Mechanisms of human cytomegalovirus persistence and latency

Human cytomegalovirus (HCMV) is a ubiquitous beta-herpesvirus that causes severe disease primarily in immunosuppressed individuals. A major characteristic of HCMV with obvious clinical importance is the ability of the virus to establish lifelong infection within the host following the initial acute infection. One strategy used by HCMV to maintain itself within the host is the establishment of cellular sites of persistent infection and viral latency. Recent studies have identified endothelial cells and monocyte-derived macrophages (MDM) as sites of HCMV persistence and latency. These studies show that endothelial cell origin and MDM differentiation pathway are critical factors that influence the characteristics of HCMV replication in these cell types. The specific HCMV genes involved in endothelial cell and MDM tropism are unknown. However, studies in the closely related murine cytomegalovirus (MCMV) model have provided considerable insight into viral genes that enable replication in these cell types. This review will focus on mechanisms of HCMV replication in endothelial cells and MDM, and on the viral genes involved in regulation of viral replication in these important cell types.