Extracellular Vesicles in Human Preterm Colostrum Inhibit Infection by Human Cytomegalovirus In Vitro

Breast milk is a complex biofluid that nourishes infants, supports their growth and protects them from diseases. The benefits of breast milk are mediated by multiple nutritional, trophic, and immunological components, able to promote maturation of infants’ immature gut, and to confer protection against infections. However, at the same time, breastfeeding represents an important mother-to-child transmission route for some viral infections, in particular for human cytomegalovirus (HCMV), with preterm infants being at a great risk of congenital disease. The discrepancy between high HCMV transmission rates and the few reported cases of infants with severe clinical illness is likely due to the protective effect of breast milk. The aim of this thesis is to investigate the anti-HCMV activity of human preterm colostrum and verify whether colostrum-derived extracellular vesicles (EVs) contribute to the colostrum protective effect. Preterm colostrum samples were collected and the EVs were purified and characterized. The in vitro anti-HCMV activity of both colostrum and EVs was tested against HCMV, and the viral replication step inhibited by colostrum-purified EVs was examined. Furthermore, after shaving experiments, we investigated the presumed role that EV surface proteins play in impairing HCMV infection by means of proteomic analysis. The obtained results confirmed the antiviral action of colostrum against HCMV and demonstrated a remarkable antiviral activity of colostrum-derived EVs. Mechanism of action studies showed that EVs do not inactivate viral particles, but they hamper the attachment of HCMV to cells, with EV surface proteins playing a role in mediating this action.