β-hydroxybutyrate potentiates anti-tumor immunity by modulating cytotoxic CD8+ T cell responses.

Ketogenic diets (KDs) have been reported to influence tumor progression through metabolic and immunological modulation of the tumor microenvironment. β-hydroxybutyrate (βOHB), the predominant ketone body elevated by KD, functions not only as an energy substrate but also as a potent signaling metabolite. Despite its role in modulating the tumor microenvironment, the direct impact of βOHB on the function of CD8+ T cell, a key mediator of anti-tumor immunity, remains incompletely understood. Here, we demonstrate that βOHB suppresses tumor growth in multiple mouse tumor models by enhancing the accumulation, survival, and effector function of tumor-infiltrating CD8+ T cells. In contrast, acetoacetate does not exert comparable immunomodulatory effects. Mechanistically, βOHB upregulates the Tcf7-Lck signaling pathway by engaging with the cell surface receptor Hcar2, an effect potentially working in parallel with its role as an HDAC inhibitor. Knockdown of either Tcf7 or Hcar2 in CD8+ T cells abolishes the promoting effect of βOHB on CD8+ T function. Our findings elucidate a metabolite-immune axis that directly regulates the functional state of tumor-infiltrating CD8⁺ T cells and provide experimental evidence linking ketone metabolism to anti-tumor immune regulation.