We found that co-culturing the SDF-1/HOXB4 fusion gene-modified MSCs (SDF-1/HOXB4-MSCs) and human umbilical cord blood CD34(+) cells significantly improved HSC cell expansion in vitro.     ///    "More importantly, co-transplantation of CD34(+) cells and SDF-1/HOXB4-MSCs markedly increased the hematopoietic potential of irradiated mice as evidenced by the rapid recovery of WBC, PLT and HGB levels in peripheral blood and of BM cellularity. "    ///    "Therefore, SDF-1/HOXB4-MSCs could have therapeutic value by improving the efficacy of clinical transplantations in patients with defective hematopoiesis.. "    ///    Our study demonstrates that SDF-1/HOXB4-MSCs markedly accelerate hematopoietic recovery and significantly improve survival among mice treated with a lethal dose of irradiation. 