Human cytomegalovirus inhibits differentiation of monocytes into dendritic cells with the consequence of depressed immunological functions

Human cytomegalovirus induces monocyte differentiation and migration as a strategy for dissemination and persistence

Human cytomegalovirus (HCMV) pathogenesis is characterized by multiple organ system involvement due to viral spread to host organs after a cell-associated viremia. The cell type responsible for HCMV dissemination is unknown. Monocytes are the most likely candidate since they are the predominant cell type infected in the blood. However, monocytes are not productive for viral replication and are abortively infected. The results presented here provide a potential answer to this conundrum. We report that primary HCMV infection of monocytes induces transendothelial migration and monocyte-to-macrophage differentiation and that these HCMV-differentiated macrophages are productive for viral replication. Together, our data suggest a novel mechanism for HCMV pathogenesis; HCMV induces cellular changes in monocytes to promote viral replication and spread to host organs.

Differential outcomes of human cytomegalovirus infection in primitive hematopoietic cell subpopulations

The cellular reservoir for latent human cytomegalovirus (HCMV) in the hematopoietic compartment, and the mechanisms governing a latent infection and reactivation from latency are unknown. Previous work has demonstrated that HCMV infects CD34+ progenitors and expresses a limited subset of viral genes. The outcome of HCMV infection may depend on the cell subpopulations infected within the heterogeneous CD34+ compartment. We compared HCMV infection in well-defined CD34+ cell subpopulations. HCMV infection inhibited hematopoietic colony formation from CD34+/CD38- but not CD34+/c-kit+ cells. CD34+/CD38- cells transiently expressed a large subset of HCMV genes that were not expressed in CD34+/c-kit+ cells or cells expressing more mature cell surface phenotypes. Although viral genomes were present in infected cells, viral gene expression was undetectable by 10 days after infection. Importantly, viral replication could be reactivated by coculture with permissive fibroblasts only from the CD34+/CD38- population. Strikingly, a subpopulation of CD34+/CD38- cells expressing a stem cell phenotype (lineage-/Thy-1+) supported a productive HCMV infection. These studies demonstrate that the outcome of HCMV infection in the hematopoietic compartment is dependent on the nature of the cell subpopulations infected and that CD34+/CD38- cells support an HCMV infection with the hallmarks of latency.