Production of recombinant human transferrin using transgenic rice cell culture

Transferrin is one of the major soluble serum proteins and is responsible for iron transport. Industrially, it is significant as a component of mammalian cell culture media, where a safe and stable supply is necessary. However, because transferrin is a glycoprotein containing 19 disulfide bonds, it is difficult to produce as a recombinant protein in bacteria, and at present it is mainly sourced from animals. In glycoprotein production, stability of the N-glycan profile is crucial, as glycans play important roles in diverse biological processes and influence the efficacy of glycoproteins. In this study, we aimed to produce recombinant human transferrin (rhTF) with stable N-glycan profiles. We generated transgenic rice calli expressing human TF (hTF) as a secretory glycosylated protein. rhTF was successfully produced as a soluble protein in the liquid culture medium of transgenic rice calli and subsequently purified. We confirmed that rhTF contained two plant-specific N-glycans and that these profiles were consistent across production batches. Purified rhTFs promoted the proliferation of cultured animal cells and human iPS cells, similar to serum-derived transferrin. Our results demonstrate new possibilities for producing recombinant glycoproteins with stable N-glycan profiles using a plant cell culture–based secretory protein expression system.