The Experimental Study Of Engraftment In SCID Mice After Ex Vivo Expansion Of Human Umbilical Cord Blood Hematopoietic Stem/progenitor Cells

Umbilical cord blood (UCB) is an alternative source to bone marrow(BM) and mobilized peripheral blood(MPB) of hernatopoietic stemlprogenitor cells. Many studies have demonstrated that UCB has been used successfully for hematopoietic reconstitution in pediatric patients and low weight adults who are in bone marrow failure. It has been shown that UCB contains abundant hematopoietic stem/progenitor cells, the content of CD34~CD38 and the numbers of colony forming cells and long-term culture-initialing cells are much greater in UCB than in BM and MPB from adults. Another characteristic of UCB transplantation is the lower severity and accident of acute graft-versus-host(GVHD) than BM and MPB. However, due to the relative volumes of placental blood and the limited number of progentor cells collected routinely, cell dose is presently a potential restriction for the widespread use of UCB for transplantation in adults. The study of ex vivo expansion of UCB hematopoietic stem/progenitor cells is an interesting projection in basic and clinical reseach of the transplantation field. Recently, several cytokines such as FL .~ TPO SCF which play essential role in early stage hematopoiesis are identified in succession. Based on the previous experimental results, we study the expansion effects of the new cytokine combination (FL+TPO+SCF 盜L-6) on purified CD34~ cells in strom-free liquid culture system, the results show that the new cytokine combination can more effectively expand CD34~ cells compared with the classical cytokine combination (SCF+IL-6盜L-3 +GM-C SF+EPO), and maintain some proportional hematopoietic stem cells in longer time(no ILL t less than 4 weeks) while generating considerable mature cells. In order to study the engraftment capability and hernatopoietic potential of the expanded cells, we establish the SCID mice model of UCB transplantation. The sublethally irradiated SCID mice are injected with expanded cord blood cells by tail vein. Four weeks after inocuration, BM cells of the sacrificed animals are obtained from both femurs and tibias and assessed for the presence of human cells by FACS and PCR. The results show that the expanded cells can engraft the BM of sublethally irradiated SCID mice and reconstitute hematopoiesis.