JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE SHORT COMMUNICATION J Tissue Eng Regen Med 2007; 1: 314–317. Published online 22 June 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/term.31 Cellular delivery of TGFβ 1 promotes osteoinductive signalling for bone regeneration Kelly K. Macdonald 1† , Charles Y. Cheung 1,2 and Kristi S. Anseth 1,2 * 1 Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424, USA 2 The Howard Hughes, University of Colorado, Boulder, CO, USA Abstract Administration of osteoinductive growth factors to wound sites, alone or in conjunction with a delivery vehicle, is an appealing treatment option for critical bone defects. The delivery of cells transfected with genes encoding for osteoinductive growth factors, such as TGFβ 1 , represents an attractive option to locally deliver constant levels of these growth factors to stimulate new bone formation at the defect site. Using non-viral transfection methods, we showed that osteoblasts can be genetically modified in vitro to secrete sustained therapeutic levels of TGFβ 1 in its active form through control of the transfected cell environment. In addition, delivery of TGFβ 1 produced by genetically modified cells that contained the proper post-translational modifications provided a more robust cellular response compared to administration of bacterially-derived recombinant TGFβ 1 . Migration and subsequent proliferation of osteoblasts are critical aspects of the initial steps in the cascade of new bone tissue formation. Exposure to mammalian-derived TGFβ 1 induced a more pronounced chemotactic response upon administration of 10 pg/ml TGFβ 1 , whereas osteoblasts showed enhanced levels of metabolic activity at 100 pg/ml, which is indicative of greater levels of cellular proliferation when compared to addition of the same levels of recombinant TGFβ 1 . This increased efficacy of cell-derived TGFβ 1 over recombinant forms of TGFβ 1 , combined with provision of a continual source of TGFβ 1 , highlights the advantages of delivering genetically modified cells over exogenous protein delivery for bone tissue engineering. Copyright  2007 John Wiley & Sons, Ltd. Received 9 January 2007; Revised 5 April 2007; Accepted 1 May 2007 Keywords TGFβ 1 ; nonviral gene therapy; bone tissue engineering The regeneration and repair of damaged bone tissue involves the migration and proliferation of osteopro- genitor cells to the wound site, followed by the dif- ferentiation of these cells into mature osteoblasts. The mature osteoblasts then secrete and mineralize extracel- lular matrix (ECM), forming new bone. During the repair process, several osteoinductive signals, growth factors and cytokines stimulate the cells and regulate their activity (Bostrom and Asnis, 1998; Bostrom, 1998; Mundy et al., 1995). While bone can regenerate new tissue without the formation of a scar, non-regenerative bone defects *Correspondence to: Kristi S. Anseth, University of Colorado, Department of Chemical and Biological Engineering and Howard Hughes Medical Institute, Campus Box 424, Boulder, CO 80309-0424, USA. E-mail: kristi.anseth@colorado.edu † Current address: Amgen Inc., 4000 Nelson Road, Longmont, CO 80503, USA. can arise from trauma, disease, developmental defor- mities and tumours. Although the exact reason for the non-union of bone in these cases is unknown, several in vivo studies have shown that the exogenous delivery of osteoinductive signals can stimulate new bone formation in critical-sized defects (Einhorn, 1999; Govender et al., 2002; Mackie and Trechsel, 1990). These results indi- cate that in at least some non-union fractures, the signals normally present during bone formation are absent or may only be present in concentrations too low to induce healing. Consequently, direct delivery of osteoinductive molecules to the wound site is an appealing treatment for non-regenerative bone defects to either enhance or replace current therapies, which typically involve bone grafts or fixation with internal or external implants. Trans- forming growth factor β 1 (TGFβ 1 ) is perhaps one of the most important growth factors for bone formation and Copyright  2007 John Wiley & Sons, Ltd.