Virus Entry is a Major Determinant of HCMV Latency in Monocytes

Human cytomegalovirus (HCMV) infection can result in either productive or latent infection, the latter enabling life-long viral persistence. Monocytes support latent infection but become permissive to productive infection upon differentiation into macrophages. The molecular basis for these differentiation-driven differences has been largely attributed to chromatin-mediated repression of the viral genome. Using metabolic labeling of newly synthesized RNA during the early stages of infection, we observed markedly lower viral transcription in monocytes compared to macrophages. Unbiased comparison of the two cell types revealed that this difference is partly due to reduced viral entry in monocytes: fewer viruses enter, and correspondingly fewer genomes reach the nucleus. Indeed, ectopic expression of known HCMV entry receptors in monocytes enhanced viral entry and consequently facilitated productive infection, demonstrating that these cells can support full replication if entry is efficient. We further identified integrin {beta}3 as a surface protein upregulated upon differentiation that plays an important role in HCMV entry into macrophages, partially accounting for the observed differences in entry efficiency. Finally, we show that cells receiving fewer viral genomes are the ones that establish latent infection and have the capacity to reactivate. Overall, our findings reveal that entry is a previously unrecognized factor contributing to latent infection in monocytes, adding a critical layer to the paradigm of HCMV latency.