Hanna S. Hong

An extensive fibroinflammatory stroma rich in macrophages is a hallmark of pancreatic cancer. In this disease, it is well appreciated that macrophages are immunosuppressive and contribute to the poor response to immunotherapy; however, the mechanisms of immune suppression are complex and not fully understood. Immunosuppressive macrophages are classically defined by the expression of the enzyme Arginase 1 (ARG1), which we demonstrated is potently expressed in pancreatic tumor-associated macrophages from both human patients and mouse models. While routinely used as a polarization marker, ARG1 also catabolizes arginine, an amino acid required for T cell activation and proliferation. To investigate this metabolic function, we used a genetic and a pharmacologic approach to target Arg1 in pancreatic cancer. Genetic inactivation of Arg1 in macrophages, using a dual recombinase genetically engineered mouse model of pancreatic cancer, delayed formation of invasive disease, while increasing CD8 + T cell infiltration. Additionally, Arg1 deletion induced compensatory mechanisms, including Arg1 overexpression in epithelial cells, namely Tuft cells, and Arg2 overexpression in a subset of macrophages. To overcome these compensatory mechanisms, we used a pharmacological approach to inhibit arginase. Treatment of established tumors with the arginase inhibitor CB-1158 exhibited further increased CD8 + T cell infiltration, beyond that seen with the macrophage-specific knockout, and sensitized the tumors to anti-PD1 immune checkpoint blockade. Our data demonstrate that Arg1 drives immune suppression in pancreatic cancer by depleting arginine and inhibiting T cell activation.

Cellular metabolism and signaling pathways are key regulators to determine conventional T cell fate and function, but little is understood about the role of cell metabolism for natural killer T (NKT) cell survival, proliferation, and function. We found that NKT cells operate distinct metabolic programming from CD4 T cells. NKT cells are less efficient in glucose uptake than CD4 T cells with or without activation. Gene-expression data revealed that, in NKT cells, glucose is preferentially metabolized by the pentose phosphate pathway and mitochondria, as opposed to being converted into lactate. In fact, glucose is essential for the effector functions of NKT cells and a high lactate environment is detrimental for NKT cell survival and proliferation. Increased glucose uptake and IFN-γ expression in NKT cells is inversely correlated with bacterial loads in response to bacterial infection, further supporting the significance of glucose metabolism for NKT cell function. We also found that promyelocytic leukemia zinc finger seemed to play a role in regulating NKT cells' glucose metabolism. Overall, our study reveals that NKT cells use distinct arms of glucose metabolism for their survival and function.

T cell proliferation and cytokine production are bioenergetically and biosynthetically costly. The inability to meet these metabolic demands results in altered differentiation, accompanied by impaired effector function, and attrition of the immune response. Interleukin-17–producing CD4 T cells (T H 17s) are mediators of host defense, autoimmunity, and antitumor immunity in the setting of adoptive T cell therapy. T H 17s are long-lived cells that require mitochondrial oxidative phosphorylation (OXPHOS) for effector function in vivo. Considering that T H 17s polarized under standardized culture conditions are predominately glycolytic, little is known about how OXPHOS regulates T H 17 processes, such as their ability to persist and thus contribute to protracted immune responses. Here, we modified standardized culture medium and identified a culture system that reliably induces OXPHOS dependence in T H 17s. We found that T H 17s cultured under OXPHOS conditions metabolically resembled their in vivo counterparts, whereas glycolytic cultures were dissimilar. OXPHOS T H 17s exhibited increased mitochondrial fitness, glutamine anaplerosis, and an antiapoptotic phenotype marked by high BCL-XL and low BIM. Limited mitophagy, mediated by mitochondrial fusion regulator OPA-1, was critical to apoptotic resistance in OXPHOS T H 17s. By contrast, glycolytic T H 17s exhibited more mitophagy and an imbalance in BCL-XL to BIM, thereby priming them for apoptosis. In addition, through adoptive transfer experiments, we demonstrated that OXPHOS protected T H 17s from apoptosis while enhancing their persistence in the periphery and tumor microenvironment in a murine model of melanoma. Together, our work demonstrates how metabolism regulates T H 17 cell fate and highlights the potential for therapies that target OXPHOS in T H 17-driven diseases.