White blood cell labeling with Technetium-99m (99mTc) using red blood cell extracellular vesicles-mimetics

Background: Extracellular vesicles, have gained increasing attention for their application in drug delivery. Here, we developed a novel method for radiolabeling WBCs with Tc-99m using RBC-derived extracellular vesicles-mimetics (EVMs), and monitored in vivo inflammation tracking of Tc-99m-WBC using gamma camera in acute inflammation mouse model. Methods: Engineered EVMs from RBCs were produced by a one-step extrusion method. RBC-EVMs were analyzed by NTA and TEM. Cells were labeled with Tc-99m by using Tc-99m-RBC-EVMs. Inflammation mice model was prepared and confirmed by F-18-FDG PET/CT. Tc-99m-WBCs were injected in mice, and their biodistribution was analyzed by gamma camera. Finding: The radiochemical purity of Tc-99m-RBC-EVMs was 100%. The Tc-99m-labeling din affect the size and morphology. The Tc-99m in the cytoplasm of RBC-EVMs was successfully confirmed by high angle annular dark field STEM (scanning transmission electron microscope). Cells were successfully labeled with Tc-99m using Tc-99m-RBC-EVMs, and the counts per minute was increased in dose- and time-dependent manners. The F-18-FDG PET/CT images confirmed establishment of acute inflammation (left mouse foot). Tc-99m-WBCs showed higher uptake in the inflamed foot than non-inflamed foot. Interpretation: This novel method for radiolabeling WBCs using RBC-EVMs. Tc-99m labeling may be a feasible method to monitor the in vivo biodistribution of cells.