Glutaminase Modulates T Cell Metabolism and Function in Inflammation and Cancer

During the immune response, helper T cells must proliferate and upregulate key metabolic programs including glucose and glutamine uptake. Metabolic reprogramming is imperative for appropriate T cell responses, as inhibition of glucose or glutamine uptake hinders T cell effector responses. Glutamine and glutaminolysis use in cancer cells has partially been explored. However, the role of glutamine and its downstream metabolites is incomplete and unclear in T cells. The first step of glutamine metabolism is conversion to glutamate via the hydrolase enzyme glutaminase (GLS). To target glutaminolysis, two different methods were employed: 1) genetic knockout of GLS using a CRE-recombinase system specific for CD4/CD8 T cells, and 2) pharmacological inhibition of GLS via the potent and specific small molecular CB839. These two models of glutaminase insufficiency were used as a tool to target glutamine metabolism during T cell activation and differentiation both in vitro and in vivo.

GLS-deficient T cells had decreased activation at early time points compared to control. Over several days, these GLS-deficient T cells differentiated preferentially to Th1-like effector cells. This was reliant on increased glucose carbons incorporating into Tri-Carboxylic Acid (TCA) metabolites. This increased effector response in vitro occurred in both CD4+ T helper cells and CD8+ cells (Cytotoxic lymphocytes, or CTLs). Differentiation of CD4+ T cells to Th1 or Th17 subsets showed decreased Th17 differentiation and cytokine production, while Th1 effector responses were increased. This increased Th1 function was dependent on IL-2 signaling and mTORC1, as reducing IL-2 or inhibiting mTORC1 with rapamycin prevented GLS inhibition-induced Th1 effector function. Th17 cells, meanwhile, were inhibited by changes in reactive oxygen species, and recovery of Th17 function was achieved with n-acetylcysteine treatment.

T cells lacking GLS were unable to induce inflammation in a mouse model of Graft vs Host disease, an inflammatory bowel disease model, or in an airway inflammatory model. Importantly, Chimeric Antigen Receptor (CAR) T cells made from GLS knockout cells were unable to maintain B cell aplasia in recipient mice. Contrary to this, temporary inhibition of GLS via small-molecule inhibition increased B cell killing in vitro and enhanced T cell persistence in both the B cell aplasia and in a vaccinia virus recall response. These results indicate a balance, where permanent deficiency of GLS is detrimental to T cell responses, but acute inhibition can actually promote T effector responses and survival. Overall, this work aims to understand how perturbations in glutamine metabolism in T cells affects differentiation and function and the role of glutaminolysis and improve therapies for inflammatory disease and cancer.