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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 × × 10 6 per lamb) or CD34-selected (1-2 × × 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 β β2-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 β β2-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. Stem

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This study aims to investigate engraftment of human cord blood and foetal bone marrow stem cells after in utero transplantation via the intracoelomic route in the sheep. Here, we performed transplantation in 14 single and 1 twin sheep foetuses at 40-47 days of development, using a novel schedule for injection. (i) Single injection of CD34(+) human cord blood stem cells via the coelomic route (from 10 to 50 x 10(4)) in seven single foetuses. (ii) Single injection of CD34(+) foetal bone marrow stem cells via the intracoelomic route with further numbers of cells (20 x 10(5) and 8 x 10(5), respectively) in three single and in one twin foetuses. (iii) Double fractioned injection (20-30 x 10(6)) via the coelomic route and 20 x 10(6) postnatally, intravenously, shortly after birth of CD3-depleted cord blood stem cells in four single foetuses. In the first group, three single foetuses showed human/sheep chimaerism at 1, 8 and 14 months after birth. In the second group, the twin foetuses showed human/sheep chimaerism at 1 month after birth. In the third group, only two out of four single foetuses that underwent transplantation showed chimaerism at 1 month. While foetal bone marrow stem cells showed good short-term engraftment (1 month after birth), cord blood stem cells were able to persist longer in the ovine recipients (at 1, 8 and 14 months after birth).

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