Enzyme-Triggered Self-Immobilization of an NIR Prodrug for Tumor-Selective Cancer Vaccination

In situ cancer vaccination, a strategy leveraging tumor antigens released from dying cancer cells to elicit antigen-specific immunity, has emerged as a highly promising modality in cancer immunotherapy. However, prevailing methodologies are constrained by insufficient selectivity for tumor killing, leading to off-target toxicity toward surrounding immune cells and consequently undermining the efficacy of in situ cancer vaccination. Herein, we develop an unprecedented self-immobilizing near-infrared (NIR) prodrug, ALPICD-2, which enables precise and efficacious in situ cancer vaccination through the synergistic integration of targeted ablation of cancer cells and preservation of tumor-infiltrating immune cells (TIICs). Mechanistically, upon activation by alkaline phosphatase enzyme overexpressed on cancer cells, the prodrug ALPICD-2 undergoes a pronounced hydrophilic switch, promoting its selective internalization and covalent self-immobilization into cancer cells with minimal off-target effects, accompanied by the activation of NIR fluorescence that enables real-time monitoring. The tumor-enriched prodrug induces potent cytotoxicity and immunogenic cell death, thereby initiating a cascade of innate and adaptive immune responses. Notably, this covalent immobilizing therapeutics effectively inhibits tumor growth and confers protection against tumor metastasis by enhancing the infiltration of effector CD8⁺ T cells and natural killer cells within tumor sites while suppressing the immunosuppressive TIICs. This study provides a powerful strategy and precise small-molecular platform for advancing in situ cancer vaccination.