Correlation of Cytokines Levels and Adhesion Molecules Expression with Stem Cell Mobilization Efficacy in Healthy Donors

Peripheral blood stem cells (PBSC) are standard source of hematopoietic stem cells for allogeneic transplantations. Mobilization of PBSC in healthy donors is induced by a short term administration of G-CSF. The biological basis of the mobilization procedure in not completely discovered. Several factors were identified influencing the mobilization efficacy however their predictive potential for detection of poor mobilizers is limited. We performed a prospective study to evaluate differences in cytokines levels and adhesion molecules expression between good and poor mobilizers. The aim was to find out whether some of these factors can predict mobilization efficacy. Sixty healthy donors (25 related, 35 unrelated) were included in the study. The median age was 39 years (26–67). All donors were treated with G-CSF 10 μg/kg/day (filgrastim, Neupogen) for 5 days. Aphereses were started on day+5. Blood levels of certain cytokines (SDF-1, ICAM, VCAM, MMP-9, IL-6, IL-8, fractalkine, TNFα, VEGF, E-selectin) were tested before G-CSF application (day+0) and at first apheresis (day+5). Adhesion molecules expression (CD11a, CXCR4, CD44, CD117, CD26, CD49d) on CD34+ cells was measured at day +5. Cytokines were assayed by multiplex xMAP or ELISA technology. CD34 positive cells and adhesion molecules were evaluated with the flow cytometry using standard protocols. In response to the G-CSF stimulation the following cytokines significantly increased: ICAM (p<0.0001), VCAM (p<0.0001), MMP-9 (p=0.0039) IL-6 (p=0.0133), TNFα (p<0.0001) and E-selectine (p<0.0001). SDF-1 (p=0.0001), IL-8 (p=0.0013) decreased and fractalkine and VEGF remained unchanged. There was a positive correlation of day+5 SDF-1 (p=0.0011) and VCAM (p<0.0001) levels with CD34+ count at day+5. As for IL-6 borderline negative correlation (p=0.0861) between day+0 cytokine level and day+5 CD34+ count was found. Afterwards the donors were divided into two groups according to the CD34+ count at day +5. The cut-off of 40.0 CD34+ cells/μl was used for distinguishing of poor mobilizers. Twenty two percent (13 donors) mobilized below and 78 % (47 donors) above the cut-off. Between good and poor mobilizers there were significant differences of ICAM levels at day+0 (p=0.0369) and day+5 (p=0.0023), VCAM at day+5 (p=0.117) and IL-8 at day+5 (p=0.0473). Using logistic regression ICAM and IL-6 measured at day+0 (before stimulation) were tested as predictors of mobilization efficacy. The ICAM level below cut-off of 100 ng/mL implies approx. 5× higher risk of poor mobilization (odds ratio 4.8, p=0.0206). Conversely the IL-6 level above cut-off of 32 pg/mL means approx. 16× higher risk of poor mobilization (odds ratio 15.6, p=0.0112). Immunophenotyping of CD34+ cells suggested an inverse relationship of CD34+ counts with two adhesion molecules expression: CD11a (p=0.0002), CXCR4 (p=0.0075). However the expression of all tested antigens was similar in both donors groups. G-CSF stimulated PBSC mobilization results in increased plasma levels of some cytokines mostly evident for ICAM, VCAM, TNFα and decreased levels of SDF-1 and IL-8. In cases of ICAM and IL-6 the kinetics of these changes correlates with the quality of PBSC mobilization in peripheral blood. Their levels measured before G-CSF mobilization might serve as predictive factor for mobilization efficacy and graft quality. Contribution of adhesion molecules to stem cell mobilization is less clear and their practical utilization for mobilization course management is low.