Short-term ex vivo expansion sustains the homing-related properties of umbilical cord blood hematopoietic stem and progenitor cells.

BACKGROUND AND OBJECTIVES The homing of stem cells to the bone marrow microenvironment following transplantation is a specific movement eventually leading to the stem cells lodging in specialized niches of hematopoiesis. The present study was designed to develop an ex vivo expansion system capable of preserving the homing potential of hematopoietic stem/progenitor cells (HSPC). DESIGN AND METHODS Umbilical cord blood (UCB) CD34+ cells were expanded in QBSF-60 serum-free medium with a simple early-acting combination of cytokines and were re-selected from the expanded products at different time points. The homing-related characteristics and expansion rate of CD34+ cells were simultaneously examined. RESULTS It was observed that the number of HSPC increased significantly under our expansion protocol. The expression of CD49d, CD44, CD11a and CD49e on expanded CD34+ cells increased or remained at the same levels as those on freshly isolated CD34+ UCB cells, while the expression of CD54 on expanded CD34+ cells was lower during the second week of culture than at the start. The spontaneous and SDF-1-induced adhesion of CD34+ cells was increased during the first 10 days of culture, with the adhesion rates reaching peak levels (62.8 12.8% and 90.5 11.7% for spontaneous and induced adhesion, respectively) on day 10. Neither spontaneous nor SDF-1-induced migration had changed significantly by day 7. INTERPRETATION AND CONCLUSIONS These data demonstrate that, although ex vivo expansion may alter cell properties, our one-week expansion protocol can preserve most of the homing-related characteristics and activities of UCB HSPC.