Human cytomegalovirus-infected cells release extracellular vesicles that carry viral surface proteins

Extracellular vesicles (EVs) released by virus-infected cells typically incorporate host and viral components inside the vesicles (cargo molecules). Here, we investigated if human cytomegalovirus (HCMV) proteins are incorporated in EV outer membrane released by HCMV-infected cells. We separated EVs from HCMV using an iodixanol step-gradient and found that the separated vesicles carried EV markers such as the tetraspanin CD63 and Rab27A. Flow analysis of individual EVs demonstrated that on average, 15 ± 3.7% of EVs were positive for gB, 5.3 ± 2.3% were positive for gH and 3.74 ± 1.5% were positive for both gB and gH. In light of previous findings demonstrating HIV envelope proteins in EV membranes, the presence of viral protein at the surface of EVs released by HCMV-infected cells indicated that viral membrane proteins incorporated in EVs released by virus-infected cells may be a general phenomenon.