Immortalized cell lines and methods of making the same

The present invention relates to methods of immortalizing various primary cell cultures, including pituitary cells, neurons, beta islet cells, glial cells, corneal epithelial cells and follicular stellate cells. The primary cells are transfected with a vector containing an establishment oncogene, resulting in non-transformed immortalized cells. The primary cells and/or the subsequent immortalized cells are cultured in a defined media containing one or more environmental factor(s) that control the proliferation and/or differentiation of the cells.