Advanced Age in Humans and Mouse Models of Glioblastoma Show Decreased Survival from Extratumoral Influence

PURPOSE

Glioblastoma (GBM) is the most common aggressive primary malignant brain tumor in adults with a median age of onset of 68 to 70 years old. Although advanced age is often associated with poorer GBM patient survival, the predominant source(s) of maladaptive aging effects remains to be established. Here, we studied intratumoral and extratumoral relationships between adult patients with GBM and mice with brain tumors across the lifespan.

EXPERIMENTAL DESIGN

Electronic health records at Northwestern Medicine and the NCI SEER databases were evaluated for GBM patient age and overall survival. The commercial Tempus and Caris databases, as well as The Cancer Genome Atlas were profiled for gene expression, DNA methylation, and mutational changes with varying GBM patient age. In addition, gene expression analysis was performed on the extratumoral brain of younger and older adult mice with or without a brain tumor. The survival of young and old wild-type or transgenic (INK-ATTAC) mice with a brain tumor was evaluated after treatment with or without senolytics and/or immunotherapy.

RESULTS

Human patients with GBM ≥65 years of age had a significantly decreased survival compared with their younger counterparts. While the intra-GBM molecular profiles were similar between younger and older patients with GBM, non-tumor brain tissue had a significantly different gene expression profile between young and old mice with a brain tumor and the eradication of senescent cells improved immunotherapy-dependent survival of old but not young mice.

CONCLUSIONS

This work suggests a potential benefit for combining senolytics with immunotherapy in older patients with GBM.

Identification and Characterization of a Novel Indoleamine 2,3-Dioxygenase 1 Protein Degrader for Glioblastoma

Indoleamine 2,3-dioxygenase 1 (IDO1) is a potent immunosuppressive enzyme that inhibits the antitumor immune response through both tryptophan metabolism and non-enzymatic functions. To date, most IDO1-targeted approaches have focused on inhibiting tryptophan metabolism. However, this class of drugs has failed to improve the overall survival of patients with cancer. Here, we developed and characterized proteolysis targeting chimeras (PROTACs) that degrade the IDO1 protein. IDO1-PROTACs were tested for their effects on IDO1 enzyme and non-enzyme activities. After screening a library of IDO1-PROTAC derivatives, a compound was identified that potently degraded the IDO1 protein through cereblon-mediated proteasomal degradation. The IDO1-PROTAC: (i) inhibited IDO1 enzyme activity and IDO1-mediated NF-κB phosphorylation in cultured human glioblastoma (GBM) cells, (ii) degraded the IDO1 protein within intracranial brain tumors in vivo, and (iii) mediated a survival benefit in mice with well-established brain tumors. This study identified and characterized a new IDO1 protein degrader with therapeutic potential for patients with glioblastoma.

IMMU-06. REDUCTION OF CD4+ T CELLS NEGATIVELY AFFECTS SURVIVAL IN OLD BUT NOT YOUNG MICE WITH GLIOBLASTOMA

OBJECTIVE

Previous work indicates poorer survival outcomes for older glioblastoma (GBM) patients ≥ 65 years of age as compared to younger patients < 65 years of age. The cellular mechanisms associated with this age-dependent survival difference remain elusive. Here we evaluated the overall survival of young and old immunocompetent mice with intracranial brain tumors that were depleted for specific immune cell populations.

METHODS

Young 6-8 weeks of age vs old 80+ weeks of age C57BL/6 mice were treated for up to 3 weeks with either IgG isotype control antibodies or with depleting antibodies against murine CD4, CD8, or NK1.1, beginning at 3 days prior to- and every 3 days post-intracranial injection of the mouse brain tumor cell lines, GL261 or CT-2A. Overall survival was compared between groups. Additionally, absolute peripheral blood mononuclear cell (PBMC) counts for CD3+ T cells, CD4+ T cells, and CD8+ T cells were analyzed between aneurysm control- and GBM-patients.

RESULTS

Older adult mice, but not younger mice, with either intracranial GL261 or CT-2A cell-based brain tumors have a significantly decreased overall survival when depleted for CD4+ T cells as compared to the IgG control-treated group, as well as groups depleted for CD8+ T- or NK-cells (P < 0.05). Coincidently, older GBM patients have fewer CD4+ T cells as compared to younger GBM patient counterparts (P < 0.05).

CONCLUSIONS

The data suggest that the levels of CD4+ T cells play more important roles in the survival of old subjects with GBM than in the younger subjects. A mechanistic understanding for this CD4+ T cell-dependent survival benefit is ongoing.

EXTH-62. EXAMINATION OF THE TUMOR MICROENVIRONMENT OF GLIOMAS TREATED WITH VIROIMMUNOTHERAPY REVEALS THE PRODUCTION OF ONCOMETABOLITES LEADING TO IMPROVED THERAPEUTIC STRATEGIES

Oncolytic viruses are considered part of immunotherapy and have shown promise in preclinical experiments and clinical trials in a small fraction of patients. To improve the response rate, it is necessary to reshape the tumor microenvironment that shields the tumor from the immune system of the patient. We engineered Delta-24-RGDOX (DNX-2440), an oncolytic adenovirus to express the T-cell activator OX40L, which triggered, in murine glioblastoma models, a dramatic reshaping of the tumor microenvironment dominated by changes in immune processes in an RNA-seq analysis of ingenuity pathways. Paradoxically, network analyses also revealed that Delta-24-RGDOX induced robust activation of the cytokine-driven immunosuppressive IDO-Kynurenine-AhR circuitry, indicating a potential mechanism of resistance of gliomas to oncolytic virotherapy. To reverse this immunosuppression, we combined Delta-24-RGDOX with clinically relevant IDO inhibitors to treat glioma-bearing mice. The combined therapy decreased the activation of the IDO network without affecting viral activity. Flow cytometry assays revealed a decrease in the presence of the immunosuppressive cell populations, MDSCs and Tregs, which presence was higher in Delta-24-RGDOX-treated tumors. These data were further confirmed in gene set enrichment analyses. Functional co-culture studies showed that the combined therapy activated splenocytes against tumor antigens and that this activation was reversed by Kynurenine. Importantly, the combination treatment eradicated the tumors in a CD4-dependent manner and significantly prolonged the survival of glioma-bearing mice. Altogether, these studies indicate that the combination treatment promotes an adaptive immune response while decreasing the immunosuppression caused by the virus-induced IDO activation. Furthermore, our data identified the striking role of immunosuppressive pathways in the resistance of gliomas to oncolytic virotherapy. Specifically, the activity of the tumor microenvironment IDO circuitry was responsible, at least partially, for the remodeling of local immunosuppression after tumor infection. Combining molecular and immune-related therapies may improve outcomes in human gliomas treated with virotherapy.

TMIC-15. AGE-RELATED MARKERS FOR SENESCENCE INCREASE IN THE OLDER ADULT EXTRATUMORAL MOUSE BRAIN DUE TO GLIOBLASTOMA

OBJECTIVE

The median age of onset for glioblastoma (GBM; IDHwt) is 68-70 years. Age is a strong prognostic factor for GBM patient outcomes such that overall survival in older adults is less than their younger counterparts – even after adjustment for MGMT promoter methylation status. Aging is associated with increased levels of senescence in the brain. Several age-related neurological disorders have been shown to improve with senolytic treatments. Here, we explored the effects and therapeutic neutralization of syngeneic brain tumors on increasing senescence levels in the extratumoral brain (ie. outside of the brain tumor) of young and old mice.

METHODS

General RNA-sequencing, as well as single-cell (sc) RNA-sequencing was performed on extratumoral tissue from young (8-12 weeks) and older adult (80-90 weeks) C57BL/6 mice with or without GL261 and key markers were validated with RT-PCR. The combined effects of the senolytics, dasatinib and quercetin, with radiation, anti-PD-1 mAb, and IDO enzyme inhibitor treatment, was also investigated.

RESULTS

General- and sc-RNA sequencing revealed a distinct gene expression profile in the extratumoral brain of older mice with syngeneic GL261 as compared to all other groups. RT-PCR results confirmed that the brain tumor increased gene expression for senescence levels, p53, and NFkB signaling in the older adult extratumoral brain. Expression of the senescence marker p16INK4A was primarily localized to oligodendrocyte progenitor cells in the older adult brain. The combinatorial treatment of senolytics with RT, anti-PD-1 mAb, and IDO enzyme inhibitor led to a synergistic survival benefit in older adult mice with GL261 as compared to the treatment with senolytics, or immunotherapy, alone.

CONCLUSIONS

The data suggest that the extratumoral brain may be responsible in-part for the poorer outcomes of older adults with GBM and that treatment approaches that target senescent cells may provide clinical benefit.

Reshaping the tumor microenvironment with oncolytic viruses, positive regulation of the immune synapse, and blockade of the immunosuppressive oncometabolic circuitry

BACKGROUND

Oncolytic viruses are considered part of immunotherapy and have shown promise in preclinical experiments and clinical trials. Results from these studies have suggested that tumor microenvironment remodeling is required to achieve an effective response in solid tumors. Here, we assess the extent to which targeting specific mechanisms underlying the immunosuppressive tumor microenvironment optimizes viroimmunotherapy.

METHODS

We used RNA-seq analyses to analyze the transcriptome, and validated the results using Q-PCR, flow cytometry, and immunofluorescence. Viral activity was analyzed by replication assays and viral titration. Kyn and Trp metabolite levels were quantified using liquid chromatography-mass spectrometry. Aryl hydrocarbon receptor (AhR) activation was analyzed by examination of promoter activity. Therapeutic efficacy was assessed by tumor histopathology and survival in syngeneic murine models of gliomas, including Indoleamine 2,3-dioxygenase (IDO)-/- mice. Flow cytometry was used for immunophenotyping and quantification of cell populations. Immune activation was examined in co-cultures of immune and cancer cells. T-cell depletion was used to identify the role played by specific cell populations. Rechallenge experiments were performed to identify the development of anti-tumor memory.

RESULTS

Bulk RNA-seq analyses showed the activation of the immunosuppressive IDO-kynurenine-AhR circuitry in response to Delta-24-RGDOX infection of tumors. To overcome the effect of this pivotal pathway, we combined Delta-24-RGDOX with clinically relevant IDO inhibitors. The combination therapy increased the frequency of CD8+ T cells and decreased the rate of myeloid-derived suppressor cell and immunosupressive Treg tumor populations in animal models of solid tumors. Functional studies demonstrated that IDO-blockade-dependent activation of immune cells against tumor antigens could be reversed by the oncometabolite kynurenine. The concurrent targeting of the effectors and suppressors of the tumor immune landscape significantly prolonged the survival in animal models of orthotopic gliomas.

CONCLUSIONS

Our data identified for the first time the in vivo role of IDO-dependent immunosuppressive pathways in the resistance of solid tumors to oncolytic adenoviruses. Specifically, the IDO-Kyn-AhR activity was responsible for the resurface of local immunosuppression and resistance to therapy, which was ablated through IDO inhibition. Our data indicate that combined molecular and immune therapy may improve outcomes in human gliomas and other cancers treated with virotherapy.

Abstract 4184: RNA-seq analyses reveal remodeling of tumor microenvironment and reversal of glioma resistance to oncolytic viruses by targeting immunometabolism

Viroimmunotherapy aims to infect cancer cells to elicit anti-tumor immune responses. In clinical trials, glioma treatment with oncolytic viruses induced durable clinical responses in a small fraction of patients. To improve the percentage of responders, it is necessary to reshape the tumor microenvironment that shields the tumor from the immune system of the patient. Thus, we engineered Delta-24-RGDOX (DNX-2440), an oncolytic adenovirus that carries the cDNA of the T-cell activator, OX40L. In this work, we observed that Delta-24-RGDOX triggered a dramatic reshaping of the tumor microenvironment dominated by strong changes in immune processes as indicated by RNA-sequencing via ingenuity pathway analyses in a murine glioblastoma model. Paradoxically, network analyses revealed that Delta-24-RGDOX also induced robust activation of the cytokine-driven immunosuppressive IDO-Kynurenine-AhR circuitry, indicating a potential mechanism of resistance of the cancer cells to oncolytic virotherapy. To reverse this immunosuppression, we combined Delta-24-RGDOX with clinically relevant IDO inhibitors to treat glioma bearing mice. Importantly, addition of the IDO inhibitor to Delta-24-RGDOX decreased the activation of the IDO network. IDO inhibition did not affect virus infection or replication in human or murine glioma cells. Flow cytometry assays revealed that the combination therapy increased the frequency of activated CD8+ T cells and decreased the presence of the immunosuppressive cell populations, MDSCs and Tregs. Gene set enrichment analyses confirmed the decrease of MDSCs and Tregs in the combination treated glioma-bearing mice compared to the virus alone. Functional co-culture studies showed that the combined therapy activated splenocytes against tumor antigens, and that this activation was reversed by kynurenine. Importantly, the combination treatment eradicated the tumors in a CD4-dependent manner and significantly prolonged the survival of glioma-bearing mice. Altogether, these studies indicate that the combination treatment promotes an adaptive immune response while decreasing immunosuppression caused by virus-induced IDO activation. Furthermore, our data identified the striking role of immunosuppressive pathways in the resistance of gliomas to oncolytic virotherapy. Specifically, the activity of the tumor microenvironment IDO circuitry was responsible, at least partially, for the remodeling of local immunosuppression after tumor infection. Combining molecular and immune-related therapies may improve outcomes in human gliomas treated with virotherapy.

Citation Format: Teresa T. Nguyen, Dong Ho Shin, Sagar Sohoni, Sanjay K. Singh, Yisel Rivera-Molina, Hong Jiang, Xuejun Fan, Joy Gumin, Frederick F. Lang, Christopher Alvarez-Breckenridge, Marta M. Alonso, Filipa Godoy-Vitorino, Lijie Zhai, Erik Ladomersky, Kristen L. Lauing, Derek A. Wainwright, Juan Fueyo, Candelaria Gomez-Manzano. RNA-seq analyses reveal remodeling of tumor microenvironment and reversal of glioma resistance to oncolytic viruses by targeting immunometabolism [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 4184.

Tumor Cell IDO Enhances Immune Suppression and Decreases Survival Independent of Tryptophan Metabolism in Glioblastoma

PURPOSE

Glioblastoma (GBM) is an incurable primary brain tumor that has not benefited from immunotherapy to date. More than 90% of GBM expresses the tryptophan (Trp) metabolic enzyme, indoleamine 2,3-dioxygenase 1 (IDO). This observation supported the historical hypothesis that IDO suppresses the antitumor immune response solely through a mechanism that requires intratumoral Trp depletion. However, recent findings led us to investigate the alternative hypothesis that IDO suppresses the anti-GBM immune response independent of its association with Trp metabolism.

EXPERIMENTAL DESIGN

IDO-deficient GBM cell lines reconstituted with IDO wild-type or IDO enzyme-null cDNA were created and validated in vitro and in vivo. Microarray analysis was conducted to search for genes that IDO regulates, followed by the analysis of human GBM cell lines, patient GBM and plasma, and The Cancer Genome Atlas (TCGA) database. Ex vivo cell coculture assays, syngeneic and humanized mouse GBM models, were used to test the alternative hypothesis.

RESULTS

Nonenzymic tumor cell IDO activity decreased the survival of experimental animals and increased the expression of complement factor H (CFH) and its isoform, factor H like protein 1 (FHL-1) in human GBM. Tumor cell IDO increased CFH and FHL-1 expression independent of Trp metabolism. Increased intratumoral CFH and FHL-1 levels were associated with poorer survival among patients with glioma. Similar to IDO effects, GBM cell FHL-1 expression increased intratumoral regulatory T cells (Treg) and myeloid-derived suppressor cells while it decreased overall survival in mice with GBM.

CONCLUSIONS

Our study reveals a nonmetabolic IDO-mediated enhancement of CFH expression and provides a new therapeutic target for patients with GBM.

CTIM-21. AN AGE-SPECIFIC BIOMARKER IN NEWLY-DIAGNOSED GLIOBLASTOMA PATIENTS TREATED WITH RADIATION, NIVOLUMAB AND BMS-986205

INTRODUCTION

We previously determined that advanced age plays a negative role in the survival outcome of human recurrent glioblastoma (GBM) patients treated with immune checkpoint blockade. Here we investigate the immunologic “signature” of younger patients who are < 65 years of age and older adult GBM patients who are ≥ 65 years of age that undergo simultaneous treatment with standard radiation, nivolumab (anti-PD-1 mAb), and BMS-986205 (a potent IDO enzyme inhibitor) and are newly diagnosed with O6-methylguanine-DNA methyl-transferase (MGMT) unmethylated GBM. Our objective was to identify age-dependent immunologic changes before and after treatment with immunotherapy.

METHODS

Patients ≥ 18 years old with newly diagnosed MGMT unmethylated GBM, KPS ≥ 70, and minimal steroid use were eligible for enrollment in this phase 1 trial. PBMCs and serum were drawn at baseline and routine post-treatment time points followed by mass spec analysis of kynurenine (Kyn) and tryptophan (Trp) metabolites, RNAseq, and 18-color flow cytometric analysis.

RESULTS

8 younger adults with a median age of 50 years old and 4 older adults with a median age of 68.5 years old were studied. The median overall survival of younger and older adults was 368 and 108.5 days, respectively (p=0.032, HR 4.8 for age). BMS-986205 treatment decreased the Kyn/Trp ratio of all patients irrespective of age. RNAseq analysis found significant age-related changes using Gene Ontology pathway analysis of T cell related immunity, lymphocyte activation, and NK cell mediated immunity. Flow cytometric analysis is ongoing.

CONCLUSIONS

Similar to what was reported in older adult mice treated with simultaneous RT, anti-PD-1 mAb, and IDO enzyme inhibitor, advanced age negatively affected the survival in older adult human GBM patients treated with an analogous clinical approach. Future determination of whether the age-related biomarker profile can be used diagnostically and therapeutically is now under investigation.

IMMU-12. TUMOR CELL IDO ENHANCES IMMUNE SUPPRESSION AND DECREASES SURVIVAL INDEPENDENT OF TRYPTOPHAN METABOLISM IN GLIOBLASTOMA

OBJECTIVE

Indoleamine 2,3-dioxygenase 1 (IDO; IDO1) is an immune checkpoint that’s characterized as a potent immunosuppressive mediator through its ability to metabolize tryptophan and wild-type IDH patient-resected glioblastoma (GBM) expresses IDO in ≥ 95% of cases. Recent findings from our group led us to investigate the alternative hypothesis that IDO possesses immunosuppressive effects that are independent of its associated metabolic activity.

METHODS

Murine GBM cell lines that overexpress either wild-type or enzyme-null IDO were created for in vivo characterization of IDO enzyme-independent immunosuppressive function. Microarray was conducted to identify human IDO expression-correlated genes, which were further investigated in human GBM cell lines, patient GBM tissues and plasma, as well as the TCGA database. Ex vivo cell co-culture assays and syngeneic mouse orthotopic GBM models were employed to study immunosuppressive mechanisms.

RESULTS

Here, we demonstrate that non-enzymic IDO activity decreases survival in experimental animals and increases the expression of immunosuppressive complement factor H (CFH) in human GBM. CFH mRNA levels positively correlate with those of IDO and many other immunosuppressive genes in patient resected GBM and can be applied as a prognostic marker in both lower grade gliomas and GBM. Similar to IDO, the increased expression of CFH in patient-resected glioma was positively correlated with an increased signature for regulatory T cells (Tregs) and myeloid-derived suppressive cells (MDSCs). High expression of CFH in tumor cells increases intratumoral Tregs levels and decreases overall survival in mice with GBM, while inducing tumor associated macrophage cell differentiation.

CONCLUSIONS

Here, we demonstrated that glioblastoma (GBM) cell IDO promotes the accumulation of intratumoral FoxP3+ regulatory T cells (Tregs) and tumor progression while decreasing overall survival - independent of IDO enzyme activity. Our study reveals a targetable non-metabolic IDO-dependent mechanism for future therapeutic intervention in patients with GBM.

DDRE-11. SECOND GENERATION IDO INHIBITORS FOR IMPROVING IMMUNOTHERAPEUTIC EFFICACY IN PATIENTS WITH GLIOBLASTOMA

INTRODUCTION

Indoleamine 2,3-dioxygenase 1 (IDO; IDO1) is a rate-limiting enzyme that metabolizes tryptophan and is expressed in >90% of patient-resected glioblastoma (GBM). IDO-mediated tryptophan metabolism has been the proposed mechanism for suppressing the immune response in GBM. Recently, we discovered that IDO also possesses non-enzymic functions that contribute to suppress the anti-GBM immune response. This finding motivated us to develop IDO-Proteolysis Targeting Chimeras (IDO-PROTACs) to degrade IDO protein rather than simply inhibiting IDO enzyme activity.

METHODS

Western blot analysis was used to determine IDO-PROTAC efficiency of IDO protein degradation among human and mouse GBM cell lines and PDX. Our lead IDO-PROTAC was tested for toxicity, blood brain barrier penetration, and pharmacokinetics (PK) in wild-type C57BL/6 mice.

RESULTS

IDO-PROTACs degrade IDO protein in both tumor and non-tumor cells with a DC50 value of ~0.5µM in human GBM tumor cells. Biolayer interferometry (BLI) studies show that IDO-PROTAC forms a binary complex with IDO protein with similar affinity comparable to parental compound – BMS986205. IDO-PROTACs induced IDO ubiquitination and the pretreatment with ubiquitin proteasome inhibitors, MG132 or MLN4924, inhibited IDO protein degradation. In vivo toxicity studies showed that treatment with IDO-PROTAC at 25 mg/kg for 3-weeks did not develop any apparent toxicity in C57BL/6 mice. PK analysis revealed that IDO-PROTAC bioavailabilty reached a peak serum and brain concentration within 30 minutes after intraperitoneal administration.

CONCLUSIONS

This study developed a lead IDO-PROTAC compound that efficiently degrades IDO protein in human GBM cells with a moderate bioavailability and blood-brain barrier (BBB) penetration. Future work will focus on the enhancement of BBB penetration, increased bioavailability, and route of administration to improve IDO-PROTAC potency for combination with other forms of immunotherapy for GBM patient treatment.

IMMU-24. IMPROVING OUTCOMES IN OLDER ADULTS WITH GLIOBLASTOMA BY REVERSING AGE-RELATED CHANGES

Wild-type IDH glioblastoma (wtGBM) represents ≥90% of human GBM patient diagnoses with a median age of onset at 68-70 years of age. We previously found a decline of GBM patient survival with progressive age and that subjects ≥65 years of age had the poorest prognosis. We also showed an age-dependent enhancement of immune suppression in the brain that negatively affected immunotherapeutic efficacy in older adult mice with syngeneic brain tumors. Here, we extended those observations while studying C57BL/6 mice with intracranial CT-2A or GL261 between 80-110 weeks old - analogous to the age of a wtIDH GBM patient diagnosis. Overall survival of older adult mice with CT-2A or GL261 was significantly decreased when subjects were lymphopenic for CD4+ T cells as compared to an IgG Ab treatment group (n=12/group; p< 0.01). CD8+ T cell or NK cell leukopenia had no effect on survival outcomes. The negative effect of CD4+ T cell lymphopenia in older adults was not observed in younger mice with brain tumors. We also investigated the increased immunosuppression in the brain and its relationship to the accumulation of senescent cells and the treatment with standard of care radiation/temozolomide (RT/TMZ). p16INK4A, a marker for senescent cells, was increased in non-tumor cells of the brain during advanced age and its expression was increased after treatment with RT/TMZ. Older adult mice with brain tumors and treated with senolytics showed decreased p16INK4A levels after treatment with RT/TMZ. Senolytic treatment also improved the efficacy of combination therapy with RT, anti-PD-1 mAb, and IDO enzyme inhibitor in older adults as compared to senolytics alone or the triple immunotherapeutic cocktail alone (n=12-15/group; p< 0.01). Collectively, the results suggest that strategies aimed at reversing the effects of the aging combined with tumor eradication therapies may be particularly beneficial for older adult human patients with GBM.

Glioblastoma as an age-related neurological disorder in adults

Background

Advanced age is a major risk factor for the development of many diseases including those affecting the central nervous system. Wild-type isocitrate dehydrogenase glioblastoma (IDH^wt GBM) is the most common primary malignant brain cancer and accounts for ≥90% of all adult GBM diagnoses. Patients with IDH^wt GBM have a median age of diagnosis at 68–70 years of age, and increasing age is associated with an increasingly worse prognosis for patients with this type of GBM.

Methods

The Surveillance, Epidemiology, and End Results, The Cancer Genome Atlas, and the Chinese Glioma Genome Atlas databases were analyzed for mortality indices. Meta-analysis of 80 clinical trials was evaluated for log hazard ratio for aging to tumor survivorship.

Results

Despite significant advances in the understanding of intratumoral genetic alterations, molecular characteristics of tumor microenvironments, and relationships between tumor molecular characteristics and the use of targeted therapeutics, life expectancy for older adults with GBM has yet to improve.

Conclusions

Based upon the results of our analysis, we propose that age-dependent factors that are yet to be fully elucidated, contribute to IDH^wt GBM patient outcomes.

IMMU-32. NON-METABOLIC IDO ACTIVITY INCREASES COMPLEMENT FACTOR H LEVELS WHICH ENHANCES IMMUNOSUPPRESSION IN HUMAN GLIOBLASTOMA

Indoleamine 2,3 dioxygenase 1 (IDO) is an immunosuppressive factor expressed in ≥90% of patient resected glioblastoma (GBM). Canonically, IDO suppresses the immune response by metabolizing the essential amino acid, tryptophan, into the downstream metabolite, kynurenine. Based on the in vivo finding that the genetic knockout of tumor cell IDO does not change brain tumor tryptophan and kynurenine levels in syngeneic mice, we recently questioned the mechanistic role of IDO in GBM. To determine whether tumor cell tryptophan metabolism is responsible for the pathogenic effects of IDO, we created IDO-deficient murine GBM cells that were reconstituted with either (i) empty expression vector, (ii) a vector expressing wild-type IDO, (iii) or a vector expressing enzyme-inactive IDO. GBM cell IDO expression increased Tregs and decreased survival, but did so independent of tryptophan metabolism. To understand how IDO causes these effects, we performed Clariom D microarray analysis of human GBM cells and discovered that complement factor H (CFH) is significantly increased in GBM cells expressing IDO but decreased by treatment with IDO siRNA. Notably, CFH siRNA decreased CFH- but not IDO-expression in GBM cells. We next found that GBM cell IDO regulates CFH levels independent of tryptophan metabolism. To determine the effects of CFH on tumor outgrowth, we intracranially-engrafted syngeneic mice with IDO-deficient murine GBM cells reconstituted with either empty expression vector or a vector expressing CFH splice variant 2. Tumor CFH significantly decreased survival from GBM bearing mice similar to that of patient-resected GBM with high CFH levels whereby patients present with a faster rate to tumor recurrence. In summary, our study is the first to report an IDO-dependent non-metabolic regulation of CFH in tumor cells and highlights a new immunotherapeutic target in patients with incurable GBM.

DDRE-09. DEVELOPING IDO-PROTACS TO IMPROVE IMMUNOTHERAPEUTIC EFFICACY IN PATIENTS WITH GLIOBLASTOMA

INTRODUCTION

Indoleamine 2,3-dioxygenase 1 (IDO; IDO1) is a rate-limiting enzyme that metabolizes the essential amino acid tryptophan into kynurenine. Recent work by our group has revealed that IDO promotes tumor development and suppresses immune cell functions independent of its enzyme activity. Moreover, pharmacologic IDO enzyme inhibitors that currently serve as the only class of drugs available for targeting immunosuppressive IDO activity, fail to improve the survival of patients with GBM. Here, we developed IDO-Proteolysis Targeting Chimeras (IDO-PROTACs). PROTACs bind to a specific protein and recruit an E3 ubiquitin ligase that enhance proteasome-mediated degradation of the target protein.

METHODS

A library of ≥100 IDO-PROTACs were developed by joining BMS986205 (IDO binder) with a linker group to various E3-ligase ligands. Western blot analysis of PROTAC-induced IDO degradation was tested in vitro among multiple human and mouse GBM cell lines including U87, GBM6, GBM43 and GL261 along a time course ranging between 1–96 hours of treatment and at varying concentrations. The mechanism of IDO protein degradation was investigated using pharmacologic ligands that inhibit or compete with the proteasome-mediated protein degradation pathway.

RESULTS

Primary screening identified several IDO-PROTACs with IDO protein degradation potential. Secondary screening showed that our lead compound has a DC50 value of ~0.5µM with an ability to degrade IDO in all GBM cells analyzed, and an initial activity within 12 hours of treatment that extended for up to 96 hours. Mutating the CRBN-binding ligand, pretreatment with the ubiquitin proteasome system inhibitors MG132 or MLN4924 or using unmodified parental compound all inhibited IDO protein degradation.

CONCLUSIONS

This study developed an initial IDO-PROTAC technology that upon further optimization, can neutralize both IDO enzyme and non-enzyme immunosuppressive effects. When combined with other forms of immunotherapy, IDO-PROTACs have the potential to substantially enhance immunotherapeutic efficacy in patients with GBM.

IMMU-40. IMPROVING OUTCOMES IN OLDER ADULTS WITH GLIOBLASTOMA BY REVERSING AGE-RELATED CHANGES OF THE CENTRAL NERVOUS SYSTEM

De novo glioblastoma (GBM) represents ≥ 90% of all GBM diagnoses and has a median age of onset at 65 years old. Because of its preponderance during advanced age, we investigated the mortality rate of older adult C57BL/6 (WT) mice with CT-2A glioma. Strikingly, we discovered a significant decrease of overall survival among animal subjects depleted for both CD4+ and CD8+ T cells as compared to the group treated with IgG control antibodies. This negative effect of lymphopenia only applied to older adults. We next questioned which of the major T cell subsets contribute to this effect and determined that the depletion of CD4+ T cells significantly decreased overall survival as compared to IgG control or CD8+ T cell-depleting antibodies (n=12/group; p< 0.01). We previously found increased immunosuppressive IDO levels in the mouse and human brain during advanced age. Although 78–86 week old WT mice have no survival benefit after triple combination immunotherapy, age-matched IDOKO mice have an impressive increase in median and overall survival – despite both groups being treated with a pharmacologic IDO enzyme inhibitor. Since IDO is potently-induced by proinflammatory cytokines, we hypothesized that a potential mechanism for the increased IDO during advanced age is associated with an accumulation of senescent cells in the brain with a proinflammatory secretory phenotype. To investigate this, 80 week old mice with intracranial GL261 were treated with (i) vehicle with IgG antibodies, (ii) the senolytic drugs dasatanib and quercetin, (iii) whole brain radiation, anti-PD-1 mAb, and IDO enzyme inhibitor, or (iv) the 5 agent combination. Only animal subjects treated with the 5 agent cocktail showed a significant increase in long-term survival in a subset of mice (n=12–15/group; p< 0.01). These results suggest that optimization of senescent cell eradication treatment may be particularly beneficial to older patients with GBM treated with immunotherapy.

TMOD-24. GENERATION AND CHARACTERIZATION OF A NOVEL TRANSGENIC IDO REPORTER MOUSE FOR IDO POSTTRANSLATIONAL MODIFICATION ANALYSIS IN SITU

Glioblastoma (GBM) is the most common and aggressive primary central nervous system tumor in adults with a median survival of 14.6 months. GBM is a potently immunosuppressive cancer due in-part to the prolific expression of immunosuppressive indoleamine 2,3 dioxygenase 1 (IDO). Tumor cell IDO facilitates the intratumoral accumulation of regulatory T cells (Tregs; CD4+CD25+FoxP3+). Although immunosuppressive IDO activity is canonically characterized by the conversion of tryptophan into kynurenine, we have utilized transgenic and syngeneic mouse models and mutant glioma lines to demonstrate that tumor cell IDO increases Treg accumulation independent of tryptophan metabolism. Here, we address the gap in our understanding of IDO signaling activity in vivo. Subcutaneously-engrafted human GBM expressing human IDO-GFP cDNA was isolated from immunodeficient humanized NSG-SGM3 mice. The tumor was immunoprecipitated for the GFP tag using GFP-TRAP followed by mass spectrometry which revealed a novel methylation site on a lysine residue at amino acid 373 in the IDO C-terminus region. Western blot analysis of IDO protein also revealed the presence of tyrosine phosphorylation. Additionally, we recently created a new transgenic IDO reporter mouse model whereby endogenous IDO is fused to GFP via a T2A linker (IDO→GFP). This model allows for the isolation of IDO+ cells in real-time and without causing cell death, thereby creating the opportunity for downstream molecular analysis of in situ-isolated GFP+ cells. Collectively, our work suggests that IDO non-enzyme activity may involve the post-translational modifications we recently identified. As IDO activity may differ between in vitro and in vivo modeling systems, we will use the new IDO→GFP reporter mouse model for an improved mechanistic understanding of how immunosuppressive IDO facilitates Treg accumulation in vivo.

Abstract 5612: Targeting the non-enzymatic function of IDO1 in glioblastoma immunotherapy

Purpose: More effective immunotherapies against GBM are urgently needed considering current failures in several phase III clinical trials. Indoleamine 2, 3-dioxygenase 1 (IDO1) has been shown to mediate tumor-induced immunosuppression through its tryptophan catabolic activity. Surprisingly, pharmacological IDO1 enzyme inhibitors have not demonstrated any survival benefit in cancer patients either mono-therapeutically or in combination with other therapies. Previously we confirmed that tumor IDO1 mRNA expression is significantly upregulated in GBM patients compared to those from patients with lower grades gliomas. Furthermore, knockdown of IDO1 in mouse GBM cells significantly increased mouse survival and decreased tumor infiltrating regulatory T cells (Treg) but did not affect tumor local tryptophan catabolism. Consistently, inhibition of IDO1 enzymatic activity on GBM-bearing mice did not yield any survival benefit. Collectively, these findings prompt us to test the hypothesis whether GBM cell derived IDO1 can suppress immune response through a non-enzymatic pathway.

Methods: IDO1-deficient mouse GBM cells were created and modified to stably express either wild-type (WT) or enzyme-null IDO1. Tumor infiltrating lymphocytes (TILs) and survival rate were analyzed from mice engrafted with these modified cells. Ex vivo co-culture of splenic monocytes with the modified GBM cells was also employed. To interrogate potential IDO1-regulated gene(s) in GBM, gene expression profile in human GBM cell lines under either IDO1 knockdown or overexpression conditions were investigated by microarray analysis and verified by real-time RT-PCR.

Result: Overexpression of WT IDO1 in GBM cells led to significantly increased Treg accumulation in GBM and much poorer survival in comparison to IDO1-deficent tumor cells. Interestingly, ablation of IDO1 enzyme activity in the enzyme-null IDO1 overexpressing tumor cells showed similar Treg accumulation as in the WT IDO1-overexpressing tumor cells and poor survival rate. Moreover, overexpression of both WT and enzyme-null IDO1 in GBM cells induced higher level of mature macrophages (CD11c-CD11b+Ly6c+Ly6glow) than IDO1-deficient GBM cells. Finally, an IDO1 regulated gene encoding a secreted protein was identified in the microarray analysis, which also demonstrates high correlation with IDO1 in many different tumor types.

Conclusions: Results from this study strongly imply an enzyme independent pathway associated with IDO1-driven immunosuppression in mouse GBM. Current investigation of the newly identified IDO1 regulated gene in the setting of human GBM will provide novel perspective in our understanding of the non-enzyme function of IDO1 in tumor immunity and enlighten the strategic design for future IDO1-based GBM immunotherapy.

Citation Format: Lijie Zhai, Erik Ladomersky, Jun Qian, Brenda Nyugen, April Bell, Kristen Lauing, Derek Wainwright. Targeting the non-enzymatic function of IDO1 in glioblastoma immunotherapy [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 5612.

Immunosuppressive IDO in Cancer: Mechanisms of Action, Animal Models, and Targeting Strategies

Indoleamine 2, 3-dioxygenase 1 (IDO; IDO1; INDO) is a rate-limiting enzyme that metabolizes the essential amino acid, tryptophan, into downstream kynurenines. Canonically, the metabolic depletion of tryptophan and/or the accumulation of kynurenine is the mechanism that defines how immunosuppressive IDO inhibits immune cell effector functions and/or facilitates T cell death. Non-canonically, IDO also suppresses immunity through non-enzymic effects. Since IDO targeting compounds predominantly aim to inhibit metabolic activity as evidenced across the numerous clinical trials currently evaluating safety/efficacy in patients with cancer, in addition to the recent disappointment of IDO enzyme inhibitor therapy during the phase III ECHO-301 trial, the issue of IDO non-enzyme effects have come to the forefront of mechanistic and therapeutic consideration(s). Here, we review enzyme-dependent and -independent IDO-mediated immunosuppression as it primarily relates to glioblastoma (GBM); the most common and aggressive primary brain tumor in adults. Our group's recent discovery that IDO levels increase in the brain parenchyma during advanced age and regardless of whether GBM is present, highlights an immunosuppressive synergy between aging-increased IDO activity in cells of the central nervous system that reside outside of the brain tumor but collaborate with GBM cell IDO activity inside of the tumor. Because of their potential value for the in vivo study of IDO, we also review current transgenic animal modeling systems while highlighting three new constructs recently created by our group. This work converges on the central premise that maximal immunotherapeutic efficacy in subjects with advanced cancer requires both IDO enzyme- and non-enzyme-neutralization, which is not adequately addressed by available IDO-targeting pharmacologic approaches at this time.

Advanced Age Increases Immunosuppression in the Brain and Decreases Immunotherapeutic Efficacy in Subjects with Glioblastoma

PURPOSE

Wild-type isocitrate dehydrogenase-expressing glioblastoma (GBM) is the most common and aggressive primary brain tumor with a median age at diagnosis of ≥65 years. It accounts for approximately 90% of all GBMs and has a median overall survival (OS) of <15 months. Although immune checkpoint blockade (ICB) therapy has achieved remarkable survival benefits in a variety of aggressive malignancies, similar success has yet to be achieved for GBM among phase III clinical trials to date. Our study aimed to understand the relationship between subject age and immunotherapeutic efficacy as it relates to survival from glioma.

EXPERIMENTAL DESIGN

(i) Clinical data: GBM patient datasets from The Cancer Genome Atlas, Northwestern Medicine Enterprise Data Warehouse, and clinical studies evaluating ICB were stratified by age and compared for OS. (ii) Animal models: young, middle-aged, and older adult wild-type and indoleamine 2,3 dioxygenase (IDO)-knockout syngeneic mice were intracranially engrafted with CT-2A or GL261 glioma cell lines and treated with or without CTLA-4/PD-L1 mAbs, or radiation, anti-PD-1 mAb, and/or a pharmacologic IDO enzyme inhibitor.

RESULTS

Advanced age was associated with decreased GBM patient survival regardless of treatment with ICB. The advanced age-associated increase of brain IDO expression was linked to the suppression of immunotherapeutic efficacy and was not reversed by IDO enzyme inhibitor treatment.

CONCLUSIONS

Immunosuppression increases in the brain during advanced age and inhibits antiglioma immunity in older adults. Going forward, it will be important to fully understand the factors and mechanisms in the elderly brain that contribute to the decreased survival of older patients with GBM during treatment with ICB.

A retrospective survival analysis of Glioblastoma patients treated with selective serotonin reuptake inhibitors

Glioblastoma (GBM) is the most common and aggressive form of malignant glioma in adults with a median overall survival (OS) time of 16–18 months and a median age of diagnosis at 64 years old. Recent work has suggested that depression and psychosocial distress are associated with worse outcomes in patients with GBM. We therefore hypothesized that the targeted neutralization of psychosocial distress with selective serotonin reuptake inhibitor (SSRI) antidepressant treatment would be associated with a longer OS among patients with GBM. To address this hypothesis, we retrospectively studied the association between adjuvant SSRI usage and OS in GBM patients treated by Northwestern Medicine-affiliated providers. The medical records of 497 GBM patients were analyzed after extraction from the Northwestern Medicine Enterprise Data Warehouse. Data were retrospectively studied using a multivariable Cox model with SSRI use defined as a time-dependent variable for estimating the association with OS. Of the 497 patients, 315 individuals died, while 182 were censored due to the loss of follow-up or were alive at the end of our study. Of the 497 patients, 151 had a recorded use of SSRI treatment during the disease course. Unexpectedly, SSRI usage was not associated with an OS effect in both naïve (HR ​= ​0.81, 95% CI ​= ​0.64–1.03) and adjusted time-dependent (HR ​= ​1.26, 95% CI ​= ​0.97–1.63) Cox models. Ultimately, we failed to find an association between SSRI treatment and an improved OS of patients with GBM. Additional work is necessary for understanding the potential therapeutic effects of SSRIs when combined with other treatment approaches, and immunotherapies in particular, for subjects with GBM.

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SSRI use was not associated with improved overall survival in GBM patients.

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Analysis included fluoxetine, citalopram, escitalopram, sertraline, paroxetine, vilazodone.

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Multiple statistical models were used to verify the findings.

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Time-dependent modeling of SSRI use was critical to avoid immortal time bias.

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Future work in animal models or prospective studies is critical.

CBMT-34. MODULATING DIETARY TRYPTOPHAN OR GUT MICROBIOTA LEVELS DOES NOT IMPROVE THE EFFICACY OF COMBINED TREATMENT WITH RADIATION, ANTI-PD-1 mAb, AND AN IDO1 ENZYME INHIBITOR IN A MODEL OF GLIOBLASTOMA

INTRODUCTION

Immunotherapy has failed to improve glioblastoma (GBM) patient survival in all phase III clinical trials to-date. We recently discovered that a combination immunotherapeutic approach that simultaneously administers radiation (RT), anti-PD-1 mAb, and an IDO1 enzyme inhibitor resulted in long-term survival of ~40% of mice intracranially-engrafted (i.c.) with syngeneic GBM (Ladomersky et al., 2018; CCR). In the same study we discovered that the survival benefit depended on the inhibitor of IDO1 in non-GBM cells. Our current study further interrogates the role of non-GBM cell IDO1 and its role in the brain tumor microenvironment.

METHODS

Mice were engrafted with 2×105 GL261 cells and treated at 14 days post-intracranial injection (i.c.) with RT and/or anti-PD-1 mAb, followed by sampling tissue at 1- and 7-days post treatment. Questioning whether dietary supplementation of Trp would overcome the immunosuppressive activity of the Trp metabolic enzyme, IDO1, mice were placed on ad libitum dietary formulations containing 0–500% normal daily intake. Since Trp is only taken in through the diet, and since bacteria also metabolize Trp, we questioned the role of the gut microbiome on immunotherapy of GBM by injecting mice with an antibiotic cocktail beginning 4 weeks prior to i.c.-injection.

RESULTS

Both RT and anti-PD-1 treatment increase IDO1 expression in the GBM-draining cervical lymph nodes at day 1 post-ic. (P< 0.001). Mice receiving normal (100%) dietary Trp, but no other supplementation levels, achieve a long-term survival benefit (P< 0.001). Unexpectedly, the depletion of gut microbiota has no effect on therapeutic efficacy (P=0.4808).

CONCLUSION

These data suggest that although both systemic and tissue-selective alterations in Trp metabolism occur after RT and anti-PD-1 therapy, modulating dietary Trp levels or gut microbiota composition does not alter treatment efficacy against GBM.

IMMU-20. ADVANCED AGING INCREASES IMMUNOSUPPRESSIVE IDO1 LEVELS THAT ARE UNINHIBITED BY IDO1 ENZYME INHIBITOR TREATMENT IN MODELS OF GLIOBLASTOMA

Immunotherapy has failed to improve the overall survival (OS) of adults with GBM in all phase III clinical trials to-date. Somewhat less appreciated is that, de novo GBM is a disease associated with a median age of diagnosis at 64 years old. Because of the strong association between advanced aging and human subjects presenting with GBM, we further investigated our previously described observation of a higher mortality rate in elderly C57BL/6 wild-type (WT) mice with intracranial GL261 as compared to young counterparts after treatment with radiotherapy (RT) and anti-PD-1 (PD1)/IDO1 enzyme inhibitor (IDO1i) (Ladomersky et al., 2018; Clinical Cancer Research). Since immunosuppressive IDO1 expression significantly increases in both the mouse and human brain during advanced aging (Ladomersky et al., 2019; Frontiers in Pharm.), we decided to study how IDO1 and aging interact during immunotherapy of GBM. We found that the pretreatment effects of an IDO1 enzyme inhibitor improve OS in young but not elderly WT mice with intracranial GL261 (n=12–15/group; p< 0.05). Strikingly, in the setting of advanced aging, IDO1-/- mice with GBM show improved OS as compared with WT mice (p< 0.01) independent of treatment with an IDO1 enzyme inhibitor. Similarly stunning, 74–80 week old IDO1-/- mice with GBM treated at 14 days post-ic. with RT and PD1/IDO1i survive significantly longer as compared to elderly WT mice administered the same treatment (n=20–22/group; p< 0.05). These results collectively suggest that, the therapeutic effects of IDO1 enzyme inhibition is less effective in the setting of old age, and provides rationale for the development of new approaches that inhibit IDO1-mediated immunosuppression independent of its association with enzyme activity for eventually improving immunotherapeutic efficacy in human subjects with malignant glioma.

IMMU-44. INHIBITING IMMUNOSUPPRESSIVE IDO1 IN ADULTS WITH MALIGNANT GLIOMA – A MOVING TARGET THAT CHANGES WITH TREATMENT, CELL OF ORIGIN, AND AGING

We previously demonstrated that glioblastoma (GBM) cell IDO1 increases intratumoral immunosuppressive regulatory T cells (Tregs; CD4+CD25+FoxP3+) and decreases overall survival (OS) in the syngeneic GL261 model. IDO1 is characterized as an enzyme that converts the amino acid, tryptophan, into kynurenine. With the finding that IDO1 expression by GBM cells promotes intratumoral Treg accumulation, it was surprising to find that this process was unaffected by the pharmacological treatment with an IDO1 enzyme inhibitor (IDO1i). This led us to question the optimal therapeutic strategy for leveraging an IDO1i against GBM. Utilizing simultaneous whole brain radiation (RT), anti-PD-1 mAb, and an IDO1i, we discovered a long-term survival advantage in ~40% of young WT mice engrafted with either GL261 or CT-2A (n=9–10/group; p< 0.01). Unexpectedly, dual treatment with RT and anti-PD-1 achieved a similar long-term survival advantage in IDO1KO-, but not in WT mice with GBM (n=14/group; p< 0.01), confirming that the therapeutic target of IDO1i was in non-GBM cells. Notably, the triple immunotherapeutic treatment was less effective in elderly mice analogous to the median age of a GBM patient diagnosis (n=20–22/group; p< 0.01) and coincident with increased IDO1 expression in the elderly human brain (n=1,152; p< 0.01). Our working hypothesis is: (i) advanced aging increases IDO1 levels in the brain; (ii) RT elicits the release of GBM cell neoantigens; (iii) IDO1+ lymph node (LN) DCs process/present GBM cell neoantigens to cognate CD8+ T cells; (iv) IDO1i treatment decreases the suppression of IDO1+ DC:CD8+ T cell priming; (v) anti-PD1 treatment enhances LN priming initialized by RT + IDO1i; (vi) brain-resident IDO1+ DCs accumulate during advanced aging and suppress the newly-generated brain-infiltrating CD8+ GBM-specific T cells independent of IDO1i. Our work highlights the immunosuppressive role of advanced aging and the need to better understand gero-neuro-immuno-oncology interactions for enhancing future immunotherapeutic efficacy in adults with GBM.

HOUT-20. TIME-DEPENDENT ANALYSIS OF SELECTIVE SEROTONIN REUPTAKE INHIBITOR TREATMENT ON OVERALL SURVIVAL OF PATIENTS WITH GLIOBLASTOMA

Glioblastoma (GBM) is the most common and aggressive form of primary brain tumor in adults. We recently investigated the hypothesis that treating GBM patients with psychosocial modifiers would be associated with improved overall survival (OS). Our study retrospectively analyzed 497 patients with GBM treated at Northwestern Medicine with or without selective serotonin reuptake inhibitors (SSRI) between the years 2000 and 2018. Information from the Northwestern Medicine Enterprise Data Warehouse was analyzed for baseline covariates including sex, age at diagnosis, type of surgery, and Charlson Comorbidity Index Score. Approximately one-third of analyzed patients were prescribed SSRIs, with highly variable treatment times. Several statistical methods were used to perform adjusted analyses including: (i) an extended Cox Proportional Hazards Model with SSRI as a time-dependent variable; (ii) a Cox Model using inverse probability weights; and (iii) a Cox Proportional Hazards model with landmark analyses. The hazard ratios (95% CIs) for each statistical model analyzing the association between SSRI treatment and OS were (i) 1.26 (0.97–1.63), (ii) 1.06 (0.8–1.4), and (iii) ranged from 1.01 (0.74–1.38) to 1.26 (0.75–2.09). Our analysis found no significant association between the time of SSRI treatment and GBM patient OS. Future work will study additional considerations for psychosocial modifier treatment and their potential effect(s) on GBM patient OS including: (i) confounders due to the extent of cancer treatment; (ii) comorbidities not associated with tumor burden; (iii) absolute leukocyte counts; and (iv) length of treatment time required for enhancing immune-mediated anti-GBM mechanisms.

IMMU-22. TARGETING NON-CANONICAL FUNCTION OF IDO1 IN GLIOBLASTOMA IMMUNOTHERAPY

Recent failure of immune checkpoint blockade, anti-PD-1 therapy in patients suffering recurrent glioblastoma (GBM) indicates that development of novel immunosuppressive mediator-targeted therapeutic strategy is critical for more effective immunotherapies against GBM. Indoleamine 2, 3-dioxygenase 1 (IDO1) has been shown to mediate tumor-induced immunosuppression through its tryptophan catabolic activity. Surprisingly, pharmacological IDO1 enzyme inhibitors have not demonstrated any survival benefit in cancer patients either mono-therapeutically or in combination with other therapies. Previously we confirmed that tumor IDO1 mRNA expression is significantly upregulated in GBM patients compared to those from patients with lower grades gliomas. Furthermore, knockdown of IDO1 in mouse GBM cells significantly increased mouse survival and decreased tumor infiltrating Tregs, but did not affect tumor local tryptophan catabolism. Consistently, inhibition of IDO1 enzymatic activity on GBM-bearing mice did not yield any survival benefit. These findings indicate that IDO1 may suppress immune response through a non-enzymatic pathway. To test this hypothesis, IDO1-deficient mouse GBM cells were created and modified to stably express either wild-type (WT) or enzyme-null IDO1. Syngeneic mice intracranially engrafted with both WT and enzyme-null IDO1 overexpressing GBM cells showed significantly increase of tumor infiltrating Tregs and decreased survival in comparison to mice engrafted with IDO1-deficient GBM cells. In contrast, no difference was observed between WT-IDO1 GBM and enzyme-null IDO1 GBM groups. Additionally, when co-cultured with splenic monocytes, both WT and enzyme-null IDO1 overexpressing GBM cells induced more mature macrophages than IDO1-deficient GBM cells. Taken together, our data strongly imply an enzyme independent pathway associated with IDO1-driven immunosuppression in mouse GBM. Validation of this novel mechanism on human GBM cells is ongoing. A soluble molecule has been identified as a potential mediator for the non-enzymatic function of IDO1. Results from this study will provide innovative strategies for IDO1-based immunotherapy against GBM.

Tumor cell IDO1 increases intratumoral immunosuppressive Tregs independent of enzyme activity

Objective

Indoleamine 2, 3 dioxygenase 1 (IDO1) is a rate limiting enzyme that converts tryptophan (Trp) into kynurenine (Kyn). IDO1 knockdown in murine glioblastoma (GBM) cells suppresses intratumoral regulatory T cell (Treg) recruitment and increases survival, but unexpectedly, has no effect on intratumoral Trp levels. Moreover, while GBM cell IDO1 overexpression increases intratumoral Treg levels, treatment with a pharmacological IDO1 enzyme inhibitor fails to reverse this effect. These novel data led us to question whether GBM cell IDO1 recruits Tregs independent of enzyme activity, in vivo.

Methods

Ido1−/− mouse GBM cells reconstituted with wild-type or enzyme-null (H350A) murine Ido1 cDNA, and IDO1−/− human GBM cells were created. HPLC for Trp/Kyn levels, cell proliferation, cell viability, and splenic macrophage-GBM cell co-cultures, were studied in vitro. Syngeneic or humanized mice intracranially-engrafted with modified mouse or human GBM cells, respectively, were studied for the effect(s) on Treg accumulation and/or survival.

Results

As compared with IDO1 WT GBM cells, IDO1 H350A GBM cells show a significant decrease of Trp metabolism without affecting cell proliferation and viability. As compared with vector control GBM cells, co-culture for both IDO1 WT and H350A GBM cells induces greater numbers of mature macrophages. Independent of enzyme activity, GBM cell IDO1 expression increases intratumoral Tregs and decreases animal survival.

Conclusions

We created novel GBM models for elucidating the mechanism of metabolism-independent, IDO1-mediated intratumoral Treg accumulation. Given the majority of cancers with IDO1 expression, we suspect that our work may be generalizable to many types of malignancies.

The Coincidence Between Increasing Age, Immunosuppression, and the Incidence of Patients With Glioblastoma

Background: Glioblastoma (GBM) is the most aggressive primary brain tumor in adults and is associated with a median overall survival (mOS) of 16-21 months. Our previous work found a negative association between advanced aging and the survival benefit after treatment with immunotherapy in an experimental brain tumor model. Given the recent phase III clinical success of immunotherapy in patients with many types of cancer, but not for patients with GBM, we hypothesize that aging enhances immunosuppression in the brain and contributes to the lack of efficacy for immunotherapy to improve mOS in patients with malignant glioma. Herein, we compare epidemiological data for the incidence and mortality of patients with central nervous system (CNS) cancers, in addition to immune-related gene expression in the normal human brain, as well as peripheral blood immunological changes across the adult lifespan. Methods: Data were extracted from the National Cancer Institute's surveillance, epidemiology, and end results (SEER)-, the Broad Institute's Genotype Tissue Expression project (GTEx)-, and the University of California San Francisco's 10k Immunomes-databases and analyzed for associations with aging. Results: The proportion of elderly individuals, defined as ≥65 years of age, has predominantly increased for more than 100 years in the United States. Over time, the rise in elderly United States citizens has correlated with an increased incidence and mortality rate associated with primary brain and other CNS cancer. With advanced aging, human mRNA expression for factors associated with immunoregulation including immunosuppressive indoleamine 2,3 dioxygenase 1 (IDO) and programmed death-ligand 1 (PD-L1), as well as the dendritic cell surface marker, CD11c, increase in the brain of normal human subjects, coincident with increased circulating immunosuppressive Tregs and decreased cytolytic CD8⁺ T cells in the peripheral blood. Strikingly, these changes are maximally pronounced in the 60-69 year old group; consistent with the median age of a diagnosis for GBM. Conclusion: These data demonstrate a significant association between normal human aging and increased immunosuppression in the circulation and CNS; particularly late in life. Our data raise several hypotheses including that, aging: (i) progressively suppresses normal immunosurveillance and thereby contributes to GBM cell initiation and/or outgrowth; (ii) decreases immunotherapeutic efficacy against malignant glioma.

Newly Diagnosed Glioblastoma: A Review on Clinical Management

Glioblastoma is an aggressive primary tumor of the central nervous system. This review will focus on clinical developments and management of newly diagnosed disease, including a discussion about the incorporation of molecular features into the classification of glioblastoma. Such advances will continue to shape our thinking about the disease and how to best manage it. With regards to treatment, the role of surgical resection, radiotherapy, chemotherapy, and tumor-treating fields will be presented. Pivotal studies defining our current standard of care will be highlighted, as will key ongoing trials that may influence our management of glioblastoma in the near future.

Commentary: preclinical efficacy of immune-checkpoint monotherapy does not recapitulate corresponding biomarkers-based clinical predictions in glioblastoma by Garg et al. (2017)

Preclinical modeling and gene expression analyses have yielded distinct observations for the role of immune checkpoint, IDO1, in glioblastoma (GBM). Accordingly, our recent work differs with Garg et al. (2017) with respect to IDO1 among preclinical and bioinformatic GBM datasets. Here, we discuss the methodological differences that affected study interpretation, and potentially, future clinical decision-making for IDO1-targeting approaches against GBM.

Abstract LB-285: Non-enzyme IDO1 activity and its immunosuppressive effects in glioblastoma

Purpose: Adult glioblastoma (GBM) is the most common primary malignant brain tumor of the central nervous system (CNS) with a median patient survival of 15-20 months. A consistent feature of GBM is the presence of indoleamine 2,3 dioxygenase 1 (IDO1) expressed by tumor cells. IDO1 is canonically characterized as an enzyme that metabolizes tryptophan (Trp) into kynurenines (Kyns). Tryptophan metabolism is the primary feature associated with IDO1-mediated immune suppression - primarily derived from in vitro study. Less appreciated is the recent find that, plasmacytoid dendritic cells (pDCs) utilize IDO1 to activate the non-canonical NFκB pathway, independent of Trp metabolism, resulting in greater levels of immunosuppression. The scientific premise of our study was therefore to determine whether GBM cell IDO1 is capable of mediating immunosuppression without associated enzyme activity.

Experimental methods: IDO1-deficient (IDO1-/-) glioma cells isolated from mice that spontaneously develop GBM [GFAP(ERT2)→Cre+/-;pTENfl/fl;Rbfl/fl;p53fl/fl;IDO1-/-] were transduced with lentiviral particles expressing wild-type or modified mouse IDO1 cDNA fused to a mGFP tag. Stably expressing cells were enriched for high IDO1/GFP expression by fluorescence-activated cell sorting and confirmed with RT-PCR and Western blotting. The effects of IDO1 modification on Trp/Kyn was quantified by HPLC. IDO1-/- syngeneic mice were intracranially-engrafted with modified GBM cells and studied for regulatory T cell (Treg; CD4+CD25+FoxP3+)/MDSC accumulation.

Results: (i) Viral transduction yielded stable expression of murine IDO1 mRNA and protein; (ii) the mGFP tag did not interfere with IDO1 enzyme activity in unmodified GBM cells; (iii) the histidine 350 to alanine (H350A), as well as aspartic acid 278 to alanine (D278A) mutations cause decreased or ablated IDO1 enzyme activity, respectively; (iv) ITIM mutation of tyrosine into glutamate (YE), as well as tyrosine into phenylalanine (YF), had a minimal effect on IDO1 enzyme activity.

Conclusions: We established new, novel, GFP-tagged mouse GBM cell lines to dissect the immunosuppressive contributions of Trp metabolism vs. non-enzyme functions as mediated by IDO1. Some GBM cell lines expressed high IDO1 with no Trp catabolic activity. GBM with IDO1-associated ITIM mutations showed marginal effects on enzyme activity. The analysis of in vitro GBM cell growth/cell death rate, invasion, and effects on co-cultured Tregs, as well as the in vivo analysis of GBM-infiltrating Treg/MDSC levels and impact on overall survival, will be presented.

Citation Format: Lijie Zhai, Jun Qian, Erik Ladomersky, Alicia Lenzen, Kristen L. Lauing, Derek A. Wainwright. Non-enzyme IDO1 activity and its immunosuppressive effects in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-285.

IDO1 in cancer: a Gemini of immune checkpoints

Indoleamine 2, 3-dioxygenase 1 (IDO1) is a rate-limiting metabolic enzyme that converts the essential amino acid tryptophan (Trp) into downstream catabolites known as kynurenines. Coincidently, numerous studies have demonstrated that IDO1 is highly expressed in multiple types of human cancer. Preclinical studies have further introduced an interesting paradox: while single-agent treatment with IDO1 enzyme inhibitor has a negligible effect on decreasing the established cancer burden, approaches combining select therapies with IDO1 blockade tend to yield a synergistic benefit against tumor growth and/or animal subject survival. Given the high expression of IDO1 among multiple cancer types along with the lack of monotherapeutic efficacy, these data suggest that there is a more complex mechanism of action than previously appreciated. Similar to the dual faces of the astrological Gemini, we highlight the multiple roles of IDO1 and review its canonical association with IDO1-dependent tryptophan metabolism, as well as documented evidence confirming the dispensability of enzyme activity for its immunosuppressive effects. The gene transcript levels for IDO1 highlight its strong association with T-cell infiltration, but the lack of a universal prognostic significance among all cancer subtypes. Finally, ongoing clinical trials are discussed with consideration of IDO1-targeting strategies that enhance the efficacy of immunotherapy for cancer patients.

IDO1 Inhibition Synergizes with Radiation and PD-1 Blockade to Durably Increase Survival Against Advanced Glioblastoma

Purpose: Glioblastoma is the most aggressive primary brain tumor in adults with a median survival of 15-20 months. Numerous approaches and novel therapeutics for treating glioblastoma have been investigated in the setting of phase III clinical trials, including a recent analysis of the immune checkpoint inhibitor, nivolumab (anti-PD-1), which failed to improve recurrent glioblastoma patient survival. However, rather than abandoning immune checkpoint inhibitor treatment for glioblastoma, which has shown promise in other types of cancer, ongoing studies are currently evaluating this therapeutic class when combined with other agents.Experimental Design: Here, we investigated immunocompetent orthotopic mouse models of glioblastoma treated with the potent CNS-penetrating IDO1 enzyme inhibitor, BGB-5777, combined with anti-PD1 mAb, as well as radiotherapy, based on our recent observation that tumor-infiltrating T cells directly increase immunosuppressive IDO1 levels in human glioblastoma, the previously described reinvigoration of immune cell functions after PD-1 blockade, as well as the proinflammatory effects of radiation.Results: Our results demonstrate a durable survival benefit from this novel three-agent treatment, but not for any single- or dual-agent combination. Unexpectedly, treatment efficacy required IDO1 enzyme inhibition in non-glioblastoma cells, rather than tumor cells. Timing of effector T-cell infiltration, animal subject age, and usage of systemic chemotherapy, all directly impacted therapy-mediated survival benefit.Conclusions: These data highlight a novel and clinically relevant immunotherapeutic approach with associated mechanistic considerations that have formed the basis of a newly initiated phase I/II trial for glioblastoma patients. Clin Cancer Res; 24(11); 2559-73. ©2018 AACR.

Infiltrating T Cells Increase IDO1 Expression in Glioblastoma and Contribute to Decreased Patient Survival

Purpose: Indoleamine 2,3 dioxygenase 1 (IDO1) mediates potent immunosuppression in multiple preclinical models of cancer. However, the basis for elevated IDO1 expression in human cancer, including the most common primary malignant brain tumor in adults, glioblastoma (GBM), is poorly understood. The major objective of this study is to address this gap in our understanding of how IDO1 expression contributes to the biology of GBM, and whether its level of expression is a determinant of GBM patient outcome.Experimental Design: Patient-resected GBM, The Cancer Genome Atlas, human T-cell:GBM cocultures, as well as nu/nu, NOD-scid, and humanized (NSG-SGM3-BLT) mice-engrafted human GBM form the basis of our investigation.Results:In situ hybridization for IDO1 revealed transcript expression throughout patient-resected GBM, whereas immunohistochemical IDO1 positivity was highly variable. Multivariate statistical analysis revealed that higher levels of IDO1 transcript predict a poor patient prognosis (P = 0.0076). GBM IDO1 mRNA levels positively correlated with increased gene expression for markers of cytolytic and regulatory T cells, in addition to decreased patient survival. Humanized mice intracranially engrafted human GBM revealed an IFNγ-associated T-cell-mediated increase of intratumoral IDO1Conclusions: Our data demonstrate that high intratumoral IDO1 mRNA levels correlate with a poor GBM patient prognosis. It also confirms the positive correlation between increased GBM IDO1 levels and human-infiltrating T cells. Collectively, this study suggests that future efforts aimed at increasing T-cell-mediated effects against GBM should consider combinatorial approaches that coinhibit potential T-cell-mediated IDO1 enhancement during therapy. Clin Cancer Res; 23(21); 6650-60. ©2017 AACR.

Non-tumor cell IDO1 predominantly contributes to enzyme activity and response to CTLA-4/PD-L1 inhibition in mouse glioblastoma

Glioblastoma (GBM) is the most common malignant brain tumor in adults with a median survival of 14.6months. A contributing factor to GBM aggressiveness is the intratumoral expression of the potently immunosuppressive enzyme, indoleamine 2,3 dioxygenase 1 (IDO1). The enzymatic activity of IDO1 is associated with the conversion of tryptophan into downstream kynurenine (Kyn), which has previously been hypothesized to contribute toward the suppression of tumor immunity. Utilizing the syngeneic, immunocompetent, intracranial GL261 cell GBM model, we previously demonstrated that tumor cell, but not non-tumor cell IDO1, suppresses T cell-mediated brain tumor regression in mice. Paradoxically, we also showed that the survival advantage mediated by immune checkpoint blockade is abrogated by non-tumor cell IDO1 deficiency. Here, we have built on our past observations and confirm the maladaptive role of tumor cell IDO1 in a novel mouse GBM model. We also demonstrate that, non-tumor cells, rather than mouse GBM cells, are the dominant contributor to IDO1-mediated enzyme activity. Finally, we show the novel associations between maximally-effective immune-checkpoint blockade-mediated survival, non-tumor cell IDO1 and intra-GBM Kyn levels. These data suggest for the first time that, GBM cell-mediated immunosuppression is IDO1 enzyme independent, while the survival benefits of immune checkpoint blockade require non-tumor cell IDO1 enzyme activity. Given that current clinical inhibitors vary in their mechanism of action, in terms of targeting IDO1 enzyme activity versus enzyme-independent effects, this work suggests that choosing an appropriate IDO1 pharmacologic will maximize the effectiveness of future immune checkpoint blockade approaches.

Abstract A064: IDO1 expression stratifies glioblastoma patient survival and correlates with dominantly immunosuppressive pathways

Purpose: The objective of this study was to evaluate the prognostic significance of the immunosuppressive molecule indoleamine 2, 3-dioxygenase (IDO1) mRNA expression in patients with low-grade glioma (LGG) and glioblastoma (GBM).

Experimental Design: Hi-RNA-seq. Illumina data mined from the cancer genome atlas (TCGA) reflecting 475 LGG (WHO grade II and III) and 172 GBM patients were utilized to characterize the pattern of IDO1 mRNA expression. Kaplan-Meier (KM) survival analysis and multivariate Cox proportional hazards regression were conducted to evaluate the significance of IDO1 expression as a stratification marker in glioma patients. mRNA expression of proinflammatory and immunosuppressive factor genes were also investigated for their correlation with IDO1 mRNA expression. Ivy GAP analysis was further utilized to localize IDO1 mRNA within different GBM anatomic niches.

Results: Expression profiling of the TCGA revealed a distinct pattern of progressively increasing IDO1 mRNA levels correlating with decreased survival both in LGG and GBM patients. In grade III LGG and GBM, IDO1 mRNA expression was significantly decreased when mutant isocitrate dehydrogenase 1 and 2 (mIDH1/2) was coincidently expressed when compared to samples with wild-type IDH1/2 expression (mean difference = 1.51, P &lt; 0.0001 in grade III; mean difference = 2.15, P &lt; 0.01 in GBM). KM analysis and multivariate Cox regression analysis found IDO1 mRNA expression levels to be an independent prognostic factor for survival among LGG (P = 0.0115; HR = 1.68) and GBM (P = 0.0076; HR = 1.82) patients. Pearson's correlation analysis identified significant associations among GBM between IDO1 and the genes encoding immunosuppressive factors including PD-L1 (r = 0.2993, P &lt; 0.0001), PD-L2 (r = 0.4871, P &lt; 0.0001), PD-1 (r = 0.3416, P &lt; 0.0001), CTLA-4 (r = 0.3534, P &lt; 0.0001), STAT3 (r = 0.2366, P = 0.0018), CD39 (r = 0.2691, P = 0.0004), BTLA (r = 0.2981, P &lt; 0.0001), Lag3 (r = 0.2567, P = 0.0007), FoxP3 (r = 0.1865, P &lt; 0.0143) and FGL2 (r = 0.4267, P &lt; 0.0001). Notably, IDO1 mRNA levels were higher in the cellular (1.398 ± 0.1257, mean ± SEM) and necrotic (1.543 ± 0.1489) GBM zones, when compared to infiltrating (0.9303 ± 0.0786) and leading margins (0.9064 ± 0.1224). Additionally, for the IDO1 paralog genes IDO2 and TDO2, which encodes indoleamine 2, 3-dioxygenase 2 and tryptophan dioxygenase respectively, no overall differential expression pattern were observed between different pathological grades nor a significant stratification in LGG and GBM patient survival.

Conclusions: Our data show for the first time that IDO1 mRNA levels can be used as an independent prognostic variable for patients with LGG and/or GBM. Given that ongoing IDO1-targeted immunotherapy clinical trials aim to inhibit enzymatic activity in malignant glioma, our data suggest that targeted subject enrollment may result in a better clinical response to therapy.

Citation Format: Lijie Zhai, Matthew Genet, Erik Ladomersky, Kristen Lauing, Meijing Wu, David Binder, Leo Kim, Jeremy Rich, Craig Horbinski, C. David James, Jeffrey A. Sosman, Orin Bloch, Derek A. Wainwright. IDO1 expression stratifies glioblastoma patient survival and correlates with dominantly immunosuppressive pathways [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A064.

Abstract B018: A novel IDO1 inhibitor combined with targeted immunotherapy durably increases survival in a mouse model of glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor, accounting for 54% of malignant glioma diagnoses. Over the course of the past 30 years, a diagnosis of GBM has remained fatal even after maximum surgical resection, radiotherapy (RT), and chemotherapy, with a median overall survival of 14.6 months. The immunosuppressive microenvironment of GBM is a major contributor to the poor patient outcome. Expression of IDO1, as well as the accumulation of tumor-infiltrating regulatory T cells contribute to the avoidance of immune surveillance. Although current immunotherapies have had some success in extending patient survival, combinatorial treatment approaches addressing both tumor growth and the potent immunosuppression may prove to be more effective. This work aimed to determine the efficacy of a novel, pharmaceutical-grade, blood brain barrier-penetrating small molecule IDO1 inhibitor, BGB-5777, in combination with PD-1 blockade and/or whole brain radiation in an immunocompetent mouse GBM model. METHODS/RESULTS: All mice were intracranially-engrafted 2×105 GL261 (syngeneic to B6 background) cells to recapitulate brain tumors. At 14 days post-intracranial injection (dp-ic.), mice were treated with IgG alone as a control (n = 7), 2Gy RT for 5 days (n = 8), 500 ug (loading dose), followed by three 200 ug maintenance doses given every 3 days, of PD-1 mAb (J43) (n = 8), or 100mg/kg BGB-5777 for 4 weeks (n = 10), with a median overall survival (OS) of 25, 25, 32, and 26.5 days, respectively. Mice treated with dual therapies including RT and PD-1 mAb (n = 10), RT and BGB-5777 (n = 8), or PD-1 mAb and BGB-5777 (n = 9), had a median OS of 30, 39, and 32 days, respectively. All mice treated with mono- or dual-therapy succumbed to tumor burden. In contrast, mice treated with concurrent RT, PD-1 mAb and BGB-5777 (n = 9) showed a significant increase in median OS to 53 days (P&lt;0.0001) with 33% of mice demonstrating a durable survival benefit of more than 150 days. Importantly, mice treated with the triple therapy and co-administered CD4 (n = 9)-, but not CD8 (n = 9)- or NK1.1 (n = 9)-depleting mAb, significantly decreased median OS to 29 days (P&lt;0.001) confirming the requirement of CD4+ T cells for efficacy of this immunotherapeutic approach. CONCLUSION: The data indicate that combining the standard of care agent, RT, with PD-1 blockade and the novel IDO1 inhibitor, BGB-5777, synergistically increases OS in a mouse GBM model. Unexpectedly, CD4+, rather than CD8+ T cells, are required for immunotherapeutic efficacy. Understanding how CD4+ T cells coordinate anti-GBM immunity, the kinetics of PD-1 and IDO1 expression after RT, and determining why CD8+ T cells are dispensable under these conditions, are current areas of active investigation in our laboratory. Ultimately, these data suggest that using radiation to induce potential immunogenicity and/or inflammation in GBM, while co-inhibiting immunosuppression, is a rational and potentially clinically-beneficial pursuit.

Citation Format: Erik Ladomersky, Lijie Zhai, Galina Gritsina, Kristen L. Lauing, Matthew Genet, C. David James, Derek A. Wainwright. A novel IDO1 inhibitor combined with targeted immunotherapy durably increases survival in a mouse model of glioblastoma [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B018.