Natural Killer Cell Metabolism in the Tumor Microenvironment

Natural Killer (NK) cells are potent innate immune effectors capable of identifying and destroying tumor cells without prior sensitization. Despite their therapeutic promise, their efficacy against solid tumors is frequently limited by the tumor microenvironment (TME). This review explores how the TME acts as a metabolic barrier, actively reprogramming NK cell metabolism to dampen their antitumor responses.

NK cells rely on robust metabolic pathways—primarily glycolysis and oxidative phosphorylation (OXPHOS)—to fuel their effector functions, such as cytokine production and cytotoxicity. In the TME, tumor cells and myeloid-derived suppressor cells (MDSCs) aggressively compete for essential nutrients like glucose and amino acids. This competition, combined with the accumulation of metabolic waste products such as lactate and adenosine, creates a hostile environment. Lactate, for instance, leads to intracellular acidification, while adenosine signaling through the A2A receptor suppresses both OXPHOS and glycolytic capacity, directly hindering NK cell activation.

Beyond simple nutrient depletion, the TME employs complex signaling to suppress NK cell metabolism. TGF-β, a cytokine prevalent in the TME, is a key inhibitor that downregulates mitochondrial metabolism and represses the mTOR pathway, a central regulator of NK cell fitness. Furthermore, the hypoxic conditions typical of solid tumors force NK cells to adapt, often leading to a reliance on glycolysis that is insufficient to maintain full effector function. While some cytokine-priming strategies (e.g., IL-15) can temporarily boost metabolic competitiveness, the authors note that chronic exposure to these same cytokines can paradoxically lead to metabolic exhaustion.