A culture medium comprising: (a) 20-100 ng / ml epidermal growth factor (EGF); (b) 10-50 ng / ml basic fibroblast growth factor (bFGF); and (c) 1-150 ng / ml of transforming growth factor alpha (TGFα), in which the calcium concentration of the medium is not greater than 0.15 mM.Un medio de cultivo que comprende: (a) 20-100 ng/ml de factor de crecimiento epidérmico (EGF); (b) 10-50 ng/ml de factor de crecimiento de fibroblastos básico (bFGF); y (c) 1-150 ng/ml de factor de crecimiento transformante alfa (TGFα), en el que la concentración de calcio del medio no es mayor de 0,15 mM.