CD81 and central nervous system cancer: A, morphological features of GSCs-derived exosomes under the transmission electron microscope; exosomes are round or oval membranous vesicles; B, particle size of exosomes determined using Nanosight; most particles have a dimension ranged from 30 to 150 nm; C, protein bands of exosome surface markers (CD63, CD9 and CD81) detected by Western blot analysis; D, expression of exosome surface markers (CD63 and CD81) detected using flow cytometry; GSCs, glioma stem cells.