Objective    To investigate the hematopoietic reconstitution by human umbilical cord blood CD34

+

cells in no obese diabetic/severe combined immunodeficiency (NOD/SCID) mi

ce.     Methods    Mononuclear cells (MNCs) were isolated from human fresh cord blood by gradient centrifugation

and then CD34

+

hematopoietic stem cells were selected by magnetic activated cell sorting. The selected cells were injected into the tail of the NOD/SCID mice after irradiation of sublethal doses. After the sample of peripheral blood were collected by cutting mouse tail at 3

7

10

and 14 d after transplantation

dynamic monitoring was performed on the mouse blood . The mice alive were sacrificed and the blood samples were harvested at 4

6

8 and 10 weeks after transplantation. The mRNA expression of human-specific gene Alu in the peripheral blood cells were analyzed by PCR.     Results    The yield proportion of CD34

+

cells accounted for 91.2%. Irradiation of sublethal doses obviously reduced the number of karyocytes and giant cells and even demolished the cells in medullary space. At the third day after transplantation

the peripheral blood cells in each department were significantly lower than those in the normal group (P0.01). From the seventh day after transplantation

peripheral blood in transplantation mice began to recover

significantly higher than negative control group [white cells: (3.90±0.53) 10

9

/L vs (1.30±0.18) 10

9

/L

hemoglobin: (139.8±5.0)g/L vs (79.8±11.0)g/L

platelets: (253.0±17.5) 10

9

/L vs (52.0±6.9) 10

9

/L

P0.01

]

. At 10 d after transplantation

peripheral blood of transplanted mice was back to the level before irradiation

with no significant difference with that of the normal group (P0.05). In 4 weeks after cell transplantation

there were more and more human-derived hematopoietic cells

human specific Alu gene was detected in the peripheral blood in mice. All mice died who received no transplantion in 2 weeks after irradiation.     Conclusion    Human-mouse chimeric immune model is built in irradiated NOD/SCID mice transplanted by cord blood CD34

+

cells. Irradiation can not destroy the bone marrow micr

oenvironment and hemopoietic stromal in NOD/SCID mice

and the mice can be used for allogeneic cell transplantation model. The hematopoietic system

humoral immunity is effective reconstructed in NOD/SCID mice after human umbilical cord blood CD34

+

cells transplantion.