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Abstract IA16: ER stress responses shape the ovarian cancer immune-microenvironment

Harnessing the intrinsic ability of our immune system to eliminate malignant cells represents the most promising new anticancer strategy since the development of chemotherapy. While cancer immunotherapy has been designated a scientific breakthrough, tumor-induced immunosuppression represents a major impediment to the success of this new approach in ovarian cancer. We uncovered that ovarian cancer inhibits the development of protective antitumor immunity by inducing a state of persistent “endoplasmic reticulum (ER) stress” in intratumoral dendritic cells (DCs) and T cells. First, we identified that sustained activation of the IRE1-XBP1 arm of the ER stress response in DCs was necessary for the aggressive and accelerated progression of primary and metastatic ovarian cancers in various preclinical models of disease. Mechanistically, intratumoral DCs exhibited constitutive IRE1-XBP1 activation, which was fueled by lipid peroxidation byproducts that caused ER stress by modifying ER-resident chaperones. Persistent XBP1 activation induced a comprehensive triglyceride biosynthetic program promoting accumulation of lipid droplets that subsequently impaired DC antigen presentation to T cells. Conditional deletion or therapeutic silencing of IRE1 or XBP1 in DCs restored their immunogenic function in the tumor and delayed ovarian cancer progression by eliciting protective antitumor T-cell responses. In addition, we recently demonstrated that ovarian cancer also triggers abnormal IRE1-XBP1 activation in T cells to control their mitochondrial function and antitumor activity. XBP1 upregulation in T cells isolated from human ovarian cancer specimens was associated with decreased intratumoral T-cell infiltration and reduced IFNG expression. Ascites fluid from ovarian cancer patients inhibited glucose uptake and caused N-linked protein glycosylation defects in T cells, leading to XBP1-driven mitochondrial dysfunction. Mechanistically, maladaptive XBP1 signaling limited the influx of glutamine necessary to sustain mitochondrial respiration under glucose-deprived conditions. Hence, ovarian cancer hosts lacking XBP1 selectively in T cells demonstrated superior antitumor immunity, delayed malignant progression, and increased overall survival. Taken together, our studies revealed that ovarian cancer provokes persistent IRE1-XBP1 signaling in immune cells to shape the tumor microenvironment and evade immune control. These findings provide a new mechanistic understanding of immunosuppression in ovarian cancer and offer novel avenues for immunotherapeutic intervention. Citation Format: Juan R. Cubillos-Ruiz. ER stress responses shape the ovarian cancer immune-microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr IA16.