Transfection is the process of introducing exogenous nucleic acids — such as plasmid DNA (pDNA), mRNA, or siRNA — into eukaryotic cells using chemical, physical, or biological methods to achieve transient or stable gene expression. Common transfection methods include lipofection (using lipid nanoparticles), calcium phosphate precipitation, electroporation, and polyethylenimine (PEI)-mediated transfection. In biopharmaceutical manufacturing, transfection is a critical step in viral vector production — particularly for AAV, adenoviral, and lentiviral vectors — recombinant protein expression, and cell line development, and must be optimized for efficiency, scalability, cell viability, and product quality as part of the upstream process development workflow.
