Journal
CLINICAL CANCER RESEARCH
Volume 20, Issue 20, Pages 5290-5301Publisher
AMER ASSOC CANCER RESEARCH
DOI: 10.1158/1078-0432.CCR-14-0514
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Funding
- American Brain Tumor Association Discovery
- NIH [NIH F32 NS073366, NIH K99 NS082381, NIH R01 CA122930, NIH U01 NS069997]
- [R01 CA138587]
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Purpose: Glioblastoma (GBM) is the most common form of malignant glioma in adults. Although protected by both the blood-brain and blood-tumor barriers, GBMs are actively infiltrated by T cells. Previous work has shownthatIDO, CTLA-4, and PD-L1 aredominantmolecular participants in the suppression of GBM immunity. This includes IDO-mediated regulatory T-cell (Treg; CD4(+)CD25(+)FoxP3(+)) accumulation, the interaction of T-cell-expressed, CTLA-4, with dendritic cell-expressed, CD80, as well as the interaction of tumor-and/ ormacrophage-expressed, PD-L1, with T-cell-expressed, PD-1. The individual inhibition of each pathway has been shown to increase survival in the context of experimental GBM. However, the impact of simultaneously targeting all three pathways in brain tumors has been left unanswered. Experimental Design and Results: In this report, we demonstrate that, when dually challenged, IDOdeficient tumors provide a selectively competitive survival advantage against IDO-competent tumors. Next, we provide novel observations regarding tryptophan catabolic enzyme expression, before showing that the therapeutic inhibition of IDO, CTLA-4, and PD-L1 in a mouse model of well-established glioma maximally decreases tumor-infiltrating Tregs, coincident with a significant increase in T-cell-mediated long-term survival. In fact, 100% of mice bearing intracranial tumors were long-term survivors following triple combination therapy. The expression and/ or frequency of T cell expressed CD44, CTLA-4, PD-1, and IFN-gamma depended on timing after immunotherapeutic administration. Conclusions: Collectively, these data provide strong preclinical evidence that combinatorially targeting immunosuppression in malignant glioma is a strategy that has high potential value for future clinical trials in patients with GBM. (C) 2014 AACR.
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