Nuclear NAD⁺ promotes innate immune memory by inhibiting KDM5A-dependent histone demethylation

Trained immunity is tightly regulated by metabolic and epigenetic reprogramming, yet how these changes are orchestrated at the chromatin level to establish long-term innate immune memory is not fully understood. Here, we show that induction of trained immunity elevates nuclear levels of nicotinamide adenine dinucleotide (NAD⁺), which directly binds to KDM5A demethylase and inhibits its activity, thereby sustaining H3K4me3 (histone H3 lysine 4 trimethylation) levels and chromatin accessibility at inflammatory gene promoters to enhance "memory" responsiveness upon restimulation. Genetic deletion or pharmacological inhibition of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme for NAD⁺ synthesis, impaired trained immunity and associated antitumor activity. Nicotinamide mononucleotide (NMN) supplementation rescued defective trained immunity-mediated antitumor activity in NAMPT-deficient and aged mice. In human cancer, NAMPT expression in myeloid cells correlated with an inflammatory tumor microenvironment. Our findings identify KDM5A as a nuclear NAD⁺ sensor that orchestrates histone methylation and chromatin accessibility required for trained immunity.