116 There are several strategies to use exosomes as a (therapeutic) vaccine. Tumor-derived exosomes carrying tumor antigens and plasmacytoma cell-derived exosomes may be used to induce tumor-specific immunity and thus to prevent tumor development.117 Despite the extensive studies on EVs, until now there are no protocols available for standardized collection, isolation and storage of EVs. Such standardized protocols are important to be able to compare results between laboratories. Despite the fact that blood is probably our most complex body fluid, EVs present in

or isolated from blood or fractions thereof have been most extensively studied so far. Although there are several recommendations Buparlisib nmr regarding the collection of blood with regard to EVs,118 for other body fluids no protocols are available. In most studies EVs have been isolated from body fluids by differential centrifugation.[3] and [47] Differential centrifugation involves multiple sequential centrifugation steps where in each step the centrifugal force is increased to separate smaller and less dense components from the previous step. Another type of separation by means of centrifugation

Akt inhibitor is density-gradient ultracentrifugation, which separates vesicles based on density.[20] and [119] Although different types of vesicles have been distinguished based on density,[3], [20] and [41] differences in density are likely too small to allow full separation of EV species. Differential centrifugation and density-gradient centrifugation protocols

are unlikely to Cyclin-dependent kinase 3 isolate only a single type of vesicle. Immunoaffinity-based assays, usually coated with a specific CD-antibody, are also used.[84] and [120] Theoretically, this method isolates only one subpopulation of vesicles. Unfortunately, in daily practice successful isolation and purification of a single population with an acceptable recovery by this technique are usually very difficult. Ideally, EVs are measured directly in freshly collected samples, but in a clinical setting this is hardly feasible at present. When samples are frozen and thawed before analysis, concentrations and exposure of PS can markedly increase in samples containing PMVs.[35] and [118] As EVs may expose one or more surface antigens of their parent cell, the cellular origin of EVs can be assessed by using antibodies directed against such cell-type specific surface antigens. Flow cytometry (FCM) is still commonly used to estimate the number of EVs. Due to the fact that the refractive index of vesicles is low, only the larger vesicles will be detected as single vesicles and the smaller vesicles will be detected only as a swarm.121 Thus, FCM will underestimate the number and concentration of vesicles. Although many researchers use annexin V to identify or isolate MVs, PS exposure by MVs is still ambiguous because exposure of PS can be due to isolation and handling procedures such as centrifugation and storage.