Isolation and identification of exosomes of brain tumor origin We select different exosome isolation methods for different isolation purposes, including the isolation and purification of brain tumor-derived exosomes from biological fluid samples such as cell culture supernatants and patient plasma using ultrafast differential centrifugation, ultrafiltration, OptiPrep density gradient centrifugation, and immunoprecipitation (IP). With appropriate methods, we can isolate and obtain relatively uniform-sized microvesicular populations with high specificity and no impact on the subsequent analysis of the results. We understand the biological activity of exosomes by measuring the size of vesicle particles and the expression levels of specific proteins TSG101, ALIX, or myelin proteolipid protein (PLP) on their membrane surface. We can combine multiple proteins as exosome markers, such as ALIX, TSG101, CD63, CD60, CD9, and CD81, and then use mass spectrometry analysis to perform a comprehensive screening of the proteome of exosomes, and observe the size and morphology of exosomes by fluorescence and electron microscopy.