Very late antigen-4 (VLA-4), which binds to the extracellular matrix protein fibronectin, is an integrin molecule known to be modulated during mobilization of CD34+ cells, and to be involved in signaling the mobilization stimuli. On the hypothesis that cell cycling status might be different depending on the level of VLA-4 expression, we investigated the DNA contents of human cord blood CD34+ cells during ex vivo expansion by recombinant human thrombopoietin and flt3-ligand with simultaneous measurement of surface VLA-4 at the 1st and 4th week. During this ex vivo expansion, expression of VLA-4 increased and almost all cells became VLA-4+ until the 4th day of culture. Expression of VLA-4 was maintained in the major population of the cultured cells until the 4th week. The cells in S/G2/M phase were greater in number in VLA-4 high fraction than in VLA-4 low fraction (n=4, p<.001). Furthermore, the fraction of cells in S/G2/M phase increased as the expression of VLA-4 became higher. These results suggest that cord blood CD34+ cells expressing high levels of VLA-4 have more proliferative activities.
Antigens, CD34/analysis* ; Cells, Cultured ; DNA/analysis ; Fetal Blood/cytology* ; G2 Phase ; Hematopoietic Stem Cells/physiology* ; Human ; Immunophenotyping ; Infant, Newborn ; Integrins/analysis* ; Receptors, Lymphocyte Homing/analysis* ; S Phase

OBJECTIVETo study the effect of ex vivo expansion on the adhesion activities of umbilical cord blood hematopoietic stem and progenitor cells (HSPC).

METHODSFresh UCB CD(34)(+) cells were cultured in a serum and stroma-free culture system. At day 7, day 10 and day 14, CD(34)(+) cells were re-selected from the expanded products. The expression of adhesion molecules (CAMs) such as VLA-4, VLA-5, LFA-1, ICAM-1, HCAM, L-selectin and PECAM-1, and the adhesion activity of the expanded CD(34)(+) cells were evaluated and compared with those of precultured fresh CD(34)(+) cells.

RESULTS(1) The CD(34)(+) cells expressing homing-related CAMs were increased (from 15-fold increase for CD(34)(+) CD(54)(+) subset to 72-fold increase for CD(34)(+) CD(49e)(+) subset at day 14). (2) The expressions of CD(49d), CD(44), CD(11a) and CD(49e) on the expanded CD(34)(+) cells were increased or sustained the same levels as those on fresh UCB CD(34)(+) cells, while the expression of CD(62L), CD(54) and CD(31) on expanded CD(34)(+) cells declined with the cultivating. (3) Spontaneous adhesion and SDF-1-induced adhesion tended to be increased in the course of the first 10 day's culture.

CONCLUSIONSThe culture system used in this study could substantially support the expansion of HSPCs expressing the above CAMs, and the expanded HSPCs would sustain their intrinsic adhesion potentials.

Antigens, CD ; analysis ; Antigens, CD34 ; analysis ; Cell Adhesion ; Cell Adhesion Molecules ; biosynthesis ; Cell Division ; Fetal Blood ; cytology ; immunology ; metabolism ; Flow Cytometry ; Hematopoietic Stem Cells ; cytology ; immunology ; metabolism ; Humans ; Receptors, Lymphocyte Homing ; biosynthesis