Cultures Through Time: Forging a Xeno-Free Future for Cell Culture-Based Virology.

As a cornerstone of modern science, cell lines are the foundational platforms for key medical advances. They enable vaccinology (through viral propagation and attenuation), gene therapy (via vector development), and biopharmaceutical production (via recombinant protein expression). Designer mammalian, avian, and insect expression systems, including Vero, MDCK, HEK293, BHK21, CHO, PER.C6, EB66, and Sf21/Sf9, have become indispensable cellular platforms, delivering enhanced biologic yields, superior genetic stability, and validated end-product biosafety. Simultaneous advances in cell culture media optimization have enabled a critical shift from serum-dependent media to serum-free, chemically defined, and xeno-free alternatives, which aim to restore compositional traceability of culture media components, reduce potential residual xenogeneic proteins in serum-supplemented media, and promote reproducibility even at the molecular level. This review emphasizes the far-reaching influence of cell culture systems as the expression powerhouse that sustains modern virology, whilst focusing on recent cell-engineering methods and optimization strategies in culture media that have facilitated this shift.