Full reconstitution of hematopoietic system by murine umbilical cord blood

Background. Murine umbilical cord blood cells (UCBCs) were studied for their ability to reconstitute the hematopoietic system. Methods. On average, 150 muL of cord blood per fetus containing 1.2 to 2 X 10(4) nucleated cells were collected from day 18.5 fetal umbilical cord, and 3 to 6X10(3) cells per fetus were obtained after separation by gradient centrifugation. Results. Although lineage marker(-), c-Kit(+), and Sca-1(+) cells were detectable among UCBCs, cells designated to be in the side population (SP) by Hoechst 33342 staining were hardly detectable within this population; the frequency of cells of this phenotype was less than 1 of 10(5). Instead, the lineage marker(-), c-Kit(+), and Sca-1(-) population contained a considerable number of SP cells. Nevertheless, UCBCs obtained from fetuses of green fluorescent protein-transgenic mice successfully reconstituted the blood cells of lethally irradiated recipients. Fluorescent cells could be readily detected in every blood cell lineage and among immature cell populations. Furthermore, fluorescent SP cells sorted from the recipient bone marrow cells could also reconstitute the blood cells in the secondary recipients, indicating that UCBCs also replenished bone marrow stem cells. Conclusion. Murine UCBC could fully reconstitute the hematopoietic system of lethally irradiated recipients including hematopoietic stem cells in bone marrow.