Impact of Dense Bodies on Host Cells and HCMV Replication

Dense Bodies (DBs) of human cytomegalovirus (HCMV) are non-infectious particles that are produced by infected cells both in-vitro and in-vivo. They efficiently enter target cells. By virtue of this antigen delivery, DBs are highly immunogenic and are thus a promising HCMV vaccine candidate. Their function in the course of HCMV infection is, however, widely unknown. In this work we addressed the question how DB-application alters HCMV infection and cellular homeostasis with a particular focus of potential side effects imparted by the use of these particles as a vaccine. In a first set of experiments we investigated whether DBs had an impact on HCMV gene expression and DNA replication. DBs were added to fibroblasts, infected with a DB-negative HCMV strain. The expression of both IE1-pp72 and pUL44 was enhanced, compared to controls. However, a consistent impact on viral DNA replication and virus release was not found on repeated experiments, rendering a distinct pro-viral effect on this level unlikely. These results are be favorable with respect to the use of DBs as a vaccine in individuals with unknown HCMV serostatus. In a second set of experiments, the impact of DB-application on the cell was tested in the absence of infection. We found that exposure of human fibroblasts to DBs failed to disperse PML nuclear bodies. These structures are nuclear multiprotein compartments that counteract herpesviral infection. To obtain a more comprehensive picture, label-free mass spectrometry was performed on DB-treated fibroblasts, endothelial cells and monocytes to address DB-induced changes in the levels of host cell proteins. Most remarkable, several interferon-stimulated proteins were found to be upregulated, suggesting that DBs induce an antiviral rather than a proviral cellular environment. Taken together the results showed that DBs are not detrimental to host cells and they thus support their further development as a vaccine.

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