The study investigates the functional delivery of viral microRNAs (miRNAs) via exosomes. Noncoding regulatory miRNAs control gene expression by repressing mRNA translation. Interestingly, miRNAs are actively secreted through exosomes, which protect them from degradation by RNases, suggesting they may function outside the producing cell. The researchers demonstrate that miRNAs secreted by Epstein-Barr virus (EBV)-infected cells are transferred to and act in uninfected recipient cells. Using quantitative RT-PCR, they show that mature EBV-encoded miRNAs are secreted by EBV-infected B cells through exosomes. These EBV-miRNAs are functional, as their internalization by monocyte-derived dendritic cells (MoDCs) results in dose-dependent repression of confirmed EBV target genes, including CXCL11/ITAC, an immunoregulatory gene down-regulated in primary EBV-associated lymphomas. The study also shows that EBV-miRNAs accumulate in noninfected neighboring MoDCs through exosome transfer and are delivered to subcellular sites of gene repression in recipient cells. Additionally, in peripheral blood mononuclear cells from patients with increased EBV load, EBV BART miRNAs are present in both B-cell and non-B-cell fractions, suggesting miRNA transfer in vivo. These findings suggest that miRNA-mediated gene silencing may be a potential mechanism of intercellular communication between immune cells, potentially exploited by the persistent human γ-herpesvirus EBV.The study investigates the functional delivery of viral microRNAs (miRNAs) via exosomes. Noncoding regulatory miRNAs control gene expression by repressing mRNA translation. Interestingly, miRNAs are actively secreted through exosomes, which protect them from degradation by RNases, suggesting they may function outside the producing cell. The researchers demonstrate that miRNAs secreted by Epstein-Barr virus (EBV)-infected cells are transferred to and act in uninfected recipient cells. Using quantitative RT-PCR, they show that mature EBV-encoded miRNAs are secreted by EBV-infected B cells through exosomes. These EBV-miRNAs are functional, as their internalization by monocyte-derived dendritic cells (MoDCs) results in dose-dependent repression of confirmed EBV target genes, including CXCL11/ITAC, an immunoregulatory gene down-regulated in primary EBV-associated lymphomas. The study also shows that EBV-miRNAs accumulate in noninfected neighboring MoDCs through exosome transfer and are delivered to subcellular sites of gene repression in recipient cells. Additionally, in peripheral blood mononuclear cells from patients with increased EBV load, EBV BART miRNAs are present in both B-cell and non-B-cell fractions, suggesting miRNA transfer in vivo. These findings suggest that miRNA-mediated gene silencing may be a potential mechanism of intercellular communication between immune cells, potentially exploited by the persistent human γ-herpesvirus EBV.