Biopharmaceuticals, including therapeutic antibodies, are rapidly growing products in the pharmaceutical market. Mammalian cells, such as Chinese hamster ovary (CHO) cells, are widely used as production hosts because recombinant antibodies require complex three-dimensional structures modified with sugar chains. Recombinant protein production using mammalian cells is generally performed with cell growth. In this study, we developed a technology that controls cell growth and recombinant protein production to induce recombinant protein production with predetermined timing. Expression of green fluorescent protein (GFP) gene and a single-chain antibody fused with the Fc-region of the human IgG1 (scFv-Fc) gene can be induced and mediated by the estrogen receptor-based artificial transcription factor Gal4-ERT2-VP16 and corresponding inducer drugs. We generated CHO cells using an artificial gene expression system. The addition of various concentrations of inducer drugs to the culture medium allowed control of proliferation and transgene expression of the engineered CHO cells. Use of 4-hydroxytamoxifen, an antagonist of estrogen, as an inducing agent yielded high gene expression at a concentration more than 10-fold lower than that of β-estradiol. When scFv-Fc was produced under inducing conditions, continuous production was possible for more than 2 weeks while maintaining high specific productivity (57 pg cell-1 day-1 ). This artificial gene expression control system that utilizes the estrogen response of estrogen receptors can be an effective method for inducible production of biopharmaceuticals.
Keywords: CHO cells; artificial transcription factor; estrogen receptor; inducible transgene expression; scFv-Fc antibody.
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