been identified. We analyzed immune microenvironment and genetic profiles of high-risk NB correlating with 11q immune status. We show in two independent cohorts that 11q-deleted NB exhibits various immune inhibitory mechanisms, including increased CD4+ resting T cells and M2 macrophages, higher expression of programmed death-ligand 1, interleukin-10, transforming growth factor-beta-1, and indoleamine 2,3-dioxygenase 1 (P<0.05), and also higher chromosomal breakages (P≤0.02) and hemizygosity of immunosuppressive miRNAs than MYCN-amplified and other 11q-nondeleted high-risk NB. We also analyzed benefits of maintenance treatment in 83 high-risk stage M NB patients focusing on 11q status, either with standard anti-GD2 immunotherapy (n=50) or previous retinoic acid-based therapy alone (n=33). Immunotherapy associated with higher EFS (50 vs. 30, P=0.028) and OS (72 vs. 52, P=0.047) at 3years in the overall population. Despite benefits from standard anti-GD2 immunotherapy in high-risk NB patients, those with 11q deletion still face poor outcome. This NB subgroup displays intratumoral immune suppression profiles, revealing a potential therapeutic strategy with combination immunotherapy to circumvent this immune checkpoint blockade.

Blocking IL1 Beta Promotes Tumor Regression and Remodeling of the Myeloid Compartment in a Renal Cell Carcinoma Model: Multidimensional Analyses.

Intratumoral immunosuppression mediated by myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM) represents a potential mechanism of immune checkpoint inhibitor (ICI) resistance in solid tumors. By promoting TAM and MDSC infiltration, IL1β may drive adaptive and innate immune resistance in renal cell carcinoma (RCC) and in other tumor types. Using the RENCA model of RCC, we evaluated clinically relevant combinations of anti-IL1β plus either anti-PD-1 or the multitargeted tyrosine kinase inhibitor (TKI), cabozantinib. We performed comprehensive immune profiling of established RENCA tumors via multiparameter flow cytometry, tumor cytokine profiling, and single-cell RNA sequencing (RNA-seq). Similar analyses were extended to the MC38 tumor model. Analyses via multiparameter flow cytometry, tumor cytokine profiling, and single-cell RNA-seq showed that anti-IL1β reduces infiltration of polymorphonuclear MDSCs and TAMs. Combination treatment with anti-IL1β plus anti-PD-1 or cabozantinib showed increased antitumor activity that was associated with decreases in immunosuppressive MDSCs and increases in M1-like TAMs. Single-cell RNA-seq analyses show that IL1β blockade and ICI or TKI remodel the myeloid compartment through nonredundant, relatively T-cell-independent mechanisms. IL1β is an upstream mediator of adaptive myeloid resistance and represents a potential target for kidney cancer immunotherapy.

An Antibody Targeting ICOS Increases Intratumoral Cytotoxic to Regulatory T-cell Ratio and Induces Tumor Regression.

The immunosuppressive tumor microenvironment constitutes a significant hurdle to immune checkpoint inhibitor responses. Both soluble factors and specialized immune cells, such as regulatory T cells (Treg), are key components of active intratumoral immunosuppression. Inducible costimulatory receptor (ICOS) can be highly expressed in the tumor microenvironment, especially on immunosuppressive Treg, suggesting that it represents a relevant target for preferential depletion of these cells. Here, we performed immune profiling of samples from tumor-bearing mice and patients with cancer to demonstrate differential expression of ICOS in immune T-cell subsets in different tissues. ICOS expression was higher on intratumoral Treg than on effector CD8 T cells. In addition, by immunizing an Icos knockout transgenic mouse line expressing antibodies with human variable domains, we selected a fully human IgG1 antibody called KY1044 that bound ICOS from different species. We showed that KY1044 induced sustained depletion of ICOShigh T cells but was also associated with increased secretion of proinflammatory cytokines from ICOSlow effector T cells (Teff). In syngeneic mouse tumor models, KY1044 depleted ICOShigh Treg and increased the intratumoral TEff:Treg ratio, resulting in increased secretion of IFNγ and TNFα by TEff cells. KY1044 demonstrated monotherapy antitumor efficacy and improved anti-PD-L1 efficacy. In summary, we demonstrated that using KY1044, one can exploit the differential expression of ICOS on T-cell subtypes to improve the intratumoral immune contexture and restore an antitumor immune response.

IMMU-19. TARGETING GLIOBLASTOMA IMMUNOSUPPRESSION AND TREATMENT RESISTANCE WITH IBRUTINIB IN COMBINATION WITH STEREOTACTIC RADIATION AND IMMUNE CHECKPOINT BLOCKADE

Abstract BACKGROUND Glioblastoma (GBM) is associated with systemic and intratumoral immunosuppression. Part of this immunosuppression is mediated by myeloid derived suppressor cells (MDSCs). Preclinical evidence shows that ibrutinib, a tyrosine kinase inhibitor FDA approved for use in chronic lymphocytic leukemia and known to be CNS penetrant, can decrease MDSC generation and function. Also, focal radiation therapy (RT) synergizes with anti-PD-1 therapy in mouse GBM models. Thus, we aimed to test the combination of these approaches on immune activation and survival in a preclinical immune-intact GBM mouse model. METHODS C57BL/6 mice intracranially implanted with the murine glioma cell line GL261-Luc2 were divided into 8 groups consisting of treatments with ibrutinib, RT (10 Gy SRS), or anti-PD-1 individually or in each combination (along with a no treatment control group). Immune cell subset changes (flow-cytometry) and animal survival (Kaplan-Meier) were assessed (n=10 mice per group). RESULTS Median survival of the following groups including control (28 days), ibrutinib (27 days), RT (30 days) or anti-PD-1 (32 days) showed no significant differences. However, a significant improvement in median survival was seen in mice given combinations of ibrutinib+RT (35 days), ibrutinib+anti-PD-1 (38 days), and triple therapy with ibrutinib+RT+anti-PD-1 (48 days, p &amp;lt; 0.05) compared to controls or single treatment groups. The reproducible survival benefit of triple combination therapy was abrogated in the setting of CD4+ and CD8+ T cell depletion. Contralateral intracranial tumor re-challenge in long-term surviving mice suggested generation of tumor-specific immune memory responses. The immune profile of the tumor microenvironment (TME) showed increased cytotoxic CD8+ T cells and decreased MDSCs and regulatory T cells in the triple combination therapy mice compared to controls. CONCLUSION The combination of ibrutinib, focal RT, and anti-PD-1 immune checkpoint blockade led to a significant survival benefit compared to controls in a preclinical model of GBM.

Abstract LB-115: An orally bioavailable inhibitor of CD73 reverts intratumoral immunosuppression and promotes anti-tumor responses

Abstract The 5' ecto-nucleotidase CD73 is dynamically expressed in distinct biological contexts as a means to increase the adenosine metabolite, which functions to limit immune activation and prevent excessive inflammation. CD73 activity is required for the final step of adenosine production. In the context of tumors, excessive CD73-mediated adenosine generation impairs anti-tumor immune responses. Here, we show that an orally bioavailable small molecule inhibitor of CD73 can prevent adenosine generation, relieve adenosine-driven immunosuppression within the tumor in vivo and generate anti-tumor efficacy. In vitro analysis confirmed the substantial suppressive effects of adenosine on murine CD8+ T cells, cross-presenting dendritic cells, and macrophages. NECA, a stable analog of adenosine, impaired immature bone-marrow precursor differentiation into CD103+ dendritic cells, a subset which is critical for tumor-derived antigen presentation to naïve T cells. Interestingly, NECA also inhibited the ability of macrophages to upregulate the M1 marker, CD80, in both the presence and absence of additional polarizing stimuli. Furthermore, OR-558, a CD73 small molecule inhibitor, could fully inhibit CD73-mediated adenosine production and completely restore T cell activation at sub-nanomolar concentrations. Prior work in CD73 germline knock-out animals has shown that EG7 syngeneic tumor growth is highly dependent on CD73. Building on this knowledge, we next we sought to evaluate CD73 inhibition on AMP to adenosine conversion ex vivo in EG7 syngeneic tumor extracts and indeed observed that OR-558 treatment could significantly impair adenosine production within the tumor milieu. This finding translated to the in vivo tumor setting, where single agent anti-tumor efficacy was observed with continuous OR-558 treatment. Anti-tumor efficacy coincided with significantly decreased intra-tumoral adenosine levels and immune modulation, such as increased intratumoral T cell activation, dendritic cell maturation, and M1 macrophage polarization. Lastly, we determined the bioavailability of orally dosed OR-558 in EG7 tumor-bearing mice and found that significant single agent anti-tumor efficacy was also achievable with once-daily oral dosing of OR-558. Taken together, these data demonstrate that adenosine has pleiotropic immunosuppressive effects and inhibition of CD73-mediated adenosine production in vivo is sufficient to reverse these immune effects and enhance anti-tumor immunity. These results support clinical development of orally bioavailable CD73 small molecule inhibitors. Citation Format: Todd Metzger, Brian Blank, Brenda Chan, Chelsea Chen, Yuping Chen, Xiaohui Du, Frank Duong, Lori Friedman, Melissa Junttila, Hiro Kawai, Wayne Kong, Jared Moore, Johnny Pham, Yosup Rew, Daqing Sun, Jessica Sun, Dena Sutimantanapi, Kejia Wu, Chien-Hung Yeh, Natalie Yuen, Tatiana Zavorotinskaya. An orally bioavailable inhibitor of CD73 reverts intratumoral immunosuppression and promotes anti-tumor responses [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-115.

Dysregulation of Glutamate Transport Enhances Treg Function That Promotes VEGF Blockade Resistance in Glioblastoma.

Anti-VEGF therapy prolongs recurrence-free survival in patients with glioblastoma but does not improve overall survival. To address this discrepancy, we investigated immunologic resistance mechanisms to anti-VEGF therapy in glioma models. A screening of immune-associated alterations in tumors after anti-VEGF treatment revealed a dose-dependent upregulation of regulatory T-cell (Treg) signature genes. Enhanced numbers of Tregs were observed in spleens of tumor-bearing mice and later in tumors after anti-VEGF treatment. Elimination of Tregs with CD25 blockade before anti-VEGF treatment restored IFNγ production from CD8+ T cells and improved antitumor response from anti-VEGF therapy. The treated tumors overexpressed the glutamate/cystine antiporter SLC7A11/xCT that led to elevated extracellular glutamate in these tumors. Glutamate promoted Treg proliferation, activation, suppressive function, and metabotropic glutamate receptor 1 (mGlutR1) expression. We propose that VEGF blockade coupled with glioma-derived glutamate induces systemic and intratumoral immunosuppression by promoting Treg overrepresentation and function, which can be pre-emptively overcome through Treg depletion for enhanced antitumor effects. SIGNIFICANCE: Resistance to VEGF therapy in glioblastoma is driven by upregulation of Tregs, combined blockade of VEGF, and Tregs may provide an additive antitumor effect for treating glioblastoma.

Abstract LB-A19: Intratumoral immunosuppression is reversed by blocking adenosine production with an oral inhibitor of CD73

Abstract Introduction: CD73 mediates the final dephosphorylation in the conversion of extracellular ATP to adenosine, a metabolite which signals through the A2 family of receptors. Like PD-1, adenosine appears to be part of a negative feedback loop to limit immune activation and prevent excessive inflammation in the context of tissue damage. However, intratumoral hypoxia likely drives excessive CD73-mediated adenosine generation and prevents optimal anti-tumor immune responses. We show that intratumoral adenosine levels are sufficient to drive pervasive suppression of multiple immune subsets in vitro and an orally bioavailable small molecule can prevent adenosine generation in vitro and within the tumor in vivo. Methods We examined the effects of adenosine signaling on multiple immune cell subsets through in vitro functional assays. We interrogated T cell activation, proliferation, and cytolytic activity, as well as NK cell function in vitro. Furthermore, we investigated and identified functional targets of adenosine signaling within T cells using transcriptomic and protein expression analyses. In addition, we performed in vitro myeloid differentiation assays to determine the effect of adenosine signaling on myeloid lineage maturation. Finally, we explored the activity of a novel, orally bioavailable inhibitor of CD73 in vitro and assessed its ability to rescue T cell activation and suppress AMP conversion to adenosine within the tumor microenvironment. Results and Conclusions We found that T cell-expressed CD73 was sufficient to drive adenosine generation from AMP in vitro, resulting in suppression of anti-CD3/CD28-induced T cell activation and proliferation and a reduced capacity to kill cognate antigen-expressing tumor cells. Adenosine-exposed T cells displayed decreased induction of markers associated with activation at both the mRNA and protein level, including Ki67, ICOS, and PD-1, while showing higher expression of naïve-associated CD73. Interestingly, we also observed a third subset of markers which were uniquely induced by adenosine. In addition to its activity on T cells, adenosine signaling caused functional suppression of NK cells in the presence of target Yac-1 cells. In the myeloid compartment, NECA, a stable analog of adenosine, prevented in vitro differentiation of CD103+ cross-presenting dendritic cells, a population which provides a critical stimulus to tumor-infiltrating T cells. Additionally, NECA impaired macrophage expression of CD80, a canonical M1 marker and mediator of T cell costimulation, in both the presence and absence of M1-polarizing IFNγ and LPS. Finally, we showed that a novel, orally bioavailable CD73 inhibitor was able to effectively inhibit AMP to adenosine conversion both in vitro and in vivo, while an anti-CD73 antibody had incomplete effects. Taken together, an orally bioavailable small molecule inhibitor of CD73 represents a potential therapeutic approach to reverse immunosuppression within the tumor microenvironment. Citation Format: Todd C Metzger, Brian R Blank, Brenda Chan, Chelsea Chen, Yuping Chen, Xiaohui Du, Frank L Duong, Valeria R. Fantin, Lori S Friedman, Jared T Moore, Daqing Sun, Jessica Sun, Dena Sutimantanapi, Qiuping Ye, Natalie Yuen, Tatiana Zavorotinskaya. Intratumoral immunosuppression is reversed by blocking adenosine production with an oral inhibitor of CD73 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A19. doi:10.1158/1535-7163.TARG-19-LB-A19

MicroRNA-92 Expression in CD133+ Melanoma Stem Cells Regulates Immunosuppression in the Tumor Microenvironment via Integrin-Dependent Activation of TGFβ.

In addition to being refractory to treatment, melanoma cancer stem cells (CSC) are known to suppress host antitumor immunity, the underlying mechanisms of which need further elucidation. In this study, we established a novel role for miR-92 and its associated gene networks in immunosuppression. CSCs were isolated from the B16-F10 murine melanoma cell line based on expression of the putative CSC marker CD133 (Prominin-1). CD133+ cells were functionally distinct from CD133- cells and showed increased proliferation in vitro and enhanced tumorigenesis in vivo. CD133+ CSCs also exhibited a greater capacity to recruit immunosuppressive cell types during tumor formation, including FoxP3+ Tregs, myeloid-derived suppressor cells (MDSC), and M2 macrophages. Using microarray technology, we identified several miRs that were significantly downregulated in CD133+ cells compared with CD133- cells, including miR-92. Decreased expression of miR-92 in CSCs led to higher expression of target molecules integrin αV and α5 subunits, which, in turn, enhanced TGFβ activation, as evidenced by increased phosphorylation of SMAD2. CD133+ cells transfected with miR-92a mimic and injected in vivo showed significantly decreased tumor burden, which was associated with reduced immunosuppressive phenotype intratumorally. Using The Cancer Genome Atlas database of patients with melanoma, we also noted a positive correlation between integrin α5 and TGFβ1 expression levels and an inverse association between miR-92 expression and integrin alpha subunit expression. Collectively, this study suggests that a miR-92-driven signaling axis involving integrin activation of TGFβ in CSCs promotes enhanced tumorigenesis through induction of intratumoral immunosuppression. SIGNIFICANCE: CD133+ cells play an active role in suppressing melanoma antitumor immunity by modulating miR-92, which increases influx of immunosuppressive cells and TGFβ1 expression.

P04.28 Effect of fibroblast activation protein-expressing stromal cells from human glioblastomas on glioma and endothelial cells

Fibroblast activation protein (FAP) is a protease selectively expressed in a number of extracranial cancers especially in cancer associated fibroblasts (CAF). CAF play an important role in the pathogenesis of malignant tumors through extracellular matrix remodeling, secretion of growth factors and cytokines, and promotion of angiogenesis and intratumoral immunosuppression. Glioblastomas (GBMs) have a unique composition of the tumor microenvironment and whether CAF are present in these tumors remains controversial. We have recently shown that FAP is upregulated in a subgroup of GBMs and is expressed in both cancer and stromal cells. The role of FAP+ stromal cells in GBM is however unknown. FAP positive stromal cells were isolated using magnetic activated cell sorting (MACS), and cultured in pericyte media. Expression of FAP and other phenotypic markers was assessed by immunocytochemistry. Conditioned media were prepared and used as a chemoattractant in a transwell migration assay. Cell growth was analyzed using the XTT assay, angiogenesis was evaluated using a 3D angiogenesis assay in type I collagen gel. A cytokine array was used to analyze soluble mediators released by FAP+ stromal cells. FAP+ stromal cells were isolated from several human GBMs and characteristically expressed mesenchymal (TE-7, PDGFR, SMA), but not endothelial (vWF) or glial (GFAP) markers. Conditioned media from these FAP+ cells enhanced the migration of glioma and endothelial cells and enhanced endothelial sprouting in a 3D angiogenesis assay. Part of the conditioned media had a mild growth promoting effect on endothelial and glioma cells. Using cytokine arrays, we identified several chemokines, growth factors and angiogenic factors produced by these FAP+ stromal cells. Our data demonstrate that FAP+ mesenchymal cells analogous to cancer associated fibroblasts participate on multidirectional interactions among cell subpopulations in human glioblastomas mediated, at least in part, by soluble factors. These FAP+ stromal cells may contribute to the invasive growth and neoangiogenesis in glioblastoma. Ministry of Health of CR grant 15-31379A, Progres Q28/1LFUK and grant LM2015064 of the EATRIS-CZ.

MicroRNA-92 expression in CD133+ melanoma stem cells regulates immunosuppression in the tumor microenvironment through integrin-dependent TGF-β activation

Abstract The existence of cancer stem cells (CSC) accounts for the high degree of chemoresistance and heterogeneity characterizing refractory melanomas. Yet, the degree to which CSCs modulate immune cells in the tumor microenvironment has yet to be revealed. The present study aims to establish a novel role for miR-92 and its associated gene networks in immunomodulation. We employed syngeneic mouse models utilizing B16-F10 melanoma cells to observe primary tumor and metastatic growth. CSCs were isolated from the parental line based on expression of the putative CSC marker, CD133. CD133+ cells were functionally distinct from CD133− cells with CD133+ cells showing increased proliferation in vitro and enhanced tumorigenesis when administered subcutaneously. Our data indicated that compared to CD133− cells, CD133+ CSCs had a greater capacity to recruit immunosuppressive cell types during tumor formation. Using microarray technology in order to expose disparities in microRNA expression between CSC and non-CSC compartments, we identified several miRs that were significantly downregulated in CD133+ cells including miR-92. We hypothesized that lower levels of miR-92 in CSCs led to higher expression of integrin subunits as predicted by gene alignment software and confirmed using qRT-PCR. Flow cytometry analysis of dissociated tumors demonstrated that tumors initiated by CD133+ cells displayed significantly higher levels of TGF-β compared to CD133− cells. Additionally, qRT-PCR for TGF-β associated genes confirmed a significant increase in expression in CD133+ cells. These data suggest that CSCs efficiently induce intratumoral immunosuppression which is potentially regulated by a miR-92 driven axis involving integrin activation of TGF-β.

AMD3100 Augments the Efficacy of Mesothelin-Targeted, Immune-Activating VIC-008 in Mesothelioma by Modulating Intratumoral Immunosuppression.

AMD3100 (plerixafor), a CXCR4 antagonist, has been demonstrated to suppress tumor growth and modulate intratumoral T-cell trafficking. However, the effect of AMD3100 on immunomodulation remains elusive. Here, we explored immunomodulation and antitumor efficacy of AMD3100 in combination with a previously developed mesothelin-targeted, immune-activating fusion protein, VIC-008, in two syngeneic, orthotopic models of malignant mesothelioma in immunocompetent mice. We showed that combination therapy significantly suppressed tumor growth and prolonged animal survival in two mouse models. Tumor control and survival benefit were associated with enhanced antitumor immunity. VIC-008 augmented mesothelin-specific CD8+ T-cell responses in the spleen and lymph nodes and facilitated intratumoral lymphocytic infiltration. However, VIC-008 treatment was associated with increased programmed cell death protein-1 (PD-1) expression on intratumoral CD8+ T cells, likely due to high CXCL12 in the tumor microenvironment. AMD3100 alone and in combination with VIC-008 modulated immunosuppression in tumors and the immune system through suppression of PD-1 expression on CD8+ T cells and conversion of regulatory T cells (Tregs) into CD4+CD25-Foxp3+IL2+CD40L+ helper-like cells. In mechanistic studies, we demonstrated that AMD3100-driven Treg reprogramming required T cell receptor (TCR) activation and was associated with loss of PTEN due to oxidative inactivation. The combination of VIC-008 augmentation of tumor-specific CD8+ T-cell responses with AMD3100 abrogation of immunosuppression conferred significant benefits for tumor control and animal survival. These data provide new mechanistic insight into AMD3100-mediated immunomodulation and highlight the enhanced antitumor effect of AMD3100 in combination with a tumor antigen-targeted therapy in mouse malignant mesothelioma, which could be clinically relevant to patients with this difficult-to-treat disease. Cancer Immunol Res; 6(5); 539-51. ©2018 AACR.

Abstract 1633: Immunotherapy for malignant mesothelioma that combines a mesothelia-targeted immune-activating protein and CXCL12/CXCR4 blockade

Abstract Background and Purpose: There is a significant unmet need for new treatment strategies for malignant mesothelioma (MM). Despite relevant advances in many cancer treatment areas, including improvements in diagnosis, staging, and the clinical course of treated patients, MM remains a highly lethal disease. The purpose of this study is to develop a combination immunotherapy for MM, which involves a fusion protein to target and evoke a cellualr immune response to mesothelin (MSLN) and the blockade of CXCL12/CXCR4 pathway to mobilize cytotoxic effector cells into tumors. Experimental Procedures: The efficacy of the MSLN targeted immune activating fusion protein (scFv-MtbHsp70), FDA-approved small molecule CXCR4 antagonist AMD3100 (plerixafor), and the combination were evaluated in two syngeneic and orthotopic murine models of MM in immune competent C57BL/6 mice. Mice received 4 intraperitoneal (i.p.) treatments from 7 days post i.p. injection of luciferase-expressing 40L and AE17 cells. Tumor growth was monitored by in vivo imaging of luciferase activity with an IVIS Spectrum. Survival time was calculated as life span from the day of tumor inoculation. In immunological studies, mice were sacrificed 4 weeks after tumor cell inoculation. Immune cells from spleens and tumors were labeled with antibodies against CD3, CD4, CD8, CD25 and Foxp3 antibodies, and examined by flow cytometry. Splenocytes were stimulated with MSLN and assessed for intracellular IFN-γ production by flow cytometry. Results: In both murine mesothelioma models, the fusion protein scFv-MtbHsp70 alone delayed tumor growth and prolonged mouse survival, which was associated with increased tumor infiltration by CD3+CD8+ T cells. Treatment enhanced the cytotoxic function of tumor-specific CD3+CD8+ T cells by evoking dendritic cell activation as well as antigen presentation and cross presentation. AMD3100 alone reduced the proportion of CD4+CD25+Foxp3+ Treg cells in tumors and decreased PD-1 expression on CD3+CD8+ T cells. The combination of the fusion protein and AMD3100 further significantly slowed tumor growth and enhanced mouse survival while augmenting tumor-specific CD8+ T-cell immune responses and abrogating intratumoral immunosuppression. Conclusion: Our findings demonstrated for the first time the synergistic effect of combination of MSLN-targeted immune-activating fusion protein scFv-MtbHsp70 and AMD3100 in treatment of MM in mice. This is a new therapeutic strategy which may significantly prolong survival of patients with this disease. Citation Format: Huabiao Chen, Binghao Li, Yang Zeng, Patrick Reeves, Qiuyan Liu, Ann Sluder, Jeffrey Gelfand, Timothy Brauns, Mark Poznansky. Immunotherapy for malignant mesothelioma that combines a mesothelia-targeted immune-activating protein and CXCL12/CXCR4 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1633. doi:10.1158/1538-7445.AM2017-1633