Transient expression is a gene expression strategy in which exogenous nucleic acids — such as plasmid DNA (pDNA) or mRNA — are introduced into a host cell without stable integration into the host cell genome, resulting in temporary protein production that typically lasts from a few days to several weeks before the genetic material is diluted or degraded. Compared to stable cell line approaches, transient expression offers significantly faster timelines, greater flexibility, and lower upfront costs, making it particularly valuable for early-stage process development, rapid antigen production, antibody screening, and the manufacturing of clinical-grade material for preclinical and Phase I studies. It is widely used in HEK293-based viral vector production platforms at CDMO scale.
