Immunophenotypic and functional characterization of CD33⁺CD34⁺ cells in human cord blood of preterm neonates

Objective To characterize CD33⁺CD34⁺ cells, a major population in human cord blood (CB) CD34⁺ cells of preterm neonates. Materials and methods The proportion of CD33⁺ cells was analyzed on CB CD34⁺ cells from preterm and full-term neonates. CD33⁺CD34⁺ cells were purified by cell sorting and analyzed on their clonogenic activity, proliferative activity in short-time liquid suspension culture, and GATA-2 mRNA expression by RT-PCR and Southern blot. Results The absolute numbers and proportion of CD34⁺ cells in mononuclear cells inversely correlated with gestational age. CD33 was expressed on a majority of CB CD34⁺ cells of preterm neonates but on only a minor population of them in full-term neonates. In addition, CD33 was dominantly expressed on CD38^-CD34⁺ cells or CD117(low)CD34⁺ cells in CB of preterm neonates. CD33⁺CD34⁺ cells of preterm cord blood had high proliferative and reproducible potentials compared with CD33^-CD34⁺ cells. CD33⁺CD34⁺ cells as well as CD33^-CD34⁺ cells from preterm CB highly expressed GATA-2, in contrast to those from BM. Conclusions These results suggest that CD33⁺CD34⁺ cells, which are a major population in CB CD34⁺ cells of preterm neonates, do not simply represent relatively mature myeloid lineage hematopoietic progenitor cells as those in adult BM CD34⁺ cells, and may contain hematopoietic stem cells or primitive progenitor cells as in fetal liver. (C) 2000 International Society for Experimental Hematology.