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.

CNSC-27. AN IDO-PROTAC HIGHLIGHTS A NOVEL TRYPTOPHAN METABOLISM- INDEPENDENT ROLE FOR IMMUNOSUPPRESSIVE IDO IN HUMAN GLIOBLASTOMA

INTRODUCTION

Indoleamine 2,3-dioxygenase 1 (IDO) is an immunosuppressive enzyme that catabolizes the essential amino acid, tryptophan (Trp), into the metabolite, kynurenine. IDO is expressed in >90% of patient resected GBM. IDO suppresses the anti-brain tumor immune response, in-part, through non-metabolic activities. To determine how IDO non-metabolically suppresses the anti-GBM immune response, IDO-protein degrader (IDO-proteolysis targeting chimera; IDO-PROTAC) effects were studied in multiple human models of GBM.

METHODS

The IDO-expressing GBM cell lines, U87, U138, as well as the patient derived xenograft (PDX) line, GBM43, were treated with either IDO-PROTAC, mutant PROTAC, IDO enzyme inhibitor, or IDO siRNA, followed by RNA-seq analysis and/or mass spectrometry with quantitative proteomics using tandem mass tag (TMT) labelling.

RESULTS

Transcriptomic analysis revealed differentially expressed genes that were commonly regulated after treatment with the IDO-PROTAC as compared to treatment with the mutant PROTAC or IDO enzyme inhibitor groups in U87, U138, and GBM43 cells. Mass spectrometry analysis found 34 unique proteins that were differentially expressed inside of human GBM cells, with an additional 20 unique proteins that were identified in the supernatant of cultured human GBM cells after IDO-PROTAC treatment. Meta-analysis of the transcriptomic and proteomic analyses identified a novel factor that was unique to IDO-PROTAC treatment. GO terms that were enriched after IDO-PROTAC treatment identified nucleoside kinase activity as well as metallocarboxypeptidase activity.

CONCLUSIONS

This study discovered multiple new targets and pathways that immunosuppressive IDO regulates through a non-metabolic function. Functional analyses that validate the newly-discovered IDO-dependent, IDO-enzyme independent factors, are ongoing.

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.

A multi-institutional phase II trial of bevacizumab for recurrent and refractory meningioma

Background

Systemic therapies for refractory meningiomas are limited with no FDA-approved therapeutics. Vascular endothelial growth factor (VEGF) is a signaling protein associated with neovascularization, peritumoral edema, and meningioma tumorigenesis.

Methods

This phase II study investigates the efficacy of bevacizumab (BEV), a VEGF binding monoclonal antibody, in patients with progressive Grade I (G1M), Grade II (G2M), Grade III (G3M) meningioma, and other non-parenchymal tumors including vestibular schwannoma (n = 4) and hemangiopericytoma (n = 4) with the primary endpoint of progression-free survival rate at 6-months (PFS-6). Non-meningiomas were included with the respective meningioma grade in the analysis. Secondary endpoints include median overall survival (mOS) and response rate.

Results

Fifty Patients (26 women; median age 54 years; range 23-81), 42 with progressive meningioma were treated: 10 G1M, 20 G2M, and 12 G3M. Prior treatments include surgical resection (41 patients), radiosurgery (24 patients), external beam radiotherapy (28 patients), and chemotherapy (14 patients). Median infusions administered were 16 (range, 2-68). Response was graded using the Macdonald's criteria. PFS-6, median PFS, and mOS were 87%, 22 months, 35 months for G1M; 77%, 23 months, 41 months for G2M; and 46%, 8 months, 12 months for G3M. Best radiographic responses include stable disease (G1M: 100%; G2M: 85%; G3M: 82%); partial response (G1M: 0%; G2M: 5%; G3M: 0%) and progressive disease (G1M: 0%; G2M: 10%; G3M:18%). The most common toxicities were hypertension (n = 19, 42.2%), proteinuria (n = 16, 35.6%), and fatigue (n = 14, 31.1%).

Conclusion

This study showed BEV is well tolerated and appears to be a promising systemic treatment option for patients with recurrent and refractory meningiomas.

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.