Transferrin is the iron-transport protein of vertebrate serum and donates iron to cells through interaction with a specific membrane receptor, CD71. Transferrin appears to be indispensable for most cells growing in tissue culture. It is referred to frequently as a growth factor because, in analogy to other growth factor-receptor interactions, proliferating cells express high numbers of transferrin receptors, and the binding of transferrin to their receptors is needed for cells to initiate and maintain their DNA synthesis. Apart from its role as an iron transport protein, transferrin acts as a cytokine and has functions that may not be related to its iron-carrying capacity. The recombinant human transferrin that is completely animal-free and blood-free. Its performance is equivalent to human transferrin in cell culture and offers significant regulatory advantages due to its safety and consistency.