Noninvasively Real‐Time Monitoring In‐Vivo Immune Cell and Tumor Cell Interaction by NIR‐II Nanosensor

Abstract Immunocytotherapy holds significant promise as a novel cancer treatment, but its effectiveness is often hindered by delayed responses, requiring evaluations every 2–3 weeks based on current diagnostic methods. Early assessment of immune cell‐tumor cell interactions could provide more timely insights into therapeutic efficacy, enabling adjustments to treatment plans. In this study, a noninvasive nanosensor (C8R‐DSNP) for real‐time monitoring of in vivo immune cell activities in the second near‐infrared long‐wavelength (NIR‐II‐L) window (1500–1900 nm), which offers deep tissue transparency, is reported. The C8R‐DSNP responds rapidly to caspase‐8, a key apoptotic signaling molecule generated during interactions between natural killer (NK‐92) cells and tumor cells. Using ratiometric NIR‐II‐L fluorescence imaging, dynamic in vivo observations of NK‐92 cells' engagement with tumor cells in a mouse model are captured. These results demonstrate tumor cells apoptosis that happens as early as 4.5 h after NK‐92 cells infusion. Additionally, in vitro urine imaging confirmed the initiation of apoptosis via cleaved fluorescent small molecules, while single‐cell tracking within blood vessels and tumors further elucidated immune cell dynamics. This real‐time NIR‐II‐L monitoring approach offers valuable insights for optimizing immunocytotherapy strategies.