Variation in long-term engraftment of a large consecutive series of lambs transplanted in utero with human hematopoietic cells

We investigated die survival and chimeric engraftment characteristics of a large consecutive series of Iambs that were transplanted with human hematopoietic cells in utero. Approximately 50% of the fetal sheep survived. Neither the transplantation of human cells into fetal sheep, nor die parity of the ewe was associated with increased mortality, as compared with die risk of surgery alone. However, a breed-associated mortality was noted. Sixty percent of surviving recipient lambs contained donor, human hematopoietic cells in blood and bone marrow (BM) cells. Chimerism ranged from 0.0001-1%. Human hematopoietic progenitors were identified in the BM in 8 of 12 chimeric sheep examined. Some lambs engrafted with human cells maintained a human chimerism for up to at least 2 years. Our data demonstrate that a large proportion of fetal sheep are capable of engrafting human cells, albeit at widely variable levels of engraftment.