THE JOURNAL OF GENE MEDICINE RESEARCH ARTICLE J Gene Med 2009; 11: 877–888. Published online 23 July 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jgm.1369 Stem cell antigen-1 + cell-based bone morphogenetic protein-4 gene transfer strategy in mice failed to promote endosteal bone formation Susan L. Hall 1,2 * Shin-Tai Chen 1,3 Reinhard Gysin 1,2 Daila S. Gridley 4 Subburaman Mohan 1,2,3,5 K.-H. William Lau 1,2,3 1 Musculoskeletal Disease Center, Jerry L. Pettis Memorial VA Medical Center, Loma Linda, CA, USA 2 Department of Medicine, Loma Linda University School of Medicine, Loma Linda, CA, USA 3 Department of Biochemistry, Loma Linda University School of Medicine, Loma Linda, CA, USA 4 Department of Radiation Medicine, Radiation Research Laboratories, Loma Linda University School of Medicine, Loma Linda, CA, USA 5 Department of Physiology, Loma Linda University School of Medicine, Loma Linda, CA, USA *Correspondence to: Susan L. Hall, Musculoskeletal Disease Center (151), Jerry L. Pettis Memorial VA Medical Center, 11201 Benton Street, Loma Linda, California 92357, USA. E-mail: susan.hall1@va.gov Received: 21 January 2009 Revised: 13 May 2009 Accepted: 1 June 2009 Abstract Background This study assessed whether a Sca-1 + cell-based ex vivo gene transfer strategy, which has been shown to promote robust endosteal bone formation with a modified fibroblast growth factor-2 (FGF2) gene, can be extended to use with bone morphogenetic protein (BMP)2/4 hybrid gene. Methods Sublethally irradiated recipient mice were transplanted with lentiviral (LV)-BMP2/4-transduced Sca-1 + cells. Bone parameters were monitored by pQCT and µCT. Gene expression was assessed by the real-time reverse transcriptase-polymerase chain reaction. Results Recipient mice of LV-BMP2/4-transduced Sca-1 + cells yielded high engraftment and increased BMP4 mRNA levels in marrow cells; but exhibited only insignificant increases in serum and bone alkaline phosphatase activity compared to control mice. pQCT and µCT analyses of femurs showed that, with the exception of small changes in trabecular bone mineral density and cortical bone mineral content in LV-BMP2/4 mice, there were no differences in measured bone parameters between mice of the LV-BMP2/4 group and controls. The lack of large endosteal bone formation effects with the BMP4 strategy could not be attributed to ineffective engraftment or expansion of BMP4-expressing Sca-1 + cells, an inability of the transduced cells to secrete active BMP4 proteins, or to use of the LV-based vector. Conclusions Sca-1 + cell-based BMP4 ex vivo strategy did not promote robust endosteal bone formation, raising the possibility of intrinsic differences between FGF2- and BMP4-based strategies in their ability to promote endosteal bone formation. It emphasizes the importance of choosing an appropriate bone growth factor gene for delivery by this Sca-1 + cell-based ex vivo systemic gene transfer strategy to promote bone formation. Copyright  2009 John Wiley & Sons, Ltd. Keywords bone morphogenetic protein 4; endosteal bone formation; ex vivo; gene therapy; hematopoietic stem cells; mice; Sca-1 + cell Introduction Osteoporosis is a debilitating disease characterized by a significant loss of bone mass, which leads to the deterioration of the mechanical integrity of the skeleton and increases the risk of nontraumatic fracture [1]. Currently, there are several effective small molecule anti-resorptive therapies for osteoporosis. Copyright  2009 John Wiley & Sons, Ltd.