Nicotinamide breaks effector CD8 T cell responses by targeting mTOR signaling.

Nicotinamide (NAM) shapes T cell responses but its precise molecular mechanism of action remains elusive. Here, we show that NAM impairs naive T cell effector transition but also effector T cells themselves. Although aerobic glycolysis is a hallmark of activated T cells, CD8 T cells exposed to NAM displayed enhanced glycolysis, yet producing significantly less IFNγ. Mechanistically, NAM reduced mTORC1 activity independently of NAD metabolism, decreasing IFNγ translation and regulating T cell transcriptional factors critical to effector/memory fate. Finally, the role of NAM in a biomedically relevant model of lung injury was tested. Specifically, a NAM-supplemented diet reduced systemic IL-2, antigen-specific T cell clonal expansion, and effector function after inhalation of enterotoxin A. These findings identify NAM as a potential therapeutic supplement that uncouples glycolysis from effector cytokine production and may be a powerful treatment for diseases associated with T cell hyperactivation.