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

Abstract We investigated the expression of CD44 molecule on CD34 + hematopoietic progenitor cells. Significantly lower expression of CD44 was observed on bone marrow (BM) CD34 + cells compared with circulating CD34 + cells in cord blood and peripheral blood. Using fluorescence-activated cell sorting, human CD34 + BM cells were fractionated into CD44 + and CD44 − populations. Immunofluorescence analysis revealed that the majority of CD34 + CD44 − cells 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 fractions. In short-term suspension cultures, cell proliferation and G 1 → S transition in the cell cycle were enhanced in CD34 + CD44 + cells. In contrast, a large part of CD34 + CD44 − cells underwent apoptotic cell death. Although 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 represent unique B-lymphocyte–committed precursors in BM, which might undergo apoptotic cell death in the early steps of B-cell differentiation.