Immunosuppression reverse engineered from cancer: Reducing nicotinamide adenine dinucleotide (NAD) impairs effector T cell function through glycolysis

Abstract

Abstract Understanding the mechanisms by which cancers evade immune responses may lead to new immunosuppressive therapies. The metabolic environment surrounding solid tumors is often enriched in lactic acid and glucose depleted, which impairs effector T cells (Teff). We observed that sodium L- and D-lactate inhibit T cell proliferation in vivo and increase Foxp3+ formation independent of acidity, while sodium pyruvate achieved the opposite. Inhibiting lactate dehydrogenase (GSK 2837808A) negated the effects of L-lactate on Teff and regulatory T cells (Treg). These findings suggested a role of NAD in controlling Teff function and Foxp3 stability. NAD is a co-factor for GAPDH (glycolysis), poly (ADP-ribose) polymerase-1 and sirtuin-1 (Foxp3 stability). We impaired NAD oxidation through oligomycin, rotenone, antimycin, or blocking NAD recycling (FK866). We used mitochondrial uncoupling, β-lapachone, and α-ketobutyrate to augment NAD oxidation, or added nicotinamide riboside to restore NAD after FK866 treatment. Reducing NAD led to decreased glycolytic flux and accumulation of pre-GAPDH glycolytic metabolites, which was reversed by increasing oxidized NAD. T cell IFN-γ production and Foxp3 turnover were increased by NAD oxidation, and impaired by NAD reduction. Blocking NAD recycling also impaired Teff proliferation and IFN-γ production, which was reversed by restoring NAD. Reducing NAD in vivo with sodium D-lactate (9 μmol/g/d x 5 d) or phenformin (70 mg/kg/d x 14 d) prolonged MHC-mismatched BALB/c to C57BL/6 cardiac allograft survival. We conclude that NAD controls T cell function through glycolysis and Foxp3 stability, which may be exploited for therapeutic immunosuppression.