From recognition to serial killing: Molecular mechanisms controlling NK-cell-mediated tumor elimination

Natural killer (NK) cells are critical regulators of tumor immune surveillance and represent an important platform for cancer immunotherapy. However, the ability of NK cells to eliminate tumor cells is determined by a multistep cellular process involving signal integration, cytotoxic interface formation, effector execution, and functional maintenance. Conventional evaluation approaches, including receptor-ligand profiling, cytokine production, CD107a degranulation and endpoint cytotoxicity assays, provide valuable measurements of overall NK activity but often fail to define the specific cellular process that limits tumor-cell elimination. Here, we propose a stage-resolved framework to interpret NK-cell antitumor cytotoxicity by dividing the killing process into four interconnected functional stages: recognition and early activation, cytotoxic synapse maturation, effector delivery and death execution, and serial killing with sustained tumor control. For each stage, we summarize the molecular mechanisms that regulate signal initiation, receptor organization, cytoskeletal remodeling, granule trafficking, target-cell death sensitivity, and metabolic adaptation. We further discuss how tumor-intrinsic resistance programs and therapeutic interventions influence individual stages of the NK-cell killing process. This framework provides a mechanistic perspective for understanding heterogeneous NK-cell dysfunction by localizing functional constraints within the cytotoxic cascade rather than relying solely on global activity measurements. By linking molecular mechanisms with stage-specific functional readouts, this approach may facilitate the identification of actionable targets, interpretation of therapeutic responses, and rational development of combination strategies in NK-cell-based cancer immunotherapy.