Highly efficient production of human interferon-α by transgenic cultured rice cells

Interferon-α (IFN-α) is an important antiviral pharmaceutical. A binary vector containing the first intron of the rice cytosolic SOD gene, the signal sequence of the 10 kDa rice prolamin, the amino-terminal region of β-glucuronidase, a thrombin recognition site, and the mature polypeptide region of human IFN-α was constructed, under the regulation of the cauliflower mosaic virus 35S promoter. Here, we report that transgenic rice cells transformed with this fusion protein vector produced a biologically active IFN-α. The vector was introduced into rice calli by Agrobacterium-mediated methods. Five lines of transgenic calli were obtained. IFN assay demonstrated that these calli expressed fusion proteins bearing biologically active IFN-α. Liquid-cultured cells exhibited stable growth and the production of active IFN-α during 10 successive generations, i.e. in 10 weeks. The expressed proteins were purified by immuno affinity chromatography and reverse-phase HPLC. Repeated selections of cultured cells that had been obtained by dividing calli into small cell aggregates considerably increased the production of IFN-α. Thrombin protease treatment of the fusion protein yielded the intact IFN-α polypeptide. Thus, transgenic suspension rice cells are expected to be useful for the production of large amounts of biologically active proteins at a low cost; moreover, such a system would be easier to employ than animal cell culture systems.