SUMMARY Although tumor-specific T cells recognize cancer cells, they are often rendered dysfunctional due to an immunosuppressive microenvironment. Here we showed that T cells demonstrated persistent loss of mitochondrial function and mass when infiltrating murine and human tumors, an effect specific to the tumor microenvironment and not merely caused by activation. Tumor-infiltrating T cells showed a progressive loss of PPAR-gamma coactivator 1α (PGC1α), which programs mitochondrial biogenesis, induced by chronic Akt signaling in tumor-specific T cells. Reprogramming tumor-specific T cells through enforced expression of PGC1α resulted in superior intratumoral metabolic and effector function. Our data support a model in which signals in the tumor microenvironment repress T cell oxidative metabolism, resulting in effector cells with metabolic needs that cannot be met. Our studies also suggest that modulation or reprogramming of the altered metabolism of tumor-infiltrating T cells might represent a potential strategy to reinvigorate dysfunctional T cells for cancer treatment.

Blockade of the coinhibitory checkpoint molecule PD-1 has emerged as an effective treatment for many cancers, resulting in remarkable responses. However, despite successes in the clinic, most patients do not respond to PD-1 blockade. Metabolic dysregulation is a common phenotype in cancer, but both patients and tumors are metabolically heterogeneous. We hypothesized that the deregulated oxidative energetics of tumor cells present a metabolic barrier to antitumor immunity through the generation of a hypoxic microenvironment and that normalization of tumor hypoxia might improve response to immunotherapy. We show that the murine tumor lines B16 and MC38 differed in their ability to consume oxygen and produce hypoxic environments, which correlated with their sensitivity to checkpoint blockade. Metformin, a broadly prescribed type II diabetes treatment, inhibited oxygen consumption in tumor cells in vitro and in vivo, resulting in reduced intratumoral hypoxia. Although metformin monotherapy had little therapeutic benefit in highly aggressive tumors, combination of metformin with PD-1 blockade resulted in improved intratumoral T-cell function and tumor clearance. Our data suggest tumor hypoxia acts as a barrier to immunotherapy, and that remodeling the hypoxic tumor microenvironment has potential to convert patients resistant to immunotherapy into those that receive clinical benefit.

Cancer and chronic infections induce T cell exhaustion, a hypofunctional fate carrying distinct epigenetic, transcriptomic, and metabolic characteristics. However, drivers of exhaustion remain poorly understood. As intratumoral exhausted T cells experience severe hypoxia, we hypothesized metabolic stress alters their responses to other signals, specifically persistent antigenic stimulation. In vitro , while CD8 + T cells experiencing continuous stimulation or hypoxia alone differentiate into functional effectors, the combination rapidly drove T cell dysfunction consistent with exhaustion. Continuous stimulation promoted Blimp-1-mediated repression of PGC1α-dependent mitochondrial reprogramming, rendering cells poorly responsive to hypoxia. Loss of mitochondrial function generated intolerable levels of ROS, sufficient to promote exhausted-like states, in part through phosphatase inhibition and consequent NFAT activity. Reducing T cell-intrinsic ROS and lowering tumor hypoxia limited T cell exhaustion, synergizing with immunotherapy. Thus, immunologic and metabolic signaling are intrinsically linked: through mitigation of metabolic stress, T cell differentiation can be altered to promote more functional cellular fates.

SUMMARY To fulfill bioenergetic demands of activation, T cells perform aerobic glycolysis, a process common to highly proliferative cells in which glucose is fermented into lactate rather than oxidized in mitochondria. However, the signaling events that initiate aerobic glycolysis in T cells remain unclear. We show T cell activation rapidly induces glycolysis independent of transcription, translation, CD28, and Akt and not involving increased glucose uptake or activity of glycolytic enzymes. Rather, TCR signaling promotes activation of pyruvate dehydrogenase kinase 1 (PDHK1), inhibiting mitochondrial import of pyruvate and facilitating breakdown into lactate. Inhibition of PDHK1 reveals this switch is required acutely for cytokine synthesis but dispensable for cytotoxicity. Functionally, cytokine synthesis is modulated via lactate dehydrogenase, which represses cytokine mRNA translation when aerobic glycolysis is disengaged. Our data provide mechanistic insight to metabolic contribution to effector T cell function and suggest that T cell function may be finely tuned through modulation of glycolytic activity.

Jackson et al. propose a role for B cell–intrinsic IFN-γ receptor signaling in spontaneous germinal center activation and autoantibody production.

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease characterized by autoantibodies targeting nucleic acid-associated antigens. The endosomal toll-like receptors TLR7 and TLR9 are critical for generation of Abs targeting RNA- or DNA-associated antigens, respectively. In murine lupus models, deletion of TLR7 limits autoimmune inflammation, while deletion of TLR9 exacerbates disease. Whether B cell or myeloid TLR7/TLR9 signaling is responsible for these effects has not been fully addressed. Here, we utilize a chimeric strategy to evaluate the effect of B cell-intrinsic deletion of TLR7 vs. TLR9 in parallel lupus models. We demonstrate that B cell-intrinsic TLR7 deletion prevents RNA-associated Ab formation, decreases production of class-switched Abs targeting non-nuclear antigens and limits systemic autoimmunity. In contrast, B cell-intrinsic TLR9 deletion results in decreased DNA-reactive Ab, but increased Abs targeting a broad range of systemic autoantigens. Further, we demonstrate that B-intrinsic TLR9 deletion results in increased systemic inflammation and immune-complex (IC) glomerulonephritis despite intact TLR signaling within the myeloid compartment. These data stress the critical importance of dysregulated B cell-intrinsic TLR signaling in the pathogenesis of SLE.

SUMMARYAlthough tumor-specific T cells recognize cancer cells, they are often rendered dysfunctional due to an immunosuppressive microenvironment. Here we showed that T cells demonstrated persistent loss of mitochondrial function and mass when infiltrating murine and human tumors, an effect specific to the tumor microenvironment and not merely caused by activation. Tumor-infiltrating T cells showed a progressive loss of PPAR-gamma coactivator 1α (PGC1α), which programs mitochondrial biogenesis, induced by chronic Akt signaling in tumor-specific T cells. Reprogramming tumor-specific T cells through enforced expression of PGC1α resulted in superior intratumoral metabolic and effector function. Our data support a model in which signals in the tumor microenvironment repress T cell oxidative metabolism, resulting in effector cells with metabolic needs that cannot be met. Our studies also suggest that modulation or reprogramming of the altered metabolism of tumor-infiltrating T cells might represent a potential strategy to reinvigorate dysfunctional T cells for cancer treatment. Abstract * Correspondence: gdelgoffe@pitt.edu.

Tumor-infiltrating T cells experience metabolic repression that hinders their function and thus response to immunotherapy. Menk et al. show that ligation of 4-1BB, a TNFR family costimulatory molecule, can promote increased metabolic sufficiency, which enables intratumoral T cell function and response to immunotherapy.