OBJECTIVETo investigate the effect and the potential mechanism of umbilical cord (UC) derived mesenchymal stem cells (MSCs) on umbilical cord blood (UCB) derived CD34+ cells in vivo homing in xenotransplanted NOD/SCID mice model.

METHODSCD34+ cells and MSCs were derived from fresh UCB and UC, respectively. CD34+ cells (5 x 10(5) per mice) and MSC cells (5 x 10(6) per mice) were co-transplanted into irradiated NOD/SCID mice intravenously. CD34+ cells (5 x 10(5) per mice) alone were transplanted into the mice as control group. CD34+ cells home in bone marrow and spleen of recipient mice were detected 20 hours after transplant by FACS and RT-PCR, and the homing efficiencies were calculated. The effect of MSCs on CD34+ cells chemotactic function was investigated after co-cultured UCB CD34+ cells with UC MSCs in vitro. After 4 and 7 days coculture, the homing related adhesion molecules (the CD49e, CD31, CD62L, CD11a) expressed on CD34+ cells were detected by FACS.

RESULTS1) The homing efficiencies in bone marrow in experimental and control group were (7.2 +/- 1.1)% and (5.4 +/- 0.9)%, respectively (P < 0.05). 2) Human GAPDH gene was detected in bone marrow in experimental group and in spleen in both groups. 3) The migration efficiency of CD34+ cells was significantly higher in experimental group (35.7 +/- 5.8)% than in control group (3.5 +/- 0.6)% (P < 0.05). 4) The expression of CD49e, CD31, CD62L on CD34+ cells kept higher level in MSCs cocultured group than in CD34+ cells alone group.

CONCLUSIONSMSCs can efficiently increase homing of CD34+ cells to bone marrow and spleen in vivo by keeping a high level of homing adhesion molecules expression and improving migration efficiency of UCB CD34+ cells.