Expression of homing-associated cell adhesion molecule (H-CAM/CD44) on human CD34(+) hematopoietic progenitor cells

We investigated the expression of CD44 molecule on CD34(+) hematopoietic pr ogenitor cells. Significantly lower expression of CD44 was observed on bone marrow (BM) CD34(+) cells compared with circulating CD34+ cells in cord bl ood and peripheral blood. Using fluorescence-activated cell sorting, human CD34(+) BM cells were fractionated into CD44(+) and CD44(-) populations. Im munofluorescence analysis revealed that the majority of CD34(+)CD44(-) cell s expressed B-lymphocyte-associated CD10 and CD19 antigens, whereas only a part of CD34(+) CD44(+) cells were positive for CD19, Myeloid and erythroid progenitor cells were found predominantly in CD34(+) CD44(+) cell fraction s. In short-term suspension cultures, cell proliferation and G(1) --> S tra nsition in the cell cycle were enhanced in CD34(+)CD44(+) cells. In contras t, a large part of CD34(+)CD44(-) cells underwent apoptotic cell death. Alt hough co-culture with BM stromal cells could partially prevent CD34(+)CD44( -) cells from undergoing apoptosis, significant increase of apoptotic cells was consistently observed. Furthermore, CD34(+)CD44(-) cells plated on BM stromal cells could differentiate into CD34(-)CD44(-)CD10(-)CD19(+) cells. These findings suggest that CD34+CD44- cells expressing CD19 would represen t unique B-lymphocyte-committed precursors in BM, which might undergo apopt otic cell death in the early steps of B-cell differentiation. (C) 1999 Inte rnational Society for Experimental Hematology. Published by Elsevier Scienc e Inc.