Protease‐Activated Plasmonic Nanosensors for Predictive Ultrasound‐Guided Photoacoustic Imaging of Tumor Responses to Adoptive T Cell Therapy

Abstract Adoptive T cell therapy (ACT) is a promising strategy for cancer treatment that harnesses a patient's own T lymphocytes to enhance antitumor immunity. A major challenge in assessing therapeutic responses following ACT is the lack of robust, noninvasive tools to monitor cytotoxic T cell activity within tumors with anatomical context. Here, a protease‐activated plasmonic nanosensor is reported for noninvasive photoacoustic (PA) imaging of ACT responses. The nanosensor comprises gold nanospheres functionalized with peptide substrates of granzyme B (GzmB), a key effector protease secreted by cytotoxic T cells. Upon peptide cleavage by GzmB, nanosensor aggregation is induced, leading to plasmon coupling and enhanced optical absorption with ≈90% efficiency in the near‐infrared optical window. This aggregation significantly amplifies PA signals, enabling sensitive detection of GzmB. The nanosensor exhibits high specificity for GzmB over other proteases and correlates optical and PA responses with antigen‐specific T cell‐mediated cytotoxicity in vitro. In murine ACT models, systemic nanosensor administration enables detection of tumor‐infiltrating cytotoxic T cell activity, producing elevated PA signals in antigen‐positive tumors compared to antigen‐negative controls before any measurable differences in tumor volume. This study presents a noninvasive approach for assessing ACT efficacy via GzmB‐activated plasmonic nanosensors combined with ultrasound‐guided PA imaging.