Differences in the Expression of Adhesion Molecules and Mobilization Efficacy in Healthy Stem Cell Donors and Patients with Hematologic Malignancies.

Stem cell mobilization is achieved by short term administration of G-CSF in healthy donors and G-CSF +/− chemotherapy in patients with malignant diseases. It is known that the crosstalk between adhesion molecules, bone marrow microenvironment, and cytokines facilitates the multi step process of stem cell mobilization from bone marrow to peripheral blood. But still, the biological basis of the large variability in mobilization efficacy remains unclear. The aim of the present study was to evaluate if poor and good mobilizers - healthy donors as well as patients with hematologic malignancies - show differences in the expression of adhesion molecules (VLA-4, L-selectin, LFA-1, PECAM-1, CD44), the chemokine receptor CXCR4 and the G-CSF receptor measured by flow cytometry on CD34 positive cells. Therefore, we investigated 200 aphereses from 132 healthy PBSC donors and 68 patients with a 4-color staining: CD34/CD45 combined with two different adhesion molecules in each sample. The quantitative (mean fluorescence intensity) and qualitative (%) antigen expression was assessed. Donors/patients were divided into three groups according to the peripheral CD34-positive cell count at the day of apheresis: ≤ 30/μl (poor mobilizer; 36 donors, 30 pts.), 31–100/μl (standard mobilizer; 56 donors, 23 pts.), > 100/μl (good mobilizer; 40 donors, 15 pts.). The quantitative antigen expression was significantly higher for LFA-1 in poor vs. good mobilizing donors (GeoMean: 22 vs. 17; p=0.007) and patients (26 vs. 18; p<0.033) and for PECAM-1 (419 vs. 240; p<0.019; only in patients). In contrast, L-selectin showed a significantly lower expression in poor vs. good mobilizing donors (55 vs. 101; p=0.006). Considering the percentage of antigen positivity, LFA-1 was expressed in a significantly higher proportion of CD34 positive cells in poor mobilizing donors (66% vs. 53%; p=0.002) as well as patients (82% vs. 51%; p<0.011). In contrast, CXCR4 and L-selectin expression was significantly lower in samples of poor mobilizing patients (48 % vs. 62%, p<0.001; 90% vs. 95%, p=0.025). VLA-4, PECAM-1, and CD44 were expressed in 100% of CD34 positive cells independent of mobilization capacity. Comparing healthy donors and patients, the qualitative and quantitative adhesion molecule expression is much lower in donors vs. patients for almost all tested antigens and independent of mobilization efficiency. In contrast, the chemokine receptor CXCR4 has a significantly higher expression in CD34+ cells of healthy donors on the one hand, suggesting its downregulation during recovery from myeloablative chemotherapy in patients on the other hand. In summary, our analyses suggest that a higher LFA-1 expression is correlated with a reduced mobilization efficacy in healthy donors as well as patients with hematologic malignancies. The expression of the other tested antigen seems to be regulated differently in donors and patients.