RAPID COMMUNICATION Sustained, Retransplantable, Multilineage Engraftment of Highly Purified Adult Human Bone Marrow Stem Cells In Vivo

Data from many laboratory and clinical investigations indi-cate that CD34+ cells comprise approximately 1 % of human bone marrow (BM) mononuclear cells, including the progeni-tor cells of all the lymphohematopoietic lineages and lympho-hematopoietic stem cells (stem cells). Because stem cells are an important but rare cell type in the CD34+ cell population, investigators have subdivided the CD34+ cell population to further enrich stem cells. The CD34+/CD38- cell subset com-prises less than 10 % of human CD34+ adult BM cells (equiva-lent t o <0.1 % of marrow mononuclear cells), lacks lineage (/in) antigens, contains cells with in vitro replating capacity, and is predicted to be highly enriched for stem cells. The present investigation tested whether the CD34+/CD38- sub-set of adult human marrow generates human he-matopoiesis after transfer t o preimmune fetal sheep. CD34+