Replication efficiencies of human cytomegalovirus-infected epithelial cells are dependent on source of virus production

Human cytomegalovirus (HCMV) is a prevalent betaherpesvirus, and infection can lead to a range of symptomatology from mononucleosis to sepsis in immunocompromised individuals. HCMV is also the leading viral cause of congenital birth defects. Lytic replication is supported by many cell types with different kinetics and efficiencies leading to a plethora of pathologies. The goal of these studies was to elucidate HCMV replication efficiencies for viruses produced on different cell types upon infection of epithelial cells by combining experimental approaches with data-driven computational modeling. HCMV was generated from a common genetic background of TB40-BAC4, propagated on fibroblasts (TB40Fb) or epithelial cells (TB40Epi), and used to infect epithelial cells. We quantified cell-associated viral genomes (vDNA), protein levels (pUL44, pp28), and cell-free titers over time for each virus at different multiplicities of infection. We combined experimental quantification with data-driven simulations and determined that parameters describing vDNA synthesis were similar between sources. We found that pUL44 accumulation was higher in TB40Fb than TB40Epi. In contrast, pp28 accumulation was higher in TB40Epi which coincided with a significant increase in titer for TB40Epi over TB40Fb. These differences were most evident during live-cell imaging, which revealed syncytia-like formation during infection by TB40Epi. Simulations of the late lytic replication cycle yielded a larger synthesis constant for pp28 in TB40Epi along with increase in virus output despite similar rates of genome synthesis. By combining experimental and computational modeling approaches, our studies demonstrate that the cellular source of propagated virus impacts viral replication efficiency in target cell types. IMPORTANCEHuman cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause serious disease under conditions of immunodeficiency and upon congenital infection. HCMV replicates in diverse cell types throughout the human body with tropism influenced by the source of the virus. Here, we investigated the contribution of viral sources to the kinetics of HCMV replication in epithelial cells using both experimental and mechanistic computational modeling approaches. These studies reveal that HCMV produced from epithelial cells exhibits a higher efficiency of replication despite similar viral DNA synthesis kinetics between viral sources. These differences likely involve a propensity of epithelial-derived virus to induce syncytia versus fibroblast-derived virus, and an accompanying higher synthesis rate of a late virion protein ultimately resulting in production of more extracellular infectious virus.