Development of mammalian cells capable of growing rapidly in serum-free media

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Cytokines and growth factors are indispensable for the propagation and maintenance of factor-dependent mammalian cells. However, cytokines are often so expensive that the use of factor-dependent cells for the industrial applications such as protein production is not practical. Here we try to establish a method to maintain cell growth with an inexpensive ligand quite different from cytokines. Based on the fact that interaction between V_H and V_L regions of anti-hen egg lysozyme (HEL) antibody HyHEL-10 becomes strong only in the presence of HEL, part of the extracellular region of erythropoietin receptor (EpoR) was replaced with either V_H or V_L region of HyHEL-10 to create Vn-EpoR or V_L-EpoR, respectively. When V_H-EpoR and V_L-EpoR were cotransfected into an interleukin-3 (IL-3) dependent pro-B cell line Ba/F3, the transfectant proliferated in a HEL dose-dependent manner without IL-3. To substitute IL-6 dependency of hybridoma cells, the intracellular domain of V_H-EpoR and V_L-EpoR was replaced with that of gp130 to create V_H-gp130 and V_L-gp130, respectively. When V_H-gp130 and V_L-gp130 genes were co-transfected to Ba/F3 cells, the transfectant proliferated in a HEL dose-dependent manner without IL-3. When V_H-gp130 and V_L-gp130 genes were co-transfected to an IL-6 dependent hybridoma cell line 7TD1, the transfectant showed clear HEL dose-dependent cell growth and monoclonal antibody production both in serum-containing and serum-free media without IL-6, resulting in significant medium cost reduction. The results further suggest the possibility of applying this technology for the control of many other cell functions by exchanging the receptor intracellular domain.