Adult mesenchymal stem cells, derived from bone marrow or other tissues, are promising candidates to achieve tissue regeneration. A major technological hurdle in wider-ranging human applications of these cells is that their optimal maintenance and proliferation in vitro requires the use of animal serum which, in turn, often contains infectious agents and elicits serious immune responses. In contrast, purified ZL's protein does not contain infectious agents nor elicits significant immune response. Thus, this protein represents a safe and effective alternative to prepare mesenchymal stem cells for transplantation therapies.