Human Cytomegalovirus modifies placental small extracellular vesicle secretion and composition towards a proviral phenotype to enhance infection of fetal recipient cells

Although placental small extracellular vesicles (sEVs) are extensively studied in the context of pregnancy, little is known about their role during human cytomegalovirus (hCMV) congenital infection, especially at the beginning of pregnancy. In this study, we examined the consequences of hCMV infection on sEVs production and composition using an immortalized human cytotrophoblast cell line derived from first trimester placenta. By combining complementary approaches of biochemistry, imaging techniques and quantitative proteomic analysis, we showed that hCMV infection increased the yield of sEVs produced by cytotrophoblasts and modified their protein composition towards a proviral phenotype. We further demonstrated that sEVs secreted by hCMV-infected cytotrophoblasts potentiated infection in naive recipient cells of fetal origin, including neural stem cells. Importantly, the enhancement of hCMV infection was also observed with sEVs prepared from either an ex vivo model of infected histocultures from early placenta or from the amniotic fluid of patients naturally infected by hCMV at the beginning of pregnancy. Based on these findings, we propose that placental sEVs could be key actors favoring viral dissemination to the fetal brain during hCMV congenital infection.