Cytomegalovirus Latency and Reactivation: Epigenetic Control and Immune–Microenvironment Crosstalk

Human cytomegalovirus (HCMV) establishes lifelong latency following primary infection and periodically reactivates under conditions of immune perturbation. Although CMV disease has classically been associated with severe immunosuppression, accumulating evidence indicates that viral reactivation also occurs in critically ill patients, during pregnancy, and in conditions characterized by immune remodeling and chronic inflammation. Recent studies have revealed that CMV latency and reactivation are governed not only by host immune surveillance but also by epigenetic regulation of the viral genome, particularly at the major immediate-early promoter (MIEP). Inflammatory cytokines, cellular differentiation, oxidative stress, and immunosenescence contribute to chromatin remodeling and activation of immediate-early gene expression, thereby promoting viral reactivation. In parallel, CMV has evolved sophisticated immune evasion strategies that enable lifelong persistence despite innate and adaptive immune responses. Emerging evidence further implicates the gut microbiota as a potential modulator of CMV latency and reactivation through both immunological and metabolic pathways. Microbiota-derived short-chain fatty acids (SCFAs), such as butyrate, may influence viral chromatin states through histone deacetylase inhibition, linking microbial metabolism to epigenetic regulation of CMV. This review summarizes current knowledge regarding the molecular mechanisms underlying CMV latency and reactivation and discusses the roles of host immunity, pregnancy-associated immune tolerance, immune reconstitution inflammatory syndrome, immunosenescence, and the gut microbiome in shaping CMV pathobiology. We also highlight unresolved mechanistic questions and future directions for understanding CMV–host–microenvironment interactions.