OBJECTIVETo study the effect of ex vivo expansion on the migration ability and the CXCR4 expression of umbilical cord blood (CB) hematopoietic stem/progenitor cells (HSPC).

METHODSCD(34)(+) cells isolated from fresh CB samples were cultured in a serum-free and stroma-free culture system. On day 7, 10 and 14, CD(34)(+) cells were re-selected from the expanded cells, and the expression of CXCR4 and the transmigration ability of these CD(34)(+) cells were evaluated respectively and compared with those of the precultured fresh CD(34)(+) cells.

RESULTS(1) SDF-1 induced a higher migration percentage of fresh or expanded CB CD(34)(+) cells than that of uninduced ones. (2) Both of the uninduced and SDF-1-induced migrations were slightly reduced in the first week and then much more reduced in the second week expansion (P < 0.05). (3) The number of the CD(34)(+)CXCR4(+) cells were significantly increased during the culture period, but there was a downtrend of CXCR4 expression on CD(34)(+) subset; the expression levels on day 10 and 14 were lower than that on day 0.

CONCLUSIONSThe expanded HSPC would sustain the chemotactic activity during one-week-culture, but with further extended culture time their intrinsic homing potential would be partly impaired.