Lentivirus-Encoded Transgenes Driven by the Commercial CMV Promoter Are Downregulated in HCMV-Infected Cells, While HCMV-Induced OAS1 Mediates Downregulation of Lentivirus-Encoded Transgenes in Bystander Cells

The study of human cytomegalovirus (HCMV) often requires the use of viral vectors to overexpress, knockdown, or complement viral or cellular factors to facilitate study of the viral replication cycle. Lentiviral vectors commonly use a CMV promoter whose sequence is adapted from the powerful HCMV major immediate-early promoter (MIEP), which allows rapid, sustained transgene expression. We observed a marked downregulation of expression of multiple transgenes driven by the CMV or related promoters in HCMV-infected cultures. Within infected cells in the HCMV-infected culture, this reduction in transgene expression was mediated by downregulation of CMV-promoter-driven transgene at the transcript level. Conversely, use of an unrelated promoter facilitated sustained transgene expression throughout HCMV infection. We also observed a marked downregulation of transgene expression within bystander cells in the HCMV-infected culture. The downregulation of transgene in bystander cells was unrelated to the promoter driving transgene expression but was mediated by an upregulation of 2′-5′-oligoadenylate synthetase 1 (OAS1) in response to HCMV in the culture. Our description of the mechanistic basis of HCMV modulation of transgene expression will allow subsequent accurate and nuanced design and interpretation of experiments utilizing lentiviral vectors in the study of HCMV replication and pathogenesis.