| Umbilical cord blood stem cells (UCBC), and umbilical cord blood stem cell transplantation (UCBT) are increasingly attrached attention to scholars at home and abroad, because of their abundant sources and easy preparation. UCBC has become an alternative source for clinical transplantation of hematopoietic stem / progenitor cells (HS/PCs). the quality and quantity of cord blood HS/PCs is the maun factor for clinical application. Compared with the bone marrow, HS/PCs from cord blood are abundant and good. At present, the main problem is the limited number of HSCs from a single cord blood and infant immunization.To the problem,a lot of serategies have been applied, such as in vitro amplification, co-transplantation with more numbers of cord blood, co-transplantation of MSCs. But it is difficult to achieve the desired result .In vitro cultivation causes deficiencies in homing capacity, the UCBT T cell delay reconstruction of immune function can not be solved by vitrocultication with MSC, etc. Therefore, we have to find new ways for the limited UCB HSC to home and implant into bone marrow. Epidemiological investigations and laboratory studies have shown that low-dose radiation (LDR) on the body and cells shows hormesis.We hypothesized that the ability of stimulating blood, and enhance anti-tumor immunity activation cord blood cells can be improved by LDR.We used cord blood mononuclear cells as transplants by into bone marrow injection and apply LDR to the umbilical cord blood and (or) mice after transplantation to study the effects of LDR on cord blood transplantation and the clinical potential of LDR. With application LDR , 87 NOD/SCID mice were randomly divided intofive groups: control; CB-MNC+ Mice; CB-MNC+ LDR Mice; LDR CB-MNC+ Mice; LDR CB-MNC+ LDR Mice Group. LDR CB-MNC cord blood was separated within the first four hours, LDR-Mice was applied within about 12 hours after transplantation, For the fourth Group,the interval in LDR CB-MNC and LDR-Mice was about 24 hours. To ensure the consistency of that the observed effect of LDR ,the mice in①②④group were sacrificed at the the 60th hour after transplantation and the mice from③at the 40th hour after transplantation. For every group,the rest of mice were killed at +7 d,+14 d and+21d after the transplantation(five mice for each time point in every group).The ollowing tests were included: the condition of the mice, the expression level of main homing adhesion factor (CD49d), implanting state of human hematopoietic cells in mice marrow (CD34-FCM, CD45-FCM. ALU-PCR, CFU-GM), the recovery state of hematopoietic and immune system (WBC count, Hemoglobin concentration, platelet count, histo-pathologic examination of bone marrow, spleen index).Results showed that the mice in control group died of marrow exhaustion in +5～+6d, a mouse from each group died within seven days after transplantation. The cause of death revealed by pathology was due to injury without signs of infection. The remaining mice survived to the end of the experiment, so the survival rate was 95%. PCR analysis of cells from bone marrow, spleen, peripheral blood showed the human genome- specific---Alu gene expression. FCM analysis :demonst rated tha cells from bone marrow expressed human CD34 and CD45 molecule were higher than those in cord blood before transplanting, With the extension of survival time, the rate was increased, the groups with LDR have more rapid growth rate and more positive rate than the group without LDR (p<0.05); but at all time points, the percentage of CD34 + and CD45 cells from LDR CB-MNC+LDR Mice mice group slightly higher than the LDR CB-MNC+Mice CB-MNC+LDR Mice group, but there was no statistical significance (p>0.05). In vitro hematopoietic stem / progenitor cells colony culture showed that there was +4d～+5d colony formation in each group, the cells from groups with LDR showed larger colony size and more cells than the group without LDR, the numbers of colonies showed no significant difference (p>0.05).After transplantation, the percentage of CD49d+ cells in the group withou LDR showed a growth trend, and in the mice bone marrow he percentage of CD49d+ cells in the group with LDR showed a lower level at initial time (+3d. p<0.05), then began to rise. +3d, there was no statistical significance among groups with LDR (p>0.05).In the recovery process, LDR CB-MNC+ LDR Mice group is fastest one to recovery, LDR CB-MNC+ Mice CB-MNC+ LDR group were inferior to the former; +21d,abd there was no statistically significant among the groups (p>0.05). By pathological analysis, there was no significant difference among the groups. Bone marrow cells were active until the end of the experiment (+21d), hematopoietic area was up to 70%, the proportion of granulocytes and red blood cells were normal and the morphology of megakaryocyte was normal as well. It was showed that : after sub-lethal doses of radiation and the transplantation, the peripheral Blood cell levels have dropped substantially, at+10d～+14d to the minimum, and then began to rise. The group with LDR were back earlier than the CB-MNC group. WBC, Plt and hemoglobin levels of the LDR Group were significantly higher than the CB-MNC group (p <0.05).The WBC and Plt level of LDR CB-MNC+LDR Mice Group were significantly higher than those of CB-MNC+ LDR Mice Group and the LDR CB-MNC+Mice group (p<0.01) However, there was no significant difference between the two latters (p>0.05); the Hb level of CB-MNC+LDR Mice were slightly higher than that of CB-MNC+LDR Mice Group and LDR CB-MNC+Mice group, but the difference was not significant (p> 0.05). At the +21d, in the mice of application LDR groups, leukocyte count returned to normal, CB-MNC group has not yet reached the normal level; At this time hemoglobin content were normal for every group; contrast to the WBC and Hb, Pit restore a more moderate rate ,then the Plt level of CB-MNC+LDR Mice were slightly higher than that of CB-MNC+LDR Mice Group and LDR CB-MNC+Mice group.These results show that: (1) The application dose of 350cGy irradiation to the NOD/SCID mice before transplantation is safe and effective for transplantation experiments; (2) 80 mice growed well, engraftment rate of 100%(FCM analysis of bone marrow cells were CD45 "0.5%), It was showed that iBMI guaranteed cord blood hematopoietic stem cells to implant and survive successfully, and wouldl become the new method of UCBT optimization; (3)Comprehensively consideration of the trends of VLA-4 and recovery of the indicators of the hematopoietic,despite the initial expression of VLA-4 declined to LDR, but HS/PCs can be alive, and LDR still play active role to promote the HS/PCs proliferation and differentiation .This may be the outcome of the synergies of other effective homing-related factors. It shows that the implantation of hematopoietic stem / progenitor cells in the hematopoietic organs was a synergetic results of a variety of factors, so further research was needed; (4)After sublethal dose of irradiation,the bone marrow can release "niches" for the cord blood stem cell implantation, and provided hematopoietic microenvironment for HS/PCs differentiation .UBSCs in mouse bone marrow prolifered and differentiated and played its hematopoietic function.LDR exerted its hormesis function on hematopoietic system hematopoietic and immune reconstitution. After LDR hematopoietic stem/progenitor cells gained greater proliferation and differentiation capacity, and the trends indicated twice radiation by LDR had a multiplier effect: reducing the death of infection, and bleeding after transplantation.LDR as a new strategy to optimize UCBT will lay the theoretical and practical basis for the clinical application...
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