The invention relates to a conditioned cell culture medium and a corresponding method to obtain it. The invention also refers to methods of using this cellconditioned medium for the maintenance, proliferation and differentiation of mammalian cells. The culture medium produced in accordance with the present invention is conditioned by the cell secretion activity of murine cells, in particular, those differentiated and immortalized transgenic hepatocytes, named MMH (Met Murine Hepatocyte). These media are employed in in vitro cell culture systems to induce maintenance, proliferation and differentiation of mammalian cells. The cells named MMH are differentiated non transformed murine hepatocytes that produce important biological molecules (e.g cytokines and growth factors) and, in accordance with the present invention, they are used in in vitro cell culture systems for the maintenance, proliferation and differentiation of mammalian cells.