A Dual-Metabolic NIR-II Probe for In Vivo Imaging of Tumor-Infiltrating Lymphocytes

Indocyanine green (ICG) is one of the few FDA-approved near-infrared (NIR) imaging probes, and its NIR-II off-peak emission shows clinical potential for medical imaging. However, its low brightness, short half-life, and lack of targeting specificity significantly limit broader clinical applications. Herein, we report a NIR fluorescent probe, ICG@Apt-PD1, for the preclinical in vivo imaging of tumor-infiltrating lymphocytes (TILs). This probe was synthesized by covalently conjugating a derivative of ICG to the pendant sulfhydryl group of a PD1-targeting aptamer (Apt-PD1). ICG@Apt-PD1 possesses an extended plasma half-life, high biocompatibility, and is metabolized via both hepatic and renal pathways, allowing for rapid clearance and reduced potential toxicity. Owing to its high brightness, photostability, and excellent tissue penetration, the probe enables high-quality NIR-II imaging of lymph nodes and permits the identification of inflammatory foci within a specific post-injection time window. Moreover, the probe achieves specific targeting of TILs through interaction with PD-1 receptors, thereby showcasing its strong potential for non-invasive in vivo imaging of TILs. Consequently, ICG@Apt-PD1 holds considerable promise for clinical translation in NIR-II imaging of lymph nodes, inflammatory foci, and TILs.