Synthetic Alternatives to Fetal Bovine Serum: Platforms, Technologies, and Prospects for Industrial Vaccine Production.

Fetal Bovine Serum (FBS) has served as the gold standard supplement in mammalian cell cultures for more than six decades due to its cocktail of growth factors, carrier proteins, hormones, and attachment factors that create an ideal proliferative microenvironment. Nevertheless, heightened regulatory pressure, ethical issues associated with the use of bovine fetuses, logistical challenges, batch-to-batch variations, and the risks of contamination by adventitious agents have driven the need to formulate synthetic, animal-origin-free (AOF) substitutes. This review examines the key technologies being explored to engineer FBS substitutes, including chemically defined media, recombinant protein fortification using precision fermentation, hydrolyzed plants, human platelet lysates (HPL), conditioned media derived from induced pluripotent stem cells (iPSCs), and genetically engineered microbial cell factories, with special consideration of their feasibility for large-scale vaccine production in Vero, BHK-21, HEK293, and MDCK cells. No single technology can presently replace FBS across all applications; however, the convergence of biologics, chemically defined media, and precision fermentation platforms promises to bridge this gap.