Xiaoshan Lin, Shuimiao Lin, Jing Zhou, Daokun Hu, Zhenhua Ding, Ying Liu, Lina Chen
Background Fractionated radiotherapy (FRT) remains a cornerstone treatment for nasopharyngeal carcinoma (NPC), yet radiotherapy-induced hypoxia within the tumor microenvironment drives CD8 + T cell exhaustion through poorly understood mechanisms. Methods We combined genetic KDM5A ablation in murine CD8 + T cells, a Transwell coculture model mimicking FRT-conditioned hypoxia, and orthotopic NPC xenografts treated with the KDM5A inhibitor CPI-455 to investigate the mechanisms underlying CD8 + T cell exhaustion. Results This study showed that FRT combined with hypoxia upregulates the histone demethylase KDM5A in CD8 + T cells in a HIF-1α-dependent manner, leading to suppression of the stemness-associated transcription factor TCF1 and induction of terminal exhaustion markers TIM3 and PD-1. Genetic ablation of KDM5A reduced TIM3 and PD-1 levels across all conditions and, importantly, restored TCF1 expression and proliferative capacity in T cells that infiltrated the FRT-conditioned hypoxic niche. In a Transwell coculture model mimicking this hostile environment, KDM5A-knockdown CD8 + T cells exhibited progressively increased TCF1 expression and decreased TIM3 levels upon migration. Moreover, KDM5A deficiency expanded the Tpex (TCF1 + PD-1 + ) pool, limited terminal Tex (TIM3 + TOX + ) conversion, restored IFN-γ secretion, and preserved proliferative function. In orthotopic NPC xenografts, CPI-455 maintained high densities of TCF1 + Tpex cells within hypoxic tumor cores and significantly reduced Tex proportions, while restoring IFN-γ secretion and proliferative capacity of infiltrating CD8 + T cells, without affecting the intrinsic hypoxia status induced by FRT. Conclusion Collectively, these preclinical findings identify KDM5A as a key mediator of spatiotemporal CD8 + T cell exhaustion driven by radiotherapy-associated hypoxia and suggest that targeting KDM5A may represent a potential strategy to overcome immune evasion and improve the efficacy of radio-immunotherapy in NPC.