Transferrin (Holo) is the primary iron binding and cell delivery molecule present in serum.

Serum-free cell culture systems require a delivery format for iron. It is the preferential delivery form of iron because cells process transferrin bound iron in a physiologically appropriate way through transferrin receptors on the cell surface. It can be used with a wide range of cells types. It is loaded with iron prior to use and can be added directly to iron poor or iron-free cell culture media. It has been used for study in treatment of breast cancer cells with holo-transferrin in combination with dihydroartemisinin results in increased tumor cell death due to elevated levels of intracellular ferrous iron.