Expression of Adhesion Molecules and c-kit on CD34 + Hematopoietic Progenitor Cells: Comparison of Cytokine-Mobilized Blood Stem Cells with Normal Bone Marrow and Peripheral Blood

We assessed the expression of the adhesion molecules leukocyte function antigen-1 (LFA-1, CD11a), intercellular adhesion molecule-1 (ICAM-1, CD54), homing-associated cell adhesion molecule (H-CAM, CD44), and c-kit (stem cell factor receptor) on the CD34⁺ progenitor population from the leukapheresis products of 23 patients (LP CD34⁺). For blood stem cell collection granulocyte colony-stimulating factor (G-CSF) or interleukin-3/granulocyte-macrophage colony-stimulating factor (IL-3/GM-CSF) was administered after cytotoxic chemotherapy. Furthermore, bone marrowand blood-derived CD34⁺ progenitor cells from 6 normal volunteers (BM and PB CD34⁺) were analyzed. LFA-1 expression was higher on PB CD34⁺ (88.2 ± 2.5%, mean ± SEM) than on BM CD34⁺ (75.3 ± 4.3%). Following cytokine administration, LFA-1 was expressed on only 59.7 ± 3.7% of LP CD34⁺ at a low fluorescence intensity, suggesting that down-regulation of LFA-1 may facilitate the egress of cells from the bone marrow and prolong their circulation. In contrast, ICAM-1 was weakly positive on CD34⁺ cells from all sources. CD44 was expressed on the vast majority of CD34⁺ cells (>95%) in all samples studied. The highest proportion of CD34⁺ cells costaining for c-kit was found in normal bone marrow (32.2 ± 3.3%). In normal peripheral blood and after cytokine mobilization, fewer of the CD34⁺ cells weakly expressed c-kit (<15%). The low percentage and level of c-kit expression may indicate that the majority of cytokine-mobilized CD34⁺ cells are lineage-committed progenitor cells, as reflected by the coexpression pattern for CD38, HLA-DR, and CD33.