Set up of fetal sheep experiments.

CB CD34⁺ cells (100 000) were injected into 4 fetal sheep (group I). Two sheep were allowed to be born and followed long-term. Sixty days after transplantation, 2 fetuses were killed and the human CD45⁺ cells pooled and then injected into 3 secondary recipients (group IV). These recipients were killed at 60 days, BM pooled, and injected into 3 tertiary recipients (group VII). A similar protocol was followed with the cells cultured for 7 and 14 days.