BACKGROUND: The aim of the present study is to evaluate the modulation CD44 and CD31 expression and apoptotic status on mobilized CD34＋ cells during continuous intravenous (i.v) administration of granulocyte-colony stimulating factor (G-CSF), elucidating the mechanism of peripheral blood progenitor cells (PBPC) mobilization in normal donors.
METHODS: Fifteen healthy donors were enrolled in this study. G-CSF (10 ㎍/kg/day) was administered for 4 consecutive days through continuous i.v. infusion. Measurement of CD34＋ cell levels and their expression of CD44, CD31 and 7-aminoactinomycin D (7-AAD) was performed. PB sampling was drawn immediately before the administration of G-CSF (steady-atate) and after 4, 8, 24, 48, 72, 96 and 120 hours of G-CSF administration.
RESULTS: Although there were considerable variations among the healthy donors, the absolute number of CD34＋ cells significantly increased at day 3 (51.12±24.83×10 3 /mL) and day 4 (46.66±24.93×10 3 /mL), compared to the steady-state level (2.03±5.69×10 3 /mL). The expression of CD44 on CD34＋ cells revealed a significant reduction from the steady-state level (579.59±133.69) after day 3 (281.02±105.15, P=0.0059) and day 4 (164.76±107.44, P=0.0002) of G-CSF administration. The expression of CD31 on CD34＋ cells also significantly decreased from the steady-state level (145.86±30.52) after day 4 (34.47±38.87, P=0.0055) and day 5 (17.33±50.68, P=0.0134) of G-CSF administration. The proportions of apoptotic
(7-AAD dim ) CD34＋ cells were also significantly decreased after day 3 of G-CSF administration.
CONCLUSION: Down-regulation of CD44 and CD31 on CD34＋ cells is likely to be involved in the mobilization of PBPC and G-CSF may acts as a survival factor for mobilization CD34＋ cells by the suppression of apoptosis during continuous i.v. administration of G-CSF in normal donors.

Keywords: Continuous i.v., G-CSF, CD34＋ cells, CD44, CD31, Apoptosis, Normal donors,