Liquid-liquid phase separation in the viral replication cycle: new paradigms and therapeutic opportunities.

Liquid–liquid phase separation (LLPS) has emerged as a central principle for organizing biomolecular condensates in eukaryotic cells, providing new perspectives on how viruses spatially and temporally coordinate infection. Accumulating evidence indicates that LLPS contributes to multiple stages of viral life cycles in diverse RNA and DNA viruses, including the formation of replication compartments, sites of genome packaging, and structures involved in immune modulation. In this review, we synthesize current data on how viral and host factors co-assemble into biomolecular condensates, highlight shared biophysical features and virus-specific strategies, and discuss whether these structures are causally required for efficient replication versus correlative markers of infection. We emphasize mechanistic insights into condensate composition, material state transitions, and functional consequences for viral replication, latency, and pathogenesis, as well as key experimental strengths and limitations underlying LLPS assignments. Finally, we summarize emerging therapeutic approaches that target viral condensates or their regulatory pathways, while underscoring that most LLPS-directed antiviral strategies remain at an early preclinical stage and face substantial challenges in specificity, toxicity, and delivery. A deeper mechanistic and quantitative understanding of viral LLPS will be essential to determine when condensates represent viable antiviral targets and how they can be modulated without disrupting critical host functions.