Natural killer (NK) cells are innate immune effectors, but their cytotoxic potential can be compromised within the immunosuppressive tumor microenvironment. Identifying molecular mechanisms that underly this dysfunction is essential for advances in cancer immunotherapy. Here we show that CLEC12B, a C-type lectin receptor, functions as an inhibitory checkpoint that restricts NK cell-mediated antitumor immunity. High expression of CLEC12B by tumor-infiltrating NK cells correlates with poor clinical prognosis in patients with hepatocellular carcinoma. We identify lipoprotein lipase as a functional ligand for CLEC12B, triggering inhibitory signaling that suppresses NK cell activation. We developed a high-affinity nanobody as a potential therapeutic that disrupts the CLEC12B-lipoprotein lipase axis, thereby revitalizing NK cell activity and suppressing tumor progression in preclinical models. Furthermore, this nanobody has potent synergistic efficacy when combined with PD-1 blockade. These findings establish CLEC12B as a promising therapeutic target for rearming the immune system against solid malignancies.
© 2026. The Author(s), under exclusive licence to Springer Nature America, Inc.