Tumors evade immune control by creating hostile microenvironments that perturb T cell metabolism and effector function 1 – 4 . However, it remains unclear how intratumoral T cells integrate and interpret metabolic stress signals. Here we report that ovarian cancer (OvCa), an aggressive malignancy refractory to standard treatments and current immunotherapies 5 – 8 , induces Endoplasmic Reticulum (ER) stress and activation of the IRE1α-XBP1 arm of the Unfolded Protein Response (UPR) 9 , 10 in T cells to control their mitochondrial respiration and anti-tumor function. XBP1 upregulation in T cells isolated from human OvCa specimens was associated with decreased intratumoral T cell infiltration and reduced IFNG mRNA expression. Malignant ascites fluid obtained from OvCa patients inhibited glucose uptake and caused N -linked protein glycosylation defects in T cells, leading to IRE1α/XBP1-driven suppression of mitochondrial activity and IFN-γ production. Mechanistically, XBP1 induction limited the influx of glutamine necessary to sustain T cell mitochondrial respiration under glucose-deprived conditions by regulating the abundance of glutamine carriers. Restoring N -linked protein glycosylation, abrogating IRE1α-XBP1 activation or enforcing expression of glutamine transporters enhanced mitochondrial respiration in human T cells exposed to OvCa ascites. XBP1-deficient T cells in the metastatic OvCa milieu exhibited global transcriptional reprogramming and improved effector capacity. Accordingly, OvCa-bearing mice lacking XBP1 selectively in T cells demonstrated superior anti-tumor immunity, delayed malignant progression and increased overall survival. Therefore, controlling ER stress or targeting IRE1α-XBP1 signaling may help restore T cell metabolic fitness and anti-tumor capacity in cancer hosts.
The role of estrogens in anti-tumor immunity remains poorly understood. Here we show that estrogen signaling accelerates the progression of different estrogen insensitive tumor models by contributing to deregulated myelopoiesis by both driving the mobilization of myeloid-derived suppressor cells (MDSCs) and enhancing their intrinsic immunosuppressive activity in vivo. Differences in tumor growth are dependent on blunted anti-tumor immunity and, correspondingly, disappear in immunodeficient hosts and upon MDSC depletion. Mechanistically, estrogen receptor alpha activates the STAT3 pathway in human and mouse bone marrow myeloid precursors by enhancing JAK2 and SRC activity. Therefore, estrogen signaling is a crucial mechanism underlying pathological myelopoiesis in cancer. Our work suggests that new anti-estrogen drugs that have no agonistic effects may have benefits in a wide range of cancers, independently of the expression of estrogen receptors in tumor cells, and may synergize with immunotherapies to significantly extend survival.
SUMMARY Despite the importance of programmed cell death-1 (PD-1) in inhibiting T cell effector activity, the mechanisms regulating its expression remain poorly defined. We found that the chromatin organizer special AT-rich sequence-binding protein-1 (Satb1) restrains PD-1 expression induced upon T cell activation by recruiting a nucleosome remodeling deacetylase (NuRD) complex to Pdcd1 regulatory regions. Satb1 deficienct T cells exhibited a 40-fold increase in PD-1 expression. Tumor-derived Transforming Growth Factor β (Tgf-β) decreased Satb1 expression through binding of Smad proteins to the Satb1 promoter. Smad proteins also competed with the Satb1-NuRD complex for binding to Pdcd1 enhancers, releasing Pdcd1 expression from Satb1-mediated repression, Satb1-deficient tumor-reactive T cells lost effector activity more rapidly than wild-type lymphocytes at tumor beds expressing PD-1 ligand (CD274), and these differences were abrogated by sustained CD274 blockade. Our findings suggest that Satb1 functions to prevent premature T cell exhaustion by regulating Pdcd1 expression upon T cell activation. Dysregulation of this pathway in tumor-infiltrating T cells results in diminished anti-tumor immunity.
Tumor-associated macrophages are major contributors to malignant progression and resistance to immunotherapy, but the mechanisms governing their differentiation from immature myeloid precursors remain incompletely understood. In this study, we demonstrate that exosomes secreted by human and mouse tumor-educated mesenchymal stem cells (MSCs) drive accelerated breast cancer progression by inducing differentiation of monocytic myeloid-derived suppressor cells into highly immunosuppressive M2-polarized macrophages at tumor beds. Mechanistically, MSC-derived exosomes but not exosomes from tumor cells contain TGF-β, C1q, and semaphorins, which promote myeloid tolerogenic activity by driving PD-L1 overexpression in both immature myelomonocytic precursors and committed CD206+ macrophages and by inducing differentiation of MHC class II+ macrophages with enhanced l-Arginase activity and IL-10 secretion at tumor beds. Accordingly, administration of tumor-associated murine MSC-derived exosomes accelerates tumor growth by dampening antitumor immunity, and macrophage depletion eliminates exosome-dependent differences in malignant progression. Our results unveil a new role for MSC-derived exosomes in the differentiation of myeloid-derived suppressor cells into macrophages, which governs malignant growth.
Gamma delta (γδ) T cells infiltrate most human tumors, but current immunotherapies fail to exploit their in situ major histocompatibility complex–independent tumoricidal potential. Activation of γδ T cells can be elicited by butyrophilin and butyrophilin-like molecules that are structurally similar to the immunosuppressive B7 family members, yet how they regulate and coordinate αβ and γδ T cell responses remains unknown. Here, we report that the butyrophilin BTN3A1 inhibits tumor-reactive αβ T cell receptor activation by preventing segregation of N-glycosylated CD45 from the immune synapse. Notably, CD277-specific antibodies elicit coordinated restoration of αβ T cell effector activity and BTN2A1-dependent γδ lymphocyte cytotoxicity against BTN3A1+ cancer cells, abrogating malignant progression. Targeting BTN3A1 therefore orchestrates cooperative killing of established tumors by αβ and γδ T cells and may present a treatment strategy for tumors resistant to existing immunotherapies.
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