A Unique Population of CD34' Cells in Cord Blood zyx Maya T. Nimgaonkal; Rochelle A. Roscoe, Jeannette Persichetti, Witold zyx B. Rybka, Alan Winkelstein, Edward D. Ball Division of Hematology/Bone Marrow Transplantation, Department of Medicine, University of Pittsburgh School of Medicine, The Pittsburgh Cancer Institute and the Central Blood Bank, Pittsburgh, Pennsylvania, USA Key Words. CD34 Cord blood Flow cytometry Transplantation Abstract. Human umbilical cord blood (CB) is a rich source of hematopoietic stem cells for both research and stem cell transplantation. In clinical studies, it appears that recovery from myeloablative therapy using CB requires significantly fewer cells than a typical allogeneic marrow transplant. This suggests that CB may be enriched for early hematopoietic progenitors. The present studies were undertaken to determine the presence of CD34+ cells in CB with the phenotypic characteristics of multi- potential stem cells. In zyxwvutsr 22 CB harvests, the average percentage of CD34+cells was 1.33 zyxwvu i 0.21% (SE), a value similar to that in adult normal bone marrows (BM). However, the distribution of CD34+ cells was distinctly different from either BM or granulocyte colony-stimulatingfactor (G-CSF) mobilized periph- eral blood stem cell harvests. CB contained a defined population of brightly staining CD34+ cells with low side scatter. These CD34 (bright) cells comprised a mean of 14.5 i 2.5% of the CB~ CD34' cells, whereas ~1% of BM CD34' cells has been shown to be CD34- bright. Eighty-five to ninety percent were negative for three antigens expressed at an early stage of stem cell maturation: CD38, HLA-DR and LFA-1. Fifty- five percent of these CD34 (bright) cells did not express the CD45RA isoform, an additional marker of immaturity. The antigen-bright cells also lacked lineage-specific antigens including CD33, CD56, CD19, CDlO and CD7 as well as CD71. Approx- imately 46% were Thy-l+,and 40% expressed c-kit receptors. These data suggest that, by phenotypic criteria, CB may be a particularly enriched source of primitive hematopoietic precursors. Correspondence: Dr. Edward D. Ball, Division of Hematology/Bone Marrow Transplantation, University of Pittsburgh Medical Center, 200 Lothrop Street, Pittsburgh, PA 15213, USA. Received August 12, 1994; provisionally accepted September 27, 1994; accepted for publica- tion November zyxwvutsrq 16, 1994. OAlphaMed Press zyxwvut 1066- 5099/95/$5 .OO/O Introduction Human umbilical cord blood (CB) is a rich source of hematopoietic progenitors and has been used as an alternative source of stem cells for bone marrow (BM) transplantation [l-71. As of 1993,26 children, aged 1.3 to 16 years, received umbilical CB stem cells [8]. Eighteen of these 26 patients showed successful donor cell engraft- ment. In these procedures, the median volume of CB and number of nucleated cells transplanted was 100 ml and 4.0 x 107/kg, respectively. By contrast, a typical BM harvest for either autolo- gous or allogeneic transplantation consists of approximately 1-1.5 liters with at least 2-4 x lo8 nucleated celldkg. Both CB and BM harvests contain similar percentages of CD34' cells, approximately 1% of the mononuclear cells [9, 101. Thus, the total number of CD34' cells in an average BM transplant is 10-15 times that of a CB transplant. It has been postulated that the repopulating activities of CB may result from a greater con- centration of immature multipotential stem cells. In vitro studies suggest that hematopoietic prog- enitors from CB have considerably greater pro- liferative capabilities than similar cells from BM [ 1 1 - 131. Broxmeyer et al. compared colony-fom- ing cells from these two sources. They found that CB and BM contain similar concentrations of colony-forming units granulocyte-macrophage (CFU-GM) [ 111. This parameter reflects the activities of lineage-committed stem cells. By contrast, CB progenitors have a greater replat- ing efficiency than adult BM, a measure of the proliferative capacities of early stem cells [12, 131. Other studies indicate that CB contained long-term culture initiating cells (LTCICs) that STEM CELLS 1995;13:158-166