Mobilization Kinetics of CD34+ Cells in Association with Modulation of CD44 and CD31 Expression during Continuous Intravenous Administration of G‐CSF in Normal Donors

The aim of the present study is to evaluate the kinetics of CD34+ cells and investigate the potential modulation of CD44 and CD31 expression on CD34+ cells during continuous i.v. administration of G‐CSF, thus to elucidate the possible mechanism of peripheral blood progenitor cell (PBPC) mobilization. Fifteen healthy donors were enrolled in this study. G‐CSF (10 μg/kg/day) was administered for four consecutive days through continuous 24‐h i.v. infusion. For measurement of complete blood counts, CD34+ cell levels and their expression of CD44 and CD31, PB sampling was performed immediately before the administration of G‐CSF (steady‐state) and after 4, 8, 24, 48, 72, 96, and 120 h of G‐CSF administration. The percentage and absolute number of CD34+ cells significantly increased at day 3 (0.55 ± 0.09%, 51.12 ± 24.83 × 103/ml) and day 4 (0.47 ± 0.09%, 46.66 ± 24.93 × 103/ml), compared to the steady‐state level (0.06 ± 0.09%, 2.03 ± 5.69 × 103/ml). At day 3 to day 5 following the onset of G‐CSF administration, a strong decrease of CD44 and CD31 expression was observed on mobilized CD34+ cells compared to controls: the relative fluorescence intensity of CD44 and CD31 was, respectively, 50%‐70% and 40%‐90% lower than that of controls. We conclude that continuous i.v. administration of G‐CSF apparently results in more rapid mobilization of CD34+ cells, and downregulation of CD44 and CD31 on CD34+ cells is likely to be involved in the mobilization of PBPC after treatment with G‐CSF.