Long-term repopulating ability of xenogeneic transplanted human fetal liver hematopoietic stem cells in sheep.

We previously reported on the successful engraftment and long-term multilineage expression (erythroid, myeloid, lymphoid) of human fetal liver hematopoietic stem cells in sheep after transplantation in utero.That the engraftment of longterm repopulating pluripotent stem cells occurred in these animals was shown here by the fact that transplantation of human CD45 + cells isolated from bone marrow of these chimeric ani- mals into preimmune fetal sheep resulted in engraftment and expression of human cells.Marrow cells were obtained from three chimeric sheep at 3.2-3.6yr after transplant.The relative percentage of human CD45+ cells present in these marrows was 3.3±0.32%.A total of 29 X 106 CD45+ cells were isolated by panning, pooled, and transplanted into six preimmune sheep fetuses (4.8 x 106 cells/fetus).All six recipients were born alive.Hematopoietic progenitors exhibiting human karyotype were detected in marrows of two lambs soon after birth.Cells expressing human CD45 antigen were also detected in blood and marrow of both lambs.Human cell expression has been multilineage and has persisted for > 1 yr.These results demonstrate that the expression of human cells in this large animal model resulted from engraftment of long-term repopulating pluripotent human stem cells.(J.Clin.Invest.