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Protein synthesis supports robust immune responses. Nutrient competition and global cell stressors in the tumor microenvironment (TME) may impact protein translation in T cells and antitumor immunity. Using human and mouse tumors, we demonstrated here that protein translation in T cells is repressed in solid tumors. Reduced glucose availability to T cells in the TME led to activation of the unfolded protein response (UPR) element eIF2α (eukaryotic translation initiation factor 2 alpha). Genetic mouse models revealed that translation attenuation mediated by activated p-eIF2α undermines the ability of T cells to suppress tumor growth. Reprograming T-cell metabolism was able to alleviate p-eIF2α accumulation and translational attenuation in the TME, allowing for sustained protein translation. Metabolic and pharmacological approaches showed that proteasome activity mitigates induction of p-eIF2α to support optimal antitumor T-cell function, protecting from translation attenuation and enabling prolonged cytokine synthesis in solid tumors. Together, these data identify a new therapeutic avenue to fuel the efficacy of tumor immunotherapy. Significance: Proteasome function is a necessary cellular component for endowing T cells with tumor killing capacity by mitigating translation attenuation resulting from the unfolded protein response induced by stress in the tumor microenvironment.

To evaluate the utility and complications of using carbon fiber implants (CFIs) compared with standard titanium alloy (TI) intramedullary implants for stabilization of impending or existing pathologic fractures.Retrospective comparison.Ninety-four patients undergoing intramedullary fixation of 100 impending or existing pathologic fractures between 2014-2019 were identified for inclusion.The primary outcome was postoperative complications. Other outcomes included implant type, pathology, indication, and adjuvant therapy.Fifty-three percent of cases used a CFI, whereas 47% of cases used a TI. There were no differences between groups with regard to anatomic location (P = 0.218), indication for surgery (P = 0.066), histology (P = 0.306), or postoperative adjuvant therapy (P = 0.308). Nineteen percent of cases incurred a postoperative complication in each group (P = 0.530), and no differences were noted with regard to complication type including implant failure (P = 0.442) and wound complications (P = 0.322). There was a cost saving of $400 with TI implants compared with CFI.This is a high-risk population for postoperative complications after stabilization of pathologic fractures. Although there were no statistical differences in complications between CFI and TI, implant choice depends on patient characteristics and surgeon preference.Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Protein Expression, Shotgun Proteomics

Quantification and viability of T cell groups

Tumor antigen–specific T cells rapidly lose energy and effector function in tumors. The cellular mechanisms by which energy loss and inhibition of effector function occur in tumor-infiltrating lymphocytes (TILs) are ill-defined, and methods to identify tumor antigen–specific TILs that experience such stress are unknown. Processes upstream of the mitochondria guide cell-intrinsic energy depletion. We hypothesized that a mechanism of T-cell–intrinsic energy consumption was the process of oxidative protein folding and disulfide bond formation that takes place in the endoplasmic reticulum (ER) guided by protein kinase R-like endoplasmic reticulum kinase (PERK) and downstream PERK axis target ER oxidoreductase 1 (ERO1α). To test this hypothesis, we created TCR transgenic mice with a T-cell–specific PERK gene deletion (OT1+Lckcre+PERKf/f, PERK KO). We found that PERK KO and T cells that were pharmacologically inhibited by PERK or ERO1α maintained reserve energy and exhibited a protein profile consistent with reduced oxidative stress. These T-cell groups displayed superior tumor control compared with T effectors. We identified a biomarker of ER-induced mitochondrial exhaustion in T cells as mitochondrial reactive oxygen species (mtROS), and found that PD-1+ tumor antigen–specific CD8+ TILs express mtROS. In vivo treatment with a PERK inhibitor abrogated mtROS in PD-1+ CD8+ TILs and bolstered CD8+ TIL viability. Combination therapy enabled 100% survival and 71% tumor clearance in a sarcoma mouse model. Our data identify the ER as a regulator of T-cell energetics and indicate that ER elements are effective targets to improve cancer immunotherapy.

Supplemental Figures S1-S11

Mixed linear modeling results for tumor curves

Protein synthesis supports robust immune responses. Nutrient competition and global cell stressors in the tumor microenvironment (TME) may impact protein translation in T cells and antitumor immunity. Using human and mouse tumors, we demonstrated here that protein translation in T cells is repressed in solid tumors. Reduced glucose availability to T cells in the TME led to activation of the unfolded protein response (UPR) element eIF2α (eukaryotic translation initiation factor 2 alpha). Genetic mouse models revealed that translation attenuation mediated by activated p-eIF2α undermines the ability of T cells to suppress tumor growth. Reprograming T-cell metabolism was able to alleviate p-eIF2α accumulation and translational attenuation in the TME, allowing for sustained protein translation. Metabolic and pharmacological approaches showed that proteasome activity mitigates induction of p-eIF2α to support optimal antitumor T-cell function, protecting from translation attenuation and enabling prolonged cytokine synthesis in solid tumors. Together, these data identify a new therapeutic avenue to fuel the efficacy of tumor immunotherapy.Significance:Proteasome function is a necessary cellular component for endowing T cells with tumor killing capacity by mitigating translation attenuation resulting from the unfolded protein response induced by stress in the tumor microenvironment.

Protein synthesis enables cell growth and survival, but the molecular mechanisms through which T cells suppress or maintain protein translation in the stress of solid tumors are unknown. Using mouse models and human tumors we demonstrate that protein translation in T cells is repressed by the solid tumor microenvironment (TME) due to activation of the unfolded protein response (UPR) via phosphorylation of the α subunit of eukaryotic translation initiation factor 2 (p-eIF2α). Given that acute glucose deprivation in T cells exacerbated p-eIF2α, we show that metabolic reprogramming toward glycolytic independence allays the UPR and p-eIF2α, enabling sustained protein translation in T cells in TME stress. UPR mitigation was associated with enhanced degradation of proteins in antitumor T cells, as proteasome inhibition resulted in eIF2α phosphorylation, attenuation of translation, and loss of antitumor efficacy. In contrast, proteasome stimulation relieved translation inhibition, inducing robust T cell tumor control, offering a new therapeutic avenue to fuel the efficacy of tumor immunotherapy.