Nicotinamide adenine dinucleotide (NAD) oxidation preserves T cell function under lactic acidosis characteristic of the tumor microenvironment (TME)

Abstract

Abstract Cancers are adept at employing metabolic events to evade host immunity. The TME is often glucose depleted and enriched with lactic acid, weakening effector T cell (Teff) function and interferon (IFN)-γ production. By contrast, immunosuppressive T-regulatory (Treg) cells are well adapted to low glucose and elevated lactate and enriched in the TME. Overcoming immunosuppressive metabolic conditions in the TME may be an important step towards improving anti-tumor immunotherapy. Here we show that NAD oxidation can protect Teffs from the immunosuppressive effects of lactic acid. We found that Teff proliferation and IFN-γ production can be controlled through NAD redox metabolism and NAD-dependent enzymes, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Metabolomic and bioenergetics studies showed that reducing NAD led to accumulation of pre-GAPDH glycolytic metabolites and impaired glycolytic flux similar to GAPDH inhibition, which was reversed by NAD oxidation. Human and murine Teffs exposed to lactate, oligomycin, rotenone, or antimycin lost GAPDH function despite sufficient glucose, limiting glycolysis and IFN-γ mRNA translation, while the Treg transcription factor Foxp3 was stabilized. Oxidizing NAD (pyruvate, mitochondrial uncoupling, β-lapachone, α-ketobutyrate) rescued Teff glycolysis and restored their function despite ambient lactate, while Foxp3 turnover increased in a poly-(ADP-ribose) polymerase dependent manner, using NAD as substrate. Our results identify a novel therapeutic approach to overcoming metabolic barriers to anti-tumor immunity, and provide new mechanistic insights into the role of NAD redox metabolism in controlling T cell function in the TME.