Modification of Cytokine Levels and CD34+ Stem Cell Adhesion Molecules during Mobilization in Multiple Myeloma (MM) Patients.

The mechanisms underlying the mobilization of peripheral blood stem cells (PBSC) are still unknown, even though studies on healthy donors and on cancer patients have hypothesised a central role for CD34+ stem cells adhesion molecules and for chemokines serum levels. The type of mobilizing regimen and the pathologic condition can exert different effects on cytokine levels and adhesion molecules expression. To evaluate the modification of these parameters during mobilization we studied 10 MM patients treated with DCEP chemotherapy (Decadron, Cyclophosphamide, Etoposide, cis-Platin) followed by G-CSF (5 mg/kg/day starting 48 hours after chemotherapy until PBSC collection).

The expression of four CD34+ cell adhesion molecules (Thy1, L-selectin, VLA4, CXCR4) was measured in the bone marrow before mobilization therapy and in the leukapheresis product. Serum levels of five cytokines (TGF-β, IL-8, HGF, VEGF-A, sVCAM-1) were assessed, through specific ELISA kits, before therapy, 5 days after the G-CSF stimulation and at stem cells collection. Each parameter was correlated with the number of CD34+ cells collected.

Thy1 significantly decreased (p=0.007) and L-selectin significantly increased (p=0.038) in nearly all cases. By contrast, no statistically significant differences were observed for VLA4 and CXCR4 due to a consistent variability. Serum levels of IL-8 showed an increase at day 5, then a significant decrease at the time of the harvest (p=0.013); VEGF-A constantly increased (p<0.001) and TGF-β decreased (p=0.001). The modifications registered for sVCAM-1 and HGF did not reach statistical significance. The expression of CD34+ adhesion molecules did not correlate with the number of PBSC collected, while among cytokines, high baseline levels of TGF-β and VEGF-A significantly correlated with high number of CD34+ stem cells yielded (p=0.016, p=0.042 respectively).

In conclusion, this study shows that during stem cells mobilization in MM Thy-1 expression significantly decreases while L-selectin increases; the behaviour of VLA-4 and CXCR4 is extremely variable. As regards cytokines, we found a statistically significant increase of VEGF-A level, while TGF-β, which induces the stem cell homing, decreases during the mobilization allowing stem cells to migrate in the peripheral blood. High baseline levels of TGF-β and VEGF-A predict a good stem cells harvest.