2.8. PKH67 Labeling of EVs and Uptake into Recipient Cells

The EVs were labeled using PKH67 Fluorescent Cell Linker kits according to the manufacturer’s instructions. To examine the uptake of EVs into recipient cells, the cells were placed onto 6-well plate coverslips at a density of 1 × 10⁴ cells per well. After 24 h, the cells were washed three times in PBS and the culture medium containing PKH67-labeled EVs solution was added to each well. Cells were cultured for 6 h at 37 °C in a humidified atmosphere with 5% CO₂ and then fixed with 3.7% paraformaldehyde solution according to the standardized protocol [27].