A Novel Route of Transplantation of Human Cord Blood Stem Cells in Preimmune Fetal Sheep: The Intracelomic Cavity

The intracelomic route for in utero hematopoietic stem cell transplantation was evaluated in preimmune fetal sheep and the engraftment characteristics were defined. Twelve twin ovine fetuses (gestational age: 40-45 days) received intracelomic transplants of human CD3-depleted (50 x 10(6) per lamb) or CD34-selected (1-2 x 10(5) per lamb) cord blood hematopoietic stem cells. Engraftment was evaluated from cell suspensions of the liver, spleen, bone marrow, and thymus by flow cytometry, cloning assays, and polymerase chain reaction (PCR) analyses of human beta2-microglobulin. Four fetuses (33%) aborted shortly after intracelomic transplantation and were not evaluable for engraftment. Engraftment was detected in four fetuses obtained from cesarean delivery on day 70 after transplantation of CD3-depleted cord blood cells. The degrees of engraftment in these four fetuses ranged from 6%-22% in the different organs (as revealed by antigenic analysis of human CD45 with flow cytometry). Three fetuses obtained after cesarean section at 102 (no. 435184) and 105 (no. 915293, no. 037568) days and one fetus delivered at term that received CD34-selected cord blood cells had human engraftment with 10%, 32%, 20%, and 10% CD45(+) cells in bone marrow, respectively. In six of eight fetuses evaluable for human engraftment, chimerism was confirmed by PCR analysis for human beta2-microglobulin, which also identified human cells in brain, spinal cord, heart, lung, and skeletal muscle. This preliminary study indicates that intracelomic transplantation of human hematopoietic stem cells in fetal lambs is feasible and effective in terms of hematopoietic engraftment.