Ultrasensitive In Vivo Imaging of Adoptive Immune Cell Distribution and Expansion Using Second Near-Infrared Conjugated Oligoelectrolyte Probes.

Monitoring adoptive cell therapy in solid tumors is critical for evaluating treatment efficacy and guiding clinical medication but is also hindered by poor sensitivity, high background signals, and disruptions of therapeutic functions in existing techniques. In this study, a membrane-mimicking conjugated oligoelectrolyte with second near-infrared (NIR-II) fluorescence, conjugated oligoelectrolytes-benzobisthiadiazole (COE-BBT), is applied for the first time to label and track chimeric antigen receptor (CAR)-engineered natural killer (CAR-NK) cells and T (CAR-T) cells in vivo. COE-BBT stably embeds in lipid bilayers through combined electrostatic and hydrophobic interactions, resists membrane crossing, and supports long-lasting labeling with a lighting-up property. The optimized labeling approach achieves high sensitivity, enabling the detection of as few as ~20 labeled cells in vitro and ~50 cells in vivo under NIR-II imaging. In orthotopic and subcutaneous glioma models, NIR-II fluorescence imaging enables continuous tracking of CAR-NK and CAR-T cell proliferation, migration, tumor homing, and blood-brain barrier penetration for up to 14 d posttransfer as the fluorescence signal is enhanced during proliferation, without compromising cell viability or cytotoxic function. The COE-BBT probe also exhibits favorable biosafety, underscoring its translational potential as a robust imaging strategy to improve solid tumor adoptive cell therapy monitoring and clinical guidance of therapeutic dosing.