I nfection of β-herpesvirus h uman cytomegalovirus (HCMV) could be life-threatening or cause life-long suffering in the majority of humans. Moreover, the viral vertical transmission during pregnancy leads to most congenital birth defects. However, treatment and prevention options currently available are extremely limited. Challenges in Studying HCMV–host Cell Interactions More than 235 kbp of double-stranded DNA (dsDNA) in HCMV make s the largest known genome of human herpesviruses. Besides, HCMV is similar to other herpesviruses with complicated transcriptional architecture, including alternative transcription start sites, alternative splicing events, and polycistronic transcripts. The complex transcriptional architecture enables strict temporal control of gene expression and the possibility of generating multiple distinct proteins from a single genomic locus. The complexity is further increased by host cellular heterogeneity and differences in i...