Text Box 2. Example of a possible change from MISEV2018 in the future as markers of non-EV co-isolated components.

The Lyden group recently reported that lipidic structures called “exomeres” contain lipids and a limited set of membrane-bound proteins, but do not feature a lipid bilayer and thus do not qualify as EVs. Exomeres were found to co-isolate with small EVs recovered from many cultured cell lines [112] but could be separated from EVs by AF4 (which unfortunately is not implementable in some laboratories). It may be necessary to evaluate this potential contaminant in all EV preparations. Proteomic analyses of exomeres identified various proteins in Table 3-category 2, above: heat shock proteins (HSPA8, HSPA1A, HSP90AB1), actin (ACT*), tubulin (TUB*), and GAPDH. Such proteins thus probably do not qualify as EV-specific components. In addition, a few proteins were identified exclusively in exomeres: hemoglobin (HBA1/A2), IDH1, MAT1A, transmembrane FAT4 (protocadherin, transmembrane plasma membrane), and EXT1/2 (exostosin, transmembrane, Golgi). Although this exhaustive study was performed with several cell lines, suggesting that the listed proteins are good candidates as specific markers of exomeres co-isolated with EVs, these results still have to be confirmed by other groups to reach validation and inclusion in the next update of the MISEV guidelines.